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 We mentioned that we consider this outdated for a new build and would prefer a supply temperature of around 30°C (86°F).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 We mentioned that we consider this outdated for a new build and would prefer a supply temperature of around 30°C (86°F).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?
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KarstenausNRW10 Mar 2023 14:21neo-sciliar schrieb:
This means you have much more water in the underfloor heating system and need a higher flow rate, which implies a larger heating system that you actually do not want, That is not quite correct, at least regarding the larger heating system. First, many manufacturers install the same pump model regardless of whether it is a 5kW or 9kW heat pump. Also, the flow rates do not increase that dramatically.
Additionally, I would add that both the supply and the return need to be taken into account. There is a significant difference between designing for 30/26 or 30/24.
The original poster should provide their heating system design data and the specifications of the heat pump.
So, the technical specifications for the Vaillant Arotherm plus series are accurate. The 55/6 model supposedly cannot achieve the required volume flow rates. However, in the neighboring thread, there was already some suspicion that the pumps might actually deliver higher performance.
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neo-sciliar10 Mar 2023 14:33On page 1 of the thread, you can see the possible volume flow rates. These clearly change with a larger heating system (580 → 790 → 1418 l/h). And of course, you can let the water flow slowly through the underfloor heating, resulting in a wider temperature difference (30/24). But then the question is whether the bathroom will still warm up enough for the household member who likes to shower. In that case, we’re talking about a bathroom radiator (of course, electric). This costs money and additional energy. Returning to my initial question: what is the original poster aiming to achieve by lowering the theoretical 35°C to 30°C? Saving energy—probably not. Saving on investment—also not. Increasing service life—also not. So, what then?
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KarstenausNRW10 Mar 2023 15:34neo-sciliar schrieb:
On page 1 of the thread, you can see the possible volume flow rates.Sorry, I didn’t notice the edit on page 1. But I’ll just increase the data listed there now. Specifically, from the 55 model from 580 liters per hour (l/h) to 860 l/h, or from the 65 model from 790 l/h to 1,205 l/h. These are actually the official maximum figures provided by Vaillant (see Vaillant). Adjustable on the unit itself. So, I would be surprised if anyone had real problems with the volume flow rates in an average KfW40-standard house. With 860 l/h, that is 14 liters per minute (l/min), you can easily heat a typical 40 energy efficiency house (I assumed about 140 to 160 square meters) with a 30-degree Celsius (86°F) flow temperature.
Aside from that, I find Vaillant’s components and options rather basic and suboptimal overall. I prefer Asian manufacturers like Panasonic, Samsung, LG, or Hitachi, who usually install decent pumps right from the start. Their entry-level models often run well over 1,000 l/h, sometimes even up to 2,000 l/h. My small Panasonic can handle up to 2,100 l/h—which I of course never need.
Yes, I have the 75/6 model, and I wouldn’t recommend it, see our arotherm thread...
https://www.hausbau-forum.de/threads/vaillant-arotherm-plus-vwl-35-55-75.42822/
It actually makes sense, as Asian manufacturers have been producing heat pumps (air-to-air as split air conditioning units) for much longer than the traditional Central European companies.
The heating engineer handles the hydraulics anyway, so the units themselves tend to be much more advanced.
If only I had been at this point two years ago...
https://www.hausbau-forum.de/threads/vaillant-arotherm-plus-vwl-35-55-75.42822/
It actually makes sense, as Asian manufacturers have been producing heat pumps (air-to-air as split air conditioning units) for much longer than the traditional Central European companies.
The heating engineer handles the hydraulics anyway, so the units themselves tend to be much more advanced.
If only I had been at this point two years ago...
Stefan001 schrieb:
We have vinyl flooring with a very rough wood-look surface in every room except the bathrooms and the utility room. Which type of vinyl did you install? We definitely want wood-look as well—whether tiles or vinyl.
Stefan001 schrieb:
edit: Much more important for efficiency is that your heat pump can modulate DOWN enough! Don’t get sold on a large heat pump only for it to keep switching on and off! I understand that—but shouldn’t it be the same whether it’s the 35/6 or 55/6 model? Or am I misinterpreting the specifications?
WilderSueden schrieb:
The adhesive installation is always direct. However, that also affects impact sound. Your construction layers are subfloor/ceiling, insulation, and then underfloor heating in the screed. When people walk barefoot on a warm floor, you can hear it. It’s because people are used to walking on their heels with shoes. With forefoot walking, there’s no noise, and it’s also quiet with slippers. That’s interesting—I would have bet that slippers make more noise than barefoot. Does choosing tiles or vinyl make a difference for impact sound?
neo-sciliar schrieb:
First of all: what is your goal? That’s not entirely clear to me. You need to distinguish between theoretical calculations and real-life conditions. My goal is to size the heating system so that all rooms get warm enough, while not using unnecessary electricity. I read all over the internet that 35°C (95°F) leads to higher electricity use and is outdated, so that made me question it.
neo-sciliar schrieb:
A flow temperature of 35°C (95°F) is normal because it refers to the design outdoor temperature (DOT). The calculations show that your house must be heated even at DOT conditions. So your heating system must be able to provide a flow temperature of 35°C (95°F). In reality, this only occurs about once every five years for two days. Most of the time, your flow temperature will fluctuate between 26 and 30°C (79 and 86°F), rarely higher. Thank you for the explanation. But when people here and in other threads mention flow temperatures of 30°C (86°F), don’t they also refer to the design outdoor temperature? And if the flow temperature at DOT is lower, doesn’t that automatically mean the flow temperature at, for example, 2°C (36°F) outdoor temperature is also lower?
KarstenausNRW schrieb:
Apart from that, I consider Vaillant components and options rather basic and not optimal. I appreciate Asian manufacturers like Panasonic, Samsung, LG, Hitachi, who usually install good pumps right from the start. Their entry-level models often run at well over 1,000 liters per hour, sometimes up to 2,000 liters per hour. My small Panasonic reaches a maximum of 2,100 liters per hour—which I obviously never need. Well, we are tied to Vaillant. That’s what the supplier mandates. They might not be the best, but I don’t think they are the worst either. At least some friends are quite satisfied with their Vaillant systems. If the heat pump breaks, can we replace it with any other manufacturer? Or is it “once Vaillant, always Vaillant”?
Tolentino schrieb:
Yes, I have the 75/6 and I would not recommend it, see our arotherm thread... That thread is very, very long 😉. Could you please briefly summarize why you wouldn’t recommend it?
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