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
Please don’t get me wrong, I am also very satisfied. Anything below 1000 ppm is a good value and absolutely within the safe range. I am just interested in how the systems perform and what airflow volumes you have set.
I could also run the system permanently at level 2, where it is still very quiet. But I don’t really see the need for that...
I could also run the system permanently at level 2, where it is still very quiet. But I don’t really see the need for that...
H
hampshire19 Oct 2020 10:18The technology is quite advanced nowadays, provided it is properly configured and sensors for the control system are appropriately placed.
When building, I would always prioritize the following fundamental factors before considering the technology:
You can ignore 200 ppm in indoor air if you have a plastic floor. Limit values are often a compromise between what is technically and economically desirable and what is healthy. Experience shows that yesterday’s limit values become today’s “disasters.” However, we like to believe that we are safe as long as we adhere to the “current” limit values.
When building, I would always prioritize the following fundamental factors before considering the technology:
- Rooms with large air volumes
- Natural building materials
- Placement of windows and doors that allows for effective manual ventilation through quick airing
You can ignore 200 ppm in indoor air if you have a plastic floor. Limit values are often a compromise between what is technically and economically desirable and what is healthy. Experience shows that yesterday’s limit values become today’s “disasters.” However, we like to believe that we are safe as long as we adhere to the “current” limit values.
guckuck2 schrieb:
You won’t be able to handle peak loads as described (two people in a confined space for hours) because the rooms cannot be controlled individually.
The result would just be that the system would constantly have to run at a higher level. Theory and practice... Here it works so well that I didn’t even install all the sensors I originally planned. The system only rarely runs at full capacity and certainly not when there are just two people in the house.
I don’t consider two people in a confined space for hours to be a peak load but rather normal conditions, and the sensors handle that very well.
In my opinion, central sensors provide little benefit in controlled residential ventilation systems without automatic room control.
At night, the bedroom shows 2000 ppm CO2, while the rest of the house is around 400 ppm—in the ventilation system, it registers 600-700 ppm, which is all within acceptable limits.
We have a CO2 sensor in both the bedroom and living area—it’s inexpensive and allows you to objectively adjust air quality to your needs.
In our case, the system runs at about 80% for an hour in the morning (device rated for 500 m³/h), operates at a low setting during the day, and runs at a medium level at night. This usually keeps CO2 levels around 400-500 ppm in the house, with nighttime levels below 800-1000 ppm in the bedrooms, and the air also feels good.
If there are several guests over, you can simply activate “party mode” at the push of a button—or alternatively, add a sensor for the system in the living room. I have considered this, but it costs around 300-400€ to save pressing a button 2-3 times a month.
At night, the bedroom shows 2000 ppm CO2, while the rest of the house is around 400 ppm—in the ventilation system, it registers 600-700 ppm, which is all within acceptable limits.
We have a CO2 sensor in both the bedroom and living area—it’s inexpensive and allows you to objectively adjust air quality to your needs.
In our case, the system runs at about 80% for an hour in the morning (device rated for 500 m³/h), operates at a low setting during the day, and runs at a medium level at night. This usually keeps CO2 levels around 400-500 ppm in the house, with nighttime levels below 800-1000 ppm in the bedrooms, and the air also feels good.
If there are several guests over, you can simply activate “party mode” at the push of a button—or alternatively, add a sensor for the system in the living room. I have considered this, but it costs around 300-400€ to save pressing a button 2-3 times a month.
Mycraft schrieb:
Theory and practice... Here it works so well that I didn’t even have to install all the sensors I originally planned. The system rarely runs at full capacity, and certainly not when only two people are in the house.
Two people in a confined space for several hours is not a peak load in my view, but rather normal conditions, which the sensors handle very well. I hope the system never runs at full capacity, as that would be neither economical nor comfortable for the residents. The control range must, of course, be much narrower.
The situation with two people is the starting point for Bookstar. He measured under these conditions and would like to change the results. As Lumpi also mentioned, a centralized measurement won’t change much in this situation because the results get too diluted. If the entire house shows poor values, then the basic setting is incorrect. This excludes individual cases like raclette with 30 people on New Year's Eve.
If you measure in a decentralized way, like Bookstar does, the only response to a higher value would be to significantly increase ventilation for the entire house. This is inefficient for the specific location measured, uncomfortable (and unnecessary) for the whole house, and uneconomical since, despite heat recovery, heat energy is still lost.
In my opinion, it is therefore important to have an appropriate basic setting in the system that can be easily and temporarily increased if needed — if at all necessary. So far I have had no need for this, which is why the green cable remains unused at the system.
guckuck2 schrieb:
In my opinion, it is important to have an appropriate baseline setting in the system that can be easily and temporarily increased if needed. If that is even necessary at all.Exactly. Usually, sensors are used for this purpose, and it works very well. The demand can then range from 0-100% without the need for the occupant to take any action.Similar topics