Air-water heat pump underfloor heating and domestic hot water heat pump separate

The buffer tank is exactly what you call a "serial" buffer. KFW certificate or energy saving ordinance certificate is not relevant to me, as I am from Austria. The buffer tank is therefore used by me because of the "smart grid" function of the heat pump in combination with the photovoltaic system, so that the self-consumption of electricity is as high as possible. Without photovoltaic, I agree with you, any kind of storage in the heating circuit makes little sense.

The separation storage is exactly what you call a "serial" buffer....

Sorry, from a technical perspective, there are "worlds" of difference between a separation storage and a serial storage. Initially, unnamed "photovoltaic influences" significantly alter sizing parameters. Perhaps you should engage intensively with your HVAC planner on this matter once again. It is much more effective to achieve a fundamental clarification beforehand than to attempt remedial measures afterwards. The often-praised "smart grid" function of the heat pump presupposes that the current photovoltaic output is provided for immediate use or made usable! Depending on the design of the photovoltaic system, this may result in considerable restrictions. In the photovoltaic-rich summer months, at best the power demand (not energy!) for hot water is creditable, as heating operation is not required. In "winter operation," "smart grid" is hardly likely to be helpful. Here, the power immediately usable from photovoltaics usually falls far short. Characteristically and sustainably, the transitional period is influenced significantly by location and user behavior. It is very helpful to overlay the immediately usable photovoltaic power with the actual power demand/requirement for heating and/or hot water in order to illustrate the real benefit of "smart grid." The concept must therefore be coherent overall. For buildings with the same external dimensions but different insulation standards and location, the economic conditions are likely to be completely different overall!

Best regards.

€uro, thanks for your inputs, we developed this concept together directly with the manufacturer of the heat pump, our energy consultant, and the planning/execution company for the electrical installation. It is clear that the "smart grid" is not the solution to all problems (surplus / lack of own power generation). Our local climate is "somewhat" special. Although I am significantly further south than you (region Austria Slovenia / Italy), it has a good influence on the yield of the photovoltaics. However, -22°C in winter and +37°C in summer are not uncommon (such temperatures occur about every other year).

...It is clear that the "smart grid" is not the solution to all problems (oversupply / lack of own power generation).

Completely correct, such "ultimate solutions" fundamentally do not exist, even if sellers claim otherwise! The development departments of the manufacturers are not fundamentally stupid; here I would unjustly issue colleagues a negative certificate, which would certainly not be justifiable professionally. What sales ultimately make out of scientific, technical level is a completely different dimension/ league The engineers of the original value creation have no influence at all!

...our local climate is "somewhat" special. Although I am significantly further south than you (area Austria Slovenia / Italy), it has a good influence on the yield of photovoltaics. However, -22°C in winter and +37°C in summer are not so unusual (such temperatures occur about every other year)

Uniformity is technically much easier to manage than extreme boundary conditions. Hourly individual extreme values are much less problematic than a sustained permanent undershooting of the design temperature. Not without reason, in Germany for my planning I do not exclusively and fundamentally use the HLB design temperature, but the individual, location-related ambient temperature profiles of the last 10 years. It is sometimes astonishing what special features result from this in the final outcome

Best regards