ᐅ Increased Supply Temperature of Underfloor Heating During Ventilation

Hello,

I know that you should simply keep the underfloor heating running when airing out the rooms, and that nowadays lowering the temperature at night doesn’t really help anymore. This is partly explained by the higher energy required to heat the system back up afterwards, as opposed to heating constantly; similar to a car journey.

However, when I keep the underfloor heating running during ventilation, I notice in the system settings of my air-to-water heat pump that the target flow temperature increases as the indoor air temperature drops—for example, from 22°C (72°F) to 30°C (86°F). In my view, this seems counterproductive because the underfloor heating starts heating up again precisely when it was supposed to maintain a constant temperature.

I can’t figure out where my thinking is going wrong...

I would appreciate any clarification!

Best regards,
Geisti

Ventilation should not cause the room to cool down significantly.

I ventilate by airing out for about 10 minutes. A room control is not active.
I don’t understand the significantly increased target flow temperature.

It sounds like an indoor sensor (control unit?) is being affected by drafts. Otherwise, without details about the system, one can only speculate: if individual room control is installed, the thermostats will open. If the heat pump is then, for example, controlled by the return temperature, it will deliver more output to maintain the return temperature. This is not ideal, but not a major issue if the supply temperature lowers quickly again.

For an air-to-water heat pump, night setback/day boost is actually beneficial. The heat pump is more efficient at higher outdoor temperatures. Today, for example, we have temperature fluctuations of over 10°C (18°F) between day and night, which makes a significant difference. But first, make sure to perform the hydraulic balancing if it hasn’t been done yet, and then gradually adjust to the correct settings.

Maybe it simply cycles and only turns on when you ventilate. Are you sure the compressor is already running at the 22°C (72°F) you mentioned as an example?

Do you control your underfloor heating with KNX or measure actual temperatures using a sensor? (Not the ERR, which can only switch on/off).

The specific heat capacity of air is so low that you can ventilate by briefly opening the windows even in the coldest winter. You just shouldn’t leave them open for 20 minutes, letting the building structure cool down. That’s why underfloor heating is not affected by it. The screed stores significantly more energy than the room air.

By the way, this is also the reason why heat recovery ventilation systems are rarely economical.