Heat pump calculation formula based on heating load

The definition of the U-value is that a steady state exists (!), that is, temperatures on both "sides" = constant. In reality, of course, wind makes a difference, but for all components that are reasonably insulated (double- or triple-glazed windows, walls with a U-value around 0.3 or better), the external heat transfer is so insignificant that the fluctuation of the total heat conduction between calm and storm is in the low single-digit percentage range, which is definitely sufficient for a rough estimate of whether the heating system is operating properly! Convection (I said: ventilation system) is quite easy to integrate, e.g., for total consumption simply air flow rate*temperature difference*heat capacity of air

The definition of the U-value is that a steady state exists (!), meaning temperatures on both "sides" are constant.

I am not entirely confident in the definition of the U-value in the narrower sense of building services engineering. Generally, there are three mechanisms: heat transfer from the room to the wall, heat conduction through the wall (simplest case: monolithic wall), heat transfer from the outside of the wall to the free environment. And the last mentioned depends significantly on whether the air is still or not.

Convection (I said: ventilation system) is quite easy to integrate, for example in total consumption simply air flow * temperature difference * heat capacity of air

You just need to know the air flow ;-).

Oh yes: don’t forget source terms (people, electrical appliances).

Well, the airflow rate in modern controlled residential ventilation systems is very easy to determine. In the optimal case, it has even been adjusted room-by-room to suit the house.

In theory, you are right that the heat transfer depends on the airflow of the air, but in the case of very poor thermal conduction, which is present here in the walls/windows/roof, it is actually irrelevant. So little energy passes through the material that the surface effect makes no difference; the outside surface basically has the outside temperature, no matter how much or little wind blows. Only with poor insulation would it happen that the outside of the "wall" heats up due to thermal conduction, and then naturally, with more airflow/wind, more energy is transported away than with less wind.

To calculate with the U-value, different = outside -12 inside 20 = 32 walls = enclosing surface 389 * 0.2 (aerated concrete 42.5) + surcharge 0.05 * 32(diff) = 3111.2 ceiling = 90 * 0.14+0.04 * 32 = 547.2 floor = ceiling = 547.2 window = 26.6 * 0.6 + 0.05 * 32 = 553.28 total 4760w = 4.76 kW now I would need to know how often the heating has to switch on and then calculate that by the cop, right? PS. The problem was found, it was forgotten to set the heating properly. Every time the utility lockout was active, the outdoor unit was switched off and the heating thought it was frozen. Thus, the frost protection was activated twice a day for 1.5h each time. Now the consumption is back at about 15 kWh

Well, the air flow rate in modern controlled residential ventilation systems is very easy to determine.

But people also sometimes open a door or a window. And a bit of leakage air is also still there (Blower Door-test).

: From the values, that already looks appropriate for such a house. Ventilation losses in my case (with a larger house, so more volume) are around 1800W at -14° during normal controlled residential ventilation operation (but pessimistically calculated with poor heat exchanger efficiency), so you might be a bit below that.
That would then be roughly about 6kW heating power for you at -12°. Over the day it will not always be -12° (-the best way to calculate is with the daily average temperature difference, I monitor and calculate this automatically with sensors, and in the last 4 years I was able to determine that the heating energy demand is exactly proportional to this value!), if it were so, it would be about 24*6=144kWh heating energy demand per day. This - divided by an average coefficient of performance - is the electricity consumption at this temperature.
If the average difference (during the day/partly warmer than -12°, maybe on average -6°?) is smaller, for example 26 instead of your 32, then it would be (since proportional) about 117kWh (at 0°C 92..). This reflects the actual consumption as evidence of the pessimism of our calculation and values on the one hand (no idea how it is with your controlled residential ventilation/ventilation, the share is not insignificant), but also of a not too bad coefficient of performance.


Compared to the 150m^3 and more that a controlled residential ventilation system transports every hour (continuously!), going in and out through the door now and then is not that much. And windows? I don’t know who your "people" are, but personally I have only opened windows for a few minutes over the last years during odor-related “emergencies” (which can happen sometimes with children, pets, and cooking yourself...), otherwise they stay closed – without any force – in our house. Actually, this is not a problem even in the bedrooms.
By the way, not even air leakage is a problem, because with today’s required values in the blower door test the exchange rate due to air leakage is quite low (also note the differential pressure at which the test is conducted/for which it applies – I was present during mine, you can clearly feel it in your ears when ramping up/down the test). Incidentally, this value can also be monitored by a controlled residential ventilation system.