Does Evaporative Cooling Make Sense in an Arid Climate WCEC Webinar Mark Modera November 17 2016 WCEC MISSION Accelerate the development and commercialization of efficient heating cooling and energy distribution solutions through stakeholder engagement innovation RampD ID: 766102
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Does Evaporative Cooling Make Sense in an Arid Climate?WCEC Webinar Mark ModeraNovember 17, 2016
WCEC MISSION“Accelerate the development and commercialization of efficient heating, cooling, and energy distribution solutions through stakeholder engagement, innovation, R&D, education, and outreach.”
WCEC Team Established April 2007Part of the Energy Efficiency Center at UC DavisMark Modera DirectorVinod Narayanan Associate DirectorTheresa Pistochini Engineering Manager 9 Full-time Engineers1 Behavioral Scientist1 Post-Doc7 Graduate Students 10 Undergrad Students2 Support Staff KEY SPONSORS California Energy CommissionCalifornia UtilitiesFederal Agencies: DOE, DOD, NASA Corporate Affiliates Special thanks to Southern California Edison for support of work presented today
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-CoolersHow can we compare energy savings with changes in water consumption?
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 airCool ventilation air indirectly by running sump water through a fin-coilEvaporative condensers (residential)Outdoor condensing unit flows water over a refrigerant coilIndirect evaporative Dedicated Outdoor Air Systems (DOAS)Ventilation for commercial buildingsSub wet-bulb evaporative fluid coolers Chill water to below wet-bulb temperature by using chilled water to cool incoming air
Evaporative Pre-Cooler for Condenser and Ventilation AirCondenser Outlet Outside Air Return Air Supply Air Condenser Air Condenser Condenser Air Evaporative Pre-cooler Ventilation Cooling Coil
Evaporative Condenser Schematic
Indirect Evaporative Ventilation (DOAS)
Indirect Evaporative Ventilation (DOAS)
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
Sub-Wet-Bulb Evaporative Cooler Testing
How Much Water to Save How Much Energy? How has water use been characterized? Pre-Coolers Water use efficiency: [-] Addresses water that is spilled or otherwise wasted Generic Metric = [ Gallons/ton-h cooling]
How Much Water to Save How Much Energy? Water-Energy Index Water Used = Water Evaporated/WUE + Maintenance Water
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 S ub-wet-bulb chillers a versus air-cooled chiller
How Much Water to Save How Much Energy? Normalized evaporation (WEI) decreases with outdoor temperature
How Much Water to Save How Much Energy? RTU 7: 13800 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)
Maintenance Water: Full-Scale Test of Evaporative Condenser No Bleed Low Bleed (+19%)
Maintenance Water: Calcium/Magnesium in CA WaterDavis, 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
Optimized Bleed Rates – Preliminary Model Results% bleed = Vbleed/Vevaporation*100% Bleed reduces magnesium precipitation but increases calcium precipitationWe use 15% bleed in calculations below Location Mg (mg/L) Ca (mg/L) Lifespan ( yr ) Riverside 17 70 10 Eastern 17 62 12 Irvine 11 45 17 Santa Ana 14 73 10 Anaheim 20 97 7 Los Angeles 177010Long Beach22039Davis533314Hypothetical701527
How Much Water to Save How Much Energy?Evaporative Pre-Cooler Test ProtocolLaboratory testing of evaporative condenser air pre-coolersWCEC tested five pre-coolers on 4-ton York RTUResults reported to pre-cooler manufacturers
Evaporative Pre-cooler Test Report
ASHRAE Standard for Evaporative Pre-CoolersASHRAE Standard 212PMethod of Test for Determining Energy Performance and Water-Use Efficiency of Add-On Evaporative Pre-Coolers for Unitary Air Conditioning EquipmentDesigned to allow utility programs to understand performance of different evaporative pre-cooler productsMeasures Evaporative Effectiveness and applies to “generic” RTURecent development: Measure Evaporative Effectiveness at multiple face velocitiesSchedule: Vote for Public Review this year
Evaporative Pre-Cooler Test Results
Evaporative Pre-Cooler Test Results
ASHRAE Standard for Evaporative Pre-Coolers Face velocity will also impact WEI
How Much Water to Save How Much Energy?EquipmentWEI (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 Field testing vs. 11 EER RTU Sub- Wetbulb Chiller 2.9 12 5.1 Lab testing vs. air cooled chiller (1 KW/ton)
Does evaporative cooling make sense in an arid climate?PROSMore savings in arid climatesMaximum electricity reduction is coincident with peak electricity demandCONS Water consumption a concern during a drought There is always another drought coming
How can we compare Water USE with Energy SAVINGS?Evaluations above show water use of 2-12 gal/kWh savingsCalifornia average water use for generation is 1.4 -2.8 gal/kWhThermal generation estimated at <1 gal/kWhHydro electric generation estimated at >10 gal/kWhWater-use generation varies by region and timeOn-site water use is larger than off-site savings Water districts do not benefit from generation savingsa Imperfect Means of Comparison 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 betterAdds a lot of complexity Issue of inappropriate water pricing clouds this comparisonDoes 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 70-100 gallons per kWh consumedEvaporative cooling consumes 2-12 gallons/ kWh saveda 6x to 50x electricity multiplierEquivalent to getting back 6-50 kWh for investing 1 kWh Does evaporative cooling make sense in an Arid Climate?
Desalination Analysis (Con’t)Increases water cost approximately 3x a still cost effective10-15% water cost times 3 a 30-45% of electricity cost savingsDesalinization can operate at night and evaporative cooling reduces peak demand during the day Does evaporative cooling make sense in an Arid Climate? Answer to the question appears to be YES (At least if there is a supply of unpotable water e.g. an ocean)
Related Upcoming Activity
Related Upcoming Activity: Zero-Water Pre-Cooler
QUESTIONS? ANSWERS?