Build Your own Passive Solar Water Heater
(Page 5 of 7)
October/November 2007
By David A. Bainbridge
If you use galvanized tanks and fittings with copper tubing, make sure the two metals are separated by appropriate non-conducting, dielectric fittings to prevent accelerated corrosion. I’ve had good luck using copper tubing, plastic dielectric connections and galvanized fittings on my tanks.
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The Heat Goes On
The only shortcoming of batch heaters is lower early morning temperatures as a result of nighttime heat loss — not a problem for people who like to shower before they go to bed, but a boosted “wake-up” factor for those who take early morning showers.
More recent research has shown we can reduce nighttime cool-down in several ways. The most effective strategy is a set of insulated lids that are closed at night and raised during the day, with reflective undersides that catch and direct additional solar energy to the tanks. But this can be difficult to operate unless the system is mounted on the ground. Automatic lids also could be made using thermal lifters commonly used to vent greenhouses. If a lid is possible, it’s a good idea: It’s easy to make an insulated hinged lid serve double duty as a reflector when it’s raised to its daytime position, and thus improve efficiency. Reflectors can extend the season into the fall and allow it to start earlier in the spring.
A simpler method to minimize heat loss relies on an ultramodern, special selective surface coating, such as Thurmalox paint. A can of spray paint sufficient to coat 50 square feet costs less than $20.
Watch Your Backup
Neglect of your conventional backup heater can result in unnecessarily high water-heating bills, in spite of the solar heater! Four common forms of neglect are inadequately insulating the room in which the conventional water heater is housed; failing to insulate the tank sufficiently (inexpensive and easy-to-install “thermal blankets” can be added in minutes); maintaining an unnecessarily high temperature setting (sometimes the fault of a bad thermostat); and allowing sediment to build up on the bottom of the tank, insulating the water from the heat source (drain sediment from the tank once a year).
Check your backup heater when you install your solar heater. In fact, even if your solar unit is only a dream at the moment, it makes good energy sense to tune up your conventional water heater right now. If it is reaching the end of its life, consider replacing it with a flash or “on demand” water heater that heats water only when it is wanted. Consumers in European countries long ago realized that it doesn’t make sense to keep 30 or 60 gallons of water hot during hours when no one needs it.
The Convenient Solution
Passive solar water heaters are cost-effective in a wide range of climates, but are easiest to build and operate in warm climates. This technology offers the energy-conscious do-it-yourselfer an attractive alternative to costly hot water and conventional energy dependence.
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