Room and Small Commercial Air Conditioners

Transcription

Technical Study Report
ROOM AND SMALL
COMMERCIAL AIR CONDITIONERS
This report was produced under the project entitled “Supporting Action
on Climate Change through a Network of National Climate Change Focal
Points in South-east Asia” (SEAN-CC) implemented by UNEP and funded by
Ministry of Foreign Affairs of the Government of Finland.
Dec 2011
Contents
SECTION 1: INTRODUCTION
1
1.1 Types of air conditioner2
1.2 Major manufacturers and market shares in ASEAN3
1.3 Efficiency of air conditioner4
SECTION 2: OUTLINE OF AIR CONDITIONER
5
2.1 Major components of air conditioner6
2.2 Refrigeration cycle7
2.3 Characteristics of refrigerant8
SECTION 3: COMPRESSOR
9
3.1 Types of compressor10
3.2 Compressor efficiency18
3.3 Latest technology in development and commercially available19
SECTION 4: EXPANSION DEVICE
20
4.1 Types of expansion device21
4.2 Capillary tube22
4.3 Thermostatic expansion valve22
4.4 Automatic expansion valve25
SECTION 5: HEAT EXCHANGER
27
5.1 Types and sub components of heat exchanger28
5.2 Evaporator30
5.3 Condenser32
SECTION 6: FAN, MOTOR AND INVERTER
33
6.1 Fan34
6.2 Motor35
6.3 Inverter37
SECTION 7: REFRIGERANT
39
7.1 Types of refrigerant40
7.2 Properties and characteristics of refrigerants41
7.3 Technological developments in refrigerant use46
8 THE TECHNOLOGY FOR AIR CONDITIONER IN ASEAN REGION,
47
AND LIFE-CYCLE ASSESSMENT OF AIR CONDITIONER
8.1 The most commonly used technology for room and small commercial
air conditioners in the ASEAN region
49
8.2 The alternative technology of ASEAN countries under the
Montreal protocol
50
8.3 The policies and market incentives based on low- or zero-GWP
refrigerant in ASEAN region
52
8.4 Life-cycle assessment of energy and green house gas for air conditioner
52
REFERENCES
56
LIST OF TABLES
Table 1-1 Differences between room and small commercial air conditioners
2
Table 1-2 Major air conditioner manufacturers in ASEAN countries
3
Table 3-1 Comparison of inverter compressor and conventional compressor
19
Table 7-1 Refrigerant safety classification
41
Table 7-2 General information of several commonly used refrigerants
43
Table 7-3 Operational information of several commonly used refrigerant
44
Table 7-4 Thermal physics and environmental characteristics for possible R22 substitutes
45
Table 7-5 Thermal performance of various kinds of R22 substitutes
46
Table 7-6 Inflammable limits of several kinds of inflammable R22 substitutes46
Table 8-1 Table 8.1 Results of life-cycle assessment 55
LIST OF FIGURES
Figure 2-1 Window-type air conditioner6
Figure 2-2 Split-type air conditioner6
Figure 2-3 Major components in an inverter split-type air conditioner6
Figure 2-4 Basic vapor-compression refrigeration cycle7
Figure 2-5 The saturated pressure with temperature of some refrigerants8
Figure 3-1 Five major types of compressors10
Figure 3-2 Fully welded hermetic compressor and semi-hermetic compressor11
Figure 3-3 The internal working of a fully welded hermetic compressor11
Figure 3-4 The working parts of a semi-hermetic compressor12
Figure 3-5 Events inside a reciprocating compressor during the pumping action12
Figure 3-6 Cross section of a scroll compressor 14
Figure 3-7 Process of forming continuous crescent-shape gas pockets in the scroll 14
Figure 3-8 Scroll orbit in a real scroll compressor 15
Figure 3-9 Cross section of a rotary compressor15
Figure 3-10 Operation of a stationary van rotary compressor16
Figure 3-11 One stage of compression as refrigerant moves through the screw compressor17
Figure 3-12 Centrifugal compressor18
Figure 3-13 Smooth speed charge scroll compressor with neodymium DC motor19
Figure 4-1 Capillary tube connected with liquid-line21
Figure 4-2 Thermostatic expansion valve21
Figure 4-3 Automatic expansion valve21
Figure 4-4 Capillary tube in a refrigerating system22
Figure 4-5 A filter-drier protects the capillary tube from circulating particles
22
Figure 4-6 An exploded view of the thermostatic expansion valve23
Figure 4-7 The valve opening is affected by the inlet pressure of evaporator24
Figure 4-8 The valve opening is affected by the outlet pressure of evaporator25
Figure 4-9 Section of automatic expansion valve25
Figure 4-10 An automatic expansion valve installed in a refrigeration system
26
Figure 5-1 Plain finned tube heat exchanger28
Figure 5-2 Wave finned tube heat exchanger28
Figure 5-3 Finned tube heat exchanger with louver fin 29
Figure 5-4 Slit fin29
Figure 5-5 Typical micro-channel heat exchanger30
Figure 5-6 Multiport tube30
Figure 5-7 Shape of fins in micro-channel heat exchanger30
Figure 5-8 Evaporator of air conditioner30
Figure 5-9 Multi-flow path evaporator31
Figure 5-10 Evaporator with a refrigerant distributor31
Figure 5-11 Finned tube condenser of a room air conditioner32
Figure 5-12 Side-air-discharge condenser of a room air conditioner32
Figure 5-13 Equipment with air discharged out of the top of the cabinet32
Figure 6-1 A propeller-type fan33
Figure 6-2 A centrifugal fan33
Figure 6-3 Improvement of fan shape33
Figure 6-4 A electric motor34
Figure 6-5 The windings of electric motor34
Figure 6-6 Poles (north and south) on a rotation magnet36
Figure 6-7 A simple sketch of a squirrel cage rotor36
Figure 6-8 Inverter controller for compressor 38
Figure 6-9 Signal to the base connection on the transistor38
Figure 6-10 The chock coil stabilizes current flow38
Figure 6-11 Modulation of sine-coded and pulse-width38
Figure 8-1 The energy efficiency label in Philippines49
Figure 8-2 The energy efficiency label in Singapore49
Figure 8-3 Finned-tube heat exchanger with 5mm diameter tube
51
SECTION 1
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1
Section 1
INTRODUCTION
1.1 Types of Air Conditioner
The definitions of room air conditioner and small
commercial air conditioner are always different
among different countries, even manufacturers.
Depending on the refrigeration capacity and
refrigerant used in some major ASEAN countries,
the differences between room air conditioner and
small commercial air conditioner are shown in
Table 1-1.
Table 1-1 Differences between room and small commercial air conditioners
Country
Capacity range (kW)
Refrigerants use
VIETNAM
Small commercial air conditioner
Room air conditioner
15 - 300
2-15
R22, R134a, R407C, etc.
Country
R22, R134a, R407C, etc.
MALAYSIA
Capacity range (kW)
Refrigerants use
2.3 - 4.4
0.7-1.8
R22 and R410A
R22 and R410A
Country
Capacity range (kW)
Refrigerants use
THAILAND
>12
<12
R-22, R-134a,R-12, R-11, R-717
R-22, R-134a, R-12, R-11, R-717
Country
PHILIPPINES
Capacity range (kW)
Refrigerants use
0.735-3.7
0.37-2.2
R-22, R-134a, R-12, R-11, R-717
R-22, R-134a, R-12, R-11, R-717
<<
2
Section 1
1.2 Major Manufacturers and Market Shares in ASEAN
To provide information on the demand for air conditioners from consumers, the major air conditioner
manufacturers and their approximate market shares of ASEAN countries are listed in Table 1-2.
Table 1-2 Major air conditioner manufacturers in ASEAN countries
VIETNAM
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
1
2
3
4
1
2
3
4
5
6
7
8
9
Manufacturers
DAIKIN
LG
REETECH
TRANE
CARRIER
PANASONIC
YORK
AIKIBI
ACSENT
MITSUBISHI HEAVY
FUJITSU
NAGAKAWA
MITSUBISHI ELECTRIC
MIDEA
KASUN
TOSHIBA
GREE
SAMSUNG
SANYO
GENERAL
OTHERS
Market Share in April 2011
11.19%
6.81%
6.36%
6.33%
5.50%
5.08%
4.35%
3.98%
3.79%
3.79%
3.39%
3.25%
3.09%
3.02%
2.85%
2.82%
2.79%
2.73%
2.66%
2.60%
13.64%
MALAYSIA
PANASONIC
YORK (American brand designed by OYL)
MITSUBISHI, HITACHI, LG, SAMSUNG, others
ACSON (local brand by OYL)
THAILAND
30%
28%
28%
14%
MITSUBISHI
LG
SAMSUNG
PANASONIC
DAIKIN
SAIJO DENKI
UNIAIR
CARRIER
Others e.g. HITACHI, TOSHIBA, YORK, FUJITSU
25%
17%
15%
13%
10%
6%
4%
2%
8%
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3
Section 1
1.3 Efficiency of Air Conditioner
Methods that are commonly used to evaluate the
performance of an air conditioner include: (1)
EER, (2) COP, and (3) SEER.
EER (energy efficiency ratio) is the ratio of the
total cooling capacity to the effective power input
to the device. The larger the EER value, the more
efficient the equipment. The EER rating is a
steady-state rating for refrigerating performance
and does not account for the time the unit
operates before reaching peak efficiency. This
operating time has an unknown efficiency. It also
does not account for shutting the system down at
the end of the cycle.
COP (coefficient of performance) is defined as
the ratio of the heating capacity to the effective
power input to the device. The larger the COP
value, the more efficient the equipment. The
COP rating is a steady-state rating for heating
performance. Just like EER, the COP rating does
not account for the time the unit operates before
reaching peak efficiency.
SEER (seasonal energy efficiency ratio) is the
cooling capacity during a typical cooling-season
divided by the total electric energy input during
the same period. The larger the SEER value, the
more efficient the equipment. The SEER rating
includes the start-up and shutdown cycles, and
so it is more reasonable for the performance
evaluation than the EER rating. In the meantime,
the SEER rating is more complicated than the
EER rating.
<<
4
SECTION 2
<<
5
Section 2
OUTLINE OF AIR CONDITIONER
2.1 Major Components of Air
Conditioner
There are two types of air-conditioners:
• window-type air conditioner – all components
in a single unit, as shown in Figure 2-1;
• split-type air conditioner – components
separated in two units (i.e. indoor unit and
outdoor unit), as shown in Figure 2-2.
Figure 2-1 Window-type air conditioner
Air conditioners can be divided into another two
types according to their function of cooling or
heating:
• single cooling air conditioner – having the
only function for cooling;
• heat-pump type air conditioner – can also run
as heat pump for heating.
Figure 2-2 Split-type air conditioner
Inverter
Compressor
Outdoor heat
exchanger
Fan-motor
Fan-motor
Indoor heat
exchanger
4 way
valve
Throttling device
Figure 2-3 Major components in an inverter split-type air conditioner
<<
6
Section 2
The components in different type air conditioners
are not the same. But all air conditioners should
contain the following main components: (1)
compressor, (2) evaporator, (3) condenser, (4)
expansion device, and (5) fan. These components
are briefly introduced in this chapter and will be
described in later chapters.
Compressor
The compressor is a vapor pump that pumps the
heat-laden refrigerant vapor from the low-pressure
side of the system (the evaporator side) to the highpressure side (the condenser side) by increasing
pressure and temperature. The types of compressors
commonly used in air conditioners include:
reciprocation, screw, rotary, scroll and centrifugal.
Evaporator
The evaporator is the component that absorbs heat
into the refrigeration system. The most commonly
used evaporator type is finned tube heat exchanger
consisting of copper tubes and aluminum fins.
Condenser
The condenser for air conditioner is the component
that rejects the heat from the system. Most air
conditioners are air cooled and reject heat to the air.
The most commonly used condenser type is fin and
tube heat exchanger consisting of copper tubes and
aluminum fins.
2.2 Refrigeration Cycle
Air conditioning systems adopt vapor compression
refrigeration cycle. Figure 2-4 schematically shows a
basic vapor-compression refrigeration cycle.
The refrigerant leaving the evaporator enters
the compressor as a saturated vapor, and it
is compressed to relatively high pressure and
temperature by the compressor. The compressor is
driven by the motor.
The refrigerant leaving the compressor enters the
condenser, where the refrigerant condenses and
there is heat transfer from the refrigerant to the
surroundings.
The refrigerant leaving the condenser enters the
expansion valve and expands to the evaporator
pressure. This pressure decreasing process is an
irreversible process, and it accompanies with
the increase of entropy. The refrigerant leaves
the expansion valve as a two-phase liquid-vapor
mixture.
The refrigerant leaving the expansion valve enters
the evaporator. It vaporizes as it absorbs heat from
the refrigerated space.
Heat rejection
3
Expansion device
The expansion device controls the refrigerant to the
evaporator. The commonly used expansion devices
include: thermostatic expansion valve, automatic
expansion valve, and the capillary tube.
Fan
The air flowing across the evaporator (or condenser)
is usually driven by a fan. The fans used in air
conditioner have two types: propeller fan and
squirrel cage fan. Depending on to structure
and noise, propeller fan is used in condenser and
squirrel cage fan is used in evaporator.
1. Evaporator
4
2
5
Work input
2. Expansion device
3. Condenser
4. Compressor
5. Motor
1
Heat removal
Figure 2-4 Basic vapor-compression refrigeration cycle
<<
7
Section 2
2.3 Characteristics of Refrigerant
Some properties of refrigerant may obviously
affect the performance of vapor compression
refrigeration cycles. The requirements on these
properties are discussed as follows.
Appropriate temperature and pressure
characteristics
The saturated pressure with temperature is an
important property of refrigerant. An appropriate
refrigerant should be in a reasonable pressure
range for its applied cases. Figure 2-5 shows the
saturated pressure with temperature of some
refrigerants.
Vapour pressure (bar)
25
20
15
10
80
70
60
50
40
30
20
0
10
-10
-20
-30
-40
-60
0
-50
5
Temperature (ºC)
R12
R404A
R134a
R407C
R600a
R410A
R290
Figure 2-5 The saturated pressure with temperature of
some refrigerants
• Low compression ratio is desirable, because
the degree of complication and difficulty
of a compressor increases directly with the
compression ratio;
• Discharge temperature of compressor should
not be excessive, to avoid problems such as
breakdown or dilution of the lubricating oil,
decomposition of the refrigerant, or formation
of contaminants such as sludge or acids.
Otherwise, any of these problems may lead to
compressor damage.
High latent heat of vaporization and low
specific volume
A high latent heat of vaporization and a low
specific volume of the refrigerant at the inlet
of the compressor are desirable for smaller
equipment and pipe size at a given cooling
capacity.
High latent heat means there is a high
refrigeration effect. The refrigerating effect is the
refrigerating capacity per unit mass flow rate of
refrigerant, also called specific refrigerating effect.
Low specific volume of the refrigerant at the inlet
of the compressor means that it will result in a
high volumetric refrigerating effect.
Lower compression work
In order to get high refrigeration efficiency, both
high refrigeration effect and low compression
work must be considered in combination.
For air conditioners, the temperature and
pressure of refrigerant should fulfill the following
requirement:
• It is desired for the pressure at the evaporating
temperature to be higher than the atmospheric
pressure, so as to avoid inward leakage of air;
• The pressure at the condensing temperature
should not be excessive, so that extra strength
of the high-side equipment is not required;
<<
8
SECTION 3
<<
9
Section 3
COMPRESSOR
3.1 Types of Compressor
Reciprocating compressor
Screw compressor
Scroll compressor
Rotary compressor
Centrifugal compressor
Figure 3-1 Five major types of compressors
The compressor is considered as the heart of an
air conditioning system, and can be described
as a vapor pump. The function of compressor is
increasing the pressure from the suction level to
the discharge level. The cool refrigerant passes
through the suction valve to fill the cylinder.
This cool vapor contains the heat absorbed in
the evaporator. The compressor pumps this heatladen vapor to the condenser so that the heat can
be rejected from the system.
Five major types of compressors are commonly
used in the air conditioners, as shown in
Figure 3-1. These are reciprocating, screw,
rotary, scroll, and centrifugal. Reciprocating
compressors are used most frequently in small
and medium-sized commercial refrigeration
systems. Screw compressors are used in
commercial and industrial systems. Rotary
compressors and scroll compressors, along
with the reciprocating compressors, are used in
residential and small commercial air conditioners.
Centrifugal compressors are used extensively
for air conditioning in large buildings; but
recently small-size centrifugal compressors have
been developed, and they can be used in air
conditioners.
<<
10
Section 3
3.1.1 Reciprocating Compressor
Reciprocating compressor compresses the vapor
by moving piston cylinder to change the volume
of the compression chamber. The main elements
of a reciprocating compressor include piston,
cylinder, valves, connection rod, crankshaft and
casing.
Reciprocating compressors are categorized by the
compressor housing. The two housing categories
are open and hermetic compressor. Room and
small commercial air conditioners usually use
hermetic compressors. Hermetic refers to the
type that all the components of the compressor
is contained in a single house, including fully
welded hermetic compressor and semi-hermetic
compressor, as shown in Figure 3-2.
Hermetic compressors
The motor and compressor are contained inside
a single shell that is weld-closed when a welded
hermetic compressor is manufactured.
Characteristics of the fully welded hermetic
compressor are as follows:
• The only access to the inside of the shell is
by cutting the shell open;
• They usually have a pressure lubrication
system, but smaller hermetic is splash
lubricated;
• The motor shaft and compressor crankshaft
are one shaft. The combination motor and
crankshaft are customarily in a vertical
position with a bearing at the bottom of
the shaft next to the oil pump. The second
bearing is located about halfway on the shaft
between the compressor and motor;
• It is usually considered a low-side device
because the suction gas is vented to the
whole inside of the shell, which includes the
crankcase. The discharge line is normally
piped to the outside of the shell so that the
shell only has to be rated at the low-side
working-pressure value;
• The pistons and rods work outward from
the crankshaft, so they are working at a
90°angle in relation to the crankshaft,
Figure 3-3.
Suction Bag
Fully welded hermetic
compressor
Rotor
Suction Tube
Stator
Balance Iron
Washer
Connecting Rod
Crankshaft
Piston
Cylinder Head
Shell
Valve Cover
Cylinder
Discharge Tube
Semic-hermetic compressor
Figure 3-2 Fully welded hermetic compressor and
semi-hermetic compressor
End Cover
Lower Bearing
Figure 3-3 The internal working of a fully welded
hermetic compressor
<<
11
Section 3
Semi-hermetic compressors
When a semi-hermetic compressor is
manufactured, the motor and compressor are
contained inside a single shell that is bolted
together. This unit can be serviced by removing
the bolts and opening the shell at the appropriate
place. The inner structure of a semi-hermetic
compressor is shown in Figure 3-4.
Following are the characteristics of the semihermetic compressor:
• The unit is bolted together at locations that
facilitate service and repair. Gaskets separate the
mating parts connected by the bolts, and the
housing is normally cast-iron or steel, so they
are normally heavier than the fully welded type;
• They generally use a splash-type lubrication
system in the smaller compressor and a pressure
lubrication system in the large compressors;
• They are often air cooled and can be recognized
by the fins in the casting or extra sheet metal
on the outside of the housing that give the shell
more surface areas;
• The motor and crankshaft combination are
similar to the motor and crankshaft in the
fully welded type except that the crankshaft is
usually horizontal.
• The piston heads are normally at the top or
near the top of the compressor and work up
and down from the center of the crankshaft.
Discharge Tube
Reciprocating compressor may be either singleacting or double-acting, and can be designed
to accommodate practically any pressure of
capacity. In a single-acting compressor, the vapor
compression occurs only once in one side of the
piston during each revolution of the crankshaft.
In a double-acting compressor, the vapor
compression occurs alternately in both sides of
the piston so that the compression occurs twice
for each revolution of the crankshaft.
In reciprocating compressor, the piston is driven
by a crankshaft via a connection rod. At the top
of the cylinder are a suction valve and a discharge
valve. A reciprocating compressor usually has
several cylinders in it.
To illustrate the principle of operation of
reciprocating compressor, here we use singleacting piston as an example. The following
sequence of events occurs inside a reciprocating
compressor during the pumping action, as shown
in Figure 3-5.
Piston moves down
Piston starts up
Piston proceeds up
Piston at top
dead-center
Valve
Rod
Inlet Filter
Oil Pump
Motor
Oil Filter
Shell
Figure 3-4 The working parts of a semi-hermetic compressor
Figure 3-5 Events inside a reciprocating compressor during the
pumping action
<<
12
Section 3
Piston at the top of the stroke and starting
down
When the piston starts down, a low pressure is
formed under the suction reed valve. When this
pressure becomes less than the suction pressure
and the valve spring tension, the cylinder will
begin to fill. Gas will rush into the cylinder
through the suction reed valve.
Piston continues to the bottom of the stroke
When the piston gets near the bottom of the
stroke, the cylinder is nearly as full as it is going
to get. There is a short time lag as the crankshaft
circles through bottom dead-center, during which
a small amount of gas can still flow into the
cylinder.
Piston is starting up
The rod throw is past bottom dead-center, and
the piston starts up. When the cylinder is as full
as it is going to get, the suction flapper valve
closes.
The piston proceeds to the top of the stroke
When the piston starts back up and gets just
off the bottom of the cylinder, the suction valve
will have closed, and pressure will begin to build
in the cylinder. When the piston gets close to
the top of the cylinder, the pressure will start
to approach the pressure in the discharge line.
When the pressure inside the cylinder is greater
than the pressure on the top side of the discharge
reed valve, the valve will open, and the discharge
gas will empty out into the high pressure side of
the system.
The piston is at exactly top dead-center
This is as close to the top of the head as it
can go. There has to be a certain amount of
clearance in the valve assemblies and between
the piston and the head, otherwise they would
touch. This clearance is known as clearance
volume. A reciprocating compressor cylinder
cannot completely empty because of the
clearance volume at the top of the cylinder. The
manufactures try to keep this clearance volume
to a minimum but cannot completely do away
with it. The piston is going to push as much gas
out of the cylinder as time and clearance volume
will allow. There will be a small amount of gas
left in the clearance volume. When the piston
starts back down, this gas will re-expand, and the
cylinder will not start to fill until the cylinder
pressure is lower than the suction pressure. This
re-expanded refrigerant is part of the reason
that the compressor is not 100% efficient. Valve
design and the short period of time the cylinder
has to fill at the bottom of the stroke are other
reasons the compressor is not 100% efficient.
3.1.2 Scroll Compressor
The scroll compressor compresses a gas by turning one scroll against another around a common
axis. The scroll compressor is becoming more
fine-tuned and is available in many more applications. A major hurdle in making the scroll
compressor a viable product has been the ability
to achieve a balance between the need for highvolume precision manufacturing and the need for
consistent high performance and efficiency, low
sound levels, and great reliability.
Because of the scroll compressor’s fewer moving
parts, it operates much more quietly than other
compressor designs and technologies. Less noise
and higher efficiencies have become two key
selling points for installing the scroll compressor
in air-conditioners.
Comparing to piston-type compressor, the scroll
compressor has higher efficiencies, reliability, and
quieter operation. The characteristics of scroll
compressor are summarized as follows:
• There are no volumetric losses through gas reexpansion as with piston-type compressors;
• The scroll compressor requires no reed valves,
<<
13
Section 3
•
•
•
•
so it does not have valve losses that contribute
to inefficiencies as piston-type compressors;
Separation of suction and discharge gases
reduces heat-transfer losses;
Centrifugal forces within the mating scrolls
maintain nearly continuous compression and
constant leak-free contact;
Radial movement eliminates high-stress
situations and allows for just the right amount
of contact force between mating scroll surfaces.
This acting allows the compressor to handle
some liquid;
Scroll compressors maintain a continuous
compression process and have no reed valves
to create valve noise. This creates very soft
gas-pulsation noises and very little vibration as
compared with piston-type compressors.
Scroll compressor operation is relatively simple.
Two spiral-shaped scrolls fit inside one another.
The two mating parts are often referred to as
involute spirals. One of the spiral-shaped parts
stays stationary while the other orbits around
the stationary member. The orbiting motion is
created from the centers of the journal bearings
and motor being offset, as shown in Figure 3-6.
1. Fixed Scroll Member
5. Connection
2. Moving Scroll member
6. Sunction Hole
3. Compressor Case
7. Discharge Hole
4. Eccentric Bearing
Figure 3-6 Cross section of a scroll compressor
rotational motion. This orbiting motion causes
continuous crescent-shaped gas pockets to be
formed, as shown in Figure 3-7. The orbiting
motion draws gas into the outer pocket and seals
it as the orbiting continues. This continuous
orbiting motion causes the crescent-shaped gas
pocket to become smaller and smaller in volume
as it nears the center of the scroll form. The gas
pocket is fully compressed and is discharged out
of a port of the nonorbiting scroll member, as
shown in Figure 3-8.
The orbital motion of one spiral-shaped is not a
(1)
(2)
(3)
(4)
(1) Gas enters an outer opening as one scroll orbits the other
(2) The open passage is sealed as gas is drawn into the compression chamber
(3) As one scroll continues orbiting, the gas is compressed into an increasingly smaller “pocket”
(4) Gas is continually compressed to the center of the scrolls, where it is discharged through precisely
machined ports and returned to the system
Figure 3-7 Process of forming continuous crescent-shape gas pockets in the scroll
<<
14
Section 3
Discharge port
rotary compressor. Rotary compressors are
manufactured in two basic design types: the
stationary vane and the rotary vane.
Figure 3-8 Scroll orbit in a real scroll compressor
Several crescent-shaped gas pockets are
compressed at the same time, which provides
for a smooth and continuous compression
cycle. Thus, the scroll compressor conducts
its intake, compression, and discharge phases
simultaneously.
Unlike piston-type compressors, the scroll
compressor has no re-expansion of discharge
gas that can be trapped in a clearance volume.
Re-expansion of discharge gas contributes
to low volumetric efficiencies in piston-type
compressors.
3.1.3 Rotary Compressor
A rotary compressor is small and light. It is
sometimes cooled with compressor discharge
gas, which makes the compressor appear to be
running too hot. A warning may be posted in the
compressor compartment that the housing will
appear to be too hot. The compressor and motor
are pressed into the shell of a rotary compressor,
and no vapor space is between the compressor
and the shell. This also reduces the size of the
rotary compressor as compared with a reciprocating compressor.
A rotary compressor is generally more efficient
than a reciprocating compressor, and it is
widely used in small- to medium-sized systems.
Figure 3-9 shows the inner structure of the
1. Discharge Tube
6. Sucion Tube
2. Cylinder
7. Sliding Vane
3. Rotary
8. Spring
4. Eccentric Shaft
9. Discharge Valve
5. Lubricating Oil
Figure 3-9 Cross section of a rotary compressor
Stationary vane rotary compressor
The components for this compressor are the
housing, a blade or vane, a shaft with an offcenter rotor, and a discharge valve. The shaft
turns the off-center rotor so that it “rolls” around
the cylinder, as shown in Figure 3-10. The
blade or vane keeps the intake and compressor
chambers of the cylinder separate. The tolerances
between the rotor and cylinder must be very
close, and the vane must be machined so that
gas does not escape from the discharge side to
the intake. As the rotor turns, the vane slides in
and out to remain tight against the rotor. The
valve at the discharge keeps the compressed gas
from leaking back into the chamber and into the
suction side during the off cycle.
As the shaft turns, the rotor rolls around the
cylinder, allowing suction gas to enter through
<<
15
Section 3
the intake and compresses the gas on the
compression side. This is a continuous process as
long as the compressor is running. The results are
similar to those with a reciprocating compressor.
Low-pressure suction gas enters the cylinder, is
compressed, and leaves through the discharge
opening.
compressing is a continuous process as long as the
compressor is running.
All the refrigerant that enters the intake port
is discharged through the exhaust or discharge
port. There is no clearance volume as in the
reciprocating compressor. This is the primary
reason why the rotary compressor is highly
efficient.
3.1.4 Screw Compressor
Instead of a piston and cylinder, the rotary compressor uses two matching, tapered, machined
screw-type gears that squeeze the refrigerant vapor
from the inlet to the outlet.
The rotary screw compressor uses an open motor
instead of the hermetic design, and a shaft seal
traps the refrigerant in the compressor housing
where the rotating shaft leaves the compressor
housing. A flexible coupling is used to connect
the motor shaft to the compressor shaft to
prevent minor misalignment from causing seal or
bearing damage.
1. Discharge Tube
6. Sucion Tube
2. Cylinder
7. Sliding Vane
3. Rotary
8. Spring
4. Eccentric Shaft
9. Discharge Valve
5. Lubricating Oil
Figure 3-10 Operation of a stationary van rotary compressor
Rotary vane rotary compressor
The rotary vane compressor has a rotor fitted to
the center of the shaft. The rotor and the shaft
have the same center. The rotor has two or more
vanes that slide in and out and trap and compress
the gas. The shaft and rotor are positioned off
center in the cylinder. As a vane passes by the
suction intake opening, low-pressure gas follows
it. This gas continues to enter and is trapped by
the next vane, which compresses it and pushes
it out the discharge opening. The intake and
Screw compressor applications are for large
systems. The refrigerant may be any of the
common refrigerants. The operating pressure on
the low- and highpressure sides of the system
are the same as for a reciprocating system of like
application.
As shown in Figure 3-11, the compression of
refrigerant in a screw compressor is accomplished
by the enmeshing of two mating helically grooved
rotors. The rotors are the main components of
the screw compressor. As the rotors turn, vapour
is drawn through the inlet opening to fill the
space between the male lobe and the female
flute. As the rotors continue to rotate, the vapor
is moved through the suction port and sealed in
the interlobes space. The vapor so trapped in the
interlobe space is moved both axialy and radially
<<
16
Section 3
Figure 3-11 One stage of compression as refrigerant moves through the screw compressor
and is compressed by direct volume reduction as
the enmeshing of the lobes progressively reduced
the space occupied by the vapor. Compression
of the vapor continues until the interlobe space
communicates with the discharge ports in the
cylinder and the compressed vapor leaves the
cylinder through these ports. The length and
diameter of the rotors determine the capacity
and discharge pressure. Longer rotors may result
in higher pressure. The large the diameter of the
rotors, the greater the capacity.
After compression, the refrigerant vapor/
lubricant mixture enters a multi-stage separator
which removes the lubricant from the refrigerant
vapor. From the separator, the vapor flows to the
aftercooler. The lubricant is also cooled, returning
to the compressor through a thermostaticallycontrolled valve. Lubrication is crucial to the
rotary screw compressor. Without proper
lubrication, the screw could be worn out quickly.
Many rotary screw models are equipped with
internal capacity control and variable volume
ratio systems to cope with variable load and
pressure operation. Such systems are particularly
desirable when the screw compressor is driven
by a constant speed electric motor but operates
under varying pressure conditions.
The characteristics of screw compressor are listed
as follow:
1.Screw compressor has fewer moving parts. So,
there is no need to service the items such as
compressor valves, packing and piston rings,
and the associated downtime for replacement;
2.The absence of reciprocation inertial forces
allows the screw compressor to run at high
speeds, and so it could be constructed more
compact;
3.The continuous flow of cooling lubricant
allows much higher single-stage compression
ratios;
4.The compactness tends to reduce package
costs;
5.Low vibration due to reducing or elimination
pulsations by screw technology;
6.Higher speeds and compression ratios help to
maximize available production horsepower.
3.1.5 Centrifugal Compressor
Centrifugal compressor has been designed
for heating, ventilation, air-conditioning and
refrigeration industries. A schematic diagram of
centrifugal compressor is shown in Figure 3-12.
Vapor enters axially at the inlet cavity (6) and
flow through the passage in the impeller (3). The
pressure and absolute velocity of the vapour rise
when the vapor passes the impeller because of the
centrifugal force. In the diffuser (8), the flow of
vapor is decelerated to further raise the vapour
pressure. The compressed vapor is collected in the
volute (1) and discharge to the delivery pipe.
<<
17
Section 3
for the power consumption of the compressors.
In order to reduce the power consumption,
cooling between stages may be needed.
3.2 Compressor Efficiency
1. Volute
5. Rotor
2. Diffuser
6. Inlet Cavity
3. Impeller
7. Impeller
4. Seal
8. Diffuser
Figure 3-12 Centrifugal compressor
The centrifugal compressor consists of a housing
and at least one rotor (5) of which the shaft is
pivotally supported by the housing, with a free
shaft end and a rotor connected with the other
end of the rotor shaft. The free end of the rotor
shaft facing away from the rotor projects into a
pressure chamber connected with the housing,
and is acted upon by a pressurized rotor. Thus,
the starting friction of the compressor is lower
and drive motors of lower output target can be
utilized. To reduce leakage along the shaft where
the vapor passes through the compressor housing,
the centrifugal compressor must be sealed in a
suitable manner.
Centrifugal compressors are well suited to
compress large volume of refrigerant for relatively
low pressure lift. Since the compressive force
generated by a single impeller wheel is small,
multiple impeller wheels arranged in series can be
employed for centrifugal compressors to increase
compression ratio. The pressure ratio across each
stage is determined by the required pressure lift
of a compressor. However, it is also necessary
to consider a suitable velocity increase in each
impeller to reduce the possible momentum losses
between the stages. The temperature of refrigerant
at the inlet of each stage has a decisive significance
The compressor’s overall efficiency can be
improved by maintaining the correct working
conditions. This involves keeping the suction
pressure as high as practical and the keeping head
pressure as low as practical within the design
parameters.
A dirty evaporator will cause the suction pressure
to drop. When the suction pressure goes below
normal, the vapor that the compressor is
pumping becomes less dense, resulting in the
compressor performance decreases. Low suction
pressures also cause the high-pressure gases caught
in the clearance volume of the compressor to
expand more during the piston’s downstroke.
This gives the compressor a lower volumetric
efficiency. These gases have to expand to a
pressure just below the suction pressure before
the suction valve will open. Because more of the
downward stroke is used for re-expansion, less of
the stroke can be used for suction. Suction ends
when the piston reaches bottom dead-center.
Low evaporator pressures cause high compression
ratios. The compression ratio is defined as follow:
Compression ratio = Absolute discharge
pressure / Absolute suction pressure
If compression ratio is too high, compressor
will not operate normally. Most manufacturers
recommend that the compression not be more
than 12:1.
Dirty condensers also cause compression ratios
to rise, but they do not rise as fast as with a dirty
evaporator.
<<
18
Section 3
3.3 Latest Technology in
Development and Commercially
Available
It is desirable to have an air-conditioner to
operate at low noise, constant temperature
control, all-day running, low frequency
compensation and instantly achieving the
set temperature. The emergence of inverter
compressor makes them achievable in an energy
efficient way.
The inverter compressor changes its capacity by
varying its rotation speed. When the compressor
rotates at high speed, it delivers high capacity
to speed up the cooling or heating without
excessively consuming energy. This is because
the speed of the compressor is controlled to
maximize the efficiency and according to the
cooling and heating load of a room. In contrast
to conventional compressors, inverter compressor
detects subtle changes in temperature and adjusts
its speed automatically. When it operates at
a low rotation speed, it efficiently maintains
the desirable temperature with minimum
temperature swings to provide a comfortable
climate. For optimum performance inverter
technology delivers only the energy needed to
satisfy the cooling and heating load of a room,
thereby reducing energy consumption.
The comparison of inverter compressor and
conventional compressor is listed in Table 3-1.
Table 3-1 Comparison of inverter compressor and conventional compressor
Inverter compressor
Conventional compressor
High rotation speed provides fast cooling and
heating
Requires a long time to reach desired
temperature
Low rotation speed efficiently maintains desired
temperature
Has uncomfortable temperature fluctuation
Low rotation speed keeps starting current low,
leaving other appliances unaffected
Needs heavy energy usage every time compressor
turns on
Precise rotation speed control provides
comfortable, consistent room temperature
Requires high starting current that affects other
appliances throughout household
Smooth speed charge scroll compressor with
neodymium concentrating winding DC motor,
as shown in Figure 3-13, is developed in recent
years, and this kind of compressor may have low
vibration and high efficiency.
Smooth
Speed
charge
scroll
New neodymium
concentrating
winding DC
motor
Figure 3-13 Smooth speed charge scroll compressor with
neodymium DC motor
<<
19
SECTION 4
<<
20
Section 4
EXPANSION DEVICE
4.1 Types of Expansion Device
The expansion device is the component necessary
for the compression refrigeration cycle to
function. The expansion device can be either
a valve or a fixed-bore device, and it is not as
visible as the evaporator, the condenser, or the
compressor.
The fixed-bore device is referred to capillary
tube as shown in Figure 4-1. The capillary tube is
usually used in room air-conditioner.
Expansion valves have two different types: (1)
thermostatic expansion valve as shown in
Figure 4-2 and (2) automatic expansion valve,
as shown in Figure 4-3. The expansive valves are
usually used in commercial air-conditioners.
Figure 4-2 Thermostatic expansion valve
Capillary
tube
Figure 4-3 Automatic expansion valve
Figure 4-1 Capillary tube connected with liquid-line
<<
21
Section 4
4.2 Capillary Tube
The capillary tube metering device controls
refrigerant flow by pressure drop. It is a copper
tube with a very small calibrated inside diameter, as
shown in Figure 4-1. The diameter and the length
of the tube determine how much liquid will pass
through the tube at a given pressure drop.
This length-to-pressure drop relationship is used
by manufactures to arrive at the correct pressure
drop that will allow the correct amount of
refrigerant to pass through the capillary tube to
correctly fill the evaporator, as shown in Figure
4-4. The capillary tube can be quite long on some
installations and may be wound in a coil to store
the extra tubing length.
The capillary tube does not control superheat or
pressure. It is a fixed-bore device with no moving
parts, and it is weak in adjusting the refrigerant
flow rate according to the load change. Therefore,
it is used where the load is relatively constant (i.e.
no large load fluctuation).
The capillary tube is an inexpensive device for the
control of refrigerant and is used often in small
equipment. This device does not have a valve and
does not stop the liquid from moving to the low
side of system during the off cycle, so the pressure
will equalize during the off cycle. This reduces
the motor starting torque requirement for the
compressor.
Condensor
Evaporator
Compressor
The capillary tube has no moving parts, and so
it will not wear out. The only problem it may
have would be small particles that may block
or partially block the tube. The bore is so small
that a small piece of carbon or solder entering
the capillary tube would cause a problem.
Manufacturers always place a strainer of filterdrier just before the capillary tube to prevent this
from happening, as shown in Figure 4-5.
Filter-drier
Liquid line
Capillary tube
Evaporator
Figure 4-5 A filter-drier protects the capillary tube
from circulating particles
4.3 Thermostatic Expansion Valve
A thermostatic expansion valve is normally
installed in the liquid line between the condenser
(high side of the system) and the evaporator
(low side of the system), and it is responsible for
metering the correct amount of refrigerant to the
evaporator. The evaporator performs best when it
is as full of liquid refrigerant as possible without
leaving any in the suction line.
A thermostatic expansion valve controls the
refrigerant to the evaporator using a thermal
sensing element to monitor the superheat. This
valve opens or closes in response to a thermal
element. The thermostatic expansion valve
maintains a constant superheat in the evaporator.
Excess superheat is not desirable, but a small
amount is necessary with this valve to ensure that
no liquid refrigerant leaves the evaporator. The
thermostatic expansion valve can be adjusted
to maintain a low superheat to ensure that the
majority of evaporator surface is effectively used,
resulting in a higher capacities and efficiencies.
Capillary Tube
Figure 4-4 Capillary tube in a refrigerating system
<<
22
Section 4
A thermostatic expansion valve consists of
valve body, diaphragm, needle and seat, spring,
adjustment and packing gland, and the sensing
bulb and transmission tube, as shown in Figure
4-6.
Sensing
bulb
connection
External equlizer
connection
Refrigerant
outlet
Thermostatic
element containing
diaphragm
Push rods
Refrigerant
inlet
Valve body
Seat
Pin carrier
Superheat spring
Spring guide
Bottom cap
Adjustment
Protective sealcap
Figure 4-6 An exploded view of the thermostatic expansion valve
The valve body is an accurately machined piece
of solid brass or stainless steel that holds the rest
of the components and fastens the valve to the
refrigerant piping circuit.
The diaphragm moves the needle in and out of
the seat in response to system load changes. The
diaphragm is made of thin metal and is under the
round dome-like top of the valve.
The needle and seat control the flow of refrigerant
through the valve. They are normally made of
some type of very hard metal, such as stainless
steel, to prevent the refrigerant passing through
from eroding the seat.
The spring is one of the three forces that act on
the diaphragm. It raises the diaphragm and closes
the valve by pushing the needle into the seat.
When a valve has an adjustment, the adjustment
applies more or less pressure to the spring to
change the tension for different superheat
settings.
The sensing bulb and transmission line are
extensions of the valve diaphragm. The bulb
detects the temperature at the end of the
evaporator on the suction line and transmits this
temperature, converted to pressure, to the top of
the diaphragm. The bulb contains a fluid, such
as refrigerant, that responds to a temperature/
pressure relationship chart just like any refrigerant
would. When the suction line temperature goes
up, this temperature change occurs inside the
bulb. As the temperature of the thermostatic
expansion valve’s sensing bulb increases, the valve
will gradually open, letting more refrigerant
into the evaporator. This will increase both the
evaporator pressure and compressor’s suction
pressure, while attempting to reduce the amount
of superheat in the evaporator. At the condition
of pressure variation, the transmission line allows
the pressure between the bulb and diaphragm to
equalize back and forth.
The fluid inside the expansion valve bulb is
known as the charge for the valve. Four types of
charge can be obtained with the thermostatic
expansion valve: liquid charge, cross liquid
charge, vapor charge, and cross vapor charge.
• The liquid charge bulb is a bulb charge with
a fluid characteristic of the refrigerant in
the system. The diaphragm and bulb are
not actually full of liquid. The liquid will
not all boil away. The temperature/pressure
<<
23
Section 4
relationship is almost a straight line on a graph.
The liquid charge bulb is usually limited to
narrow-operation-range applications or special
functions like desuperheating in the high side
of the system.
• The cross liquid charge bulb has a fluid that
is different from the system fluid. It does not
follow the temperature/pressure relationship.
It has a flatter curve and will close the valve
faster on the rise in evaporator pressure. Liquid
cross charges are good for low-temperature
applications.
• The vapor charge bulb is actually a valve that
has only a small amount of liquid refrigerant
in the bulb. When the bulb temperature
rises, more and more of the liquid will boil
to a vapor until there is no more liquid. The
pressure curve will be flat. This acts to limit
the maximum operating pressure the valve will
allow the evaporator to experience. These valves
are often referred to as maximum operating
pressure valves.
• The cross vapor charge bulb has a similar
characteristic to the vapor charged valve, but
it has a fluid different from the refrigerant
in the system. This gives a different pressure
and temperature relationship under different
conditions. These special valves are applied to
special systems.
The seat in the valve is stationary in the valve
body, and needle is moved by the diaphragm.
One side of the diaphragm gets its pressure from
the bulb, and the other side gets its pressure from
the evaporator and the spring. The diaphragm
moves up and down in response to three different
pressures. These three different pressures act at the
proper time to open, close, or modulate the valve
needle between open and closed. These three
pressures are the bulb pressure, the evaporator
pressure, and the spring pressure. They all work as
a team to position the valve needle at the correct
position for the load conditions at any particular
time.
Pressure of Sensing bulb 0.414MPa
Pressure of Spring 0.078MPa
Pressure of Evaporator 0.336MPa
Liquid Refrigerant
Vapor Refrigerant
1.0ºC
1. The Spensing Bulb 2. Adjusting Screw 3. Spring 4. Push Ord 5. The diaphragm
Figure 4-7 The valve opening is affected by the inlet pressure of evaporator
<<
24
Section 4
0.336MPa
Liquid Refrigerant
0.096MPa
Vapor Refrigerant
1. The Spensing Bulb 2. Adjusting Screw 3. Spring 4. Push Ord 5. The diaphragm
Figure 4-8 The valve opening is affected by the outlet pressure of evaporator
The pressure from the evaporator on the
diaphragm could be the inlet pressure of the
evaporator (as shown in Figure 4-7) or the
outlet pressure of the evaporator (as shown in
Figure 4-8). The structure of the thermostatic
valve using the inlet pressure of the evaporator is
simpler than that using the outlet pressure of the
evaporator; while the superheat of the evaporator
controlled by the type shown in Figure 4-7 is
normally larger than the type shown in Figure
4-8.
5
6
7
7
4
3
2
1
4.4 Automatic Expansion Valve
The automatic expansion valve is an expansion
valve that meters the refrigerant to the evaporator
by using one or more sensors. This device is also
a valve that changes inside dimension in response
to its sensing elements. The automatic expansion
valve has the ability to maintain a constant
pressure in the evaporator, and may not depend
on the superheat. Figure 4-9 shows a section of
automatic expansion valve.
The automatic expansion valve is built much
the same as the thermostatic expansion valve
1. Liquid and Vapor out
5. Push Rod
2. Spring
6. Winding
3. Need
7. Valve Body
4. Push Rod
8. Liquid in
Figure 4-9 Section of automatic expansion valve
except that it does not have a sensing bulb. The
body is normally made of machined brass. The
adjustment of this valve is normally at the top of
the valve. There may be a cap to remove, or there
may be a cap to turn. This adjustment changes
the spring tension that supports the atmosphere
<<
25
Section 4
in pushing down on the diaphragm. When the
tension is increased, the valve will feed more
refrigerant and increase the suction pressure.
The automatic expansion valve responds to load
changes, depending on the detected parameters
from the sensors. The sensors can be those of
pressure or temperature. Figure 4-10 shows an
example of using an automatic expansion valve in
a refrigeration system, using temperature sensors
by the automatic valve. Two temperature sensors
for respectively measuring the wall temperatures
at the middle position and the outlet of the
evaporator, and the measured two temperatures
are used to control the opening of the valve.
1
3
θ1w
θ1w -θ2w2
θ2w
PM
4
1. Evaporator
2. Compressor
3. Condensor
4. Automatic expansion valve
Figure 4-10 An automatic expansion valve installed in a
efrigeration system
<<
26
SECTION 5
<<
27
Section 5
HEAT EXCHANGER
5.1 Types and Sub Components of
Heat Exchanger
The heat exchangers in air conditioner are known
as evaporator and condenser, depending on their
functions.
The function of evaporator is to transfer
heat between high temperature room air and
low temperature refrigerant. The function
of condenser is to transfer heat between low
temperature outdoor air and high temperature
refrigerant.
Four types of fins are widely used in finned tube
heat exchangers for air conditioners, i.e. plain
fin, wave fin, louver fin and slit fin.
Among different types of finned tube heat
exchangers, the plain fin heat exchanger has the
lowest airside pressure drop, but it has the lowest
capacity of heat exchange. Its low capacity of
heat exchange results in that the plain fin is not
extensive used in heat exchangers. Figure 5-1
shows a finned tube heat exchanger using plain
fins.
The heat exchangers have many variations in the
shape and arrangement of heat transfer surface.
Finned tube heat exchangers and micro-channel
heat exchangers are the commonly used heat
exchangers in air conditioners.
The finned tube is the most common type used
in air conditioner. The finned tube exchanger
has the fins installed on the bare tube to enhance
the heat transfer from the air to the refrigerant
in the tube. The application of fins increases the
overall evaporator surface and so the evaporator
efficiency can be improved.
Finned tube heat exchangers are used extensively
in residential and commercial air conditioning
applications. In order to make them effective,
there must be good thermal contact between
the fins and tubes. This can be accomplished by
several ways. The most commonly used way is to
slip the fin over the tubes and expand the tubes
by pressure so that the fin locks onto the tube
surface. As the finned tube provides more surface
area per unit of length and width for the heat
transfer, a finned tube evaporator occupies less
space than a bare-tube or plate surface evaporator
of the same capacity does.
Figure 5-1 Plain finned tube heat exchanger
The surface of wave fin is stamped in wave
configuration, as shown in Figure 5-2. The
capacity of heat exchange of wave fin is higher
than plain fin, but less than that of slit fin and
louver fin. The wave fin is extensive used in the
outdoor condenser of air conditioner, because the
dust will not accumulate in the wave fin as much
as in the slit fin and louver fin.
Figure 5-2 Wave finned tube heat exchanger
<<
28
Section 5
Figure 5-3 shows a finned tube heat exchanger
with louver fin. The louver fin does not only
break the boundary, but also make the wind have
an angle with fin. So the louver fin has a high
capacity of heat exchange. However, the airside
pressure drop of louver fin is also high.
Round
tube
The configuration of slit fin is shown in Figure
5-4. The slit fin can efficiently break the
boundary layer near the fin. This will increase the
capacity of heat exchange. But this also brings
higher airside pressure drop.
Louver
Hole for round
tube
Louver
Air flow
Louver fin in finned tube
heat exchanger
Louver fin
Figure 5-3 Finned tube heat exchanger with louver fin
Hole for round tube
Slite
Figure 5-4 Slit fin
<<
29
Section 5
The micro channel heat exchanger is also one
type of heat exchanger used in air conditioner. A
typical micro channel heat exchanger consists of
multiport tubes, multilouver fins and manifolds,
as shown in Figure 5-5.
The shape of the fins in a micro-channel heat
exchangers is V-shape or square shape, as shown
in Figure 5-7.
Multilouver fin
V-shape fin
Manifold
Multiport
tube
Cu-AI
joint
Figure 5-5 Typical micro-channel heat exchanger
There are different types of multiport tubes, e.g.
extruded tube, inner-finned tube and folded
tube, as shown in Figure 5-6.
Extruded tube
Inner-finned tube
Square shape fin
Figure 5-7 Shape of fins in micro-channel heat exchanger
5.2 Evaporator
The evaporator in a refrigerant system is
responsible for absorbing heat into the refrigerant
from indoor air. This heat-absorbing process is
accomplished by maintaining the evaporator
at a lower temperature than indoor air, and the
temperature should be low enough for removing
latent and sensible heat from cooler.
There are three ways to increase heat exchange
capacity of evaporator.
The first method is to increase heat transfer
area. For the limit space of indoor part of
air conditioner, the finned tube area should
be limited. However, the manufacturers can
optimize the shape of the evaporator to increase
the space for laying more finned tube, as shown
in Figure 5-8.
Folded tube
Figure 5-6 Multiport tube
Traditional
arrangment
With more
finned tubeå
Figure 5-8 Evaporator of air conditioner
<<
30
Section 5
The second method is to use enhanced fins, such
as slit fin or louver fin, as shown in Figures 5-3
and 5-4. It should be noted that the evaporator
operating under dehumidifying condition may
produce water droplets or water films which can
block the slit or louver, resulting in the decrease
of heat exchange capacity and the increase of
airside pressure drop.
Inlet
The third method is to optimize the refrigerant
flow circuit. When a refrigerant flow path in
an evaporator becomes too long and excessive
pressure drop occurs, it is advisable to have more
than one path in parallel, as schematically shown
in Figure 5-9. However, when more paths are
used, a distributor must be used to distribute the
correct amount of refrigerant to the individual
paths, as shown in Figure 5-10.
Outlet
Block 1
Inlet
Block 1
12
Outlet
24
23
23
Air flow
10
22
10
21
Air flow
21
22
20
8
8
19
7
18
6
6
17
18
17
16
4 15
4
14
3
2 13
2
13
Figure 5-9 Multi-flow path evaporator
Refrigerant
distributor
Evaporator
Figure 5-10 Evaporators with a refrigerant distributor
<<
31
Section 5
5.3 Condenser
The condenser is a heat exchange device similar
to the evaporator, as shown in Figure 5-11.
Different from the evaporator, it rejects the heat
from the system absorbed. The heat is rejected
from a hot superheated vapor in the first part
of the condenser. The middle of the condenser
rejects latent heat from the saturated vapor,
which is in the process of phase changing to a
saturated liquid. The last part of the condenser
rejects heat from subcooled liquid, subcooling
the liquid to below its condensing temperature.
In fact, the three functions of a normal condenser
are to desuperheat, condensate, and subcool the
refrigerant.
Air flow
Figure 5-12 Side-air-discharge condenser of a
room air conditioner
Top-air-discharge condenser
Some large room and small commercial air
conditioner may use top-air-discharge condenser,
as shown in Figure 5-13. In this type condenser,
the hot air and noise are discharged from the top
into the air. The fan and motor are on top of the
equipment, and rain, snow, and leaves can fall
directly into the unit, so the fan motor should be
protected with a rain shield.
Air discharge
Figure 5-11 Finned tube condenser of a room air conditioner
The condenser is operated at higher pressures and
temperatures than the evaporator and is often
located outside. Most air conditioner is air cooled
and rejects heat to the air. Depending on the
air discharging direction, condensers have two
different types: side-air-discharge condenser
and top-air-discharge condensers.
Air
Air
suction
suction
Figure 5-13 Equipment with air discharged out of the
top of the cabinet
Side-air-discharge condenser
Most room air conditioners use side-air-discharge
condenser. This kind of air conditioner discharges
the air out the side, as shown in Figure 5-12.
<<
32
SECTION 6
<<
33
Section 6
FAN, MOTOR AND INVERTER
6.1 Fan
A fan can be described as a device that produces
airflow or movement. Several different types of
blows produce this movement, but all can be
described as non-positive-displacement air moves.
applied. So the squirrel cage fan is commonly
used in the indoor unit of a split-type air
conditioner.
In air conditioners, fans are known as two types:
propeller fan and the forward curve centrifugal
fan, also called the squirrel cage fan, or blower
wheel.
Propeller fan is used in condenser fan
applications, as shown in Figure 6-1. It will
handle large volume of air at low pressure
differential. The propeller can be plastic, cast iron,
aluminium, or stamped steel. The propeller fan
makes more noise than the centrifugal fan so it is
used in condenser where noise is not a factor.
Figure 6-2 A centrifugal fan
useless fan surface cut
(efficiency 50% up)
example
(oil flow)
Large fan surface
Revolutions per minute (RPM) reduced, no
change in air flow
Figure 6-1 A propeller-type fan
Squirrel cage fan or centrifugal fan, is shown in
Figure 6-2. This fan has a forward curved blade
and a cut-off to shear the air spinning around
the fan wheel. This air is thrown by centrifugal
action to the outer perimeter of the fan wheel.
The centrifugal fan is very quiet when properly
Long
edge
Figure 6-3 Improvement of fan shape
<<
34
Section 6
Optimization of fan shape in order to enhance
the fan efficiency has been done. Cut useless fan
surface and enlarge the fan edge, as shown in
Figure 6-3, can help to increase the fan efficiency.
6.2 Motor
Motors are used as the prime movers of air (i.e.
fan) and refrigerant (i.e. compressor).
Motors have a stator with windings, a rotor,
bearings, end bells, housing, and some means to
hold these parts in the proper position, as shown
in Figure 6-4 and Figure 6-5.
The stator is a winding that, when energized,
will generate a magnetic field because there
will be current flowing through it. The rotor
is the rotating portion of the motor and is
made of iron or copper bars bound on the ends
with aluminium. The rotor is not wired to the
power source like the stator is. The motor shaft
is connected to the rotor; therefore, when the
rotor turns, so does the motor shaft. The motor’s
bearings allow for low-friction rotation of the
rotor. Bearing help reduce the friction and
the heat generated by the motor’s moving and
rubbing parts and surfaces. The motor housing,
end bells, and base hold the motor components
in place and provide a means for securely
mounting the motor itself.
Figure 6-5 The windings of electric motor
Electricity and magnetism are used to create the
rotation of the electric motor to drive the fans
and compressors. Magnets are known to have two
different electrical poles, north and south. Unlike
poles of a magnet attract each other, and like
poles repel each other. If a stationary horseshoe
magnet were placed with its two poles (north
and south) at either end of a free-turning magnet
as in Figure 6-6, one pole of the horseshoe
magnet would line up with the opposite pole of
the horseshoe magnet. If the horseshoe magnet
were an electromagnet and the wires on the
battery were reverses, the poles of this magnet
would reverse, and the poles on the free magnet
would be repelled, causing it to rotate until the
unlike poles again were lined up. This is the basic
principle of electric motor operation. In this
example, the horseshoe magnet acts as the stator,
and the free-rotation magnet acts as the rotor.
In a two-pole split-phase motor the stator has
two poles with insulated wire windings. When an
electrical current is applied, these poles become
an electromagnet with the polarity changing
constantly.
Figure 6-4 A electric motor
The rotor may be constructed of bars, as shown
in Figure 6-7. This type is called a squirrel cage
rotor. The rotor is positioned between the run
windings. When an alternating current (AC)
is applied to these windings, a magnetic field is
<<
35
Section 6
produced in the windings and magnetic field
is also induced in the rotor. The bars in the
rotor actually form a coil. This is similar to the
field induced in a transformer secondary by the
magnetic field in the transformer primary. The
field induced in the rotor has a polarity opposite
to that in the run windings. The opposite poles
of the run winding are wound in different
directions. If one pole is wound clockwise,
the opposite pole would be wound counterclockwise. This would set up opposite polarities
for the attraction and repulsion forces that cause
rotation.
The attracting and repelling action between the
poles of the run windings and the rotor sets up
a rotating magnetic field and causes the rotor to
turns. The motor starting method determines the
direction of motor rotation. The motor will run
equally well in either direction.
Figure 6-6 Poles (north and south) on a rotation magnet
Copper bars
Copper
end ring
Shaft
Welds at all joints
Figure 6-7 A simple sketch of a squirrel cage rotor
Single-speed motors
Single-speed motors have types of single-phase,
split-phase and three-phase.
Single-phase motors usually use the power supply
of either 115V or 208V to 230V. Some single-
phase motors are dual voltage. The motor has two
run windings and one start wingding. The two
run windings have the same resistance, and the
start winding has a high resistance. The motor
will operate with the two run windings in parallel
in the low-voltage mode. When it is required
to run in the high-voltage mode, the technician
changes the numbered motor leads according to
the manufacturer’s instructions.
Split-phase motors have two distinctly different
windings. They have a medium amount of
starting torque and a good operating efficiency.
They split-phase motor is normally used for
operation fans in the fractional horsepower range.
The speed of motor is determined by the number
of motor poles and by the method of wiring the
motor poles. The technician can change the speed
of a two-speed motor at the motor terminal box.
Three-phase motors have some characteristics that
make them popular for many applications from
about 1hp into the thousands of horsepower.
These motors are very efficient and require
no start assist for high-torque applications.
Three-phase motors have no starting windings
or capacitors. They can be thought of as having
three single-phase power supplies. Each of the
phases can have either two or four poles. Each
phase changes the direction of current flow at
different times but always in the same order.
A three phase motor has high starting torque
because of the three phases of current that operate
the motor. Three-phase motors are used mainly
on commercial equipment.
Two-speed motors
Two-speed compressor motors are used by some
manufactures to control the capacity required
from small compressors. For example, a residence
or small office building may have a high airconditioning load at the peak of the season and
low load as a minimum. A two-speed compressor
<<
36
Section 6
may be desirable to accomplish the capacity
control for this application.
Two-speed operation is obtained by wiring the
compressor motor to operate as a two-pole motor
or a four-pole motor. The automatic changeover
is accomplished with the space temperature
thermostat and the proper compressor contactor
for the proper speed. For all practical purposes,
this can be considered two motors in one
compressor housing. The compressor uses
either motor, based on the capacity needs. This
compressor has more than three motor terminals
to operate the two motors in the compressor.
Variable-speed motors
Variable-speed motors are developed in order to
meet the desire to control motors to provide a
greater efficiency for the fans and compressors.
Most motors do not need to operate at full speed
and load except during the peak temperature
of the season and could easily satisfy the airconditioning load at other times by operating
at a slower speed. When the motor speed is
reduced, the power to operate the motor reduces
proportionately. When motors are initially
started, they draw locked-rotor amperage,
which can be five to seven times greater than the
number of times the motor starts, and so the rate
of power consumption is reduced. For example,
if a home or building needs only 50% of the
capacity of the air-conditioning unit to satisfy
the space temperature, it would be advantageous
to reduce the capacity of the unit rather than
stop and restart the unit. When the power
consumption can be reduce in this manner, the
unit becomes more efficient. In addition, having
(for example) a compressor motor operate at a
lower speed for longer period of time will result
in more even cooling of an occupied space.
The frequency (cycles per second) of the power
supply and this number of poles determine the
speed of a conventional motor. The variablespeed motors can operate at different speeds with
the use of electronic circuits. Several methods are
used to vary the frequency of the power supply
depending on the type of motor. The fan motors
may be controlled through any number of speed
combinations base on the needs of the system.
Two types of motors that may be found in
equipment today are the squirrel cage induction
motor and the electronically commutated direct
current (DC) motor. Instead of brushes rubbing
on an armature, the motor is electronically
commutated. This motor would be applied to
a fin application as it is a fractional horsepower
motor.
Variable-speed AC motor operation can now
be accomplished with electronic components.
The electronic components can switch power on
and off in microseconds without creating an arc;
therefore, open-type contacts are not necessary
for the switching purposes.
6.3 Inverter
Inverters in air conditioners are mainly installed
for compressor, and also used for fan.
The inverter for compressor is driven by an AC
power which is obtained by converting AC power
from mains into DC power with the rectifier,
and inverting the DC power into three phase
AC power with the inverter based on a waveform
signal form the waveform output circuit so
as to have a desired frequency and voltage, as
shown in Figure 6-8. The inverter compressor
can reduce power consumption, power surges
(from starting AC motors), and deliver constant
pressure. Currently, these advantages are achieved
with the technology at heavy expense associated
with the drive and the sensitivity of these drives,
particularly, to heat and moisture.
<<
37
Section 6
Compressor
Motor
Power
Supply
Inverter
Control
Unit
Winding
Voltage
DC Motor
Figure 6-8 Inverter controller for compressor
Inverters have also been used for fan motor.
The application of DC inverter fan motor may
increase the efficiency of the fan motor from
about 35% to about 75%.
Inverters produce the correct frequency to the
motor for the desired speed. Conventional motor
speeds are controlled by the number of poles,
and the frequency is a constant value. Inverters
can actually control motor speeds down to about
10% of their rate speed and up to about 120%
of their rated speed by adjusting the hertz to a
desired value.
There are different types of inverters. A common
one is a six-step inverter, and there are two
variations. One controls voltage and the other
controls current. The six-step inverter has six
switching components, two for each phase
of a three-phase motor. This inverter receives
regulated voltage from the converter, such as the
phase-controlled inverter, and the frequency is
regulated in the inverter.
The voltage-controlled six-step converter has a
large capacitor source at the output of the DC
bus that maintains the output voltage, as shown
in Figure 6-9. When the control system sends a
signal to the base connection on the transistor,
the transistor turns on and allows current to flow
through the device. When the signal is dropped,
the transistor turns off. Notice that the controllers
are transistors that can be switched on and off.
The current-controlled six-step inverter also has
the voltage controlled at the input. It uses a large
coil, often called a choke, in the DC output bus,
as shown in Figure 6-10. This helps stabilize the
current flow in the system.
The pulse-width modulator inverter receives a
fixed DC voltage from the converter, and then
it pulses the voltage to the motor. At low speeds,
the pulses are short; at high speeds, the pulses
are longer. The pulse-width modulator pulses
are sine coded to where they are narrower at the
part of the cycle close to the ends. This makes the
pulsating signal look more like a sine wave to the
motor. Figure 6-11 shows the signal the motor
receives. This motors speed can be controlled very
closely.
Motor
Variable
DC
Coltage
Capacitor
Figure 6-9 Signal to the base connection on the transistor
Choke Coil
Motor
DC Voltage
controlled
Figure 6-10 The chock coil stabilizes current flow
Figure 6-11 Modulation of sine-coded and pulse-width
<<
38
SECTION 7
<<
39
Section 7
REFRIGERANT
A refrigerant is a working substance that
circulates constantly in the refrigeration system.
It achieves refrigeration through its own changes
in state. In the evaporator, the refrigerant absorbs
heat from the cooling medium (such as water
or air) and changes to gaseous state. In the
condenser, it condenses by transferring heat to
the surrounding air or water.
If compressor can be regard as the heart of the
refrigeration system, then the refrigerant is the
blood of the refrigeration system. The importance
of the refrigerant is evidently clear.
Once a refrigerant is selected for use, the other
parts of the refrigeration system should be
made compatible. All the designing would be
to allow the refrigerant to perform even better.
For example, the compressor would usually be
designed and manufactured solely for a particular
kind of refrigerant; the refrigeration system would
also be redesigned and re-optimized for the
refrigerant.
7.1 Types of Refrigerant
Most refrigerants are made from two molecules,
methane and ethane. These two molecules simply
contain hydrogen and carbon and are referred to
as pure hydrocarbons (HCs). Pure hydrocarbons
were at one time considered good refrigerants,
but were not used after the 1930s in any large
scale because of their flammability.
Any time some of the hydrogen atoms are
removed from either the methane or ethane
molecule and replaced with either chlorine or
fluorine, the new molecule is said to be either
chlorinated, fluorinated, or both. Abbreviations
are used to describe refrigerants chemically and
to make it simple for technicians to differentiate
between them. The following are some
common abbreviations: Chlorofluorocarbons
(CFCs), Hydrochlorofluorocarbons (HCFCs),
Hydrofluorocarbon (HFC), and Hydrocarbons
(HCs).
CFC refrigerants
The CFCs contain chlorine, fluorine, and carbon
and are considered the most damaging because
their molecules cannot be destroyed as they
reach the stratosphere. CFC molecules have a
very long life when exposed to the atmosphere
because of their stable chemical structure. This
allows them to be blown up to the stratosphere
by atmospheric winds where they react with
ozone molecules and cause destruction. CFCs
also contribute to global warming. As of July 1,
1992, it became illegal to intentionally vent CFC
refrigerants into the atmosphere.
HCFC refrigerants
The HCFC refrigerants contain hydrogen,
chlorine, fluorine, and carbon. They have a
small amount of chlorine in them, but also have
hydrogen in the compound that makes them less
stable in the atmosphere. These refrigerants have
much less potential for ozone depletion because
they tend to break down in the atmosphere,
releasing the chlorine before it reaches and reacts
with the ozone in the stratosphere. R22, a widely
used refrigerant in air conditioners, is of HCFC.
However, the HCFC group is scheduled for total
phase out by the year 2030. R22 is an exception,
with an earlier phase out date for new equipment
in 2010 and total production phase out in 2020
under the Montreal Protocol. As of July 1, 1992,
it became illegal to intentionally vent HCFC
refrigerants to the atmosphere. HCFCs do have
some ozone-depletion potential, but it is much
lower than most CFCs.
<<
40
Section 7
HFC refrigerants
The third group of refrigerants is the HFC group.
HFC molecules contain no chlorine atoms and
will not deplete the earth’s protective ozone layer.
HFCs contain hydrogen, fluorine, and carbon
atoms. HFCs do have small global-warming
potentials. HFCs are the long-term replacements
for many CFC and HCFC refrigerants. It
became unlawful to intentionally vent HFC
refrigerants to the atmosphere on November
15, 1995. R134a, a pure HFC refrigerant, can
be used in air conditioners, but is not widely
considered as a suitable R22 substitute. R410A,
a mixture of HFC-125 and HFC-32, is currently
the most important HFC group refrigerant for air
conditioners.
As people become more knowledgeable
about refrigerants and more concerned about
environmental protection, they first added an
important environmental performance evaluation
standard- ODP (Ozone Depletion Potential).
High ODP value means the refrigerant have
more harm to ozone molecule.
HC refrigerants
The fourth group of refrigerants is the
hydrocarbon group. These refrigerants have no
fluorine or chlorine in their molecule; thus,
they have no ozone depletion potential. They
contain nothing but hydrogen and carbon. They
do, however, contribute to global warming.
Hydrocarbons are used as stand-alone refrigerants
in Europe, but are not used as stand-alone
refrigerants in the United States because they are
flammable. Small percentages of hydrocarbons
are used in many refrigerant blends in the United
States but are not flammable when mixed in such
small percentages. Some popular hydrocarbons
include propane, butane, methane, and ethane.
Table 7-1 shows the refrigerant safety
classification according to the stipulations of
ASHRAE Standard 34, where, “A” and “B”
represent low toxicity and high/strong toxicity,
respectively; “1”,”2” and “3” represent noninflammability, weak inflammability and high/
strong inflammability, respectively. People
sometimes simplify things by saying that “A”
represents no toxicity.
7.2 Properties and Characteristics
of Refrigerants
Regarding the evaluation criteria for a good
refrigerant, there have been a lot of related
documents and information on them. For
example, safety aspect (non-toxic, noninflammable and non-explosive); cost aspect
(cheap and easily obtainable); high efficiency;
good environmental performance.
Another important environmental performance
evaluation standard is GWP (Global Warming
Potential). The higher the GWP value is, the
more harmful the refrigerant is.
Besides ODP and GWP, the Flammability
is another important evaluation standard of
refrigerants.
Table 7-1 Refrigerant safety classification*
Lower
Toxicity
Higher
Toxicity
Higher
Flammability
A3
B3
Lower
Flammability
A2
B2
No
Flammability
A1
B1
*Note:
Class A refers to refrigerants for which toxicity
has not been identified at concentrations less
than or equal to 400 ppm by volume, based on
date used to determine Threshold Limit Value-
<<
41
Section 7
Time Weight Average (TLV-TWA) or consistent
indices.
Class B refers to refrigerants for which there is
evidence of toxicity at concentrations below 400
ppm by volume. based on date used to determine
Threshold Limit Value-Time Weight Average
(TLV-TWA) or consistent indices.
Class 1 refers to refrigerants that do not show
flame propagation when test in air at 0.101MPa
and 21ºC.
Class 2 refers to refrigerants having a lower
flammability limit (LFL) of more than 0.1 kg/
m3 at 0.101 MPa and 21ºC and the heat of
combustion (HOC) less than 18936 KJ/kg.
Class 3 refrigerants are highly flammable. They
have a lower flammability limit (LFL) of less than
0.1 kg/m3 at 0.101 MPa and 21ºC or the heat
of combustion (HOC) greater than or equal to
18936 KJ/kg.
7.2.1 Properties and characteristics of
commonly used refrigerants
Tables 7-2 and 7-3 show some information as
well as concise performance comparison of several
commonly used refrigerants.
7.2.2 Properties and characteristics of
several kinds of refrigerant candidates
Currently there are several alternatives of R22,
such as R410A, R290, R32, R161 and R1270.
Because R410 has been well known, this section
will introduce the properties and characteristics of
other four refrigerants. All these four refrigerants
are inflammable, although they have different the
extent of inflammability.
The ODP of R290 is 0 and its GWP is close
to 0. Therefore, R290 has good environmental
performance.
However, R290 is a Class A3 refrigerant. It has
strong inflammability. Technical problems still
exist regarding how it can be used safely.
In the European market, there are already a small
number of air conditioners using R290. They are
mostly closed air conditioning systems with small
capacities such as portable air conditioners.
Advantages of R290: Both ODP and GWP are
0; Ultimate substitution can be achieved in one
step;
Weak points of R290: Difficult to overcome
problems resulting from inflammability.
R32
R32 is considered as a Class A2 refrigerant and
it has weak inflammability. The widely used
refrigerant R410A is developed by mixing R32
with R125 in 50:50 proportion in order to
overcome the problem of R32’s inflammability.
R125 is a fire extinguishing agent, resulting in
R410A being non-inflammable.
Based on the latest trend of standard revisions
in the United States, the inflammability of R32
may be labeled as A2L. This means it has weak
inflammability within A2 or it is closer to A1
(non-inflammability).
A brief comparison of R410A, R290 and R32 is
listed as follows:
1.ODP is 0 for all;
2.R32 has intermediate inflammability;
3.R32’s GWP is 650 and this is also in the
middle of 0 (R290) and 1730 (R410A).
R290
R290 (i.e. propane) is a natural refrigerant.
<<
42
CHF2CF3
CF3CH2F
CHF2CH2CF3
CH3CH2CH3
chlorodifuloromethane
difluoromethane
2,2-dichloro-1,1,1-trifluoroethane
Pentafluoroethane
1,1,1,2-tetrafluoroethane
1,1,2,2,3-Pentafluoropropane
Propane
R-125/143a/134A(44/52/4)
R-32/125/134a(23/25/52)
R-32/125(50/50)
R-12/152a(73.8/26.2)
R-125/143a(50/20)
Butane
Ammonia
Water
Carbon dioxide
22
32
123
125
134a
245fa
290
404a
407C
410A
500
507a
600
717
718
744
CO2
H2O
NH3
CH3CH2CH2CH3
CHCl2CF3
CH2F2
CHClF2
CCl2F2
dichlorodifluoromethane
12
CCl3F
Chemical Formula
trichlorofluoromethane
Chemical Name
11
Refrigerant
Number
44
18
17
58.1
44
134.05
102
120
153
52
86.5
120.9
137.4
Molecular
Mass
A1
A1
B2
A3
A1
A1
A1
A1
A1
A3
B1
A1
A1
B1
A2
A1
A1
A1
Safety Group
N/A
N/A
N/A
<1
<1
8.8
14.6
32.6
1.4
5.6
12.1
102
80
Atmospheric
Lifetime (Yrs)
Table 7-2 General information of several commonly used refrigerants
0
0
0
0
0.74
0
0
0
0
0
0
0.2
0
0.055
1
1
ODP
1
<1
0
~0
6010
1730
1530
3260
~0
820
1300
2800
90
650
1500
8100
3800
GWP
Section 7
<<
43
163.068
209.702
126.187
124.663
24
-30
-41
-52
28
11
12
22
32
123
149.352
-1
-33
100
-78
600
717
718
744
-34
-52
410A
-47
168.554
-44
404a
407C
500
144.170
-46
290
507a
220.370
15
-42
245fa
209.398
412.090
402.031
200.863
139.294
158.191
132.954
146.914
-48
-26
125
134a
136.550
135.026
Boiling Point
(ºC)
Refrigerant
Number
Velocity of
Sound
(m/s at 4ºC)
31
374
132
152
71
106
70
86
73
97
154
101
66
184
78
96
112
198
Temp
(ºC)
7.38
22.06
11.33
3.80
3.72
4.43
4.79
4.64
3.78
4.25
3.63
4.06
3.63
3.66
5.78
4.99
4.14
4.41
Press
(MPa)
Critical Point
42.9
37
38.8
Bubble
(ºC)
42.9
37
38.8
Dew
(ºC)
0.3
10.8
1.0
Glide
(ºC)
0.092
1.545
0.162
0.194
0.166
0.230
0.157
0.198
0.167
-.120
0.536
0.256
0.189
0.534
0.149
0.208
0.237
0.546
Viscosity
(MPa/s at
4ºC)
2.705
4.419
4.645
2.340
1.395
1.080
1.529
1.425
1.402
2.544
1.307
0.919
1.275
0.996
1.300
1.300
0.943
0.862
Specific Heat
(KJ/kg•K at
4ºC)
Table 7-3 Operational information of several commonly used refrigerant
0.105
0.570
0.546
0.115
0.075
0.083
0.113
0.101
0.076
0.104
0.088
0.090
0.069
0.082
0.151
0.151
0.074
0.095
Thermal Cond
(W/m•K at 4ºC)
Section 7
<<
44
Section 7
Compared to R290, R32 has weak inflammability.
Its superiority lies in that:
• With the same charge, the safety risk of R32
is lower;
• With similar safety controls, a larger charge
can be allowed for R32. This means that
refrigeration and air conditioning equipment
of larger capacities can be allowed.
R161
It is China that proposes R161 as a refrigerant at
the first time. R161 also has inflammability but
its inflammability is weak compared to R290.
Its inflammability is however significantly higher
than that of R32 and it belongs to Class 3. R161
has already passed the acute/short-term toxicity
tests to prove that it is non-toxic.
As R32 has a GWP of 650, it is still not friendly
enough to the environment. In addition, the
compressor exhaust temperature of the R32
system is higher than those using R290 or
R410A, resulting in a major challenge for the
stability of the entire system.
Advantages of R161: The inflammability of
R161 is weaker than that of R290;
Advantages of R32: The ODP of R32 is 0;
GWP is 650 (lower than that of R410A); The
inflammability is weaker than R290;
R1270
The main reason to recommend R1270 (i.e.
propylene) is that R1270 is highly compatible
with R22 systems.
Weak points of R32: Very possible to be replaced
again in the future; Higher compressor exhaust
temperature.
Weak points of R161: R161 had never been
considered as a refrigerant before. There are also
few researches on its properties.
Summarization of properties of several R22
substitutes
The important properties of several R22 substitutes
are summarized in Table 7-4 to Table 7-6.
Table 7-4 Thermal physics and environmental characteristics for possible R22 Substitutes
GWP
Relative
Charge
Relative CO2
Emission
Equivalent
During Leak
86.47
1810
1.0
1810
--
52.02
675
0.6
405
-77.6
-42.1
44.10
20
0.51
10.2
-99.4
R161
37.6
48.06
12
0.56
6.7
-99.6
R410A
-51.4
72.58
2100
0.84
1764
-2.5
R407C
-43.6
86.20
1800
1.0
1800
0
R134a
-26.1
102.03
1430
1.18
1687
-0.1
R1234yf
-29.4
114.01
4
1.32
5.3
-99.7
CO2
-78.4
44.01
1
0.51
0.51
-100
Boiling
Point
(ºC)
Molar
Mass
R22
-40.8
R32
-51.7
R290
Refrigerant
CO2 Emission
Reduction
Proportion (%)
<<
45
Section 7
Table 7-5 Thermal performance of various kinds of R22 substitutes
pe/MPa
pc/MPa
t2
Δt
COP
q0
qv
R22
Refrigerant
0.627
2.179
100.7
0
3.43
151.82
3779.61
R32
1.029
3.523
122.23
0
3.15
231.49
5876.06
R290
0.59
1.900
77.65
0
3.34
256.15
3095.94
R161
0.554
1.937
93.92
0
3.49
279.78
3386.42
R410A
0.104
3.485
97.55
0.1
2.99
142.40
5212.58
R407C
0.678
2.498
89.14
4.7
3.12
137.68
3750.77
R134a
0.378
1.481
78.41
0
3.44
138.84
2401.29
R1234yf
0.399
1.453
74.43
0
3.30
108.73
2262.59
Table 7-6 Inflammable limits of several kinds of inflammable R22 substitutes
Refrigerant
R32
R290
R161
R1234yf
ISO Safety Class
A2
A3
A3
A2
LFL (%)
14.4
2.1
3.8
6.2
LFL (kg/m3)
0.306
0.038
0.076
0.293
UFL (%)
29.3
10.0
-
12.3
HOC (KJ/kg)
9400
50400
26600
10300
7.3 Technological Developments in
Refrigerant Use
R22 has been used for many years and is
still widely used because of its good thermal
properties. But R22 is an Ozone depletion
substance, and should be phased out.
R410A does not deplete ozone, and is once
thought as a successful R22 substitute. In order
to replace R22 by R410A, the air conditioner
should be redesigned, e.g., decreasing the tube
diameter in order to bear the high pressure of
R410A.
As both R410A and R22 have high GWP, none
of them can be used for long time, and new
refrigerants to replace them are under searching.
R1234yf is one alternative refrigerant for air
conditioner because it is a low GWP substance.
But application of R1234yf may obviously
decrease the cooling capacity and energy
efficiency of the air conditioner. In order to
overcome the problems, R1234yf is used in a
mixture with R32. Application of R1234yf-R32
mixture may result in better performance of the
air conditioner than that using pure R1234yf,
but the performance is still lower than that using
R410A. Besides, the adding of R32 may result in
higher GWP than pure R1234yf.
R290 is a 0 ODP and 0 GWP substances, and
it is really a good refrigerant from the viewpoint
of environment protection. However it is very
inflammable. In order to decrease the risk
of firing caused by application of R290, the
refrigerant charge should be strictly controlled.
<<
46
Section 7
One practical way for this purpose is to use
smaller diameter tubes, such as 5 mm tubes,
in heat exchangers of air conditioners. The
limitation of the refrigerant charge of R290
in a single air conditioner result in that the
application of R290 is limited in the range of
small room air conditioners.
R32 is also inflammable but its inflammability
is weaker than R290. That is why R32 seems
to have the possibility to be applied in the air
conditioners which are too large to be charged
by R290. But the application of R32 may
result in too high refrigerant outlet temperature
of compressor. One method to overcome the
problem is to let the refrigerant status at the
evaporator outlet be at two-phase, so that the
compressor can be cooled by the refrigerant
liquid unevaporated in the evaporator.
In order to decrease the effect of refrigerant
on the environment as well as other problems
related to refrigerant, technologies to reduce
the refrigerant charge is quite welcome. One
approach to reduce the refrigerant charge is to
use smaller diameter tubes in finned tube heat
exchangers. Experimental results show that
the finned tube heat exchanger using 5 mm
diameter tubes can reduce refrigerant charge
about 20%~30%, comparing with that of 7mm
tube heat exchanger. Another approach is to use
all-aluminum micro-channel heat exchangers.
According to the claim of all-aluminum microchannel production enterprises, the reduction
results from the application of micro-channel
heat exchanger may decrease the refrigerant
charge by 40%. However, there are still series of
unresolved issues such as difficulty in removing
condensate or frosting. So all-aluminum
micro-channel heat exchangers can currently be
used only on outdoor units of air conditioners
limited for cooling, and cannot be used as heat
exchangers in heat pumps.
<<
47
SECTION 8
<<
48
Section 8
THE TECHNOLOGY FOR AIR CONDITIONER IN ASEAN
REGION, AND LIFE-CYCLE ASSESSMENT OF AIR
CONDITIONER
8.1 The Most Commonly Used
Technology for Room and Small
Commercial Air Conditioners in the
Asean Region
Technology level of air conditioner
To illustrate and evaluate the technology level
of air conditioner, the energy efficiency of air
conditioner is employed as criterion. In this
section, EER is used as evaluation criteria to
represent the efficiency of air conditioner. Basing
on the questionnaire results, the EER standards
of different ASEAN countries are respectively
shown as follows.
In Philippines, the present lower limit of EER
is 2.3. The energy efficiency label of Philippines
is shown as Figure 8-1. In Thailand, the present
lower limit of EER is 2.82 for air conditioner
with refrigeration capacity below 8000 W,
and the lower limit of EER is 2.53 for the air
conditioner with refrigeration capacity from 8001
W to 12000 W. Starting from September, 2011,
Singapore will ban the sale of low efficiency air
conditioner in its market. The energy efficiency
label of Singapore is shown as Figure 8-2 (The
low efficiency air conditioner refers to those
whose label has none hook, or some only one
or two hook in its label). In 2010, Vietnam
established the lower limit of EER as 2.5 for
air conditioner. Although Indonesia does
not have a clear efficiency standard until now,
the government of Indonesia is considering
establishing an energy standard. Malaysia does
not have a clear efficiency standard until now.
In ASEAN region, most countries have
established or are considering establishing energy
Figure 8-1 The energy efficiency label in Philippines
Figure 8-2 The energy efficiency label in Singapore
standard. Depending on the EER standard, the
technology level of air conditioner in ASEAN
region is lower than some Asia countries, such as
Japan, Korea and China.
<<
49
Section 8
The most commonly used technology
Refrigerant
In ASEAN countries, although some air
conditioners manufacturers are trying to
promote R290 as alterative refrigerant, most air
conditioner manufacturers are still using R22
and R410A, whose GWP are high, as the most
commonly used refrigerant.
Type of air conditioner
In ASEAN region, the most commonly used air
conditioners contain two types: the split type and
the window type. And for ASEAN region’s hot
climate, most of ASEAN countries adopt singlecool air conditioner.
In Indonesia, the split type of air conditioner
has about 98% market share, and most of these
are single-cool air conditioner. In Philippines,
the window type of air conditioner has about
80% market share, and the split type of air
conditioner only has 20% market share. Most
of air conditioners in Philippines are of single
function for air cooling. In Vietnam, most air
conditioners are split type, and 94% of split type
are single-cool air conditioners because of its hot
climate. In Thailand domestic market, the most
commonly used air conditioners are of single-cool
split type. In Malaysia, the most commonly type
of air conditioner is single-cool split.
Type of heat exchanger
Because the energy standard is low or not
established in most ASEAN countries, the
commonly used finned tube heat exchangers
are made of 7 mm or 9.52 mm diameter tubes,
which are convenient to produce but require
more material cost than smaller diameter tubes.
However, with the increase of copper price,
some air conditioner manufacturers are trying to
develop finned tube heat exchangers with 5 mm
diameter tubes to replace 7 mm diameter tubes.
Depending on the manufacturing level in
ASEAN region, the thickness of commonly used
fin is 0.105 mm or larger. The fin with such a
thickness requires more material cost and has a
higher air-side pressure drop, comparing with fin
with 0.095 mm thickness which is commonly
used in Japan, China and Korea.
8.2 The Alternative Technology
of ASEAN Countries Under the
Montreal Protocol
To decrease the emission of greenhouse gas and
increase the energy efficiency of air conditioner,
ASEAN manufactures improve their technology
in two major ways:
• Using environment friendly refrigerant;
• Decreasing refrigerant charge by using new
technologies, such as application of small
diameter tubes.
Using environment friendly refrigerant
The “Montreal Protocol” signed in
1987 stipulates the restricting of using
chlorofluorocarbons and other ozone-depleting
chemical substances. There was research to show
that, pertaining to the mitigation and control
of global warming, the results of the “Montreal
Protocol” are five to six times higher compared
to the “Kyoto Protocol”. Because of this, the
“Montreal Protocol” was praised by Kofi Annan,
Secretary-General of United Nations, to be the
“single most successful international agreement
to date”. Currently, 191 developed countries
and developing countries have signed the said
agreement, and they are gradually phasing out
95% of the ozone-depleting chemical substances.
In recent years, a new change is that some
ASEAN countries are currently trying to
more closely link refrigerant substitution with
greenhouse gas emission control.
<<
50
Section 8
In Malaysia, the government created a National
Steering Committee (NSC) to oversee the
implementation of the national action plan,
which paved the way for Malaysia’s ratification
in 1989. The NSC is comprised of a Technical
Committee and Industrial Working Groups
(IWGs) on solvents, foam, aerosol, mobile air
conditioning, refrigeration and fire protection.
Other IWGs were established later to keep pace
with the Protocol’s amendments. In 1996, the
Department of the Environment created the
Ozone Protection Unit (OPU) to serve as the
focal point and monitor Malaysia’s phase-out
activities. Malaysia’s local air conditioner uses R22
as well as R410A as refrigerant for commercial
and residential units. There is an interest now to
look into the use of small diameter 5mm tubes
for the heat exchanger units.
In Vietnam, the government made some strict
policies to prohibit using refrigerant with highODP:
• CFC (R11/R12, etc.) is prohibited from Jan.
1, 2010;
• HCFC (R22/R123, etc.) is prohibited from
Jan. 1, 2040;
• Reducing the CFCs consumption in the
refrigeration and air-conditioning service
sector;
• Complying with the phase-out schedule for
CFCs under the Montreal Protocol.
Decreasing refrigerant charge by application of
small diameter tubes
Owing to the concerns of inflammability, ODP
and GWP, more attention will increasingly be
given to technologies that can reduce refrigerant
charge. One excellent way to reduce refrigerant
charge is to use small diameter tube heat
exchangers to replace current heat exchangers.
In room air conditioners and small commercial
air conditioners, the diameter of most tubes in
heat exchanger is 7 mm or larger. To reduce the
cost and refrigerant charge, some air conditioner
manufactures are using 5 mm diameter tubes to
replace 7 mm or larger diameter tubes in heat
exchangers.
To achieve the goal of application tube with
5 mm diameter, the fin should be optimized
accordingly.
In ASEAN countries, a very few manufacturers
are researching on heat exchangers with 5 mm
diameter tubes. The 5 mm finned tube heat
exchanger is shown in Figure 8-3.
In Thailand, the most likely alternative
technologies of refrigerant are shown as follow:
• Transition from CFC to HCFC and HFC
alternatives;
• R-12 (CFC) to be R-401A(HCFC) /
R-401B(HCFC);
• R-502(CFC) to be R-402A(HCFC) /
R-402B(HCFC);
• R-12 (CFC) to be R-134a(HFC).
Figure 8-3 Finned-tube heat exchanger with 5 mm diameter tube
<<
51
Section 8
8.3 The Policies and Market
Incentives Bbased on Low- or ZeroGWP Refrigerant in ASEAN Region
8.4 Life-cycle Assessment of Energy
and Green House Gas for Air
Conditioner
According to the requirements of United Nations
Framework Convention on Climate Change, the
production and consumption of refrigerants with
high-GWP should be reduced and eventually
phase-out. To fulfill this responsibility, ASEAN
countries’ air conditioner manufacturers have
the responsibility to use refrigerants with lowor zero-GWP as replacement for refrigerants
with high-GWP. However, for the limitation
of technology and the increasing of cost, most
ASEAN’s air conditioner manufacturers have
not commonly used refrigerant with low- or
zero-GWP.
This section is to evaluate the energy and green
house gas for air conditioners in ASEAN region,
considering the influence of refrigerant type, air
conditioner type and energy efficiency.
Malaysia
In Malaysia, the local air conditioner
manufacturer tries to promote R290 (Propane),
whose GWP is 20, as a drop-in replacement into
R22 system during installation. But considering
the increasing of cost coming with new
refrigerant, R290 does not adopted by most of
manufacturers.
Vietnam
In Vietnam, some air conditioner manufacturers
try to transition from CFCs to the HCFC/HFC/
natural gas alternatives. But application of low
GDP refrigerants in air conditioners is still not
paid attention to.
Thailand
In Thailand, the most commonly used refrigerant
was R22 and R410A. Some joint ventures for
air conditioner producing are sharing research
results of applying low-GWP refrigerants (e.g.
HFO1234yf) from their father companies.
However, these companies have no clear plan
to apply these low-GWP refrigerants in their
products.
8.4.1 Conditions of life-cycle assessment of air conditioner in ASEAN
Air conditioner type, EER and refrigerant
The most commonly used air conditioners
contain two types: window type and split type.
The range of EER of commonly sold air
conditioners in markets is from 3.2 to 3.6. This
section will take air conditioners respectively
with EER of 3.2, 3.4 and 3.6 as examples to
accomplish the life-cycle assessment.
Considering the actual air conditioners sold in
the markets, this section will take air conditioners
respectively with three refrigerants of R22,
R410A and R290 in analyzing.
Service life and energy-consuming hours
In ASEAN region, most of air conditioners may
be used for 10 years, and some can be used for 15
years or longer.
Related to the ASEAN’s climate type, air
conditioners are used for averagely 8 hours per
day in an entire year. During the operation of the
air conditioner, the main energy consumption
components (i.e. compressor and fan) might
be stopped when the required temperature is
achieved. It could be assumed that half of the
operation duration of air conditioner is of nearly
no energy consuming. Thus, the annual energy
consuming hours of the air conditioner is:
365 x8x50%=1460 hours
<<
52
Section 8
Then, for air conditioner with a life of 10 years,
the total energy-consuming hours are:
1460x10=14600 hours
For air conditioner with a life of 15 years, the
total energy-consuming hours are:
1460x15=21900 hours
Green house effect resulted from refrigerant
emission
For a window type air conditioner, it could be
assumed that all the refrigerant inside is not be
collected when the air conditioner is disused. So
the green house effect caused by the refrigerant
emission is determined by the entire refrigerant
charge in the air conditioners.
For a split type air conditioner, it could still be
assumed that all the refrigerant inside is not be
collected when the air conditioner is disused.
However, different from a window type air
conditioner, there is unavoidable refrigerant
leakage in a split type air conditioner because
not all of pipelines are sealed. Assuming the
total recharged refrigerant in the whole life is
equal to the initial refrigerant charge in a split
air conditioner, and then the green house effect
caused by the refrigerant emission in the split
type air conditioner is determined by two times
of the initial refrigerant charge.
8.4.2 Calculation method for life-cycle assessment
The evaluation of life-cycle assessment for air conditioner mainly output two values: the energy
consumption and the emission of Green House Gas (GHG).
The energy consumption is assessed by Eq. (8-1).
Energy Consumption (kJ)=
Refrigeration capacity (W)
EER
x Energy-consuming time (h)
(8-1)
The emission of Green House Gas is assessed by Eq. (8-2) to (8-4).
Energy consumption (kJ)
GHGEnergy(kg)=
x GHGcoal (kg/kg)
Combustion valuecoal(kJ/kg)(8-2)
GHCRefrigerant (kg)=GWP (kg/kg) x Refrigerant charge (kg)
(8-3)
Green House GasTotal (kg)=GHGEnergy (kg) + GHGRefrigerant (kg)(8-4)
where, GHGEnergy is the amount of green house gas due to energy consumption; Combustion valuecoal is
the combustion value of coal with a value of 29260 kJ/kg; GHGcoal is green house gas emission due to
coal combustion with a value of 2.62 kg per 1kg coal combustion; GHGRefrigerant is the amount of green
house gas due to refrigerant; GWPs of R22, R410A and R290 are 1500, 1730 and 0, respectively.
<<
53
Section 8
8.4.3 Results of life-cycle assessment of
air conditioner
1. Influence of EER
• When EER changes from 3.2 to 3.4, the
emission of green house gas decreases 5.4%
at most;
• When EER changes from 3.2 to 3.6, the
emission of green house gas decreases
10.8% at most.
2. Influence of refrigerant type
• When the refrigerant changes from R22 to
R410A, the GHG emission of air conditioner decreases 3.9% at most;
• When the refrigerant changes from R22
to R290, the GHG emission of air of air
conditioner decreases 55.1% at most.
3. Influence of service life
• When service life increases from 10 to 15
years, the energy consumption increases
about 34%, and emission of green house gas
decreases 34% at most;
• When service life increasing, the proportion
of refrigerant GHG emission in total GHG
emission decreases in accord. So the GHG
emission difference between air conditioners with different refrigerant decreases in
accord, when service life increase from 10 to
15 years.
<<
54
2500
R290
17
18
R22
R410A
16
3.6
R290
15
R22
R410A
14
3.4
13
15
R290
R410A
12
11
3.2
0.9
R22
R290
10
9
1.1
0.9
1.1
1.35
0.85
1.05
1.3
0.8
1
1.25
1.35
R22
R410A
8
3.6
7
0.85
R290
1.05
1.3
0.8
1
1.25
Regrigerant
Charge(kg)
6
R22
R410A
5
3.4
4
10
R290
R410A
3.2
3
2
EER
Refrigerant
R22
Service
Life
(Year)
1
No.
Capacity
(W)
5.4x107
5.9x107
6.2x10
7
3.6x107
3.9x107
4.1x10
7
Energy
Consumption
(kJ)
5000
5300
5600
3300
3500
3700
GHG
Energy
(kg)
Table 8.1 Results of life-cycle assessment
0
1954
2070
0
1833
1965
0
1730
1875
0
1903
2025
0
1816
1950
0
1730
1875
Window
0
3909
4140
0
3667
3930
0
3460
3750
0
3806
4050
0
3633
3900
0
3460
3750
Split
GHG Refrigerant (kg)
5000
6954
7070
53200
7133
7265
5600
7330
7475
3300
5203
5325
3500
5316
5450
3700
5430
5575
Window
5000
8909
9140
5300
8967
9230
5600
9060
9350
3300
7106
7350
3500
7133
7400
3700
7160
7450
Split
GHG Total (kg)
Section 8
<<
55
REFERENCES
[1]
International Copper Association & Shanghai Jiao Tong University. Air-Conditioner
Questionnaire for ASEAN Countries. April, 2011.
[2]
MarchWIN. Report for International Copper Association - Development Direction for Next
Generation of Environmentally Friendly Refrigerants. August, 2010.
[3]
Zezhao Hua, Hua Zhang, Baolin Liu, Shenyi Wu. Refrigerant Technology. Science Press, 2009.
[4]
Guoliang Ding, Chunlu Zhang, Li Zhao. Calculation methods, tables and diagrams for thermal
properties of new refrigerants. Shangahi: Shangahai Jiaotong University Press, 2003.
[5]
Ruzhu Wang, Guoliang Ding. Novel technologies in refrigeration and air conditioning. Beijiang:
Science Press, 2002.
[6]
Guoliang Ding, Hua Ouyang, Hongguang Li. Digital design for refrigeration and air
conditioning appliances. Beijing: Architectural Industry Press, 2008.
[7]
William C. Whitman, William M. Johnson, John A. Tomczyk, Eugene Silberstein. Refrigeration
& Air Conditioning Technology. Delmar CENGAGE Learning, 2009.
[8]
International Standard ISO 5151: Non-ducted air conditioners and heat pumps-Testing and
rating for performance. 2010.
[9]
ASHRAE. ANSI/ASHRAE Standard 34-1997: Designation and Safety Classification of
Refrigerants. Atlanta, Ga., ASHRAE, 1997.
[10] Houghton et al. 1995 IPCC Report: HFCs Table 2.9; CFCs and HCFCs Table 2.2, 1996.
[11] Ozone Secretariat UNEP, 1996.
[12] ARTI Refrigerant Database, based on WMO and IPCC assessments, August 1998. GWP shown
are for 100 year integrated time horizon.
[13] NIST Standard Reference Database 23, Version 6.01 (NIST 1996).
[14] ASHRAE Fundamentals Handbook chapter 20, 2001.
<<
56

Room and Small Commercial Air Conditioners

Transcription

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