ᐅ Heat Pump Calculation Formula Based on Heating Load

You will only have certainty if you have the missing heat meter retrofitted. Everything else is just guessing.

So the heat pump was actually set up incorrectly. I hope that was the cause and that the frost protection mode led to the high consumption.

As far as I can tell, Rotex has a built-in heat meter.

But if there are Excel sheets, formulas, or something similar available, I would like to try calculating the theoretical consumption.

I also tried the 3.3 kWh * 1800h, or heating load + domestic hot water * factor (3.3+1)*1.14,
or using U-values and COP, which gives me about 9.3 kWh,
or V * Vn + A * An calculated * HT / 2.8 / 365.

However, none of these values produce a result that makes sense.
If there are so many values involved, there must be formula collections to calculate with these values.

Ps.
Neighbors also have heat pumps but no KfW subsidy; they live in bungalows instead of 1.5-storey houses and said that at temperatures below -10°C (14°F), consumption can reach 15 kW per day.

In theory, you can do more than just estimate, but it requires quite a bit of work.
The heating load calculation usually provided for the overall assessment is often somewhat basic and prepared before the actual construction.
For my house, after construction, I calculated the heating load room by room. Basically, all you need is an Excel spreadsheet where the heat transfer is calculated for each room and all walls. The formula for each room is essentially the same, differing only in wall areas (including windows and frames), temperature difference (outdoor temperature stored in a variable cell), and thermal conductivity, which you can calculate, for example, using a U-value calculator available online based on the materials used.
At the end, you get a fairly accurate idea of how much heating power is needed at different temperatures (you can also factor in mechanical ventilation with heat recovery if you want). In my case, this correlated quite well with actual experience, but I also carefully adjusted the heating circuits and the heating system settings (heating curve) myself. The advantage is that the indoor temperature has remained constant within about 0.3°C (0.5°F) for four years without the need for the electric resistance heaters (ERRs) to kick in.
I would recommend to the original poster to first turn all ERRs fully on, if available, and regulate the indoor temperature over several weeks using the heating curve so that the system doesn’t produce too much heat that might get shut down unnecessarily. It also helped me to increase the hysteresis on the heating supply temperature so the system starts up less frequently and runs longer at once. Right now is an ideal time for adjustments since heating is active. When it gets warmer outside, fine-tune again. By knowing the two points on the heating curve, you effectively define the entire system behavior.

Edit:
Heat loss of a wall for the table:
U-value (in W/m²·K) * area * (indoor temperature - outdoor temperature)

For the total heating load, you can of course also simply sum all external walls, roof, and floor.

However, all the calculations are static. They cannot be more accurate than a rough estimate. It is simply not possible to calculate precisely; all verifications are designed only to provide an approximate annual result.

If you have a lot of free time and access to a computing center, you can create a detailed finite element model (FEM) of your house. In theory, this would allow you to simulate changing outdoor temperatures and solar gains. Of course, wind would also need to be taken into account. Indoors, the temperature remains relatively stable, and internal gains can be simulated as well.

That would be an interesting research project but is not feasible in practical terms. Therefore, these formulas exist so that you can roughly estimate the amount of energy going in and out.

Lumpi_LE schrieb:
The calculations are all static, though. It doesn’t get any more precise than a rough estimate.
You simply can’t calculate it exactly; all verifications are designed only for an approximate annual result.

If you have a lot of free time and access to a computing center, you could recreate your house as an FEM model in full detail. In theory, you could then simulate varying outdoor temperatures and solar gains. You would also have to consider wind, of course. Indoors, you actually have a relatively stable temperature and can simulate internal gains accordingly.

The calculations are quasi-static because spreadsheet software allows for referencing, so it is indeed possible to include outdoor temperature dependency in the calculation. This is already a very good approximation, especially for winter and autumn during overcast weather (and ideally with a light-colored exterior wall).

The U-value (etc.) basically applies to a static or steady-state condition. A dynamic calculation of heat conduction for a house and slow processes is actually “overkill.”

Otherwise, you are correct that the information from heating load and annual heating energy calculations is generally of limited practical use—except for some details. For example, wall and window surface areas are usually calculated quite precisely, so you can incorporate those values into your own calculations. But I wouldn’t use FEM for a house either; that’s like using a minigun to shoot mosquitoes...

The calculation of the U-value (thermal transmittance) must be supplemented by ventilation losses (convection).

Static/dynamic: The U-value is not constant but mainly depends on the weather, especially the wind.