Extremely high pellet consumption (200kg in 3 days) in a Kfw70 multi-family house!

55 kWh/(m²*a) primary energy or final energy? As already mentioned, pellet always calculates primary energy very quickly and nicely for you. Of course, you are right - there was a calculation error; it would be 14,000 kWh per year and apartment or 150 kWh/m²a - which is rather a lot (not catastrophically much, but a lot).

I think I would raise this at your next owners' meeting and try to get the heating engineer back to see what else can be optimized.

Hello. According to the energy certificate, primary energy! The usable area of the apartment building would be about 950 m², total living area in the apartments 550 m². I have calculated with 550 m². Was that a mistake????

I do not know the energy saving ordinance calculation from you - if you have it digitally, you can attach it here. Read the Wiki article and then you will know where the problem of the value "Primary energy demand according to [Energieeinsparverordnung]" is.

I also think that the usable area within the insulated building envelope has a "heating demand". Likewise, I had higher heating costs in my first year. The screed may have dried on its own, but as a rule, there is still more moisture in the house than in the second year. Otherwise, I find 38° supply temperature quite high; our heating system doesn’t even reach that at -20°. However, I don’t know your underfloor heating system, how closely it was installed, etc. Overall, a faulty configuration could be to blame (wrong heating curve, for example), so that the heating system is "choked" by valves in the residential units in addition to too high a supply temperature. Also, theoretically, someone in one of the apartments could always have the windows open and take hot baths three times a day.

I don't believe that the 38°C supply temperature is too high; on the contrary, it seems too low to me. He has a "wood-fired" boiler. These need to be operated at higher temperatures (60°C) so that no soot can form on the heat exchanger. He also has solar thermal. The system will probably have a return flow temperature lift. There are two ways to transfer the heat into the rooms. Either by high volume flow and a small delta T between supply and return, or by pumping slower and higher heat transfer. Due to their design, heat pumps must use the first method and wood combustion the second. It is best to speak with the person who designed the system or a competent heating engineer.

You get low supply temperature, as you say, through a mixer. High supply temperature is rather unusual for underfloor heating due to the system; if at 0 degrees it is already that high, at -15 degrees you are already near 60 degrees, then you either have hot feet or extreme stop and go, which is not good for such burning (and if there is a buffer against cycling, you can still mix to a low temperature!). If the underfloor heating is designed for that, unfortunately it is harder to change the heat generator later. Of course, you should talk to the heating engineer... With mine, I had the experience that "as long as it's warm" was the main thing, efficiency didn't matter to him, and we did not contractually define a maximum energy consumption. I had to optimize the heating curve and actually all other system settings myself.

from on the go

I don't think that the 38°C flow temperature is too high; on the contrary, it seems too low to me. He has a "wood-burning" boiler. These have to be operated at higher temperatures (60°C) so that no soot can form on the heat exchanger. He also has solar thermal. The system will probably have a return temperature increase. There are two ways to transfer the heat into the rooms. Either by a high volume flow and a low delta T between flow and return, or by pumping slower and higher heat transfer. Due to their design, heat pumps must use the first method, and wood combustion the second. It is best to speak with the person who designed the system or a competent heating technician.

Thank you for your information. So you also don't think that in a kfw70 multi-family house (6 units, living area approx. 550m2, building area 950m2) about 2-3 tons in the winter months, 1 ton in the transitional period (extrapolated to the year approx. 15 tons) is too high? According to the energy certificate, the building should need 55 kW primary energy. That would be about 6 tons of pellets per year. And not almost three times that....

Thanks!