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

What helps us with cross-ventilation: in the early morning hours, open both sides of the main room and let a fairly large fan/wind machine with a 50 cm diameter standing on the windowsill blow air outside; it has a high throughput and pulls the air through the ground floor from the other side.

As soon as the outside temperature reaches the inside temperature, we close the windows and shut the blinds on the south side by 90%. 25°C was the maximum on the hottest days.

Only in the bedroom upstairs is that a problem: the woman and child usually sleep until around 8 a.m., so by then it is usually no longer possible to ventilate. And since the child goes to bed around 7:30 p.m., just like during the day (large south-facing window front), neither ventilation nor opening the blinds is possible. Therefore, 25°C is the standard there most of the time... if at all, we would wish for an air conditioner there.

Hehe, when I hear the word wind machine, I think of those monster devices from the movie. or something. :D

you might as well speed straight through to the Czech Republic

…with the unfortunately still empty car :)

A brief interim report because I spoke with the craftsman who installed the ventilation system.

He said that the residential ventilation with heat recovery should be turned off on hot days (above 29° outside temperature) because the air drawn in then has about 24° (a loss of about 5°) and would no longer contribute to cooling. At 34° outside temperature, for example, 29° warm air would be drawn in. He said this is probably one of the main reasons for the higher temperatures.

He also suggested the following: The ventilation system can be set so that only fresh, cold air is drawn into the bedroom in the evening and at night, while in the living room only the warm, used air is extracted and directed outside (i.e., cross ventilation). For this, 2 doors would have to be left open, which my tenant already does anyway. The cross ventilation using the ventilation system has the advantage that even on warm summer nights with no wind (air practically "stands still") a slight continuous airflow is created, which otherwise would not be possible or would require a fan – as was also suggested here.

Furthermore, he said that it is a misconception if people think that manual ventilation is no longer allowed once a ventilation system is installed. The ventilation system is only intended as support. In winter, in my opinion, it may well be the case that windows are no longer opened and fresh air is only obtained via the ventilation system.

Hello, I haven’t read everything but a temporary relief is a fan with a cloth soaked in cold water hanging in front of it. Or a bowl of ice cubes in front of the fan. Personally, however, I wouldn’t want to use the energy to make the ice cubes just to have them cool my apartment afterwards.

By the way, we live in an old building (built around 1910 or so) and in our south-facing living room it only goes below 25-28 degrees when we keep the balcony door wide open all night... Then in the evening, when there is still a light on somewhere, hornets come in immediately. At the office at work, for weeks I also have a maximum of under 25 degrees until about 7:30 in the morning, often over 30 in the afternoon. At these temperatures, it’s hardly avoidable without technology.

A short-term remedy is a fan with a cloth soaked in cold water hung in front of it. Or a bowl of ice cubes in front of the fan.

But that is a Pyrrhic victory. For a minimum of evaporative cooling you increase the humidity, which also makes it muggy. A fan is completely sufficient. By the way, I do it exactly the opposite. In summer I run the dehumidifier and accept the little heat it produces for pleasantly dry air ;)