indirect solar water heater
Active, closed loop solar water heater: A large, flat panel called a flat plate collector is connected to a tank called a solar storage/backup water heater by two pipes. One of these pipes is runs through a cylindrical pump into the bottom of the tank, where it becomes a coil called a double-wall heat exchanger. This coil runs up through the tank and out again to the flat plate collector. Antifreeze fluid runs only through this collector loop. Two pipes run out the top of the water heater tank; one is a cold water supply into the tank, and the other sends hot water to the house.
An indirect solar water heater, also known as an active closed-loop system, is a solar heater that circulates a fluid other than water (such as diluted antifreeze) through a collector. The collected heat is transferred to the household water supply using a heat exchanger. Indirect solar water heaters are popular in climates prone to freezing temperatures.