Increased supply temperature in underfloor heating during ventilation

Hello,

I know that you should simply keep the underfloor heating running when ventilating and that a nighttime setback no longer brings any benefits. This is justified, among other things, by the higher energy expenditure when restarting the heating and having to reheat everything, as opposed to heating constantly; comparable to a car trip.

However, when I keep the underfloor heating running during ventilation, I see in the system configurations of my air-water heat pump that the target flow temperature increases with the cooling of the room air temperature from, for example, 22°C to 30°C. But in my view, this is exactly counterproductive because now the underfloor heating suddenly heats up again, although the goal was for it to continue heating constantly. I cannot figure out where my flaw in thinking lies...

I would appreciate some clarification!

Best regards
Geisti

The room should not cool down so significantly due to the ventilation.

I ventilate by fully opening the window for about 10 minutes. A room control is not active. I do not understand the significantly increased desired flow temperature.

Sounds like an indoor sensor (control unit?) is being affected. Otherwise, without knowing details about the system, one can only speculate: if individual room control is installed, the thermostats will turn on. If the heat pump is then controlled, for example, by return temperature, it will deliver more power to maintain the return temperature. Yes, that's not ideal, but not a disaster if the flow temperature drops again quickly.

By the way, for an air-to-water heat pump, a nighttime reduction/daytime increase is advantageous. The heat pump is more efficient at higher outdoor temperatures. Today, for example, we have over 10° fluctuation between day and night, which makes a big difference. But first carry out the hydraulic balancing if not done yet and slowly approach the correct settings.

Maybe it just cycles and only turns on when you ventilate. Are you sure that the compressor is already running at the 22° you mention as an example?

Did you control your underfloor heating with KNX or do you get actual temperatures from a sensor? (Not the ERR, they can only switch on/off).

The specific heat capacity of air is so negligibly low that you can ventilate with shocks even in the deepest winter. You just must not leave it open for 20 minutes and let the building fabric cool down. That’s why the underfloor heating doesn’t care. The screed stores significantly more energy than your room air. By the way, that’s also the reason why heat recovery in ventilation is rarely economical.