ᐅ Air Too Dry! – Should I Replace My Old Ventilation System with an Enthalpy Recovery Ventilation System?

wiltshire schrieb:

That’s funny. For comfort, I open a window anytime – no matter how much the heating system cost.

It’s no secret that a mechanical ventilation system with heat recovery tends to dry out the air. If everything works correctly (and is properly designed = enthalpy heat exchanger), then I don’t need to open windows.
But if I have to ventilate by opening windows anyway (for whatever reason), then I could have done without the mechanical ventilation system.
For me, it’s not about saving 50€ on heating costs, but about the technical equipment.

I would first check the settings of the mechanical ventilation system. Do I need powerful ventilation everywhere, or is a normal level sufficient? For example, measure CO2, use basic ventilation only, and adjust the overall air volume accordingly. Achieving 20-25% humidity in winter is not easy. So far, with both centralized and decentralized systems, I have had difficulty getting below 40% in winter.

However, there is a misconception here. The ventilation system does not dry the moist outdoor air through any kind of magical technology; rather, in winter, the outdoor air is already dry (cold air holds less water) and is warmed indoors, which lowers the relative humidity inside.

Normally, people ventilate by opening windows much less often during winter, so the moist exhaled air helps maintain the indoor humidity.

Therefore, increasing window ventilation will only be effective in sufficiently humid and not too cold weather, but at that time, even with controlled mechanical ventilation, the air will not become very dry.

We still have the same problem. We have a Schwörerhaus WGT400, which is equivalent to Vallox or Maico. I wanted to retrofit the system for a long time, but reducing the ventilation to level 1 at night helps a lot, so I measure a humidity of 34-36%. From 7 a.m. it automatically switches to level 2.

tomtom79 schrieb:

From 7 o'clock, it automatically switches to level 2.

Depending on your lifestyle—such as being away from home due to work or school—you can of course adjust the schedule accordingly.

We cannot get below 42% with the enthalpy exchanger in the middle of winter.
The trick is that in the laundry room, we deliberately chose a heat pump dryer, which runs quite often with two children. There is an exhaust duct from the mechanical ventilation with heat recovery system in the laundry room. The very humid air releases enough moisture to the dry outdoor air (supply air). Of course, we reduce the ventilation rate of the mechanical ventilation system to about 15%. However, the ventilation runs 24/7. We never feel that this does not provide enough fresh air.
20% would not be comfortable for the mucous membranes and so on in the long term.

A moisture-stabilizing effect is also achieved with clay plaster. With just a 2.5–3 mm (0.1–0.12 inch) layer, the plaster in typical rooms reaches a moisture absorption capacity roughly equivalent to the maximum moisture capacity of the air volume at room temperature – in a 25 m² (269 ft²) room, this is about 800 g (1.76 lbs) of water vapor. Below 50% relative humidity, the clay plaster releases moisture; above 55%, it absorbs moisture. The further the relative humidity is from this "neutral range," the faster this process occurs. The quite favorable ratio of about 1:1 (room air to moisture storage) may surprise some, but it can be verified through calculation.
Of course, this does not prevent complete drying out of a room due to possibly improperly set controlled residential ventilation, but it is likely to have a pleasantly balancing effect. Unfortunately, it is not a cheap retrofit measure.