Heat recovery in ventilation systems.

In well insulated buildings the ventilation heat is sometimes higher than the heat losses by transmission. For a air change rate of 0,8 per hour the specific heat flux must be calculated with 25 w/m², so heat recovery can save some energy. In all considerations the saving in the heating system must be compared with the additional energy for the fans, because this energy is of a higher quality. To optimize the heat recovery system, the different designs of the heat exchanger, the annual running hours and the annual hours for heat recovery must be taken into account. Heat recovery heat exchangers can be optimized with an efficiency of about 60%. To reach a higher overall efficiency a heat pump included in the system is a good possibility in special cases. To compare the different systems and combinations an overall COP can be derived not only for the heat pump but also for the heat exchanger. This is very important for the right decisions, because the aim can not be to save heating energy by spending more electricity.