Installing air conditioning --> KFW funding gone?

I would like to have a source for that. Until then I say: "Nonsense!"

The physics behind my claim: Delta t in winter ~ 35° Delta t in summer ~ 10°

Why the latter should need 3 times more energy with the same technology...

Please do not calculate with maximum but with the average – the average temperature in the winter half-year 2020/2021 (= heating period) for example in Bavaria was 1.9 °C.

So just under 20 Kelvin dT. Not 35.

And in addition: solar radiation supports the heating system – up to about 8° and some sun I don’t necessarily need heating. In other words, you have a “tailwind.” In summer it is exactly the opposite – now the heating technology has to work against it, so “headwind.”

I would like to have a source for that. Until then, I say: "Nonsense!"

The physics behind my claim:
Delta t in winter ~ 35°
Delta t in summer ~ 10°

Why the latter should need 3 times more energy with the same technology...

I am glad that someone with physical knowledge doubts this!

My source: a phone conversation with the technician of our house manufacturer. He himself lives in an old prefabricated house (42 years) and bought mobile air conditioners for it, which unfortunately rely on the discharge of the generated warm air THROUGH the open window. Energetically, that is practically irrelevant.

The reason for my call was that I wanted to know if, in my place, he would actually want to install the heat pump with cooling function sold by the house manufacturer or rather go straight for a proper air conditioner.

He would make the structural preparations for a real air conditioner if he were building new. Reason: prefab houses do not provide the MASS to buffer temperatures. (Church in Mediterranean climate!)
If the air does not cool down significantly at night, you simply cannot exchange it meaningfully.
Unlike the massive church, today’s buildings are built with strong solar gains through huge south-facing windows. Lots of input, little output.

If you tell me where to look, I would also gladly check my energy report for the house.

I am having my patient day today. So:

So about 20 Kelvin dT. Not 35.

Still more than my assumed maximum! In summer, right?

And on top of that: the solar radiation supports the heating system – up to about 8° and some sun, I don’t necessarily need heating. In other words, you have a "tailwind".

And in summer you have cool nights and steep sun angles that don’t shine directly through the south-facing windows. Even balance, I would say.

In summer it is exactly the opposite – now the heating technology has to work against it, so "headwind".

Each system always works against the respective energy inflows and outflows. At a location with an annual average temperature of 22°, one could probably achieve a balance between cooling energy and heating energy. Unfortunately, Germany has about 10°. So probably more heating than cooling is done. If I look around, the ratio of heaters to air conditioners supports my theory. ;-)
And yes, if you cleverly play with windows and shading, you can save energy both in summer and in winter.

I stick to my statement that I would like sources. Until then, my experience with a total of five heat pumps in three households and some logic (see above) will have to suffice.

Currently my old building:
Heating: 5000 kWh, Cooling 1500 kWh

New building (KfW55), occupied by parents:
Heating: 2300 kWh, Cooling 300 kWh

That can and will certainly fluctuate depending on location and the conditions of the occupants and the house. However, I do not see your basic statement that cooling costs three times as much energy as heating confirmed. Rather the other way around.

I am glad that someone with physics knowledge doubts that!

A thermos flask doesn’t care whether you pour iced tea or coffee in it...

He himself lives in an old prefab house (42 years) and bought mobile air conditioners for it, which unfortunately rely on the exhaust of the produced warm air THROUGH the open WINDOW.

That disqualifies him from advising on air conditioning. Those things are simply energy guzzlers. Please don’t buy them! Oh, and please also don’t do the nonsense with the wet towel and the fan. That just makes it even more humid. It helps as much as scratching when treating bee stings.

... who would want to install the heat pump with cooling function sold by the house manufacturer or rather go straight for a proper air conditioner.

If you build a house with a lot of mass, underfloor heating, concrete core activation, etc., it’s never wrong to take advantage of the heating system’s cooling function. A manufacturer who charges extra for this should be excluded immediately. Apart from an additional condensate alarm (which can easily cost €50), it only requires a checkmark in the heat pump’s software. If that’s not the case, the heat pump is already scrap metal. BUT: this can only work as a supplement to at least one air-to-air heat pump (air conditioner), because the relevant part—the part that positively influences the “indoor climate”—is the dehumidification of the air. And underfloor heating can’t do that. On the contrary: if I cool the air in the house, the relative humidity rises and “everything sticks.” However, the two systems complement each other very well: the “Big Bertha” (heater) with, for example, 5 kW, can extract a serious amount of heat energy from the house. At the same time, a small, energy-saving air conditioner can dehumidify the air, which also works very well across room boundaries. So the answer is yes. Both.

He would make the structural preparations for a proper air conditioner if he built new.

I would install it right away. Cheaper, cleaner, currently even subsidized. Two friends have recently built, both (against my suggestion) installed no air conditioning (after all, it’s so well insulated!!). One family has been sleeping in the basement for days, the other has none and is puking. (Admittedly, no one has admitted that I was right yet ;-)

If you tell me where I can look, I’ll gladly also look into my energy certificate for the house.

For what? In my opinion, every semi-detached new build should have a (small) air conditioner installed. Just like controlled residential ventilation and the roof fully covered with photovoltaic. Then it’s perfect.

Sorry, I realized too late that it wasn't you who claimed the "3 times more energy."

Even at the risk of being attacked right away.
We have now had our first stress test:
Starting point:
36.5 cm aerated concrete, south-facing, very large window areas, venetian blinds, underfloor heating on the ground floor and upper floor, attic converted with low-temperature radiators connected to the underfloor heating, brine pump with cooling function, and controlled residential ventilation.

Here (Rhineland) it has been 34-36 degrees for many days in a row.
The heating switched to cooling mode, the controlled residential ventilation runs day and night with bypass on the lowest level, windows always closed, even at night. Venetian blinds down during the day, slats at 50%.
Result, depending on time of day 23-25 degrees.
I find that great and also very pleasant. The floor is not cold, as is often said, and the temperature is just right. Personally, I also find it very unpleasant to come in from the garden at 35 degrees and the house is only 21/22 degrees. The contrast is too strong for me. The 23-25 degrees still feel very cool. Of course, humidity at 65% could be better. But maybe that will improve. It is said that humidity is higher in a new building in the first years.
If not, that is okay too. I found it very pleasant and am very satisfied with our summer heat protection without air conditioning.

Just offering a different perspective.