Drainback solar water heating systems

A drainback system is a hybrid that combines the best of open and closed loop designs. The part resembling a closed-loop system exists between the solar thermal collector and drainback tank, which is used to preheat water. The part of the drainback system between the preheat tank and the regular water tank resembles an open-loop system.

Drainback systems consist primarily of:

• a water tank,
• a smaller tank that stores heat-transfer fluid,
• a solar panel array that collects heat from the Sun, and
• a heat transfer system that transfers heat to the water tank.

A heat-transfer fluid only circulates through the system when the panels are collecting a usable amount of heat from the sun's rays. The heat transfer loop is only filled with the transfer fluid when the pump operates. At other times such as at night, the pipe loop is full of air. When working properly, this configuration prevents the freezing of the heat transfer fluid.

strengths

Drainback systems can run years without owner intervention or maintenance. They "just work". Drainback systems are less likely to cause significant damage than open-loop draindown systems, if the system fails to protect against freezing weather. Drainbacks can be turned off during high-heat days (such as when one goes on vacation) without damaging the system or causing it to lose expensive heat-transfer fluid. Also, if a heat-transfer fluid is used, it needs changed less frequently than in a standard closed-loop system; about every seven to ten years instead of every 3 to 5 years.

weaknesses

Drainback systems require the feed and return pipes between the drainback tank and collectors to be installed so that the water will completely drain out when the pump turns off; Usually an incline of 0.25inch per horizontal foot is sufficient. Furthermore, the pipes need to be mounted so there are no dips or sagging points. Drainbacks heat water slightly less efficiently than direct open-loop systems (and better than closed-loop systems that use anti-freezing solutions as heat-transfer fluid).

Drainback water heating systems in the catalog

DekkaSupply.com > Solar and Radiant Hydronic Heating > Drainback systems and modules