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Does Evaporative Cooling Make Sense in Arid Climates?

WESTERN COOLING EFFICIENCY CENTER // wcec.ucdavis.edu

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Pre-Cooler 1 Pre-Cooler 2 Pre-Cooler 3 Pre-Cooler 4 Pre-Cooler 5


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Evaporative E�ectiveness

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COP Dry WEI SL (DTWB 22.2) WEI SL (DTWB 11.1)WEI SL (DTWB 8.3) WEI SL (DTWB 5.6) WEI SL (DTWB 2.8)WEI Experimental Data Point COP Dry Experimental Data Point

WEI ( DTWB= 21.8)

WEI ( DTWB= 6.2)

WEI ( DTWB= 5)

WEI ( DTWB= 13.8)

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WEI ( DTWB= 6.2)

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Inlet air temperature

Outlet air temperature

Explores the trade-off between water use and energy savings, using three different water alternatives—by employing energy and cost analyses of small-scale evapora-tive cooling technologies.

Water Energy Index (WEI)Experimental data collected from retrofitted 4-ton York RTU air cooled condensing unit with flow rate of 0.13 cubic meter per second per kW cooling used to calculate WEI. WEI includes: volume of water for evaporation and an additional 15% maintenance water:WEI=WL /EL × 1.15

DOES EVAPORATIVE COOLING MAKE SENSE IN ARID

CLIMATES?

I. Summarizes measured energy savings and coincident water consumption for two small-scale

types of “modern” evaporative cooling technologies: evaporative pre-coolers for packaged

vapor-compression equipment and residential evaporative condensers.

II. Explores the trade-off between water use and energy savings, using three different water

resources (tap water, rain water, desalination water) employing energy and cost analysis.

Water Energy Index (WEI)

The experimental data collected from retrofitted 4 ton York RTU air cooled condensing unit with

flow rate of 0.13 cubic meter per second per kW cooling used to calculate WEI.

Include both the volume of water for evaporation and additional 15% maintenance water:

𝐖𝐖𝐖𝐖𝐖𝐖𝐖𝐖𝐖𝐖𝐖𝐖 = 𝐖𝐖𝐖𝐖𝐋𝐋𝐋𝐋𝐖𝐖𝐖𝐖𝐋𝐋𝐋𝐋

× 1.15

where,

EL �kWhElectricity saving

kWhCooling� = � 1

COPBase� − � 1

COPPre−cool� Normalized Eletctricity Savings

WL[ LkWhCooling

] = EE × (WSat. − Win) × Qc × ρairρwater

× hr3600 s

Water Consumption

Normalized Electricity Savings

DOES EVAPORATIVE COOLING MAKE SENSE IN ARID

CLIMATES?

I. Summarizes measured energy savings and coincident water consumption for two small-scale

types of “modern” evaporative cooling technologies: evaporative pre-coolers for packaged

vapor-compression equipment and residential evaporative condensers.

II. Explores the trade-off between water use and energy savings, using three different water

resources (tap water, rain water, desalination water) employing energy and cost analysis.

Water Energy Index (WEI)

The experimental data collected from retrofitted 4 ton York RTU air cooled condensing unit with

flow rate of 0.13 cubic meter per second per kW cooling used to calculate WEI.

Include both the volume of water for evaporation and additional 15% maintenance water:

𝐖𝐖𝐖𝐖𝐖𝐖𝐖𝐖𝐖𝐖𝐖𝐖 = 𝐖𝐖𝐖𝐖𝐋𝐋𝐋𝐋𝐖𝐖𝐖𝐖𝐋𝐋𝐋𝐋

× 1.15

where,

EL �kWhElectricity saving

kWhCooling� = � 1

COPBase� − � 1

COPPre−cool� Normalized Eletctricity Savings

WL[ LkWhCooling

] = EE × (WSat. − Win) × Qc × ρairρwater

× hr3600 s

Water Consumption

Water Consumption

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COP Dry WEI SL (DTWB 22.2) WEI SL (DTWB 11.1)WEI SL (DTWB 8.3) WEI SL (DTWB 5.6) WEI SL (DTWB 2.8)WEI Experimental Data Point COP Dry Experimental Data Point

WEI ( DTWB= 21.8)

WEI ( DTWB= 6.2)

WEI ( DTWB= 5)

WEI ( DTWB= 13.8)

WEI

(L/

KW

h sa

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s) C

OP(

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WEI

(L/

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Outdoor Dry-bulb Temperature (°C) Outdoor Dry-bulb Temperature (°C)

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WEI (DTWB= 21.8)

WEI ( DTWB= 6.2)

WEI ( DTWB= 5)

WEI (DTWB= 13.8)

Inlet air temperature

Outlet air temperature

PROJECT RESULTS:Does Evaporative Cooling Make Sense in Arid Climates?


Energy Base AnalysisDesalination produces 80-280 liters of potable water for 1 kWh consumed

• Evaporative cooling consumes 9-40 liters of water per 1 kWh saved

• Equivalent to getting back 2-30 kWh for investing 1 kWh (electricity multiplier)

• Desalinization can operate at night and evaporative cooling reduces peak demand

during the day

Economic AssessmentDesalination rate $1.65 per 1000 liters produced

• Electricity costs of $0.08-$0.37 per kWh

• $1 in desalination water yields $1.20-$25 in electricity cost savings, depending upon

the technology employed and the local cost of electricity

Demand Response with Evaporative Pre-Coolers• Evaporative pre-coolers provide the largest impact at peak demand times

• Water use efficiency is highest at peak times

• Planning project to test evaporative pre-cooler response time

PROJECT RESULTS:Multi-Tenant Light Commercial—Modeling


Parameter Baseline Best

RTU Efficiency COP = 2.9 COP = 6

Evaporative Pre-Cooler No Yes

HVAC Economizer No Yes

Cool Roof No Yes

WindowsSHGC = 0.38U-Factor = 4.088

SHGC = 0.25U-Factor = 3.236

Skylights NoneSHGC = 0.8 U-Factor = 3.24

LightingLinear fluorescent T8 lightingLPD (retail) = 1.14 W/sf

LED LPD = 0.87 W/sf

Daylight Harvesting Control System

None Continuous dimming

• The MTLC prototype building was modeled

with 18 variable parameters

• The parametric analyses consisted of

approximately 500,000 simulations

The parameters that were common among the top 10 performing configurations

saves 27% electricity annually over the baseline configuration.

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Electricity Savings from Duct Sealing

Avg Ceiling Ins. No Ceiling Ins.

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Electricity Savings from Duct Sealing

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Modeled building

PROJECT RESULTS:A New Termination Control Method for a Clothes Drying Process in a Clothes Dryer


• DOE estimates that energy savings

between 4 – 62% are possible with

improved dryer controls

• Achieving 20% savings in natural gas

dryers with 10% market penetration would

save 6 million therms annually in California

• WCEC testing has shown that typical

natural gas dryers run with inlet

temperatures above 300°F and a

significant amount of the air bypasses

the burner

Researchers at Hong Kong Polytechnic University (Ah Bing Ng, Shiming Deng, 2008) have demonstrated control scheme proof of concept in a laboratory setup

OUTDOOR AIR

HEATING COIL

COOLING COIL

BURNERINLET AIR

EXHAUST

DRUM

Pressure Relief

Vgas

E

Tin

ENVIRONMENTAL CHAMBER

DRYER

DRUM

Tout,air Tout

Fan

Tcab

Troom

RHTcab

Tcab

Clothes Dryer Testing Diagram

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Inlet air temperature Outlet air temperature Clothes surface temperature

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Control Scheme Proof of ConceptWCEC Laboratory Findings

PROJECT RESULTS:Performance Evaluation of a Thermal Storage SolutionUsing ice to store thermal potential


• WCEC tested a thermal storage solution in our environmental control chamber,

and used the results to suggest design improvements and build a predictive

performance model.

• The predictive model was used to estimate performance for a next generation

thermal storage solution

• Successful completion of the tests is an example of the breadth of WCEC’s

expertise in energy efficient technologies

CONDENSER

RHQ, cond

T P,T

P,T

T,DB

E

LEGEND

P = Pressure, Refrigerant

T = Temperature, Refrigerant

Q = Flow

RH = Relative Humidity

= Power

TDP = Dewpoint Temperature

TDB = Dry Bulb Temperature

TICE = Ice Temperature

TWATER = Water Temperature

= Sensor

E

REC

EIV

ER

REC

EIV

ER

HX1

ICE BOX

TICE TICE

TICE TICE

Water Pump

EVAPORATOR

P,T

Qevap

TDB

TDPTDP

P,T

E

Refrigerant PumpE

HX2

TDB

TXV

COM

PRES

SOR

TDB

TWATER

TWATER

Sight Glass Sight Glass

Laboratory testing diagram

PROJECT RESULTS:Performance Evaluation of a Thermal Storage SolutionUsing ice to store thermal potential


02468

10121416

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EER

Predicted Annual EER

3-ton Ice Storage System SEER 16 Split System SEER 13 Split System

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kWh

Predicted Annual Daytime kWh Use

3-ton Ice Storage System SEER 16 Split System SEER 13 Split System

PROJECT RESULTS:High Performance Waste Heat Recuperators for Heat Recovery Cycles


Motivation and Challenges• Waste heat recovery in ships can lead

to enhanced efficiency and longer

times between refueling.

• There has been recent interest in sCO2

cycles for power generation and waste

heat recovery.

• Challenge is in designing a reliable

recuperator,

• Cyclic operation

• Corrosion

• Low pressure drop designs needed

Problem StatementDesign a low pressure drop recuperator

for sCO2 waste heat recovery cycle while

running in system pressure as high as 200

bar (3000 psi) for a large naval ship.

Benefit to US NavyNovel recuperator designs for high pres-

sure sCO2 waste heat recovery cycle using

Additive Manufacturing:

• High effectiveness recuperator

• Compact

• Low pressure drop on exhaust side

• No weld/braze joints in AM- potentially

more reliable

SCO2TurbineCompressor

Cooling

Heating

PROJECT RESULTS:High Performance Waste Heat Recuperators for Heat Recovery Cycles


Low temperature exhaust gases to atmosphere

Variation of recuperator length and pressure drop of ex-haust gases with sCO2 exit temperature based on the model developed for designing the recuperator

Hot exhaust gases from Generator

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