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Training my sense of CO2 ppm

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Re: Training my sense of CO2 ppm

#51

Post by jonstewart »

moduspol wrote: post #24
macNchz wrote: post #12

I've had an Awair monitor for a few years and enjoy keeping a fairly close eye on the numbers, but from what I've experienced so far I'm convinced sure I'd be able to train myself to discern CO2 levels. If anything it has mostly just encouraged me to open the windows, even just for a bit, whenever possible, and to always use the kitchen exhaust fan with our gas stove (and motivated me to buy an induction range in the…

Same here. I was truly surprised at how fast the CO2 goes up with our gas stove on. The only thing worse is when we use our unvented gas logs in the fireplace. We're switching houses next month and I'm seriously considering putting in an ERV. It's just a little tricky to explain to friends and family because it kind of makes you sound like a crazy person. But CO2 is measurable! And there is clear science about bad ef…

Yeah, I want to put in an ERV, too, to have the sense of fresh air all year round.

Re: Training my sense of CO2 ppm

#52

Post by b112 »

bumbledraven wrote: post #29
b112 wrote: post #27

Earlier quoted context omitted.

I may be misunderstanding, but if you claim outside is 415 and that's that, it's wildly inaccurate. Where you live, time of day, lay of land, all matters. Winter (no trees or vegetation with photosynthesis), and there is naturally more local CO2. Live deep in the country, in a forest, in the summer, when trees have loads of water and are at max output? Less CO2. At night, more CO2, for all those trees, that greenery,…

Just how "wildly" inaccurate are we talking about? What should the outside CO2 readings actually look like under those conditions?

As an example, close to a busy road, you may as well double the number in parent. Calibration by outside air is strange.

Re: Training my sense of CO2 ppm

#53

Post by stanislavb »

CoastalCoder wrote: post #7

I think the elephant in the room is calibration of the CO2 detector. When I looked into this a few years ago, I couldn't find any accuracy guaranties for CO2 meters marketed for households / greenhouses. The closest thing I could find were laboratories that could test CO2 meters in chambers with known CO2 concentrations. But IIRC the pricing for those labs was prohibitively expensive. - There were literally no guaran…

I use the same CO2 meter as the author has showcased. It's amongst the most accurate ones on the market at the moment (home grade). It uses a The Non-dispersive infrared sensor (NDIR) which is much more accurate than most sensors on devices sold online for $100-200. In fact, it actually measures instead of "estimates" the level of CO2 (as most cheap ones do).

Re: Training my sense of CO2 ppm

#54

Post by saaaaaam »

I have a fantastic way that I’ve trained my CO2 sense: an Italian greyhound. Anything above 900ppm and he barks and gets quite frantic above 1100ppm. I’m now able to anticipate the barking and normally realise at about 850ppm that we need to go for a walk and open the windows.

A vet friend theorised that because they have a completely disproportionate and crazy cardiopulmonary system (huge lungs and heart compared to overall volume) they are particularly sensitive to CO2 because they inhale more of it and it goes into their blood and brain much faster.

As soon as we open a window he calms - in winter I don’t take him out, I just ventilate the room.

Re: Training my sense of CO2 ppm

#55

Post by MatteoFrigo »

GuB-42 wrote: post #33
CoastalCoder wrote: post #7

I think the elephant in the room is calibration of the CO2 detector. When I looked into this a few years ago, I couldn't find any accuracy guaranties for CO2 meters marketed for households / greenhouses. The closest thing I could find were laboratories that could test CO2 meters in chambers with known CO2 concentrations. But IIRC the pricing for those labs was prohibitively expensive. - There were literally no guaran…

If you don't care about errors of a few percent you should be able to make your own calibration chamber. You just need an airtight container of a known volume, a source of CO2 and a maybe a fan. Put your CO2 detector inside the box, with fresh air, your CO2 source and the fan, and see if the result matches. You may need to do some calculations. For your source of CO2, you have a few options: combustion of a known qua…

I actually went down this path about 25 years ago, and I learned the hard way that CO2 hides in organic materials in a way that mostly invalidates the calibration.

I had a semi-sophisticated device consisting of a lightweight plastic cylinder that could move up and down when filled with gas, and a way to know the volume with accuracy (single-digit milliliter error out of five liters). I had a tank of pure CO2 and an air intake, coupled with valves that let me fill the cylinder with any desired mixture of CO2 and air. I wrote an automatic program that created a calibration curve in various proportions (100ppm CO2, 200ppm CO2, ..., up to 5000ppm) and collected the sensor value.

The results of this procedure made no sense, because the sensor reading collected during the calibration, e.g. at 1000ppm, was totally different from the sensor reading in response to a 1000ppm concentration created outside the calibration loop. After several days of investigation, it turned out that the problem was that I was using tubes of some carbon-based plastic material. Somehow the CO2 mixes with the plastic and is slowly released afterwards, altering the mixture. Everything worked fine after I replaced the tubes with silicon-based silicone tubes.

Re: Training my sense of CO2 ppm

#57

Post by [deleted] »

scottlamb wrote: post #41
abirkill wrote: post #37

Earlier quoted context omitted.

The auto-calibration systems on cheaper consumer sensors also cause issues if they rarely see air that has low CO2 levels. Because these sensors can't measure absolute CO2 levels, only relative CO2 levels, they provide an absolute figure by looking for the lowest CO2 concentration they've seen over a period of time, usually around a 72 hour rolling window. This works acceptably if the sensor is frequently exposed to…

> Unfortunately, when I last looked, I couldn't find any consumer-grade sensors which used dual-NDIR sensors, only more expensive and less aesthetic commercial sensors. In the end I built my own using a CDM7160 sensor connected via I2C to a ESP8266, which reports over MQTT. Looks like that's been discontinued. [1] Any advice for folks trying to build one now? [1] https://www.figarosensor.com/topic/2020/11/Discontinua…

[deleted]

Re: Training my sense of CO2 ppm

#58

Post by lsh123 »

I have a cheap (about $20-25 a couple years ago) sensor from Amazon in my plane. It calibrates itself when I turn it on and I check it works on the ground before every flight - open the window after starting the engine and see co2 going up ;) Granted, I don’t really care about any small errors or small changes - I want the sensors to warn me if co2 concentration goes up significantly (e.g. because of leaks from exhaust system).

Re: Training my sense of CO2 ppm

#59

Post by gsich »

abirkill wrote: post #37
CoastalCoder wrote: post #7

I think the elephant in the room is calibration of the CO2 detector. When I looked into this a few years ago, I couldn't find any accuracy guaranties for CO2 meters marketed for households / greenhouses. The closest thing I could find were laboratories that could test CO2 meters in chambers with known CO2 concentrations. But IIRC the pricing for those labs was prohibitively expensive. - There were literally no guaran…

The auto-calibration systems on cheaper consumer sensors also cause issues if they rarely see air that has low CO2 levels. Because these sensors can't measure absolute CO2 levels, only relative CO2 levels, they provide an absolute figure by looking for the lowest CO2 concentration they've seen over a period of time, usually around a 72 hour rolling window. This works acceptably if the sensor is frequently exposed to…

Auto calibration can be disabled, popular sensors that can do this are MH-Z19 and MH-Z14 (also cheap ones).

Re: Training my sense of CO2 ppm

#60

Post by gsich »

greggsy wrote: post #31
CoastalCoder wrote: post #7

I think the elephant in the room is calibration of the CO2 detector. When I looked into this a few years ago, I couldn't find any accuracy guaranties for CO2 meters marketed for households / greenhouses. The closest thing I could find were laboratories that could test CO2 meters in chambers with known CO2 concentrations. But IIRC the pricing for those labs was prohibitively expensive. - There were literally no guaran…

If I understand correctly, they’re calibrated at the factory, which is probably in China, which might have vastly differing CO2 levels depending on whether the winds blowing up or downstream of any heavy industry or metropolitan centre?

I don't think this is what is meant by "calibration".
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