ᐅ Underfloor heating heat demand with at least 60 mm of screed
Created on: 24 Dec 2017 10:42
K
krischaaan
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
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
C
chand198626 Dec 2017 19:05@Joedreck
Significantly more only with a noticeably (!) thicker screed.
KlaRa is obviously right that the discussion is pointless given the binding standards.
The physical principle is the same as with the greenhouse effect: If, with identical input, the point where energy is transferred to another system (whether from the floor surface into the room or from the atmosphere into space) is moved away from the heat source, the heat source must work harder to maintain the steady-state condition IN = OUT.
The reason is that a temperature gradient across the screed thickness is necessary to transfer heat from the heating pipes to the surface. At 60 vs. 100 mm (2.4 vs. 4 inches) this is probably completely negligible. Therefore, irrelevant for practical applications.
Significantly more only with a noticeably (!) thicker screed.
KlaRa is obviously right that the discussion is pointless given the binding standards.
The physical principle is the same as with the greenhouse effect: If, with identical input, the point where energy is transferred to another system (whether from the floor surface into the room or from the atmosphere into space) is moved away from the heat source, the heat source must work harder to maintain the steady-state condition IN = OUT.
The reason is that a temperature gradient across the screed thickness is necessary to transfer heat from the heating pipes to the surface. At 60 vs. 100 mm (2.4 vs. 4 inches) this is probably completely negligible. Therefore, irrelevant for practical applications.
I always assumed that it really doesn’t matter and that it’s just a shift in timing.
I thought: same insulation, same energy input = same energy output into the house.
I can understand that there is a different surface temperature. I just thought that the energy is “pushed” longer (unfortunately, I don’t have the exact word for this) and that the total energy input remains the same as a result.
I’m assuming your explanation is correct; I just don’t understand it [emoji23]
I thought: same insulation, same energy input = same energy output into the house.
I can understand that there is a different surface temperature. I just thought that the energy is “pushed” longer (unfortunately, I don’t have the exact word for this) and that the total energy input remains the same as a result.
I’m assuming your explanation is correct; I just don’t understand it [emoji23]
You are on the right track but should not overlook the losses through the building envelope. If your “slow feed” is slower than the rate at which energy is being “pushed” out of the house, you will end up not heating at all. Therefore, you need to increase the supply temperature to compensate for the screed thickness (insulation). However, this also increases the heat losses from your underfloor heating into the concrete slab, etc., resulting in higher energy consumption.
To explain it another way: when you slow down heat transfer by adding insulation, the energy input is not the same, and you use less energy. Consequently, your house will naturally be cooler. But since you want to maintain a constant temperature, you have to raise the supply temperature to achieve the same heating speed again, with the consequences described above.
To explain it another way: when you slow down heat transfer by adding insulation, the energy input is not the same, and you use less energy. Consequently, your house will naturally be cooler. But since you want to maintain a constant temperature, you have to raise the supply temperature to achieve the same heating speed again, with the consequences described above.
C
chand198626 Dec 2017 20:3777.willos explanation is correct.
What you refer to as "pushing more energy in" would only be loss-free if the heat loss downward (or to all other directions rather than the desired one) were zero. Thanks to good insulation, it is small but still not zero.
The energy stored in the screed is not transferred 100% to the heated room. Instead, only 100 – x % is delivered. The x always has to be compensated by the heating system and increases with every additional thickness of the screed. The thicker the screed, the longer your "pushing more energy in" takes, and the more heat flows away in unwanted directions.
If the floor surface temperature is to remain the same, the underfloor heating must provide differing outputs for different build-up heights of the same material.
The analogy to the greenhouse effect is only true under one condition: our planet as a whole is naturally perfectly insulated underneath, unlike a detached house.
What you refer to as "pushing more energy in" would only be loss-free if the heat loss downward (or to all other directions rather than the desired one) were zero. Thanks to good insulation, it is small but still not zero.
The energy stored in the screed is not transferred 100% to the heated room. Instead, only 100 – x % is delivered. The x always has to be compensated by the heating system and increases with every additional thickness of the screed. The thicker the screed, the longer your "pushing more energy in" takes, and the more heat flows away in unwanted directions.
If the floor surface temperature is to remain the same, the underfloor heating must provide differing outputs for different build-up heights of the same material.
The analogy to the greenhouse effect is only true under one condition: our planet as a whole is naturally perfectly insulated underneath, unlike a detached house.
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