Omit the single room rule? Controlled residential ventilation + gas heating, new construction

I also found the ERR pointless and we omitted it despite it being mandatory. All those extra valves that consume power unnecessarily and provide no benefit because the system is so sluggish, no thanks. When everything is finished, we simply leave all the shut-off valves completely open and then regulate at the stove (water-bearing pellet boiler for the living room, so to speak). Since we have to load the pellet bags by hand anyway, a certain amount of regulation already takes place this way. Furthermore, we have a buffer tank. And on each floor, there is a wood stove in case you really need additional heat. (Gas heating was not possible due to lack of pipe and because of kfw, "proper heating boiler" was not possible due to missing basement/heating room. So the stove in the living area remained).

The hybrid balancing is carried out by the heating installer via the flow of the individual heating circuits? If I now think that the bathroom should be 1 degree warmer, the flow would have to be increased manually at the HKV, if there are 2 HKs for the bathroom then both to the same extent? Can you mix up a lot there and also affect other rooms?

Not much gets mixed up there, but yes, the other rooms will then become slightly cooler. Therefore, you have to perform the balancing yourself in the end until everything fits. If the bathroom does not get warm enough despite high flow, then the supply temperature must be increased and at the same time you have to throttle all other circuits so that they do not get too warm. Therefore, it is important to plan the underfloor heating according to your desired temperature per room, especially for the bathroom. The issue becomes problematic especially with heat pumps where this regularly is a problem.

If I want to lower or raise the whole house, would I have to shift the supply curve in parallel on the thermostat?

As a permanent setting, yes. Otherwise, there are holiday functions, setpoint shifts via timer, etc., per heating system.

Does it actually make sense with controlled residential ventilation and underfloor heating to lower from, e.g., 16:00 to 0:00 and raise from 0:00 to 16:00 to represent the inertia and reduce by 1-2 degrees at night?

No – that happens automatically via the heating curve. Goal: constant temperature in the house, which also makes balancing easier. Only with heat pumps using air as a source or photovoltaics do additional interventions make sense.

The hydraulic balancing must be done by the installer of the system or by someone commissioned to do it. However, what has been ordered applies here, and a rough adjustment is sufficient to be considered flawless. In other words, the warmest room (bathroom) must reach 24 degrees.

A hydraulic balancing so that every room reaches the more or less exact desired temperatures is not trivial, and for this reason, there are the ERR. This way, the heating can always be run a bit higher and, in the case of impending overheating, simply throttled with the thermostat.

Does it actually make sense with controlled residential ventilation and underfloor heating to lower the temperature for example from 4 pm to 12 am and raise it from 12 am to 4 pm to represent the inertia and to go down 1-2 degrees at night?

With a low-temperature underfloor heating system, you have to think exactly the opposite of a usual radiator heating system, and this is where many already fail at the first step (probably also those who even imposed the ERR obligation on us). A night setback makes little sense and, if at all, then just the other way around. In other words, you have to heat at night and lower during the day. Because you need the warmth in the morning and evening. More or less like you described, but even then the savings are in the permille range.

An outdoor temperature-controlled regulation with (yes, one) thermostat in the south and a precisely done hydraulic balancing are sufficient to run the system efficiently. The controlled residential ventilation then does its work and mixes the temperatures. A 2-3 degree difference is possible. More is rather wishful thinking.

An outdoor temperature controlled regulation with a (yes a) thermostat in the south

Why in the south? That completely distorts things when the sun is beating down on it.
With us, the sensor is in the north.

Why in the south? That completely distorts it when the sun beats down on it. Here, the sensor is in the north.

Yeah, I don’t quite understand that now either, the outside temperature sensor is supposed to reflect the actual outside temperature, protected as much as possible from wind and sun.....

The boxes of the ERR can also be wallpapered over and the electrician can be commissioned to combine the control loops on a circuit breaker (fuse).

With us, all thermostats are completely open because otherwise the heating cycles too often (now at zero degrees outside temperature it runs twice for four hours a day instead of every two to three hours for less than 60 minutes because an ERR was opened and the return temperature was lowered too much as a result).

BTW:
The payback period of a controlled residential ventilation system is about 60 to 100 years.