Humidity Recovery

ERV or HRV for MVHR?

As an alternative to the PAUL standard heat exchanger, most of our heat recovery units can also be equipped with a highly efficient, moisture-transmitting counter flow heat exchanger (ERV, enthalpy heat exchanger or latent heat exchanger).

In living spaces with low humidity, it provides a convenient humidity, due to the additional moisture recovery from the extract air. The warm and cold air flows are separated by a selective polymer membrane film (dpoint technologies). The hygiene is ensured at any time due to the anti-microbial properties of the membrane (Microban®), only heat and water vapour are transferred. The transfer of gases, pollutants and smells is excluded (see image below).

Enthalpy

Up to 75% moisture recovery ensures a convenient room climate at any time, without the air overly drying out in the cold season. This is especially important for larger dwellings with low occupancy levels, as the internal moisture generation is in dis-balance with the ventilation requirement of a large building envelope.

Compared to cellulose based moisture heat exchangers, which have only a limited life-span, the patented PAUL enthalpy exchanger achieves not only best heat recovery performance of its kind, but it is also hygienic and durable. The Passivhaus certified heat recovery rate of the Novus 300F with enthalpy exchanger is 84%. Although this is 9% less than the standard heat exchanger, the increased humidity levels indoor mean a latent heat gain due to the reduced evaporation losses. This closes the performance gap in terms of heat recovery between the two systems.

Another advantage of ERV units is that low humidity levels in the heating season can be avoided, which sometimes occur with HRV systems in larger dwellings with few occupants.

Low humidity levels can affect our health and well-being. They also greatly increase the life-span of corona viruses.

The ideal relative indoor humidity ranges between 40 and 60% rh.

PAUL MVHR units can be ordered either with enthalpy heat exchanger, e.g. Novus 300F, 450F, Focus 200F, or the standard heat exchange core can be swapped over for an enthalpy core. The PAUL climos 200F unit comes as a standard with humidity recovery.

The Zehnder ComfoAir Q units Zehnder can also be provided with an enthalpy core. For this option, the CAQ units will not have any defrost pre-heater as the risk of condensation freezing in the heat exchanger is minimised, especially for the UK winter climates. This means that the enthalpy version is inherently frost protected down to about minus 6 deg. C, or lower, depending on the humidity level of the extract air. If the outdoor temperatures drop lower than that, the system will go into frost protection mode to prevent frost in the HX core. If there is a pre-heater installed (retrofitted or after conversion from HRV to ERV), the electrical usage of the pre-heater will drop substantially, as it will only activate below -6 deg.C.