Comment by microtonal | Hacker News Reader

Comment by microtonal | Hacker News Reader

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No, it is crap. Yes, it is Sensirion, but it uses a thermal conductivity sensor, which is a very indirect method of measuring CO2. One part of the sensor emits heat and the other senses it and the idea is that heat transfer changes with different CO2 concentrations. However, a lot of other factors influence this as well, such as ambient temperature/humidity (which is why the sensor incorporates measurements from an SHT sensor), but also gas mixture, etc. You only get good readings at lab conditions. Even below 1000 ppm, I would often see readings that are 300 ppm from more expensive, known-good CO2 meters.

If you want a CO2 meter on the cheap, either wire up an optical NDIR sensor like the SenseAir S88 (22 Euro) up to an esp32, which is possibly the best sensor you can get for the money (slightly cheaper version of the sensor that the AraNet4 uses). Or if you want something standalone with a display, get the SwitchBot Meter Pro CO2 for ~50 Euro, which uses a photoacoustic NDIR, but is still miles better than the sensor in the ALPSTUGA. Can also be hooked up with HA through an ESPHome BLE proxy or with the SwitchBot Hub.

You can find a comparison of the IKEA sensor with other affordable sensors here:

https://danieldk.eu/hardware/smart-home/ikea-alpstuga

(Upd: the IKEA does have lower accuracy, with ±100 ppm instead of ±30 ppm. From the SEN63C datasheet)

You forget to mention that it is ±100ppm plus ±10% of the ambient ppm, which makes a big difference. At 1000ppm it's ±(100ppm + 0.10*1000) = 200ppm and that's only in an environment with 25C, 50% RH, and 1013 mbar. So, that does not tell you much, given that thermal conductivity is very sensitive to environmental factors.

if you just want to know if CO2 is too much, 300ppm precision is fine.

I dont need to know the exact level, just give me a green/yellow/red LED and make it cheap so I can have a sensor in every room

No, it's not. You generally want to ventilate an office when you reach 1000ppm, but then the IKEA will often warn you already at 700ppm. 700ppm is fine.

"Generally" is a vibe measurement to begin with. You won't notice any difference at all between 700ppm and 1000ppm. It's once you start hitting 2000ppm you are getting noticeable brain fog.

Had bad ventilation in my old apartment (built 1888) so got a co2 monitor. Started feeling the effect at 1100-1300ppm, so would open it in home assistant and check, never below and never above really. During winter when it was -10 so couldn't keep the window open all the time.

I disagree. I feel a very steady and progressive deterioration starting at 600 ppm. It becomes significant at 800 ppm. The studies back up the latter threshold.

Unfortunately it will be hard for you to know how much of that effect is placebo. Unless you tested this with some kind of double-blind setup.

You're not wrong, but indoor CO2 at these sub-1000 levels is a useful proxy metric for bioeffluent VOCs which are an objectively tiring subset of total VOCs. Ventilation lowers both. This explains the observation better than nocebo theory. See https://www.aivc.org/resource/effects-carbon-dioxide-and-wit...

You would not notice a difference if you weren’t checking the CO2 ppm. You primed your brain to ‘feel’ the effects of higher CO2 by reading a study and are experiencing the nocebo effect.

If it makes you feel better I don’t see a problem with it.

Indoor CO2 is likely overrated here at these sub-1000 levels but it's a useful proxy metric for bioeffluent VOCs which are a tiring subset of total VOCs. Ventilation lowers both. This explains the observation better than nocebo theory. See https://www.aivc.org/resource/effects-carbon-dioxide-and-wit...

Interesting study, thanks for sharing! I am starting to see more space temp/CO2 combo sensors in commercial office conference spaces, if the CO2 rises above the setpoint, the VAV opens to let air in to reduce CO2 (and bioeffluent VOCs, according to this study.)

you assume that the error will always be in one direction

and if sometimes you ventilate a bit sooner than required, at 700, what?

businesses will not put $200 meters in every room

Have you looked at the prices of meeting room furniture? A $200 meter is not a significant cost measured against what it costs to furnish the room in the first place. It only becomes significant is you treat it as a line item disconnected from the room it's in

businesses will not put $200 meters in every room

There are good $50 Euro meters. Besides that, I am not sure if that is true, at my wife's workplace, they put high-end CO2 meters in every larger room where multiple people meet. Admittedly, this was during COVID, so a lot of organizations were using CO2 levels as a proxy for finding whether a room was properly ventilated.

Presumably there is still the need to ventilate. So the concentration can also be measured more centrally. That is how the mechanical ventilation unit in my house works. For both humidity and CO2.

$200 is nothing compared to the lost productivity.

You put one CO2 sensor in the return air duct and tie it to outside air control.

You generally want to ventilate almost continuously, so if a circulation fan kicks on at 700 instead of 1000 that's really not a big deal.

But if I open a window at 700ppm, so what?

Maybe you live in a place where the room temperature is the same as outside. Here in winter, it means sitting in the cold.

No I live in Sweden.

You can open the window for a bit to air out, should be done even in the winter :)

Suddenly there's not enough CO2 in the room and you get overly awake! Bummer! /s

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