Service water heat pump with return flow utilization

Currently, I am considering the heating system for my complete renovation project. It will be fully equipped with underfloor heating.

As the primary heating system, a air/water heat pump will probably be used. Heating load here is about 5.5kW (is currently being revised again and may slightly increase). To work as efficiently as possible, I want to avoid a large buffer tank here and, if possible, set the heating water only to the necessary flow temperature for the underfloor heating. -> So no domestic hot water generation.

Now there are domestic hot water heat pumps that use the return flow as an energy source. Here I would have the great advantage that I could install this DHW heat pump directly behind the shower and thus save myself a circulation line. I can also slightly cool the building in summer with it, as it would use the underfloor heating as a kind of collector.

Now the question arises how sensible something like this is? Here I also have to size the main heat pump somewhat larger and during the transition period this must run as long as the DHW heat pump needs to heat the domestic water. For this, the main heat pump runs more efficiently as never more than the flow temperature is needed and I do not cool down my basement through a DHW heat pump that uses ambient air as an energy source.

You can do everything. But just for financial reasons alone, it’s total nonsense – two heat pumps instead of one. Off the top of my head: the high additional investment doesn’t even pay off until your house is demolished. Circulation line is also not a must. I wouldn’t know why I would seriously need one. Gimmick, but nothing more.

I believe you have a misconception. The heat pump has two operating modes: heating and hot water. When needed, it switches from heating to hot water and has a higher flow temperature for a while. During this time, heating is not active (the screed continues to emit heat). However, you also need the higher flow temperature with the [BWWP].

So far I have had a conversation with a heating engineer who wanted to sell me all sorts of things. It has somehow turned into a 600-liter buffer tank that works with a fresh water station. However, this means I need a significantly higher temperature in the tank than I actually need for the heating system's supply line.

But I also don't know if this heating engineer is the right one, since he considers the tank as the center of the system. In my opinion, it should be designed as small as absolutely necessary and only for the supply temperature of the underfloor heating.

Well, the way from the basement (where the heat pump is located) to the bathroom (on the upper floor) is quite a distance, so I would have to wait longer for the water to really get warm in the floor.

Then the matter is clear. Remove the buffer tank and control both the heating and hot water directly, each with the optimal flow temperature. The screed buffers enough.

Whether you want circulation, you have to decide for yourself. You are simply trading comfort for permanent energy loss.

I hope that the screed can buffer enough. It is a thin-layer system with 1-2cm actual screed height.

You could turn on the circulation in winter (actually no loss since the heat stays in the house) and turn it off in summer.

So I have to keep looking for another heating installer. Slowly, I really feel that none of them really know anything about heat pumps even remotely. One wanted to massively oversize it so that a heating rod would never be necessary, and the other sees a gigantic buffer as the centerpiece.