Is preparing for an air conditioner worth it?

Regarding the initial question: I would install a small (2.5 kW) device at a high, central location in the house directly during construction.

If you let it run as soon as the room temperatures get too high and only turn it off again when the heat phase is over, you just have to leave the doors open and you have comfortable humidity throughout the house and – in the case of a new building – also comfortable temperatures.

Of course, it is better to have a device in every room – but eventually that just gets damn expensive.

Why should an air conditioner worsen the energy efficiency of a building? They are funded by Bafa because they IMPROVE the energy efficiency of buildings.

Do you have any evidence for that? We were told that a controlled residential ventilation system with air conditioning function (inverter) breaks the KfW55 requirements.

"According to the definition of § 3 paragraph 1 no. 31 Building Energy Act, only heat and cooling demands for heating, domestic hot water, and cooling are considered when determining the 'heat and cooling energy demand.' Electricity demands for, e.g., auxiliary energy, ventilation, and lighting are not taken into account. The heat and cooling energy demand thus refers to the amount of energy needed annually to meet the building-related heat and cooling demand for heating, hot water preparation, and room cooling, including the thermal effort for transfer, distribution, and storage." (p. 67, - List of Technical FAQ - BEG WG / BEG NWG - Efficient Houses / Efficiency Buildings)

And since air conditioners require a lot of electricity, this also (negatively!) affects the building’s energy value. At least that is how I understand it.

Well, if there is no official cooling energy demand, it might be a ventilation and auxiliary energy demand and therefore does not apply? I would be more concerned about the additional thermal bridge due to the pipe penetration. Perhaps not all contractors are equally careful there...

To what extent is the air conditioning a necessity? Shouldn't it depend on how much the house heats up during the summer months? If the energy consultant calculates that I do not need air conditioning, everything should be fine. The same applies to the heating demand. If I want to heat the house to 30° instead of the standard temperature and therefore choose a larger heater, KFW won't object either, right?

Once again, the details regarding Bafa: "The funding program for cooling and air conditioning systems promotes the use of climate protection technologies in commercial applications. Split and multi-split air conditioners are not eligible for funding in this program and private individuals are not entitled to apply. Split and multi-split air conditioners can (...) be funded as heat pumps. The prerequisite is that they are mainly used for space heating - an additional air conditioning function is basically 'co-funded'." -> It is not about direct/deliberate funding, but rather a kind of "side effect" for air conditioning.

That was not the point of the last question at all. It was about whether the installation of an air conditioning unit alongside the heat pump can be detrimental to achieving a KfW standard.