Internal heat pump in the basement not possible due to groundwater?

Split = At least two heat generators Whereas these cannot be operated with R290.

I'm just reading this now. Unfortunately, you are mistaken. Split means the refrigeration circuit is divided. A split heat pump can just as well be operated monovalently in terms of heating mode. In other words, only the heat pump produces hot water and heats.

And just so you know... in my basement there is an indoor air-to-water heat pump. It's a monoblock. My neighbor has a split unit. It is also operated monovalently.

@

R32 has a boiling point of -52°C, whereas R290 has one of -41°C. That is why R744 (-57°C) is also used in refrigeration technology. Both R290 and R744 are natural refrigerants with the BEG bonus.

For what reason do you want to install an indoor unit outside and not operate it monovalently? The basic idea is to save costs and use better technology.

---
Always related to new construction as in the EP, so no hybrid solutions like in NWG or existing buildings.

@
Therefore, your neighbor still cannot operate the split heat pump monovalently.
The terms exclude each other. MONO = ONE heat generator and not split or multisplit = at least two. (Splitting is nothing other than dividing)

It does not matter at all where the monoblock is located; if it is inside, it is not an outdoor monoblock but an indoor monoblock.

The term monoblock is technically irrelevant and only indicates a configuration where everything is contained within one housing.

No idea what you want to tell me with this refrigerant confusion.

With a split system, you don’t have two heat generators. It’s called split because the components are divided into two housings. Not because there are two heat generators.

Monoblock is opposed to split.

Monovalent is opposed to bivalent.

One is a "design" the other is how it is operated.
But I don’t even know why I’m starting this again.

Thank you for the numerous responses. Novelan itself, at least after telephone consultation, sees no problems with an indoor installation.

The reasons why an indoor installation is preferred:
- Noise sensitivity. Even though the devices are now very quiet, I do not want it to be placed under the bedroom window. That would be the shortest route. Elsewhere on the property would require very long lines.
- Aesthetics.
- Space conditions on the property
- Lifespan of the device if it is not exposed to the weather

Here is the excerpt regarding the groundwater conditions:
"Ground and/or layered water was detected in all drillings. The highest water level was recorded after completion of drilling at drill site BS1 at 3.40 m below ground level (Baukote -3.62 m). The detected groundwater levels represent low water levels due to the prolonged drought. ... . In the groundwater measurement point, groundwater rises up to about 1.5 m below ground (~365.25 mNN) have been recorded in the last 10 years.
...
The design water level can only be estimated and is set at Baukote -1.75 m, taking into account a natural fluctuation range of the groundwater of ±1.75 m. The earth-contacting components must be classified according to DIN 18533-1 in water exposure class W2-E (pressing water) and sealed accordingly."

So I can't contribute much to the groundwater topic. Ours is also installed indoors in the basement and the intake/exhaust air goes through light wells. Unfortunately, I can’t tell you exactly how it was with the groundwater, but we had to build with a white tank. Unfortunately, I also can’t tell you what was done with the light wells, whether they were sealed again, that might be the case, I just don’t remember anymore.

Regarding indoor installation:

It was also a topic for us that we couldn’t find a good place, with our neighbors who have the "same" plot the thing is basically next to the terrace. I think that’s terrible. At the spot where the light wells are now, three plots come together and three houses stand close to each other, back then (planning about 4 years ago) it was too risky for us regarding noise development. Today I might think about it again.
Indoor installation definitely also has disadvantages.
Efficiency, if there is any disadvantage at all there, I would disregard. Better to focus on making sure the rest of the setup fits. (Design, sizing, components e.g. without buffer, spacing etc.)
That influences efficiency much more than the indoor or outdoor issue.
Disadvantages, as partially already mentioned, you have to keep a very close eye on the planning and execution. The wall openings have to fit, be properly insulated, etc.
Crucial is sound decoupling. The indoor unit must stand on a properly decoupled base. Also, the pipes must be flexible etc. Otherwise, structure-borne noise transmits to the building.
Then you should definitely equip the utility room with a soundproof door. (Please also consider this in the ventilation planning if there is one, because with soundproofing an overflow doesn’t work).

Actually, from my current knowledge I would reconsider whether indoor or outdoor again. But for the reason that you are much freer in the choice of the heat pump and I believe the noise level of the outdoor units has actually improved significantly.

Should the device then need to be replaced hopefully in the distant future, there is always the option to choose an outdoor unit then. Of course, it is more effort because you have to close the wall openings again, but it’s not as if you’d have to rebuild the entire house.