ᐅ Heat pump for 148 sqm KfW55 house

Is there a generally accepted minimum operating time that is considered gentle on the materials?

This varies from manufacturer to manufacturer and depending on the type of construction. The settings are often configured at the factory to always ensure the minimum operating time. Buffers and hydraulic diverter valves further guarantee this. Often, this is between 10 and 15 minutes.

In a new building with underfloor heating, a hydraulic separator and usually a heating buffer can be avoided if the underfloor heating is well planned and executed. A hydraulic separator, in particular, can become an efficiency killer (as can a bypass valve).

However, this requires careful planning, execution, and operation.

Search online for flow30 and study the topic in detail.

This will only cause you unnecessary headaches with the developer project. You already have fundamental issues regarding the sizing. There won’t be much happening with "flow30."

Buffer, valve, safety valve, and pressure relief valve are the compensators for poor hydraulic work. Therefore, I can understand any manufacturer who requires such components. Unfortunately, the installer is often just as inexperienced as the homeowner 🙄

Thanks for all the responses.

Here are a few photos. In the bathrooms, the pipe spacing is closer to 10cm (4 inches), while in the living areas it is about 15cm (6 inches).

@SaniererNRW123
It is a developer, although the company often interprets the boundaries with the general contractor (GC) as fluid. The notarized contract was in two parts: the land came from the project GmbH, and the construction contract from the construction GmbH, all subsidiaries. We knew this and still chose it. I do not regret it; I would choose the land again. However, if I had the choice, I would have picked the GC myself. Especially regarding contract terms, we had no flexibility, and we did try.
Construction time: 52 weeks
No contractual penalties
At least it is a consumer building contract

@Bauenaberwie
We received the heating load calculation after being advised that we could actually arrange the pump ourselves.
Standard heating load: 5115 W
Design heating load (with warm-up factor): 6233 W

Talking with the tradespeople on site and clarifying minor things works fairly well depending on the trade, but especially with the plumbing... not at all. A one-man company who seems completely overwhelmed, with his wife acting as secretary.

Getting in touch with the developer is also insufficient. On the phone, only sharp or non-decisive secretaries, and almost no answers to emails.
Instead, we get mildly threatening letters:
Because they cannot procure the heat pump on time, the house will be finished without it.
To dry the screed, they are renting us a “hot box” for €275 per week (3 weeks rental).
Afterwards, they provide a fan heater for 8 weeks (free of charge, no less) so the trades like the tilers can continue working.
Then we are supposed to accept the house without the heat pump, which will be installed later.

That’s where it gets out of hand.
In our opinion, the “hot box” should be provided rent-free, since we are already paying enough for electricity costs.
We do not want to accept the house without the heat pump, and according to the building code, we are not obliged to do so.

@Baranej
Thanks for the encouragement. It will probably be the 8kW unit at some point. We just have to make the best of it.

@Alessandro
Thanks for the tip about the planning tool.
I entered the data. It looks like a 6kW system (blue line) is recommended, but the 8kW is close. Screenshots attached.