ᐅ LW heat pump Alpha Innotec LWDV with 12 kW?

Daniel-Sp, I can only tell you what is stated in the offer. It includes two storage tanks (300 liters (79 gallons) domestic hot water and 200 liters (53 gallons) buffer tank for heating). The calculation was done by an external engineering office, according to their statement. The 0.16 value is supposed to represent approximately 20 W/m², which, in my opinion, is not realistic. Below 30 W/m², it will not be warm enough to feel comfortable.

freisinger schrieb:

With the 0.16 value, approximately 20 W/m2 should be necessary, which in my opinion is not realistic. Below 30 W/m2 it won’t be warm enough to feel comfortable.

How do you arrive at this statement? Did you calculate it? If so, based on what? Were internal gains taken into account? Calculation according to PHPP? Or is this just the heating engineer’s gut feeling?
As an example: we have a heat transfer coefficient (HT) of 0.201, no mechanical ventilation with heat recovery, natural outdoor temperature of -12°C (10°F) and so far this year not below -4°C (25°F).
Calculated heating load (not according to PHPP!) is 4400 W at 22°C (72°F) room temperature. That is 22°C (72°F) indoor air temperature. The heat pump runs 4–8 hours per day at minimal load of 2 kW with supply temperatures around 24–26°C (75–79°F). The calculations usually include many safety margins.
If the HT of 0.16 is correct, then the heating load is simply that low—so be happy. But if you oversize the heat pump because you are afraid of being cold, you will only have operational problems.
Critically check the heating load calculations and buy a suitably sized heat pump accordingly.
The same applies to the sizing of the underfloor heating; do not simply calculate using watts per square meter, but consider the heating load of each room. An internal corridor has a significantly lower heating load per square meter compared to a bathroom with windows, external walls, and a higher desired temperature! Designing with a fixed wattage per square meter throughout the entire house will result in the bathroom being too cold and the corridor too warm. Unfortunately, this approach is common practice.
Regarding the buffer tank: if the heating engineer insists on installing one, then choose the smallest available and connect it on the return side—no separate decoupling buffer!
I believe you need to study the topic more thoroughly. You will not be able to remove the underfloor heating after installation. Tiles and sinks can easily be replaced. Most homeowners spend much more time and effort on designing bathrooms and kitchens and do not pay enough attention to the heating system. Don’t make that mistake. Unfortunately, you will have to check the calculations yourself; don’t rely on someone who will not live in the house and bear the energy costs later.

Daniel-Sp: Please don’t misunderstand. This is not based on my claims but solely on what the heating technician says. I’m a layperson, researching and looking for ways to make the right decision.
It is really difficult these days to find a competent heating engineer who doesn’t just stick to their “old” methods.
I am also studying the design of underfloor heating in more detail. However, it will only work if I find a heating technician who shares the same understanding.