Solar Water Heating

Technology Outline

4) Common Type of Solar Water Heating Systems

Solar water heating systems can be divided into 2 categories, the direct type (open-loop type) and the indirect type (closed-loop type), depending on whether the incoming is heated up directly or indirectly via a heat exchanger.

(a) Direct type (open-loop system)

In an open-loop system, the incoming water (i.e. water to be used) circulates directly through the solar collectors.

(b) Indirect type (closed-loop system)

In a closed-loop system, the incoming water is not heated up directly at the solar collectors. Instead, a working fluid (e.g. freon, propylene glycol, distilled water) is employed in the collectors and circulates in a closed loop. The working fluid circulates through a heat exchanger inside a water tank, where heat is transferred to the incoming water.