EVAPORATIVE COOLING FOR LAB DESIGN:Balancing the Use of Energy and Water
Megan Gunther, PE, LEED AP BD+C, WELL APBuilding Performance Consultant
Affiliated Engineers, Inc.
LEARNING OBJECTIVES
• Develop an understanding of evaporative cooling and where it is best applied
• Realize the impact evaporative cooling can have on cooling load reduction
• Gain an understanding of the energy:waternexus and how to balance energy and water for cooling
• Learn how to use tools to predict energy savings and water consumption associated with these systems
What is evaporative cooling?
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What is evaporative cooling?
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e•vap•o•ra•tive cool•ingnounreduction in temperature resulting from the evaporation of a liquid, which removes latent heat from the surface from which evaporation takes place
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• Graphical representation of the thermodynamic parameters of air•Dry-bulb temperature•Wet-bulb temperature•Dew point temperature• Relative humidity•Humidity ratio• Enthalpy
A quick introduction to psychrometric charts…
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Let’s focus on…
Dry Bulb (°F)
Wet Bulb (°F)
Enthalpy (heat or energy of the air)
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Cooling Coil Load 101
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1. OA91, 66
2. CC52, 52
1. OA Enthalpy30.65 Btu/lb da
2. SA Enthalpy21.4 Btu/lb da
San Jose, CA
Design Day Example
1. Hot outside air enters the coil
Chilled water in coil absorbs heat
2. Cool air leaves the coil
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Cooling Coil Load 101
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1. OA91, 66
2. CC52, 52
2. SA Enthalpy21.4 Btu/lb da
1. OA Enthalpy30.65 Btu/lb da
San Jose, CA
Design Day Example
Airflow(CFM) x Heat Removed =
Cooling Load (tons)
Heat removed from air
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Back to evaporative cooling.
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Stage 1: Indirect Evaporative Cooling
1. OA91, 66
“Indirect” as no water is added to air stream
Wet surface heat exchanger
2. IEC75, 61
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Stage 2: Direct Evaporative Cooling
“Direct” as water is added to air stream
Cools and humidifies the air
1. OA91, 66
2. IEC75, 61
3. DEC63, 61
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Stage 3: Supplemental Cooling Coil (when necessary)
4. CC52, 52
When air now enters the cooling coil it is significantly reduced in temperature
1. OA91, 66
2. IEC75, 61
3. DEC63, 61
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Now let’s look at what that means for cooling load.
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IDEC reduces the heat the cooling coil needs to remove
4. CC52, 52
Without IDEC, cooling coil load is sized to bring 91°F air down to 52°F
1. OA91, 66
2. IEC75, 61
3. DEC63, 61
With IDEC, cooling coil load is sized to bring
63°F air down to 52°F
Heat removed from air without IDEC
Heat removed from air with IDEC
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Benefits of evaporative cooling
• Significantly reduces (and at some hours eliminates) annual chiller energy
• Trade-off for chiller energy reduction is slight increase in fan energy• Supply fan• Scavenger fan
• Reduction in overall building energy consumption
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Evaporative works well
Evaporative may work
Evaporative not recommended
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Energy:Water Nexus
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18
Evaporative works well
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Also drought prone
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The Folsom Dam between 2010 and 2014
Cost of water & sewer are rising
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Recent national
surveys show
average
increases in
water/sewer rates
in the US range
between 7% and
9% per annum
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Water for energy…
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23
Coal
36 gal/kWh1
Nuclear
44 gal/kWh1
Natural Gas
35 gal/kWh1
Hydroelectric
65 gal/kWh2
Volumes represent high end of consumption1Source: Macknick et al. 20112Source: UNESCO-IHE 2011
4.64 gallons of water consumed for every kWh of electricity consumed in California
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Energy for water…
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Case Study 1
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New Construction Lab Building
• Location: South San Francisco, CA
• Building size: 93,000 ft2
• Baseline HVAC system: VAV reheat with water-cooled chillers
• 40% Lab, 60% Office
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Proposed Design
• Indirect evaporative cooling only
• Air-cooled chillers due to reduced chiller plant size (under 300 tons)
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Evaluating Energy
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Baseline: VAV reheat with water-cooled chillers
Proposed: VAV reheat with indirect evaporative cooling and air-cooled chillers
Baseline Proposed (IEC) Savings
Installed Chiller Capacity: 320 tons 240 tons 25%
Chiller Operating Hrs. 3,218 hrs/yr 2,343 hrs/yr 28%
Chiller + Fan Energy 134,000 kWh/yr 127,000 kWh/yr 5%
Equipment Capital Cost $ 4,330,000 $ 3,532,000 18.5%
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Evaluating Water
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Baseline: VAV reheat with water-cooled chillers
Proposed: VAV reheat with indirect evaporative cooling and air-cooled chillers
Baseline Proposed (IEC) Savings
Site Water Consumption 2,220,300 gallons 1,422,200 gallons 36%
Chiller + Fan Energy 134,000 kWh/yr 127,000 kWh/yr 5%
Source Water Consumption 621,760 gallons 589,280 gallons 6%
Total Water Consumption 2,842,060 gallons 2,011,480 gallons 30%
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Energy & Water
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0
20000
40000
60000
80000
100000
120000
140000
160000
Baseline Proposed
Ener
gy (
kWh
)
Energy Consumption
Chiller Energy Supply Fan Energy Scavenger Fan Energy
0
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
Baseline Proposed
Wat
er (
gallo
ns)
Water Consumption
Site Water Source Water
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Case Study 2
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Lab Retrofit in Existing Building
• Location: San Jose, CA
• Program size: 20,000 ft2 (within 50,000 ft2
total building area)
• Baseline HVAC system: VAV reheat with water-cooled chillers
• 100% laboratory
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Project Scope
• Retrofit existing office space into BSL2 laboratories
• New air handling system
• Existing chilled water plant (water-cooled chillers & cooling towers)
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0
40
80
120
160
200
240
280
320
360
Existing Built Out New Lab Fit Out
Co
olin
g Lo
ad (
Ton
s)Increased Cooling Demand
Chiller Plant Capacity
New lab fit out cooling demand is 140 tons
compared to the existing office fit out cooling demand
of 70 tons.
Building demand exceeds existing chiller plant capacity.
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Cooling Demand Reductions with Evaporative
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3. CC52, 52
1. OA91, 66
2. IEC75, 61
Without IDEC, cooling coil load is sized to bring 91°F air down to 52°F
With IDEC, cooling coil load is sized to bring
75°F air down to 52°F
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Building Cooling Demand
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0
40
80
120
160
200
240
280
320
360
Existing Built Out New Lab Fit Out With Evaporative Cooling
Co
olin
g Lo
ad (
Ton
s)
Chiller Plant Capacity
Evaporative cooling reduced the cooling load on the
chiller plant from 140 tons to 105 tons.
25% cooling load reduction for new lab fit out.
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Conclusions
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Conclusions
• Evaporative cooling works well in dry climate types
• While it may seem to be water intensive, evaporative cooling may actually save water
• It is important to balance energy and water savings, remembering to account holistically for site and source energy and water consumption
• Evaporative cooling can potentially decrease your peak chiller demand by 25%
• Indirect evaporative cooling coupled with air-cooled chillers can offer benefits over conventional VAV with water-cooled chillers & cooling towers in the right climate
• For retrofit projects, evaporative cooling may eliminate the need to install additional chiller capacity to support increased cooling demand
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Q & AThank you.
Megan Gunther, PE, LEED AP BD+C, WELL APBuilding Performance Consultant
Affiliated Engineers, Inc.