Air flat-plate collector.
An air-based collector is a type of solar collector in which air is is used as the medium for heat transfer instead of a liquid. The heat thus obtained from the incident solar energy is stored in holders, which may be filled with gravel, for example. The energy collected from air-based solar collectors can be used for ventilation air heating, space heating, or crop drying. Several different types of air-based collectors and their corresponding suitability for these three primary applications are listed in the table below.
|type of collector||ventilation air heating||space heating||crop drying|
|unglazed perforated plate||very good||poor||very good|
Designs for the first three collector types are simple. The collectors usually weigh less than liquid-based collectors because they don't have pressurized piping. Another advantage of air-based collectors is that they don't have freezing or boiling problems. All four of these air-based collectors can be integrated into buildings and form part of a building's envelope.
The advantages of such a system over a water collector include the absence of problems associated with corrosion and with freezing and overheating. Also, air is a fast-reacting heat transfer medium and rock is a cheap storage medium for heat. Nevertheless, air collectors are not common due to the low heat storage capacity of air and rock. They are also difficult to regulate.