Hacker News Reader

Comment by dilippkumar | Hacker News Reader

Tangential, but I've had this monitor[0] at home for about 2 years and I can recommend it.

I live in a place that's generally cold for a large part of the year, so I have all windows shut for most of the time. I've discovered that tracking CO_2 levels is a very good proxy for general air quality, and a good measure of both when to open windows and for how long to keep windows open.

For my apartment, I was surprised that the amount of time I needed to keep the windows open was 5x longer than what I initially assumed (I assumed 5 mins would be enough. Data shows that I need about 25 mins to get CO2 levels down to around 500ppm). I was also surprised to see how much more rapidly CO2 builds up when I have just 2 additional people at home.

[0] https://www.airthings.com/view-plus

View on HN

I use an Awair, also in a cold climate. Seeing the data for my air quality motivated me to install an air exchanger. Having the monitor allowed me to see how much we needed to exchange in order to keep the CO2 at a decent level.

For anyone with a modern home that is sealed up average or better, an air monitor indoors is almost a must.

On the topic of the number of people and CO2, I'm tempted to have it alert me when I'm out of town and the CO2 rises. I have an alarm, but who would think to defeat the innocent looking air monitor on the shelf?

Or intruders may be conveniently alerted when you are out of town :) Who knows who built that monitoring app and which npm modules it imported.

Awair let's you hit the device on the LAN and get JSON, so the software is all mine. You don't have to let it connect out or report to anyone else. That is one of the reasons I picked it, I like my smart home to stay home.

What's the intended purpose of the system alerting you when you're out of town?

Presumably, an unexpected increase in CO2 would be a proxy for intruders.

Yes, what is kinda fun is I can tell what time my kids are out of bed (really it if their room) just by the changes in co2.

Everyone was gone today at the same time (rare with WFH and home school). I can see within about a minute when we arrived home.

Or houseplants dying.

Ha, if only it were that sensitize. I have an air exchanger, so I don't think the plants will change it enough to matter. I expect that normal air infiltration would cycle more air than plants.

Airthings has some good hardware and I like the e-ink display but it has terrible terms of use that severely restrict your ownership rights.

Here are some excerpts from Airthings T&Cs [1] that I find very problematic:

In 15.4. of Airthings T&C it writes: “We own and shall retain ownership of all rights to all data and information collected via the Services provided to you…”

Furthermore, in 15.2 Airthings claims all rights for modifications that you might carry out on the Airthings monitor: “You hereby assign to Airthings all right, title, and interest (including Intellectual Property Rights) that you may have in any custom developments, modifications, or derivative works of the Services and Products created or developed by or for you, including but not limited to design, artwork, technology, software, data, functionality, and documentation.”

I wrote about it in a review with our monitor [2].

[1] https://www.airthings.com/en/legal/terms-of-use

[2] https://www.airgradient.com/blog/airgradient-vs-airthings/

(Edited and included Airthings T&C)

> I assumed 5 mins would be enough. Data shows that I need about 25 mins to get CO2 levels down to around 500ppm

I also noticed that just cracking a window doesn't seem to do much according to the CO2 monitor, except letting the heat escape.

The trick is to open multiple windows/doors wide and get some cross ventilation going. This gets CO2 down in only a few minutes. It's called stoßlüften in German.

Way too expensive for a device like that, at $300. They usually go for $10-20 at Aliexpress.com. But it has rounded corners, so I guess suits the Americans.

In addition to measuring VOCs, specifically alcohols, instead of CO2 using NDIR, the cheap ones can have additional algorithms that skew the readings.

I purchased an INKBIRD Air Pollution Monitor. It has an internal battery, doesn't connect to other devices or networks, is inexpensive, and is irrationally inaccurate sometimes.

A reviewer found the same behaviour and confirmed what I knew through tests with dry ice (solid CO2) and isopropanol alcohol. It measures CO2, not VOCs, but some constantly running calibration or data fitting algorithms lead to wild overshoot and undershooting compared to higher-quality monitors.

Finding an inexpensive and accurate CO2 monitor may be possible, and aliexpress.com is the home of inexpensive. But without testing and possibly a teardown, you will not likely get an accurate and affordable monitor.

The extremely cheap ones might be fake, they're computing estimated CO2 based on VOC, rather than actually measuring it with NDIR.

What’s the risk of co2 build up in doors?

Making you more stupid https://www.smithsonianmag.com/science-nature/the-carbon-dio...

Maybe that is why we get good ideas while taking a walk?

The effect persists in well ventilated buildings (good thought though)

Getting sleepy, getting a headache, performing worse physically and mentally. Might be more stuff if you look into it, but to me this is the obvious stuff that matters and already justifies frequently opening windows.

Did you skip the headline/title of the post?

How accurate is this?

I have several CO2 monitors including some from AirThings, Aranet4, and a industrial sensor in the form of a Vaisala GMP252 CO2 probe. They all track closely enough that I don't worry about it. The Vaisala is rated to +/- 40PPM which is accurate enough for living space environmentals.

Which one has a good price/accuracy ratio?

I don't have any equipment to calibrate it or measure it's calibration against. However, when I leave the windows open for extended periods of time, the CO2 levels hit levels that are within 50ppm of [0]. (I live in a different city from this station, with different population density, traffic patterns and all sorts of other micro-climate stuff that can contribute to a baseline difference. Additionally, CO2 levels swing by several hundred ppm when the air quality goes bad, and the ~50ppm range is insignificant in comparison)

It seems good enough for how I use it. I wouldn't conduct chemistry experiments using this as an instrument.

[0] https://gml.noaa.gov/ccgg/trends/monthly.html

All these devices calibrate by periodically measuring the lowest ppm in a given period, and assigning it a value of 420. That's how they always accurately measure CO2 with the windows open.

Reply on news.ycombinator.com