Floor construction new build single-family house kfW55

Electric heating is treated better!? Please explain once...

The so-called primary energy factor of electricity is gradually being lowered. This is partly due to the fact that the share of renewable energies for electricity production is steadily increasing and is already well over 30% (which I consider remarkable).

Electricity, among other things due to high transmission losses and the poor efficiency of central supply with large power plants, had a very poor primary energy factor of, I believe, 2.7, now it is 2.4 (I hope the value in my head is correct).

The KFW calculations are – which makes sense in terms of an overall view – calculated with the primary energy factor.

Thus, air-to-water heat pumps are also increasingly better rated in the calculation.
With a PEF of electricity of almost 3 and a COP of the air-to-water heat pump of about 3 (or worse, depending on hot water supply) one could argue. Now, with a PEF of 2.4, it simply pays off immediately.

Cheaply sourced electricity for the air-to-water heat pump: 20ct/kWh.
Gas (PEF 1.1) costs about 6ct/kWh.
An air-to-water heat pump with a COP of 3 is therefore almost on par.

As correctly stated here by another user, this does not mean that one KFW class less also means lower direct heating costs. Because you pay for the supply of the respective energy source. Not the primary energy demand.

Thorsten

As correctly stated here by another user, this does not mean that one KFW class less also means lower direct heating costs. Because you pay for the consumption of the respective energy source. Not for the primary energy demand.

Addendum:
Neighbor with a comparable house (size, enclosed space, KFW class, number of residents) has an air-water heat pump, he pays (annual average!) almost 70 euros/month for electricity for heating/hot water. We pay on average 48 euros/month in gas costs.

Ah okay. Makes sense and is consistent.

To provide an answer to the original question:

I just looked at our energy calculation for our KFW55@[Energieeinsparverordnung 2016].
We have a basement.
The U-value for the slab under the basement is 0.25 W/m²K. So for the entire basement floor (including the floor structure with impact sound and thermal insulation)

This value is therefore very close to yours.
Under the slab, a 10cm Styrodur WLG 037 was installed, whereas according to the energy calculation, an 8cm WLG 040 would have been sufficient. So I probably have a slightly better value than the calculated one, or something else is used in the floor structure as opposed to the calculation, so that the mix amounts to 0.25 again. I don’t know anything about this either and can only compare the mathematical figures.

Under the floor slab, a 10cm Styrodur with WLG 037 was installed, whereas according to the energy calculation, 8cm WLG 040 would have been sufficient. So I probably have a slightly better value than the calculated one, or something else is used again in the floor construction than calculated, so that it balances out to 0.25 in the mix. I have no clue about this and can only compare the mathematical numbers

You already mentioned the stones you are building with in another thread (I hope I am not confusing you now). The stone mentioned there has a U-value of 0.21 W/(m² K) and would therefore at least not be suitable for KFW 55 determination according to the reference value method. Now you write here the U-value of your floor slab, which represents a precise bullseye according to the aforementioned method. And you even say it is too good. I wonder which components in your house have the U-values that tip the balance in the other direction. That leaves only the roof and windows, with the latter being a nasty cost factor if overdone. Not counting the front door. I’m really interested because we also have to deal with this topic more intensively currently. It would be great if you could briefly list your values.

I will join the topic and provide the values of our KfW 55 house (construction start early 2017):

Base slab: 10 cm perimeter insulation and 20 cm reinforced concrete --> U-value: 0.19 W/(m²K)
Lower 2/3 of external masonry: 15 cm aerated concrete + 18 cm core insulation panels (035) + 1 cm finger gap + 11.5 cm facing brick --> U-value: 0.15 W/(m²K)
Upper 1/3 of external masonry: external thermal insulation composite system (render facade) 15 cm aerated concrete + 18 cm polystyrene rigid foam insulation + 1 cm silicone resin plaster --> U-value: 0.16 W/(m²K)
Roof (cold roof, insulation on wooden upper floor ceiling): gypsum board + 26 cm insulation + vapor barrier --> U-value 15 W/(m²K)
Windows/doors: 5-chamber plastic windows with triple pane thermal insulation glazing --> U-value: 0.95 W/(m²K)

I hope I can give you a good comparison with these values.