Are in the formula from the last page somewhere the costs for the heating system? This shows that the formula is wrong.
The spreadsheet is preloaded with typical values for an one family house in Germany.
The calculation shows 120mm is the optimum for the insulation. A 400mm insulation is over 15 years about 4,000.-EUR more expensive.
But where is the price for the heating system? NO! The price for the heating system is not mentioned. A very good insulated house needs a much smaller cheaper heating system than a bad insulated house. The difference can be in this example more than 10,000.-EUR.
This spreadsheet tries to prove You complete wrong, when You use for 400mm insulation 4,000.-EUR more, but does not tell You, that a good insulated house needs 10,000.-EUR less for the heating system. So this is a typical flying dwarf computation.
Who sends this wrong formula to every architect, not mentioning the price of the heating system? Who sends this wrong formula to all architects to sell more expensive heating system and less insulation?
A vendor of heating systems? No?!? This formula about the optimal insulation is the pride of a producer of themal insulation.
Mankind can fly to the moon, but unable to built an environment friendly house.