This question about reliability, precision and accuracy of home CO2 meters, appears repeatedly and, the truth, I felt that it was time to write a few lines about it because there are very little informed opinion on the internet and it can be difficult to know the truth among so many opinions.
This article is pending review, differentiating between reliability, accuracy and precision and making their difference clear.
Although the answer is not that simple, I will start by saying that yes, that home meters are just as reliable, accurate and precise as commercial ones (be careful, the range we are talking about), although there are always some nuances. Next, I will reel off why.
DISCLAIMER OF LIABILITY
I have wanted to publish this article for a long time, without daring at all.
Of course I will start by saying that this is just another opinion, my informed and honest opinion. I hope nobody gets on top of me ...
I don't have to be right, I have simply dedicated myself to writing what I think about this matter.
I will not be held responsible if my opinions cause a new political conflict, world disorder or the zombie apocalypse.
I am aware that I am getting into a Marshy ground, where there are important economic interests of a booming industry. I'll accept all kinds of criticism in the comments, as long as they're polite, though I will prefer the constructive ones.
The reliability, precision and accuracy of a homemade meter
Keep in mind that, unless you compare it with a € 10,000 meter, the CO2 sensor that the "professional" meter will carry is exactly the same as the home one (or worse, because the Senseair S8, which we are using is one of the best, within "What you can afford", and there are many commercial meters that use sensors terrible). In addition, the CO2 sensor is factory calibrated by the manufacturer, so it should dial right out of the box.
I bet the vast majority of manufacturers of commercial CO₂ meters are not calibrated by their manufacturers one by one, but simply rely on the calibration of the sensor manufacturer, as we do.
Sensors, over time they are decalibrating (Also the meters of 200 or 300 €) and that commercial meter for which you have paid 100, 200 or 300 € is decalibrated just like yours, so its precision in the measurements will be the same as yours and will depend exclusively on the care you put when calibrating it (same yours as the € 300).
Here we can talk about something important, and that is "The education" (information and knowledge) that most of the people who buy a commercial sensor have is little pulling to null (not to mention the rickety manual you will receive with the commercial meter), while A user who builds his meter with love, following a tutorial like the one in this blog, has the concern and desire to learn and does not have a rickety manual, but a whole blog with a lot of information about it and a community of users who participates, helps and contributes their knowledge and experiences.
How many manuals of commercial meters correctly explain to the user how to calibrate the device?
Definitely, the home CO₂ meter will measure very well (exactly the same as the 300 €) but the exact CO2 concentration will depend on what there really is at the time of calibration (same as in the 300 €) and as both one and the other must be calibrated from time to time and you will never know the exact CO2 concentration unless you have it calibrated to a laboratory (both one and the other).
What can we expect in terms of precision in the measurements, both in one case and in another (and as long as the calibration is done correctly)? 100 ppm? It seems enough to me! When we talk about health and CO₂ (or Covid and CO₂) it's not those little differences that make the difference.
What makes the difference is that some users live with very high concentrations of CO₂ without even suspecting it And it is having a CO₂ meter that opens their eyes. Some users have said in the Telegram group (come over and see it) "I have built the meter, but it does not work well, it shows more than 1000 ppm and it does not stop going up" to realize that those figures they were correct. Not already 1000 ppm, but it is easy to have 2000, 3000 ppm and more, if we neglect the ventilation (myself in the room where I work, if I do not ventilate, at the end of the day I am always above 3000 ppm).
What is a CO₂ meter like?
A commercial CO₂ meter is a device used to measure the concentration of carbon dioxide in the air and that consists of a detection sensor, electronic components and firmware, or computer program, that makes these three parts work.
Really CO2 measurement is performed by a single component, the CO₂ sensor, and the rest of the components and firmware only works for that sensor to work and tasks related to the use of those readings.
When I say "make that sensor work," I mean things like:
- Provide you with feeding correct
- Yes there are drums, keep it charged and in optimal condition
When I say "tasks related to the use of those readings" I mean things like:
- Allow us to see the measurements in some way (a screen, for example). Can you imagine a meter that had no way to see the measurements?
- Allow the user to communicate with him (turn it on, turn it off, calibrate it, configure alarms, if it has them, etc)
- Various things such as self-checks, measure and show us the temperature or humidity (in the models that have these functions), etc.
Really the precision of the meter will depend, fundamentally on the following things:
- Of the sensor used (there are better and worse)
- Of the optimization of the electronics (that the sensor supply is stable and clean)
- From the user: That he knows what he is doing, that he calibrates it properly and gives it good use and maintenance, etc.
In the image below you can see the inside a commercial CO₂ meter, Kecheer brand (although it is also sold under other brands such as Baugger, KKmoon, KKTECT, S SMAUTOP and Brisunshine). As you see, it's not very different from ours. In this case it uses a CO₂ sensor from the manufacturer Honeywell, but this same meter They also sell it with the Senseair S8 sensor that we usually use in our project (and probably with others).
What does a commercial CO₂ meter provide?
If we think about it, a commercial meter provides the following advantages:
Everything ready for use
Normally with a commercial meter all you have to do is buy it, open the box and press the power button.
This, which in principle is very good, has an important disadvantage: user has no idea howmo that device works and therefore it is very likely that it will not be misused and that it will be properly maintained.
Many users do not know that their meter must be calibrated by themselves from time to time so that it provides correct measurements (well, even commercial meters that do not have any type of calibration are given).
The normal thing is that a commercial meter comes with Clear instructions, even if it's in English, most of the time.
Clear instructions, often means instructions short and scarce without entering any point that the user may find a complication.
Brands are very concerned that their product is presented as easy to use. Often this means that the instructions will disregard warnings, cautions and procedures relatively complex that can give the user the appearance of difficulty.
An aesthetic product with a good finish
Here we have an important point in favor of commercial meters.
A meter enters through the eyes and most of the people they distrust a meter with a homemade look, thinking that their measurements cannot be of quality, confusing the part for the whole.
To the fans, there is no doubt, what costs us the most is to give our projects a good finish. No matter how hard we try, we can't compete (with some honorable exceptions) with commercial terminations.
Even the most basic and cheap commercial CO2 meters look good (regardless of whether their construction materials look more or less cheap). No hanging wires or holes that are not perfectly round will be visible, and they usually have a good lettering.
The manufacturer's warranty
The manufacturer's warranty, I said? Sorry to laugh!
There is no doubt that there are manufacturers that ensure to give a exceptional service, with a service quality aftermarket (selling your product at a price consistent with this service).
But most of the time, we will not count on this quality service.
When we talk about the lower-middle range of commercial CO₂ meters, which is what most users buy, what we find are very low-quality Chinese products that, like so many other low-priced Chinese products, are intended for give the minimum and fail to the minimum. They are intended to be cheap.
And now the landlord. What can go wrong (or right)?
Actually, most home CO2 meters they are quite simple devices:
- They receive the measurement from the CO2 sensor and
- They show it to the user in some way (as the sensor sends it)
In principle the meter does nothing else, does not manipulate the measurement or have to calculate anything in particular, however, there are things that can go wrong ...
There are two main types of problems that can arise with a home meter: those of software and those of hardware.
Although most meters do not have to interpret the measurements provided by the CO2 sensor, nor do they have to modify them at all, problems can occur.
- A bug in the firmware that modifies the measurement before showing it to the user
- An error in the programming of the communication with the CO₂ sensor that makes it not "understand" what the sensor is sending and take one thing for another ...
Both in one case and another I think the solution is simple (and it is exactly the same as you would use with a commercial meter, which is not without these problems either): Choose a homemade CO₂ meter project well documented, built by enough people, with good results, and reputable.
Here, the range of problems may be somewhat greater. Basically we can find the following problems (of the project, not of the assembly, which could give many other problems):
- Power failures. The most common and that if you follow a good tutorial you should not suffer (and not only that it teaches you to avoid them, but it teaches you to anticipate and identify them).
Did I say the range of bugs was greater? Well no. I lied. What happens is that feeding problems are not uncommon (not in commercial meters) and can be a problem.
Normally in the instructions of a project worth its salt, they will talk at length about food. You just have to read and follow the instructions.
If you have to pay attention to one thing in particular, meter projects that include rechargeable batteries:
It is not easy to design the stage that supplies a meter that can be used both connected to current and with batteries (when it is one or the other, it is not so critical). I guarantee that more than 80% of the maker projects have problems in the feeding stage.
As in the case of software, I think the solution is simple (and it is exactly the same as you would use with a commercial meter, which is not without these problems either): Choose a homemade CO₂ meter project well documented, built by enough people, with good results, and reputable.
Some of the users with access to professional meters have made some very interesting measurements. Below, I include the data of some of them, with the permission of the users:
You have used a professional CHAUVIN ARNOUX CA 1510 meter. It is a CO2 meter, not just commercial, but a professional and certified CO2 meter, which costs more than € 400.
The user has performed two rounds of measurements with the two gauges simultaneously (the Chauvin Arnoux and the Senseair S8 LP eMariete Gauge with sensor). These are the results, in his own words:
During the day
«On air for 1 hour: S8 / CH 412/426. Empty room: 656/665. Room occupied by me with closed door, evolution in half an hour: 850/868, 948/939, 1032/1020, 1063/1080 (on some occasions the Senseair scored higher). Empty room again: 726/732 and now with the door open, 798/793, the data from the photos from 10 minutes ago 802/811 »
In the evening
«Comparing during the night, very similar measures, that is if the Chauvin is« certified », the Senseair too, and even better, because it reaches lower values abroad (as I put above, I am in an unpopulated area with a small city than 8000 inhabitants below, at the bottom of the valley, 1 km away). Consulting both graphs, I report the data every hour in a room of about 25 cubic meters, with a person sleeping with the door and windows closed: S8 / CH. At 3 1371/1345, at 4 1686/1667, at 5 1833/1882, at 6 2024/2060, at 7 2165/2191, at 8 2335/2352 at 8.50 (maximum) 2374 / 2437, the window opens ajar at that time, at 9.30 534/643 and the final minimum at 10: 431/452. »
If you have also been able to do tests with a home meter and a commercial one, tell me in the Telegram group to include it!
And if you have pictures of its interior, even better.