Hello Forum!
I wanted to discuss air exchange rates and, more generally, your indoor air quality. Especially now in winter, we rely about 99% on our ventilation system and only rarely open the windows (for example, after cooking).
Our system is a Zehnder Q350 and usually runs on level 1. According to the app, this corresponds to about 160 cubic meters per hour.
I read that a person needs approximately 30 cubic meters per hour of fresh air. So, if two people are in a room, they would need 60 cubic meters of fresh air. But the system only supplies 160 cubic meters distributed over the whole house. Does that mean the air quality must slowly deteriorate?
This is exactly the phenomenon I can also measure. I bought a CO2 meter from Amazon that shows me the ppm.
It reads 470 ppm in every room in the morning, which matches outdoor air quality. After a few hours, the value rises to about 850 ppm. Then it stays relatively stable, probably because we leave the room regularly.
When I set the ventilation system to level 2, about 220 cubic meters per hour, the value decreases slightly again.
How do you handle this? What ventilation rates do you use, and have you had similar experiences?
Good luck
I wanted to discuss air exchange rates and, more generally, your indoor air quality. Especially now in winter, we rely about 99% on our ventilation system and only rarely open the windows (for example, after cooking).
Our system is a Zehnder Q350 and usually runs on level 1. According to the app, this corresponds to about 160 cubic meters per hour.
I read that a person needs approximately 30 cubic meters per hour of fresh air. So, if two people are in a room, they would need 60 cubic meters of fresh air. But the system only supplies 160 cubic meters distributed over the whole house. Does that mean the air quality must slowly deteriorate?
This is exactly the phenomenon I can also measure. I bought a CO2 meter from Amazon that shows me the ppm.
It reads 470 ppm in every room in the morning, which matches outdoor air quality. After a few hours, the value rises to about 850 ppm. Then it stays relatively stable, probably because we leave the room regularly.
When I set the ventilation system to level 2, about 220 cubic meters per hour, the value decreases slightly again.
How do you handle this? What ventilation rates do you use, and have you had similar experiences?
Good luck
Our Q350 runs continuously in automatic mode at level 2 with 175m³/h (175 cubic meters per hour).
The air volumes for each level can be set individually during installation, either by yourself or the installer.
When we take a shower, the system automatically increases to level 3 (there is a function in the menu) until the humidity level returns to normal. I estimate this lasts about 30 minutes.
We are generally satisfied with our air quality. I have not noticed anything negative so far. However, I have never used a measuring device.
The air volumes for each level can be set individually during installation, either by yourself or the installer.
When we take a shower, the system automatically increases to level 3 (there is a function in the menu) until the humidity level returns to normal. I estimate this lasts about 30 minutes.
We are generally satisfied with our air quality. I have not noticed anything negative so far. However, I have never used a measuring device.
Mycraft schrieb:
At the beginning, you describe that your approach doesn't work satisfactorily, so which is it?Actually, I am completely satisfied. I just wonder whether it is really to be expected that the measurable air quality decreases with two people in a room and doesn’t stay constant at the achievable minimum of 450 ppm CO2.But I see, I guess ordinary people don’t really think about these things.
A
Alessandro19 Oct 2020 13:32CO2 behaves like a heavy gas. Although it is denser than air particles, CO2 circulates throughout the entire room when entering or opening a door.
Plaster can absorb and release CO2.
CO2 sensors tend to drift over time. Many calibrate themselves automatically, while some require manual calibration over time (zero-point calibration).
The CO2 measurement cells have variable tolerances depending on temperature. Typically, tolerances at 21°C (70°F) are around 10% of the measured value or approximately ±75 ppm. Of course, this depends on the measurement range. In the worst case, you might have two sensors with maximum tolerances in opposite directions, resulting in a difference of 150 ppm.
All of this leads to measurement deviations and fluctuations.
As you can see, a CO2 sensor is a better indicator of air quality but should be considered more of an estimate from a measurement perspective.
Generally speaking:
0–750 ppm = very good air quality
751–1250 ppm = good to moderate air quality
1251–2000 ppm = moderate to poor air quality.
With two people in a closed bedroom, CO2 levels can easily reach between 5000 and 10,000 ppm, depending on room size and duration of stay.
Besides a CO2 sensor, it can also be useful to install a VOC sensor. This measures several gases, such as adhesives from materials, cleaning agents, cigarette smoke, cooking odors, and many other gases that can cause headaches and migraines.
Plaster can absorb and release CO2.
CO2 sensors tend to drift over time. Many calibrate themselves automatically, while some require manual calibration over time (zero-point calibration).
The CO2 measurement cells have variable tolerances depending on temperature. Typically, tolerances at 21°C (70°F) are around 10% of the measured value or approximately ±75 ppm. Of course, this depends on the measurement range. In the worst case, you might have two sensors with maximum tolerances in opposite directions, resulting in a difference of 150 ppm.
All of this leads to measurement deviations and fluctuations.
As you can see, a CO2 sensor is a better indicator of air quality but should be considered more of an estimate from a measurement perspective.
Generally speaking:
0–750 ppm = very good air quality
751–1250 ppm = good to moderate air quality
1251–2000 ppm = moderate to poor air quality.
With two people in a closed bedroom, CO2 levels can easily reach between 5000 and 10,000 ppm, depending on room size and duration of stay.
Besides a CO2 sensor, it can also be useful to install a VOC sensor. This measures several gases, such as adhesives from materials, cleaning agents, cigarette smoke, cooking odors, and many other gases that can cause headaches and migraines.
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