ASHRAE Rocky Mountain Chapter Evaporative Cooling

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ASHRAE Rocky Mountain ChapterEvaporative Cooling
Rick Phillips, P.E., LEED AP Senior Mechanical
Engineer The RMH Group, Inc. May 2, 2014
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Fundamentals
Evaporation
Dry Bulb Temperature
Wet Bulb Temperature
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
Cooling Effectiveness ()
EDB LDB EDB EWB
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Indirect Evaporative Cooling
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Hybrid Indirect Evaporative Cooler with Energy
Recovery
(Could be DEC)
(Used as IEC)
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Psychrometrics
DIRECT
INDIRECT
INDIRECT / DIRECT
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Direct Evaporative Cooling Pad Performance

• Bin weather data, Denver, CO
• Doesnt include fan temperature rise

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Indirect/Direct Evaporative Cooling System
Performance

• Bin weather data, Denver, CO
• Doesnt include fan temperature rise

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Typical Meteorological Weather Data (TMY2)

• Hourly weather data for a typical year (not
  averaged)
• Includes typical extreme weather conditions
• Database includes conditions like this
• 78F DB, 66F WB
• Under these conditions, direct evaporative
  cooling does not perform well.

12 PAD (LAT) Final Room Conditions 67F
DB 74F DB, 76 RH
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Typical Meteorological Weather Data (TMY2)

• Number of hours/year with high WB
• gt 60F 378 hours
• gt 63F 146 hours
• gt 65F 33 hours
• Using a 63F DAT requires 67 more airflow than
  using 55F DAT.

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Systems that Can Use Higher SAT
Displacement Ventilation UFAD Data Centers (hot
aisle/cold aisle)
63?F - 68?F 60?F - 64?F 64?F - 80?F
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For Conventional VAV Applications

• Combine chilled water with direct evaporative
  cooling
• Advantages
• Can reduce chiller ton-hours/year by 2/3 ().
• Can deliver 55F DAT at any time.
• Dont 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

• Fan Upstream 35 less CC energy

(compared to DEC upstream of of CC)
(compared to CC upstream of DEC)
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For which types of buildings does evaporative
cooling work?

• 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 direct
• evaporative 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

• 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

• 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 dont understand how to maintain it or fix
  problems

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Maintenance and Operation

• Dry the pad out daily.
• Drain the sump weekly.
• Run the pad wild.
• Dont 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

• Scale buildup prevention
• Continuous bleed or automatic control
• Biocides

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Control Sequence

• 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

• Legionella disease
• Over humidification
• Smell
• High maintenance
• High water usage

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Typical HVAC SystemsEstimated Total Water
Consumption
Air Cooled Chiller 2.8 COP 10 Lb. H2O
Ton-Hr Ton-Hr
DX Air Conditioner 2.8 COP 10 Lb. H2O
Ton-Hr Ton-Hr
Water Cooled Chiller 5.55 COP 25 Lb. H2O
(150 ton 300 ton) Ton-Hr Ton-Hr
Evaporative Cooler 80oF O.A. 21 Lb. H2O
(Direct/Indirect) Ton-Hr Ton-Hr

• Assumptions
• Power plant overall efficiency of 35
• Average O.A. temperature of 80oF
• Cooling tower bleed rates of 20 to 33

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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

• 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

• 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
  reduction

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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 AHU Equip. Cost 9,500
6,000 Hookup/Controls 2,500
2,000 Total 12,000 8,000