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Evaporative-Cooled vs. Air-Cooled Chillers:Kirtland AFB Case Study
www.amec.com
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DISCUSSION TOPICS
Brief Overview of Air-Cooled and Evaporative-Cooled CondenserTechnologies
Pros and Cons
Scope and Results of Kirtland AFB Study
Conclusions and Recommendations
Q&A
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AIR-COOLED CONDENSER BASICS
Refrigerant hot gas is cooled andcondensed in Air-to-Refrigerant Heat
Exchanger (coil).
Air-Cooled Condenser efficiencydepends on ambient air dry bulb
temperature, i.e. the higher OAT is, the
more power is required to compress
hot gas in order to condense it into
liquid.
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EVAPORATIVE-COOLED CONDENSERBASICS
Treated water is sprayed over condensercoil. Part of water is evaporated thus
lowering surface temperature of the
condenser and the air drawn across it.
Remaining water is collected in drain pan
and recirculated back to sprayer. Make-up city water is added to replace
evaporated water.
Refrigeration system efficiency is increasedby 25-50% compared to air-cooled due to
lower vapor compression pressure, thus
reducing compressors energy.
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AIR-COOLED AND EVAPORATIVE-COOLEDCONDENSER COMPARISON
PROS OF AIR-COOLED vs. EVAPORATIVE-COOLED:Smaller cabinet
Lighter weight
No condenser water piping and treatment
Lower equipment cost
Lower maintenance cost
No water consumption for condenser operation
PROS OF EVAPORATIVE-COOLED vs. AIR-COOLED:
20-40% lower electrical consumption of the chiller
Quieter operation
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KIRTLAND AFB ENERGY STUDY
OBJECTIVE:
Increase the energy efficiency of existing facilities on various Air
Force Bases in order to reduce the building annual operating cost.
STUDY SCOPE:
Evaluate life cycle costs of replacement of existing Air-Cooled
Chillers with Evaporative-Cooled Chillers at seven (7) buildings.
Life Cycle Cost Analysis compared costs associated with
Evaporative-Cooled Chillers against Status Quo (air-cooled chillers),
and included:
Capital Cost Estimate (material and labor) at +/-30% accuracy.
Maintenance Cost analysis.
Operating Cost Analysis (electricity and water).
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KIRTLAND AFB ENERGY STUDY RESULTS
BUILDINGNO.
CHILLERTONNAGE
EVAPORATIVE-COOLEDCHILLERS
AIR-COOLEDCHILLERS
1005 60 $178,000 $74,000
20140 60 $178,000 $74,000
322 70 $204,000 $84,000
1017 90 $262,000 $113,000
20222 100 $279,000 $130,000
20361 165 $389,000 $176,000
472 250 $471,500 $235,000
CAPITAL COST COMPARISON FOR EVAPORATIVE AND AIR-COOLED CHILLERS
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KIRTLAND AFB ENERGY STUDY RESULTS
CHILLERTONS
ELECTRICITY
KWh x 1,000 / COST
(chil ler only)
CITY WATER ANDSEWER
(chiller only)
MAINTENANCE
(chil ler only)
AIR-COOLED EVAP-COOLED
AIR-COOLED
EVAP-COOLED
AIR-COOLED
EVAP-COOLED
60 49 / $3,920 28 / $2,240 $0 $323 $1,600 $2,000
60 49 / $3,920 28 / $2,240 $0 $323 $1,600 $2,000
70 56 / $4,480 30 / $2,400 $0 $353 $1,600 $2,000
90 34 / $2,720 16 / $1,280 $0 $196 $2,400 $3,200
100 66 / $5,280 39 / $3,120 $0 $463 $2,400 $3,200
165 102 / $8,160 56 / $4,480 $0 $665 $2,400 $3,200
250 200 / $16,000 108 / $8,640 $0 $1,260 $2,400 $3,200
ANNUAL OPERATING COST COMPARISON FOR EVAPORATIVEAND AIR-COOLED CHILLERS
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KIRTLAND AFB ENERGY STUDY RESULTS
10- YEAR LIFE CYCLE COST COMPARISON FOR EVAPORATIVEAND AIR-COOLED CHILLERS
BLDGNO.
CHILLERTONNAGE
LCC OFEVAPORATIVE-
COOLED
CHILLERS
LCC OF AIR-COOLED
CHILLERS
COST RATIO OFAIR-COOLED /EVAP-COOLED
CHILLERS1005 60 $301,000 $201,000 67%
20140 60 $301,000 $201,000 67%
322 70 $350,000 $233,000 62%
1017 90 $462,000 $293,000 64%
20222 100 $513,000 $335,000 65%
20361 165 $757,000 $557,000 74%
472 250 $1,386,000 $1,191,000 86%
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KIRTLAND AFB ENERGY STUDY RESULTS
10- YEAR LIFE CYCLE COST COMPARISON FOR EVAPORATIVEAND AIR-COOLED CHILLERS
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CONCLUSIONS
Mid-range (50-150 tons) Air-Cooled Chillers may cost less than Half ofEvaporative-Cooled Chillers, which require:
Special corrosion resistant coatings on condenser coils.
Water spraying equipment. Larger cabinet size to accommodate water spraying equipment.
Water treatment equipment, water and sewer piping.
Air-Cooled Chillers are more available and its pricing is morecompetitive than Evaporative-Cooled Chillers..
Evaporative-Cooled Chillers require a larger foundation, water anddrain piping, and water treatment equipment.
EVAPORATIVE-COOLED CHILLERS MAY NOT BE THE BESTOPTION, BECAUSE:
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CONCLUSIONS (continued)
Evaporative-Cooled Chillers consume a significant amount of PotableMake-Up Water, which is in short supply and is costly in high-desert
dry and arid areas. Additional Maintenance Cost to treat Make-Up Water and clean
condenser coils, which partially offsets energy savings.
Energy Consumption of mid-range chillers is only 10-15% of the Totalbuilding energy consumption; therefore the 25-40% Energy Savings
for Evaporative-Cooled Chillers amount to only 5-7% of the Total
Energy bill reduction
EVAPORATIVE-COOLED CHILLERS MAY NOT BE THE BESTOPTION, BECAUSE:
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RECOMMENDATIONS
Review and Evaluate All Costs related to installation andoperation of Evaporative-Cooled Chillers before making adecision.
Capital
Energy
Water
Maintenance
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QUESTIONS AND ANSWERS
THANK YOU!Corry Freeman, CEM
Staff Mechanical Engineer
AMEC
mailto:[email protected]:[email protected]7/27/2019 Evaporative Cooled vs Air Cooled Chillers Kirtland AFB Case Study
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QUESTIONS AND ANSWERS
BACK-UP SLIDES
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BRIEF HISTORY OF EVAPORATIVE COOLING
Records of Evaporation Cooling use for human comfort trace back to
2,500 BC.
In 16th Century, Leonardo Da Vinci is known to be first to design aMechanical Evaporative Cooler a hollow wheel moving through a
water bath.
In early 20th Century, Willis Carrier developed a psychrometric chartsimilar to ones in use today along with the development of a formula
that linked the transformation of sensible heat into latent heat during the
adiabatic (no external heat input or output) saturation of air.
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TYPES OF EVAPORATION COOLINGEQUIPMENT
Direct Evaporative Coolers
Simply draw air through a moistened wick material and delivers the cooled(but more humid) air to the space to be conditioned.
Supply air temperature is limited by outside air wet-bulb temperature.
Indirect Evaporative Coolers
Operate similarly to a direct evaporative cooler but uses a heat exchanger.
Stream of outdoor air passes through the heat exchanger, gets cooled by theheat exchanger cold surfaces, and then is delivered to the space.
The benefit of this is that the cooled air does not pick up any humidity as it
does in the direct evaporative process. The drawback is the delivered air
does not get as cool as in a direct evaporative process because it is limited
by the ambient wet bulb temperature and the heat exchanger efficiency. Mechanical refrigeration
Uses Vapor Compression Cycle consisting of Compression, Condensing,
Expansion, and Evaporation stages.
Water is sprayed on condenser coil to increase refrigerant condensing rate,
thus saving AC system energy.