Settings for the heat pump

In May 2023, we switched from a gas heating system to a heat pump.

[*]Outdoor air heat pump Alpha Innotec LWDV 91 (LWDV 91-1/3-HSDV 12M-3)
[*]Hydraulic station inside HSDV with E rod 9 KW
[*]PSD750 buffer storage tank with domestic hot water module type BWM F35 V2

For heating, we have underfloor heating on the ground floor and radiators on the upper floor.
Hot water target temperature: 50 degrees

In summer, without heating, we turned off the hot water generation at night and experienced a heat loss of about 5 degrees in the hot water in the buffer storage tank.

Now in winter, with heating, I am trying some settings. I am surprised that with heating operation (24 hours) and hot water generation only during the day, we have a heat loss of about 15 degrees in the hot water in the buffer storage tank. Is that normal?
In the morning, it then takes a very long time for the tank to heat back up to the target temperature of 50 degrees.

Now in winter, with the heating on, I am trying out some settings. I am surprised that with heating operation (24 hours) and hot water production only during the day, we have a heat loss of about 15 degrees in the hot water in the buffer tank. Is that normal?

Without knowing the system in more detail, I would boldly assume that the water from the buffer tank is being circulated as heating water in the underfloor heating. This of course means - as long as the heat pump is not running because the water in the buffer tank is still warm enough - that the water gradually cools down. Since you did not heat in summer, you don’t notice anything there.

Whether this has to be the case with your installed system and hydraulics, or if it is a planning/implementation error, cannot be said without closer knowledge of the system and hydraulics. In the green forum there is someone with a similar problem.

Without knowing the system in detail, I would boldly assume that the water from the buffer tank is circulated as heating water in the underfloor heating. This naturally means – as long as the heat pump is not running because the water in the buffer tank is still warm enough – that the water will gradually cool down. Since you did not heat in the summer, you do not notice anything there.

Whether this has to be the case with the system and hydraulics installed with you, or whether it is a planning/implementation error, cannot be said without a closer knowledge of the system including hydraulics. There is someone in the green forum with a similar problem.

Attached is the conceptual diagram. I hope this helps.

Confirms my statement. Without the heat pump being on, the water is taken from the buffer to heat. I don't know if it can be set differently. I am not familiar with the heat pump / the system.