Ventilation requirements in modern buildings.

Besides the hygienic aspect, also the aspect of energy saving of heating residential buildings is very important. This is only possible by mechanical ventilation with heat recovery. This paper describes a part of the large variety of systems, which are nowadays available on themarket. The main difference of these systems are: * single room unit/decentral unit and * central unit for one dwelling or a single family building. For the heat recovery are used: * only a plate heat exchanger (return air/supply air) * only a heat pump (return air/supply air or return air/heating water) or* a plate heat exchanger combined with a heat pump (return air/supply air). As heat source for the heat recovery are used: * only the return air * the return air mixed with the flue gas by using a gas heating system.