ᐅ Lowering the Supply Temperature in Underfloor Heating Systems More Complex Than Expected?

KarstenausNRW schrieb:

Apart from that, I completely agree with you that 35 degrees Celsius (95°F) is outdated. However, this allows for simpler and more cost-effective planning, making the house cheaper...

Caution: Restrictions must still be considered! Even the popular engineering office could only calculate a supply temperature of 34°C (93°F) for my KfW55 house without having to resort to additional wall heating everywhere. Sounds strange, but it’s true.

For a timber frame house, this should not be the case. So, in this particular case, you are right. 😉

OWLer schrieb:

I had the problem with this requirement that the low supply temperature would have required a small temperature difference. The Vaillant Arotherm Plus 55/6 would not have achieved that temperature difference in my case. Only the 75 model could deliver the required pump capacity (pumping water through the heating coils – not the compressor) according to the datasheet (1x00 liters/hour).

Basically, it applies that lower supply temperature = SMALLER heat pump, as long as it can provide the necessary pump capacity for the heated water.

How is the provider calculating this, and what is their reasoning?

Thanks – this could be the same issue for us. We’re also looking at the 55/6 or 35/6, though I’m actually quite indifferent between the two because according to the datasheet I don’t see any disadvantages in terms of more frequent cycling or higher electricity consumption with the 55/6.
Of course, I don’t want the 77 model. Once the detailed calculations come up, I will ask again if that’s the reason.
So far, we’ve only received these general statements. I don’t yet know exactly how the provider is calculating.

RotorMotor schrieb:

In my opinion, the biggest challenge is always to heat the bathroom properly.

That usually requires very tight pipe spacing, circuits, and loops along the wall so that it’s comfortable at a supply temperature of 30°C (86°F) without additional radiators.

For our bathroom, an electric fan heater (1800 W) is included to raise the temperature up to 24°C (75°F) if needed. Although I tend to lean towards installing an infrared wall panel later to replace the fan heater. But the bathroom will probably indeed be the biggest challenge.

ypg schrieb:

Find the mistake! One word doesn’t fit. There are two solutions 😉

I said that I’m aware that laminate floors don’t compare to tiles or vinyl in terms of heat. I just wasn’t sure if it might be different for cold.

Stefan001 schrieb:

Regarding the floor covering, it depends on the installation method. Glued vinyl is very good; vinyl installed floating over cork insulation and impact sound insulation is not.

Whether the heat is warm or cold doesn’t matter; it’s about thermal conductivity.

I am satisfied with both glued vinyl and tiles. But I personally don’t notice a difference since I don’t have a consumption comparison with just tiles.

Isn’t additional impact sound insulation also installed under glued vinyl?
In which rooms did you choose vinyl instead of tiles, and why?

KarstenausNRW schrieb:

Five-digit costs are possible – the house manufacturer wants to make a good profit with special requests. The material and additional installation effort will probably only be in the lower four-digit range.

That naturally raises the question of whether it will be worthwhile in the end. As far as I understand, reducing the supply temperature from 35°C (95°F) to 30°C (86°F) could save about 5–6% electricity. But the supply temperature of 35°C (95°F) only applies at the standard outdoor temperature, which might occur for only about three weeks per year.
Once the exact calculations are available, we will definitely follow up to see if anything can be done about it.

JohnnyEH schrieb:

Isn’t additional impact sound insulation also installed with glued vinyl?
In which rooms did you choose vinyl instead of tiles, and why?

In our case, the vinyl was glued directly onto the screed or leveling compound. The vinyl is about 3mm (1/8 inch) thick.
We have vinyl with a wood look and a very rough surface in every room except the bathrooms and the utility room.

I really don’t like the feel of tiles, especially since I often drop things. Wood wasn’t suitable due to its water resistance (and the price...), and laminate for me just combined all the downsides from different options.

One point to consider might be indoor air quality, but honestly, I haven’t given that much thought. Many people who do tend to get into more esoteric territory 😉

Edit: Much more important for efficiency is that your heat pump can modulate down LOW ENOUGH! Don’t let anyone sell you an oversized heat pump that just keeps switching on and off!

OWLer schrieb:

Note: Restrictions also have to be applied here! Even the well-known engineering office could only calculate a supply temperature of 34°C (93°F) for my KFW55 house without having to use additional wall heating everywhere. Sounds strange, but that's how it is.

Pipe spacing? Even in a renovated old building, I was able to have it designed for 30/26 (86/79°F) at 22°C (72°F) room temperature.

JohnnyEH schrieb:

Isn’t an underlay for impact sound insulation also installed with glued vinyl?

The vinyl is always glued directly. However, this does have an effect on impact sound insulation. The structure consists of a base plate/ceiling, insulation, and then the underfloor heating embedded in the screed. If people walk barefoot because the floor is warm, you can hear it. The reason is the heel strike pattern learned when wearing shoes. Walking on the ball of the foot does not make noise, and neither do slippers.

@JohnnyEH There are a few things getting mixed up here. I initially had the same confusion when planning the heating system.

First of all: what is your actual goal? That isn’t entirely clear to me. You need to distinguish between the theoretical calculations and real-world conditions.

The 35°C (95°F) supply temperature is normal because it refers to the design outdoor temperature (DOT). The calculations show that your house must be warm even at the DOT. So your heating system needs to achieve a supply temperature of 35°C (95°F). In reality, this only happens for about two days every five years. Most of the time, your supply temperature will fluctuate between 26 and 30°C (79 and 86°F), rarely going higher.

Now you’re asking the theorist to reduce the supply temperature (just to remind you, this only applies at the DOT) in their calculations. That means they have to reduce the pipe spacing (significantly in your example), otherwise your house won’t warm up at the DOT. This results in much more water volume in the underfloor heating system, requiring a higher flow rate, and thus a larger heating system — which you actually don’t want, because you lowered the supply temperature. Your smaller heat pump will quickly run into flow issues. The larger one will start cycling heavily, consume more electricity, and suffer faster wear. To handle this, you could add a buffer tank, but that costs extra and reduces efficiency… and all this just because you want to lower the theoretical 35°C (95°F) value that hardly ever gets reached in practice anyway.

Clear? My advice: forget that idea.