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 We mentioned that we consider this outdated for a new build and would prefer a supply temperature of around 30°C (86°F).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 We mentioned that we consider this outdated for a new build and would prefer a supply temperature of around 30°C (86°F).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?
H
Hausbau55EE11 Mar 2023 09:04RotorMotor schrieb:
With Styrofoam insulation placed below and above the pipes, the energy primarily stays in the water and ends up in the return line.
The main issue, as mentioned, is that the 30m (98 feet) of pipe under the bathtub restricts the flow.
So, it barely or does not transfer heat, but it reduces the flow throughout the entire circuit and thus the performance of this circuit. At least you are now stating no or hardly any heat transfer in your formulation. And maybe you have some kind of calculation after all?
My house has 20cm (8 inches) of mineral wool insulation on the exterior walls, and the attic is insulated even better... I keep wondering why I even need to heat?
I’m stepping out of this discussion now.
H
Hausbau55EE11 Mar 2023 09:09Daniel-Sp schrieb:
Exactly, warm air is drawn out of the room with the highest desired temperature, the bathroom, and air from the cooler rooms flows in.With 2 air-to-water heat pumps in the bathroom and controlled residential ventilation, maintaining 24°C (75°F) in the bathroom while keeping 20°C (68°F) in all other rooms becomes a real challenge???
H
HoisleBauer2211 Mar 2023 09:33RotorMotor schrieb:
With Styrofoam insulation below and above the pipes, the energy mainly stays in the water and returns through the return line.
The main issue, as mentioned, is that the 30m (98 feet) of piping under the bathtub restricts the flow.
So it hardly releases any heat but reduces the flow throughout the entire loop, which lowers the performance of that loop. That makes a lot of sense. Yet, the heat isn’t really “lost,” it’s just not where it can be felt.
Daniel-Sp schrieb:
Exactly, you pull warm air out of the room with the highest desired temperature—the bathroom—and cooler air from the other rooms flows in to replace it. You’re absolutely right, but if the temperature difference is only about 2 degrees, and the heat is stored more in the room’s thermal mass than in the air, then it’s not a big problem. The gap under the door is usually about 1cm (0.4 inches) thick if done properly...
Allthewayup schrieb:
I recently discussed this topic (reducing the supply temperature to 30°C (86°F)) with our general contractor as well. He said he has to base the calculations on 35°C (95°F) because that is what the standard requires. If he doesn’t comply, I could hold him liable in case the target values are not met in practice.
[...]
I accepted that for now since the contract guarantees me a turnkey house and I can hardly demand every calculation in detail. Personally, I’m not happy about it, but unfortunately, that’s usually the case when building with a general contractor. Before signing, I didn’t really think this could become such a big issue. That’s unfortunately how it is. Nobody thinks about it beforehand. But don’t let that stop you from designing the underfloor heating system for a 30°C (86°F) installation temperature (if that’s feasible based on calculations!) and just not guaranteeing the temperature. Even with a 30°C (86°F) pipe layout design, you can still achieve 35°C (95°F). This way, the discussion will focus on the length of piping and the pipe spacing rather than temperatures.
I thought about it in advance myself, but my general contractor “misunderstood” it. It ended up with me having to pay for an external design and a few hundred euros extra for wall heating in the bathroom. It was worth it to me.
HoisleBauer22 schrieb:
Back to the thread topic: The main insight for me so far in this discussion is that the investment (with a general contractor: several thousand euros) is never worthwhile. For just a few months of heating… And ideally you have a photovoltaic system that reduces energy costs in the colder months… Because it really only involves a few meters of tubing, two larger heating circuit manifolds, and about two extra hours of work for the general contractor. The “several thousand euros” are a kind of compensation for convincing the crew to make an effort instead of just installing the standard routine as usual.
A
Allthewayup11 Mar 2023 11:29OWLer schrieb:
Unfortunately, that’s how it is. No one thinks about it beforehand. But don’t let that stop you from designing the underfloor heating system for a 30°C (86°F) installation temperature—if calculations show it’s possible—and simply not guaranteeing that temperature. Even with the 30°C installation design, you will be able to reach 35°C (95°F). Then you’ll just be discussing pipe length and spacing rather than temperatures. In the further discussion, he mentioned that he plans the pipe spacing at 10cm (4 inches), and theoretically, this should allow us to operate well below the 35°C (95°F) supply temperature. However, how this fits into the overall design is unclear to me.
I probably won’t see how the system is ultimately designed until it’s installed; I won’t receive a design beforehand, and I can’t separate this as an individual trade because he refuses to cooperate with that.
There is so much in house construction that you should read up on in depth—where do you draw the line when you’ve awarded a general contractor? In the end, you often realize, “I could have just hired individual trades myself.” But the lack of knowledge about construction processes and the associated fear of making mistakes, forgetting something, or overlooking details drives many to choose a general contractor. Once construction is actually underway and you start researching the trades yourself, doubts often arise—just too late, of course.
Still, I stand by my decision; I have no other option now—think positive! 🙂
H
HoisleBauer2211 Mar 2023 11:40Allthewayup schrieb:
I will not receive any preliminary planning You have the right, for example, to have the heating system design checked according to DIN standards together with an expert, as it is implemented in your house. Therefore, the general contractor must provide you with the plans. You might want to ask a (construction law) attorney whether you can copy them in on your correspondence with the general contractor. Sometimes a bit of gentle pressure helps. Legally, no one should be able to deny you the right to inspect the construction work. Please correct me or feel free to provide relevant court rulings.