Solar thermal collectors and applications

Water systems

There are many variations of systems used for both solar space heating and service hot water production. The basic configuration is similar to the solar water heating systems outlined in Sections 5.1.3 and 5.1.4. When used for both space and hot water production this system allows independent control of the solar collector-storage and storage-auxiliary-load loops as solar-heated water can be added to storage at the same time that hot water is removed from storage to meet building loads. Usually, a bypass is

provided around the storage tank to avoid heating the storage tank, which can be of considerable size, with auxiliary energy.

A detailed schematic of a liquid-based system is shown in Fig. 36 [97]. In this case a collector heat exchanger is shown between the collector and the storage tank, which allows the use of antifreeze solutions to the collector circuit. Relief valves are also required for dumping excess energy if the collector temperature reaches saturation. Means of extracting energy for service hot water are indicated. Auxiliary energy for heating is added so as to ‘top off’ that available from solar energy system.

A load heat exchanger is shown in Fig. 36 to transfer energy from the tank to the air in the heated spaces. The load heat exchanger must be adequately designed to avoid excessive temperature drop and corresponding increase in the tank and collector temperatures.

Advantages of liquid heating systems include high collector Fr, smaller storage volume, and relatively easy adaptation to supply energy to absorption air conditioners (Section 5.3.2).