Decision on Insulation Thickness (Economic Calculation)

According to the architect, the energy demand is as follows Thickness Final energy Primary energy demand 12 cm 17.70 31.87 14 cm 17.66 31.78 16 cm 17.04 30.67 18 cm 17.01 30.62

Hello,

if the insulation is made of the same material in each case, then the numbers cannot be correct. Someone made a calculation error, or the 16 cm and 18 cm insulation is qualitatively significantly better.

By "significantly better quality" do you mean the "savings" are too much?

I was able to follow the calculation relatively well based on the U-value formulas and in relation to the "small" amount of exterior facade, the difference seemed realistic to me.

If there are calculation errors here, then the program with which the architect has issued his energy saving ordinance certificates in recent years would be incorrect. All other parameters were left unchanged.

Best regards
Markus

Sorry, but the error is almost obvious. The extrapolation from 12 to 14 to 14 to 16 does not fit. Simple rule of three.

This is not how insulation works ...

But if all other parameters remain the same, then the change in energy demand when increasing the insulation thickness from 12 to 14 cm is of the same order of magnitude as from 14 to 16 cm or 16 to 18 cm.

However, if all other parameters remain the same, then the change in energy demand when increasing the insulation thickness from 12 to 14 cm is of the same order of magnitude as from 14 to 16 cm or 16 to 18 cm.

But his building loses energy not only through walls, but also through the floor, roof, windows and doors, thermal bridges, and ventilation.

The OP should not confuse the calculated primary energy demand with a consumption forecast. Actual consumption depends not least on the behavior of the occupants.

For the consideration of economic efficiency, one cannot only look at consumption costs, but must also consider savings, e.g. through lower investment in building services engineering. Smaller heat pump, fewer drilling meters, etc. More insulation can lead to more subsidies (KFW, regional programs, climate settlements, etc.). Or one insulates so much that underfloor heating is no longer necessary (7-10K€ savings -> passive house).