ᐅ Cooling with a heat pump through underfloor heating?

driver55 schrieb:

That logically isn’t correct. Insulation delays the temperature equalization between inside and outside!

Yes, I already understood that ;-)
I just wanted to point out that it is often mistakenly assumed that insulation only keeps heat inside.
However, it also keeps heat out, because insulation generally has no direction.

moHouse schrieb:

Large window areas facing south can simply no longer be the goal

Due to the sun’s position throughout the day and year, east and west-facing windows often cause much more of a problem in summer if they are not shaded.
South-facing windows can usually be shaded quite effectively with a modest roof overhang.

But yes, shading should always be the top priority and needs to be properly planned.

The 2 to 3 degrees gained from underfloor cooling can at best be seen as a supplement.
In my opinion, though, it is perfectly sufficient to have 23°C (73°F) instead of 26°C (79°F) in living and sleeping areas during summer 2023.

RotorMotor schrieb:

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

Here’s a rough estimate for windows:
Heat gain through unshaded windows can easily reach 200 W/m² (20.9 W/ft²) of window area.
For a nice sliding patio door measuring 5 x 2 m (16.4 x 6.6 ft), that alone means 2000 W (about 2 kW), which is 100 times the heat gain from controlled mechanical ventilation with heat recovery. ;-)

In principle, this exactly matches your feeling.
Insulation prevents heat from entering or leaving, controlled mechanical ventilation also does not let heat in or out.
But windows let heat in quite easily if they are not shaded — this happens through radiation rather than convection.

From what you say, I assume you don’t have external blinds or shutters?

We have roller shutters, but in the first spring after moving into the new house, we did not expect such a high heat build-up (as you just calculated) just from sunlight through the windows. We naively assumed that the windows were well insulated thermally, so we thought the house would neither gain nor lose heat. Eventually, we understood how important shading is, but the first sunny days in May still caused a lot of heat inside.
As you said, the house neither lets heat in nor out. So, we had to actively cool, and since then we have paid more attention to shading. However, even now in summer, the house continues to warm up, and we regularly cool it. We don’t close all the roller shutters all at once because it makes the house very dark and gloomy. So, we try to find a practical balance between darkening the rooms and cooling.

If I were to build again and had the budget, I would probably invest in smart home technology with automatically controlled shading. I didn’t realize at all how important that was during the first build.

Would you keep the controlled mechanical ventilation running normally in summer? We don’t have a summer bypass, so it always runs with heat recovery. If it’s 32°C (90°F) outside and inside it’s only 24°C (75°F) because of the air conditioning, then running the controlled ventilation will make the house warmer again, right? The cooled indoor air is exhausted, and the 32°C (90°F) outside air comes inside? Then I would have to use more energy to cool it down again. Or am I misunderstanding something?

moHouse schrieb:

Without getting too much into a fundamental debate or the environmental aspect:
I do wonder, though, how sensible this all really is. When you have a disappointing summer like this year and you’re already glad that the air conditioning is working because otherwise the house would be unbearable due to the large window areas heating it up. It’s no surprise to me that someone like Hofreiter no longer sees single-family homes as a model for the future.
If this becomes common practice, future energy standards will focus much more on effectively preventing the house from overheating. Huge south-facing windows simply won’t be the target anymore.

We don’t have huge south-facing windows. Just a regular patio door and two moderately sized windows, one in the living room area and one in the kitchen.
By the way, we haven’t drawn any energy from the grid for the air conditioning yet; we usually run it during the day when the sun is out and our photovoltaic system is generating electricity for it.

kati1337 schrieb:

We don’t have large windows facing south. Just a standard patio door and two moderately sized windows, one in the living area and one in the kitchen.
By the way, we haven’t drawn any energy from the grid for the air conditioning yet; we usually run it during the day when the sun is shining and our photovoltaic system is generating electricity.

And at night, when the photovoltaic system isn’t producing energy but there are still tropical nights, do you keep the air conditioning off?

kati1337 schrieb:

We have roller shutters; in the first spring after moving into the new house, we just didn’t expect such a high heat build-up (as you calculated) from the direct sunlight through the windows.

Yes, retrofitting external blinds is usually very expensive and often not very attractive, so active cooling is probably the only option. Thanks to solar panels, though, it’s not quite as bad. 😉

kati1337 schrieb:

Would you keep the mechanical ventilation with heat recovery running normally in summer? We don’t have a summer bypass, so it runs with heat recovery. If it’s 32°C (90°F) outside, 24°C (75°F) inside because of the air conditioning, and I run the mechanical ventilation, won’t it warm the house up again? The cooled air from the AC gets exhausted, and 32°C (90°F) air comes in? Then I’d have to use energy again to cool it down. Or am I mistaken?

Yes, keep it running, because that matches my calculations quite closely. You need fresh air, and with heat recovery, it only adds about 25W of extra heat. Manually ventilating would bring in much more heat! Plus, your AC probably cools with 3000W or more. You won’t notice that 1% increase in electricity consumption from the mechanical ventilation, but you will definitely have better air quality.