ᐅ Central ventilation system – is humidity recovery necessary?
Created on: 30 Dec 2019 16:17
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ludwig88sta
Hello everyone,
for our planned single-family house with 2 floors and a basement, we have decided on a central ventilation system for all rooms with heat recovery within the thermal envelope. The brand and model are not yet determined.
I have read here on the forum a few times about an additional moisture recovery feature (MRF?), since otherwise the indoor air tends to become too dry (of course, the ventilation system also removes the moisture that naturally occurs in the room, which usually makes the air feel comfortable). I wanted to ask if anyone can confirm these issues and whether this is more common in timber frame houses or also occurs in brick houses?
Did you install additional moisture recovery in your ventilation system? How much extra cost does it involve? I assume there are also additional maintenance costs because it involves another motor and related components.
Best regards
ludwig88sta
for our planned single-family house with 2 floors and a basement, we have decided on a central ventilation system for all rooms with heat recovery within the thermal envelope. The brand and model are not yet determined.
I have read here on the forum a few times about an additional moisture recovery feature (MRF?), since otherwise the indoor air tends to become too dry (of course, the ventilation system also removes the moisture that naturally occurs in the room, which usually makes the air feel comfortable). I wanted to ask if anyone can confirm these issues and whether this is more common in timber frame houses or also occurs in brick houses?
Did you install additional moisture recovery in your ventilation system? How much extra cost does it involve? I assume there are also additional maintenance costs because it involves another motor and related components.
Best regards
ludwig88sta
L
ludwig88sta30 Dec 2019 17:57Thank you. However, the enthalpy exchanger also seems to be controversial!?
Enthalpy exchangers come with a challenge. "The process of moisture recovery cannot be controlled. If a lot of moisture is produced inside the house, it could become too humid," says Schnieders. In such cases, there is a risk of mold growth if moisture condenses on thermal bridges. The only way to counteract this is by significantly increasing the air exchange rate or ventilating through the windows.
Schnieders recommends ventilation systems with moisture recovery only for large residential buildings with low occupancy. They could also make sense if the incoming air is heated. Essentially, it’s important to carefully consider: how many people live in the building, and how much moisture is generated. "Often it turns out that moisture recovery is not necessary. Usually, it is sufficient to slightly reduce the airflow rate to keep indoor humidity at an appropriate level," explains the passive house expert. He also notes that systems with moisture recovery typically have about a ten percent lower heat recovery efficiency.
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Enbausa(.)de
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ludwig88sta30 Dec 2019 18:00It’s also unfortunate when there is a risk of bringing moisture problems back into the house through an enthalpy exchanger, which the ventilation system was actually meant to eliminate.
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ludwig88sta30 Dec 2019 18:04opalau schrieb:
I don’t understand why the type of construction would affect the need for an enthalpy heat exchanger?Because different construction methods handle indoor moisture differently over time. For example, brick tends to absorb moisture and then release it again after a while, unlike timber frame construction with vapor barriers in the walls. Also, interior finishes can significantly influence indoor humidity levels—for instance, using clay plaster, which helps regulate moisture.
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