ASHRAE Rocky Mountain Chapter Evaporative Cooling
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Transcript of ASHRAE Rocky Mountain Chapter Evaporative Cooling
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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
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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
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Direct Evaporative Cooler
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Media
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Performance
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CoolingEffectiveness =(%)
EDB – LDB
EDB – EWB
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Indirect Evaporative Cooling
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Hybrid Indirect Evaporative Cooler with Energy Recovery
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(Used as IEC)
(Could be DEC)
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Psychrometrics
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DIRECT INDIRECT INDIRECT / DIRECT
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Direct Evaporative Cooling Pad Performance
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Bin weather data, Denver, CO Doesn’t include fan temperature rise
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Indirect/Direct Evaporative Cooling System Performance
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Bin weather data, Denver, CO Doesn’t include fan temperature rise
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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
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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.
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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
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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
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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)
: :
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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
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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
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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
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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.).
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Direct Evaporative Cooler Piping
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Water Treatment
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Scale buildup prevention
Continuous bleed or automatic control
Biocides
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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
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Myths
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Legionella disease Over humidification Smell High maintenance High water usage
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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
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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)
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Case Study − Golden Hill Office Center
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Indirect/direct evaporative cooling process
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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
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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