Cooling with heat pump via underfloor heating?

Since the attic can sometimes reach sauna-like temperatures in summer, the COP drops to zero and the system consumes unnecessarily more electricity than needed. So if you want an efficient system, it must be installed outside or the heat exchanger must be able to be freely ventilated with outside air in the attic.

It is also not enough to change the name if the functionality of an air conditioner (= producing cold) is not present.

That is not true. They are all the same systems. Only heat pumps for heating underfloor systems are not allowed to cool down as much as the same devices which directly cool the air. There are just small differences in construction and software that define certain limits.

But every heat pump for heating can also be used for cooling and every "air conditioner" which is always frowned upon and people almost boo when you mention it can be just as easily converted into a heating heat pump for underfloor heating.

Marketing and advertising slogans are everything. One is vehemently rejected by customers and the other is gladly accepted. And underneath the casing, both are the same system.

That is not true. They are all the same systems.

Then I expressed myself incorrectly. Due to the application, the heat pump cannot operate as an air conditioner. Technically, they are both the same and of course closely related to the refrigerator. There you can clearly see what happens with strong cooling – condensation water. That is why the underfloor heating only works "semi-optimally" ;-)

I am glad that our heat pump can do that, it helps in summer. Air conditioning is better though, ceiling cooling is better. 2. It works with the heat pump, but then it costs more than 1000€.

We have both, an air-to-water heat pump for heating and an air conditioning system. The climate specialist also explained to us during the briefing that it is basically a heat pump, like the heating system. But with 3 split units mounted on the walls that exchange air in the room, and not through piping in the floor. We chose air conditioning and against the special cooling function of the air-to-water heat pump. I have heard from most sources that on really hot days, when you want to cool, it is not enough to lower the temperature by 2-3°C as is possible with an air-to-water heat pump/floor pipes. It was important to us that especially on days above 35°C we have a functioning cooling system, and if it is 37°C outside, I don't want it to be 34°C inside the house.

Absolute priority number 1 should be to design a house in such a way that overheating does not occur in the first place. It's crazy to knowingly stumble into this problem and then install an air conditioner. If a heat pump can "only" cool 2-3° and that is not sufficient, in my view this represents a serious planning error.

You mean the popular large window fronts, which are then darkened most of the time with [Rollläden], [Raffstores] or similar?

I'd rather use an air conditioner and leave the light and view as they are intended.