Performance of Solar Water Heating Systems in the United States Danny Parker & Camilo Gil Florida Solar Energy Center ACEEE Hot Water Forum June 2009, Asilomar,, California
Rebate situation in Florida 30% Federal Tax Credit Residential: $500 per system rebate Commercial: $15/1000 Btu of rated collector capacity Utilities: SDHW with load control is attractive FPL currently none, but under development Progress Energy: $450 with load control Gulf Power: $1000
HWS Lab: Efficiency Results: (COP) March 10- June 3, 2009
Plumbing heat losses pre.
Analysis: Impact of Pipe Insulation Pipes were already insulated exterior in pre period Located pre and post days where day and day prior had similar weather: temperature and insolation Analyzed change to system COP from insulating interior piping
Importance of Pipe Insulation Non-solar systems: no measureable change Dramatic impact on solar systems Flat plate differential system: COP increases from 5.54 to 8.30 Solar fraction from 84% to 89% PV pumped system: COP from 3.69 to 6.06 Solar fraction from 76% to 85% ICS system: COP from 1.86 to 2.12 Solar fraction from 51% to 58% ½ closed cell foam insulation: R-3; recommend 1 insulation be used on solar circulation piping
What will make a more effective solar program for California? Find a way to move to tankless gas or fully condensing auxiliary gas water heater rather than 2 tank system (flue/piping losses) Minimize length of piping runs Insulate piping runs with at least 1 foam insulation Consider that optimal tilt is greater than latitude since winter water heating loads are greater than summer ones Minimize pump circulation power; PV pumps or variable speed AC pumps Water Heating kw Demand 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 2 4 6 8 10 12 14 16 18 20 22 24 Time of Day: EST Jan: 7.8 kwh/d Feb: 7.6 kwh/d Mar: 7.5 kwh/d Apr: 6.2 kwh/d May: 5.6 kwh/d Jun: 5.1 kwh/d Jul: 4.8 kwh/d n= 186
January DHW Demand Profiles Electric Resistance= 7.7 kwh/day Heat Recovery System = 5.1 KWh/Day (34% reduction) Solar = 3.8 kwh/day (51% reduction) Differences of both significant at 99% level Average Daily DHW kw 0.7 0.6 0.5 0.4 0.3 0.2 0.1 FPC Residential Monitoring Project: January DHW Demand Profile: DHW System Type Peak Electric Resistance (n=153): 7.7 kwh/d HRU (n=26): 8.7 kwh/d Solar (n=4): 3.8 kwh/d 0.0 0 2 4 6 8 10 12 14 16 18 20 22 24 Hour of Day (EST)
July DHW Demand Profile 0.7 Electric Resistance= 5.0 kwh/day 35% lower than Jan. Heat Recovery System = 3.5 kwh/d 40% reduction Average Daily DHW kw 0.6 0.5 0.4 0.3 0.2 Electric Resistance (n=153): 5.0 kwh/day HRU (n=26): 3.5 kwh/d Solar (n=4): 2.3 kwh/d Peak Solar= 2.3 kwh/d 0.1 54% reduction 0.0 0 2 4 6 8 10 12 14 16 18 20 22 24 Hour of Day (EST)
Objectives To simulate performance of solar water heating systems in detail around the United States Latest simulation tools (TRNSYS and EGUSA) indexed to real world performance Hourly simulation Use most recent TMY3 weather data Include variation in water heating loads with mains water temperature Evaluate popular system types
Simulating Solar Water Heating Single family house 3 bedrooms, 2 stories, 1800 sqft No shade from trees or adjacent buildings Roof: 6/12 pitch; 27 o tilt Azimuth: 180 degrees EGUSA software; prediction based on TRNSYS
Simulating Solar Water Heating
Varying mains water temperature with climate 84 82 Average water temperature Mean: 75.6 o 80 Temperature ( o F) 78 76 74 72 70 68 66 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month
Assumptions: Hot Water Equipment Assumptions: Hot Water Equipment Types of Conventional Systems: Natural Gas Storage Tank EF = 0.59 Electric Storage Tank EF = 0.9 Location: Garage Capacity: 50 gallons Consumption: 60 gallons per day Set Temp: 120 F ASHRAE 90.2 draw profile Inlet water temperature varies with location Simulate 212 TMY3 locations and determine contours Detailed spreadsheet with results for individual locations 68 California locations simulated to generate contours for CA
Assumptions: Solar Systems Integrated Collector Storage (40 gal) Connects to standard gas tank in garage Cover area: 30.1 sqft Heat loss coefficient: 17.1 Btu/hr-F Transmittance: 0.82 Capacity: 41.2 gallons Not available in any month temps < 28 F
Solar system: Flat Plate Surface area: 40.0 sqft or 64.0 sqft Loss coefficient: 0.734 Btu/hr sqft F Transmittance absorptance: 0.78 Storage tank volume: 80 gallons Two tank system with natural gas Heat exchanger correction factor: 0.88 120 Watt pump
Simulated annual energy consumption in kwh for a standard electric water heater in the continental U.S.
Simulated annual fractional energy savings (%) for a 32sqft ICS water heater with standard electric as backup with respect to the standard electric alone
Simulated annual fractional energy savings for a 40sqft closed loop solar water heater with standard electric as backup with respect to standard electric in the United States
Simulated annual fractional energy savings (%) for a 64sqft closed loop water heater with standard electric as backup with respect to the standard electric in the United States
Simulated annual absolute energy savings (kwh) for a 40sqft closed loop water heater with standard electric as backup with respect to the standard electric
Simulated annual energy consumption in therms for a standard gas water heater in the continental United States
Simulated annual fractional energy savings (%) for a 32sqft ICS water heater with standard gas as backup with respect to the standard gas in the United States
Simulated annual fractional energy savings (%) for a 40sqft closed loop water heater with standard gas as backup with respect to the standard gas in the United States
Simulated annual fractional energy savings (%) for a 64sqft closed loop water heater with standard gas as backup with respect to the standard gas alone in the continental U.S.
U.S. Analysis: Conclusions for Electric U.S. Analysis: Conclusions for Electric Avg. Electricity: 3800 kwh/yr [2130-5050 kwh] Varies by more than 2:1 from lowest to highest energy Savings by Prototype System Economics depend on absolute savings ICS system: 39% savings; 17% - 73% Best performance in non-freezing climates Closed loop: 40 sqft system: 58% saving; 35% to 91% Highest solar fractions in FL, Western Texas, SW, SW CA Highest absolute savings in northern NM, AZ, UT, CO, NV Closed loop: 64 sqft system: 71%; 48% to 96% Large absolute savings all over the U.S.
U.S. Analysis: Conclusions for Gas U.S. Analysis: Conclusions for Gas Avg. Electricity: 210 therms/yr [122 275 therms] Varies by more than 2:1 from lowest to highest energy Savings by Prototype System with a two-tank system Economics depend on absolute savings ICS system: 25% savings; 11% - 47% Best performance in non-freezing climates Closed loop: 40 sqft system: 40% saving; 23% to 67% Highest solar fractions in FL, Western Texas, SW, SW CA Highest absolute savings in northern NM, AZ, UT, CO, NV Closed loop: 64 sqft system: 53%; 24% to 77% Large absolute savings all over the U.S. Better performance with solar systems with tankless, non center-flue system: +15-20% from this choice
Results for all California TMY3s
Simulated annual energy consumption in kwh for a standard electric water heater in California
Simulated annual energy consumption in therms for a standard gas water heater in California
Simulated annual fractional energy savings (%) for a 32sqft ICS water heater with standard gas as backup with respect to the standard gas in California
Simulated annual fractional energy savings (%) for a 40sqft closed loop water heater with standard gas as backup with respect to the standard gas alone in California
Simulated annual fractional energy savings (%) for a 64sqft closed loop water heater with standard gas as backup with respect to the standard gas alone in California
CA analysis: Conclusions: Gas CA analysis: Conclusions: Gas Average Natural Gas Use: 180 therms/yr [64-200] Solar Fraction by Prototype System ICS system: 36% savings; 21% - 50% Best performance in Southern California Closed loop: 40 sqft system 53% average; 34% to 69% Closed loop: 64 sqft system 65%; 48% to 78% Highest absolute savings in cold/ sunny places: Bishop/Sandberg. Santa Maria one of best places in U.S. Better performance with tankless gas or fully condensing system if practical
CA analysis: Conclusions: Electric Avg. Electricity: 3300 kwh/yr [2150-4640 kwh] Savings by Prototype System ICS system: 56% savings; 33% - 73% Closed loop: 40 sqft system 73% average; 51% to 91% Closed loop: 64 sqft system 84%; 66% to 96% Better performance with solar systems because of less heat loss from auxiliary tank