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Solar Water Heating Solar Collector Active Systems Passive Systems
Passive systems have the advantage of lower initial cost and higher reliability because of the absence of pumps, controllers, or sensors. However, they have the disadvantage of possible pipe freeze in north European countries like Ireland.
The market for lower-cost passive-solar domestic water heaters (PSDWH) has been limited by the problem of freezing and bursting of insulated supply and return lines that connect to the thermal storage on or under the roof. Using insulation to protect the pressurized piping—as is current industry practice with PSDWH—severely restricts the market for PSDWH. Freeze-protection valves (FPV)—also called "dribble valves"—protect water pipes by inducing a small flow of warm water through the piping when the temperature drops below the FPV set point (typically ~35°F for piping protection), thus preventing freeze. The valves are used in many industries to protect piping from freezing in exposed locations as far north as Finland and Norway. The above diagram shows the basic collection and distribution system of a typical Irish house fitted with freeze protection.
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