Heat pump: buffer tank, capacity and modulation

We also have ERR in the new building, simply to have the possibility to regulate. We have most of the controllers turned up fully and the flow settings regulate the rest. The specialist company did that. But in some rooms like in the office, for example, we have turned the heating completely off. What comes in there through air exchange ([Kontrollierte-Wohnraumlüftung]) and the waste heat produced by the PCs is completely sufficient to heat the room. Often, that is even enough to make the room several degrees too warm.
The storage room is also turned off; my potatoes don’t need a warm room. However, the room is so small and the door is opened so often that you don’t notice much difference.
Since in winter we might well find ourselves in situations where we need to heat the office or storage room as well, we have the ERR. I don’t want to mess around with the heating circuit (HKV) now if anything changes in our heating behavior, as the specialist company did the hydraulic balancing there.

In the bathroom we have electric towel radiators, which can be used to add heat if you want it a bit warmer there. I like to turn them on sometimes when I want a cozy towel, but often it gets too warm for me if the thing runs only during a bath.

Hi,

If you reduce the temperature spread with the heat pump from 37/29 to 35/31, there is enough flow for the heat pump, with the same heat output, and the heat pump will be happy.

Regarding the heating load: It looks like the correct calculation. I can't say if the values are right, but they should be. Why your consumption is lower than what fits the heating load can't be said from a distance and with the documents available.
With additional insulation on the top, the heating load will not exceed 9 kW. Even in the current state, a 9 kW heat pump would be sufficient.
Many 9 kW models can modulate down as far or almost as far as the 5-7 kW ones. It’s simply the same technology with different power electronics.

Regarding the energy consultant: 8k is the KfW maximum value. Makes sense for appropriate objects with complete renovation to a KfW efficiency house. You are right, that this is completely exaggerated in your case.
And why does the energy consultant sell/install heat pumps??

At some point, I increased the circulation pump of the heating system. After that, the temperature spread was significantly lower, and since then the bathroom has also been getting properly warm. Unfortunately, I don’t know exactly how high the temperature spread is off the top of my head. I will have to pay attention to that soon. Looking at the weather forecast, we will probably turn on the heating sometime next week.

I also noticed the thing about consumption and heating load. I don’t know what outdoor temperature the plumber used as a base back then. It could be that he took -20 °C and the conversion via the "full load hours" is based on a different value. Or our south-facing windows actually have such a strong effect. Until -5 °C at night and +5 °C and sun during the day, we get by without heating.

Silly question about heating load and heat pump size: The heating load is usually calculated for -10 °C. The heat pump’s power is usually given at +7 °C, e.g. 9 kW. At -7 °C, however, it is only 7 kW (Panasonic Aquarea). So, isn’t oversizing then necessary? I find the performances hard to compare because some apparently already include some electric heating rods. Otherwise, I can’t explain why, for example, the Viessmann Vitocell 250 delivers a higher heating capacity at -7 °C than at +7 °C. (8.1 kW at +7 °C and 11.1 kW at -7 °C).

I already told him that the price of the energy consultant is completely exaggerated. Now he seems to be offended. Thanks for the info that 8000 € is the KfW maximum value.
It is officially a consulting firm, but it also includes a heating specialist. Presumably, the heating specialist was the origin, and then he expanded it to energy consulting. But that is also the one who wants 43 k€ for a heat pump just like that. Crazy!

Best regards,

Andreas

Yes, the Panasonic Aquarea LT 9kw ultimately only delivers 7.5kw plus electric heater. Alternatively, there is the 9kw TCAP (I believe not yet as Generation L, only J). However, it cycles more frequently because the minimum output is twice as high. I would double-check the heat load calculation, especially whether the design temperature matches the climate / NAT for your location, and based on your descriptions, I would rather recommend the 9kw LT (or from another manufacturer with similar performance data). No guarantee from a distance. I would avoid consultants with affiliated installation companies. It can be done if it’s about individual measures/solo heating replacement. Considering the costs involved, definitely.

The performance of the heat pump is usually given at +7, e.g. 9 kW. But at -7°C it is only 7 kW (Panasonic Aquarera).

Important. You need the heating capacity at subzero temperatures, not +7°C. Manufacturers should actually be required to present the heating capacity curve as the first priority. No one is helped by the top efficiency and performance values at A7/W35.

Important. You need the heating capacity at subzero temperatures, not +7°C. Actually, manufacturers should be obliged to present the heating capacity curve as the first priority. No one is helped by the top efficiency and performance values at A7/W35.

I don’t really know if A7/W35 is that uninteresting. In Germany, for large parts of the winter we are already close to A7, the days below that are more the exception than the rule, and with the help of the climate catastrophe and neglected need for action, they will probably tend to become even more relevant in the future—excluding extreme weather events.

What I mean, using the example of February 2022:
Average temperature at 4.22 - nevertheless, in the warmer areas in that month there were 24(!) of 28 days at or above 7°C.

I don't really know if A7/W35 is that uninteresting.

Not that. But the manufacturers give the max power there and not the lowest possible power/maximum restriction.