Freshwater station and buffer tank: technically better choice?

- Buffer tanks (like any other storage tanks) have heat loss. Better tanks are better insulated, but the water stored in them still loses heat, meaning energy. This is also true for a domestic hot water tank, however, here you have 400l compared to 800l.

- Heat pumps are more efficient the lower the temperature that has to be "produced." With a heating buffer, you do not send, for example, water heated to 35 degrees directly into the underfloor heating but first into the heating buffer. To ensure that 35 degrees actually come out of the buffer into the underfloor heating, you send the water in a few degrees warmer to the buffer to usually later withdraw it from there and cool it down to the required flow temperature using a mixing valve. Another efficiency killer.

- Then, it also depends on the overall hydraulic scheme. That is, what is connected where and how in the circuit.

There is nothing inherently wrong with fresh water systems. This is the more hygienic way to produce hot water. It just costs more to install. However, if you use fresh water, it should not be connected to a heating buffer but to a tank dedicated solely to fresh water. Heating water is still sent directly to the underfloor heating. In this case, you also do not need 800l. Whether 400l is sufficient for 6-7 people with fresh water, I don’t know well enough.

800l heating buffer tank with a heat pump is a no-go

This is not very well justified so that it is comprehensible for me. You are certainly very experienced (if I read your posts), so it would be interesting to know the reasoning.

thanks for the explanation. According to that, would a direct underfloor heating connected to the heat pump, a smaller or precisely dimensioned storage tank for the fresh water, and fresh water be the ideal solution for a new building?

thanks for the explanation. Accordingly, would a direct underfloor heating connected to the heat pump, a smaller or exactly dimensioned storage tank for the fresh water, and a fresh water system be the ideal solution for a new building?

Whether it is ideal must be decided by each individual. If the somewhat higher initial investment is acceptable and everything is correctly dimensioned, it is definitely a very good solution with which you have very little to worry about.

You should also make sure that fresh water has sufficient flow capacity.

800l heating buffer with a heat pump is a no go

You can't say that as a general rule. A thermal storage tank is currently the cheapest and most efficient way to store electricity temporarily. So if you have photovoltaic panels on your roof and your heat pump is connected to the photovoltaic system, a 1000l buffer tank can also make sense.

You can't say that in general. A thermal storage is currently the cheapest and most efficient way to store electricity temporarily. So if you have photovoltaic panels on the roof and your heat pump is coupled with the photovoltaic system, then even a 1000l buffer tank can make sense.

How much of the photovoltaic power can the heat pump take? And when will the energy be needed again? Losses until then? And what if the sun doesn't shine? Who heats up the buffer then? The calculation is not quite that simple.