Is nighttime lowering of the heat pump sensible?

Without night setback, the pump has to run on low "flame" to compensate for the ongoing losses. With night setback, it then has to work properly, you are right, because then the pump has to compensate for the ongoing losses plus the losses from the night. Because I assume you want it to be warm the next morning/day.



That can work, but without concrete numbers it cannot be determined. The savings are likely to be in the per mille range.

It is usually coldest just before sunrise. So basically at the time when you start heating the house again. By the time you have comfortable temperatures again, you are already out of the house, but you have used a bit more energy to warm up the floor. Wouldn't a daytime setback be more sensible if no one is home during the day? Shortly after noon, heating starts again. Then when you are home, it is warm, and the heat pump can heat at warmer temperatures. However, the temperatures have been set so that it is comfortable in the house; both too cold and too warm are not very pleasant. The savings are probably not that great, but you lose some comfort.

Actually, there is no need to lower anything. The systems nowadays regulate everything by themselves. The temperatures are set, and heating occurs until they are reached and maintained.

A reduction, especially with underfloor heating, is a completely unnecessary intervention in a coordinated system.

Especially since the nighttime electricity rate is cheaper than during the day

Actually, there is no need to lower anything. Modern systems regulate everything by themselves. The temperatures are set and it heats until these are reached and maintained.

Lowering, especially with underfloor heating, is a completely unnecessary interference in a coordinated system.

Well, I have a brine-water heat pump. It operates via an outdoor sensor. You can set room temperatures, but these are regulated through an unspecified evaluation of supply and return temperatures. If it is 10 degrees colder at night than during the day, the heat pump naturally wants to run a higher supply temperature according to the heating curve. That means when the temperature drops, the pump initially has to work to raise the supply temperature. My approach was to achieve, through a set nighttime setback, that the supply temperature remains more or less constant. Even if the temperature drops at night.

With the brine heat pump, you will hardly save anything, but try this: Every heat pump control system has a setting parameter somewhere for "Max. supply temperature in heating mode." Just lower it step by step; after each reduction of 1 K, wait 3 to 4 days to see if the room temperature in the house changes. At some point, you will notice, then go 1 to 2 K higher again and that’s fine. However, in my opinion, it will hardly bring measurable savings. It would be different with an air-water heat pump; at night—when the heat source temperature is significantly lower—you could reduce more strongly and then slightly overheat during the day (warmer outside air = heat source) and thus use the building’s storage mass to bridge the night without loss of comfort. I will try that at my place next autumn...