Evaporative-Cooled vs. Air -Cooled Chillers: Kirtland...
Transcript of Evaporative-Cooled vs. Air -Cooled Chillers: Kirtland...
Evaporative-Cooled vs. Air-Cooled Chillers: Kirtland AFB Case Study
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DISCUSSION TOPICS
Brief Overview of Air-Cooled and Evaporative-Cooled Condenser Technologies
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 and condensed in Air-to-Refrigerant Heat Exchanger (coil).
Air-Cooled Condenser efficiency depends 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 CONDENSER BASICS
Treated water is sprayed over condenser coil. 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 increased by 25-50% compared to air-cooled due to lower vapor compression pressure, thus reducing compressor‘s energy.
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AIR-COOLED AND EVAPORATIVE-COOLED CONDENSER COMPARISON
PROS OF AIR-COOLED vs. EVAPORATIVE-COOLED:Smaller cabinetLighter weightNo condenser water piping and treatmentLower equipment costLower maintenance costNo water consumption for condenser operation
PROS OF EVAPORATIVE-COOLED vs. AIR-COOLED:20-40% lower electrical consumption of the chillerQuieter 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
BUILDING NO.
CHILLER TONNAGE
EVAPORATIVE-COOLED CHILLERS
AIR-COOLED CHILLERS
1005 60 $178,000 $74,000
20140 60 $178,000 $74,000
322 70 $204,000 $84,0001017 90 $262,000 $113,00020222 100 $279,000 $130,00020361 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
CHILLER TONS
ELECTRICITYKWh x 1,000 / COST
(chiller only)
CITY WATER AND SEWER
(chiller only)
MAINTENANCE(chiller 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 $3,200165 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 EVAPORATIVE AND AIR-COOLED CHILLERS
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KIRTLAND AFB ENERGY STUDY RESULTS
10- YEAR LIFE CYCLE COST COMPARISON FOR EVAPORATIVE AND AIR-COOLED CHILLERS
BLDG NO.
CHILLER TONNAGE
LCC OF EVAPORATIVE-
COOLED CHILLERS
LCC OF AIR-COOLED
CHILLERS
COST RATIO OF AIR-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 EVAPORATIVE AND AIR-COOLED CHILLERS
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CONCLUSIONS
Mid-range (50-150 tons) Air-Cooled Chillers may cost less than Half of Evaporative-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 more competitive than Evaporative-Cooled Chillers..
Evaporative-Cooled Chillers require a larger foundation, water and drain piping, and water treatment equipment.
EVAPORATIVE-COOLED CHILLERS MAY NOT BE THE BEST OPTION, BECAUSE:
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CONCLUSIONS (continued)
Evaporative-Cooled Chillers consume a significant amount of Potable Make-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 Total building 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 BEST OPTION, BECAUSE:
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RECOMMENDATIONS
Review and Evaluate All Costs related to installation and operation of Evaporative-Cooled Chillers before making a decision.Capital EnergyWaterMaintenance
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QUESTIONS AND ANSWERS
THANK YOU!Corry Freeman, CEM
Staff Mechanical EngineerAMEC
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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 a Mechanical Evaporative Cooler – a hollow wheel moving through a water bath.
In early 20th Century, Willis Carrier developed a psychrometric chart similar 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 COOLING EQUIPMENT 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 the
heat 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.