Reversible Air-Water Heat Pump vs. Air Conditioner with Heating Function

In this thread it is explained several times that hybrid or multiple solutions usually do not really make sense (also economically), otherwise they would probably have long been established on the market as a jack of all trades. Here, too, it is complex and from my point of view I would first of all advise you to reduce the insulation quality below Kfw40. I had a house with 36er Poroton and now one below Kfw40. I could not have imagined it that way, but in fact the rooms cool down significantly less, which means you have to supply less heat. Regardless of the heating system, that would be my first step. From that and the fact that we absolutely wanted a fireplace and use it often, the decision was made for a supporting infrared heating system, although this is still designed as the main heating system but is used rather less frequently. Then we have a Daikin multi-split in 3 areas and for us the system only fits in this combination and to our lifestyle. I read occasionally that people constantly need 23-24 degrees, among other things, which is different for us. Often I also read that air-to-air heat pumps or air conditioners feel like a hairdryer, which is of course meant disparagingly. Ultimately, you really have to look at it closely yourself, preferably live-test it, also because everyone is naturally convinced of their own system and often no other opinions come into play. Everything is possible and there are advantages and disadvantages for everything. The heat input through windows also plays a role; for example, from the end of February to November we often need no additional heating at all. My opinion is therefore the high insulation standard and definitely a standalone controlled ventilation system AND an air conditioner. Whether you then still need an expensive air-to-water heat pump with/without underfloor heating depends entirely on you; for us that was answered by the fireplace and we are very satisfied with our energy consumption. I would also always install a controlled ventilation system again, because the air quality is really noticeable to me and also gives me the good feeling of sitting on the sofa virtually outdoors. That’s how it is for me! Our air conditioner cost 10k but is equipped with generous units, costs virtually no electricity due to photovoltaics, and in winter we use it occasionally for supplementary heating, e.g. in the morning when the sun does not yet bring enough warmth into the room or briefly in the evening. I do not find that unpleasant and even if a warm breeze were noticeable I would find that pleasant. You can also look at where to place the units, plus there is a swivel mode etc. Electricity consumption is low, also because it only runs in power mode for a while and then continues at a low level. These are my experiences and the opinion that actual cooling is only achievable with an air conditioner. By the way, our hot water comes from an AroStor heat pump.

Yes, the question is whether the rooms with supply air are not exactly the rooms I want to cool? I would say, for the most part, 'yes'.

What about exhaust air from the associated kitchen? And the other pipes?

The last point is more meant like 'I want the air-water heat pump because it is the basis of the house ... if I have the air-air heat pump, I can additionally use it to relieve the air-water heat pump or move it into efficiency-optimized areas'

You don’t need to relieve the air-water heat pump. That’s nonsense. You just want to connect an air conditioning system to the controlled ventilation system. THAT doesn’t work.
Cooling 2.5 kW, for example, with the mentioned device. That’s manageable. You will never achieve “real” cooling without a real air conditioning system or concrete core activation.
And you will always feel the cooling then as well.

Addendum: Before you think about active cooling of the house, the planner (and of course you) should first consider good passive cooling. By that I mean summer thermal protection. This can be the orientation of the house (I would never ever come up with the idea of placing the living area with terrace fully in the southern sun, only to then have to work with shading because it gets too hot), roof overhang, window areas and orientation, and of course – as Arauki11 also wrote – the insulation standard and materials used, etc. Then the issue of heat in the house (especially with a controlled residential ventilation system, where you don’t keep opening the windows to let warm air in) will not be such a big problem.

One more addition to nordanney. Although only 10km apart, it never gets as warm in our small town as in the neighboring big city, so the buildings never heat up as much and can also cool down a bit at night. Before, we lived very rurally secluded by the creek among many trees, where it was cool in the evenings even in midsummer. A 10° difference to the big city during both day and night was not unusual in summer. One should also take the microclimate into account here, and it makes it difficult to infer from one building to another besides one's own habits.

One more addition to nordanney. Although only 10km away, it never gets as warm in our small town as in the neighboring big city, so the buildings there never heat up as much and can cool down a bit again at night. Before, we lived very rurally secluded by the stream among many trees; even in midsummer it was cool in the evenings. A 10° difference to the big city both day and night was not unusual in summer. You should therefore also include the microclimate here, and it makes it difficult to infer from one building to another alongside individual habits.

Exactly, these are further parameters and added to them are one’s own factors, like the perception of heat. I know from myself that I feel extremely uncomfortable when it is humid or if I have to be in an overheated room or even sleep there. Ergo, my decision was in favor of air conditioning, and I love it just knowing it is there. Today it is already so warm that I might have run the AC lightly during the day if I had been there. But as already writes, the topic begins much earlier. In this respect, interested parties should provide more information about their house and their situation here.