ᐅ Underfloor heating heat demand with at least 60 mm of screed

Hello dear experts,

I have a question:
We are currently building our single-family home. The house is being constructed to KFW 55 standard and under the Bavarian 10,000 houses program (variant 1.6). The building has a calculated value of "maximum heating demand of 10 kWh/m²".

Included in the requirements is:

Underfloor heating with at least 60 mm (2.4 inches) screed

I passed this information on to my screed contractor... They said this is not practical because the heating-up times increase significantly and the energy demand would be higher compared to a thinner screed... Basically the opposite of the intended energy storage benefit.

What do you think about this???

Thanks for your answers.

Best regards and happy holidays!
Christian

The company is correct that heating times will increase. However, this does not matter since new buildings are heated continuously for 24 hours anyway.
The argument about energy demand is complete nonsense because the house loses a certain amount of energy in the form of heat. The heating system must compensate for this. Whether this happens within one hour at a high temperature or over four hours at a moderate temperature makes no difference.
All the energy remains within the thermal envelope.
In fact, you actually lose more energy at higher temperatures because the temperature gradient is greater.

Therefore, there are no concerns regarding the required screed!

Joedreck schrieb:
Whether this happens within 1 hour at high temperature or over 4 hours at moderate temperature makes no difference.

Joedreck schrieb:
All the energy remains within the thermal envelope.
Strictly speaking, more energy is actually lost at higher temperatures because the temperature difference is greater.

I do see the seed of a self-contradiction here 😉 .

It is true, of course, that thinner screed requires a lower supply temperature to achieve the same surface temperature compared to thicker screed.

Heat transfer requires a temperature gradient – if the distance increases because the screed is thicker, the temperature under the screed must be higher to achieve the same temperature at the surface.

In this respect, I would agree with the heating engineer – exactly by how much, 0.x or y.z °C (degrees Celsius), I don’t know offhand.

Hmm, I wonder what the problem is supposed to be... I have 70mm (2.8 inches) of screed, and I thought that was rather too thin for underfloor heating.

There is no "problem."

However, the efficiency of the underfloor heating depends, among other things, on how poorly heat is transferred downward and at the same time how much better it is transferred upward to the floor surface. This ratio, combined with the pipe spacing, sets the basic physical conditions for efficiency.

The system also works with 100mm (4 inches).

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

Less thick screed also means less thermal mass... therefore, this results in longer heating times and higher energy demand to maintain temperatures.