Indirect (closed loop) heating systems transfer heat to the potable water through the means on a heat exchanger. This is necessary especially in areas where climates are cold as mains water contains impurities which may deposit on the inside of the collector tube. This system transfers a special heat transfer fluid through the collector circuit, keeping the system from freezing. The heat transfer fluid may be 100% water or a mixture of water and glycol. Systems with glycol have greater protection in freeze conditions.
Closed Loop systems allow easy changing between multiple heat exchangers for multiple applications. Special hot water tanks are available with internal heat exchangers (also known as coils), with or without electric backup. Twin coil tanks are also available that allow surplus solar energy to be directed to a spa, pool or floor.
However, indirect systems are generally more complicated than direct systems because a tank with a heat exchange coil or an external heat exchanger is required. The collector loop with run at higher temperatures because of this. The antifreeze fluid may need to be renewed every 3-5 years.
There are a number of indirect systems that could be used, such as close-coupled systems or remote storage systems. Close coupled systems generally come in 2 main types, the jacketed heat exchanger and the demand side coil heat exchanger.
To see our solar heating cylinders, see our solar cylinders page.