However, since most rooms have internal heat loads (machines, lighting, processing systems, people) which increase the extract air temperature above the setpoint value, it is necessary to check whether this causes the room to heat up and thus reduces the output of the energy recovery unit.
The European regulation EU 1253 - 2014 also takes account of this situation by demanding a "thermal bypass" for all energy recovery systems. For the plate heat exchanger, this means that at least one air stream is routed past the exchanger via a bypass. Together with the face and bypass damper, a bypass system is created with which the output of the energy recovery unit can be reduced or switched off. As a side effect, if the bypass is located in the outside air, it can also prevent the plate heat exchanger from freezing.