Decision on Insulation Thickness (Economic Calculation)

Just roughly estimated, the "12cm wall" should have a U-value of 0.27, and the 18cm one should reduce it to 0.19. (I simply assumed plaster, 20cm concrete, ETICS, plaster)

So that must have a significantly greater effect than 20 euros/year.

You only get a better feeling once you have the energy calculation in your hands.

But I am a layman, so maybe don't put too much value on my opinion.

But it remains a mystery to me how one wants to comply with the Energy Saving Ordinance 2016 with 12cm.

So I have the energy saving ordinance certificate.

It works both with and without controlled residential ventilation.
It is probably due to the geothermal energy - it "punches through everything."

Therefore, the question remains: 12 or 16 - 18 doesn’t seem to make sense price-wise.

Regards
Markus

It remains confusing to me, but that doesn't matter.

I still maintain that an increase in the insulation thickness by 50% must have a significantly greater impact on the heating demand. See my comparison of the U-values above. In that respect, I believe your calculation must be wrong. Off the top of my head, I would say that the insulation could save you somewhere between 10 and 20% of the heating costs. However, I cannot prove that due to lack of knowledge.

Other starting points are, of course, the insulation values of the windows. Ventilation losses are at least eliminated with controlled residential ventilation.

What I just don't understand: You take an energy carrier (geothermal energy) that is relatively expensive, add controlled residential ventilation, which is also not cheap, and then want to save a few euros on the insulation? I somehow don't understand that yet. I mean, we are talking about 2,000 euros here and thus not even close to 1% of the construction costs. Honestly. Every kWh of heat that never leaves the house in the first place is better than every newly produced kWh...

I would even go so far as to install as much photovoltaic on the roof as physically fits (<10 kWp) with controlled residential ventilation + brine-water heat pump, but that's another topic again.

I am also skeptical, so I'm asking. Hopefully someone can still say something about the correct calculation method.

Regarding the remaining points, I can write a bit more detailed in due course.

The fact is that we now also have to watch the money – if 18 doesn’t bring anything compared to 16, I don’t necessarily need it now.

I have already set 16 for myself – since the existing offers are still unnegotiated, I assume that we can manage it within the budget with 16.

Regards Markus

I have now taken a closer look at the Energy Saving Ordinance calculation.
Your estimates were not that bad.

For the exterior wall, I have a U-value of 0.268 for 12cm, and about 0.205 for 16cm.
According to the calculation, the affected wall area is just under 200sqm.

If you only change this, the final energy demand changes from 17.27 to 16.71 and the primary energy demand from 31.09 to 30.08.

As mentioned, all other parameters remain the same (roof insulation, heating system, windows, door, ...).

Upon closer inspection, I noticed that there is also a projection (i.e., "overall balance") listed there. No idea how realistic it is, but still quite helpful:

12cm per year
- Primary energy demand 9961 KWH
- Final energy demand 5534 KWH
16 cm per year
- Primary energy demand 9637 KWH
- Final energy demand 5354 KWH

Difference
- Primary energy demand 324 KWH
- Final energy 180 KWH

If I apply the calculation mentioned by (I think from denz.) based on the primary energy demand and simply assume a yearly performance factor of 4, that would mean:
324 KWH per year / 4 performance factor = 81 KWH per year additional electricity demand.

Assuming an electricity price of €0.3, this results in additional costs of €24 per year.

If I now consider the additional cost of €1300, it’s rather not worth it. 18cm is even less worthwhile.
If the negotiations allow a good discount, I think we will do it anyway.

Hope I haven't made any mistakes anywhere.

Regards
Markus

There is not that much heat loss through the facade, so the savings are not that high if you increase the insulation on that side. By the way, it's the same with renovations of existing buildings, there are 100 other things you should do before you tackle the facade :-)