Solar Domestic Hot Water Patrick Patterson July 16, 2003
Types of heating systems Hardware System applications Financial analysis & Economics Recommendations Case studies Topics Overview
Four Types of Heating Systems Open Loop System Closed Loop System Active System Passive System
Open & Closed Loop Design Characteristics Open Loop System Closed Loop System • Solar heated water flows directly into existing water heater, or secondary storage tank • Used in household and pool applications • Water flowing across panels is what comes out of the faucet • Antifreeze (glycol) is used along with a heat exchanger to transfer heat • More common in household applications • Liquid flowing across panels does not mix with faucet water
Open Loop System Comparison • Advantages • Disadvantages • System can freeze in cold climates • System can overheat • Pipes do not completely drain when not in use • Repair is expensive! • May be more difficult to fit to existing system • Less expensive type of system, no heat exchanger implementation • Easier to interface with current system • Good efficiency • Good for warm climates where freezing is unlikely
Closed Loop System Comparison • Advantages • Disadvantages • Must purchase antifreeze • Must implement heat exchanger • May be more difficult to fit to existing system • Will not freeze • Will not overheat • Good for cooler climates where freezing is likely • Pipes drain when system it not working
Passive Systems • Is very heavy • Ugly to look at • Will not freeze • Utilizes thermosyphon • Not very efficient—especially in low intensity sunlight
Open Loop SystemHousehold Application Solar heated water runs directly into a secondary storage tank, or an existing hot water heater.
Open Loop SystemSwimming Pool Application Open loop drain back systems pumps pool water up to panels and gravity brings it back down
Closed Loop SystemHousehold Application Closed loop system in which glycol is heated and circulated through a heat exchanger to transfer heat to water
Closed Loop SystemPool Application Closed loop systems prevent chemically saturated pool water from coming in contact with solar panels.
SDHW Hardware Components • Heat Exchanger • Solar Panels • Differential Controller • Glycol (antifreeze) • Circulation pump • Pipes & Sensors
Heat Exchangers • Used to transfer heat from exchange medium to water
Solar Panels http://www.vascosolar.com
Solar Panels Futuristic looking Cold day in Vermont
Differential Controllers & Sensors • Differential Controllers allow flow of solar heated water into storage tank if temperature differential is within a specified range. Differential Controller High temp. differential controller • Sensors relay water temperature data to controller which determines if solar heated water should be circulated to raise water temperature. Bolt-on sensor Screw-in sensor
Glycol (Antifreeze) • Make sure your antifreeze has corrosion inhibitors! • Unless you wish to shorten the life of your system.
Circulation Pumps • Pumps circulate water through solar panels. They are activated by the differential controller when it senses too large a differential between hot water supply and water coming from panels. Industrial size pump Residential pumps Two types of pumps: AC & DC
Pipes • Pipes should be well insulated to maximize efficiency • Preferably made from copper
SDHW Economics • 30% of household energy consumption goes to heating water • Solar water heaters pay for themselves in 3-10 years! (depending on usage) • Total cost over product life is less than all other water heating systems • Oregon offers a tax credit of up $1,500 for residential solar energy projects. • Additional property value resulting from installation of solar equipment is exempt from property taxes under Oregon state law until December 31, 2012 http://www.energy.state.or.us
Calculation of Hot Water Costs • (gallons/wk) x (52 wks./yr.) = gallons/yr. • (69.5) x (52) = 3,614 • (gallons/yr.) x (8.34 lbs./gal.) = lbs/yr. • (3,614) x (8.34) = 30,140.8lbs/yr. • (lbs/yr.) x ((temp. rise x (1 btu/of/lb h20)) = btus/yr • (30,140) x ((120-50) * 1) = 2,109,853.2 http://cru.cahe.wsu.edu
Calculation of Hot Water Costs • (btus/yr) / (tank eff.= 0.85) = total btus/yr. (required) • (2,109,853.2) / (0.85) = 2,482,180 • (Total Btus/yr) / (3413 Btus/kWh) = total kWh/yr. (required) • (2,482,180) / (3413) = 727.1 (2 kWh/day) • (Total kWh/yr.) x (Cost/kWh) = total cost/yr. (electric) • (727.1) x (0.09) = $65.44 = $5.45/month http://cru.cahe.wsu.edu
How Much Do You Spend? Compiled by the Oregon State University Extension Program June 1997.
How Much Will SDHW Help? • (collector size) x (agsr.) = energy received • (energy received) x (efficiency) = kwh/day • (required kwh/day) – (recvd. Kwh/day)=savings • (4’x8’ or 2.97m2) x (5.6kwh/m2) = 16.6kWh/day potential contribution to H20 heating needs.
How Much Will You Save? • http://www.infinitepower.org/calc_waterheating.htm
Domestic Hot Water Heating Statistics Energy losses in electric water heaters Energy losses in gas water heaters
Itemized Part List http://www.solardev.com
Recommended System http://www.solar-components.com/actvdhw.htm
Case Study #1Joyce & Andy Melrose Park, PA. Two 3’x7’ roof mounted drain-down solar hot water collectors provide hot water on sunny days. On cloudy days a gas hot water heater is available to assist if needed. A water submeter measures all domestic hot water. A gas submeter measures all gas used by the MorFlo water heater
Case Study #2Gaithersburg, MD. This 400 square foot array heats an indoor swimming pool in Gaithersburg saving the owner substantially on her propane bill each month. The array was originally to be located on the roof of the pool house, but we chose to locate it on top of a 50 foot storage shed about 170 feet from the house. Pipes were trenched from the array to the pool pump room where the solar heat is transferred to the pool water via heat exchanger.
Conclusion & Closing Thoughts • Solar heating is efficient • Pays for itself in less time than any PV systems • Tax incentives are more appealing PV systems • Carefully consider your times of hot water consumption
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