Building a single-family house in NRW

Primary energy doesn't matter at all, you don't pay for it.

The correct calculation is of course the following. If you use 1 kWh of electricity and save 20 kWh of thermal energy but the air heat pump has an annual performance factor of 3.5, then you save accordingly only (!!!) 5.7 kWh of electricity for each kWh of electricity consumed by the controlled residential ventilation.

Links, sources, etc. are not allowed here anyway. On the Visionair website, a ratio of 1 to 25 is given and Manfred Lusch says the following: about 1 to 25 up to 1 to 40.

1 to 15 up to 1 to 20 are more realistic empirical values, which are also partly used for calculations in the pink forum.

In a classic existing house with double glazing and poor profiles, uninsulated walls, poorly insulated roof, etc., the 20% figure is correct. In a modern house built to the 2016 Energy Saving Ordinance standard and maximally insulated but still with normal window ventilation, you can expect at least 30%, but rather up to 50%.

I like that because I like such numbers. I also have a few. I can save bazillions of quark crystals if I disregard the specific heat capacities of air compared to screed, masonry, and plaster and switch off the warp drive in the Delta Quadrant and instead allow myself to be hypertranscided by the controlled residential ventilation inverter. By the way, KFW0 is free for that.

Exactly at that point it gets interesting.

So we stick with 17.5 kWh of thermal energy and use a ground-source heat pump instead of an air-water heat pump with an annual performance factor of 4.5... So we are slowly approaching parity. Now add a house that already requires little heating energy (insulation) and the controlled residential ventilation soon needs more energy than the heating.

This is exactly where it gets interesting.

So let's stick with 17.5 kWh of thermal energy and instead of an air-to-water heat pump, take a brine-to-water heat pump with an annual performance factor of 4.5... So we're slowly approaching parity. Now add a house that already requires little heating energy (insulation) and the controlled residential ventilation will soon need more energy than the heating.

17.5 / 4.5 = 3.9 and not parity.

How good the insulation is or isn't would be completely and 100% irrelevant. Insulation changes 0.0 (exactly 0.0 - not just rhetorically meant) to the heat loss through ventilation.

And even if it were otherwise a passive house with quadruple glazing, 100 cm EPS insulation, etc. - at best it remains the factor 1 to 3.9.

By the way, in my calculation above I even implicitly assumed an annual performance factor of 5.5 for the heat generator. We have 26.54 cents per kWh electricity and 4.82 cents per kWh gas - those are the prices here. With a brine-to-water heat pump with an annual performance factor of 4.5, the price for thermal energy would be 5.90 cents instead of 4.82 cents - 22.4% more.

It gets really interesting when it clicks: The controlled residential ventilation just about pays for itself, of course only very narrowly, including financing, maintenance and auxiliary energy. But the comfort functions and mold protection come free on top.

With rising energy prices in the future or if the controlled residential ventilation is used as a certain base load of the photovoltaic system for self-consumption, the economic case shifts further in favor of controlled residential ventilation. The comfort functions and mold protection - yes, those remain free on top.

3.9-1=2.9... another step towards break-even. And now costs for maintenance and filters... let's leave that. The calculation is tight (additional investment costs not considered).

We already had the discussion about comfort. Doesn’t exist.

Dust filter... fine by me. But allergies are more likely to increase than decrease. Want some Sagrotan?

And even a house without controlled residential ventilation doesn’t necessarily get moldy. So mold protection... fine by me. But I have that too without controlled residential ventilation. So also not a definitive argument.

This is slowly going too far here. But self-consumption alone doesn’t make a photovoltaic system owner rich. It just barely pays for itself and doesn’t save a cent. Controlled residential ventilation or not. I have a pool in the garden... I don’t save a cent through photovoltaic. If the photovoltaic system lasts 10 years, I’m slowly reaching the point where one starts to save.

Man, now your discussion is only just starting... Now please calculate again the potential savings for a fixed glazing against the old windows with RC2... Opening the windows is obsolete anyway... Then please also stick the insulation on the inside of the walls, so at least you can't hurt yourself on the many saved money during the air gaps...