evaporative cooled vs air cooled chillers kirtland afb case study

7/27/2019 Evaporative Cooled vs Air Cooled Chillers Kirtland AFB Case Study

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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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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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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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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

[email protected]
mailto:[email protected]:[email protected]


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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.

evaporative cooled vs air cooled chillers kirtland afb case study

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