Surcharge for cooling function of air-water heat pump?

We were offered cooling for the air-water heat pump at €2800. After researching online (there is unfortunately little information available), the consensus was that more than 1-2 degrees cooler would not be achievable. Therefore, we preferred to invest €5000 in an air conditioner and did not take the cooling package. From a purely physical perspective, it also doesn't make sense to me what the purpose of this would be (except for cold feet). Because the underfloor heating is, after all, on the floor, and it is the warm air that rises, not the cool air.

I see it the same way. We invest the extra cost in a Mitsubishi split air conditioning system with three indoor units. At least it will be cool when it needs to be.

Funny, we did exactly the same.

With my Panasonic heat pump, the cooling function was already included. I used it quite often in the summer as well. It can definitely prevent rooms from heating up during the height of summer, provided there is shading. Cold floors are certainly an argument, but in the bathroom you can then also turn off the underfloor heating loop. I don't have any other technical devices for cooling. You just have to limit the supply temperature to prevent condensation from forming. I have never operated it below 18°C. I find the cooling function quite useful, but I wouldn't pay a four-digit amount for it; I'd rather get a proper air conditioner that also dehumidifies. You still have the humidity when cooling via underfloor heating, and that is often the unpleasant part. You could also run a loop from the heat pump to a fan coil unit, then you would also have an air conditioner, but there are still further details to consider here.

But do you, for example, not find the cold tiles in the bathroom unpleasant? Or does it not make a noticeable difference?

Not really, at least not for us. We don’t have floor tiles anywhere in the house. I set the minimum supply temperature in cooling mode to 20 +C. It’s (for us) not too unpleasant. Since it’s like this throughout the whole house, the comfortable temperatures work out – we have an open floor plan and apart from the guest toilet and utility room, the few doors are always open – so “it” spreads quite well. But in my opinion, that really comes down to personal taste; one person wants it lightly tempered and another wants ice-cold air in a few spots in the house. Vive la différence ...

The shading naturally also comes into play. Without this, you don't even need to think about the underfloor heating cooling function.

From a purely physical standpoint, it doesn't make sense to me what that's supposed to be good for (except for cold feet). Because the underfloor heating is on the floor, and it is the warm air that rises, not the cool air.

Yes, that is also an aspect. Physics is a tricky thing... The cooler air is then needed more from about 1 meter height, and the pure cooling function alone cannot provide that without additional measures.

Conclusion: If it is included or only a few hundred extra charges, then you can/should do it. Otherwise, rather not and go directly for active air cooling.

Shading naturally also comes into play. Without it, there is no point in even considering the underfloor heating cooling function.

Yes, that is also an aspect. Physics is just one of those things... You need the cooler air more from about 1m height, and the pure cooling function alone cannot provide that without additional measures.

Conclusion: If available and including or with only a few hundred extra cost, then you can/should do it. Otherwise, better not and go directly for active air cooling.

Good point. I might then also give up on the cooling function of the underfloor heating and install air conditioning in 2-3 rooms.