ᐅ Newly built apartment (KfW-55 standard) cannot be cooled below at least 25 °C.

Hello,
I have rented out a new apartment (built in 2021, KfW-55 standard). The tenant recently informed me that since spring, the indoor temperatures have consistently been at least 25°C (77°F) or higher. On warm days, it even reaches up to 28°C (82°F), although she keeps all the aluminum shutters closed during the day (no home office). Cross-ventilation at night doesn’t bring the temperature below 25°C (77°F). She is asking for advice on how to cool the apartment down a bit during the summer.

What could be causing this?
The apartment has a decentralized ventilation system and underfloor heating, which is naturally turned off in summer.
The apartment faces southwest and has large window areas.

Could it be that the ventilation system continuously brings in warm outside air on hot days, causing the temperature to rise so much?
Should the ventilation system be turned off during the day?
But why doesn’t the apartment cool down at night, even though there seems to be cross-ventilation and the nights are cooler?

Do you have any tips? I am a bit overwhelmed.

Best regards,
Robert

Same here. No chance.

I turned off the ventilation during the summer. Then only the bathroom is ventilated automatically. With underfloor heating combined with a heat pump, you can also cool. However, this consumes a lot of electricity.

Aluminum roller shutters are often criticized as a bad idea. In the past, wooden shutters were used. They are much better but too heavy for today’s floor-to-ceiling windows.

In the past, building practices were generally more sensible, with building physics in mind. A new building is basically like a plastic bag. What can you expect? To counteract the effects of this “plastic bag,” you then have to rely on technology. It’s all problematic, but that’s how it is.

In the next life, I would build with straw and clay. That insulates very well and doesn’t have the plastic bag effect.

Bertram100 schrieb:

I turned off the ventilation system during the summer. Then, only the bathroom is ventilated automatically. With underfloor heating combined with a heat pump, cooling is also possible, but it’s quite energy-intensive.
Aluminum roller shutters are often criticized as a bad idea. In the past, wooden shutters were used, which are much better, but they are too heavy for today’s floor-to-ceiling windows.

Buildings used to be designed much more sensibly with building physics in mind. A new build today is basically like a plastic bag. What can you expect? You then need technical systems to counter the plastic bag effects. It’s all a hassle, but that’s just how it is.

In the next life, I would build with straw and clay. They offer great insulation and don’t have the plastic effect.

And can turning off the ventilation in summer help cool the apartment or at least prevent high temperatures? The mechanical ventilation with heat recovery (MVHR) system is usually set up by the builder so it can’t be completely switched off. However, I saw in a separate user manual that it is indeed possible.

The underfloor heating is combined with a heat pump. But I’m not sure if it’s that simple to switch it to cooling mode.

I’m not familiar with heat pumps or the technology involved. Check the menu options or try calling the installer during the week. An air-to-water heat pump can probably do that.

Yes, definitely turn off the automatic air supply during the day. You can switch it back on at night. That way, colder night air is brought in, and no warm daytime air enters during the day.

Besides, for weeks now, daytime temperatures have hardly fallen below 25°C (77°F), with occasional heat waves. That means even the newly built house will warm up.

Right at the start of the summer heat, I simply bought large suction cups from Ikea and used them to make these kind of "stylish" curtain holders. I persistently hung cloths on the glass surfaces both inside and outside. My front door is made of glass and conducts heat very well. While people in Villa Ribo are still sweating, a cloth is hanging in Villa Bacho 😀 It reduced the indoor temperature by about 3°C (5°F) compared to the neighbors.

Hanging lightweight layers of material in front of window surfaces works best.

Thank you very much. It’s reassuring to read that turning off the ventilation during the day actually helps. My tenant probably won’t be allowed to use the tip with the cloths, as this is a condominium association and any changes to the external appearance would likely be objected to.