Freeze protection of Solar Water Heater

Freeze protection measures prevent damage to the system due to the expansion of freezing transfer fluid. Drainback systems drain the transfer fluid from the system when the pump stops. Many indirect systems use antifreeze (e.g., propylene glycol) in the heat transfer fluid.

In some direct systems, collectors can be manually drained when freezing is expected. This approach is common in climates where freezing temperatures do not occur often, but can be less reliable than an automatic system as it relies on an operator.

A third type of freeze protection is freeze-tolerance, where low pressure water pipes made of silicone rubber simply expand on freezing. One such collector now has European Solar Keymark accreditation.