In both direct and indirect systems, automatic recirculation is used for freeze protection. When the water in the collector (panel) reaches a temperature near freezing, the controller turns the pump on for a few minutes to warm the collector with water from the tank and repeats until temperatures are above freezing.
In addition there is a freeze protection valve located at the collector, when the copper piping connected to it reaches 45 degrees, it opens allowing a small amount of water to trickle out of the collector (panel) and simply runs off the roof.
A third option (not necessary) allows you to manually drain the collector (panel) of approx. 3 gallons of water if you so choose. Ask us more and we advise you.
Collectors are basically of 3 types namely Flat Plate Collectors, Evacuated tube, and Passive, thermosyphon. Solar Flat Plate collectors are the most widely used collectors for Water Heating systems because of their Simplicity in design, easy operation and Installation & they return the highest payback per dollar invested.