“Air-to-air energy recovery” refers to the transfer of sensible heat, or sensible and latent heat, between air streams. The 2000 ASHRAE Handbook—Systems and Equipment compares the most common technologies for air-to-air energy recovery.

Sensible-energy recovery systems transfer only sensible heat. Adding sensible heat raises an air stream’s dry-bulb temperature; removing sensible heat lowers the dry bulb. (Removing sensible heat may cause condensation, too, but it never prompts moisture transfer to the colder air stream.)

Common examples of sensible-energy recovery devices include coil loops, fixed-plate heat exchangers, heat pipes, and sensible-energy rotary heat exchangers (sensible-energy wheels). All of these devices perform identically on the psychrometric chart; only their effectiveness differs.

Total-energy recovery systems not only transfer sensible heat, but latent heat as well — that is, energy stored in water vapor in the air stream. Such systems raise and lower both the dry bulb and dew point of an air stream.

Common examples of total-energy recovery devices include total-energy rotary heat exchangers (also known as total-energy wheels) and fixed-membrane heat exchangers.

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