Controlled Residential Ventilation & Heat Pump: Viessmann vs. Vaillant vs. Zehnder?

I don’t know the exact amount off the top of my head, but it’s over €10,000.

I’m just not sure how that’s supposed to work with a prefabricated house. Laying the plumbing necessarily involves another trade, and if something were to happen later, I strongly suspect they’d blame each other...

I’ll just bring it up when we’re there, then we’ll see how they react.

I read a bit more last night and tried various calculation methods, but I gave up; I’d rather leave that to the experts because the results are very different—so different that I want to first see the calculation and planning from the house builder.

I entered the entire house into AIRplan; there were a few boxes to tick that I didn’t understand, but the differences were minimal to none. The following values for the airflow came out here:
Reduced ventilation: 146 m³/h
Nominal ventilation: 209 m³/h
Intensive ventilation: 272 m³/h

On an Austrian site "xxx.komfortlüftung.xx" there is also a sizing aid, but the following values came out for us there:
Minimal device airflow: 123 m³/h
Operating airflow: 306 m³/h
Maximum device airflow: 429 m³/h

The assumption was each time the entire house size including all usable spaces and basement rooms, so roughly 235 m².

At least through AIRplan I now understand how the distribution of the vents works; their scheme was quite interesting and now also explains the number of vents from our contract. The house builder only included the two heated basements in the cellar, also as we assumed from the previous page regarding the cubic meters in the cellar. Surely, a bigger bill would come up again if we now want to include the other basement rooms too...
How is this usually done in a concrete basement that’s not finished? Do the pipes run along the ceiling and holes have to be drilled into the walls?

I wouldn’t leave out the basement if you’re rebuilding anyway. You can’t hide the ventilation ducts better than now.

I don’t want to contradict you because I don’t really have expertise and surely overlook something, but isn’t the ventilation in the basement ultimately overkill when it comes to the price-performance ratio?

Of course, controlled residential ventilation throughout the entire house, including the basement, would be a "comfort gain." At the same time, operating it costs money, and personally, I would want to save myself from running the system continuously in rooms where you hardly ever spend time. Especially since these are probably heated differently and the efficiency of heat recovery would decrease here?

I've already given this topic some thought, especially because we want to use the two heated basements as "cold" basements for now. But since we already have them in the offer and hopefully this will also save us from moisture problems, we would like to have them planned for the time being.

My thought here was whether it is possible to manually open and close the valves in the basement, depending on usage. Is something like that possible? Ideally, it would also be best to simply run the flow at a minimum moisture protection level. No idea if something like that is standard...

I don't know the exact amount off the top of my head, but it's over €10,000.

I'm just not sure how that should work with a prefab house. Laying the piping necessarily interferes with another trade, and if something goes wrong later, one will probably blame the other...

I'll just bring it up when we're there, then we'll see how they react.

I read a bit more last night and also tried different calculation methods, but I'm giving up on that; I'll leave it to the experts because the results vary so much, so much that I first want to see the calculation and planning from the house builder.

I entered the entire house in AIRplan; there are a few checkboxes to tick that I don't understand, but the differences were very small or nonexistent. Here are the values for the volume flow:
Reduced ventilation: 146 m³/h
Nominal ventilation: 209 m³/h
Intensive ventilation: 272 m³/h

On an Austrian site "xxx.komfortlüftung.xx" there is also a sizing aid, but for us, these values come out:
Minimum device volume flow: 123 m³/h
Operating volume flow: 306 m³/h
Maximum device volume flow: 429 m³/h

The assumption here was each time the entire house size including all usable areas and basement rooms, roughly 235 m².

But at least through AIRplan, I now understand how the valve distribution works; their scheme was quite interesting and now also explains the number of valves in our contract. The house builder only included the two heated basements in the cellar, so just as we assumed a page before based on the cubic meters in the cellar. That would surely result in a bigger bill again if we want to include the other basement rooms now...
How do you actually do it in a concrete basement that is not finished? Do the pipes then run along the ceiling, and do holes have to be drilled in the walls?

Well, actually, that's not a problem; you just have to specify the amount of air you want overall and per room. Plus the requirement that the air velocity should be 3 - 3.5 m/s in the duct and 1 - 1.5 m/s at the disc valves. With that, they can calculate the appropriate dimensions and the required number of disc valves per room.
For the basement, usually, a ceiling breakthrough is made, and a drywall box is installed where the disc valves sit (but please not next to the door :p).

I don't want to contradict you because I honestly don't really know, and I'm probably not considering something, but isn't ventilation in the basement ultimately overkill when it comes to the price-performance ratio?

Of course, controlled residential ventilation throughout the house, including the basement, would be a "comfort gain". At the same time, operation costs money, and personally, I would want to save myself from running the system continuously in rooms where you are hardly ever.
Especially since these are probably heated differently, and the efficiency of heat recovery would decrease here?

I know what you mean, but almost always, in the basement, you only need the air quantity for moisture protection, so in this case, that would be 0.3 to 0.5 (0.5 if you possibly have laundry or a party in the basement) of 73 m³. You can always squeeze this air quantity of max. 36.5 m³/h out of a system, and it costs maybe €5 more electricity per year.
Regarding the costs for building the air duct, it's really about that (see above), but honestly, I'd rather spend €1,000 more on something that actually brings value than €1,000 more, for example, on an entrance door that has a wood look instead of white and brings no added value except that it's not white.
Unfortunately, when building, people often save in the wrong places or set the wrong priorities.

Can you maybe say a few words about the values I mentioned?

I just entered the house in Helios as well and came to almost identical values as with AIRplan:
Reduced ventilation: 148m3/h
Nominal ventilation: 212m3/h
Intensive ventilation: 275m3/h

The recommendation was also a 500m3/h device, just as you already suggested.

How is the device determined here? (I once read something about nominal ventilation x2, is that roughly correct?)

The values were determined according to DIN, probably also why the result is almost the same as AIRplan, can you explain the Austrian deviation (do you even know their methodology)?

Maybe get the contact of the heating installer, if possible. I also completely broke my head beforehand about what it should be. Read data sheets, watched videos, etc. Two weeks ago, the initial meeting with him took place, and I told him my preferences. Two days later, he called me and informed me that the delivery times are over a year. The floor slab is currently being poured. A year is therefore far too long if the screed has to be dry in 6 months. It’s not worth it to me not to make progress for half a year either. In the end, it became a Vaillant, since only they can deliver "soon". That means it is very possible that you just have to take whatever you get.