ᐅ Newly built apartment (KfW-55 standard) cannot be cooled below at least 25 °C.
Created on: 21 Aug 2022 08:52
F
Forsberg21
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
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
The houses are insulated. This means that the phase shift changes. When the heat is stored in the building material, it takes time to release it again. This is especially true for cavity wall construction or external thermal insulation composite systems (ETICS).
Monolithic structures can potentially cool down faster.
In the example with the 20cm (8 inches) concrete... there is simply so much mass present that it needs to be cooled down first.
Monolithic structures can potentially cool down faster.
In the example with the 20cm (8 inches) concrete... there is simply so much mass present that it needs to be cooled down first.
I also believe that several factors come into play, making it only partially meaningful to compare older buildings with new constructions.
I live in the suburban outskirts of a large city. When we drive into the city, there can easily be a temperature difference of 5-10°C (9-18°F). Especially in summer, rural areas absorb and use a lot of heat through natural vegetation, while the concrete blocks in the city act like heat storage.
Assuming we are not comparing an old building in the countryside with a new build in the city, the plots in new residential developments are often smaller than before or the areas are being densified. Also, there are usually no trees yet, terraces are larger... let’s not even talk about the “stone front gardens.” All this causes the surrounding air to be noticeably warmer, similar to what happens in the city.
We have a beige, large terrace on the west side made of 8cm (3 inches) thick paving slabs. Although it is light-colored, in summer it became almost impossible to sit on the terrace from midday without overheating. The living room behind it warmed up significantly, despite the shutters being closed.
Since we installed a roof with an awning, the terrace and therefore the living room behind it have become much more comfortable.
On the ground floor, we hardly have any temperature issues during summer. The tiles on the ground floor also contribute to a comfortable feeling.
Upstairs, we ventilate thoroughly at night. This generally works well for getting through the summer.
However, this only works as long as it cools down at night and doesn’t stay above 25°C (77°F) like it can in the city.
I live in the suburban outskirts of a large city. When we drive into the city, there can easily be a temperature difference of 5-10°C (9-18°F). Especially in summer, rural areas absorb and use a lot of heat through natural vegetation, while the concrete blocks in the city act like heat storage.
Assuming we are not comparing an old building in the countryside with a new build in the city, the plots in new residential developments are often smaller than before or the areas are being densified. Also, there are usually no trees yet, terraces are larger... let’s not even talk about the “stone front gardens.” All this causes the surrounding air to be noticeably warmer, similar to what happens in the city.
We have a beige, large terrace on the west side made of 8cm (3 inches) thick paving slabs. Although it is light-colored, in summer it became almost impossible to sit on the terrace from midday without overheating. The living room behind it warmed up significantly, despite the shutters being closed.
Since we installed a roof with an awning, the terrace and therefore the living room behind it have become much more comfortable.
On the ground floor, we hardly have any temperature issues during summer. The tiles on the ground floor also contribute to a comfortable feeling.
Upstairs, we ventilate thoroughly at night. This generally works well for getting through the summer.
However, this only works as long as it cools down at night and doesn’t stay above 25°C (77°F) like it can in the city.
Georgian2019 schrieb:
KfW70 standard with a solid 36.5cm (14.4 inches) wall and double-glazed windows: the indoor temperature is usually around 23 degrees Celsius (73°F). When it was frequently above 30 degrees Celsius (86°F) outside, the living room sometimes reached 25 degrees Celsius (77°F) because the patio door was often open. Otherwise, there is always at least one window tilted open at night, and early in the morning with temperatures of 17-19 degrees Celsius (63-66°F), the house is ventilated, while window shutters on the south and west sides remain closed during the day.
I know why I didn’t build KfW55 or 40 houses... basically plastic houses with ventilation systems. With a passive house and a ventilation system, we have never experienced 25 degrees Celsius (77°F) indoors. Usually, it stays around 20-23 degrees Celsius (68-73°F) without air conditioning.
So, that can’t be the reason.
Shading and cool air at night. This year, we only had two or three nights with temperatures over 20 degrees Celsius (68°F). How much and how long the air cools down at night depends on other factors. You live in an established neighborhood with a lot of greenery. Your garden no longer releases heat into the air, whereas a parking lot would continue to radiate heat for a long time.
haydee schrieb:
In our Passive House with a ventilation system, we've never had 25 degrees Celsius (77°F) inside. Usually it’s around 20-23 degrees Celsius (68-73°F) without air conditioning.
So the temperature itself can’t be the reason.
Shading and cool night air. This year, we only had 2 or 3 nights with temperatures above 20 degrees Celsius (68°F).
How much and how long the air cools down at night depends on other factors. You live in an established neighborhood with quite a bit of greenery. Your garden no longer releases heat into the air, whereas a parking lot would continue to radiate heat for a long time. So what exactly is the reason that you seriously have a maximum of 20 degrees Celsius (68°F), 23 at most, and I have 25 degrees Celsius (77°F)? Are we talking about the ground floor or the upper floor? Do you leave the windows open at night, or how exactly does that work?
Snowy36 schrieb:
So what is the reason that you seriously have a maximum of 20 degrees up to 23, and I have 25? Are we talking about the ground floor or the upper floor? At night, do you keep the windows open or how exactly does that work? Don't believe everything.
No one here has 20 degrees after weeks of drought, sun, and blue skies… except at 3 a.m. at an open window.
M
motorradsilke1 Sep 2022 05:11Nutshell schrieb:
Don’t believe everything.
No one here has seen 20 degrees after weeks of drought, sun, and clear skies… except at 3 a.m. by an open window I think they meant the outside temperatures. With good ventilation, you can then also achieve cool indoor temperatures.
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