Underfloor heating heating demand with at least 60 mm screed

Hello dear experts,

I have a question:
We are currently building our single-family house. The house is being built according to KFW 55 and the Bavarian 10,000 Houses Program (Variant 1.6). The building has a calculated value of "maximal heating demand of 10 kWh/m²"

Included in this is the regulation, among other things:

Underfloor heating with at least 60 mm screed

I communicated this to my screed company... They said this is not sensible because the heating times increase significantly and the energy demand would be even higher than with a thinner screed... Exactly the opposite of the intended possibility for energy storage.

What do you think about this???

Thanks for your answers.

Regards and happy holidays!
Christian

The company is right in that the heating-up times increase. But that doesn't matter at all, since in new buildings heating is done anyway for 24 hours. The thing with the energy demand is complete nonsense, since the house x loses energy in the form of heat. The heating system has to compensate for that. Whether this happens within 1 hour at a high temperature, or in 4 hours at a moderate temperature is completely irrelevant. All the energy remains in the thermal envelope. Strictly speaking, you actually lose more energy with a higher temperature because the temperature gradient is greater. So there are absolutely no concerns regarding the required [Estrich]!

Whether this happens within 1 hour at a high temperature, or in 4 hours at a moderate temperature, is completely irrelevant.

All the energy remains in the thermal envelope. To be precise, you actually lose more energy with a higher temperature because the temperature gradient is greater.

I see the seed of a contradiction there ;) .

Of course, it is correct that thinner screed requires less supply temperature to achieve the same surface temperature than thicker screed.

Heat transfer requires a temperature gradient – if the path becomes longer because the screed is thicker, it must be warmer under the screed for the same temperature to arrive at the top.

In that respect, I would agree with the heating engineer – by how much 0.x or y.z °C it is, I do not know offhand.

Hmm, so I wonder what the problem is supposed to be... I have 70mm of screed and back then I found it rather too thin for [Fußbodenheizung].

There is no "problem." But the efficiency of the underfloor heating depends, among other things, on how poorly heat is transported downwards and at the same time how much better it is transported upwards to the floor. This ratio + the installation spacing provides the rough physical framework conditions for efficiency. The whole thing also works with 100mm.

That is clear... but it is also clear that insulation goes under the underfloor heating, so heat transfer downward is rather irrelevant.

Less thick screed also means less storage surface at the same time... ergo, higher heating times and higher energy demand to maintain temperatures here as well.