Lower Energy Costs With Rooftop Air

Transcription

Lower Energy Costs with
Rooftop
Air-Conditioning
Package Units
Sponsored by
Mike West, PhD, PE
Advantek Consulting, Inc
Package Unit Efficiency Factors
 Sensible and latent performance ratings
 Unit efficiency ratings (IPLV, SEER, or EER)
 Fan motor drive and efficiency rating
 Fan is 10 to 20% of unit power draw [kW]
 Fan is 20% to 50% of unit energy usage [kWh]



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Number of stages / capacity control
Geographical location / climate
Likelihood of maintenance
Total life-cycle installed and operating costs
including options
 Copyright Advantek Consulting, Inc. 2008
EER Rating Specification
Efficiency Ratings




EER – Energy Efficiency Ratio MBH per kW
SEER – Seasonal EER MBTU per kWh
IPLV – Integrated Part-load Value MBH per kW
Energy Star – light commercial HVAC equipment uses 7–10%
less energy than standard equipment.
Energy Star package units can save $3 to
$4 per square foot over the life of the
equipment. For example, a 12,000 square
foot building using an ENERGY STAR
qualified HVAC product, could save $36,000
to $48,000 over 15 years, more than
enough to justify the upgrade cost.
Energy Star efficiency rating
 Units rated at 65,000 to 135,000 Btuh

11.0 EER or higher -and- 11.4 IPLV or higher
 Units rated at 135,000 to 250,000 Btuh

10.8 EER or higher -and- 11.2 IPLV or higher
 Three-phase equipment rated below 65,000 Btuh

SEER 13.0 or higher
Air conditioner EER ratings are measured at outdoor temperature of 95°F, indoor 80ºF dB
67ºF WB or 50% Relative Humidity.
IPLV takes into account the higher efficiency of air conditioning units at part load. IPLV is
measured using ARI Standard weightings and provides more of an “apples to apples”
comparison than EER alone.
SEER was intended to rate efficiency over an entire cooling season, not a single outdoor
temperature. In theory, SEER is calculated by total amount of cooling (Btu) over the entire
season divided by the total Watt-hours it will consume. SEER is used only for units 5-tons
and less.
SEER ratings
In some cases manufacturer’s simply rate SEER as
0.875 x EER at 82°F outdoor (instead of ARI 95°F)
“The SEER of a system is determined by multiplying the steady state energy efficiency
ratio (EER) measured at conditions of 82°F outdoor temperature, 80°F db and 67°F wb
indoor entering air temperature by the Part Load Factor (PLF) of the system.
(The PLF is supplied by the government.)”
The PLF is a measure of the cyclic performance (CD) of a system and is calculated as
follows, where CD is Cyclical Data:
PLF = 1.00 - (CD x 0.5)
"The cyclic performance (CD) value in the above equation has been determined by the
government to be 0.25." The government contends that the PLF should equal:
1.00 - (.25 x .5)
1.00 - .125 = 0.875, which yields: PLF of 0.875
Rating Specifications
Savings Estimates / Quick
Need estimated annual operating hours, cost of electricity.
MBH unit size = Tons x 12
EER1 = rating of standard efficiency unit
EER2 = rating of high efficiency Energy Star unit
Hours = annual operating hours ~ 1.3 x CDD
Rate = $ cost of electricity, demand and tax per kWh
Savings =
(
MBH MBH
EER1 EER2
) x Hours x Rate
Capacity selection
Avoid Oversizing
• Performance Ratings are at steady-state
• Larger units costs more & use more power
Example: compare power of 2 units at full load
15 ton: 15.7 kW
17½ ton: 18.9 kW added cost of $1500
Added electric demand of 3.2 kW ~ $400 per year
Documented sizing calculations should be performed using accepted
ACCA or ASHRAE procedures. ACCA methods have sufficient built-in
safety factors. Use ASHRAE design conditions.
Don’t exaggerate outdoor design temperatures by using the AHR 95 F
test point, or an unrealistically low indoor space condition such as 70
or 72 F.
Load-calc Lessons Learned
Perform an accurate hourly load calculation
Use the correct project location weather data
1.
2.
3.


Peak Sensible Load
Maximum Latent Load
Lowest SHR
Reasonably estimate infiltration airflow ACH
Or, if an hourly load calc is not feasible, calculate the
cooling load at three design conditions:
ASHRAE Fundamentals 2003 Chapter 27, Miami 0.4%
F.2005 Chapter 28 data available on CD-ROM
1.
2.
3.
Cooling: 91db / 78wb / 125 grains
Dehumidification: 83db / 79 wb / 145 grains
Latent-Part-Load: 75db / 72 wb / 116 grains
Equipment Specification Tips
Use manufacturer’s performance software or tables to
determine actual unit capacity (don’t use nominal)
Select the model closest in capacity to the load
Specify that TAB shall include supply air CFM, fan RPM,
External SP, and EAT–LAT
OA CFM must meet ASHRAE 62, provide exhaust makeup,
and pressurize the building 0.02 to 0.04 in.wg [5 to 10 Pa]
Request prices - be able to support and defend your
equipment specification with hard economics.
The importance of carefully
selecting the design airflow …
The SHR of a DX package unit will try to follow it’s capacity
curve to match the SHR of the space load. Load SHR
drops as the space humidity drops, yet equipment SHR
increases as entering wet bulb drops.
 If airflow is too low, temperature may rise and energy is wasted.
 If airflow is too high, humidity may be excessive at times.
 Higher airflow increases fan kW, but cooling capacity also
increases, so EER usually goes up at the higher fan speeds.
 However, too high a fan speed means the latent load will not be
met at times and fan energy use will be excessive.
Air Delivery Considerations
Air leakage and heat gain from ducts significantly
reduce air-conditioning system efficiency.
The insulation level of traditional ducting is typically
only R-4 to R-6 (1.5 to 2.2 inches).

Specify R-8 (2¾ to 3 inches)
Larger ducts typically mean lower static pressure, less
leakage and higher system efficiency, if well insulated.
With no attention, duct leakage rates can be 10% to 15% of
total system airflow, sometimes higher.

Specify ASHRAE Leakage Class-3 on the design drawings
Test and Balance the Unit and Duct System
Test and Balance
Package Units are not Plug-and-Play
Engineering observation of startup is a must.


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
Set fan speed and airflow according to design engineers
specifications. Verify rotation direction of fan.
Check and adjust refrigerant charge according to
manufacturer’s procedure.
Adjust and calibrate fresh air damper and linkage to
obtain design amounts of fresh air.
Properly install high-efficiency filters.
Commissioning
Example: Motorized Fresh-air
damper with Economizer
Commissioning
Some problems can be identified in the design phase:
 sizing, supply and outside airflows, controls
Most problems can be identified at the
project site:
1.
2.
3.
4.
5.
6.
Leak-test curb and ducts under pressure
Calibrate thermostats and sensors
Check ceiling diffusers for short-circuits
Functional performance test in all modes
Operations and maintenance training
Checkup visits at 30 and 90 days
Equipment Selection
Factory Equipment Options
 Select evaporative condenser option wherever available
 Motorized fresh-air damper with Economizer
 Dehumidification enhancements needed below SHR ~ 0.65
 Face and bypass damper, heat pipes, liquid reheat, hot gas reheat



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Filter pressure drop sensor so filter losses remain low
BACNET Communications interface
Avoid High Static Drive – Use static regain duct design, and
VFD or staged air-volume with SP or LAT control
DCV - Demand Controlled Ventilation based on return air CO2
Field Installed
 LPA liquid pressure amplification for low ambient conditions
 EER-Plus desuperheater / subcooler for the adventurous
 Auxiliary Condenser - increased heat rejection is a plus
Stages and Capacity Control
This unit has 1compressor, thus 1
refrigerant circuit
Single scroll compressor
Digital ScrollTM provides
variable capacity control
This unit has 2 compressors, but only 1 refrigerant circuit
1
2
This unit has 4 compressors and 4 refrigerant circuits, but
only 2 control stages. Modification to 4 stages is simple.
1
2
3
4
Model Selection
This unit has a Thermostatic Expansion Valve (TXV)
Evaporator coil
TXV
Evaporative Condenser
 Wet condenser coil uses evaporative
cooling like a cooling tower, except
refrigerant flows inside copper tubes.
 Less condenser fan HP
 Energy savings are typically 20% 30%, up to 40% in dry climates



Highly climate dependent
Near-peak versus off-peak operating
hours and MC wet-bulb temperatures
wb 10 to 30 degrees cooler than db
 Integrated water treatment system,
chemical and/or ozone
 Stainless steel, copper, PVC, FRP
 Desuperheater coils not wetted
Evaporative Condenser - AAON
Savings Estimates / Calculator
http://www1.eere.energy.gov/femp/procurement/eep_unitary_ac_calc.html
Range is still 8.9 to 13.5
Estimate based on location and type
Billed rate including kW demand and tax
Annual Hours of Operation
http://www.accuratehvac.com/accurate_residential/estimator/2/hvac_costest.htm
1
2
3
4
5
600 to 900 hours
900 to 1400 hours
1400 to 2000 hours
2000 to 2800 hours
2800 to 4000 hours
Hours of Operation = 1.3 x CDD
http://lwf.ncdc.noaa.gov/img/documentlibrary/clim81supp3/annualcoolingDD_hires.jpg
• $4194 - $3200 = $994 savings per year
• Cost of 10-ton high efficiency (EER 13.5) unit: $7,000
• Cost of a standard (EER 10.3) typical unit: $5,000
• Upgrade cost for a high-efficiency unit: $7,000 - $5,000 = $2,000
• Payback period = $2,000 / $994 = 2 years to recover higher price
• Return on investment = $994 / $2000 = 49% every year for life of equipment
Lifetime savings for 5 units: $82,370 in today’s dollars (15 years)
assuming a 4.1% annual increase in electricity
Cost of 5 units: 5 x $7,000 = $35,000
Benefit / Cost Ratio = 83,370 / 35,000 = 2.4
Market Availability
ENERGY STAR Partner List Results
Look for Product Manufacturers in a different Country and State:
All Countries
New Search Refine Search
Results 1 - 7 of 7
Name
Carrier
Corporation
Daikin U.S.
Corporation
Goodman
Manufacturing
Company, L.P.
All States
Go
All # A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Product Type
Location Award Category (Year)
Central ACs and Air-Source Heat Connecticut
Pumps, Furnaces, Geothermal
Heat Pumps, Light Commercial
HVAC, Programmable
Thermostats, Room Air
Conditioners
Light Commercial HVAC
New York
Central ACs and Air-Source Heat
Pumps, Furnaces, Light
Commercial HVAC, Room Air
Conditioners
Lennox Industries Central ACs and Air-Source Heat
Incorporated
Commercial HVAC,
Programmable Thermostats
Rheem-Ruud
Central ACs and Air-Source Heat
Manufacturing
Commercial HVAC,
Programmable Thermostats
Trane Company Light Commercial HVAC
York International Central ACs and Air-Source Heat
Corp. UPG
Commercial HVAC
Texas
Texas
Excellence in Efficient
Products(2003,2004,2005,2007)
Arkansas
Tennessee
Oklahoma
1.
2.
3.
4.
5.
6.
7.
Carrier
Daikin
Goodman
Lennox
Rheem-Ruud
Trane
York
Market Availability
• Carrier
•
•
•
•
Centurion EER 11.5-12.5, SEER 14.1-15.0, to 5-tons
Centurion EER 11.0-12.7, IPLV 12.0-13.7, 6 to 25-tons
WeatherMaster EER 11.8 to 25-tons
Goodman
SEER 13 to 5-tons
EER 11.5 to 7.5-tons
Lennox
Strategos EER 12.5-14.3, IPLV 13.5-16.4, to 20-tons
L-Series EER 12.2 to 30-tons
T-Class EER 11.0 to 25-tons
S-Class EER 10.8 to 50-tons
Trane Precedent SEER 15 to 5-tons, EER 11.5 to 10-tons
Voyager Hi-E EER 10.4-11.5 to 25-tons
York Affinity SEER 13-16.5 to 5-tons
Predator EER 11.5 to 12½-tons
Savings Example / Quick
MBH unit size = 20-Tons x 12 = 240 MBH
EER1 = rating of Lennox T-Class = 10.8
EER2 = rating of Lennox Strategos = 12.6
Hours = annual operating hours ~ 1.3 x CDD = 3000
Rate = cost of electricity = $0.12 per kWh billed
Savings =
Savings =
(
(
MBH MBH
EER1 EER2
240
240
10.8 12.6
) x Hours x Rate
) x 3000 x 0.12
$1,143 per year savings
Design-in Maintainability
Numerous energy surveys clearly show that lack of
preventative maintenance is by far the major cause of
air conditioning performance degradation.
Common and costly problems include:
 clogged, corroded cooling and condenser coils
 sizeable duct leaks and cabinet air leaks
 low refrigerant, even in brand-new units
 maladjusted or stuck air dampers
 un-calibrated or nonfunctioning controls or sensors
Design for Easy Access
Provide Manuals and Training
Model Selection
Likelihood of maintenance is important.
VS.
Model
Selection
filter compartment
access door
Fiberglass pre-filters
MERV-11 final filters
Ease of Maintenance
Filter rack was specified to fit 2-inch pre-filters and
2-inch final filters. Angled position of top filters
improves flow.
Refrigerant Charge
Both Over- and Under-charging are common
Even a 5% adjustment is worthwhile
“…the air conditioning system can be performing below
its capacity because of poor maintenance and maintain
comfort while energy use increases.”
“I don’t see anyone really checking charge right, most
technicians only do a touch method.”
“I have even found 8 ounces overcharge on brand new
units.” [total charge is 5 to 8 pounds]
Preventative maintenance program
… critical to realizing rated performance for the life of the unit.
Lower Energy Costs with
Rooftop
Air-Conditioning
Package Units
Thank you!
Mike West, PhD, PE
Advantek Consulting Engineering, Inc.
[email protected]

Lower Energy Costs With Rooftop Air

Transcription

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