Integral device Stibel Eltron LWZ 504 with central supply air

But it doesn’t sound like the system itself is poorly designed.... rather your plumber miscalculated / installed it incorrectly

I also assume here that it is an error by the technician, since the LWZ from StiebelEltron sells well and there are no such experiences in the "rosa" forum either.

It would have become known if a heat pump were so extremely loud that normal life in the house is no longer possible.

So .... I didn’t know until now, nor have I read anywhere, that you should only operate the heat pump at a maximum of 50 percent load. We have normally high ceilings: 2.44m clear height in the basement and upper floor, 2.56m on the ground floor. The living area including the "Wohnkeller", that is, the area the ventilation system has to handle, is just under 240 m². To make it clear again, it’s not necessarily the noise level, but the "sound", that deep thumping, humming, roaring that is just always there. Especially in the evening, it almost drives me crazy, and I simply turn the system off. My plumbing company is currently playing dead ... apparently they don’t know what to do either at the moment. By the way, I’m really only talking about the ventilation system. When the compressor starts up, it feels like a helicopter is starting ... just kidding, but it is really loud. I have now set the heating program so that the heating, i.e. the compressor, only works when we are not at home, so during the week in the mornings and early evening ... how this is supposed to work in winter ... we’ll see.

Sounds like a constructive fault, maybe the installation, some kind of thermal bridge.

240sqm x 2.50m ceiling height x 0.4/h air exchange rate = 240m3/h air throughput per hour for nominal ventilation.
That is too much for the device if you want to pay attention to noise and energy consumption.

In the cold winter, a heat pump can certainly run 24 hours a day to cover the heat demand. By then at the latest you will have a problem.

If I see it correctly, the 504 also has “only” 6kW heating capacity. Is the basement also heated? That would not be very much for 240sqm heated area either, without wanting to anticipate a heating load calculation.
Or do you have very good insulation?

Is the nominal ventilation required? We have fewer m3/h... and the humidity is really "low"... The THZ 504 has over 8kW output at A-7/W35. How is it decoupled at the floor? The system should stand on its own concrete slab, which is separated from the actual floor slab by a Styrodur board, and be laterally decoupled from the screed/floor with at least a "blue screed tape." The ventilation requires 2 large (rectangular) silencers, with flexible ducts leading to the distribution from them.

So we have an LWZ 504 in our KFW 55 house (160 sqm, two people) since 2017 and it runs great, it is not oversized. We are very satisfied, but we have not yet tried the cooling function (although it would be ideal right now with the heat wave). But we are a bit afraid for our beautiful wooden floor. Because if something was not calculated/connected correctly, condensate could form, which would ruin the solid wood floor. That’s why we are considering installing a proper cooling module in the ventilation system. Because the LWZ can only cool 2-3 degrees above the underfloor heating anyway, it is of course not a real air conditioning.

Regarding noise development, I can say that ours is relatively quiet. Between the utility room and our bedroom is only our narrow dressing room, yet we don’t hear it there at all. It was decoupled accordingly (floor) and some kind of silencers were also installed. Since we have everything on one floor/level, we decided to install a soundproof door in the utility room so that you can hardly hear the washing machine, dryer, and heating system in the living area and bedroom. And that is indeed the case. Anything else would be a disaster, as I am very sensitive to noise. Therefore, something must have been installed/implemented incorrectly with the noisy LWZ 504 described above. I also know some other acquaintances who have also installed this model in their new builds and for them it is also as quiet as ours.