Wednesday, May 10, 2006

Solar Water Heating

[Green Building Guidlines-4th edition]

Water heating ranks as the 2nd largest household energy expense. To minimize this big energy user consider installing a solar domestic hot water (DHW) system. A typical solar DHW system is sized to provide up to 70% of the annual water heating load. Most water heaters operate by preheating water for a standard water heater that, when needed operates as a backup to increase the water temperature. Thus the temperature and availability of hot water is not afffected and energy is saved.

There are 2 categories of DHW systems: indirect and direct systems. Direct systems are generally only suitable for nonfreezing climates.

Systems range in cost from $1500 to over $5000.

Some Systems: Thermosyphon, Direct Circulation, Drain Back, Closed Loop, Batch/integral Collector Storage Systems

Rules of Thumb
+For maximum year-round collection the collectors should be1) tilted from the horizontal at an angle within 20 degrees of the latitude and 2) an an orientation within 45 degrees to the east or west of true south

+Collectors for any type of solar water heater should be located as close as possible to the water heater tank to minimize the amount of connecting pipe

+where freezing is possible indirect closed loop or drain-back systems are often most approriate.

+Consider pre-plumbing homes to accomodate a future solar water heating system installation.
Install pre-plumbing if the home meets the following criteria:1) the home's roof can support solar panels within 45 degrees of due south and 2) there is space for plumbing between the roof adn the utility room or other location where you might locate a solar water storage tank.

The cost of approximately $250 will save homeowners who later install such a system a lot of time and expense. To install pre-plumbing, run two 3/4" type M copper lines and 24V control wire down an interior wall from the highest point of the roof that will hold the solar panels to the utility room or location of the future solar tank. Be sure to insulate the copper lines to a minimum of R-6 and to solder all joints with lead free solder.

Web resources:
American Solar Energy Society
Solar Energy Industries Association
U.S. Department of Energy: Solar water Heating
Solar Energy International
Northeast Sustainable Energy Association: Solar Water Heating

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