ᐅ Cooling with a heat pump through underfloor heating?

Mycraft schrieb:

You mainly need it in winter. In summer, it’s useless.

Yes, but only if there is an imbalance. If moist air is already coming in, it can’t regulate anything. Moist air goes out → through the moisture enthalpy exchanger → new moist air comes in. The result in summer → moisture everywhere. In winter, however, no, because then there is a temperature difference and the humidity can be regulated and slightly increased by the exchanger, so it doesn’t drop to unexpected lows inside the house.

No, that’s just marketing talk. Sure, you bring in slightly cooler air later, but the amounts are negligible. RotorMotor explained it quite well.

No, that’s wishful thinking. Underfloor heating cooling only gives you a slightly cooler floor but hardly cooler air inside the house, and most importantly, the humidity stays inside. Four degrees difference is unrealistic, unless the house is in a forest and hardly gets any sunlight.

Four degrees is not unrealistic. I spoke with homeowners two months ago who built exactly this way with the contractor we are working with, and the house is not in a forest. It wasn’t a showcase home, so not a “paid opinion.” When I asked what they would recommend, the primary temperature control was over underfloor heating, with up to a 4-degree temperature difference.

kati1337 schrieb:

These are calculated values. In practice, we have experienced that without air conditioning, you can’t keep the indoor temperature at 23°C (73°F) when it’s 30°C (86°F) outside. Unless you shade the house like a bunker. In reality, it also gets warmer inside, and the problem is that with heat recovery ventilation, you can no longer lower the temperature.

You are unfortunately mixing quite a few things.
I calculated the heat gains from controlled mechanical ventilation for you.

Here’s a rough estimate for windows:
The heat gain through unshaded windows can easily reach 200 W/m² (19 W/ft²) of window area.
For a nice sliding patio door measuring 5 m by 2 m (16 ft by 6.5 ft), that alone means 2000 W (about 2 kW), which is 100 times more than the heat gain from controlled mechanical ventilation with heat recovery. ;-)

In principle, this matches exactly your experience.
Insulation neither lets heat in nor out, controlled mechanical ventilation neither lets heat in nor out.
Windows, on the other hand, let a lot of heat in if they are not shaded — through radiation, not convection.

From what you say, I guess you don’t have external blinds (such as venetian blinds or roller shutters)?

Acof1978 schrieb:

For us, the temperature control via underfloor heating costs around 4,000 €.

What exactly is supposed to cost 4,000 €? An extra charge for a heat pump with cooling function? You have (or are planning) a ground source heat pump, right?

Acof1978 schrieb:

When I asked what you would recommend, the first thing was heating through underfloor heating and the temperature difference of up to 4 degrees.

I don’t think your goal is to actually reach the “up to” value (at least it isn’t mine), nor only within the first few days (which is why it says “up to”). Once the sun shines on your house for a few days, those “up to 4” degrees usually shrink to “up to 2” degrees, and combined with the existing indoor humidity, it really can only be considered a placebo.

RotorMotor schrieb:

Insulation neither lets heat in nor out,

That is logically incorrect. Insulation slows down the temperature equalization between inside and outside!

Acof1978 schrieb:

For us, the temperature control via underfloor heating costs about 4,000 € (approximately 4,400 USD). The most expensive part seems to be the control switches. This is included in our price. We will also apply through BAFA. I believe we should get 35% of that amount reimbursed.

Phew... 4,000 € (approximately 4,400 USD) is too much for underfloor heating cooling for me. You would get correspondingly less through BAFA. But that is not yet certain for us.

kati1337 schrieb:


When we built our house, I considered the air conditioning more of a luxury. Now, after the first summer living here, I’m really glad to have it. It is very difficult to keep the heat out of such a well-insulated, new house. Just the sunlight streaming through the windows heats up the house. You either have to shade so thoroughly that you might as well be living in a cave, or you let the light in. The amount of heat energy gained from 1 meter (3.3 feet) of window area exposed to the sun is not insignificant—I severely underestimated this during construction.
And once the warm air is inside during summer, it is hard to get rid of it without air conditioning. The only things I can think of are not ventilating during the day and then trying to ventilate at night to get the warm air out.

Without getting too deep into a fundamental debate or discussing environmental aspects:
I do wonder if all of this really makes sense. If you’re already relieved to have air conditioning during a disappointing summer like this year because otherwise it’s almost unbearable as the windows heat the house up so much. It doesn’t surprise me that someone like Hofreiter no longer sees the single-family home as a model for the future.
If this becomes common practice, future energy standards will need to focus much more on effectively preventing a house from overheating. Huge windows facing south simply can’t be the goal anymore.