TGA planner difficulties, underfloor heating supply temperature + wastewater ventilation

What is planned in the shower? For example, I have tiles in the shower and the underfloor heating is also installed underneath. Very pleasant.

Will also be tiled, but an over-tileable shower element is to be installed. This is then made of Styrofoam and accordingly, just like at the bathtub, no underfloor heating will be installed there. Possibly something could still be installed at the bathtub and shower, but it is probably not supposed to change anything in the calculation.

... then maybe execute part of the heating as a wall heating. Maybe there should be a wall for the shower or something.

Yes, that would be the goal. Is my idea sensible to change the calculation basis so that the installation distance in the rest of the house is reduced? In principle, yes, a silly approach but somehow I feel better positioned if the VA is lower. After all, it is something that will last for a few decades.

- Keep the installation spacing in the bathroom at 5cm, if possible add some wall area (let’s see what’s possible) and lower the target temperature in the calculation to 22/23°C.
- This should reduce the supply temperature and thus also reduce the installation spacing in the rest of the house (20°C design temperature in living areas)

I would suggest the same, to use 20 cm throughout the entire house, arguing that needing 40°C supply temperature anyway to heat the bathroom is absurd. This blocks all optimization options afterward, or the possibility to be satisfied with 21°C in the bathroom, possibly with an infrared mirror or bathroom radiator.

Regarding efficiency: the 40°C is the supply temperature in the peak load case, i.e., at -12/14/16 °C outside temperature. This temperature is not maintained continuously, but only 1-2 weeks per year. Therefore, the electricity consumption will not be twice as high, but only slightly higher.

A recent Swiss study (Quality monitoring of small heat pumps and statistical evaluation 2018 – Mick Eschmann, Interstate University of Technology NTB) examined measurements from small heat pumps in operation with 35°C in the design case (surface heating) and 55°C in the design case (radiators) and determined average SCOP values of 4.2 for 35°C and 3.2 for 55°C.
40°C would then (assuming a linear relationship) result in approximately 3.95, i.e., about 6-7% increase in electricity consumption for the same heat demand compared to a 35°C design.
In fact, the relationship is likely not linear, since the physical process (compression) does not require energy in a linear way. Therefore, temperature changes in the lower range are less relevant than at the high end. -> reducing from 55°C to 50°C is more important than from 40°C to 35°C.

Much more important than the last °C in the supply temperature is a proper balancing and operation of the system to operate the heat pump properly without short cycling and buffer tank (which require higher supply temperature). Nevertheless, the approach to reduce the required supply temperature as much as possible is correct.

That way you rule out all optimization options afterwards,

Thanks, that’s also my idea. In the bathroom, there are additionally electric towel warmers anyway.

Regarding efficiency: the 40°C is the flow temperature under load conditions, i.e. at -12/14/16 °C outside temperature.

I think it’s -14 for us. She also used that argument to justify her planning. Actually, the flow temperature is much lower because it’s usually warmer.

Therefore, temperature changes in the lower range are less relevant than at the top. -> going down from 55°C to 50°C is more important than from 40°C to 35°C.

Thanks for the explanations. Makes sense. Of course, you always have to see how far you can and want to push efficiency. I’m also happy to give up 2-3 degrees if it would be expensive/complicated/prone to errors. But I won’t give up out of laziness.

Much more important than the last °C in the flow temperature is a proper balancing and operation of the system to run the heat pump properly without short cycling and buffer storage (which requires higher flow temperature).

Well, you can imagine how someone plans who works like my planner. “A buffer storage must be there, otherwise the heat pump just keeps short cycling.” It was already work to explain to her that I don’t need an ERR in the dressing area, which has a heated area of 2.5 sqm due to closets. The dressing area doesn’t even have a door as separation.

At least the heat pump is rather undersized for the heating load, which, in my understanding, is better than too big.

Regarding the balancing, I’m curious about the sanitary installer. So far, the executing trades have been quite good.