Drainback

First developed in the 1980’s, the Closed-Loop Drainback Systems have proven themselves to be reliable and highly efficient. They are essentially a non-pressurized closed-loop system that uses water as a heat transfer fluid (a minor glycol mix in freezing areas). A small drainback reservoir is added to the collector loop, and the system is filled with water/mix to the top of the reservoir. Because the collectors are located above the reservoir, they remain dry when the system’s pump(s) is off.
When the collectors are hotter than the water in the storage tank, the system activates automatically to heat the water. Then, when the water in the storage tank is hotter than the collectors, or reaches a pre-determined cut-off temperature, the system shuts down the pump and the water drains back to the reservoir. The panels are then empty. They are installed with a slight tilt, 1/4 inch per lateral foot to allow full drainback when not in use.
Problems addressed:
– Freeze protection is gravity based with a small amount of food based glycol.
– The pump is shut down when the water temperature is maxed out, and at night, draining all excess water/mix from the collectors
– Fewer components than other systems, reducing the risk of problems, and lowering any repair/ replacement costs.

drainback-pic

drainback-with-storage-tank

Some Areas or Graphics Reprinted with Permission: Silicon Solar Inc,  Copyright 2008-2009 All Rights Reserved  DogStar Solar Inc, Copyright 2009

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