A great part of energy consumption in a ventilation system goes to heating outside air. Great reductions in operational expense can be achieved by transferring the heat from the expelled air to the cold air that is taken in.
Heat recovery systems can be divided into several main groups, depending upon their functionality:
- Return air
- Cross-current heat exchangers
- Rotary heat exchangers. See illustrations
- Coil loop recovery systems
- Heat pipes or thermosiphon recovery system
- Heat pumps
The various systems are characterised by having different degrees of efficiency for temperature and humidity.
When selecting a heat recovery system, it is important to consider both the operating expenses and fulfilment of the requirements for the interior environment.