Is a row return storage useful for an air heat pump?

Hey,

we are building a KfW-70 house, which is supplied with energy and heated by an air-to-water heat pump (underfloor heating).

The builder has now offered us a so-called "series return flow storage tank," which is supposed to collect the excess energy initially and release it back into the rooms when they cool down. If we do not accept this, we would have to keep a heating circuit open that can no longer be temperature-controlled but through which the heat continuously flows. This area would then typically always be a little warmer (1-3 °C more than desired).

Is anyone of you also installing an air heat pump and has such a series return flow storage tank? What are your experiences with it? For us, it is mainly about whether such a storage tank is worthwhile in terms of energy and cost or whether it only pays off after such a long time that it can safely be omitted.

The model offered to us is as follows:

Vaillant compact heating series return flow storage tank heat pump RS 100 (100 l) for 1,356 EUR (including VAT).

Many thanks in advance for your opinions and happy building to everyone!

Stephie

Well, a storage tank worsens the balance. The problem is when the underfloor heating cannot dissipate the heat if the heating circuits are closed or barely open. You have to accept a nearly uniform temperature in almost all rooms and as many open circuits as possible. Then the heat pump can deliver its full performance. Please do not forget: A heat pump is not a gas boiler, but works best with the lowest possible supply temperatures. To still provide the heating output, the surface area has to compensate for it. A living behavior like in the 1980s with night setback, some warm and many cold rooms, and closed doors is only possible with the new heating systems with loss of efficiency, if at all! Much success with the further planning!