Air-to-water heat pump - Nest Thermostat

Is it just about the money? When I see that the recommended system controller from Vaillant costs... 450€ each

No.

The ERR system has its justification. Especially in schools, offices, or temporarily used buildings. In rental apartments, it is also, in my opinion, mandatory to install these controllers.

I also don't believe that it is fundamentally sensible to do without the ERR. This decision always depends on the individual construction project and its parameters.

Rhenish regards

The example is not well chosen. I need water at 80° in a few weeks. Now I can heat the water now and then keep it warm for weeks, or I heat the water in a few weeks when I need it. Guess who uses less energy. I already understand that normally switching back and forth shortly consumes more energy than maintaining a constant temperature. It just depends on the intervals at which the energy is needed.

And even short-term ramping up and down can sometimes be more sensible, depending on how much energy the rooms lose to the outside. Imagine the extreme (100% energy loss to the outside), you have a radiator outside and want to warm yourself at the radiator in the evening. You will hardly run the radiator at level 3 all day and waste energy uselessly, but rather turn it up only when you are sitting in front of it. We had that at the beginning in the last apartment with 60cm natural stone exterior walls and empty rooms all around. You simply couldn’t heat fast enough because the warmth went away in all directions. If the radiators were not running at full load, it was cold in the place.

Great example, but it has nothing to do with an insulated new building. As I told you: You can also turn off a room without [ERR] if you think that is good.

It was also an extreme example to show that it depends on the circumstances and cannot be generalized.

I haven't quite understood your solution without ERR yet? How do you handle such cases? For example, bathing the child once a week at 24°. Does that mean the bath is always 24°?

Here I also agree with the construction expert, in rental apartments and houses with radiators the ERR certainly make sense, because with rapid temperature changes etc., the ERRs unfold their saving power...

In a highly insulated modern house the ERR cause more consumption than they save... everything can be wonderfully adjusted directly at the heating system and if the system has been properly calibrated, nothing needs to be changed.

Slight deviations in the rooms are also possible, I also have about a 3K spread in the house depending on where the room is located. Simply adjust (or have adjusted) the volume flows.

Longer absences from the house can also be programmed directly into the heating system so that it knows no heating is needed at all.

And to heat up a bathroom, an electric heater has to be installed as Sebastian already said.

The low-temperature heating system in a modern single-family house and radiators or underfloor heating in the rental apartment or an older house are simply fundamentally different. But many think in familiar patterns and then transfer them 1:1 to a system that works completely differently. Like "We've always done it this way."

And regarding the law of conservation of energy, yes it certainly applies, but in the house you don’t only have the walls; heat is lost through everything: walls, ceilings, windows, doors, sloping roofs and of course you also have ventilation losses... no matter how you look at it, you ventilate now and then, because without it you then have additional problems bigger than ERRs.

How can one be exempted from the requirement according to [Energieeinsparverordnung]?