Solar Domestic Hot Water
Patrick Patterson
July 16, 2003
Topics Overview
• Types of heating
• Financial analysis &
• Hardware
• Recommendations
• System applications
• Case studies
systems
Economics
Four Types of Heating Systems
Open Loop System
Active System
Closed Loop System
Passive System
Open & Closed Loop Design
Characteristics
Open 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
Closed Loop System
•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
•Less expensive type of
system, no heat exchanger
implementation
•System can freeze in cold
climates
•Easier to interface with
current system
•Pipes do not completely
drain when not in use
•Good efficiency
•Repair is expensive!
•Good for warm climates
where freezing is unlikely
•May be more difficult to
fit to existing system
•System can overheat
Closed Loop System Comparison
 Advantages
• Disadvantages
•Will not freeze
•Must purchase antifreeze
•Will not overheat
•Must implement heat
exchanger
•Good for cooler climates
where freezing is likely
•Pipes drain when system
it not working
•May be more difficult to
fit to existing system
Passive Systems
• Is very heavy
• Ugly to look at
• Will not freeze
• Utilizes thermosyphon
• 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
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.
SDHW Hardware Components
 Heat Exchanger
 Glycol (antifreeze)
 Solar Panels
 Circulation pump
 Differential Controller
 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.
• Sensors relay water
temperature data to controller
which determines if solar heated
water should be circulated to
raise water temperature.
Differential
Controller
Bolt-on sensor
High temp. differential
controller
Screw-in sensor
Glycol (Antifreeze)
 Make sure your antifreeze has corrosion inhibitors!
 Unless you wish to shorten the life of your system.
Circulation Pumps
Industrial size pump
Residential 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.
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)
http://cru.cahe.wsu.edu
= 2,109,853.2
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 #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.
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
Sources
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http://www.energy.state.or.us/renew/Solar/Support.htm
http://www.w-esco.com/cases.html
http://www.aaasolar.com/aaapics/aaapics.htm
http://www.solarexpert.com/dhw-heat.html
http://www.nrel.gov
http://www.scsolar.com/Solar_Hot_Water_and_Pool_Heating.htm
http://www.jc-solarhomes.com/solar_water_heating.htm
http://www.rerc-vt.org/shw_investing.htm
http://www.eere.energy.gov/erec/factsheets/solrwatr.pdf
http://www.solardev.com/poolmanual.php
http://cru.cahe.wsu.edu/CEPublications/eb1833e/eb1833e.html
http://www.eere.energy.gov/buildings/components/waterheating/solarhot.cfm
Home Power Issue #94 April/May 2003
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http://www.geocities.com/n3sjh/joel/
http://www.solardev.com/
http://www.lightheat.com/thermomax.htm
http://www.vascosolar.com/hotwater.html
http://www.eere.energy.gov/femp/prodtech/rightcol.html
http://www.infinitepower.org/calc_waterheating.htm
http://www.eere.energy.gov/power/consumer/hc_calculations.html
http://www.thermomax.com/Solar%20Hot%20Water.htm
http://www.phillysolar.org/pv_status3.htm
http://www.cwsenergy.com/projects.html
http://sunstar-solutions.com/ASLwaterheaters.htm
http://hem.dis.anl.gov/eehem/95/950103.html