52b8100c_na___Solar_Hot_Water__A_Primer__3
[0] Closed Loop Heat Exchanger [1] Closed loop; Cold climates [2] Very good freeze protection; Basic principles well understood by conventional plumbing trades; No problems with hard water; can be powered by PV [3] 
Most complex of all systems, with many parts; Heat exchanger & antifreeze reduce efficiency; Fluid may break down at high stagnation temperatures
Arizona Solar Center - Your Guide to Solar and Other Renewable Energy Sources in Arizona - Solar Hot Water: A Primer
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