Solar Domestic Hot Water

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Solar Domestic Hot Water

• Patrick Patterson
• July 16, 2003

2
Topics Overview

• Types of heating systems
• Hardware
• System applications

• Financial analysis Economics
• Recommendations
• Case studies

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

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Open Loop System Comparison

• Disadvantages

• Advantages

• 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

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Closed Loop System Comparison

• Disadvantages

• Advantages

• 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

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Passive Systems

• Is very heavy
• Ugly to look at
• Will not freeze
• Utilizes thermosyphon
• Not very efficientespecially in low intensity
  sunlight

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

• Open loop drain back systems pumps pool water
  up to panels and gravity brings it back down

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Closed Loop SystemHousehold Application
Closed loop system in which glycol is heated and
circulated through a heat exchanger to transfer
heat to water
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Closed Loop SystemPool Application
Closed loop systems prevent chemically
saturated pool water from coming in contact with
solar panels.
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SDHW Hardware Components

• Heat Exchanger
• Solar Panels
• Differential Controller

• Glycol (antifreeze)
• Circulation pump
• Pipes Sensors

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Heat Exchangers

• Used to transfer heat from exchange medium to
  water

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Solar Panels
http//www.vascosolar.com
15
Solar Panels
Futuristic looking
Cold day in Vermont
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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.

Screw-in sensor
Bolt-on sensor
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Glycol (Antifreeze)

• Make sure your antifreeze has corrosion
  inhibitors!
• Unless you wish to shorten the life of your
  system.

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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
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Pipes

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

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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
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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
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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
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How Much Do You Spend?
Compiled by the Oregon State University Extension
Program June 1997.
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How Much Will SDHW Help?

• (collector size) x (agsr.) energy received
• (energy received) x (efficiency) kwh/day
• (required kwh/day) (recvd. Kwh/day)savings
• (4x8 or 2.97m2) x (5.6kwh/m2) 16.6kWh/day
  potential
• contribution to H20 heating needs.

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How Much Will You Save?

• http//www.infinitepower.org/calc_waterheating.htm

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Domestic Hot Water Heating Statistics
Energy losses in electric water heaters
Energy losses in gas water heaters
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Itemized Part List
http//www.solardev.com
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Recommended System
http//www.solar-components.com/actvdhw.htm
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Case Study 1Joyce Andy Melrose Park, PA.
Two 3x7 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
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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.

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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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Sources

• 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_He
  ating.htm
• http//www.jc-solarhomes.com/solar_water_heating.h
  tm
• http//www.rerc-vt.org/shw_investing.htm
• http//www.eere.energy.gov/erec/factsheets/solrwat
  r.pdf
• http//www.solardev.com/poolmanual.php
• http//cru.cahe.wsu.edu/CEPublications/eb1833e/eb1
  833e.html
• http//www.eere.energy.gov/buildings/components/wa
  terheating/solarhot.cfm
• Home Power Issue 94 April/May 2003

• 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_calcu
  lations.html
• http//www.thermomax.com/Solar20Hot20Water.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