My recommendation is to get an indoor CO2 monitor for your bedroom that can alarm whenever levels go above 1000 ppm. From what I understand high end office are being equipped with such systems with direct control of the ventilation systems for exactly this reason.
For home use a mid-range unit is sufficiently accurate, precise, and reliable. I use the Extech CO200 personally. Don’t but a cheap unit because those have calibration drift after a few months. And recalibration is not trivial.
- What is the real world accuracy I can expect from this kind of sensor, with and without calibration?
- is it enough for calibration just to go outside and assume some number between 400 and 500 (assuming outside means not just next to industrial chimney)? If not, what would be better calibration process?
I'm using an NDIR-based USB-CO2-meter (~40 €, allegedly USB only for power, but it actually spits out measurement data over USB) and I think it's pretty accurate. When I put it outside it generally reflects ambient CO2 pretty accurately (440-450 ppm) and I found through blind-testing that "air staleness" correlates very well with CO2 concentration. For me, air feels noticeably stale at around ~700-800 ppm, which seems largely inline with academic results.
You can actually see when the device acquires a reading, because the tube flashes.
Re your other questions; yeah I gather there is some experimentation involved, even with out of the box commercial products.
If others have suggestions on chips or products to buy for the household, I would greatly appreciate it! The MH-Z19 looks like an option for me. Commercial products seem too unreliable for the price.
I think that is CO2e, which should be a different thing to my understanding. (CO2e is used to estimate the greenhouse gas potency of other gases like methane. Whereas I think eCO2 is some kind of estimate of amount of CO2 in the air, but what, exactly, I do not know)
because my google-fu was not good enough to find those....
Regardless, I would be curious on the same questions about real world accuracy on those as well.
I have two of them, one inside and one outside. They both go down to roughly 400 ppm and the indoor one goes very high when it's all cooped up inside. The outdoor one fluctuates since I'm in an urban area. I believe they are accurate to within about 10%.
During the smoke event, they combined with my indoor/outdoor pm2.5 sensors have been extremely useful.
You should be using the newer version, MH-Z19B, not MH-Z19.
The protocol is compatible though.
Also note they come in up-to-3000ppm and up-to-5000ppm variants. Be sure to get the latter.
In case it helps anyone: a very fast way to get it working and get graphs is to connect it to a Raspberry Pi running HomeAssistant. Takes a few clicks and 3 lines of config.
Even keeping the bedroom door open helps. I did some tests with a CO2 meter - with the door closed it reached 1100ppm after a nights sleep. With the door cracked open it was around 700ppm.
One thing is that air diffuses out fairly effectively even with the door closed, presumably through gaps in the door frame. Quick calculation (welcome any corrections, numbers pulled from quick online searches):
I agree, I've measured this as well. Window in adjacent room (with open door between rooms), window opened 5-10cm, CO2 level stays pretty much down.
I've also found that when all windows are closed, an air purifier seems to help (or a fan, lowest level is fine). Obviously it doesn't remove the CO2, but it seems to prevent buildup in the one corner where you are (bed, desk). I'm sceptical it's a problem but the data shows it is.
Yes, that’s the limitation of current technology. thankfully it’s doable with only a few minutes of attention and no tools or specialized requirements.
1000 ppm is an absolute limit, the vast majority of the population will experience measurable effects above this threshold. And it’s surprising how often that’s exceeded in normal everyday environments.
I think this wasn't about compromised air quality indoors. Rather general level of CO2 in the atmosphere. What help are ventilation systems then? You'd need to have submarine scrubbers in place to do something about it, and/or cans of liquid oxygen.
I think their point was that increasing CO2 in atmosphere makes it more difficult to keep indoor levels acceptable.
First, if you start from 600pm instead of 300, you reach 1000 ppm faster. Adding to the insult, it is much more difficult to ventilate the excess CO2 away, if the air you use to ventilate contains in itself already 600ppm instead of 300ppm.
Indoor air usually has significantly elevated CO2 levels compared to outdoor air.
More ventilation cannot push the levels below the levels of outdoor air, but it can get them close.
Their argument that assuming today's already inadequate ventilation systems don't change, more outdoor CO2 = more indoor CO2, pushing it above some arbitrary threshold (which is far above predicted outdoor CO2 levels).
I do think we should think about passing out personal CO2 alarms now and in the future. The problem would be calibration like you said and cost for a new unit.
For home use a mid-range unit is sufficiently accurate, precise, and reliable. I use the Extech CO200 personally. Don’t but a cheap unit because those have calibration drift after a few months. And recalibration is not trivial.