Newly built apartment (KfW-55) cannot be cooled, always at least 25 °

Hello, I have rented out a new apartment (built in 2021, KfW-55). The tenant has now informed me that since spring, the temperature in the apartment is always at least 25 ° or higher. On warm days even up to 28 °, although she keeps all the aluminum shutters closed during the day (no home office). Cross-ventilation at night also does not bring the temperatures below 25 °. She is asking for tips on how to cool the apartment down a bit in summer.

What is the reason for this? The apartment is equipped with a decentralized residential ventilation system and underfloor heating, which is of course always off in summer. The apartment faces southwest and has large window surfaces.

Could it be that because the ventilation system constantly brings warm air in from outside on hot days, the temperatures rise so much? Should the ventilation system be turned off during the day? But why can’t the apartment cool down at night, even though it is apparently cross-ventilated and nights are cooler after all?

Do you have any tips? I am unfortunately overwhelmed.

Best regards Robert

With us, same here. No chance

I turned off the ventilation in summer. Then only the bathroom is ventilated automatically. With underfloor heating and a heat pump, you can also cool. However, it is power-intensive. Aluminium roller shutters are touted as hot nonsense. In the past, wooden roller shutters were used. They are much better. But too heavy for today's floor-to-ceiling windows. Actually, buildings were constructed much more sensibly with building physics in mind in the past. A new building is basically a plastic bag. What do you expect from that? To counter the plastic bag effects, you have to use technology again. It's all rubbish but that's how it is. In the next life, I would build with straw and clay. It insulates very well and has no plastic effect.

I turned off the ventilation in the summer. Then only the bathroom is ventilated automatically. With underfloor heating combined with a heat pump, you can also cool. However, it is electricity-intensive. Aluminum roller shutters are touted as hot nonsense. In the past, wooden roller shutters were used. They are much better. But too heavy for today's floor-to-ceiling windows.

Actually, in the past, buildings were constructed much more sensibly with building physics in mind. A new building is basically a plastic bag. What do you expect? To counter the plastic bag effects, you then have to use technology. It's all rubbish but that's just how it is.

In the next life, I would build with straw and clay. It insulates very well and has no plastic effect.

And can the apartment be cooled down a bit or can high temperatures be avoided by turning off the ventilation in the summer? The WRL is actually set by the construction company so that it cannot be completely turned off. However, I have seen in a separate manual that it is indeed possible.

The underfloor heating is combined with a heat pump. But I am not sure if it can be switched to cooling that easily.

I don't know anything about heat pumps and technology. Take a look in the menu or call the installer during the week. An air-to-water pump can probably do that.

Yes, definitely turn off the automatic supply during the day. At night, you can turn it back on. Then colder night air is supplied and no warm day air during the day.

Besides, we have hardly had temperatures below 25° during the day for weeks, with short heat waves. Then it's over with the new building too, and it gets warm.

Right on time for the summer heat start, I simply bought the large suction cups at Ikea and made such "chic" curtain holders with them. I kept hanging cloths on the glass surfaces both inside and outside without giving up. My front door is made of glass and very heat-conductive. While they are still sweating in Villa Ribo, a cloth is hung up in Villa Bacho. :D It brought me 3° less indoor temperature compared to the neighbors.

Hanging lightweight material in layers in front of the window surfaces helps best.

Thank you very much. It is already good to read that turning off the ventilation during the day helps somewhat. My tenant will probably not be allowed to implement the tip with the cloths, as this is a homeowners' association and it would certainly be objected that the external appearance suffers.