ᐅ Is it worthwhile to lower the heat pump temperature at night?

@HAL06120

Without a nighttime setback, the pump has to run at a low “setting” continuously to compensate for ongoing heat losses. With a nighttime setback, you’re right that the pump has to work harder because it has to make up not only for the regular losses but also for the additional losses during the night. I assume you want it to be warm the next morning/day.

@Joedreck

That can work, but without specific figures, it’s hard to determine. However, the savings are likely to be in the fraction of a percent range.

It is usually coldest just before sunrise. This means that the house needs to be reheated around that time. By the time the indoor temperature becomes comfortable again, people have already left the house, but more energy was used to warm up the floor. Wouldn’t a daytime setback be more practical if no one is home during the day? Heating can then resume shortly after midday. The house will be warm when people are at home, and the heat pump can operate more efficiently at higher temperatures.

However, the temperature settings are usually chosen to keep the house comfortable—neither too cold nor too warm. The energy savings from adjusting temperatures are likely small, but some comfort is lost.

Actually, there is no need to lower the temperature. Modern systems regulate everything automatically. The temperatures are set, and heating continues until they are reached and maintained.

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

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

Mycraft schrieb:
Actually, there is no need to lower the temperature. Modern systems regulate everything automatically. The temperatures are set, and the heating runs until these levels are reached and maintained.

Reducing the temperature, especially with underfloor heating, is a completely unnecessary intervention in a harmonized system.

I have a brine-to-water heat pump. It operates using an outdoor sensor. You can set room temperatures, but these are controlled by an unspecified calculation based on the supply and return temperatures. If it is 10°C (18°F) colder at night than during the day, the heat pump will naturally increase the supply temperature according to the heating curve. This means that when the temperature drops, the pump has to work first to raise the supply temperature. My approach was to use a programmed night setback to keep the supply temperature more or less constant, even when the temperature falls at night.

With a ground-source heat pump, you probably won’t save much, but try this: Every heat pump control system has a setting for "max. supply temperature in heating mode." Gradually lower this value step by step; after each 1°C (1.8°F) reduction, wait 3 to 4 days to see if the indoor temperature changes. Eventually, you will notice a difference—then raise it by 1 to 2°C (1.8 to 3.6°F) again, and that should be fine. In my opinion, however, this will hardly result in measurable savings.

It’s different with an air-to-water heat pump; at night—when the heat source temperature is significantly lower—you can reduce the supply temperature more, and during the day (warmer outside air as the heat source), you can slightly overheat to make use of the building’s thermal mass to bridge the night without any loss of comfort. I plan to try this approach next autumn at my place...