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Does Evaporative Cooling Make Sense in an Arid Climate? WCEC Webinar
Mark Modera November 17, 2016
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WCEC MISSION “Accelerate the development and commercialization of efficient heating, cooling, and energy distribution solutions through stakeholder engagement, innovation, R&D, education, and outreach.”
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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
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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?
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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
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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
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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.
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Indirect Evaporative Ventilation (DOAS)
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Indirect Evaporative Ventilation (DOAS)
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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
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Sub-Wet-Bulb Evaporative Cooler Testing
Nexajoule
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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]
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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
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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
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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
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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)
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Maintenance Water: Full-Scale Test of Evaporative Condenser
No Bleed Low Bleed (+19%)
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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
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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
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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
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Evaporative Pre-cooler Test Report
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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
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Evaporative Pre-Cooler Test Results
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Evaporative Pre-Cooler Test Results
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ASHRAE Standard for Evaporative Pre-Coolers
Face velocity will also impact WEI
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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)
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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
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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
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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
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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
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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)
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Related Upcoming Activity
Dispatchable Pre-coolers for Demand Response
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Related Upcoming Activity: Zero-Water Pre-Cooler
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QUESTIONS? ANSWERS?
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