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 We mentioned that we consider this outdated for a new build and would prefer a supply temperature of around 30°C (86°F).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 We mentioned that we consider this outdated for a new build and would prefer a supply temperature of around 30°C (86°F).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?
Tolentino schrieb:
However, the architect is also assigned site supervision as a recommended standard and is supposed to ensure that all trades coordinate properly. The general contractor’s site manager works in the interest of the general contractor and, in this role, is often less helpful to the client than a dedicated site manager. So far, I haven’t met a single architect I would even remotely trust with this responsibility! My sample size is still small, but I believe such an architect is more the exception than the rule.
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neo-sciliar13 Mar 2023 08:44Happy Monday... just when you’re getting into the weekend... folks, folks.
I already tried to explain this last week. Designing the heat pump based on the standard heating load temperature (NAT) with a 35°C (95°F) flow temperature has almost nothing to do with the actual values experienced in everyday life. This is a calculation value that determines the size of the heat pump and the layout of the underfloor heating. And this is done in coordination.
Yes, you can have all of this changed, and the heating engineer can adjust their calculations accordingly. I’ll keep this for follow-up and wait for your HELP posts:
- HELP: I just can’t get my heat pump settings right. The heating curve can’t be adjusted so that the house feels comfortable at every outdoor temperature; either it’s too cold inside at -5°C (23°F) outside or too warm at +8°C (46°F). I have to keep readjusting it.
- HELP: My heat pump cycles constantly. It switches on every hour and runs for just 15 minutes. Is that normal?
- HELP: I get an overpressure fault. I have to reset my heat pump several times a day.
- My wife complains the bathroom is too cold. Which electric bathroom radiator can you recommend?
- And finally: my heat pump broke down after only 7 years, compressor failure. Never again Vaillant.
Is it really worth it? Again: we also sized for 35°C (95°F) flow temperature, and in real life, we never reach that. In the bathroom, the pipe spacing is 5cm (2 inches), in other rooms 10cm (4 inches), and in the bedrooms 15cm (6 inches). As a result, the flow temperature can be designed for the regular rooms, and the bathroom is automatically about 2 degrees warmer.
Finally: your energy consumption mainly depends on your usage behavior. You can’t cheat physics; the heat you want to have must be consumed (the formula with delta-T, energy conservation, etc.). Yes, you can lower the flow temperature and lay the underfloor heating pipes closer together. I claim that won’t bring you much.
I would invest five-figure additional costs differently (for example, in a nice photovoltaic system).
And last but not least: yes, you have the right to review the plans. But the general contractor is under no obligation to build exactly what the client wants. I assume the construction contract has already been signed by both parties. The general contractor MUST do exactly what is stated there. Everything else is goodwill.
I already tried to explain this last week. Designing the heat pump based on the standard heating load temperature (NAT) with a 35°C (95°F) flow temperature has almost nothing to do with the actual values experienced in everyday life. This is a calculation value that determines the size of the heat pump and the layout of the underfloor heating. And this is done in coordination.
Yes, you can have all of this changed, and the heating engineer can adjust their calculations accordingly. I’ll keep this for follow-up and wait for your HELP posts:
- HELP: I just can’t get my heat pump settings right. The heating curve can’t be adjusted so that the house feels comfortable at every outdoor temperature; either it’s too cold inside at -5°C (23°F) outside or too warm at +8°C (46°F). I have to keep readjusting it.
- HELP: My heat pump cycles constantly. It switches on every hour and runs for just 15 minutes. Is that normal?
- HELP: I get an overpressure fault. I have to reset my heat pump several times a day.
- My wife complains the bathroom is too cold. Which electric bathroom radiator can you recommend?
- And finally: my heat pump broke down after only 7 years, compressor failure. Never again Vaillant.
Is it really worth it? Again: we also sized for 35°C (95°F) flow temperature, and in real life, we never reach that. In the bathroom, the pipe spacing is 5cm (2 inches), in other rooms 10cm (4 inches), and in the bedrooms 15cm (6 inches). As a result, the flow temperature can be designed for the regular rooms, and the bathroom is automatically about 2 degrees warmer.
Finally: your energy consumption mainly depends on your usage behavior. You can’t cheat physics; the heat you want to have must be consumed (the formula with delta-T, energy conservation, etc.). Yes, you can lower the flow temperature and lay the underfloor heating pipes closer together. I claim that won’t bring you much.
I would invest five-figure additional costs differently (for example, in a nice photovoltaic system).
And last but not least: yes, you have the right to review the plans. But the general contractor is under no obligation to build exactly what the client wants. I assume the construction contract has already been signed by both parties. The general contractor MUST do exactly what is stated there. Everything else is goodwill.
What you’re saying is all well and good. Here’s a brief détournement on how it was for me. The planners had no clue and just entered random values into the software.
- Flow temperature 40°C (104°F)
- Maximum heating circuit length 156 meters (512 feet)
- Pipe spacing 20cm (8 inches), 10cm (4 inches) in the bathroom
The argument was the same: this only applies with NAT, otherwise the flow temperature is lower and the bathroom won’t get warm…
I’m still glad I challenged it. It’s great that your design works well at 35°C (95°F). But I can’t conclude from that that the original poster shouldn’t thoroughly engage with this to ensure the planning is done properly.
- Flow temperature 40°C (104°F)
- Maximum heating circuit length 156 meters (512 feet)
- Pipe spacing 20cm (8 inches), 10cm (4 inches) in the bathroom
The argument was the same: this only applies with NAT, otherwise the flow temperature is lower and the bathroom won’t get warm…
I’m still glad I challenged it. It’s great that your design works well at 35°C (95°F). But I can’t conclude from that that the original poster shouldn’t thoroughly engage with this to ensure the planning is done properly.
Especially when, according to the design plan, it was carried out with 10 and 5 cm (4 and 2 inches) even at 35°C (95°F), then the practitioners simply did something different, or if it was designed that way, he must have quite a high heating load. Maybe his NAT is -18°C (0°F)? In that case, he should not consider his building as generally applicable.
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neo-sciliar13 Mar 2023 13:47As far as I'm concerned... it's not my money. I have an annual heating demand of 8500 kWh at a reference outdoor temperature of -11°C (12°F).
@JohnnyEH I’ll repeat myself: I wouldn’t spend a single cent just because a datasheet shows a lower flow temperature. I would invest that money in obtaining cheap electricity.
@JohnnyEH I’ll repeat myself: I wouldn’t spend a single cent just because a datasheet shows a lower flow temperature. I would invest that money in obtaining cheap electricity.
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