Solar thermal collectors and applications

Air systems

Air systems are indirect water heating systems that circulate air via ductwork through the collectors to an air-to - liquid heat exchanger. In the heat exchanger, heat is transferred to the potable water, which is also circulated through the heat exchanger and returned to the storage tank. Fig. 33 shows a double storage tank system. This type of system is used most often, because air systems are generally
used for preheating domestic hot water and thus auxiliary is used only in one tank as shown.

The main advantage of the system is that air does not need to be protected from freezing or boiling, is non­corrosive, and is free. The disadvantages are that air handling equipment (ducts and fans) need more space than piping and pumps, air leaks are difficult to detect, and parasitic power consumption is generally higher than that of liquid systems.