Solar Domestic Hot Water Patrick Patterson July 16, 2003

Topics Overview Types of heating systems Types of heating systems Hardware Hardware System applications System applications Financial analysis & Economics Financial analysis & Economics Recommendations Recommendations Case studies Case studies

Four Types of Heating Systems Closed Loop System Open Loop System Active System Passive System

Open & Closed Loop Design Characteristics Solar heated water flows directly into existing water heater, or secondary storage tankSolar heated water flows directly into existing water heater, or secondary storage tank Used in household and pool applicationsUsed in household and pool applications Water flowing across panels is what comes out of the faucetWater flowing across panels is what comes out of the faucet Antifreeze (glycol) is used along with a heat exchanger to transfer heatAntifreeze (glycol) is used along with a heat exchanger to transfer heat More common in household applicationsMore common in household applications Liquid flowing across panels does not mix with faucet waterLiquid flowing across panels does not mix with faucet water Open Loop System Closed Loop System

Open Loop System Comparison Less expensive type of system, no heat exchanger implementationLess expensive type of system, no heat exchanger implementation Easier to interface with current systemEasier to interface with current system Good efficiencyGood efficiency Good for warm climates where freezing is unlikelyGood for warm climates where freezing is unlikely System can freeze in cold climatesSystem can freeze in cold climates System can overheatSystem can overheat Pipes do not completely drain when not in usePipes do not completely drain when not in use Repair is expensive!Repair is expensive! May be more difficult to fit to existing systemMay be more difficult to fit to existing system Disadvantages Disadvantages Advantages Advantages

Closed Loop System Comparison Will not freezeWill not freeze Will not overheatWill not overheat Good for cooler climates where freezing is likelyGood for cooler climates where freezing is likely Pipes drain when system it not workingPipes drain when system it not working Must purchase antifreezeMust purchase antifreeze Must implement heat exchangerMust implement heat exchanger May be more difficult to fit to existing systemMay be more difficult to fit to existing system Disadvantages Disadvantages Advantages Advantages

Passive Systems Is very heavy Is very heavy Ugly to look at Ugly to look at Will not freeze Will not freeze Utilizes thermosyphon Utilizes thermosyphon Not very efficient—especially in low intensity sunlight Not very efficient—especially in low intensity sunlight

Open Loop System Household Application Solar heated water runs directly into a secondary storage tank, or an existing hot water heater.

Open Loop System Swimming Pool Application Open loop drain back systems pumps pool water up to panels and gravity brings it back down Open loop drain back systems pumps pool water up to panels and gravity brings it back down

Closed Loop System Household Application Closed loop system in which glycol is heated and circulated through a heat exchanger to transfer heat to water

Closed Loop System Pool Application Closed loop systems prevent chemically saturated pool water from coming in contact with solar panels. Closed loop systems prevent chemically saturated pool water from coming in contact with solar panels.

SDHW Hardware Components Heat Exchanger Heat Exchanger Solar Panels Solar Panels Differential Controller Differential Controller Glycol (antifreeze) Glycol (antifreeze) Circulation pump Circulation pump Pipes & Sensors Pipes & Sensors

Heat Exchangers Used to transfer heat from exchange medium to water Used to transfer heat from exchange medium to water

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 Controllers allow flow of solar heated water into storage tank if temperature differential is within a specified range. Sensors relay water temperature data to controller which determines if solar heated water should be circulated to raise water temperature. Sensors relay water temperature data to controller which determines if solar heated water should be circulated to raise water temperature. Screw-in sensor Screw-in sensor Bolt-on sensor Bolt-on sensor Differential Controller Differential Controller High temp. differential controller

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. 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 Pipes should be well insulated to maximize efficiency Preferably made from copper Preferably made from copper

SDHW Economics 30% of household energy consumption goes to heating water 30% of household energy consumption goes to heating water Solar water heaters pay for themselves in 3-10 years! (depending on usage) 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 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. 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 Additional property value resulting from installation of solar equipment is exempt from property taxes under Oregon state law until December 31,

Calculation of Hot Water Costs (gallons/wk) x (52 wks./yr.) = gallons/yr. (gallons/wk) x (52 wks./yr.) = gallons/yr. (69.5) x (52) = 3,614 (69.5) x (52) = 3,614 (gallons/yr.) x (8.34 lbs./gal.) = lbs/yr. (gallons/yr.) x (8.34 lbs./gal.) = lbs/yr. (3,614) x (8.34) = 30,140.8lbs/yr. (3,614) x (8.34) = 30,140.8lbs/yr. (lbs/yr.) x ((temp. rise x (1 btu/ o f/lb h 2 0)) = btus/yr (lbs/yr.) x ((temp. rise x (1 btu/ o f/lb h 2 0)) = btus/yr (30,140) x ((120-50) * 1) = 2,109,853.2 (30,140) x ((120-50) * 1) = 2,109,

Calculation of Hot Water Costs (btus/yr) / (tank eff.= 0.85) = total btus/yr. (required) (btus/yr) / (tank eff.= 0.85) = total btus/yr. (required) (2,109,853.2) / (0.85) = 2,482,180 (2,109,853.2) / (0.85) = 2,482,180 (Total Btus/yr) / (3413 Btus/kWh) = total kWh/yr. (required) (Total Btus/yr) / (3413 Btus/kWh) = total kWh/yr. (required) (2,482,180) / (3413) = (2 kWh/day) (2,482,180) / (3413) = (2 kWh/day) (Total kWh/yr.) x (Cost/kWh) = total cost/yr. (electric) (Total kWh/yr.) x (Cost/kWh) = total cost/yr. (electric) (727.1) x (0.09) = $65.44 = $ 5.45/month (727.1) x (0.09) = $65.44 = $ 5.45/month

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 (collector size) x (agsr.) = energy received (energy received) x (efficiency) = kwh/day (energy received) x (efficiency) = kwh/day (required kwh/day) – (recvd. Kwh/day)=savings (required kwh/day) – (recvd. Kwh/day)=savings (4’x8’ or 2.97m 2 ) x (5.6kwh/m 2 ) = 16.6kWh/day potential (4’x8’ or 2.97m 2 ) x (5.6kwh/m 2 ) = 16.6kWh/day potential contribution to H 2 0 heating needs. contribution to H 2 0 heating needs.

How Much Will You Save?

Domestic Hot Water Heating Statistics Energy losses in electric water heatersEnergy losses in gas water heaters

Itemized Part List

Recommended System

Case Study #1 Joyce & 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 #2 Gaithersburg, 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. 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 consumption

Sources Home Power Issue #94 April/May 2003 Home Power Issue #94 April/May