Cooling with heat pump via underfloor heating?

The air and thus also the humidity are gone because of the ventilation system, right?

No, because in summer fresh air with the same humidity comes in in equal parts. In winter it is different because dehumidification works here. In summer, however, it does not, as the (large) temperature difference is missing.

No, because fresh air with the same humidity comes in again in equal parts in summer. In winter this is different because dehumidification works here. In summer, on the other hand, it does not because the (large) temperature difference is missing.

Even with an enthalpy heat exchanger? Because we will have one of those too.

As far as I understand it as a layman, it can regulate the humidity.

How is the interaction between: underfloor heating, underfloor heating temperature control and ventilation system? The air and thus also the humidity is lost to the ventilation system, right?

In the summer months, our ventilation system only runs at night. If I run it during the day, no matter how much I shade, I am pumping warm outside air into the house. Then there is the heat recovery of modern systems - it can partially be switched off via bypass / summer cassette, but it doesn’t help if it’s 30 degrees outside. The underfloor heating does not run at all because the heating system is in summer mode. The air conditioning runs daily, on and off, and dehumidifies / cools. I would never want to live without air conditioning again; it is quietly humming quality of life on the wall.

In the summer months, our ventilation system runs only at night. If I run it during the day, no matter how much I shade, I’m just pumping warm outside air into the house. Then there’s the heat recovery of modern systems – you can partially switch it off via bypass/summer cassette, but it doesn’t help when it’s 30 degrees outside.
The underfloor heating doesn’t run at all because the heating system is in summer mode. The air conditioning runs daily, on and off, and dehumidifies/cools. I would never want to live without air conditioning again; it’s quietly humming quality of life on the wall.

Can the ventilation system not cool the air a bit? As far as I have read, it is possible. Also, the underfloor heating would be running since it is supposed to cool. It is clear that temperature control via underfloor heating is nowhere near as effective as air conditioning. But it’s enough if you go from outside into a room cooled by 4 degrees. That already gains a lot for little money.

In the summer months, our ventilation system only runs at night. If I let it run during the day, no matter how much I shade, I end up pumping warm outside air into the house.

It may not have much to do with the actual topic, but:

The heat input through the central controlled residential ventilation with activated heat recovery (HRV) is minimal!

With 23°C inside and 30°C outside, the delta T is 7 degrees.
At 100 m³/h, this results in a maximum of only 250W if the by-pass is active.
With heat recovery at 90% efficiency, only 25W remain.
This is really negligible.

So, do not turn off the central controlled residential ventilation even in summer and activate the by-pass only at night!

Can't the ventilation system cool the air a bit? As far as I have read, it is possible. Also, the underfloor heating would run, as it is supposed to cool. It is clear that tempering via underfloor heating is not nearly as effective as an air conditioner. But it is enough if you go from outside into a room that is 4 degrees cooler. Then you have already gained a lot for little money.

We did not buy the cooling function of the system because I had read in online research beforehand that it can only achieve 2-3 degrees (if things go well), and cold air does not rise either -> cold feet problem. There are probably systems where ventilation is combined with air conditioning. We have a normal, central ventilation system. It has no cooling function. The heat pump’s cooling function (if we had bought it) would only cool via underfloor heating.

When we built the house, I considered the air conditioning more of a luxury. Now, as the first summer in the house is running, I am really glad to have it. Because it is very difficult to keep the heat out in such a well-insulated, new house. Just the sunlight through the windows heats the house up. Either you shade so consistently that you could live in a cave, or you let the light in. The amount of heating energy that 1 meter of window front with sunlight produces is not to be underestimated, I massively underestimated this during construction. And once you have the warm air inside the house in summer, it becomes difficult to get it out again without air conditioning. The only idea I have is not to ventilate during the day and then try to get the warm air out at night by ventilating. But in a summer like we had in 2019, it was often still around 30°C at night. That is very uncomfortable to sleep in at those temperatures.

In May, I once managed to have 28°C in the house even though the outside temperature was only 18°C. I had not shaded the windows and the ventilation system was running without the summer cassette, meaning with 98% heat recovery. Over several sunny days, it got warmer and warmer in the house. We only got rid of the warm air again when we manually set the ventilation system to summer mode (some exhaust air during the day, higher ventilation level at night) and already cooled down again in May with the air conditioning units.