1. Does Evaporative Cooling Make Sense in an Arid Climate? WCEC Webinar
Mark Modera
November 17, 2016

2. WCEC MISSION
“Accelerate the development and commercialization of efficient heating, cooling, and energy distribution solutions through stakeholder engagement, innovation, R&D, education, and outreach.”

3. WCEC Team
KEY SPONSORS
California Energy Commission
California Utilities
Federal Agencies: DOE, DOD, NASA
Corporate Affiliates
Special thanks to Southern California Edison for support of work presented today
Established April 2007
Part of the Energy Efficiency Center at UC Davis
Mark Modera Director
Vinod Narayanan Associate Director
Theresa Pistochini Engineering Manager
9 Full-time Engineers
1 Behavioral Scientist
1 Post-Doc
7 Graduate Students
10 Undergrad Students
2 Support Staff

4. Does Evaporative Cooling Make Sense in an Arid Climate?
Presentation Overview
Does Evaporative Cooling Make Sense in an Arid Climate?
What do we mean by Evaporative Cooling?
How much water is consumed to save how much energy?
ASHRAE Standard 212P – Rating Performance of Evaporative Pre-Coolers
How can we compare energy savings with changes in water consumption?

5. What do we mean by Evaporative Cooling?
Evaporative pre-coolers for condensers (and ventilation air)
Reduce temperature of air entering condenser coil by direct evaporative cooling of outdoor air
Cool ventilation air indirectly by running sump water through a fin-coil
Evaporative condensers (residential)
Outdoor condensing unit flows water over a refrigerant coil
Indirect evaporative Dedicated Outdoor Air Systems (DOAS)
Ventilation for commercial buildings
Sub wet-bulb evaporative fluid coolers
Chill water to below wet-bulb temperature by using chilled water to cool incoming air

6. Evaporative Pre-Cooler for Condenser and Ventilation Air
Condenser Outlet
Condenser
Ventilation Cooling Coil
Condenser Air
Condenser Air
Evaporative Pre-cooler
Outside Air
Supply Air
Return Air

7. Evaporative Condenser Schematic
Performance/efficiency of unit more closely linked to wet bulb temperature, not a close tie to dry bulb temperature. Very successful in hot/dry climates where there is a significant difference between dry and wet bulb temperature.

8. Indirect Evaporative Ventilation (DOAS)

9. Indirect Evaporative Ventilation (DOAS)

10. Sub Wet-Bulb Evaporative Chillers
Use pre-cooling of outdoor air to drop wet bulb temperature
Allow production of water (and air) at temperature lower than outdoor-air wet-bulb temperature

11. Sub-Wet-Bulb Evaporative Cooler Testing
Nexajoule

12. How Much Water to Save How Much Energy?
How has water use been characterized?
Pre-Coolers
Water use efficiency:
𝑊𝑈𝐸= 𝑚 𝑤𝑎𝑡𝑒𝑟−𝑒𝑣𝑎𝑝𝑜𝑟𝑎𝑡𝑒𝑑 𝑚 𝑤𝑎𝑡𝑒𝑟−𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 [-]
Addresses water that is spilled or otherwise wasted
Generic Metric
𝑚 𝑤𝑎𝑡𝑒𝑟−𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 𝑡𝑜𝑛 𝑐𝑜𝑜𝑙𝑖𝑛𝑔 𝑑𝑒𝑙𝑖𝑣𝑒𝑟𝑒𝑑 = 𝑚 𝑤𝑎𝑡𝑒𝑟−𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 𝑡𝑜𝑛 −ℎ 𝑐𝑜𝑜𝑙𝑖𝑛𝑔 𝑑𝑒𝑙𝑖𝑣𝑒𝑟𝑒𝑑
[Gallons/ton-h cooling]

13. How Much Water to Save How Much Energy?
Water-Energy Index
𝑊𝑎𝑡𝑒𝑟 𝐸𝑛𝑒𝑟𝑔𝑦 𝐼𝑛𝑑𝑒𝑥= 𝑊𝑎𝑡𝑒𝑟 𝑈𝑠𝑒𝑑 𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑖𝑡𝑦 𝑆𝑎𝑣𝑒𝑑
𝑊𝑎𝑡𝑒𝑟 𝐸𝑛𝑒𝑟𝑔𝑦 𝐼𝑛𝑑𝑒𝑥= 𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑡𝑜𝑛 ℎ 𝑘𝑤 𝑡𝑜𝑛 𝑅𝑒𝑓 − 𝑘𝑤 𝑡𝑜𝑛 𝐸𝑣𝑎𝑝
𝑊𝑎𝑡𝑒𝑟 𝐸𝑛𝑒𝑟𝑔𝑦 𝐼𝑛𝑑𝑒𝑥= 𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑘𝑊ℎ 𝑠𝑎𝑣𝑒𝑑
Water Used = Water Evaporated/WUE + Maintenance Water

14. How Much Water to Save How Much Energy?
Evaporated Water
Key means of cooling
Pre-Cooler: Determined by condenser fan flowrate, wet bulb depression and evaporative effectiveness
Maintenance Water
Required to maintain equipment longevity
Depends on incoming water quality
Research suggests that most manufacturers use too much maintenance water
Energy Savings
With/Without analysis for evaporative pre-coolers on RTUs
Ventilation cooling with DOAS systems vs. RTU
Indirect evaporative cooling as RTU replacement
Sub-wet-bulb chillers a versus air-cooled chiller

15. How Much Water to Save How Much Energy?
𝑊𝑎𝑡𝑒𝑟 𝐸𝑛𝑒𝑟𝑔𝑦 𝐼𝑛𝑑𝑒𝑥= 𝑔𝑎𝑙𝑙𝑜𝑛𝑠 𝑡𝑜𝑛 ℎ 𝑘𝑤 𝑡𝑜𝑛 𝑅𝑒𝑓 − 𝑘𝑤 𝑡𝑜𝑛 𝐸𝑣𝑎𝑝
Normalized evaporation (WEI) decreases with outdoor temperature

16. How Much Water to Save How Much Energy?
RTU 7: gal/1620 kWh = 8.5 gal/kWh-saved (actual 188% bleed)
4800 gal/1620 kWh = 2.9 evaporated-gal/kWh-saved
5500 gal/1620 kWh = 3.4 gal/kWh-saved (15% bleed)

17. Maintenance Water: Full-Scale Test of Evaporative Condenser
No Bleed Low Bleed (+19%)

18. Maintenance Water: Calcium/Magnesium in CA Water
Davis, CA
Water hardness is made up of different combinations of Ca and Mg
Our lab tests indicate that optimal maintenance water use varies significantly between Ca and Mg

19. Optimized Bleed Rates – Preliminary Model Results
Location
Mg (mg/L)
Ca (mg/L)
Lifespan (yr)
Riverside 17 70 10
Eastern 62 12
Irvine 11 45
Santa Ana 14 73
Anaheim 20 97 7
Los Angeles
Long Beach 2 39
Davis 53 33
Hypothetical 15 27
a Average steady state sump concentration (mM=milimolar)
b Calculated based on a mass balance approach for steady state conditions for 1000 cycles (mols is similar to a unit of mass)
c Calculated based on a mass balance approach for steady state conditions; unprecipitated component is in sump
d Determined by difference between initial unused coil mass and final coil+scale mass
e Xray diffraction was used to assess mineral phase; these results are preliminary
% bleed = Vbleed/Vevaporation*100%
Bleed reduces magnesium precipitation but increases calcium precipitation
We use 15% bleed in calculations below

20. How Much Water to Save How Much Energy?
Evaporative Pre-Cooler Test Protocol
Laboratory testing of evaporative condenser air pre-coolers
WCEC tested five pre-coolers on 4- ton York RTU
Results reported to pre-cooler manufacturers

21. Evaporative Pre-cooler Test Report

22. ASHRAE Standard for Evaporative Pre-Coolers
ASHRAE Standard 212P
Method of Test for Determining Energy Performance and Water-Use Efficiency of Add-On Evaporative Pre-Coolers for Unitary Air Conditioning Equipment
Designed to allow utility programs to understand performance of different evaporative pre-cooler products
Measures Evaporative Effectiveness and applies to “generic” RTU
Recent development: Measure Evaporative Effectiveness at multiple face velocities
Schedule: Vote for Public Review this year

23. Evaporative Pre-Cooler Test Results

24. Evaporative Pre-Cooler Test Results

25. ASHRAE Standard for Evaporative Pre-Coolers
Face velocity will also impact WEI

26. How Much Water to Save How Much Energy?
Equipment
WEI (gallons/KWh w/15% bleed)
Notes
Min
Max
Avg
Evap Pre-Cooler
4.3
10.9
7.6
Lab testing on 11 EER RTU
Evaporative Condenser
6.1 17
11.6
Lab testing vs. air-cooled R-22
IDEC DOAS
1.9
6.5
3.5
Field testing vs. 11 EER RTU
IDEC RTU Replacement (0% OA)
7.5 29 13
Sub-Wetbulb Chiller
2.9 12
5.1
Lab testing vs. air cooled chiller (1 KW/ton)

27. Does evaporative cooling make sense in an arid climate?
PROS
More savings in arid climates
Maximum electricity reduction is coincident with peak electricity demand
CONS
Water consumption a concern during a drought
There is always another drought coming

28. How can we compare Water USE with Energy SAVINGS?
Does evaporative cooling make sense in an Arid Climate?
How can we compare Water USE with Energy SAVINGS?
Evaluations above show water use of 2-12 gal/kWh savings
California average water use for generation is gal/kWh
Thermal generation estimated at <1 gal/kWh
Hydro electric generation estimated at >10 gal/kWh
Water-use generation varies by region and time
On-site water use is larger than off-site savings
Water districts do not benefit from generation savings
a Imperfect Means of Comparison

29. Why not compare Water COST with Energy COST Savings?
Does evaporative cooling make sense in an Arid Climate?
Why not compare Water COST with Energy COST Savings?
Water Costs Roughly 10-15% of the value of Energy Cost Savings
Does not count demand charges
Would make it look better
Adds a lot of complexity
Issue of inappropriate water pricing clouds this comparison

30. Does evaporative cooling make sense in an Arid Climate?
Desalination is Worst-Case Water-Use Scenario
(but allows us to compare apples with apples)
Desalination produces gallons per kWh consumed
Evaporative cooling consumes 2-12 gallons/ kWh saved
a 6x to 50x electricity multiplier
Equivalent to getting back 6-50 kWh for investing 1 kWh

31. Does evaporative cooling make sense in an Arid Climate?
Desalination Analysis (Con’t)
Increases water cost approximately 3x a still cost effective
10-15% water cost times 3 a 30-45% of electricity cost savings
Desalinization can operate at night and evaporative cooling reduces peak demand during the day
Answer to the question appears to be YES
(At least if there is a supply of unpotable water e.g. an ocean)

32. Related Upcoming Activity
Dispatchable Pre-coolers for Demand Response

33. Related Upcoming Activity: Zero-Water Pre-Cooler

34. QUESTIONS? ANSWERS?