Air-to-water heat pump - Nest Thermostat

I want to see you achieve temperature differences of 5-7 degrees in a modern house (preferably with [Kontrollierte-Wohnraumlüftung]). Moreover, such cooling down of a room is very inefficient because the adjacent rooms have to compensate for it. In the worst case, this can lead to building damage...

By the way, you can also throttle a room as desired without [ERR] – simply turn the valve off. Well, it’s then not on a fancy, digital NEST thermostat, but the effect is the same.

One has to give up the idea that rooms can be air-conditioned (that’s what such statements mean) – that worked in grandma’s house (only worked, it was never really good), but not in today’s houses.

I wonder the same.
But if the underfloor heating is so slow that it takes a day to heat up by 1 degree, I can hardly heat up the children's room spontaneously (e.g. bad weather, child inside)... or can I?
So, here comes a smart thermostat idea: most of them include weather data. They then know: aha, cold snap tomorrow, I'll give the command to heat up by 1°.
Or am I making a mistake here?

Faulty reasoning, because no weather forecast provides such precise data - you can see that every day from your weather app. And then for the exact location?

A well-adjusted heating curve with a weather-controlled system is sufficient - the sensor should, of course, be installed accordingly.

You are assuming incorrect desires that a surface heating system cannot provide - and that no one implements practically either. The vast majority adjust their thermostats only once in their life...

Again: With a controlled residential ventilation system, you have nearly the same temperatures everywhere in the house!

We do not have a controlled residential ventilation system. Ok, thanks for your comments. We will consider all of this thoroughly.

Why no controlled residential ventilation? Just out of interest?

Well, we assume that the room air has been heated to the desired temperature, so the floor has a slightly higher temperature.

Now the sun comes into play and primarily heats the floor, because the sun's rays hit here and the greatest energy output occurs here.

With ERR, the room is decoupled from the overall system and "cooled down" until the air temperature reaches the setpoint again. So most likely until the late evening hours. Meanwhile, there is overheating of the room and you have to ventilate out or sweat the additionally introduced energy. All other rooms in the house must continue to be heated because the sun does not shine everywhere. The heat generator is therefore in operation. Since the ERRs also have hysteresis, the room will cool down below the set value and will have to be reheated at night.

Without ERR, the room remains in the overall system, the water in the underfloor heating is heated by the sun because the sun shines on the floor. Through circulation, the additional heat does not stay in the room but is transferred to the entire system. There is significantly less overheating of the room and the rooms on the north side also get some sun. The heat generator also has to provide much less energy to maintain the temperature in the overall system.

The ERRs are what they are—a last resort.

You can also compare it casually to a car ride...

With ERR, full throttle is driven all the time and you control the speed only with the brake.
Without ERR, you give only as much gas as necessary and maintain the desired speed.

What do you think, which driving style is more efficient?

In addition, there's the not to be underestimated power consumption of the ERRs and the additional control valves and the regulation. Each valve typically consumes 2W and runs 24/7 during a typical heating period, adding up to about 150kWh of electricity costs in an average household alone, which roughly translates to 40 euros per year that can be saved. And now I'm only talking about the valves; the rest of the unnecessary control also consumes electricity.