ASHRAE Rocky Mountain ChapterEvaporative Cooling

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Rick Phillips, P.E., LEED AP Senior Mechanical Engineer

The RMH Group, Inc.

May 2, 2014

Fundamentals

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Dry Bulb Temperature

Wet Bulb Temperature

Evaporation

Wet Bulb Depression = DB – WB

Design Day in Denver 93° DB, 59° WB

Direct Evaporative Cooler

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Media

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Performance

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CoolingEffectiveness =(%)

EDB – LDB

EDB – EWB

Indirect Evaporative Cooling

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Hybrid Indirect Evaporative Cooler with Energy Recovery

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(Used as IEC)

(Could be DEC)

Psychrometrics

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DIRECT INDIRECT INDIRECT / DIRECT

Direct Evaporative Cooling Pad Performance

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Bin weather data, Denver, CO Doesn’t include fan temperature rise

Indirect/Direct Evaporative Cooling System Performance

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Bin weather data, Denver, CO Doesn’t include fan temperature rise

Typical Meteorological Weather Data (TMY2)

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Hourly weather data for a typical year (not averaged)– Includes typical extreme weather

conditions Database includes conditions like

this:– 78°F DB, 66°F WB

• Under these conditions, direct evaporative cooling does not perform well.

12” PAD (LAT) Final Room Conditions

67°F DB 74°F DB, 76% RH

Typical Meteorological Weather Data (TMY2)

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Number of hours/year with high WB– > 60°F – 378 hours

– > 63°F – 146 hours

– > 65°F – 33 hours Using a 63°F DAT requires 67%

more airflow than using 55°F DAT.

Systems that Can Use Higher SAT

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Displacement Ventilation

UFAD

Data Centers (hot aisle/cold aisle)

63F - 68F

60F - 64F

64F - 80F

For Conventional VAV Applications

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Combine chilled water with direct evaporative cooling

Advantages–Can reduce chiller ton-hours/year by 2/3 ($$).–Can deliver 55°F DAT at any time.

• Don’t have to oversize fans and ducts.–Can limit humidity levels in the building.

Note: still requires a full-sized chiller

CHW/DEC Component Arrangement for Optimal Performance

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* Fan Upstream – 35% less CC energy

(compared to CC upstream of DEC)

(compared to DEC upstream of of CC)

: :

For which types of buildings does evaporative cooling work?

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Direct evaporative cooling alone Warehouses Vehicle repair facilities Any type of building with low internal cooling loads Makeup air for commercial kitchens Gymnasiums Spaces that are open to the outdoors

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For which types of buildings does evaporative cooling work?

Indirect evaporative cooling combined with directevaporative cooling Commercial office buildings Retail spaces Recreation center Any type of building with moderate to low internal cooling

loads

Direct and/or indirect evaporative cooling combined with CHW or DX cooling

Any type of building

Pros

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Saves energy Works well in the Denver climate Low tech and easy to maintain with unskilled labor Lower cost than a chilled water cooling plant Can also be used to cheaply humidify air Direct evaporative cooling is inexpensive

Cons

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If not maintained properly, can produce odors If wrong materials are used, can have corrosion

problems Poor construction can result in leaks and water

carryover, resulting in flooding of the space below the unit

People don’t understand how to maintain it or fix problems

Maintenance and Operation

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Dry the pad out daily.

Drain the sump weekly.

Run the pad wild.

Don’t recirculate air.

Pads last approx. 8-12 years.

Pipe for maintenance (strainers, PRV, flowmeters, etc.).

Direct Evaporative Cooler Piping

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Water Treatment

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Scale buildup prevention

Continuous bleed or automatic control

Biocides

Control Sequence

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Economizer (OA) Direct evap first Indirect/direct (if used) Direct with chilled water High humidity lockout 100% outside air whenever

direct evap is active

Myths

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Legionella disease Over humidification Smell High maintenance High water usage

Typical HVAC SystemsEstimated Total Water Consumption

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Assumptions

•Power plant overall efficiency of 35%

•Average O.A. temperature of 80oF

•Cooling tower bleed rates of 20% to 33%

Air Cooled Chiller 2.8 COP = 10 Lb. H2O

Ton-Hr

DX Air Conditioner 2.8 COP = 10 Lb. H2O

Ton-Hr

Water Cooled Chiller 5.55 COP = 25 Lb. H2O

(150 ton – 300 ton) Ton-Hr

Evaporative Cooler 80oF O.A. = 21 Lb. H2O

(Direct/Indirect) Ton-Hr

Case Study − Golden Hill Office Center

212,000 sf office building constructed in 1983

Designed in conjunction with SERI (NREL)

Model project for energy-conscious design

National ASHRAE First Place Energy Award for New Construction, 1988

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Case Study − Golden Hill Office Center

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Features– 100% indirect/direct evaporative cooling system– Solar hot water heating– Three 10 kW roof-mounted photovoltaic arrays– Passive solar design with east-west axis– Six high-efficiency, condensing boilers– Natural ventilation for parking garage– Heat and light reclaimed from atriums to offices– South side window overhangs– 38 kBtu/sk/year measured without atrium; DOE

1995 energy evaluation of comparative buildings is 90 kBtu/sf/year

– 43 kBtu/sf/year measured with atrium– 28 kBtu/sf/year with light shelves (not installed)

Case Study − Golden Hill Office Center

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Indirect/direct evaporative cooling process

Case Study − CU-Boulder ATLAS Center

66,000 sf of classroom, performance, and study space

Opened for classes in August 2006

Features direct evap + CHW cooling, carbon dioxide monitoring, and VAV systems

Certified LEED-NC Gold 4 points for optimizing energy

performance – 30% reduction29

Case Study − CU-Boulder Wolf Law Building

Five-story, 184,000 sf Opened for classes in

August 2006 Features direct/indirect

evap + CHW cooling, carbon dioxide monitoring for demand ventilation, and VAV systems

Certified LEED-NC Gold

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Case Study − CSM Student Recreation Center

110,000 sf facility Direct/indirect evaporative

cooling only– $500,000 deferred cost for

chiller plant Natatorium

– IEC– Outside air for humidity control

Competition gymnasium– DEC/IEC

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Case Study − Colorado Springs Utilities Laboratory

Project Description– 45,000 sf (2/3 laboratory space,

1/3 office space)– Direct evaporative cooling with

chilled water, energy recovery– Designed with the Labs-21/LEED

Guidelines– Certified LEED-NC Silver– 50% energy savings compared to

base case– USGBC-CO Bldg. of the Year Award

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Case Study − Colorado Springs Utilities Laboratory

2 AHUs – 62,000 cfm for labs, 25,000 cfm for offices

Annual chiller operating costs with chilled water cooling only - $17,900

Annual chiller operating costs with combined chilled water/ evaporative cooling - $5,900

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Case Study − Colorado Springs Utilities Laboratory

Cost of adding direct evaporative cooling modules

Payback with addition of evaporative cooling

= First Cost/Yearly Savings

= $20,000/$12,000

= 1.67 years (20 months)

Lab AHU Office AHUEquip. Cost $9,500 $6,000Hookup/Controls $2,500 $2,000

Total $12,000 $8,000