Central ventilation system - is moisture recovery necessary?

What shocks me the most are the air exchange rates that you can read here.

Who recommends 0.5/h. For our house (approx. 425m³ air volume), that would mean an air volume flow of over 200m³/h. With such fantasy values (who in the world still recommends such absurd values nowadays?), it doesn't surprise me that any room humidity is completely ventilated out.

Do you also think about the power consumption of the system and the heat loss of the system? At airflows >200m³/h, heat recovery is perhaps still at 75...80%, the rest is blown out.

30m³/h per person in the household, then you have 120m³/h in a 4-person household and the heat exchanger also achieves its 90-95% heat recovery that the manufacturer advertises. The energy consumption of the fan decreases exponentially (keyword flow resistance / Bernoulli / exponential increase with flow velocity...) and room humidity also does not drop absurdly even without an enthalpy exchanger.

Best to set daily programs with increased ventilation during meal/shower times, etc. Also depending on the day of the week. Our Vitovent 300-W offers many setting options. The air volume flow per ventilation level can be easily coded via the service menu, just have a look in the manual.

I'm now at a daily average (!) of only 0.2/h or 85m³/h and CO2 is completely uncritical around the clock. What may also help some people: adjust the diffusers and exhausts so that the volume flows also fit the room and the duct length. Our installers were not very thorough there and had everything more or less equally opened according to feeling, resulting in most circulation taking place between the living room - utility room and kitchen, while hardly any air exchange took place in the bedrooms...

Our installers were not very thorough and had everything more or less set equally wide-open by feel, with the result that most of the circulation took place between the living room - utility room and kitchen, while there was hardly any air exchange in the bedrooms...

Our Zehnder system was calibrated by Zehnder themselves for about 2 hours. Good thing.

More decisive than the air change rate (which probably very few people can determine anyway) is the air quality, and it can best be determined by the CO2 level.

To exclude the mixing of air streams, usually a KVS is used, which however exceeds the (financial) limits.

Could it be that the KVS is not offered for single-family homes for this reason? Because I haven't read anything about the prices of a KVS. Do you have concrete figures / experiences?

KVS does not make sense for such small systems. Especially since the space requirement increases. It only really makes sense for air volumes beyond 1000 m3/h, which would be a bit excessive for single-family houses.

More decisive than the air exchange rate (which probably very few can actually determine) is the air quality, and this can best be determined by the CO2 level.

But even here, a lot of alarm is made about nothing. If the user fails to convert % into ppm and therefore has no reference for the measured CO2 content, this is all quite pointless.

- Deadly: 8% = 80,000 ppm
- Harmless: anything under 2.5% = 25,000 ppm
- "Like fresh air": anything under 0.15% = 1,500 ppm
- Fresh air 0.04% = 400 ppm

Even in a completely sealed bedroom with 2 people and the door closed, one will hardly reach concentrations above 2,500 ppm by the end of the night. So even then, you are only at 10% of a concerning CO2 concentration. As soon as the door is slightly ajar, you stay at a maximum of 1,500 ppm.

But no, the construction industry naturally comes up with a completely independent study claiming that in a 4sqm bedroom, there is a risk of headaches due to CO2 after just 2 hours and that one absolutely should consider active ventilation.

I basically think controlled residential ventilation is good, which is why we have one, but you shouldn't also drive yourself crazy and run the thing 24/7 on the highest setting to enforce some imaginary air exchange rates at the cost of dry air, high electricity consumption, and high heat loss, just so the CO2 meter always stays as close as possible to 400 ppm.