ᐅ Design of Underfloor Heating for a KfW 55 Energy-Efficient House with a Ventilation System
Created on: 17 Feb 2023 16:29
D
dream2023
Dear users,
I am a bit overwhelmed with whether our underfloor heating is being planned correctly. The house is still in the shell stage. I have requested the installation plans and heat load calculations from the general contractor. The heat load was calculated according to DIN EN 12831. I have this calculation and the results from the planning office.
The pipe spacing is mostly 18cm (7 inches), except in the bathrooms (once 6cm (2.5 inches), once 12cm (5 inches)) and the utility room (24cm (9.5 inches)). What unsettles me more is the fact that in both bathrooms an undercoverage of the heat load is stated ("missing heat ...kW"). Additional heating devices are not planned there so far.
May I post the planning documents if I redact personal information and the data of the planning office?
Best regards
I am a bit overwhelmed with whether our underfloor heating is being planned correctly. The house is still in the shell stage. I have requested the installation plans and heat load calculations from the general contractor. The heat load was calculated according to DIN EN 12831. I have this calculation and the results from the planning office.
The pipe spacing is mostly 18cm (7 inches), except in the bathrooms (once 6cm (2.5 inches), once 12cm (5 inches)) and the utility room (24cm (9.5 inches)). What unsettles me more is the fact that in both bathrooms an undercoverage of the heat load is stated ("missing heat ...kW"). Additional heating devices are not planned there so far.
May I post the planning documents if I redact personal information and the data of the planning office?
Best regards
First of all, it’s good to hear that you had a productive conversation and that you have a solid basis for discussion. The fact that the planner uses dimpled membrane and the heating engineer staples it makes me think that there are (almost) only amateurs working in that area of planning. However, my sample size is still too small to make a scientifically based judgment. 😉
In my opinion, compromises won’t really help you much in this area. It’s a house you will probably live in for at least the next 20–30 years and hopefully use for much longer afterwards. Just as a comparison: we even have 15m² (160ft²) less living space upstairs than you and 8 heating circuits. Unfortunately, our building is rated under the building energy law rather than KfW55, so it’s somewhat less efficient, but the theoretically better construction method you have should not lead to a reduction in the number of heating circuits, but rather to a reduction in the supply temperature — that means more heating circuits, shorter distances between them, and shorter heating loops. I would recommend asking him to use a larger heating circuit distributor and to keep the pipe lengths ideally under 100m (330ft), preferably around 80m (260ft). You also have a storage room upstairs, right? Does it need to be heated? Wouldn’t it be sufficient if it is only slightly warmed as people pass through on their way to a room? This way, you save a connection and can also better balance the pipe lengths. Of course, you will pay a bit more, but as long as that goes to the heating engineer, it’s well-invested money.
Regarding KfW, I don’t think you need to worry. They receive the calculations, and everything you plan with the heating engineer is an improvement anyway. They most likely won’t notice any of it.
In my opinion, compromises won’t really help you much in this area. It’s a house you will probably live in for at least the next 20–30 years and hopefully use for much longer afterwards. Just as a comparison: we even have 15m² (160ft²) less living space upstairs than you and 8 heating circuits. Unfortunately, our building is rated under the building energy law rather than KfW55, so it’s somewhat less efficient, but the theoretically better construction method you have should not lead to a reduction in the number of heating circuits, but rather to a reduction in the supply temperature — that means more heating circuits, shorter distances between them, and shorter heating loops. I would recommend asking him to use a larger heating circuit distributor and to keep the pipe lengths ideally under 100m (330ft), preferably around 80m (260ft). You also have a storage room upstairs, right? Does it need to be heated? Wouldn’t it be sufficient if it is only slightly warmed as people pass through on their way to a room? This way, you save a connection and can also better balance the pipe lengths. Of course, you will pay a bit more, but as long as that goes to the heating engineer, it’s well-invested money.
Regarding KfW, I don’t think you need to worry. They receive the calculations, and everything you plan with the heating engineer is an improvement anyway. They most likely won’t notice any of it.
S
stjoob_at21 Feb 2023 15:25In 2023, I would not accept a 35°C (95°F) supply temperature for a heat pump. That’s why I would always plan for wall heating within the temperature ranges. The point about 15°C (59°F) and 24°C (75°F) has already been made. More than a few degrees difference between rooms is not acceptable. Large differences in heating circuit lengths are also hydraulically problematic. Deviations of more than 25-33% between the shortest and longest circuit lengths must be strictly avoided.
If the heating specialist is "only" a subcontractor of your main contractor, the general contractor (GC) is your negotiation partner. I would not accept that compromise either. The recommended maximum of 100 m (330 feet) per heating circuit has been quickly increased by 20% to 120 m (395 feet). And, as always, a low supply temperature should remain your goal.
H
HoisleBauer2221 Feb 2023 21:44Dogma schrieb:
What I mean is, even if calculations are based on 35 degrees, you can actually go lower and it will still stay warm In my case, the calculation is based on 40 degrees Celsius (104°F), and the basement also has underfloor heating. Do you think it would be possible to “go even lower” as well? It’s a KfW55 house.
K
KarstenausNRW22 Feb 2023 11:36HoisleBauer22 schrieb:
My system is designed for 40 degrees,I seriously wonder how a heating system in a new build can be designed for 40 degrees at all. That only works if a) it was designed for an outdoor temperature of minus 60 degrees Celsius (−76°F), or b) an indoor temperature of 28–30 degrees Celsius (82–86°F) is desired, or c) a caregiver or butcher did the planning, or d) pipe spacing of 30 cm (12 inches) was used to offer the cheapest possible solution. In summary: This is the worst nonsense about heating system design in new builds that we have read here in years.
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