ᐅ Lowering the Supply Temperature in Underfloor Heating Systems More Complex Than Expected?
Created on: 9 Mar 2023 22:07
J
JohnnyEH
Hello everyone!
We are currently discussing the supply temperature for the underfloor heating system with our prefab house provider.
The house is a timber frame panel construction and meets the KFW40 standard.
According to the construction description, the provider sets the supply temperature of the underfloor heating to 35°C (95°F). We mentioned that we consider this outdated for a new build and would prefer a supply temperature of around 30°C (86°F). We were then told that with a supply temperature of 30°C (86°F), a larger heat pump and a completely different heating system design would be required, and the additional costs could quickly reach five figures. Such extra costs obviously would not make financial sense.
Until now, I thought the supply temperature was primarily determined by the pipe spacing and would be lower if the pipe spacing was reduced.
Why could a lower supply temperature lead to a larger heat pump? What am I missing?
I should add that the heating load calculation and the exact determination of the heat pump have yet to be done. In any case, a Vaillant Arotherm Plus will be used.
Additionally, a question about the floor covering.
We know that tiles are optimal for underfloor heating but vinyl is almost equivalent. We will also have an active underfloor cooling system installed (via the air-to-water heat pump). Does either floor covering—tiles or vinyl—have advantages for cooling? Or would laminate flooring actually be the best option for cooling?
We are currently discussing the supply temperature for the underfloor heating system with our prefab house provider.
The house is a timber frame panel construction and meets the KFW40 standard.
According to the construction description, the provider sets the supply temperature of the underfloor heating to 35°C (95°F). We mentioned that we consider this outdated for a new build and would prefer a supply temperature of around 30°C (86°F). We were then told that with a supply temperature of 30°C (86°F), a larger heat pump and a completely different heating system design would be required, and the additional costs could quickly reach five figures. Such extra costs obviously would not make financial sense.
Until now, I thought the supply temperature was primarily determined by the pipe spacing and would be lower if the pipe spacing was reduced.
Why could a lower supply temperature lead to a larger heat pump? What am I missing?
I should add that the heating load calculation and the exact determination of the heat pump have yet to be done. In any case, a Vaillant Arotherm Plus will be used.
Additionally, a question about the floor covering.
We know that tiles are optimal for underfloor heating but vinyl is almost equivalent. We will also have an active underfloor cooling system installed (via the air-to-water heat pump). Does either floor covering—tiles or vinyl—have advantages for cooling? Or would laminate flooring actually be the best option for cooling?
D
Daniel-Sp10 Mar 2023 20:24Hello,
what does the contract specify? Do you have a contractually guaranteed right to review or obtain this document?
The announcement of five-figure additional costs is probably meant to nip any discussion in the bud...
Regards
what does the contract specify? Do you have a contractually guaranteed right to review or obtain this document?
The announcement of five-figure additional costs is probably meant to nip any discussion in the bud...
Regards
A
Allthewayup10 Mar 2023 21:06I recently had this discussion (reducing the supply temperature to 30°C (86°F)) with our general contractor (GC) as well. He said he has to calculate based on 35°C (95°F) because that is what the standard requires. If he doesn’t comply with this, I could potentially hold him liable if the target values are not met in practice. This also protects the GC to some extent, and they are not very keen on building a house optimized right to the limit; their design must comply with established engineering standards and the general consensus.
However, he added that reducing the supply temperature to 32°C (90°F) — or even down to 30°C (86°F) in milder winters — would not be a problem; the heat pump can easily handle it, he said. He himself operates at only 28°C (82°F) with a 10cm (4 inch) pipe spacing, and we have similar heating loads. Oh, and we have also planned for a few square meters of wall heating loops in the bathrooms, which makes me feel a bit more relaxed about this now.
For the time being, I accepted this, since the contract entitles me to a turnkey house, and I can hardly demand detailed calculations for every aspect. I’m not personally thrilled about that, but that’s probably how it is when building with a GC. Before signing, I didn’t really consider that this could become such a big issue — meaning being more involved in planning and “optimizing” the build. Still, I wouldn’t have saved money by going with separate trades, and I probably would have had much more work with the project than I already do.
If I understood some posts here correctly, a 10cm (4 inch) pipe spacing should be sufficient to allow some flexibility with the supply temperature. Ultimately, the 35°C (95°F) figure exists mostly on paper to achieve the target room temperatures, but that doesn’t mean these have to be your personal comfort temperatures (some people are fine with only 16°C (61°F) in the bedroom).
However, he added that reducing the supply temperature to 32°C (90°F) — or even down to 30°C (86°F) in milder winters — would not be a problem; the heat pump can easily handle it, he said. He himself operates at only 28°C (82°F) with a 10cm (4 inch) pipe spacing, and we have similar heating loads. Oh, and we have also planned for a few square meters of wall heating loops in the bathrooms, which makes me feel a bit more relaxed about this now.
For the time being, I accepted this, since the contract entitles me to a turnkey house, and I can hardly demand detailed calculations for every aspect. I’m not personally thrilled about that, but that’s probably how it is when building with a GC. Before signing, I didn’t really consider that this could become such a big issue — meaning being more involved in planning and “optimizing” the build. Still, I wouldn’t have saved money by going with separate trades, and I probably would have had much more work with the project than I already do.
If I understood some posts here correctly, a 10cm (4 inch) pipe spacing should be sufficient to allow some flexibility with the supply temperature. Ultimately, the 35°C (95°F) figure exists mostly on paper to achieve the target room temperatures, but that doesn’t mean these have to be your personal comfort temperatures (some people are fine with only 16°C (61°F) in the bedroom).
R
RotorMotor10 Mar 2023 21:21Allthewayup schrieb:
If I understood some of the posts here correctly, a 10cm (5 inches) installation spacing should be enough to adjust the supply temperature. It’s not only the spacing that matters, but especially the length of the loops.
A
Allthewayup10 Mar 2023 21:24RotorMotor schrieb:
Not only the spacing is important, but especially the length of the loops.Yes, they should not be too long and should not have extreme differences in length, I assume.H
Hausbau55EE10 Mar 2023 21:30RotorMotor schrieb:
When the bathtub is placed in a polystyrene box, underfloor heating beneath it is rather counterproductive, as the heating loops reduce the flow without adding any heat.
The heat output under the bathtub with a polystyrene enclosure will certainly not be the same as for a freestanding tub. However, the heat output will not be zero, so this area will still contribute to meeting the required heating demand.
R
RotorMotor10 Mar 2023 21:31Hausbau55EE schrieb:
The heat output underneath the bathtub with the polystyrene box will certainly not be the same as with a freestanding tub. However, the heat output will not be zero, so this area will help cover the required heating demand. Have you calculated or tested this, or is it just a feeling?