Humidity Recovery

ERV heat exchange cores
for larger dwellings

ERV or HRV for MVHR?

MVHR and Humidity

MVHR systems inherently dehumidify. Unlike active dehumidifiers this process is passive and costs only a fraction of the cost.

So, drying clothes inside, cooking and bathing is not a problem with a correctly specified MVHR.

However, in some cases MVHR can overshoot the mark and dry out the dwelling too much in winter. This is expecially the case in very large dwellings, where a lot of ventilation is needed. For this reason PAUL has invented a different type of heat exchange core, that prevents such over-dehumidification risk.

What is ERV?

As an alternative to the standard heat exchanger, most of our heat recovery units can also be equipped with a highly efficient, Enthalpy Heat Exchanger (ERV), which are moisture-transmitting counter flow heat exchangers.

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.

Please avoid cheaper cellulose based enthalpy heat exchangers, which have only a limited life-span.

How Does an ERV Core Work?

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.

Advantages of ERV

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. It is ok, if the humidity increases in summer up to 75%. Please be aware that the indoor temperature will affect the relative humidity. The colder a room, the higher its rh value.

Latent Heat Gains Through ERV

The heat recovery rate of an ERV core is typically a bit less compared to a HRV core, but 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.

Which MVHR Units Can Take ERV Cores?

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.

Other MVHR units with optional ERV cores: Zehnder ComfoAir 160, 180, 200.