Air Conditioning Systems Student Resource Package No: NR71314

Transcription

Air Conditioning Systems
Student Resource Package No: NR71314
Nominal Student Hours:
72 Hours.
Delivery:
Competence in this training program can be
achieved through either a formal education
setting or in the workplace environment.
Recognition of Prior
Learning:
The student/candidate may be granted
recognition of prior learning if the evidence
presented is authentic and valid which covers the
content as laid out in this package.
Package Purpose:
This package provides the student with the
underpinning knowledge and skills to install,
commission, service and fault find residential
and commercial air conditioning systems.
Suggested Resources:
Australian Refrigeration and Air Conditioning
Vol 1&2.
Various Manufacturers Service and Installation
Manuals.
Assessment Strategy:
The assessment of this package is holistic in
nature and requires the demonstration of the
knowledge and skills identified in the student
package content summary. To be successful in
this package the student must show evidence of
achievement in accordance with the package
Competence:
This package should be supported by workplace
exposure to the various applications under the
guidance of a licensed mentor.
HVAC & Refrigeration, Ultimo 2006
Air Conditioning & Ventilation
Compiled by S. Doumanis, P. Lamond, G. Riach & R. Baker
Additional Resources:
Dossat Roy J., Horan Thomas J., Principles of Refrigeration, Fifth Edition, Prentice
Hall
Kissel, Thomas, Motors, Control and Circuits for Refrigeration and Air Conditioning
Systems, Reston Publication Co. Inc. 1992.
Langley B.C., Refrigeration and Air Conditioning, Reston Publishing Co. Inc., 1986.
AS 1101.5 – Piping, Ducting and Mechanical Services for Buildings.
AS 2913:1987 – Evaporative Air Conditioning Equipment.
AS 2991.1:1987 – Acoustics – Method for the Determination of Airborne Noise
Emitted by Household and Similar Electrical Appliances.
AS 3179:1993 – Approval and Test Specification, Refrigerated Room Air
Conditioners.
AS / NZS 1668.1 - Fire and Smoke Control in Multi Compartment Buildings.
AS / NZS 1668.2 – Mechanical Ventilation for Acceptable Indoor Air Quality.
AS / NZS 3000:2000 - Electrical Installation Wiring Rules.
AS / NZS 3008 - Cables
AS / NZS 3666.1, 2 and 3 - Air Handling and Water Systems in Buildings – Microbial
Control.
NSW Code of Practice for the Control of Legionnaires’ Disease.
NSW Ozone Protection Act, 1989, (As a 22 December 1999).
NSW Ozone Protection Regulation, 1997, (As at 31 August 2004).
NSW Public Health Act.
SAA HB40.1 and 2:2001, Australian Refrigeration and Air Conditioning Code of
Practice.
SAA / NZ HB32 - Control of Microbial Growth in Air Handling and Water Systems
of Buildings.
Standards Australia, Residential Air Conditioning Code of Good Practice, 1997.
2
Compiled by S. Doumanis, G. Riach and R. Baker.
Videos:
Air Conditioning; TAFE SA Cat No 84.06 (8 mins)
Air Conditioning Commissioning; TAFE SA Cat No.88.024 (12 min 38 sec)
Air Conditioning Maintenance; TAFE SA Cat No.88.00 (8 min)
Fan Installation; TAFE SA Cat No 84.065 (11 min)
Fans and Airflow; TAFE SA Cat No 88.007 (12 min)
Filters; TAFE SA Cat No 8.003 (9 min)
Instruments Air Flow Measurement; TAFE SA Cat No 84.069 (11 min)
Reading Site Drawings (Air Conditioning); TAFE SA Cat No.88.024 (5 min)
Reverse Cycle Air Conditioning; TAFE SA Cat No.88.070 (6 min)
Sounds Like Noise; TAFE SA Cat No 84.066 (8 min)
1, 2, 3 – The Chilling Factor; TAFE SA Cat No.94.03 (14 min)
Assessment:
Grade Code: 72
GRADE
CLASS MARK (%)
DISTINCTION
CREDIT
PASS
>=83
>=70
>=50
Assessment Events:
1.
Residential Air Conditioning Theory Test
Assignment
20%
20%
2.
Ventilation
30%
3.
Commercial Air Conditioning Theory Test
30%
Total Marks:
Theory Tests:
100%
Short answer Questions / electrical drawings
This assessment covers the contents of this student resource
package.
3
Content Summary:
Assignment: Residential Air Conditioning.
6
Occupational Health Requirements, the Codes, the Standard,
the Act and Regulations.
7
Residential Air Conditioning Systems
Types of Residential Air Conditioning Systems
10
Typical Wiring Diagram
11
Room Air Conditioner (RAC)
12
Split Systems
13
Ducted Systems
13
Package Systems
14
Cassette Systems
14
Evaporative Systems
15
Air Distribution ARAC
15
Heat Load Calculations
19
Sizing of the System
19
Cooling Load Estimator
20
Calculating the Residential Air Conditioning System Capacity
21
Air Flow Rates
22
Supply Air Register & Duct Sizes
23
Duct Sizes
24
Ventilation
Sick Building Syndrome
34
Legionella Bacteria Office Buildings
34
Mode of Transmission
34
Prevention and Control of Legionellosis in Office Buildings
35
The Process of Air Conditioning
36
Ventilation
36
Natural Ventilation
36
Mechanical Ventilation
36
Test Equipment
38
Terms Associated with Air Distribution
42
Practical Exercise: Air Balancing
43
4
The Underlying Principles of Air Distribution
44
Noise
44
Draughts
45
Air Stratification
45
Ducting
49
Dampers
53
Fans & Fan Laws
59
Filtration
64
Air Conditioning Fundamentals
70
Psychrometrics
70
Package (Unitary) Units
86
Heat Load Estimating
109
Evaporative Coolers
116
Central Plant Systems
124
Heating Systems
154
Humidification Systems
164
Thermal Storage Systems
170
Specialised Systems
176
5
Residential Air Conditioning Assignment
1.
Draw a plan of a residential home with at least three bedrooms to be air
conditioned with a split duct AC system.
2.
Determine the required cooling capacity for the residence specifying the
indoor and outdoor conditions.
3.
Select a suitable split ducted air conditioning system that will have
sufficient capacity for the application.
4.
On the house plan show the position of both the fan coil unit and the
condensing unit.
5.
Design the supply and return air ducting for the system and show layout
with all sizes on the plan. Include all sizing of supply diffusers and return
air grille.
6.
Select suitable pipe sizes for the suction, liquid and condensate lines,
showing all calculations and layout on the plan
7.
Prepare an electrical wiring diagram for the system indicating all field
wiring that is required for both power supply and controls.
8.
Prepare a materials list for all equipment and materials that is required to
complete the installation.
9.
Prepare a costing estimate including all equipment, materials and labour
that is required to complete the installation.
10.
In total, a minimum of five plans of the residence will be required:
Base plan.
Location of fan coil unit and condensing unit.
Duct layout showing sizes of ducts, supply air diffusers and return air
grille. (This may be divided into two plans – one for duct layout, the
second for supply air diffuser and return air grille locations).
Piping layout.
Electrical layout.
6
Occupational Health Requirements, the Codes, the
Standard, the Act and Regulations.
Occupational Health Requirements, the Codes, the Standard, the Act and Regulations
are used to provide a standard set of guidelines which you must follow. The following
codes are only a sample of the many codes that outline the standards that must be
observed.
AS 1668.1 - Fire and smoke control in multi compartment buildings.
This code sets out the minimum requirements for the design, construction, installation
and commissioning of mechanical and air conditioning systems for fire and smoke
control in multi compartment buildings.
AS 1668.2 – Mechanical ventilation for acceptable indoor air quality.
Sets out the requirements for air-handling systems that ventilate enclosures by
mechanical means. It sets minimum requirements for preventing an excess
accumulation of airborne contaminants or objectionable odours.
AS 1668.2 Supp1:1991- Mechanical ventilation for acceptable indoor air quality
– Commentary (supplements to AS 1668.2 -1991).
Provides guidance in the application of the Code by explaining the intent of those
clauses that could be subject of requests of interpretation.
AS / NZS 3000:2000, Electrical Installation Wiring Rules.
Provides requirements for the selection and installation of electrical equipment and
design and testing of electrical installations, especially with regards to the essential
requirements for safety of persons and livestock from physical injury, fire or electric
shock.
AS/ NZS 3666.1 – Design, installation and commissioning
This code outlines the minimum requirements for the design, installation and
commissioning of air handling and water systems in buildings to assist in the control
of micro-organisms, particularly those associated with Legionnaires Disease etc.
AS/ NZS 3666.2 – Operation and maintenance
This code outlines the minimum requirements for the operation and maintenance of
air handling and water systems in buildings to assist in the control of microorganisms, particularly those associated with Legionnaires Disease etc.
AS/ NZS 3666.3 – Performance-based maintenance of cooling water systems
Outlines a performance-based approach to the maintenance of cooling water systems
with respect to the control of micro-organisms, including water treatment with
monitoring, and assessment and control strategies to help create a low risk
environment within the cooling water system.
NSW Ozone Protection Act, 1989.
An Act to empower the regulation and prohibition of the manufacture, sale,
distribution, use, emission, re-cycling, storage and disposal of stratospheric ozone
depleting substances and articles which contain those substances; and for other
purposes.
7
NSW Ozone Protection Regulation, 1997.
The regulations are designed for use with the Ozone Protection Act.
NSW Public Health Act.
This Act sets out the manner that “wet areas” and ductwork that must be maintained
and provides for penalties against owners, occupiers and maintenance personnel of
buildings.
SAA HB40:2001 – Australian Refrigeration and Air Conditioning Code of
Practice.
SAA HB40.1:2001 – Reduction of Emission of Fluorocarbon Refrigerants in
Commercial and Industrial Refrigeration and Air Conditioning Applications.
This handbook covers all systems classifiable as commercial and industrial
refrigeration and air conditioning systems, including heat pumps and has been
developed with the intention of reducing emissions of fluorocarbon refrigerants into
the atmosphere.
SAA HB40.2:2001 – Reduction of Emission of Fluorocarbon Refrigerants in
Residential Air Conditioning Applications.
This handbook covers all systems classifiable as residential air conditioning systems,
including heat pumps and has been developed with the intention of reducing
emissions of fluorocarbon refrigerants into the atmosphere.
SAA / NZ HB32 – Control of microbial growth in air handling and water systems
of buildings.
Provides guidance for microbial control of both air handling and water systems of
buildings. The handbook is intended to provide users with additional information to
support the specific requirements of AS / NZS 3666 Parts 1 and 2.
Department of Fair Trading
Department of Fair Trading has no requirements relating to the installation of
residential air conditioning other than that the contractor holds a contractors licence
and that the contractor employs tradespersons who hold a qualified supervisors
licence and hold a current Controlled Substance Licence from the relevant authority.
Environmental Protection Authority (EPA)
The EPA issues regulations in regard to noise pollution and clauses 45 to 47 are
relevant to residential air conditioning. However, local councils usually address noise
complaints using both the EPA and their own policy guidelines.
The EPA also issues maximum acceptable sound levels that all equipment should
comply with. This noise level must be displayed on the outdoor unit.
Local Councils
Local Council requirements currently differ from Council to Council with some
requiring that a Building Application (BA) be submitted before the installation takes
place. Some require BA only for new dwellings that have air conditioning indicated
on the drawings of for ducted system over a certain capacity. Some councils; do not
have any involvement unless a complaint is logged.
8
Generally, council requirements are that any noise produced from air conditioning
systems must not be greater than 5dBa at the property boundary above the level of
background noise that is produced from cars, trains, aeroplanes etc.
Summary
The number of Acts of Parliament, Regulations, Standards and local council rulings in
this area reflect the necessity for stringent and diligent work by people maintaining
buildings which the general public have access to.
You need to consult the above references and your local authority to ensure you are
complying with all requirements and are not personally liable should a problem arise.
Legionella, apart from the sensational periodic outbreaks, still kills several people in
Australia every year. The incidence of people suffering from ‘Sick Building
Syndrome’ is harder to gain reliable statistics on but the problem is very real and must
be kept in mind when working on air handling units and ducting systems.
9
Residential Air Conditioning Systems
Types of Residential Air Conditioning Systems:
The following details the various types of residential air conditioning systems
available:
•
•
•
•
•
•
Room Air Conditioning (RAC).
Split System.
Ducted System
Package System
Cassette System
Evaporative.
The majority of residential air conditioning systems with the exception of the
evaporative come in reverse cycle. The installation of most residential air
conditioning systems require a separate dedicated electrical circuit of 15 amperes
and installed by a licence electrician with all work complying with AS 3000 &
3008 Wiring Rules.
Note: any system that rates below 5kW can be plugged into a 10 ampere GPO.
In low ambient conditions (7°C and below) a de ice thermostat which is fitted to
the outdoor unit cycles the indoor and outdoor fans off and switches the system
back to its cooling mode until the ice is removed.
It may also be necessary to have a low ambient thermostat to control a set of
booster heaters. The low ambient thermostat closes when the ambient temperature
falls below 7ºC and energises the booster heaters. The outdoor unit operates when
the booster heaters are energised.
Note:
Refer to the attached electrical circuit diagram of a 12 kW ducted
air conditioning system incorporating a 3 kW booster heater and a
de-ice cycle.
10
11
Room Air Conditioner (RAC)
These units vary in capacities between 2 to 6 kW. To help reduce noise most window
units are fitted with rotary compressors and fan motors that operate smooth and quiet.
Motorised air swings are fitted to direct conditioned air throughout the conditioned
space. A damper is provided to enable fresh air to be introduced into the room if
required. Refrigerant is achieved by a capillary tube,
Exploded view of a Room Air Conditioner
Split Systems
Split systems consist of two individual factory assembled units separated from each
other, but interconnected by the refrigerant piping. The condensing unit is pre-charged
with sufficient refrigerant to allow up to 20 metres of pipe work between the two
units. Technical advances in compressor design, has led to higher refrigeration
capacities between 2 to 10 kW.
The condensing unit is mounted externally and contains the condenser coil, condenser
fan or fans, compressor, reversing valve and associated piping and unit controls.
Refrigerant control may be achieved by a capillary tube, thermostatic expansion valve
or accurator.
12
Wall Mounted Split System Cassette
The indoor fan coil unit usually consists of an air filter, evaporator coil, evaporator
fan and electrical controls for system operation. Multiple evaporator split systems are
now available which have up four fan coil units operating from a single condensing
unit.
The main advantage of split systems is the ease with which they can be installed and a
low noise level in the conditioned space due to the condensing unit being remotely
located.
Ducted Systems
This system is almost identical to the split system. The major difference is that the fan
coil unit is mounted in the ceiling or under floor space and connected to a system of
duct work to distribute the conditioned air to different areas of the building.
Ducted Reverse Cycle Air Conditioning System
13
Typical Residential Outdoor Condensing Unit
Package System
Package units can be installed in residential or commercial buildings and consist of a
condensing unit, evaporator cooling coil and supply air fan etc all installed together in
the one unit. Package units are fully factory wired and only require electrical supply
connection.
These units are designed installed either internally or externally, however they are
usually mounted outside to reduce the introduction of noise to the conditioned space.
The conditioned air from the package unit is distributed and returned the via supply
and return air ducts.
Cassette System
14
The cassette system is similar to the wall hung split system but instead of indoor unit
being mounted on the wall it is fitted flush into the ceiling.
Indoor Unit
Supply Air
Supply Air
Return Air
Outdoor Unit
Evaporative Systems
Evaporative cooling uses the effect of “Latent Heat” to cool the air as it passes
through a water- soaked porous material. These materials can be pads of cotton covered straw and heat is absorbed from the air and changes some water to vapour.
The evaporative cooler draws its water supply via a pump from a basin which is
supplied with mains water by way of a float level valve.
Cross section of Porous pad that is laden with water during operation
The amount of moisture already in the air will determine the amount of cooling of the
air. For example in dry inland areas temperatures can be reduce by 15°C therefore the
system is less effective nearer the eastern coast because the incoming air will contain
and absorb more moisture making it less efficient.
Air should never be recirculated through an evaporative cooler because relative
humidity will increase as the air is cooled and moisture added. Fresh air should only
be brought through the cooler and be exhausted through the open windows etc of the
conditioned space to be effective.
15
Domestic type Evaporative Cooling System
16
Air Distribution ARAC
Fans:
There are four main types of fans used in air conditioning systems and these are as
follows:
•
Forward-curve or multi-vane centrifugal
Applications: residential air conditioning systems
.
These are quiet and compact with a low tip speed and are used on low to
medium pressure air conditioning/ ventilation applications. They require an
oversized motor as power varies with the duct resistance. Efficiency: 50-60%.
•
Backward-curve limit load centrifugal
Applications: Large commercial air conditioning system
These on large systems with high duct resistance and are suitable for variable
volume systems because of low power characteristics. However high tip speed
results in high noise level.
Efficiency: 70-75%
•
Propeller used for condenser fan motors and ventilation fan motors.
Applications: Wide variety uses in various installations.
17
These are cheap and simple to install. They can move a lot of air as long as
there is no resistance. Installation of a cowl ring increases efficiency.
Efficiency: less than 40%.
•
Axial flow.
Suitable for installations with a run of ducting they are very compact with
straight through flow. They are suitable for variable-pitch operation when used
in installations with variable loads. They are suitable for low pressure
installations and are more efficient than propeller types. Relatively high tip
noise.
Efficiency: 60-65%
Ducting: ARAC
Flexible Fire Rated Ducting
The duct work is designed to transport air as economically and quiet as possible.
Ducts can be rigid or flexible and come in a range of various shapes, sizes and
manufacturing for a range of diverse applications.
All ducts should be:
• As straight and smooth as possible.
• Fireproof
• Able to carry all the air required and distributed to branches outlets.
• Insulated to prevent loss or gain of heat.
18
•
•
Air tight.
Low noise transmission to the conditioned space.
Filters: ARAC
Air conditioning systems filter the air for a number of reasons eg to reduce the amount
of dust, smoke and other fumes from entering the conditioned space and to help the
evaporator coil from becoming blocked.
The main types of filters in order of efficiency are:
• Absolute filters.
• Electrostatic filters.
• Metal viscous filters.
• Viscous filters.
• Dry filters.
• Water sprays.
Absolute filter:
These are specialised filters mainly used in laboratories and hospital operating
theatres. They are constructed of special materials to ensure filtration to 99.9%
efficiency. They cannot be serviced or cleaned and must be replaced as necessary.
Electrostatic filters:
These filters use high voltage wires in the air stream to ionise an particles passing
between them. This “positively” charges the particles which now pass between a bank
of collector plates which are alternatively positive and negatively charged. The
particles are repelled from the positive plates and attracted to the negative plates
where they will collect.
They are popular for commercial use as well as hospitals and other clean areas.
Metal viscous filters:
The surface of these filters is covered entirely with adhesive oil. The honeycomb –
shaped aluminium passages deflect the air so that it strikes the oil covered aluminium
surface where it will collect.
Viscous filters:
These are a dry filter medium which is covered with adhesive oil. This will improve
the filtration considerably regardless of quality of the filter media.
Dry filters:
These filters come in various grades, qualities and forms. They range from a washable
pad as used in residential air conditioners that will collect dust and fluff to
commercial dry filters that are thrown away when the filter has absorb its maxim
quantity of dirt.
19
Water sprays:
This type of filter is reasonably efficient but increases the space humidity therefore
limiting its use. However it is successful in evaporative coolers.
Registers:
The positioning of the outlets of the room being conditioned is determined by a
number of factors including:
• The number of outlets preferred.
• Shape and size of the room.
• Location of the ducting.
The importance of the outlet positioning cannot be underestimated enough. An “under
throw” of air will result in a “drop” of the conditioned air in the centre of the room.
However an “overthrow” of the air could cause it to strike the opposite wall and
bounce back onto the occupants of the room causing draughts. Another disadvantage
of long throw outlets is the noise level as high face velocities are necessary. Several
outlets are preferable to one in large or odd shaped rooms.
Stratification of air is the term used to describe formation of separate layers of warm
and cold air due to poor circulation in a conditioned space.
Supply Air Duct (SA)
Package
AC
System
SA Diffuser
SA Register
Return Air Grille
Noise:
Noise is usually associated with high air velocity, poorly designed supply and return
outlets and uninsulated duct work.
20
Vibration:
Vibration is associated by poorly installed duct work and fittings.
Where necessary flexible duct joints, spring or rubber mounted hangers to help
eliminate or reduce vibration should be used.
21
Heat Load Calculations
Sizing of the System:
It is necessary to carry out a heat load calculation to determine the capacity for an air
conditioning system. The following should be taken into account to determine the
total heat load process:
•
•
•
•
•
•
Amount of external glass
Construction of external walls
Partitions
Insulation if any
Floor (Slab or ventilated).
Internal heat sources i.e peoples,lights,machines
Consideration should also be given as to whether the whole house is to be air
conditioned or should be separated by day / night zones. Zoning reduces the total
systems capacity, capital cost.
Whilst minimising capital cost it can result in an unsatisfactory system if incorrectly
designed and installed.
Window shading and insulation
Window shading / tinting, insulation (walls and ceiling) and the reduction of air
infiltration or leakage can dramatically reduce the air conditioning capacity required
on a new installation.
Use of Air Conditioning Survey Form
The Air Conditioning and Refrigeration Equipment Manufacturers Association of
Australia (AREMA) in conjunction with the Commonwealth Scientific and Industrial
Research Organisation (CSIRO) has been prepared to provide the industry with a
standard air conditioning load estimation form.
This form has been designed for commercial applications. For residential installations
only the Solar Heat Section (items 1 – 7) are used.
Note refer to attached survey form.
22
Residential Air Conditioning
Cooling Load Estimator
JOB NAME:
LOCATION:
TELEPHONE:
FAX:
ESTIMATOR:
SYSTEM RECOMMENDATIONS:
MAKE:
CAPACITY: (Watts)
ELECTRICAL SUPPLY
(Consumer Mains):
Single Phase:
SINGLE PHASE
REQUIREMENT:
10 Amp GPO:
No.
Item
3.
4.
5.
6A.
6B
7.
15 Amp GPO:
Cooling Factors
NIL
2.
Three Phase:
Area
m2
External Glass - Solar Heat
(Use all windows at one
selected time).
1.
MODEL:
57
170
375
549
353
50
50
50
492
6K
38.0
19.0
10.5
17.0
13.0
20.0
10.0
8.5
South
South East
East
North East
North
North West
West
South West
Horiz.
Design db temp. diff (Kelvin)
All Windows Single glass
Double glass
Outside Walls Cavity brick
Hollow brick
Brick veneer
Weatherboard
Partitions
Internal walls
Ceiling Unconditioned above
Ceiling
Pitched roof above
(sunlit)
No insulation
roof
50mm insulation
Floors
Over unconditioned room
Over enclosed crawl space
Over ventilated crawl space
Slab on ground
Watts
10 am
4 pm
Shades
Shades
In
Out
NIL
In
16
60
38
38
57
38
110 41
246 95
50
32
356 139
50
32
230 88
113
72
35
13
435 284
35
13
621 404
35
13
508 331
318 123 524 341
8K
10K
(12K)
51.0 64.0 (77.0)
25.5 32.0
38.0
14.0 17.5 (21.0)
24.5 26.0
28.0
17.0 20.0
26.0
27.5 31.5
38.0
12.0 17.0 (20.5)
12.0 14.5
17.0
Out
16
16
13
13
28
110
154
126
129
14K
90.0
44.5
24.5
30.5
30.0
40.0
24.5
18.5
50.0
12.0
53.0
13.0
56.0
14.0
59.5
15.0
62.5
15.5
6.5
1.0
8.5
0.0
9.0
1.0
12.0
0.0
12.0
1.0
15.5
0.0
14.5
1.0
19.0
0.0
17.0
1.5
22.0
0.0
Total
23
Calculating the Residential Air Conditioning System Capacity
To calculate the air conditioning capacity of a residential house or apartment calculate
each of the room areas to be condition in m2 and multiply by a load factor of between
120watts for passive areas and up to150 watts for areas with higher heat loads ie high
solar, heat from appliances and occupant loads.
Construction:
• Brick veneer
• Roof insulated
• Internal curtains on all windows
Lounge Room:
5m x 6.5m x 120 watts / m2 = 3900 watts
3.9 kW
Kitchen & Dinning
4m x 5m x 140 watts / m2
= 2800 watts
2.8 kW
Master Bed Room
5m x 4m x 130 watts / m2
= 2600 watts
2.6 kW
Bedroom No: 2
3.7m x 3m x 120 watts / m2 = 1342 watts
1.332 kW
Bedroom No: 3
3.3m x 3m x 120 watts / m2 = 1888 watts
1.188 kW
Sitting Room
3.6m x 4 x 120 watts / m2
1.728 kW
= 1728 watts
Total = 13548 watts
13.548 kW
In this application for energy savings we will divide the house into a day and night
zone.
Zone 1, Day Zone
• Family room
= 3.9 kW
• Kitchen & dining room
= 2.8 kW
Total = 6.7 kW
Zone 2, Night Zone
• Master bedroom
• Bedroom 2
• Bedroom 3
• Sitting room
= 2.6 kW
= 1.332 kW
= 1.188 kW
= 1.1728 kW
Total = 6.848 kW
24
Using a Panasonic Brochure: the smallest available unit with a total cooling capacity
of 8.3 kW and an indoor air volume of 475 L/s.
Air Flow Rates:
Formula =
Total Air Volume L/s
Total Kilowatts Required
= L/s per kW
Zone 1
475 L/s
6.7 kW
= 70.89552239 L/s per kW
Family room
= 3.9 kW x 70.89552239 L/s
= 276.5 L/s
Dining & kitchen
= 2.8 kW x 70.89552239 L/s
= 198.5 L/s
Total = 475 L/s
Zone 2
475 L/s
6.848 kW
= 69. 36331776 L/s per kW
Master bedroom
= 2.6 kW x 69.363317776 L/s
= 180.34 L/s
Bedroom 2
= 1.332 kW x 69.363317776 L/s
= 92.4 L/s
Bedroom 3
= 1.188 kW x 69.363317776 L/s
= 84.4 L/s
Sitting room
= 1.728 kW x 69.363317776 L/s
= 119.9 L/s
Total = 475 L/s
25
Supply Air Register & Duct Sizes
Formula:
X = L/s for room
1000
Therefore:
Y=
X
2.5
(Register velocity)
Y x 1000 =
the answer in mm
Zone 1
Family room
(2 Registers)
276.5 L/s
2
= 138.25 L/s
138.25
1000
= 0.13825
0.13825
2.5
=
0.0682 = 0.2612 x 1000 = 261mm
300 mm registers
Dining room & kitchen
(2 Registers)
198.5 L/s
2
= 99.25 L/s
99.25
1000
= 0.9925
0.09925
2.5
=
0.0397 = 0.199 x 1000 = 199mm
225mm registers
Zone 2
Master bedroom
(1 Register)
= 0.18034
180.34 L/s
1000
0.18034
2.5
=
0.072136
= 0.269 x 1000 = 267mm
26
300mm register
Bedroom 2
(1 Register)
92.4 L/s
1000
0.0924
2.5
= 0.0924
=
0.03696
= 0.192 x 1000 = 192 mm
225mm register
= 0.182 x 1000 = 182 mm
225mm register
= 0.219 x 1000 = 219mm
225mm register
Bedroom 3
(1 Register)
82.4 L/s = 0.0824
1000
0.0824
2.5
=
0.03296
Sitting room
(1 Register)
119.9 L/s = 0.1199
1000
0.1199
2.5
=
0.04796
27
Duct Sizes
Recommended Duct Velocities for Residential Applications 2.5 to 4 m/s
Formula:
Area (m2)` = Volume L/s
Velocity m/s
Zone 1
Family room (2 Registers at 138 .25 L/s)
Convert L/s to m3/s:
m3/s = 138.25 = 0.138 m3/s
1000
Recommend velocity = 3 m/s.
Therefore:
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.046m x 4
3.142
0.318 = 0.046m2
3
= 0.242 x 1000 = 242mm
Duct size = 250mm
Family room supply air duct to 300mm x 250 x 250mm branch take off (BTO).
m3/s = 276.5
1000
= 0.2765 m3/s
Recommend velocity = 3.5 m/s.
Therefore:
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.079 x 4
3.142
0.2765 = 0.079m2
3
= 0.317 x 1000 = 317mm
Duct size = 300mm.
28
Kitchen (1 Register at 99.25 L/s).
m3/s = 99.25
1000
= 0.09925 m3/s
Recommend velocity = 3 m/s. Therefore: 0.09925
3
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.033 x 4
3.142
= 0.033m2
= 0.205 x 1000 = 205mm
Duct size = 200mm.
Supply Air Duct family room / kitchen (276.5 L/s + 99.25 L/s) = 375 .75 L/s.
m3/s = 375.75 = 0.37575 m3/s
1000
3
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.107 x 4
3.142
= 0.107m2
= 0.369 x 1000 = 369mm
Duct size = 350mm.
29
Dining Room (1 Register at 99.25 L/s).
m3/s = 99.25
1000
= 0.09925 m3/s
3
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.033 x 4
3.142
= 0.033m2
= 0.205 x 1000 = 205mm
Duct size = 200mm.
Supply Duct family room, kitchen & dining
(276.5 L/s + 99.25 L/s + 99.25 L/s) = 475 L/s.
m3/s = 475
1000
= 0.475 m3/s
Recommend velocity = 4 m/s. Therefore: 0.475 = 0.11875m2
4
Diameter =
CSA x 4
`3.142 (PYE)
Diameter =
0.11875 x 4 = 0.388 x 1000 = 388mm
3.142
Duct size = 400mm.
30
Zone 2
Bedroom 3 (1 register 82.4 L/s).
m3/s = 82.4
1000
= 0.0824 m3/s
3
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.027 x 4 = .187 x 1000 = 187mm
3.142
Duct size = 200mm.
Bedroom 2 (1 register 92.4 L/s).
m3/s = 92.4
1000
= 0.0924 m3/s
3
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.0308 x 4 =
3.142
0.252 x 1000 = 252mm
Duct size = 250mm.
31
Supply air duct to bedrooms 2 & 3 BTO (92.4 L/s + 82.4 L/s) = 174.8 L/s.
m3/s = 174.8
1000
= 0.1748 m3/s
Therefore:
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.0499 =
3.142
0.1748 = 0.0499m2
3.5
0.252 x 1000 = 198mm
Duct size = 200mm.
Sitting room (1 Register 119.9 L/s).
m3/s = 119.9 = 0.1199m3/s
1000
Recommend velocity = 3 m/s. Therefore: 0.1199 = 0.03997 m2
3
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.03997 =
3.142
0.215 x 1000 = 215mm
Duct size = 200mm.
32
Main Air Duct to sitting room and bed room BTO
(119.9 L/s + 92.4 L/s + 82.4 L/s) = 294.7 L/s.
m3/s = 297.4 = 0.2947m3/s
1000
Therefore:
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.0842 X 4 =
3.142
0.2947 = 0.0842 m2
3.5
0.322 x 1000 = 322mm
Duct size = 300mm.
Master bedroom (1 Register 180.34 L/s).
.
m3/s = 180.34 = 0.18034m3/s
1000
Recommend velocity = 3. m/s.
Therefore: 0.18034 = 0.06 m2
3
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.06 X 4 =
3.142
0.2727 x 1000 = 272mm
Duct size = 300mm.
33
Supply duct to master bedroom, sitting room bedroom 2 & bedroom3.
(180.34 L/s + 119.9 L/s + 92.4 L/s + 82.4L/s) = 475 L/s.
m3/s = 475
1000
= 0.475m3/s
Recommend velocity = 4. m/s.
Therefore: 0.475 = 0.11875 m2
4
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.11875 X 4 =
3.142
0.388 x 1000 = 388mm
Duct size = 400mm.
Return Air
2 return ducts
475 L/s
2
= 237.5 L/s
m3/s = 237.5 = 0.2375m3/s
1000
Recommend velocity = 2.5. m/s.
Therefore:
Diameter =
CSA x 4
3.142 (PYE)
Diameter =
0.095 X 4 =
3.142
0.2375 = 0.095 m2
2.5
0.3477 x 1000 = 347.7mm
Duct size = 350mm x 2.
34
Review Questions:
Q.1
What qualifications do you need to install residential air conditioning systems?
Q.2
What requirements do local councils require before you install a residential air
conditioning system?
Q.3
What are the advantages of a split system when compared with a room air
conditioner?
Q.4
Give two advantages a ducted system has compared to a split system:
Q.5
List one advantage and disadvantage of an evaporative cooler:
Q.6
List the four main types of fans used in air conditioning systems and give an
application for each one:
Q.7
Name three types of air conditioning filters and their applications:
35
Q.8
State three factors that determine the position of outlets in a conditioned space:
Q.9
Define what is meant by the term stratification:
Q.10
What could be done to reduce vibration and noise from air conditioning duct
work?
36
Ventilation
Sick Building Syndrome.
Sick building syndrome is mainly caused by the lack of preventative maintenance in a
building. The main responsibility of a building manager is to initiate and maintain a
regular preventative program to cover system checks, filter changes, drain pan
cleaning, scheduling of housekeeping functions and pesticide spraying. In order to
maintain the building, the building manager must monitor the maintenance and
cleaning of the above, especially the use of chemicals.
An inadequately maintained building can result in:
Drain pans becoming reservoirs for bacteria and mould.
Duct work becoming a ‘garden’ for moulds and spores to grow.
Cooling towers breed Legionella.
Clogged filters which in turn decrease air flow and ventilation rates.
As well as improper maintenance, the design of the HVAC (Heating, Ventilation and
Air Conditioning) system can be a major contributing factor to ‘Sick Building
Syndrome’. Another factor that must be considered as a negative impact on indoor air
quality is contaminants / pollutants.
The main pollutants include:
Tobacco smoke.
Ozone from copy machines.
Formaldehyde from new furnishings, glues, partitions or panelling.
Carbon monoxide from air intakes located near loading docks, streets or
parking lots.
Volatile organic compounds from felt tip markers, cleaning compounds, paints
and solvents.
Legionella Bacteria in Office Buildings.
Since the first documented Legionellosis outbreak at the Bellevue Stratford Hotel in
Philadelphia, numerous epidemic and sporadic Legionellosis cases have been
reported.
The ecology of Legionella in a water system is not fully understood, however, studies
do indicate that water temperatures between 20 and 45OC favour Legionella growth.
Bacteria do not multiply below 20OC and cannot survive in temperatures above 65OC.
These organisms may remain dormant and proliferate when temperatures are suitable.
The presence of sediment, scale, sludge and organic matter can serve as a source of
nutrients for these bacteria. Legionella bacteria also colonise on certain types of water
fittings, pipe work and materials used in the construction of water systems.
Mode of Transmission.
The mere presence of Legionella bacteria in the water systems does not cause the
disease itself.
37
Legionellosis factors:
Environmental reservoirs: Lakes, streams, rivers, etc are the natural reservoirs
for Legionella bacteria.
Amplification factors: Showers, whirlpools, tap water faucets, water storage
tanks, cooling towers, humidifiers, evaporative condensers and respiratory
therapy equipment are common sources for amplification of Legionella
bacteria because of the temperature ranges that they operate within.
Mechanism of dissemination: The prevailing mode of transmission is through
the breathing of airborne water droplets or particles (aerosol) containing viable
Legionella that then passes deeply into the lung and deposited in the alveoli.
Prevention and Control of Legionellosis in Office Buildings.
The most effective control for diseases, including Legionellosis, is to break as many
factors as possible in the creation of the diseases.
In office buildings, the risk of Legionellosis can be minimised by measures that do not
allow the proliferation of Legionella in the water systems, and reducing exposure to
water droplets and aerosols.
The following actions should be taken for prevention purposes:
Minimise the release of water spray.
Avoid water temperatures and conditions that favour the proliferation of
Legionella and other micro-organisms.
Avoid water stagnation.
Avoid materials that harbour bacteria and other micro-organisms, or provide
nutrients for microbial growth.
Maintain the cleanliness of the system and the water in it.
Use water treatment.
Ensure the correct and safe operation, and maintenance of the water system
and plant.
When an outbreak of Legionella occurs, the most common control measures are:
Super chlorination.
The free residual chlorine levels should be greater than 2 ppm (routine
chlorine treatment of the water supply may not eliminate Legionella bacteria).
Heating of water systems.
For heating, the temperature of the hot water system should be maintained at
55 – 75OC for several hours.
38
The Process of Air Conditioning
Comfort levels for occupants of buildings can be achieved by a variety of processes,
from the opening of windows to full air conditioning by mechanical means.
‘Discomfort’ results from extremes of temperature (for which the only solution is
heating or cooling) and from ‘stuffy’ conditions (which result from poor air
movement, high humidity and concentrations of odour or smoke). Ventilation can
usually provide the remedy for stuffy conditions.
Ventilation
The word ‘ventilation’ means to remove polluted air from inside a space and replace it
with air from outside the space. This replenishes the oxygen supply, dilutes odours
and removes smoke.
Ventilation is needed for comfort and health.
These places usually need ventilation:
Buildings and rooms occupied by people at work
Machine and plant rooms where heat is generated
Process plants requiring quick cooling of foods, confectionery, print, etc
Areas with toxic or unpleasant fumes.
There are two methods commonly used, they are:
Natural ventilation.
Mechanical ventilation.
Natural Ventilation
The simplest way to provide ventilation is to open windows and / or doors. The
amount of ventilation depends upon:
Size and type of windows / doors
Location of the windows / doors
Velocity and direction of the wind
Opening obstruction
Temperature difference between inside and outside conditions.
Mechanical Ventilation
This method requires a mechanical device, normally a fan and motor for positive
ventilation.
Mechanical ventilation performs one or all of the following functions:
Creation of sufficient air movement to eliminate stagnation.
Removal of toxic fumes, smoke and other pollutants.
Control of space air temperature.
Provide fresh ventilation air for people that occupy a space.
The most economical way to maintain health and comfort conditions of a space is by
replacing the air. This is done by bringing in outside air to ventilate the space. Fresh
air can be mechanically introduced into an area in two ways:
39

Supply air systems / forced ventilation. Fresh air is pumped into the area being
ventilated resulting in positive pressure, causing the stale air to be pushed out
or ventilated through door grills, windows etc.
Forced draft / natural exhaust ventilation.

Exhaust air systems / induced ventilation. Air is sucked out of the ventilated
area resulting in negative pressure, causing fresh air from around the area to be
drawn in through door grills, windows etc.
Induced draft / natural infiltration ventilation.
Mechanical ventilation systems contain the following components:
Fan:
Designed to provide the quantity of supply or exhaust air from
the ventilated space.
Filters:
(a) To prevent dirt particles entering the ventilated space from
the outside air.
(b) To prevent grease build-up in the ducting of exhaust
systems.
Ducting:
Designed to deliver or exhaust air to or from various locations
within the ventilated space.
Dampers:
Used to restrict or divert the air as it passes through the
ductwork.
Grills, Registers, Diffusers: Used to control the air flow to the ventilated
areas and to prevent entry of objects into the ductwork.
(Registers are usually in the wall, diffusers are usually in the
ceiling).
40
Test Equipment
Anemometer
The anemometer is a device used to measure the velocity of air travelling through a
duct or grille. Readings are measured in metres per second (m/s).
Air flow is measured in cubic metres per second (m3/s), therefore:
Air Flow (m3/s) = Velocity (m/s) x Area (m2)
1 m3/s = 1000 L/s
E.g. Calculate the air flow rate in L/s, leaving a duct 300mm x 250mm, having a
velocity of 2.1 m/s.
Air Flow = Velocity x Area
= 2.1 m/s x 0.3 m x 0.25 m
= 0.1575 m3/s
= 0.1575 m3/s x 1000
= 1.575 L/s
The most common locations to take velocity readings are:
In front of the evaporator coil in order to determine the face velocity of the
coil (and ultimately the capacity).
Under each of the Supply Air diffusers to determine the Discharge Air
velocity (and ultimately balance the air distribution system).
Under each of the Exhaust Air grilles to determine Exhaust Air velocity.
There are three (3) type of anemometer:

Rotating Vane Anemometer, which
provides a reading in metres so it can
be used in conjunction with a stop
watch in order to get a velocity in
metres per second (m/s).

Deflective Vane Anemometer, which provides a direct
reading in metres per second (m/s).
41

Hot Wire Anemometer, which provides a
direct electronic readout by measuring the
cooling action of moving air on a hot strand
of wire.
There are two methods practised when using anemometers. They are:

The Sweep Method, where the
anemometer is moved at a slow and
steady pace, commencing from one
corner and ‘sweeping’ across the entire
face of the coil or area to be tested and
then returning to the starting point.
Upon completion of the sweep, the
anemometer and the stop watch are
stopped and the anemometer reading is
divided by the time taken to complete
the sweep resulting in an averaged
reading in metres per second (m/s).
Anemometers used for this method generally have an inbuilt timer, if not it
will be necessary to utilise a stop watch.
Total of the meter reading
Velocity (m/s) = ------------------------------------------Time taken to obtain the reading

The Patch Method, is predominantly
used when the anemometer does not
have a timing factor and a stop
watch is used. In this method, a
number of readings are taken across
the face of the coil or area to be
tested for a given time per reading.
For each reading taken, divide the
reading by the time taken. Next it is
necessary to add all the readings
together and then divide the total of
the readings taken by the number of
readings taken to provide an average
reading.
42
Reading A1 Reading A2 Reading A3
Velocity (m/s) = --------------- + ---------------- + ---------------- etc
Time
Time
Time
Total of all meter readings
Average Velocity (m/s) = ---------------------------------Total number of readings
Manometer
The manometer is a device used to measure relatively low pressures or more
commonly, pressure devices.
Manometers are made in two (2) different styles. Both are used to measure the
pressure difference across an object, e.g. filter, coil, and fan:
The U-Tube Manometer. In order to read the amount of pressure applied, read
the value corresponding to the fluid level on one side of the tube and double it.

Inclined Manometer. In order to read the amount of pressure applied, read the
value according to the fluid level in the tube.
The Pitot-Tube
The Pitot-Tube is a device that is usually used together with an inclined manometer to
measure the static pressure, total pressure and velocity pressure within a ducted
system.
Using the Pitot-Tube
Connect the inclined manometer to the Pitot-Tube so that it will measure velocity
pressure. Ensure that the tube is pointing into the airflow and is held as straight as
possible.
43
Reading patterns for Pitot-Tubes
Taking Readings
Drill a series of holes (refer above diagram) and take several readings in each hole.
Find the average velocity pressure of the readings.
To convert average velocity pressure (Pa) to velocity (m/s):
_______________
Velocity = 1.29 x √Velocity Pressure
Air Flow Pressures in Ducts
There are three (3) air flow pressure to consider in a duct. They are:
Static pressure
Velocity pressure
Total pressure
Static pressure is the pressure which acts equally in all directions against the walls of
a tube, pipe or duct. It can best be measured by placing a probe against a small hole in
the wall of the duct. It is pressure necessary to overcome the friction of the moving
air, and is measured using the manometer.
44
Velocity pressure is the actual pressure due to speed or velocity of the air. It is
measured by using a tube facing directly into the airflow, but because the static
pressure also enters the tube, another tub is placed at a small in the wall of the duct to
measure static pressure. Thus the two tube’s static pressure balances each other out,
leaving only the velocity pressure being measured.
Total pressure is the sum of the static pressure and the velocity pressure. It is
measured by the tube facing directly into the airflow.
Terms Associated with Air Distribution
Damper
A device used to vary the volume of air passing through the duct by
changing its CSA (Cross Sectional Area).
Turning Vanes
Sheet metal blades or vanes placed in the ductwork at the point
of a bend. They are shaped like the bend to help the air travel smoothly
around it.
Throw
The horizontal distance that the air will travel once it leaves the supply
duct.
Drop
The vertical distance that the horizontally projected air will fall.
Terminal Velocity This is the average air stream velocity at the end of the throw. It
is taken at a height of 2 metres from the floor and should be
approximately 0.25 m/s.
Spread
The distance that the air stream increases in width once it leaves the
outlet. The angel of spread is usually 30O from the direction of throw.
Spread can be achieved in both the vertical and horizontal planes.
Primary Air The conditioned air being delivered to the space along the supply duct.
Secondary Air
The air already occupying the space with which the primary air
mixes.
45
Practical Exercise: Air Balancing
Task
To balance the supply air volume being delivered by an air-distribution system using
the proportional air balance method.
Equipment
Suitable air handling system with a minimum of three outlets.
Air measurement instruments such as:
o Anemometer
o Air measuring hood
Tape measure.
Screwdriver or Allen keys suitable to adjust air dampers.
Procedure
1.
Operate the air supply system and allow conditions to stabilise.
2.
Fully open all air volume control dampers, branch dampers and louvers on
outlets. Check that coils, filters, etc are clear and that the fan is operating
to the required duty.
3.
Using the correct air measuring instrument, measure the air velocity from
each outlet.
4.
Calculate the volume flow rates (L/s) from all outlets. Add the values
together to obtain total supply air volume (L/s).
5.
Calculate the proportional quantities for each outlet.
6.
Starting from the outlet furthest from the fan, balance the system.
Note: record all readings and calculations in the Table of Results. Number the
outlets with number 1 being the furthest from the fan.
Outlet
Number
Outlet
Velocity
m/s
Outlet Size
mm x mm
Table of Results
Outlet
Actual
2
Area m
Volume
m3/s
Design
Volume
m3/s
1
2
3
4
5
6
46
Proportional
Factor
The Underlying Principles of Air Distribution
The principles are to achieve control over the air movement within a space so that:
Noise levels are kept to a safe minimum.
Draughts at the occupied level are avoided.
Air stratification is avoided.
There are no stagnant pockets of air.
Noise
Discomfort due to monotonous low frequency sound waves or piercing high
frequency sound waves can be at the very least, an annoying distraction, at worst,
result in deafness.
As air moves through a length of ductwork or passes through a register, irregular
vibrations occur in the air. The frequency of these vibrations will determine whether
or not you can hear them.
As the velocity of air is increased, so the noise that is generated becomes more
audible.
The level of noise generated is measured in decibels (dB).
Note that a degree of background noise has become desirable in many office buildings
where separation between offices’ is provided by partitions. The noise provides a
degree of privacy for the occupants in each of the ‘booths’.
The sound of ‘wind’ in the atmosphere is generally audible once the air velocity
reaches 6 m/s (20 kph).
Many registers (diffusers) tend to generate a whistling noise once the air velocity
reaches 2.5 m/s.
The following table provides the recommended maximum outlet velocity to expect in
various building types.
Application
Libraries, sound studios, operating theatres
Churches, domestic residences, hotel bedrooms,
hospital rooms and wards, private offices.
Banks, theatres, restaurants, classrooms, small
shops, general offices, public buildings, ballrooms.
Commercial kitchens, factories, warehouses,
department stores, workshops, gymnasiums.
Maximum Outlet Velocity
1.75 m/s to 2.5 m/s
2.5 m/s to 4.0 m/s
4.0 m/s to 5.0 m/s
5.0 m/s to 7.5 m/s
The noise level may be reduced by:
Internally insulating the ductwork (sound absorbed).
Externally insulating the ductwork (sound is attenuated).
Sealing cracks and joints around windows and doors.
Reducing the outlet velocity (as per the above chart).
47
Draughts
Air movement is required to ensure uniform distribution of the supply air throughout
the zone being conditioned but if the velocity of the secondary air (air within the
room) is toon high the occupants will feel a draught.
A relationship exists between:
The secondary air velocity.
The difference between the primary air temperature and the secondary air
temperature.
The activity of the occupants within the room.
The combination of these factors will determine whether or not the majority of people
occupying the room at the moment will experience a draught.
The table below shows the accepted head height velocity of the secondary air for both
the heating and the cooling cycles.
Activity
Example
Sitting for long periods
Sitting for short periods
Light work
Heavy work (warm area)
Office work
Restaurants
Shops, light manufacturing
Dancing, cooking, factories
Maximum Velocity (m/s)
Cooling
Heating
0.1
0.2
0.15
0.3
0.2
0.35
0.3
0.45
Air velocities below 0.075 m/s will give a feeling of stagnation.
The difference between the primary air temperature and the secondary air temperature
should never exceed 12K.
Example: For the neck region, a velocity of 0.3 m/s at a temperature of 0.5K below
the room temperature will be acceptable to 80% of the occupants. If the velocity in the
same room is dropped to 0.2 m/s then 90% of the occupants will be happier.
Generalisation: The maximum air velocity within a zone is generally assumed as 0.21
m/s while a minimum velocity of 0.12 m/s is necessary to ensure distribution of
temperature throughout the zone.
Air Stratification
When air settles into layers it is said to be stratified. This is a very common problem
in heating applications where the hot air rises (forming a layer of hot air near the
ceiling), and the cold air falls (forming a layer of cold air near the floor).
48
Air Stratification
This problem can be overcome by forcing the air to circulate within the zone but, as
you will see in the following diagrams, the placement of the supply and return air
registers within the zone will determine whether or not you will obtain optimum air.
The following diagrams illustrate the various places that the registers have been
placed in relation to each other, together with the problems of each setup.
Example 1
Here you can see that during summer months the cool primary air falls to the occupied
level (where it is needed), and the warm air rises to the ceiling where it is removed
and returned to the cooling coil. This is ideal.
However, during the winter months the warm supply air will travel straight across the
ceiling and pass out through the return air duct. The cold air will remain in the
occupied zone leaving the occupants quite uncomfortable. The air has become
stratified.
49
Example 2
In this situation you can see that during the summer months, the cool supply air will
travel straight across the floor and pass out through the return air duct (possibly
resulting in a draught around the lower parts of the body), while the hot air will be
trapped in the ceiling area. The air will be stratified once again.
However, during the winter months, the warm supply air will rise up through the zone
(passing through the occupied zone), while the cold air will fall to the floor from
where it is removed and returned to the heating coil. This setup is ideal for the heating
cycle.
Example 3
This setup is the most common. The circulation pattern during the cooling cycle will
be similar to those in Example 1 diagrams, (except that a small portion of primary air
may be drawn into the return air duct if they are too close to each other).
Once again the circulation pattern during winter is totally inadequate but many
systems today are setup so that the primary air velocity is increased during the heating
cycle in an effort to drive the warm air down into the occupied zone.
50
Example 4
Stratification will occur during the cooling cycle but after a period of time will
eventually settle at a fairly high level within the zone. This is generally acceptable
because the separation layer is often above the occupied level.
A cold spot will occur in the far side of the zone during the heating cycle, so your
feeling of comfort will totally depend on where you happen to be seated within the
room.
Example 5
Hot spots will occur in the top corners of the zone during the cooling cycle but a good
portion of the occupants will feel comfortable because there is good circulation
through the centre of the room. The main problem is that the warm air is not being
returned to the cooling coil.
Stratification will occur during the heating cycle but after a period of time will
eventually settle at a low level within the zone. It will be acceptable to those
occupants that are standing or moving around but not very acceptable to those who
are sitting for long periods because they will feel a cold draught around the legs.
51
Ducting
Ducting is generally formed by folding sheet metal into the desired shape however;
many large buildings make use of wall and roof cavities to transfer the air between
floors.
Both Return and Supply Air ducts may be insulated but the Supply is more commonly
insulated to:
• Provide sound control (noise attenuation)
• Prevent condensation (when dewpoint temperatures are high)
The duct may be any shape but is generally round, square or rectangular.
The best shape is round. It has the lowest material usage and the lowest friction loss
(low resistance therefore low pressure drop).
The next best is square. It is the easiest to manufacture (cheapest).
The most practical is rectangular. It will fit into most cavities.
Calculating Duct Size
Round Duct CSA = π × d2
4
Where CSA = Cross Sectional Area
π = Pi or 3.14159265
d = Diameter
.
Square Duct
Size (each side) = √CSA
Rectangular Duct
W=2×h
Duct Layout
Trunk Ducted System
• Uses minimum sheet metal but is complicated to manufacture and install.
• Provides best control of air flow.
52
Extended Plenum System
• Uses a greater amount of sheet metal but branch ducts may be fitted after the
extended plenum has been installed (making installation much easier).
Box Plenum System
• Cheapest to manufacture and simplest to install.
Changing the Size and Shape of Ductwork
• This is known as a reducer. It is used to change the size of a duct run.
•
This is known as a transition. It is used to change the shape (and size if
necessary) of a duct run.
53
Overcoming Pressure Drop in Ductwork
Any ducted system is a compromise between the pressure drop created when trying to
move air and the cross sectional area of the duct through which the air has to travel.
The following guides should be considered in an effort to reduce resistance within a
duct run.
54
This is a poorly constructed supply air reducer. The eddy currents created will result
in excessive pressure drop.
•
The eddy currents developed in this return air reducer are not as bad but still
result in unwanted pressure drop.
•
This is the desirable way to construct a reducer in the supply air duct. Eddy
currents will not form and therefore the pressure drop along the duct run will
be minimal.
•
The guide vanes will force the air to follow the shape of the duct and thereby
prevent eddy currents from forming at the point of expansion.
55
Dampers
A damper is used to restrict or divert the air as it passes through the duct work (i.e. it
controls the amount of air flowing throughout its length).
Various types have been developed for different purposes.
Parallel Blade Damper
This type of damper is not suitable for the control of air volume because the reduction
in air volume is not proportional to the damper movement (i.e. the damper must close
to approximately 80% in order to reduce the air volume by approximately 50%).
It is only used when an open or closed situation is required, e.g. fire dampers.
If automatic operation is required it may be fitted with a 2 position damper motor.
It also tends to force air to one side of the duct.
Opposed Blade Damper
This type is used where modulating volume control is required.
If automatic operation is required then it is fitted with a proportional damper motor
(modulating motor).
56
Splitter Damper
This type is generally used to balance each of the branch ducts.
Once set, it does not normally need to be moved again. The travel of the damper
should be restricted in order to prevent damage due to air pressure against the blade.
Butterfly Damper
This damper is used in round duct to control the air volume along a branch.
The handle must be locked in position once adjustments have been made.
57
Fire Dampers
If the ductwork passes through a fire rated wall then a fire damper must be installed
inside the ductwork at that point. It is held in the open position by a fusible link.
If the fire penetrates the ductwork then the link will melt and the damper will close
preventing the fire from travelling into the next zone.
An access panel should be located in the ductwork near the fire damper so that regular
inspections may be made on the link and repaired if necessary.
The specification and installation requirements for fire dampers are covered in AS
1682 (Parts 1 & 2).
58
Grilles, Registers, and Diffusers
59
Review Questions
1. What is the velocity of air? _________________________________________
_______________________________________________________________
2. What is the volume flow rate of air? _________________________________
_______________________________________________________________
3. What is static pressure? ___________________________________________
4. What do the following abbreviations stand for?
OA _____________________________________________________
RA _____________________________________________________
SA ______________________________________________________
EA ______________________________________________________
5. What are eddy currents? ___________________________________________
_______________________________________________________________
6. How do we measure air in a duct? ___________________________________
_______________________________________________________________
7. How do we measure air leaving an outlet? _____________________________
_______________________________________________________________
8. Which is the better duct for supplying air – round, square or rectangular?
Explain your answer.
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
9. Find the Volume Flow Rate of air passing through the coil.
_______________________________________________
_______________________________________________________________
_______________________________________________________________
60
10. What are the two methods to measure air flow over a coil? Explain both
methods; you may draw diagrams to assist your explanation.
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
61
Fans and Fan Laws
Fans are used in the air conditioning industry to:
• Supply air over a cooling / heating coil;
• Supply fresh air from outside;
• Remove unwanted air from toilets, kitchens, etc;
• Pressurise a stairwell during the event of fire;
• Return air to the air conditioning units in large applications;
• Assist the evaporation rate in cooling towers.
There are two basic types of fan:
• Centrifugal
• Axial
Centrifugal Fans
Centrifugal fans are capable of delivering large volumes of air against a considerable
resistance.
For these reasons, centrifugal fans are commonly used in the systems to overcome
filter resistance and duct resistance.
Types of Centrifugal Fan
• Forward curve
• Backward curve
Forward Curve
The most commonly used centrifugal fan type. It will move a large volume of air at a
relatively slow speed. The impeller usually contains 32 to 64 narrow blades.
Power consumption will increase as the volume flow rate of the fan increases (i.e.
speed increases) making it possible to overload the fan motor if the speed is increased
too high.
The disadvantage of the fan is that if the duct runs go too long, the static pressure
becomes erratic and therefore smooth air supplies are affected.
Backward Curve
This fan type must be run at a relatively high speed in order to achieve the desired
volume flow rate and is therefore heavier in construction (usually made from steel).
The impeller will generally contain 12 to 24 deep blades.
Its biggest advantage is that it will develop a very high static pressure and is therefore
suitable for use in high rise office buildings where duct runs are long. ‘Air Foil’
construction dramatically improves the fan’s efficiency.
Its disadvantages are:
• Cavitation, which occurs with excessive air volumes, thus decreasing the
amount of air delivered down the duct;
• Noise
62
Axial Fans
There are three primary types of axial fan:
• Propeller fans – provide a high volume of air but at a relatively low static
pressure. They are therefore not suitable for use in moving air through
ductwork. They are widely used for exhausting and ventilating purposes. A
cowling placed around the fan will improve its performance quite
considerably.
• Tube axial fans – are mounted in a round section of duct (or tube). They are
capable of developing higher static pressure than the propeller fan due to the
airfoil blades and the small clearance between the blade tip and the tube
housing.
• Vane axial fans – are similar to the tube axial fan except that the guide vanes
have been fitted to reduce the rotary motion imparted to the air by the spinning
action of the blade. This allows the fan to operate at higher static pressures and
improved efficiency.
63
Fan Laws
The following factors play a major role in the Fan Laws:
• Speed
• Volume Flow Rate
• Static Pressure
• Power Consumption
With constant Density and variable Speed,
• The Volume Flow Rate will vary proportionally to the speed;
• Static Pressure will vary to the speed, ‘squared’;
• Power Consumption will vary to the speed, ‘cubed’.
Speed & Volume Flow Rate
V1 n1
=
V2 n2
Speed & Static Pressure
Ps1 ⎛ n1 ⎞
=⎜ ⎟
Ps2 ⎜⎝ n2 ⎟⎠
Speed & Power Consumption
Q1 ⎛ n1 ⎞
=⎜ ⎟
Q2 ⎜⎝ n2 ⎟⎠
2
3
Example 1
A motor rotating at 1000 rpm n1 is delivering air at 300 L/s V1 with a static pressure
of 150 Pascals Ps1 whilst consuming power of 1.5 kW Q1
What would be the new volume flow rate V2 the new static pressure Ps 2 and the new
power consumption Q2 if the motor speed is increased
to 1200 rpm n2 ?
n1 = 1000 rpm
V1 = 300 L/s
n2 = 1200 rpm
V2 = ?
Ps1 = 150 Pa
Q1 = 1.5 kW
Ps 2 = ?
Q2 = ?
Volume Flow Rate:
V1
V2
=
V2 =
n1
n2
V1n2
n1
=
300 × 1200
1000
=360 L/s
64
Static Pressure:
Ps1 ⎛ n1 ⎞
=⎜ ⎟
Ps 2 ⎜⎝ n2 ⎟⎠
Ps 2 =
2
Ps1
⎛ n1
⎜⎜
⎝ n2
2
⎞
⎟⎟
⎠
=
=
150
⎛ 1000 ⎞
⎜
⎟
⎝ 1200 ⎠
2
150
0.6944443
=216 Pa
Power Consumption:
⎛n
= ⎜⎜ 1
Q2 ⎝ n 2
⎞
⎟⎟
⎠
Q1
Q2 =
3
Q1
⎛ n1
⎜⎜
⎝ n2
⎞
⎟⎟
⎠
=
3
=
1500
⎛ 1000 ⎞
⎜
⎟
⎝ 1200 ⎠
3
1500
0.5787035
=2592 Watts
=2.59 kW
65
Example 2
A fan running at 650 rpm n1 supplies air at 4200 L/s V1 with a static pressure of 250
Pascals Ps1 whilst the motor is consuming 2.1 kW Q1
If the fan speed is reduced to 480 rpm n2 calculate:
Volume Flow Rate:
V1
V2
=
V2 =
n1
n2
V1n2
n1
=
4200 × 480
650
=3101 L/s
Static Pressure:
Ps1 ⎛ n1 ⎞
=⎜ ⎟
Ps 2 ⎜⎝ n2 ⎟⎠
Ps 2 =
2
Ps1
⎛ n1
⎜⎜
⎝ n2
2
⎞
⎟⎟
⎠
=
=
250
⎛ 650 ⎞
⎜
⎟
⎝ 480 ⎠
2
250
1.8337671
=136 Pa
Power Consumption:
⎛n
= ⎜⎜ 1
Q2 ⎝ n 2
⎞
⎟⎟
⎠
Q1
Q2 =
3
Q1
⎛ n1
⎜⎜
⎝ n2
⎞
⎟⎟
⎠
=
3
=
2100
⎛ 650 ⎞
⎜
⎟
⎝ 480 ⎠
3
2100
2.4832261
=846 Watts
=0.85 kW
66
Filtration
Sick Building Syndrome
According to Honeywell, who spent years analysing some 30 typical buildings, the
greatest cause of ‘Sick Building Syndrome’ (SBS) is improperly maintained and
managed HVAC (Heating, Ventilation and Air Conditioning) Systems.
Honeywell ‘experts’ studied buildings with manifest problems difficult to diagnose,
but over 50% reported ‘SBS’ symptoms.
If more than 20% of the occupants complain of fatigue, headaches, irritation of the
eyes or throat, and the symptoms last more than two weeks and disappear when the
occupants leave the building, SBS is suspected.
In several cases, exposure to indoor contaminants may cause disease or impairment
called Building Related Sickness.
Often, particular pollutants are identifiable, but increasing ventilation does not get rid
of the problem. Examiners found multiple problems in 11 buildings of the 30 analysed
with chemical contaminants responsible for 75% of the complaints; 15% by normal
thermal problems; microbiological agents and humidity that was too high or too low
accounted for the remaining 10% of concern.
A combination of disorders were found including design and operation problems that
embrace maintenance, load and control changes. Investigators determined that dirty
air intakes, dirty filters, fouled heating and cooling coils were the main culprits.
Air Cleaning
Air entering an air conditioned space must be filtered to:
Keep the fan, coils and registers clean and therefore ensure high operation
•
efficiency.
Prevent dirt particles from entering the air conditioned spaces. This applies
•
especially to Precision Assembly Rooms and Operating Theatres.
• Reduce allergic attacks to Hay-fever and Asthma sufferers.
67
Particle Sizes
All particles are of different size. Typical examples are:
Human hair – 100 microns
•
Smallest particles visible to the naked eye – 20 microns
•
Human blood corpuscle – 10 microns
•
Tobacco smoke particulate – 0.25 micron
•
Filter Rating
The specification label of filter media will generally provide one or more of the
following values:
Pressure drop across the filter
•
Velocity and rated pressure
•
Filter capacity - % rating
•
Washing method
•
Filter Types
1. Dry Arrestance Filters – remove particles from the air by trapping them between
fibres of the filter mat. Materials may include:
Cloth
•
Felt
•
Glass fibre
•
Paper
•
Synthetic
•
These types are usually for dust particles. To improve their efficiency,
manufacturers have included ‘adhesive’ compound on the entry side of filters,
they are disposable when dirty.
Construction Types of Arrestance Filters
Panel – used in domestic and package units.
•
Roll filters – a continuous roll of filter media used on central plant air
•
conditioning systems. The Pressure Drop (PD) as sensed across the filter
activates a mechanism which ‘rolls / advances’ the filter media. As the roll is
expended it will require replacement.
68
•
•
Bag filters – used in club / pub applications, more surface area of the media is
exposed to the air flow, thus improving the efficiency. They are good for
acoustic control.
Corrugated filters – are panel filters produced in a corrugation style. This
improves efficiency because of the greater surface area.
2. HEPA Filters (High Efficiency Particle Arrestance)
This type of filter construction is achieved under strict guidelines. They MUST
provide an average filtering efficiency of 99.998%.
They are made from a glass paper media that is packed in a very dense concertina
fashion. When looked through, you will see no light at all.
3. Wet and Viscous Filters
The filter media is impregnated with oil.
•
Cleaning is very difficult.
•
Small applications – kitchen exhausts using panel construction.
•
Large applications – high rise office air conditioning using continuous roll
•
filters rotating slowly through an oil bath.
Cleaning is an extremely messy job. Avoid if possible, or give to an
•
apprentice.
4. Electrostatic Precipitators
The air is passed through a wire grid arrangement that is connected to a DC power
supply of between 13,000 to 20,000 Vdc. The grid is known as the ioniser because
it causes the dust particles to become electrostatically charged.
Once the particles have become charged they pass through a set of collector plates
(cells) that are placed parallel to the air stream and connected to a DC power
supply of approximately 6,000 Vdc.
The charged particles are attracted to the plates that have been covered with an
adhesive. The plates must be washed and the adhesive re-applied during
maintenance.
69
Review Questions
1.
Explain what is meant by ‘Sick Building Syndrome’. ____________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________
2.
List four (4) actions that can be taken to overcome the causes of ‘Sick
Building Syndrome’.
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
3.
If most occupants of a building are complaining of being tired after being in
the building for a short period what is the most likely cause?
_______________________________________________________________
_______________________________________________________________
4.
What is the most likely cause of dirty smudging around ceiling diffusers?
_______________________________________________________________
_______________________________________________________________
5.
What is the name given to the study of the properties of air?
_______________________________________________________________
6.
Define ‘metabolic’ rate.
_______________________________________________________________
7.
Define ‘occupied zone’.
_______________________________________________________________
8.
What is the term given for the introduction of fresh air in an enclosed space?
_______________________________________________________________
70
9.
List the following properties of standard air.
Dry bulb temperature ___________C
Relative humidity ___________%
Barometric pressure ____________hPa
10.
Define the term ‘comfort conditions’.
_______________________________________________________________
11.
What is the full name of the following abbreviations?
OA ___________________________________________________________
RA ___________________________________________________________
MA ___________________________________________________________
SA ____________________________________________________________
12.
In what part of a split system is the supply fan found?
_______________________________________________________________
13.
List three factors that affect human comfort in a conditioned space.
a) _____________________________________________________________
b) _____________________________________________________________
c) _____________________________________________________________
14.
Name two methods used to move the air in an enclosed space.
a) _____________________________________________________________
b) _____________________________________________________________
15.
What is the name of the refrigeration component that reverses the flow of
refrigerant in a reverse cycle system?
_______________________________________________________________
16.
Will solar heat penetrate glass?
Yes
⁪
No
⁪
17.
Why do you feel cold when the temperature is below comfort conditions?
_______________________________________________________________
71
18.
19.
Match each piece of equipment with its correct use by placing the number of
the ‘Use’ next to the equipment name. (It is possible for a piece of equipment
to have more than one use).
Equipment
Use
⁪
Chiller set
1
House
⁪
Evaporative cooler
2
Small offices
⁪
Room air conditioner
3
Office building
⁪
Split air conditioner
4
Factory
⁪
Packaged air conditioner
5
Shop
List four factors that affect the quantity of heat lost by perspiration.
a) _____________________________________________________________
b) _____________________________________________________________
c) _____________________________________________________________
d) _____________________________________________________________
20.
Why do you feel hot when there is no air movement around you on a hot day?
_______________________________________________________________
21.
On the following diagram show:
a) the air movement (by drawing arrow heads on the indicator lines)
b) the type of air, either OA, RA or SA
72
Air Conditioning is defined as the process of treating air to control simultaneously its
temperature, humidity, cleanliness, distribution and noise to meet the requirements of
the conditioned space.
Purpose of Air Conditioning
The purpose of Air Conditioning is to serve two primary applications. These include:
• The promotion of human physical well being
• The improvement of industrial processes.
Psychrometrics
Introduction
Psychrometrics is the study of the properties of mixtures of air and water vapour and
is the basis for all Air Conditioning process calculations.
Terminology
• Dry Bulb Temperature (OC DB)
The temperature of air measured by an ordinary thermometer
•
Wet Bulb Temperature (OC WB)
The temperature of mixtures of air and water vapour measured by a
thermometer whose bulb is covered with a wetted wick and exposed to a
rapidly moving air stream
•
Relative Humidity (RH %)
The ratio of the actual water vapour in the air compared to the water vapour in
the air when the air is completely saturated at the same temperature
•
Saturation Temperature (Dew Point Temperature) (OC)
The temperature at which condensation of moisture begins.
•
Specific Humidity (Moisture Content) (g / kg)
The ratio of mass of water vapour to mass of dry air in a given volume of
moist air.
•
Enthalpy – Total Heat (kJ / kg)
A thermal property indicating the quantity of heat in the air.
•
Specific volume of dry air ( L / kg OR m3 / kg)
The volume occupied by 1 kg of dry air.
73
Revision of psychrometric chart
There are various conditions of air that may be studied using the assistance of a
psychrometric chart.
These conditions include:
• Dry bulb temperature
• Wet bulb temperature
• Relative humidity
• Enthalpy
• Specific volume of Dry Air
• Specific humidity (Moisture Content)
• Saturation temperature (Dew Point Temperature)
See ARAC for further details of how the conditions listed above can be found on a
Psychrometric process
The psychrometric chart can also be used to study various processes in Air
Conditioning.
These processes include:
1. Cooling and Dehumidification
2. Sensible Cooling
3. Sensible Heating
4. Dehumidification
5. Evaporative Cooling
6. Humidification
7. Heating and Humidification
8. Chemical Dehumidification
(Note: 6, 7 and 8 are not done by a standard Air Conditioning Unit)
See ARAC for further details of where the processes are located on a psychrometric
chart.
74
The air conditioning process
The air conditioning process can be shown on a psychrometric chart. The process
shown below is a cooling process.
Psychrometric calculations
Air Conditioning calculations may be assisted by a psychrometric chart. Some
common calculations drawn from a psychrometric chart include the following:
Mixed air dry bulb condition
The Health Act of NSW regulations and AS1668, Part 2 requires a minimum
percentage of fresh air to be introduced into a conditioned space, to offset stale air and
odours.
When this process is put into practice the cooling capacity would be influenced by the
condition of the air entering the coil. This air is made up of return air (B) from the
conditioned space and air from outside (C) and is known as Mixed Air (D).
A formula that may be used to calculate this condition is:
t MA.DB =
(V
RA
× t RA. DB ) + (VOA × t OA.DB )
(VRA + VOA )
Where:
t MA.DB = Mixed air dry bulb temperature
VRA
=
Volume flow rate of the return air
t RA.DB = Return air dry bulb temperature
VOA
=
Volume flow rate of the outside air
tOA.DB = Outside air dry bulb temperature
75
Apparatus dew point temperature
Apparatus Dew Point (ADP) refers to the effective surface temperature of the
conditioning coil.
Put simply, the ADP is the lowest achievable temperature of the air leaving the
cooling coil if the coil apparatus was 100% efficient and no air bypassed the coil.
(WB = DB = Saturation Temperature)
The ADP is found by extending the coil process line, from the nixed air (D) to the air
leaving the coil (A), through to the saturation temperature line. The intersection is the
ADP.
In practice, the air leaving the cooling coil is never as cold as the ADP due to the
Bypass Factor.
Bypass Factor
The bypass factor is the portion of the air that is considered to pass through the
conditioning coil completely unaltered.
The formula for the bypass factor is:
BF =
t LDB − t ADP
t EDB − t ADP
Where:
BF = Bypass Factor
t LDB = Dry bulb temperature of the air leaving the coil (oC)
t EDB = Dry bulb temperature of the air entering the coil (oC)
t ADP = Apparatus due point temperature (oC)
76
Total Heat
Total heat of the coil is the amount of heat (both sensible and latent) that is added or
removed during the process. The total heat of a process can be found:
• From the psychrometric chart
• By calculation. If the latent and sensible heat of the process is known.
From the psychrometric chart
TH = hMA - hSA
Where:
TH = Total heat (kJ/kg)
hMA = Enthalpy of the mixed air (kJ/kg)
hSA = Enthalpy of the supply air (kJ/kg)
By calculation:
TH = SH + LH
Where:
SH = Sensible heat (kJ/kg)
LH = Latent heat (kJ/kg)
77
Sensible Heat
Sensible heat is when there is a change in temperature but there is no change in
moisture. Sensible heat of the coil can be found using the following methods:
• By calculation if the latent and sensible heat of the process is known
• By calculation using the sensible heat ratio
SH = hE - hSA
Where:
SH = Sensible heat
hE = Enthalpy of the process if there was no moisture content change (kJ/kg)
hSA = Enthalpy of the supply air (kJ/kg)
By calculation:
SH = TH – LH
Where:
SH = Sensible Heat (kJ/kg)
Calculation using the Sensible Heat Ratio (SHR)
SH = TH X SHR
Where:
SHR = Sensible Heat Ratio (see below on how to attain)
78
Sensible heat ratio
Sensible heat ratio is the ratio of sensible heat to the total heat load on the room or
coil. The remaining proportion is latent heat.
Sensible heat ratio can be found using the following methods:
• By calculation if the latent heat and sensible heat of the process is known
• From the psychrometric chart (see ARAC for details).
Latent heat
Latent heat takes into account the change in moisture content that takes place through
a process. The latent heat of the coil can be found:
• By calculation if the latent heat and sensible heat of the process is known
LH = hMA - hF
Where:
hMA = Enthalpy of the mixed air (kJ/kg)
hF = Enthalpy of the process if there was no change in dry bulb temperature
By calculation
LH = TH – SH
79
Where:
Determining the refrigerating capacity
• Plot the psychrometric chart locating the mixed air and supply air
• Determine the enthalpy change between the mixed air and the supply air
• Calculate the volume of the circulating air
V = A×ω
Where:
V = Volume flow rate (m3/s or L/s)
A = Duct area (m2)
ω = Velocity (m/s)
Calculate the mass flow rate of the air through the coil
This is the mass of air flowing through the cooling coil.
m=
V
v
Where:
V = Volume flow rate (L/s)
m = Mass flow rate (kg/s)
v = Specific volume (m3/kg or L/kg)
Note: The specific volume is measured from the same condition on the psychrometric
chart as the point where the velocity was determined. That is the supply air duct,
return air duct, etc …
Calculate the coil capacity
The coil capacity relies on two major factors, these being the mass flow rate of the air
flowing through the coil and the enthalpy difference between the air entering the coil
and the coil and the air leaving the coil.
Q = m x Δh
Where:
Q = Coil capacity (kJ/.s or kW)
m = Mass flow rate (kg/s)
Δ h = Difference in enthalpy (kJ/kg)
80
Moisture removal rate
This is used to theoretically determine the condensate capacity.
A simple calculation can approximate the amount of water deposited on the coil
during full load conditions within a specified environment.
mw = m SA X (wEA − wLA )
Where:
mW = Moisture removal rate (g/s)
m SA = Mass flow rate of the supply air (kg/s)
wEA = Moisture content of the air entering the coil (g/kg)
wLA = Moisture content of the air leaving the coil (g/kg)
To transform these units to litres per hour
g 60 X 60 kg
=
=
s
1000
hr
1kg = 1 litre of water, therefore:
1kg 1L
=
hr hr
81
Practical exercise: Plotting a psychometric chart
Task
To plot the conditions on the chart record various values
Procedure
Plot the following conditions +30OC DB / 24OC WB on the psychrometric chart.
From the plotted points, draw and record the related conditions listed below.
Conditions
Results
Moisture
Dew Point Temperature
Relative Humidity
Specific Volume of Dry Air
Enthalpy of the Air
82
83
Calculation exercise:
Psychrometric calculations
Task
To plot a systems operation conditions on a psychrometric chart and calculate various
values using the formulas learnt in this module.
Procedure
1.
Plot the following conditions on a psychrometric chart
Outside Air (OA) = 30OC DB / 24OC WB
Return Air (RA) = 24 OC DB / 50% RH
Supply Air (SA) = 12OC DB/11OC WB
Supply Air Quantity = 1500 L/s
Outside Air Quantity = 150 L/s
2.
Determine the following:
a. Mixed Air Conditions
Formula =
b. Apparatus Dew Point temperature (ADP)
Show plotting on psychrometric chart.
c. Coil Bypass Factor
Formula =
d. Amount of Total Heat absorbed by the cooling coil. Total heat may be
found from the psychrometric chart.
e. The Sensible Heat Ratio of the (a) cooling coil (b) room.
This may be found from the psychrometric chart
84
f. Amount of Sensible Heat absorbed by the cooling coil.
Formula =
g. Amount of Latent Heat absorbed by the cooling coil
Formula =
h. Mass flow rate of the air through the cooling coil
Formula =
i. Cooling coil capacity.
Formula =
j. Amount of water (in litres) deposited in the condensate tray in one
hour at full load operation, under the specified conditions
Formula =
85
86
Review questions
1.
What is meant by the term ‘Psychrometric’?
2.
List the important gases that mix to form dry air.
3.
What is meant by the term ‘Mixed Air Condition’?
4.
List five factors that need to be addressed if the calculated bypass factor is
higher than the rated design of the cooling coil
5.
Define Apparatus Dew Point.
87
6.
A cooling coil has an ADP of 10OC and the mixed air condition onto the
cooling coil is 23OC DBG, 60% RH. What will happen to the moisture
content of the air? Explain your answer.
7.
An electric reheat coil is located in the supply air duct. Will this device
remove moisture from the air stream? Explain your answer.
8.
List the two major factors that determine the capacity of a cooling coil.
9.
What is meant by the term Sensible Heat Ratio, (SHR) and what is the
purpose of identifying the Room Sensible Heat Ratio?
10.
List the seven air conditioning processes that may be identified on the
88
Package (Unitary) Units
Applications
Package units are installed into various commercial applications, including small
office buildings, computer rooms or a single floor of a multi-storey building.
Types
Package units are self contained systems that are either air-cooled or water-cooled.
In air-cooled package units, the condenser is remotely located outside to ensure good
heat transfer.
In water-cooled package units, the condenser is located adjacent to the compressor
with the ancillary water piping and cooling tower located externally from the package
unit.
89
General information
Advantages
Cheap installation cost in comparison to a central plant, ease of service and all
components are centrally located together in one housing.
Disadvantages
The disadvantages of using a package unit in multi-storey buildings are the energy
consumption costs, noise control, service accessibility (i.e. fan bearing changes) and
equipment failure.
Air distribution
The package unit may be installed within the conditioned space with a ‘free blow’
system, or it may be installed internally or externally with ductwork for air
distribution.
Air filtration
The units are usually fitted with panel type filters and electrostatic filters may also be
fitted for ducted systems.
Refrigerant
The refrigerant found in the majority of package units is R22, although some early
Carrier systems (‘50K’ series) employed R500 to overcome inefficient performance
from those units imported from America designed for 60Hz electrical supply. Other
refrigerants will be and are used as R22 is phased out.
Fans
The fans are commonly forward curved blade, centrifugal fans with a static pressure
of 200 to 600 Pascals.
Cooling capacity
Package units may vary in capacity from 1 kW to 1000 kW.
Heating methods
The Package Unit Air Conditioning system may provide heating as well as cooling.
Heating can be achieved by means of electric heating elements or for package units
incorporating air cooled condensers by means of reverse cycle operation.
90
Operating conditions
TABLE 1: RECOMMENDED OPERATING CONDITIONS OF AIR CONDITIONING
PACKAGE UNITS
Apparatus
Condition
Consideration
Depends on location & fresh
Air on cooling coil
24OC – 27OC
air intake.
Depends on coil bypass factor
Air off cooling coil
10OC – 15OC
and airflow rate through coil.
An excellent split would be 12
to 15 Kelvin but 12 is
Coil split
Approximately 12 K
common. Depends on coil
bypass factor, condition of coil
and airflow rate.
No greater than 2.5 m/s as
Cooling coil face
Optimum of 2.5 m/s
condensation droplets will be
velocity
thrown down the air stream.
These conditions are
Saturated suction
commonly found on package
On R22 +4OC @ 464 kPa
operating conditions
units using R22.
Depends on location and water
Water cooled on R22
approx. 38OC @ 1360 kPa flow rate.
Saturated condensing
temperatures
Air cooled on R22 approx. Depends on airflow rate and
45OC @ 1630 kPa
coil condition.
No lower than 150 kPa
Depends on compressor type
above operating suction
Oil pressure
and recommended oil pump
pressure (semi hermetic &
pressure ratings.
open drive)
Depends on location,
Condenser
condition of condenser coil,
temperature difference 12 to 15 Kelvin
ambient conditions and
(air cooled)
airflow rate over coil.
Depends on water flow rate,
Condenser
cooling tower fan setting, and
temperature difference 8 to 10 Kelvin
efficiency of the cooling tower
(water cooled)
and water supply.
Depends on ambient wet bulb
Tower approach
Recommended 6 K
conditions.
Depends on cooling tower fan
Tower range
Approx. 4 to 6 Kelvin
temperature setting and water
flow rates.
Maintenance procedures
General information
The extent of any preventative maintenance program varies according to location and
actual operating conditions. After a suitable trial period, local conditions may
determine some modification to the program, i.e. clean air filters weekly instead of
monthly.
91
Monthly inspection generally includes the following
1. Clean air filters, inspect media for damage and ensure that filters are clear of
debris.
NOTE: Filter media should be replaced annually as efficiency reduces following
repeated washing, or replaced to filter manufacturer’s specifications where non
washable medias are used.
2. Check refrigerant charge. The sight glass in the liquid line indicates the correct
balance. Care should be taken when viewing the glass from the initial start up,
as it requires approximately 10 – 15 minutes for the system to fully circulate
the refrigerant. During this time a bubbling sight glass can occur.
3. Inspect all drive belts for tightness and wear. Do not over tighten, as excessive
bearing wear will occur.
4. Check blower wheels for tightness on shafts, dust build up, etc.
5. Check condensate tray and drain for cleanliness. If necessary flush tray out
thoroughly.
6. Check all cabinet components and ensure all panels are adjusted correctly to
close onto the door seals.
7. Check thermostat for the correct set point.
Annual inspection generally includes the following
1. Fit gauges to the compressor and note operating pressures. Check efficiency of
compressor.
2. Test the superheat setting of the TX valve by placing a digital thermometer on
the suction line at the TX bulb and comparing with the saturated suction
temperature. Correct temperature difference settings should be between 4 and
7 K.
3. Where heating elements are fitted into the ductwork and connected via heater
safeties into the electrical control circuit, check the manual reset safety
thermostat for correct operation by removing the evaporator motor fan fuses,
and allowing still air heating to activate the safety control.
To reduce the time taken to cut out the heating elements, re-position the bulb
closer to the element surface.
4. Using a tong type ammeter, check all motor amperages and compare against
nameplate ratings. Record voltages between phases and neutral.
5. Replace filter media.
92
6. Check pressure of high and low pressure cut out settings as follows:
High Pressure
Water cooled unit cut out:
Average water temperature through condenser
32OC
Condenser temperature difference
+ 8K
Safety margin
+ 5K
Cut out temperature
45OC
O
45 C = 1630 kPa (R22) cut out setting – manual reset

Air cooled unit cut out:
Designed ambient condition i.e. Penrith (different locations will
have different design ambient conditions)
35OC
Condensing temperature difference
+ 15 K
Safety Margin
+ 5K
Cut out temperature
55OC
55OC = 2080 kPa (R22) cut out setting – manual reset
Low Pressure
Cut out – any pressure above 0 kPa i.e. 150 kPa
Suggested cut in (auto reset)
350 kPa
7. Check cabinet base and panels for paint damage and rust. Apply corrective
treatment as necessary.
Package unit system servicing
The following information discusses the major safety controls fitted to a package unit
and identifies the major causes for them to ‘trip’.
It is by no means a complete analysis of the reciprocating system. Instead, its
intention is to familiarise you with the operation of the package unit and provide the
necessary background for you to analyse and accurately report any developing
problems.
High pressure control
Sensing the compressor discharge pressure, the high pressure control monitors the
efficiency of the condensing process. Poor efficiency, reflected by high condensing
pressure conditions, is usually caused by:
- Dirty condenser
- Excessive refrigerant charge
- Reduced water flow rate (water cooled condenser)
- Reduced air flow rate (air cooled condenser)
Low pressure control
The low pressure control monitors the pressure at which the refrigerant is evaporating
in the evaporator tubes. Low evaporator pressure is generally caused by:
- Refrigerant shortage
- Faulty expansion valve
- Restricted liquid line filter drier
- Failure of compressor to unload
- reduced supply air flow rate
93
Oil pressure control
The oil pressure control senses the difference between the oil pump discharge
pressure and the pressure within the compressor crankcase. The difference is net oil
pressure or effective oil pressure. Low oil pressure is usually the result of:
- Oil shortage
- Faulty or worn oil pump
- Faulty crankcase heater allowing refrigerant to condense in the compressor
sump.
94
Practical Exercise 1:
Reading an electrical circuit diagram of a
package unit.
Task
To read an electrical diagram of a package unit and identify its operation by
answering a series of questions.
Procedure
From the electrical schematic diagram below of a Package Unit Air Conditioning
System, answer the questions which follow.
De-ice cycle
Each outdoor coil has its own de-ice unit. A remote sensor is positioned to initiate a
de-ice cycle at a coil temperature of -5OC. The de-ice cycle will be terminated when
the temperature rises to 10OC. A timer safety limits the de-ice period to 10 minutes.
The de-ice control has a lockout that limits de-icing to once every 33 minutes.
95
Abbr.
CCH
Crankcase Heater
Abbr.
HT
Heating Thermostat
Abbr.
OFR
CM
Compressor Motor
IFC
Indoor Fan Contactor
OTOL
Outdoor Fan Relay
Outdoor Thermal
Overload
CMC
IFM
Indoor Fan Motor
CST
Compressor
Contactor
Compressor Start to
Start Timer 10 mins
IFOL
RVC
Reverse Cycle Valve
CT
Cooling Thermostat
LP
Indoor Fan Thermal
Overload
Low Pressure
Control
TD
Time Delay
HP
High Pressure
Control
OFM
Outdoor Fan Motor
TM
Internal Motor
Thermostat
Comp No 1
Comp No 2
Amps
Per
Phase
Description
Description
Description
FLA
LRA
FLA
LRA
FLA
LRA
Outdoor
Fan No
1
FLA
2 x 14
2 x 78
2 x 14
2 x 78
11
66
1.6
Supply Air Fan
Outdoor
Fan No
2
FLA
Outdoor
Fan No
3
FLA
1.6
1.6
1. The indoor fan motor trips out on thermal overload, will the compressors be
able to run, YES or NO? Explain your answer.
2. What is the purpose of CST1 and CST2 coils?
3. Explain in step form the De-ice cycle.
4. How many condenser fan motors will operate if condenser fan motor No. 2
trips out on internal motor thermostat?
96
5. The system’s cooling thermostat is calling for full cooling. How long will it
take before compressor No. 4 would start after compressor No. 1 is energised?
6. Compressor CM1 fails to start when called for full cooling because of a burnt
out contactor coil. From the diagram determine how many compressors would
be able to operate during this fault condition.
7. Do the four crankcase heaters cycle off during compressor operation? Explain
your answer.
8. It states that compressor No.1 has a LRA rating of 2 x 78. What does the LRA
stand for and what does LRA rating mean?
9. Compressor No. 1 is very short of refrigerant causing Low Pressure Control to
perform its safety operation. What would be the operating characteristics of
the system having this fault? (Note that the LP controls are manual reset).
10. What will happen to the system during the heating cycle if the neutral wire
connected to the De-ice control on stage 1 heating mode breaks?
97
11. In the space provided, reproduce the schematic wiring diagram into an
Electrical Ladder control circuit diagram. Also identify the electrical
components.
98
System operating characteristics
Task
To determine the standard operating conditions of a package unit.
Equipment

Package unit
Service manifold gauges
Thermometers
Trade tools
Safety

Remember to work safely at all times.
Wear protective clothing, footwear and safety glasses when working around
machinery and refrigerants.
Do not play around when working around machinery.
Be aware that machinery may start at any time.
Practice safe working procedures at all times.
Procedure
1.
2.
3.
4.
5.
Inspect unit.
Open all necessary valves and run unit.
Fit manifold gauges.
Allow system to equalise after 15 minutes of operation.
In the space provided below record the following information:
Suction Pressure
kPa
Discharge Pressure
kPa
Saturated Suction Conditions
O
kPa
Saturated Condensing Conditions
O
kPa
C
C
Cooling coil air ON
O
O
Cooling coil air OFF
O
O
C DB
C WB
C DB
C WB
K
Condenser Temperature Difference
Supply air quantity
L/s
Return air quantity
L/s
Outside air quantity
L/s
Percentage of fresh air
%
99
Pressure difference across the return air filters
Pascals
O
C DB
Ambient conditions
% RH
Amperes
Current draw on compressor motor
Unit Model No.
Unit Make – Brand Name
Cooling load (nameplate)
Watts
Heating load (nameplate)
Watts
Type of fan shaft bearings
Type of fan pulley
Fan belt size
Conclusions
1. Plot the necessary operating condition on a psychrometric chart.
2. Calculate
- Cooling Coil Operating Capacity (Psychrometric)
- Coil Sensible Heat Ratio
- Coil Operating Bypass Factor
- Coil ADP
100
Maintenance procedures for package units
Task
To construct a preventative maintenance program.
Procedure
Complete the maintenance schedule for a water cooled package unit with semi
hermetic compressors and electric heating elements.
Note: Tick only one column for each item.
ITEMS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
MONTHLY
3
MONTHLY
6
MONTHLY
Compressor
Shaft sea
Safety controls
Operating Pressures
Oil Level
Conditioners
Filters
Bearings / Grease
Fan belts
Condensate drain
Evaporator coil
Refrigeration System
Leak test
Refrigerant charge
Operating conditions
Cooling Tower / Condenser
Clean sprays
Grease bearings
Drain, clean basin
Clean water strainer
Electrical Supply and
Control Circuit
Tighten connections
Calibrate / set controls
Check overloads
Check amperage
101
ANNUALLY
Troubleshooting for package units
Task
To practice the skills of identifying faults based on symptoms.
Procedure
1. For the chart of a commercial air conditioning system, list in each of the
boxes, faults that you would expect to find for each of the symptoms listed.
Note: Only use each FAULT once.
2. Answer the problems listed after the chart.
FAULT 1
High ambient conditions.
TX valve hissing and
superheat is high. Short
cycling and current draw on
compressor is low.
Runs but not
cooling efficiently
FAULT 2
Condenser fan running,
refrigerant charge OK
and there is no evidence
of non-condensables.
Tripping out on HP
control
FAULT 3
Space temperature too
high. Initial operating
pressures normal then
after a short time period
low suction pressures
occur, high suction
superheat, sight glass
showing full.
Intermittent short
cycling
COMPRESSOR
Not Running
Condenser fan running,
compressor contactor deenergised, coil shows
continuity and resistance
normal
FAULT 4
Running
continuously
High back pressure, low
head pressure, gas charge
OK, superheat normal.
FAULT 5
102
Short cycling
System cycling on LP
control, ice formation on
coil, very low suction
superheat, high room
temperatures, filters
clean. No air movement
through room.
FAULT 6
Problem 1
On inspection of a large DX package unit you find the package unit pumped down
and cut out on Low Pressure Control, but the unit is not short of refrigerant
What two possible TX valve faults could cause this symptom?
What could cause these faults?
How would you rectify these faults?
Problem 2
On a service call you find a lecture theatre with a package A/C system that has an air
cooled condenser on the roof with all four condenser fans running. A low ambient
temperature exists and there is insufficient cooling in the conditioned space.
What is the fault?
How would you rectify this problem?
103
Problem 3
On a hot and humid day, you are called to a package unit with a water cooled
condenser. The operating head pressure is 1700 kPa on R22 and the supply condenser
water entering the condenser is 36OC.
What are two possible causes of this problem?
How would you rectify these two possible faults?
Problem 4
The suction pressure on a package unit is too low, ice has built up on the coil and the
plant performance has reduced.
What are three possible causes for this condition?
104
Fault finding
On a package unit that has been ‘tricked up’ with faults by your teacher, analyse the
system and record the symptoms, possible faults and the method of rectifying these
faults.
(Remember to work safely at all times).
Fault 1
Symptoms
Possible faults
Remedies
Fault 2
Symptoms
Possible faults
Remedies
105
Fault 3
Symptoms
Possible faults
Remedies
Fault 4
Symptoms
Possible faults
Remedies
106
Fault 5
Symptoms
Possible faults
Remedies
107
Review questions
1.
What components make up an air conditioning package unit?
2.
Where is the package unit designed to be installed?
3.
What are the common types of compressors found in a package unit?
4.
What type of metering device is commonly used in large capacity package
units?
5.
When are water cooled condensers used in package units?
108
6.
List four applications where an air conditioning package unit is likely to
be found.
7.
Give three reasons why a package unit would be chosen rather than any
other type of air conditioner.
8.
Name two types of fans commonly used with package units and where in
the unit you would find them.
9.
What type of filtration medium is used to clean the air through a package
unit?
10.
Many package units are fitted with lockout relays. What is their purpose?
109
11.
List three advantages and three disadvantages of package units in
commercial office applications.
Advantages
Disadvantages
12.
Solid state crankcase heater relays are commonly fitted to package units.
What is their function?
13.
List the two most common types of heating systems used in Package
Units.
14.
From the diagram ‘Typical package air conditioning unit with service
panels removed’ in ARAC, Volume 2, Chapter 20, design a maintenance
check sheet and report form to be used by the employees od a fictitious
firm when carrying out the maintenance to a package unit air conditioning
system.
110
Notes
111
A.R.E.M.A heat load estimating sheet
A.R.E.M.A is the acronym for Air Conditioning and Refrigeration Equipment
Manufacturers Association.
This Association and the Commonwealth Scientific and Industrial Research
Organisation (CSIRO) combined their expertise and developed an Air Conditioning
Heat Load Estimation Sheet in the interests of providing the HVAC industry with a
standard air conditioning load estimation procedure.
This Heat Load Estimating Sheet is a basic estimating procedure and is recommended
only for use on domestic and small to medium commercial heat load applications.
There are more in depth heat load estimation sheets that are used on more complex
heat load designs. Many design engineers consult such methods as the Carrier AIRAH
Heat Load Design Sheet format found in their System Design Manual.
A.R.E.M.A heat load estimation example (ARAC, Volume 2, Chapter 22)
Using your text to guide you, carefully go through the procedures in the example
while referring to the A.R.E.M.A Heat Load sheet on the next page.
112
Air Conditioning Survey Form
No.
Area m2
Item
Cooling Factors
selected time).
1.
South …………….x.…………
South East ……….x………….
East ……………...x………….
North East ……….x………….
North …………….x………….
North West ………x………….
West ……………..x………….
South West ………x………….
Horiz. ……………x………….
2.
3.
Double glass
4.
Hollow brick
Brick veneer
Weatherboard
5.
6A.
Partitions
Internal walls
Ceiling
6B
Ceiling
6C
7.
8.
9.
10.
11.
12.
13.
14.
............
………
………
………
………
………
………
………
………
Pitched roof above
No insulation
50mm insulation
Flat roof above
No insulation
50mm insulation
Floors
Slab on ground
Infiltration (S.H.)
Refer Table 1 – l/s
Lights
Watts
Special heat sources
Refer Table 2 (Sens. Heat)
People (Sens.Heat)
Quantity
Room S.H. sub total (Items 1 to 11)
Duct Gain
Room total sens. Heat (Items 12 + 13
Outside Air
[Use highest quantity only]
15.
A. Room volume m3 x 0.5
= …………..l/s
B. People x Rate Table 3
= …………..l/s
4 pm
Shades
Shades
In
Out
NIL
In
Out
57
170
375
549
353
50
50
50
492
6K
38.0
38
110
246
356
230
35
35
35
318
16
41
95
139
88
13
13
13
123
8K
51.0
60
57
50
50
113
435
621
508
524
10K
64.0
38
38
32
32
72
284
404
331
341
(12K)
(77.0)
16
16
13
13
28
110
154
126
129
14K
90.0
19.0
25.5
32.0
38.0
44.5
38.0
10.5
14.0
17.5
(21.0)
24.5
21.0
17.0
13.0
20.0
10.0
8.5
24.5
17.0
27.5
12.0
12.0
26.0
20.0
31.5
17.0
14.5
28.0
26.0
38.0
(20.5)
17.0
30.5
30.0
40.0
24.5
18.5
28.0
26.0
38.0
20.5
17.0
50.0
53.0
56.0
59.5
62.5
12.0
13.0
14.0
15.0
15.5
6.0
69.0
73.0
77.0
80.0
84.0
23.0
17.0
18.0
19.0
19.5
20.5
9.0
6.5
1.0
8.5
0.0
9.0
1.0
12.0
0.0
12.0
1.0
15.5
0.0
14.5
1.0
19.0
0.0
17.0
1.5
22.0
0.0
9.6
12.0
14.4
16.8
19.2
Incand. x 1.0
Fluor x 1.25
Sitting 72.0
Activity
Light 80.5
Factors for design Temp. Diff.
8K
9.6
10K
12K
12.0
18.
Infiltration from 8 ………….l/s
20.
Heavy 89.5
Add 10% if duct external to conditioned space
Cooling
Total Sensible Heat (Items 14 + 15)
LATENT GAINS COOLING
Refer Table 1 (Latent Heat)
People (Latent.Heat)
Quantity
Client
Address
NIL
16.
17.
19.
Watts
10 am
14.4
14K
16K
16.8
19.2
Cooling
X Factor from Table 4 ……………………………...
Sitting 45.5
Activity
Light 80.5
Heavy 160
21.
Room total latent heat (Items 18 to 20)
Cooling
22.
Outside Air from 15……….l/s
23.
Total Latent Heat (Items 21 + 22)
Cooling
24.
Grand Total Heat (16 + 23)
Cooling
25.
S.H.R. Room 14/(14 + 21) = ………………….Equipment 16/24 = ………………………
X Factor from Table 4
TOTAL
Compiled By
Date
HEATING
Factors
Watts
12K
77.0
51.5
14.5
14.4
Not
Used
Not
Used
Not
Used
R.S.H.
R.T.H
14.4
Sub
total
Factor
Table 5
Heating
Design Conditions
Summer OC
Ambient
db
wb
Room
db
wb
Diff.
db
wb
Winter OC
Ambient
db
Room
db
Diff.
db
wb
wb
wb
Room Area
m2
Room Volume
m3
Table 1 - Infiltration
Item
Description
Table 4 – Outside Air Latent Heat
l/s (Item 8)
No. people x
1.0
No. people x
Swing heavy use
4.0
No. people x
Revolving
1.0
Open
282
Tight fitting
Area m2 x 0.5
Average fitting
Area m2 x 1.0
Poor fitting
Area m2 x 3.5
Use manufacturer’s rating l/s
Swing med. Use
Doors (standard)
Windows (one
wall only)
Exhaust Canopy
Latent Heat
Item 10
Conditioner fan motor
Hair dryer (helmet)
Coffee percolator 5kW
Electronic equipment
Other motors
Refrigerators
Input Watts
548
1900
Input Watts
Input Watts
Input Watts
Nil
97
585
Nil
Nil
Nil
Smoking rate
42
8.4
15.9
24.3
33.3
43.5
54.0
66.0
Table 4B – Room Condition
Wet
Dry bulb temperature OC
bulb
20
22
24
26
28
temp.
O
16.2
13.8
11.1
8.9
6.0
12 C
22.5
20.1
17.4
15.0
12.3
14OC
29.1
26.7
24.0
21.6
18.9
16OC
36.3
33.9
31.2
28.8
26.1
18OC
44.4
41.4
39.0
36.3
33.9
20OC
-50.4
47.7
45.0
42.3
22OC
You may interpolate if necessary.
l/s
3.5
7.0
10.0
20.0
Check Factors
Watts
m 2 floor
(Items 18 & 22)
=
Wet
bulb
28 30 32 34 36 38 40
temp.
O
18 C 26.1 23.7 21.0 18.6 16.2 13.5 11.1
20OC 33.9 31.2 28.8 26.1 23.7 21.0 18.6
22OC 42.3 39.9 37.2 34.5 32.1 29.4 27.0
24OC 51.6 49.8 46.2 43.8 41.1 38.4 36.0
26OC 61.5 59.1 56.4 54.0 51.3 48.6 45.9
28OC 72.6 61.9 67.2 64.8 61.1 59.4 56.7
-81.9 79.2 76.5 73.8 71.1 68.4
30OC
Table 3 – Outside Air – Smoking
None
Low
Medium
High
.
Table 4A – Ambient
Watts
Sens. Heat
Item 10
.
Factor
Table 2 – Special Heat Sources
Description
Table 4A
Less Table 4B
=
Table 5 – Heating Factors
Factors for other Temp. Diff.
Temp. Diff.
Factor
l/s
=
Room volume m 3
10K
14K
16K
18K
0.85
1.17
1.33
1.50
Calculate a 12K load and multiply by the
factor above for the selected Temp. Diff.
NOTE: Major totals approximated to
Total Air Supply =
nearest 10 watts.
Item 14
1.2 x Temp. Rise
A.R.E.M.A heat load on computer
The basic AREMA Heat Load procedure has been applied by various manufacturers / suppliers to
operate various Heat Load computer programs. Once familiar with a program, the computer
makes it easier to use than the paper sheet because t does all the calculations for you.
Some of these programs include:
Camel
A.R.E.M.A load estimating
Carrier E2-II
114
A.R.E.M.A heat load estimation
Task
To practice the skills of using an AREMA heat load estimation sheet to determine the
heat load in a conditioned space.
Specifications

Application
Office space

Design Room Conditions
22OC DB / 50% RH

Windows
All windows are single glass
Window height is 1.6 meters
Shading is provided by Venetian blinds

Outside wall material
Hollow Block
Wall height is 2.6 meters

Ceiling and floors
The office is unconditioned above
The office is above an open space

Lighting
The office has 10 fluorescent lights each
rated at 40 watts

Auditioned heat sources
One tea urn
One refrigerator
One microwave oven (1000 watts)

People load
There are five office staff and one
manager

Office hours

Design ambient conditions for Sydney
9am to 5pm, 5 days per week
o Summer:
35.5OC DB and 24OC WB
o Winter:
7OC DB
Note: Design ambient conditions for summer and winter are available for all major
cities throughout Australia (and the world). Many of these tables can be found in the
Carrier Design Manual 1 as well as on computer system analysis heat load programs.
Procedure
Referring to specifications above and the diagram on the next page, complete with the
AREMA sheet provided, determine:
Grand total heat load for cooling
Sensible heat ratio for the room
Total heating load for winter
Air Conditioning Survey Form
No.
Area m2
Item
Cooling Factors
selected time).
1.
South …………….x.…………
South East ……….x………….
East ……………...x………….
North East ……….x………….
North …………….x………….
North West ………x………….
West ……………..x………….
South West ………x………….
Horiz. ……………x………….
2.
3.
Double glass
4.
Hollow brick
Brick veneer
Weatherboard
5.
6A.
Partitions
Internal walls
Ceiling
6B
Ceiling
6C
7.
8.
9.
10.
11.
12.
13.
14.
............
………
………
………
………
………
………
………
………
Pitched roof above
No insulation
50mm insulation
Flat roof above
No insulation
50mm insulation
Floors
Slab on ground
Infiltration (S.H.)
Refer Table 1 – l/s
Lights
Watts
Refer Table 2 (Sens. Heat)
People (Sens.Heat)
Quantity
Room S.H. sub total (Items 1 to 11)
Duct Gain
Room total sens. Heat (Items 12 + 13
Outside Air
[Use highest quantity only]
15.
A. Room volume m3 x 0.5
= …………..l/s
B. People x Rate Table 3
= …………..l/s
4 pm
Shades
Shades
In
Out
NIL
In
Out
57
170
375
549
353
50
50
50
492
6K
38.0
38
110
246
356
230
35
35
35
318
16
41
95
139
88
13
13
13
123
8K
51.0
60
57
50
50
113
435
621
508
524
10K
64.0
38
38
32
32
72
284
404
331
341
(12K)
(77.0)
16
16
13
13
28
110
154
126
129
14K
90.0
19.0
25.5
32.0
38.0
44.5
38.0
10.5
14.0
17.5
(21.0)
24.5
21.0
17.0
13.0
20.0
10.0
8.5
24.5
17.0
27.5
12.0
12.0
26.0
20.0
31.5
17.0
14.5
28.0
26.0
38.0
(20.5)
17.0
30.5
30.0
40.0
24.5
18.5
28.0
26.0
38.0
20.5
17.0
50.0
53.0
56.0
59.5
62.5
12.0
13.0
14.0
15.0
15.5
6.0
69.0
73.0
77.0
80.0
84.0
23.0
17.0
18.0
19.0
19.5
20.5
9.0
6.5
1.0
8.5
0.0
9.0
1.0
12.0
0.0
12.0
1.0
15.5
0.0
14.5
1.0
19.0
0.0
17.0
1.5
22.0
0.0
9.6
12.0
14.4
16.8
19.2
Incand. x 1.0
Fluor x 1.25
Sitting 72.0
Activity
Light 80.5
Factors for design Temp. Diff.
8K
9.6
10K
12K
12.0
18.
Infiltration from 8 ………….l/s
20.
Heavy 89.5
Add 10% if duct external to conditioned space
Cooling
Total Sensible Heat (Items 14 + 15)
LATENT GAINS COOLING
Refer Table 1 (Latent Heat)
People (Latent.Heat)
Quantity
Client
Address
NIL
16.
17.
19.
Watts
10 am
14.4
14K
16K
16.8
19.2
Cooling
X Factor from Table 4 ……………………………...
Sitting 45.5
Activity
Light 80.5
Heavy 160
21.
Room total latent heat (Items 18 to 20)
22.
Outside Air from 15……….l/s
Cooling
23.
Total Latent Heat (Items 21 + 22)
24.
Grand Total Heat (16 + 23)
25.
S.H.R. Room 14/(14 + 21) = ………………….Equipment 16/24 = ………………………
Compiled By
Date
HEATING
Factors
Watts
12K
77.0
51.5
14.5
14.4
Not
Used
Not
Used
Not
Used
R.S.H.
R.T.H
14.4
Sub
total
Factor
Table 5
Heating
Design Conditions
Summer OC
Ambient
db
wb
Room
db
wb
Diff.
db
wb
Cooling
Winter OC
Ambient
db
Room
db
Diff.
db
wb
wb
wb
Cooling
Room Area
m2
Room Volume
m3
X Factor from Table 4
TOTAL
Table 1 - Infiltration
Item
Description
l/s (Item 8)
No. people x
1.0
No. people x
Swing heavy use
4.0
No. people x
Revolving
1.0
Open
282
Tight fitting
Area m2 x 0.5
Average fitting
Area m2 x 1.0
Poor fitting
Area m2 x 3.5
Use manufacturer’s rating l/s
Swing med. Use
Doors (standard)
Windows (one
wall only)
Exhaust Canopy
Table 2 – Special Heat Sources
Watts
Description
Sens. Heat
Item 10
Latent Heat
Item 10
Conditioner fan motor
Hair dryer (helmet)
Coffee percolator 5kW
Electronic equipment
Other motors
Refrigerators
Input Watts
548
1900
Input Watts
Input Watts
Input Watts
Nil
97
585
Nil
Nil
Nil
Table 3 – Outside Air – Smoking
Smoking rate
l/s
None
Low
Medium
High
3.5
7.0
10.0
20.0
Check Factors
Watts
m 2 floor
=
Table 4 – Outside Air Latent Heat
Table 4A
.
Less Table 4B
.
Factor
(Items 18 & 22)
=
Table 4A – Ambient
Wet
bulb
28 30 32 34 36 38 40
temp.
18OC 26.1 23.7 21.0 18.6 16.2 13.5 11.1
20OC 33.9 31.2 28.8 26.1 23.7 21.0 18.6
22OC 42.3 39.9 37.2 34.5 32.1 29.4 27.0
24OC 51.6 49.8 46.2 43.8 41.1 38.4 36.0
26OC 61.5 59.1 56.4 54.0 51.3 48.6 45.9
28OC 72.6 61.9 67.2 64.8 61.1 59.4 56.7
-81.9 79.2 76.5 73.8 71.1 68.4
30OC
42
8.4
15.9
24.3
33.3
43.5
54.0
66.0
Table 4B – Room Condition
Wet
bulb
20
22
24
26
28
temp.
16.2
13.8
11.1
8.9
6.0
12OC
22.5
20.1
17.4
15.0
12.3
14OC
29.1
26.7
24.0
21.6
18.9
16OC
36.3
33.9
31.2
28.8
26.1
18OC
44.4
41.4
39.0
36.3
33.9
20OC
-50.4
47.7
45.0
42.3
22OC
Table 5 – Heating Factors
Factors for other Temp. Diff.
l/s
=
Room volume m 3
Temp. Diff.
Factor
10K
14K
16K
18K
0.85
1.17
1.33
1.50
Calculate a 12K load and multiply by the
factor above for the selected Temp. Diff.
NOTE: Major totals approximated to
nearest 10 watts.
Total Air Supply =
Item 14
1.2 x Temp. Rise
Evaporative Coolers
Evaporative coolers utilise the evaporation of water to cool the air stream through a
conditioned space. They are said to cool ‘up to the wet bulb line’.
Evaporative coolers are very effective in cooling dry locations, e.g. inland country
areas away from lakes, dams, etc.
In coastal areas the air has higher moisture content; therefore the efficiency of an
evaporative cooler is dramatically reduced.
Components
The components that make up an evaporative cooler include:

Water pump.

Water distributors.

Panel fill (Aspen).

Centrifugal fan with cowling (volute).

Simple water regulating method.

Water make-up valve.

1, 2, or 3 speed fan motor.

Water holding basin.
Basic operation
A water pump located in the sump of the cooler pushes water up into the distribution
trays. The trays disperse the water evenly over the fill that is held in the panels of the
cooler walls.
As the surface water evaporates, the temperature of the air (sensible heat) flowing
through the material in the panels drop.
The lowest possible temperature that the water can drop to is that of the wet bulb
temperature of the ambient air entering the cooler.
The loss of sensible heat is equal to the gain in latent heat. (ADIABATIC, heat energy
is neither lost nor gained during the process).
In some instances additional cooling can be achieved by adding in a cooling coil
before the wet medium. The coil has water recirculated through it from a conventional
cooling tower. Such ‘two stage’ systems add significantly to the cost of a system and
seldom can be economically justified. They do however result in a lower humidity in
the conditioned space.
119
Advantages
Lower capital cost than refrigerated air conditioning systems.
Lower energy consumption.
Large fresh air ventilation rate – excellent in areas of higher exhaust air
requirements, e.g. kitchens.
Disadvantages
Conditions inside are largely dependant on those outside.
Suitable for hot and dry climatic areas.
Provision must be made for the exhaust of large air quantities.
Larger ducts are required to handle the higher air quantities.
Precautions
Evaporative coolers are a cheap alternative to refrigerated air conditioning (about 25%
of the running cost and much cheaper to install), but a number of limitations apply to
their use.

They add a great deal of moisture to the air, therefore problems with mould
can occur.
The room must be well ventilated in order to exhaust the room air.
The unit must never be undersized for the load.
Room air must not be circulated.
120

Units are best suited to dry inland areas where high Wet Bulb Depressions are
experienced. Performance is poor in coastal areas.
The psychrometric process of evaporative coolers
As mentioned, the cooling process of an evaporative cooler is achieved ‘up to the wet
bulb line’. As air flows through the wetted pads, the air remains at the same heat
content but the moisture content increases. This is displayed on the psychrometric
chart below.
The drier the air the greater the ability the air has of absorbing this moisture. The
‘wetter’ the air, the less effective it is of absorbing the moisture and this results in
higher supply air temperature.
This ability of absorbing the moisture is referred to as the Saturation Efficiency.
Therefore, if an evaporative cooler was used in inland regions with low Relative
Humidity it would be more efficient than an evaporative cooler used in coastal areas
or near large water ways with high air Relative Humidity levels.
121
Review Questions
1. Explain the basic operation of an evaporative cooler.
2. List the six major components that make up an evaporative cooler.
3. The evaporative cooler operates mainly by cooling the water flowing over the
pads.
Answer:
True /False
4. Evaporative cooler performance is very susceptible to changes in the ambient wet
bulb temperature.
Answer:
True /False
5. The amount of water circulated over the pads is of little concern to the effective
operation of an evaporative cooler.
Answer:
True /False
6. What causes the Wet Bulb temperature to be lower than the Dry Bulb
temperature?
122
7. Define the term WET BUL DEPRESSION.
8. Unlike conventional Air Conditioning systems, all windows and doors of the
conditioned space should remain open. Why?
9. For an evaporative cooler to be effective, recirculated air should not be introduced
into the conditioned space through the cooler. Explain why.
10. Explain why an evaporative cooler is less effective in coastal regions compared to
inland regions.
11. Many registered Bowling Clubs, Leagues Clubs and RSL Clubs in coastal regions
employ the use of evaporative coolers. Other than some direct cooling, what is
their other main purpose for using these evaporative cooler applications?
12. Why can the evaporative cooler only cool the air passing over the pads to a
maximum of approximately 80% of the difference between dry bulb and wet bulb
temperatures?
123
13. In accordance to the Australian Standard 3666.1:1995 where can an evaporative
cooler be located?
14. In accordance to the Australian Standard 3666 and the NSW Code of Practice for
the Control of Legionnaire’s Disease, what must be done to an evaporative cooler
if it is not in use during the winter months?
15. Why should a water filter be fitted to the underside of the water pump of an
evaporative cooler?
16. From the diagram in ARAC Volume 2 Chapter 19 of an evaporative cooler,
design a maintenance check sheet and report form to be used when maintaining an
evaporative air cooling system.
124
Notes
125
Central Plant Systems
As the name implies, central plant systems refer to Air Conditioning equipment being
situated in a centrally located, sound controlled plant room.
They may also be referred to as ‘built up’ systems, as not all central plants have the
same components as the package unit.
Instead they are all individual applications to meet medium to large commercial
applications. Such factors as cost, design parameters, cooling and heating load
requirements, and humidity control, and customer preference determine what
equipment is found in an Air Conditioning plant room.
126
Basic types
There are 2 basic types of central plant systems. They are:
Direct expansion system
The surface of the aluminium finned evaporator is cooled by the direct expansion of a
refrigerant within the copper tubing (usually metered by an Externally Equalised TX
valve).
The coil has a multi-pass configuration to keep the pressure drop in the coil as low as
possible and to keep the coil surface temperature as even as possible.
It is also ‘close tubed’ to encourage as much turbulence as possible (reduces the
Bypass Factor). The fin spacing is generally between 300 to 500 fins per metre (2 to 3
mm per fin) which is much closer than can be used in medium and low temperature
refrigeration coils because ice is not formed on the high temperature (5OC) air
conditioning coils.
The coils Face Velocity is generally maintained at around 2.5 m/s. If this is exceeded,
then moisture may be blown off the coil and into the ductwork or conditioned space.
The air off (or Supply Air) temperature varies between 10OC and 14OC.
Chilled water (Chiller) system
The water is passed through the cooling coil delivered from the chiller unit at a
temperature between 5OC and 7OC. The coils are normally bottom fed and self venting
(by an air trap and a vent port that is provided at the top of the trap).
127
The water flow rate is generally maintained at around 1 m/s resulting in a water
temperature rise of around 6K to 8K through the coil.
The air off temperature varies between 10OC and 14OC.
Whether it is the Direct Expansion or Chilled water system they both require ducting
to deliver the air into the air conditioned space.
Central plant air distribution systems
There are various designs of ducting systems that meet the specific needs of each
individual application. Some of the more common duct design practices include:
Single zone low velocity system
This is the simplest form of all air system designs. The single zone low velocity
system, as the name implies responds to only one set of space conditions in a single
zone. The unit may be installed within or remotely from the space it serves and may
operate with or without distributing ductwork. Properly designed systems can
maintain temperature and humidity closely and efficiently and can be shut down when
desired without affecting the operation of adjacent areas.
Its use is limited to situations where variations occur almost uniformly throughout the
zone served or where the load is stable.
A single zone system would be applied to small department stores, individual shops in
an arcade, computer rooms, warehouses, churches, auditoriums and cafeterias.
Controlling the single zone system is accomplished by sequential operation of the
cooling and heating coils. Dehumidification can be accomplished by a ‘deep’ cooling
coil condensing out some of the water content (latent heat removal), sensibly cooling
the air and then re-heating to comfort levels. Single zone systems without reheat offer
128
cooling flexibility but cannot control summer humidity independent of temperature
requirements.
Terminal air conditioning unit
A variant of the single zone low velocity unit is the terminal air conditioning unit.
Terminal air conditioning units can be fitted with both chilled water and hot water
coils. Where more than one terminal air conditioning unit is fitted, they can be
interconnected with four types of water circuit piping arrangements, they are the:
One pipe system
Two pipe system, either reverse return or the direct return
Three pipe system
Four pipe system
One pipe system
This is where one pipe is looped around the building and acts as both the supply and
the return. The size of the piping is the same throughout because all the water flows
through this one pipe run. The length of the supply and return piping to each unit is
the same.
At each branch a take-off is used to direct water from the main line to flow through
the coil as required. The water temperature will vary throughout the pipe.
The coils must be designed to have a low pressure drop in order to keep the pump
head of the system within reasonable limits.
One pipe systems are extensively used for heating in residences and small commercial
buildings. They are not extensively used for cooling.
Two pipe system
Similar to the one pipe system but has instead two main water circuits, a supply and a
return. There are two configurations used, the direct return and the reverse return.
The direct return is the cheaper of the two systems to install due to it having shorter
pipe runs but has the additional cost of having to balance the system to ensure it
works correctly.
The reverse return though is more costly to install but has the advantage of being selfbalancing.
129
Two pipe systems are used for either heating or cooling in residences and small
commercial buildings. Change over from heating to cooling for seasonal variances is
done either automatically or manually.
Three pipe system
This arrangement uses two supply pipes (one for hot water and one for chilled water)
and one return. A three way valve is used for each unit to control the temperature in
each unit. Additional control valves (not shown below) are required to prevent
excessive flow of water through either the chiller or the boiler.
Not commonly used due to the potential problems of extreme temperature returns
back to the chiller or boiler, high operating costs and maintenance problems.
130
Four pipe system
Though more expensive to install due to additional piping costs, this system offers the
better control of all the piping arrangements. This arrangement consists of two supply
pipes (one for hot water and one for chilled water) and two return pipes (again one for
hot water and one for chilled water). In this arrangement there is no mixing of the two
water circuits, cold water will return to the chiller and hot water will return to the
boiler or heat exchanger.
An additional benefit of this arrangement is that dehumidification is also made
available at all units simultaneously.
The four pipe system is often used in large building applications.
131
Multi zone system
The multi zone system is applicable for serving a relatively small number of zones
from a single, central air handling unit. The requirements of the different zones are
met by mixing cold and warm air through dampers at the central air handler in
response to zone thermostats. The mixed conditioned air is distributed through the
building by a system of single zone ducts. Either packaged units complete with all
components or field fabricated apparatus casings may be used. Smaller low heat load
zones sharing the system are affected by lower space temperatures therefore reheat
coils are needed to overcome these problems. Expense in running costs gets charged
to the consumer, storeowner, etc.
New multi zone units are now being used which have individual heating and cooling
coils for each zone supply duct. These systems use less energy than units with
common coils; the supply air is heated or cooled only to that degree required to meet
the zone load.
Individual space thermostats control the zone mixing dampers.
Applications: small office buildings, schools, stores, etc.
Dual duct systems
The dual duct high velocity system is an ‘all air’ system that gives very close control
of zone temperatures. Although it is a highly expensive system to install it has been
applied to a number of important public works buildings in Australia. The central
plant comprises of a single fan, usually of the backward-curved type for high pressure
supply (1000 to 1500 Pascals). The fan directs air to two ducts, one containing the
heating coil and the other the cooling coil. The ducts contain the high pressure air that
is then piped to the air distribution units throughout the building. These are usually
round and much smaller than the more typical low velocity, low pressure ducts of
other systems.
These ducts run throughout the buildings and branch off into smaller lines supplying
the mixing boxes that proportion the hot and cold air according to the needs of the
area being supplied. In the boxes, the velocity pressure is also reduced, to pressures of
about 100 Pascals, so that normal ceiling distribution outlets can be used.
The beauty of this design is the ability of this system to maintain constant volume of
air to the mixing boxes and the way in which this is uniquely controlled within the
mixing box.
Within the mixing box are two actuating motors, one for hot air damper control and
one for cool air damper control. For full heating, the heating damper would be fully
open and the cooling damper closed. As the heating load reduces, the room thermostat
senses the temperature rise, and calls for some cooling by opening the cold air
damper/valve. The immediate result is an increased air volume. The extra air raises
the box pressure. The increased pressure is sensed by a pressure measuring device,
(Static Pressure Regulator) which controls the hot air damper, and it closes
proportionally to the opening of the cooling valve.
As further cooling is required, the room thermostat opens the cold air damper and the
static pressure regulator closes the hot duct in response to pressure changes. The
132
mixing box may supply air to one or up to six outlets, depending on the size of the
zone under control of one thermostat.
Most valves and dampers, when half open will supply more than 50% of the fully
open flow. Therefore the volume supplied by a mixing box will increase when both
dampers are partly open. In all cases, a pressure reducing baffle in the middle of the
box ensures good mixing and reduces the downstream air velocity.
Face and bypass system
A face and bypass damper control set up may be used with direct refrigerant or
secondary refrigerant coils. When a face and bypass damper is used, the coil does a
better job of moisture removal as the coil is maintained at a lower temperature.
The important facet of the duct design and size is that the bypass damper is to be sized
to offer the same pressure drop across the cooling coil to avoid all the airflow
bypassing the coil.
Economiser cycle
The economiser cycle makes sure of free conditioning by avoiding the use of
mechanical cooling during periods of low ambient (outside) temperatures.
133
Variable air volume system
Variable air volume systems have one distinct advantage over the constant volume
design systems. That is the VAV’s ability to conserve energy of the operation of the
entire air conditioning plant. The principal of Variable Air Volume (VAV) operation
is, as the name implies, varies the air volume to suit the desired conditions.
VAV’s are located within a box and are the last component before the air is
discharged from the outlets, (Terminal VAV Units). A space thermostat which if it
senses the room is down to temperature, signals the VAV to close the air off. In most
cases this can be as low as 20% of maximum air volume. When the thermostat senses
undesirable warm room temperatures, the VAV is opened up to allow full volume
flow rate of air. Because the VAV systems modulate the air volume, the pressure in
the ducts will modulate as well. This modulating static pressure can be used to reduce
or increase the air supplied and the power consumed. This can be through one of the
accepted fan modulating techniques.
These include:
1. Fan bypass or spill air, whereby a static pressure regulator senses an increase
in static pressure and modulates a control bypass damper that recirculates the
air back to the return air duct or to a wasted area, i.e. roof space.
2. Variable speed fan. Using a supply air static controller to vary the speed of
the fan. Becoming the most common of the stated applications.
3. Inlet vane control. This is where the inlet vanes on the fan itself are
positioned by an actuator responding to a signal from the static pressure
sensor.
Although the principal is the same for all VAV’s the manufacturing designs differ.
Two commonly used terminal VAV units are:
Expanding bellows design, whereby the expansion of a bellows is used to
restrict the airflow into the conditioned space. Air pressures may be supplied
either from the pneumatic control system, or from the supply duct air which is
always at a higher pressure than the air in the VAV bow (system powered). A
regulator and room thermostat in each case controls Bellows pressure.
Air valve design, whereby two components make up the air valve. The
damper is moved back and forth across the air slots in the cylinder to vary the
airflow. The power to move the damper coming either from the system air
pressure, or pneumatic or electric motor. The ability of a large control unit to
supply a number of satellite terminals can be achieved by the ‘Air valve
design’.
Induction units
Induction units are specially designed air – water systems that are fitted around the
perimeter of buildings. They are fitted to remove the sensible heat load (primarily
solar heat load) through the windows, removing this load from the main air
conditioning system.
134
Maintenance procedures
Like the package unit, Central Plant Air Conditioning Systems require preventative
maintenance programs to ensure the highest performance of operation and prevent
unnecessary faults and avoid excessive expense to the owner of the plant.
The central plant and associated equipment installed within a central plant system has
been designed to give long trouble free service when operated and maintained
correctly.
To gain optimum performance and maximum service life, it is important that a regular
inspection and maintenance program be carried out.
This section is a guide only to establish such a program. In all instances, you should
refer to the appropriate sections of the manufacturer’s manual. Their
recommendations will take first priority.
All electrical, mechanical and rotating machinery constitute a potential hazard,
particularly for those not familiar with its design, construction and operation.
Accordingly, the operation, maintenance and repair of any such items of plant should
be undertaken only by personnel qualified to do so. All such personnel should be
thoroughly familiar with the equipment, the associated systems and controls, and the
procedures set out in the relevant literature from the manufacturers.
Safety
Maintenance personnel must exercise good judgement along with proper safety
practices to avoid damage to equipment and prevent personal injury.
It is assumed that your company has established a safety program based upon a
thorough analysis of industrial hazards.
Before operating or performing maintenance on the plant and associated components
described in this manual, it is suggested that the safety program be reviewed to ensure
that it covers the hazards arising from high speed rotating machinery. It is also
important that due consideration be given to those hazards which arise from the
presence of electrical power, hot oil, high pressure and temperature liquids, toxic
liquids and gases, and flammable liquids and gases.
Proper installation and care of protective guards, shutdown devices and other pressure
protection equipment should also be considered an essential part of any safety
program.
Also essential are special precautionary measures to prevent the possibility of
applying power to the equipment at any time when maintenance work is in progress.
In general, all personnel should be guided by all basic rules of safety associated with
the equipment.
General maintenance procedures
The maintenance instructions that follow are general in nature and assume adequate
trade knowledge on the part of you to engage in these maintenance procedures.
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The schedules for routine preventative maintenance activities are based on the
expected plant usage rates for a twelve (12) month period.
Refrigeration leaks
All joints should be checked with a reliable leak detector. When the plant is new,
these checks should be made frequently. It is recommended that a general inspection
be carried out at least every six (6) months.
Watch for any traces of oil on fittings or under the refrigeration equipment,
compressor, etc. as this may indicate gas leaks. Check with a detector if in doubt. In
particular, check joints such as flanges, valves, flare nuts.
Always keep the valve bonnets and caps securely closed when not operating the
valve. Check around the coil and the return bend and headers.
Electric motors
Check where necessary for motor casing temperature rise.
Blow through motor terminal boxes to remove accumulated dust and if possible,
check motors for current input at full load and for insulation resistance.
Check the operation of motor overloads.
Bearing lubrication
For general purposes the following instructions can be followed:
Grades of grease acceptable for the general lubrication of bearings, for fans, pumps,
etc. are:
Castrol EPL 2
Castrol EPL 3
Shell Oil Co. Aust Ltd.
Alvania No: 2
Shell Oil Co. Aust Ltd.
Alvania No: 3
The interval between lubrication depends on:
The grade of grease used.
Temperatures at which the bearing operates.
The size and speed of the bearings.
The hours and severity of use.
It is not possible to give definite figures on lubricating intervals because grease in a
bearing does not suddenly lose its lubricating ability; rather the loss is gradual.
Lubrication intervals should be determined by experience but the following
information may be used as a guide. It may be found that the intervals established
could be safely extended, particularly where the unit is operated intermittently. But it
is possible that they may be found to be too long where operating conditions are
extremely severe.
Washing out and repacking bearings
Generally, all open type bearings should be completely washed out and repacked at
least every three (3) years. This can be satisfactorily done by washing out housings,
bearings and caps with a mixture of oil and petrol or other degreaser. Before opening
136
up the bearings, all dirt and foreign matter should be removed from the vicinity of the
bearing caps.
After washing, the bearing should be examined for signs of wear. If in good condition,
it should be repacked by pressing fresh grease well into the case, race and balls and
rollers and all spaces within the bearing itself should be completely filled. After
repacking the bearing, any surplus grease should be wiped off.
The labyrinth grooves (shaft seals) in the bearing, should be scraped out, cleaned with
petrol and when dry, refilled with fresh grease. The bearing caps should be filled half
to two-thirds full with grease.
Greased for life bearings (sealed bearings)
These bearings require no servicing as they are sealed and are to be replaced
completely when no longer serviceable. These bearings need only to be checked
regularly for unusual noise or overheating, which if evident, indicates that the bearing
requires replacement. For equipment undergoing a general overhaul, (e.g. 3 years) it
may be advisable at that time to replace all such bearings.
Vee-belt (v-belt) drive maintenance
V-belts should be tightened only sufficiently to prevent slip on starting. Too tight a
drive will cause undue wear and possible bearing failure. Correct tension may be
gauged approximately by depressing the belts with the hand when deflection should
be 12 mm to 25 mm, depending on the length of the drive.
When adjusting the tension make sure alignment of pulleys is maintained. In renewing
belts, renew all belts in the one drive, with a matched set to obtain even tension. The
size of the belts is stamped into the top of each belt. Refer to the relevant
commissioning sheet for belt sizes.
Refrigeration chillers
The systems are fully charged with oil at start-up and levels should be checked
regularly. Regularly check operating pressures as indicated on plant and record oil
data.
At least once a year, check operation and set points of all operating and safety
controls. Ask the chiller manufacturer to provide their yearly maintenance and service
programme.
Pump maintenance
Refer at all times to the manufacturer’s instructions for maintenance procedures for
the pump installed.
For general purposes however, the following should be observed at all times:
Pumps should never be run dry.
Pump couplings must be properly aligned at start-up and be checked regularly.
Glands (packed and mechanical) must be properly lubricated (refer
manufacturer’s instructions) and checked regularly.
Bearings (pump and drive) to be lubricated as under Bearing Maintenance.
Bearings MUST be treated as per manufacturer’s instructions. Do not over
grease.
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Pump cavitation must be investigated and stopped immediately.
Pumps should not vibrate.
Chilled and condenser water piping systems
All joints should be checked for leaks. When the plant is new, these checks should be
made frequently. It is recommended that a general inspection be carried out at least
every six (6) months.
Regularly check operating pressures and temperatures, as indicated on appliance, and
record all data. At least once a year, check operation and set points of all operating
and safety controls and record all results.
Water systems should be completely drained and flushed with cleaning agents
whenever water treatment has not been carried out for a prolonged period, or if system
performance indicates that the pipes or heat exchangers need cleaning.
Regularly check operation of all chemical feed devices and repair as necessary and
check condition of all control devices such as thermostats and valves.
Disposable panel air filters
Check filter media regularly and shake out dust.
When static pressure across the filter exceeds 125 Pa replace the media with new
media. When a filter is being installed, it must be first installed over the inner frame,
then the assembly inserted into the holding frame. Be very careful to ensure a seal is
formed between the media and the mounting frame. Equipment, especially air
conditioning units, should not be run without filters.
Fan Coil Unit Panel Filters fitted with dry media, cleanable type, should be cleaned as
follows:
Remove surface lint and loose dirt with a vacuum cleaner attachment or by
gently rapping over a newspaper.
Flush water through inlet (dirty) side of filter. In severe cases, immersion and
agitation in cold water, mild detergent may be necessary. Rinse thoroughly
and dry.
If filters are of a different type, follow filter manufacturer’s instructions.
138
Interlock circuit operation
Task
To practice the skills of reading and interpreting an electrical circuit diagram to
determine the operation of an air conditioning system.
Procedure
1. Read the central plant circuit diagram that incorporates interlocking, located
after the following questions.
2. Answer the following questions.
a. What type of air conditioning system is operated by the circuit diagram? List
the main components.
b. Explain the operation of the Oil Pressure Safety Switch.
c. The evaporator fan motor trips on O/L, will the compressor run? Why?
d. The flow switch sensed low water flow in the condenser water circuit. List in
sequence, what will happen to the operation of this system.
139
e. The cooling tower fan thermostat is out of calibration and the water
temperature in the tower has risen to 38OC. What will happen to this system
while this condition remains under full load cooling?
f. The compressor motor contactor coil has 180 volts supply. What could cause
this problem and how will the system react to this fault situation?
140
141
Practical Exercise 2: Central plant system operating characteristics
Task
To observe and record the normal operating characteristics of a central plant system.
Equipment

Central plant air conditioning system.
Sling psychrometer.
Anemometer.
Digital thermometers.
Safety

Procedures
1. Start the system and allow the central plant to operate for 15 minutes before
recording readings.
2. Observe the start sequence of plant and note the interlocking procedures below
in step form.
3. Record the following:
I. SA
I. Dry Bulb Temperature
II. Wet Bulb Temperature
III. Volume Flow Rate
142
O
C DB
O
C WB
L/s
II. OA
O
O
III. RA
C DB
C WB
L/s
O
O
C DB
C WB
L/s
IV. Water Flow rate through cooling coils under full load conditions.
L/s
.
V. Saturated Suction
I. Pressure
kPa
II. Temperature
VI. Saturated Condensing
I. Pressure
O
C
kPa
II. Temperature
VII. Chilled water temperature
I. Supply
O
C
O
C
O
II. Return
C
VIII. Condenser water temperature
I. Supply
O
C
O
II. Return
C
IX. Pressure drop across air filtration system in fan coil unit
Pa
4. Plot the air conditioning process on a psychrometric chart.
5. Determine the following:
i. Mixed Air Dry Bulb Temperature
143
ii. Condenser Heat Rejection Capacity
iii. Cooling Coil Capacity
144
Routine preventative maintenance
Task
To identify what preventative maintenance should be carried out and how often.
Procedure
In the following tables, indicate the time intervals (one, three, si and twelve monthly)
for each maintenance procedure activity.
Note: Only tick one box for each maintenance activity.
•
Cooling Tower – General mechanical maintenance (not microbial control).
Plant
Cooling
Tower

Maintenance Item
Frequency in months
1
3
6
12
Check operation
Fan motor and fan
Inspect structure
Lubricate fan shaft bearings
Check motor voltage and current
Check fan bearing locking collars
Inspect unit and record the following
details:
General condition, date of last service,
any environmental or physical changes
in the area including new installations,
any recommendations.
Centrifugal water pumps
The mechanical seal should not require attention, however, if the seal leaks
check their rubber components are clean and seated properly. Mating surfaces
may require inspection for damage. During inspection handle all parts
carefully.
Plant
Maintenance Item
1
Water
Pumps
Frequency in months
3
6
12
Check for leaks
Check coupling
Check seal or gland packing
Check motor
Check strainer
Check current
Lubricate bearings
Overhaul pump and motor every 3
years.
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The fan coil unit
Plant
Maintenance Item
Fan Coil
Units
Check operation
Check belt tension
Recalibrate controls and record settings
Check and clean filters
Check condensate trays and drains
Check all cabinets and all coils etc. for
corrosion or damage
Check all motor currents and record
results
Check room temperature by sling
psychrometer
Check all safety circuits
Check fan and motor bearings every 5
years

Frequency in months
1
3
6
12
Filters
Dry media, cleanable type.
Plant
Maintenance Item
Air
Filters
Check condition of all filters
Inspect air media and issue report on all
filters
FAN COIL UNITS
Check, clean or replace air filters as
necessary

Frequency in months
1
3
6
12
Chiller
Always refer to the chiller manufacturer’s Installation, Operation and
Maintenance Manual, before commencing maintenance on a chiller.
General maintenance procedures
Use the periodic maintenance program to ensure maximum performance and
efficiency from the chiller units.
Daily and weekly maintenance.
Log each chiller unit.
Check oil level.
Check oil and refrigerant pressures as per manual. Inspect liquid line sight
glass.
Visually inspect the entire system for noisy operation, loose panels, leaks and
chattering.
146
Plant
Maintenance Item
Frequency
147
12
monthly
Check oil level
Check operating pressures and
temperatures
Check water temperature
Check operation
Check refrigerant leakage
Check refrigeration strainers
Manufacturer’s service
Oil analysis
Check operation and setting of all
controls
6
monthly
3
monthly
Weekly
Chillers
Fault finding exercise
Task
To practice the skills on the following hypothetical faults that may be encountered in
a central plant air conditioning system.
Procedure
For each problem and symptoms, identify a possible cause and recommended action.
Compressor fails to start
Problem and symptoms
Full voltage at motor terminals but
motor will not run
Inoperative motor starter
Open contacts of safety control or
thermal overload
Electric circuit test shows no
current on line side of motor starter
Electric circuit test shows current
on line side but not on motor side of
fuse
Motor starter holding coil is not
energised
Compressor will not operate
Open contacts on high side pressure
switch. Discharge pressure above
cut-in setting
System will restart by resetting oil
pressure control switch
Starter will not pull in
Control circuit will not energise
Probable cause
Recommended action
Probable cause
Recommended action
Compressor stops
High pressure control has cut out
Low pressure control has cut out
Thermal overload has cut out
Winding thermostat has cut out
Oil pressure control has cut out
Freeze protection has cut out
148
Compressor short cycles
Compressor will not load or unload,
cuts out on freeze protection control
Normal operation except too
frequent stopping and starting
Valve may hiss when closed. Also
temperature change in refrigerant
line through valve
Normal operation except too
frequent stopping and starting on
low pressure control switch.
Bubbles in sight glass
Suction pressure too low and
frosting at drier. Motor starts and
stops frequently
Probable cause
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Recommended action
Fault finding
Task
To practice the skills of recording information, recognising symptoms and identifying
faults.
Equipment

Air conditioning unit
Thermometers
Service gauges
Anemometer
Tools
Calculator
Pressure/Temperature chart
Safety

Procedure
1. The teacher will set up a fault on an air conditioning system that you will fault
find, repair, and report on below.
2. Use the form below to record the system readings.
3. Determine and record below the symptoms, the fault and the remedy.
1
2
3
4
5
6
7
8
9
10
11
12
13
Ambient temperature
Air on condenser
Air on evaporator
Air off evaporator
Temperature ‘split’ across evaporator coil
Saturated suction temperature
Equivalent saturated suction temperature
Saturated condensing temperature
Discharge temperature
Evaporator temperature difference
Condenser temperature difference
Suction line pressure drop
Evaporator superheat
150
14
15
16
17
18
19
20
Suction line superheat
Condenser sub-cooling
Liquid line sub-cooling
Airflow through evaporator
Outside air quantity
Liquid indicator condition
Receiver level
Answers:
Fault Diagnosis
Symptoms
Remedy
151
Review Questions
1. Explain the difference between a constant volume, variable temperature central
plant system and a variable volume, constant temperature central plant system.
2. List two major types of compressors and their refrigerants used in large flooded
evaporator chiller sets.
3. What device would be used to determine low water flow in a chilled water
supply? Explain how it functions, mechanically and electrically.
4. List three secondary refrigerants that may be used to cool an air conditioned
space.
5. List two advantages and two disadvantages of the multi zone air conditioning
system over a split zone air conditioning system.
152
6. What is the purpose of reheat in the supply duct of a multi zone air conditioning
system?
7. Explain the purpose of the mixing boxes in a dual duct system.
8. What is the design purpose of a Face and Bypass system?
9. What is an ‘Economy Cycle’ when referring to a central plant air conditioning
system and what are its benefits?
10. When would the economiser cycle open on the modulating OA damper to 100%?
153
11. Why must the operation of fresh air, spill air and mixing dampers be coordinated
in large air handling systems?
12. Explain two advantages of Variable Air Volume systems over a constant volume
air conditioning system in a general office space.
13. List two methods used to maintain the static pressure in the duct once the VAV
begins to reduce the airflow into the room.
14. What type of diffuser is recommended for VAV systems? Explain why.
15. Describe the difference in application between a basic shut-off VAV box and a
VAV box fitted with a reheat coil.
16. Where would an induction unit be located in reference to the air conditioned
space?
154
17. Describe the importance of selecting the correct secondary chilled water
temperature for induction systems.
18. An induction unit mixes primary and secondary air. Explain with a diagram where
this mixing takes place.
19. Explain the difference between a central plant and a terminal air conditioning unit.
20. List three advantages of terminal air conditioning units over central fan systems.
21. A centrifugal chilled water set operates on a suction pressure below 0 kPa gauge
pressure. If a refrigerant leak occurred, how would the leak be found?
22. What governs the maximum pressure that the chiller set can be checked for leaks?
155
Heating Systems
Heating systems are included in most air conditioning applications. There are various
forms of heating systems used in the HVAC industry.
They range from electric heater elements, steam and hot water to reheat reclamation.
The installation of any one of these systems depends on cost, efficiency,
specifications and system reliability.
Hot water coils
An aluminium finned copper coil, usually 2 or 3 rows deep, is placed in the
supply air stream.
The face area of the hot water coil is generally lower than that of the cooling
coil in order to increase the air velocity to approximately 3.5 m/s.
The velocity of the hot water that is travelling through the coil is usually
maintained at around 1.0 m/s.
The water generally enters the heating coil at around 85OC and leaves at
around 75OC.
A rise in temperature of around 20 K is usually achieved across the heating
coil.
A three way modulating valve may be used to maintain a constant supply air
temperature by diverting the supply water around the coil when the desired
conditions are almost achieved.
156
Steam coils
Steam at a pressure of approximately 100 kPa (a saturation temperature of
approximately 120OC), is supplied from a boiler to a finned tube coil mounted in the
air handler.
As the steam passes through the coil it gives up its Latent Heat of Condensation to the
air (approximately 2200 kJ/kg) and leaves the coil as hot water.
A coil only 1 row deep is all that is generally needed due to the high efficiency of this
system (the latent heat transfer is extremely high and the temperature of the steam is
also high).
Air velocity over the coil face is generally maintained at 3.5 m/s with a steam flow
rate of around 0.15 kg/s through the coil.
Electric elements
Usually installed in the zone ducts, with stages of capacity across 1, 2 or all 3 phases
to balance the current draw of the system and provide a degree of capacity control
(with the aid of a Step Controller).
The ductwork in the immediate vicinity of the heater elements must be fire rated
(Millboard is a popular insulator).
A high limit (hi-limit) thermostat with manual reset must be fitted in case of:
Fan motor seizure.
Fan motor burnout.
Fan belt breakage.
Air blockage (filters, etc).
157
They are generally not used in systems over 35kW.
Reverse cycle
A four way solenoid valve known as a Reversing Valve is fitted into the refrigerant
circuit. During heating, the energised valve connects the suction line to the condenser
and the discharge line to the evaporator.
This is the most efficient method of generating heat, however it is heavily dependant
upon the temperature of the outside air.
Many reverse cycle systems are designed to operate in ambient temperatures as low as
-8OC but they tend to go through a De-Ice cycle too often and they rely heavily upon
electric element heaters to achieve comfort conditions.
As a general rule, this style of heating is not used when the ambient temperature falls
below 0OC. The coils are no longer referred to as the evaporator and condenser, but
the indoor and outdoor the coils.
158
Larger systems should not be fitted with a Capillary Tube metering device. They
should instead use two TX valves (one at the inlet to each coil), and two check valves
(to provide a path around each TX valve when flow is required in the opposite
direction).
An Accurator also can be used as a reversing valve. It is like a check valve and
capillary built into one. It is cheaper than two (2) TX valves and check valves.
159
Heat reclaim
Similar in design to the hot water coil except that a boiler is not used to generate the
hot water.
The warm water that is normally sent to the cooling tower from refrigeration
equipment is instead redirected to the hot water coil in the air handler.
The quantity of water being redirected to the hot water coil is generally controlled by
a three way modulating bypass valve (normally located near the tower).
Heat energy required for the heating of the air conditioned space is thereby reclaimed
from the refrigeration plant.
This type of system is generally only found in supermarkets where the refrigeration
plant is large enough to provide the heating requirements of the building.
160
Hot water coil capacity
Task
To calculate the capacity of a hot water coil.
Procedure
Answer the following questions:
1. A hot water pump is supplying hot water to a heating coil at 5 L/s. The water
is returning to the boiler system at 75OC. The hot water supply temperature is
85OC.
Calculate the heating coil capacity.
2. A heating coil has a rated capacity of 3.5 kW. The water temperature entering
the coil is 75OC and the leaving temperature is 180OC.
Calculate the required mass flow of water to achieve this rated capacity.
161
Fault finding
Task
To practice the skills of fault finding on heating systems.
Procedure
Answer the following questions:
1. When checking a boiler having a rated capacity of 150 kW, it was found that
the water flow was 1.8 L/s with water entering at 59OC and leaving at 78.5OC.
Would you consider this to be operating as it should? Why?
2. An electric reheat system has tripped out on hi-limit thermostat.
The technician checked the fan motor and electric elements and found them to
be functional. What are three possible causes for the heater to be tripped on
hi-limit thermostat?
3. A customer complained that conditions are cold in the conditioned space
served by Air Handling Unit No. 1 0f the system shown in the diagram below.
List five possible faults that could cause this complaint and how you would
check them before you can rectify the fault.
162

163
Review Questions
1.
List four methods used to heat air in an air conditioning application.
2.
What is heat reclamation?
3.
List two uses for heat reclamation.
4. List two main reasons for using individual duct heating elements or coils
instead of reverse cycle air conditioning, to heat an office space.
5. Describe the purpose and operation of de-ice controls fitted to reverse cycle air
conditioning systems.
Purpose:
Operation:
164
6.
List three electrical safety features that can be incorporated into an electric
heater control circuit.
`
7.
What is the major advantage of reverse cycle air conditioning?
8.
List three types of hot water boilers.
9.
What is the importance of boiler fluing?
10.
What are photo-electric cells used for in hot water boilers?
165
Humidification Systems
Humidity is life! Man, beast and plant need the right air humidity for their well being.
Many production processes, modern computer techniques, proper storage of all kinds
of goods and the preservation of works of art would be unthinkable without controlled
air humidity. Insufficient humidity is corrected by humidification and steam
humidification is eminently suited to bringing the air humidity to the proper level.
The humidity present in the air consists of water vapours; that is water in gaseous
state. Humidification means raising the content of water vapour in the air and
humidification employing steam is the best and obvious route because it has no
detrimental side effects.
Humidity control
The humidity controller is selected according to the permitted (or economical)
humidity tolerances.
Room control is preferred in air conditioning systems, locating a humidity sensor
either in the room itself or in the return air duct. Supply air humidity control should be
used only where room humidity control is impracticable for technical reasons. The
humidifier must be controlled continuously. Close humidity tolerances can be
maintained only by using a proportional-integral (PI) controller. The controllability of
the humidifier depends on the stability of the control loop under continuous control
and on sufficiently long switching intervals under on/off control. This calls for careful
selection and adjustment of both the humidifier and the control device.
Types of humidification systems
There are three basic types of humidification systems:
Water spray method.
A fine spray of water is injected into the air stream generally after it has passed
through the Heating Coil (to improve moisture absorption).
Spray eliminators must be fitted downstream of the spray header to prevent excess
water from entering the ductwork.
Atomising humidifiers are more effective because the water is broken into very small
droplets making it easier for the air to absorb more moisture.
166
Open pan method.
A pan of water is located in the ductwork and heated by an electric element. The
energy input is generally controlled by a humidistat. It may be a two position (either
On or Off) control or a Proportional (modulating) control. Scale tends to form quickly
on the heated surfaces, therefore regular water treatment is necessary.
Direct steam method.
A number of various designs have been developed but all primarily inject wet steam
into the air stream.
Control may be achieved by switching the boiler on and off (only on small boilers), or
by the use of a two way modulating valve in the steam line. A humidistat provides the
switching in each case.
167
Air humidification by steam:
Is hygienically irreproachable (sterile).
Causes no smells.
Avoids deposits of mineral constituents from the water in air ducts and rooms.
Allows optimal regulation of the air humidity.
Involves almost no change in the air temperature (i.e. it is isothermal).
And is simple to dimension.
Installation
Careful planning and installation are necessary to ensure sterile humidification with
steam. The steam must be absorbed properly by the air to avoid condensation because
damp surfaces are an ideal breeding ground for micro-organisms!
Water vapour absorption capacity of air
The absorption capacity of the air for water vapour is determined by the particular
state of the air in question. The air stream will absorb the moisture offered to it in the
form of water vapour only up to the saturation limit of 100% relative humidity. For air
conditioning, a safety margin from the saturation point must be maintained in the air
after humidification, in order to avoid condensation on the duct walls.
Condensate is precipitated if:
The saturation limit falls below the value of the calculated air state under
falling temperature, with supply air temperature fluctuations before the
humidifier.
The humidifier performance is not adapted or not controlled adequately to the
part load demand during the transition periods.
The operating airflow is greatly reduced, as in plants with variable volume
flow, or with badly fouled air filters.
The air ducts run through cold rooms; here what matters is the inside wall
temperature of the duct, where the dew point may be under stepped, and not
the saturation limit at air temperature.
168
Humidification distance
The installation location of the steam distributor is predetermined by the design of the
air conditioning system. During operation, the water vapour emerging from the steam
distributor pipe is visible in the form of mist for a certain distance.
Only after covering this humidification distance is steam/air mixing sufficient to
prevent condensation on downstream parts of the system.
The appropriate minimum distance from the steam distributor must be maintained for
the various parts of the system.
Safety provisions
Compulsory safety devices are fitted according to instructions given by the
responsible project engineer.
To avoid possible costly moisture damage, the following safety provisions are
indispensable:
Interlock with ventilation switch-on.
Flow is monitored for air delivery (differential pressure switch etc).
Safety humidistats are fitted in the supply air duct and rooms.
Additional safety provisions:
Continuous supply air humidity limitation necessary for humidification under
certain operating conditions.
Separate monitoring of the room air humidity by minimum and maximum
humidistat with fault signalling.
Selective remote indication for monitoring the humidifier function.
Connection to PC, building management system via serial interface.
169
Review Questions
1.
List four methods to humidify air.
2.
What controls the Relative Humidity in the conditioned space? Where should
this device be located?
3.
Why is it recommended to fit water sprays prior to a cooling coil?
4.
List three advantages of direct steam humidifiers over the other types.
5.
List the minimum maintenance requirements as stated by AS/NZS
3666.2:1995.
170
6.
List the two major factors that need to be considered as to where to locate the
humidifier.
7.
List the three minimum considerations required of AS/NZS 3666.1:1995 for
the operation of humidifiers.
8.
List three applications of humidifiers.
9.
What are humidifiers used to prevent in computer rooms?
10.
What are the major limitations on reticulated air humidification systems?
171
Thermal Storage Systems
The concept of thermal storage as applied to cooling systems is not new. Not long
after mechanical refrigeration for air conditioning became a practical reality in the
1930’s, the technology was extended to include thermal storage. Thermal storage was
/ is used to handle infrequent short term cooling loads such as those in churches and
theatres, and process applications such as dairies.
The reason for using thermal storage was to minimise the initial cost of the cooling
system. For example, a church might have a cooling load of 150 kW over a five hours
period, occurring once a week. Rather than install a 150 kW system to operate for 5
hours, thus producing 750 kW-hours of cooling, a 15 kW system could be installed to
operate and store cooling for 50 hours.
The same total cooling capacity (750 kW-hours) was produced and the system cost
was substantially reduced, even when the cost of the storage equipment was included.
This concept was practical as long as the time available to generate cooling storage
was much greater than the time of cooling use. Only under these circumstances would
the reduction in the cost of the refrigeration system more than offset the cost of
storage. Thermal storage continues to be applied to cooling systems with these
characteristics.
Thermal storage is now drawing interest for broader application in comfort and
process cooling systems because of major changes in rate structures in the electric
power industry. Many electric utility companies experience the greatest demand for
electricity during the summer, largely to satisfy the comfort cooling needs of their
customers. Consequently, the amount of power that the utility must generate peaks
during daylight hours when the cooling requirements are the highest.
Many comfort and process cooling loads exist for only a few hours each day and
commonly occur during hours of peak power demand.
Since conventional cooling systems produce cooling when it is needed, they operate
when power costs are the highest. Thermal storage systems however, minimise energy
costs by generating cooling capacity at off peak times and storing it for future use.
Cooling load applications that can benefit from thermal storage are office buildings,
schools and college buildings, religious institutions, laboratories, large retail stores,
libraries, museums and the public use areas of hotels (such as meeting rooms).
Thermal storage can also be used for many industrial processes, such as occur in
dairies, breweries and other types of plants with batch cooling cycles.
Thermal storage systems
Thermal storage systems for cooling produce chilled water that can be pumped to
comfort cooling coils or some other heat exchanger. There are two basic types of
thermal storage systems that will provide chilled water for cooling:
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Chilled Water Storage Systems
Chilled water storage systems commonly utilise a packaged refrigeration system
consisting of a compressor, condenser, and an evaporator that chills water. Frequently,
the condenser is water cooled and requires condenser water pumping system and a
cooling tower to reject the condenser heat to the atmosphere. As shown in Figure 1,
the chilled water is pumped into water storage tanks, which are usually constructed of
concrete or steel at the jobsite. When chilled water is required for cooling, it is
pumped out of the tanks to the load and returned to the storage tanks.
Although this system is simple in concept, it
becomes more complex when executed. This is
primarily due to the limited cooling storage
capacity of chilled water, which achieves cooling
by raising the temperature of the stored chilled
water. With an 8 K temperature rise, 33kJ can be
stored per kg of water, which translates into about
0.1 m3 per kW hour of cooling.
For example, on an installation requiring a 2100
kW conventional system, 1840 m3 of space would
be needed for storage!
Another major consideration in the design of
chilled water storage systems is blending of the
warm water returning from the system with the
stored chilled water. If water is returned from the
system to the same tank where the chilled water is
stored, the two masses mix, thereby raising the
temperature of the water being pumped to the
cooling coils. It therefore becomes imperative to
minimise the blending process. Several antiblending techniques have been developed and
implemented with varying degrees of success. The
most successful techniques are also the most expensive; the cost of the storage tanks
increases, as does the cost and complexity of the control system.
So while it would appear that chilled water storage is a natural marriage of cooling
system technology and the thermal storage concept, closer examination shows that
there are substantial cost, operational and space problems that must be solved.
Ice Storage Systems
Ice storage systems are designed to form ice on the surface of the evaporator tubes,
and to store it until chilled water is needed for cooling. The ice is melted by the warm
water when the chilled water pump is on, thereby re-cooling the water before it is
pumped back out to the heat load.
It consists of a multiple tube serpentine coil, submerged in a tank of water, with a
water agitation device included to provide uniform ice build-up and melt-down. The
tank is fully insulated and provided with covers to minimise infiltration of foreign
matter.
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As seen earlier, the space
required to store adequate
quantity of chilled water can
be enormous. In this regard,
ice storage has a decided
advantage over chilled water
storage, since the basis for
storage is the latent heat of
fusion of water, which is 335
kJ per kg. This means that
each kilogram of water can
provide 335 kJ of cooling
when it is frozen into ice
compared to chilled water
which has a capacity of 4.19
kJ/kg K.
Theoretically, the reduction in storage volume is inversely proportional to the increase
in cooling capacity per kg of water. In practice however, it is less due to the presence
of the evaporator coil and water in the Ice Chiller. The end result is that chilled water
with an 8 K range requires 100 litres per kW-hour of storage, while an ice builder
requires just 25 litres per kW-hour, or one fourth the volume of chilled water storage.
Therefore the cost of the required Ice Storage System is substantially less than the
cost of chilled water storage systems. The return water flows into the ice builder and
is cooled by the melting ice, providing a leaving water temperature of approximately
2OC.
A potential disadvantage of ice storage systems is hat more energy is required to make
ice than is required to chill water because a lower evaporator temperature is require to
produce ice than to produce chilled water at 5OC. The penalty for the lower evaporator
temperature however can be greatly reduced by choosing the most efficient
condensing method, the evaporative condenser. For example, at 26OC design wet bulb
temperature, an evaporative condenser can be selected to operate on an ice storage
system at 35OC condensing temperature where a water cooled chiller would be
selected for 40OC condensing temperature. The lower condensing temperature nearly
offsets the power penalty caused by the lower evaporator temperature on an ice
storage system.
On the basis of initial cost and space advantages, with essentially no penalty in power
consumption, ice storage is usually the best choice in the selection of a thermal
storage system for cooling.
Ice storage system design flexibility
Ice storage systems can be designed to operate in a variety of ways to meet specific
application requirements.
These range from “full storage” to “compressor aided” modes.
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A full storage system is one which has been selected to generate all of the cooling
capacity for the facility or process during the hours when off-peak electrical rates are
in effect, which is usually during evening and early morning.
The refrigeration system is operated and ice forms on the coil surface of the Ice
Thermal Storage System until a predetermined thickness is obtained. A sensor then
shuts down the refrigeration system.
When cooling for the building or process is required, the chilled water pump
circulates water from the ice chiller to the load. The return water is cooled by the
melting ice, and this process continues until the daily cooling requirement is satisfied.
After the electricity rates return to the off-peak schedule, a timer permits the
refrigeration to re-starts and the ice is then rebuilt during off-peak hours for use in the
next cooling cycle.
By definition then, a full storage system makes maximum use of the thermal storage
concept. Its objective is to achieve minimum operating cost by avoiding high demand
charges and/or higher energy charges. However, since all of the cooling capacity is
stored, the total ice storage system is the most costly to install. Quite frequently, the
operating cost savings will not be sufficient to justify the initial cost.
Heating storage system
In the Northern Hemisphere, thermal storage for heating purposes is often as popular
as cooling storage systems are in Australia. There are a number of methods used, the
“Earth storage and geothermal heat exchanger system” being one of the more popular.
Earth storage and geothermal heat exchanger
One method of thermal storage little used in Australia is the use of the earth for both
heat storage and geothermal heat exchange. The “Earth storage and geothermal heat
exchanger system” uses the earth mass for storage of thermal energy as well as heat
exchange using heat contained in the earth mass.
Large steel tanks filled with liquid are buried into the earth. Thermal energy is gained
from the ground itself and/or solar collectors and/or other heat producing equipment
(i.e. heat pump condensers).
Most thermal exchange occurs within one metre of the tank while the effects from the
thermal process could reach as far as 10 metres from the tank/s. The temperature of
the tank can range from approximately 11OC to 30OC.
The heat stored is reused for heating during cooler periods in place of the more
expensive heating methods described in “Heating Systems”.
Different variants of this system can be found around the world. Should you wish to
investigate this method of thermal storage further, you should see the Internet for
details.
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Review Questions
1.
What is the main purpose for using thermal storage?
3. Briefly explain the operation of either a chilled water or ice thermal storage
system.
3.
List three major types of thermal storage systems.
4.
Why use ice storage, rather than merely cooling water or brine?
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5.
List two major advantages of thermal storage systems.
6.
List three applications which would benefit from using chilled water or ice
thermal storage.
7.
Would you need a larger or smaller refrigeration system compared to a
conventional air conditioning system to cool in the building?
8.
Describe the difference between block tariff and demand tariff.
9.
Describe the purpose of adding glycol to the primary chilled water of a
thermal storage system.
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Specialised Systems
‘Specialised Systems’ are systems specially designed for applications which have
their own unique requirements.
Types of specialised systems may include:
Bowling alleys.
Clean rooms.
Libraries and museums.
Laboratories, etc.
Two specific types of specialised systems are:
Computer Rooms
NOTE: Due to technological advances, the requirements for computer rooms are
constantly changing; for example: under Air Cleanliness, reel to reel tapes are
mentioned as is, under Relative Humidity, nylon carpet; neither of which are
commonly in use today.
The major concerns with modern computer rooms are:
The heat generated within the ‘server racks’
Consistency of temperature and relative humidity with minimal fluctuations.
In general, temperature is maintained with a differential of 1 K of the set-point
usually 21OC plus or minus 1 K,) whilst relative humidity is maintained with a
differential of 3 to 5% of the set-point (usually 50%RH plus or minus 3 to 5%).
Computer rooms, both large and small, are treated as close control, high sensible heat
load applications (as are electronic telephone exchanges).
All computer oriented equipment operates at very high levels of performance and
must therefore be located within a ‘correct’ and ‘closely controlled’ environment. Air
conditioning systems used to provide this environment must be capable of achieving
high control over:
Air cleanliness.
Relative humidity.
Temperature (in this order of importance).
Air cleanliness
The disk drives and reel to reel tapes used for data storage on modern computers are
capable of travelling at extremely high speeds, with extremely close tolerance
between the head and the surface of the disk or tape.
Any minute airborne particles picked up and caught between these two surfaces will
instantly destroy a large section of the data held on the disk and possibly damage the
reading / writing heads of the drive. Particles the size of a single grain of tobacco
smoke are capable of causing this!
Any technician servicing or maintaining this type of air conditioning system must not
only be aware of the conditioning requirements for the environment but also aware
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that he/she is probably carrying harmful dust particles into the environment on their
body, clothes and equipment. The following precautions should always be observed to
minimise this risk:
Do not smoke or consume food or beverages in a computer room.
Always advise the operators before commencing any task that may result in
the production of airborne particles (e.g. lighting an oxy-acetylene torch,
blowing out coils, etc).
Avoid wearing dirty or dusty clothing into the room, (consider keeping a clean
set of clothes in the van).
Some of the larger computer rooms provide additional safeguards against these
problems, such as:
Air locks at the entrance of the room.
Personal vacuum cleaners to remove any loose dust on clothing.
‘Sticky’ floor pads to remove dirt from the soles of shoes.
Relative humidity
The strict control of Relative Humidity in a computer room is of vital importance to
the efficient operation of the high speed printers commonly found in modern
premises.
If the RH% is too high then the paper will expand and clog or jam the printer head. If
the RH% is too low then static electricity may develop in the paper resulting in the
failure of the solid state components within the printer.
Another source of static build-up due to low RH% levels is the nylon carpet used in
the room. (Static earth straps are often worn by the operators and also placed in the
carpet to minimise the problem).
The air conditioning system must therefore be capable of providing humidification
and dehumidification control in order to prevent these problems.
Humidification is usually provided by a separate steam humidifier, (sometimes
located remotely from the refrigeration unit).
Dehumidification is often obtained by altering the airflow rate through the evaporator
coil (usually by changing the supply air fan speed).
Temperature
The main concern is the internal temperature of the computer itself. The computer
system functions through the use of ‘solid state’ components which tend to suffer
from self heating.
High operating temperatures will cause these devices to literally self destruct so a
relatively cool environment must be provided to ensure efficient, long term operation.
Older computers required fairly close temperature control but the later models are
capable of operating within a fairly broad range of temperatures. Most will not
experience overheating problems until the room temperature exceeds 32OC. The main
reason for close temperature control in these rooms is the effect that temperature
change can have on relative humidity.
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Another consideration is the people that must work within this environment. Most
modern computers will provide adequate performance within the human comfort
environment (i.e. 22OC: 50% - 55%RH).
General design considerations
Computer room systems should only provide enough outside air to satisfy the
requirements of the workers occupying the room and to maintain a positive pressure
within the room relative to the surrounding rooms. In most situations, 5% OA is
sufficient.
Because the occupancy levels and fresh air requirements are usually low, a Sensible
Heat Ratio of approximately 0.9 should be sufficient when calculating the heat load
on the plant. This will ensure that the system can handle the minimum moisture loads
placed on it but, at the same time, will not cause false humidification of the room.
Air supply systems
Air supply systems generally fall into one of the following two types:
Overhead systems
Air is generally discharged across the top of the room directly from a package unit.
These units generally have a throw of approximately 10 metres and care should be
taken to ensure that the supply air is not obstructed in any way.
Floor plenum systems
These systems supply air under a ‘false’ floor that has been erected a minimum of
300mm above the original floor. The raised floor is made using a steel frame over
which are placed high strength tiles. Supply air grilles are installed wherever required
by simply removing a tile and inserting the grille.
Raised Floor (Floor Plenum) Computer Room Installation
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This system has many advantages in that great flexibility is provided in the location of
the supply air grilles.
Conditioned air may be passed directly into the computer housing by placing a grille
under the computer, (many large computers are designed to take full advantage of
this). Air conditions are generally maintained at around 18OC and 45%RH for these
systems, (please refer earlier notes at commencement of Computer Rooms).
Hospitals
The ventilation requirements within a hospital are very diverse. For this reason, the
Ventilation Code should be consulted for further information on the actual
requirements of each different room within the hospital.
Operating theatre
The air supplied to this room is recommended to be 100% Outside Air but recent
filtration capabilities allows 50% Outside Air to be used in operating theatres.
The return air removed from this room must be exhausted to the outside of the
building.
The filters used to clean the supply air must have a filtering efficiency of
99.99%. The only filter capable of providing this is the Absolute Filter. Most
ventilation systems will use a number of different types in front of the primary
filter in order to maximise its functional life.
The pressure within the room must be maintained at 25 Pa above the pressure
of the rooms immediately surrounding it.
Temperature and relative humidity levels are maintained at 22OC and 50%.
General wards
The return air must be filtered (and preferably deodorised with active carbon
beads).
The pressure within these rooms should be maintained at 25 Pa above the
atmospheric pressure.
Temperature and relative humidity levels are maintained to meet comfort
conditions.
The air supplied to these rooms may be a mixture of return air and outside air.
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Review Questions
1.
What type of air filter is recommended for an operating theatre’s air
conditioning system?
2.
How would a mechanic identify if the filter media is blocked or dirty in an
operating theatre?
3.
What is the minimum percentage of outside air to be introduced into an
operating theatre?
4.
What type of unit is used in operating theatres?
5.
What may occur in a computer room if the RH% is 30%?
6.
What may occur in a computer room if the RH% is 65%?
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