The transfer of partial mass flows from one air flow to the other is referred to as (internal) leakage. It is caused by leaks as a result of a pressure difference (seal leakage) or is function-related, such as the co-rotation of a rotor. This is pointed out in the guideline VDI 3803 sheet 5. At the same time, key figures are defined to indicate the size and type of leakage.

The European Regulation EU 1253-2014 limits the energy consumption of ventilation systems with a capacity greater than 250 m³/h for non-residential premises (NRVS). The reference configuration of the bidirectional ventilation system BVS is a casing with two fans, a heat recovery system HRS and one supply air and one exhaust air filter each.

Since the first energy crisis in 1973, heat recovery in HVAC systems has become the benchmark in the industry – even though there was previously no obligation to use it and no mention of minimum thermal efficiency. With the implementation of the Ecodesign Directive...