Freeze protection valves (FPV) have been used in direct solar domestic water heating systems (SDWH) in mild climates to prevent freeze damage of the collector. Pipe freezing in passive systems can also be prevented using these valves. A limiting factor on where FPVs might be used is the amount of water consumed through use of the valve. An experiment was performed to determine the average flow rate through FPVs over a range of air and water supply temperatures. The experimental flow rate data was then used in a simulation to determine the annual flow through FPVs for 215 sites throughout the continental United States. A correlation between the annual flow and the site air-freezing index (AFI) was then developed in order to increase the spatial data density to over 3,300 sites using AFI data. U.S. maps were generated to display the results graphically. The maps show that there is great potential to increase the market of direct and passive SDWH by using FPV versus using pipe insulation only, although valve reliability remains a concern.
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