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
glazed flat-plate	good	poor	good
back-pass	fair	no	fair-good
trombe wall	no	good	no

 

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.