Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Training my sense of CO2 ppm

interconnected.org

Post reply on HN
Print view View original

61–70 of 98 posts

Re: Training my sense of CO2 ppm

#61

Post by abirkill »

gsich wrote: post #59
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…

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

This is true, but I don't think any consumer-grade sensor systems offer this as an option? I guess it might be useful if you're building your own sensor, and can't afford/justify a dual-NDIR sensor.

My understanding is that with single-NDIR sensors (like the MH-Z14 and 19), the auto-calibration is intended to overcome gradual particle buildup and beam degradation in the sensor chamber. While disabling it will prevent the scenario I described, you'll instead end up with gradual sensor shift as the sensor ages. I guess this could be minimised by manually calibrating the sensor outdoors on a regular basis.

Dual-NDIR sensors split a single beam into two chambers, so any degradation of the sensor beam affects both measurements, and the particle buildup in both chambers should also be approximately equal over time, so they should remain accurate over an extended period without any requirement for calibration. I built mine about 4 years ago and I do occasionally check to make sure they read ~400ppm when placed outdoors, last check was around 420ppm which suggests they're behaving reasonably well as they age.

Re: Training my sense of CO2 ppm

#62

Post by ta988 »

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…

This is not easy at all. Your source of CO2 if it is a bottle will have a pressure. Your bicarb should be dry to make sure you weight it properly. If you want to measure ratios of 100 above 100ppm the home made way is decent, but for atmospheric/domestic variations that's not going to cut it. Plus as the other commenter said, CO2 creeps into plastics and leach slowly after so you have to let your system equilibrate which then opens you at the effects of porosity and diffusion.

Re: Training my sense of CO2 ppm

#63

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

#64

Post by travisjungroth »

lsh123 wrote: post #58

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 exhau…

I've never heard of that. Do you have a CO sensor as well? Those are common, mostly in a very cheap one-time-use dot form.

Re: Training my sense of CO2 ppm

#65

Post by ericpauley »

lsh123 wrote: post #58

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 exhau…

Are you sure this isn’t a carbon monoxide (CO) sensor? While exhaust might increase CO2 as well, pilots are usually far more concerned about CO poisoning and usually use CO detectors.

Re: Training my sense of CO2 ppm

#66

Post by paulcole »

PragmaticPulp wrote: post #48

CO2 concentrations are an ongoing topic of debate. There are studies that show no measurable cognitive changes up to CO2 concentrations in the thousands of PPM, while other studies seem to show cognitive changes at much lower amounts. I tend to think that people with CO2 sensors tend to over-focus on CO2, when really what they’re feeling is the general stuffiness of a room. CO2 isn’t the only thing that accumulates i…

I wondered this too. Like yeah you’re going to be cognitively drained after being in a crowded closed meeting room for a long time. Is it because you were talking and working or because of the CO2.

Re: Training my sense of CO2 ppm

#67

Post by [deleted] »

paulcole wrote: post #66
PragmaticPulp wrote: post #48

CO2 concentrations are an ongoing topic of debate. There are studies that show no measurable cognitive changes up to CO2 concentrations in the thousands of PPM, while other studies seem to show cognitive changes at much lower amounts. I tend to think that people with CO2 sensors tend to over-focus on CO2, when really what they’re feeling is the general stuffiness of a room. CO2 isn’t the only thing that accumulates i…

I wondered this too. Like yeah you’re going to be cognitively drained after being in a crowded closed meeting room for a long time. Is it because you were talking and working or because of the CO2.

[deleted]

Re: Training my sense of CO2 ppm

#68

Post by hackerlight »

whalesalad wrote: post #8

I feel terrible above like 900/1000ppm but I’m sure it’s also a good proxy for whatever other garbage and voc’s are in the air. When my monitor reaches 800 I’ll throw my window exhaust fan on for a few hours to circulate the air in my home.

How many people, in what square metreage, over how many hours, does it take you to go from ambient levels to 800?

I can take your figures and calculate the same for my conditions by rejiggering the input assumptions instead of buying a monitor.

Re: Training my sense of CO2 ppm

#69

Post by hackerlight »

kadoban wrote: post #5

Is there any kind of CO2 scrubbing that's at all practical for home? I'm curious what the effects would be of going below ambient/outdoor levels, especially since those are rising (if slowly).

Indoor plants do practically nothing.

The most effective is cross ventilation. I no longer live in places without cross ventilation, it's too hard to air out quickly unless the windows are huge.

It's also good to have windows facing the direction of typical wind direction in whatever geography you're living in.

Re: Training my sense of CO2 ppm

#70

Post by lancewiggs »

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?

You can calibrate the Aranet4 at any time by putting it outside, and it will set that as 420ppm. Obviously the ambient CO2 levels are raising slightly each year, so this is not entirely perfect.

We have tried a number of different CO2 sensors over the years (mainly from Ali Express), and recently purchased 2 Aranet4’s. We were pleasantly surprised that they report identical readings in the same location.

Post reply on HN