Cooling with heat pump via underfloor heating?

If a heat pump can "only" cool 2-3° and that is not enough, in my view there is a serious planning error.

Objection: If I look back at the development of recent years, the planning error lies in building in Germany. In Sweden, for example, summers are not that hot ;-) Eventually, the heat gets into every house – planning or not. And then you are stuck, because not only the cold is kept outside, but also the heat inside. Then only an air conditioner helps.

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

Yes, sounds plausible. Since we still plan to renovate our facade, it might be sensible to have empty conduits installed, to at least keep the option open later. The bedrooms are on the upper floor. The final solution is not yet decided. How big should the empty conduits be? It could also be a ventilation system installed in the attic to help in summer. Should I create a new thread for this?

The only right decision. With today's (intentional) construction methods without relying on special gimmicks.

Absolute priority number 1 should be to design a house in such a way that overheating doesn't occur in the first place. It's completely crazy to knowingly stumble into this problem only to then install an air conditioner.

Not everyone wants to live in a bunker. The focus of all the regulations (Energy Saving Ordinance and co.) is on the winter months in order to save heating energy and avoid that oh-so-evil CO2. In summer, however, the effect does not reverse (how should it), so the heat gains just remain inside.

If a heat pump can only cool 2-3° and that's not enough, in my view, there is a gross planning error.

No, there is no planning error here. This is what is possible without additional measures and only with the advertised underfloor heating cooling, no matter what the general contractor/developer/broker/manufacturer says. Purely from a physics point of view.

How big should the empty conduits probably be?

DN50 is sufficient per indoor unit. But you also have to think about the condensate drain. So if you are already planning, you need to provide a little more than just empty conduits.

In Germany, we only have a few hot weeks, so far I have always managed very well without cooling. Now it is almost May and still single-digit temperatures. From September onward, summer is over. In between, as always, many cool and rainy periods.

I also think that natural shading or trees are the better (sufficient) solution than air conditioners.

South-facing windows are well controlled with roof overhangs or building recesses; after all, the sun does us the favor of changing its position with the seasons. A roof can also be designed so that the attic does not become a sauna. West/East with external shading (venetian blinds or those strange deciduous trees). It would be a planning error to ignore such things and design houses where "only" 2-3° heat pump cooling is not sufficient.

This certainly doesn't fit every architecture, but it does for the vast majority of single-family homes.

Greetings from the physicist in the bunker with window area of 40% of the living space 8-)

I also think that natural shading or trees are the better (sufficient) solution than air conditioning.

Sure, they will have grown so big in 10-20 years that the house will also get some shade. Provided there is enough space on the towel-sized plot and the neighbor has nothing against it. Until then, it means sweating or air conditioning.

That certainly doesn’t fit every architecture, but for the vast majority of single-family homes it does.

It’s the other way around. For the vast majority of single-family homes built nowadays, no bigger jumps are possible, especially regarding architecture. One step to the left and one step to the right. Everything else exceeds the budget of the average home builder. Just look at the new housing developments. That any kind of summer heat protection was even thought of can often be seen only in a few houses. What were the most popular and most built houses in Germany in 2020 and 2019 again? Oh yes, Flair 152 and Citylife 143 V. Unfortunately, that’s the reality: off the shelf and with as little variation as possible. This also includes front/rear projections and longer roof overhangs, not to mention external shading. Don’t get me wrong. In a perfect world you could of course do without air conditioners, but for that, the construction method of modern houses would have to be changed, and that comes with costs. In the end, the average builder takes what is simply cheaper overall.

Greetings from the physicist in the bunker with window area of 40% of the living area

Great, that makes you one of the few exceptions (there are supposed to be some... I’ve heard).