
Show HN: Low cost CO₂ monitoring (your office) with Prometheus and Go - leastangle
https://github.com/larsp/co2monitor
======
Animats
This is another way to do IoT wrong - collecting data but just displaying it.

The idea is to use CO₂ levels to control your HVAC system. The HVAC system
should be able to draw fresh air from outside or recirculate air from inside,
depending on CO₂ level. This is a standard option on modern HVAC systems, and
there are standard sensors for it. Better systems sense temperature, CO₂, CO,
humidity, and smoke. This is a huge win for rooms where the people load varies
widely, such as hotel function rooms and classrooms. Such control systems save
money, because, when nobody is using the room, they detect that CO₂ is low and
cut down the ventilation rate. When the room fills up, the CO₂ level goes up,
the fans speed up and the outside air intakes open until the CO₂ level comes
down.[2] There are smart control units which manage heat, fans, vents, and air
conditioning compressors. The hardware pays for itself in power consumption.

And yes, you can get this stuff Internet-enabled, although that's mostly for
remote maintenance. The HVAC works just fine without connectivity.

Surprisingly, this technology is a tough sell. Except for convention hotels.
They get this. They're in the competitive business of keeping large numbers of
people comfortable and coming back. They have big rooms where the people load
may go from zero to a thousand in minutes, and go back down an hour later.
It's a huge win for them.

[1]
[http://www.airtesttechnologies.com/support/reference/CO2SeqO...](http://www.airtesttechnologies.com/support/reference/CO2SeqOfOperation.pdf)
[2]
[https://buildingcontrols.honeywell.com/literature/Advanced_R...](https://buildingcontrols.honeywell.com/literature/Advanced_RTU_Retrofit_Solution_Program_Sell_Sheet-01-00041.pdf)

~~~
dualogy
> _Surprisingly, this technology is a tough sell._

Well, in the Office for regulating CO2-vs-O2 it's competing with the timeless,
very-low-maintenance and low-cost combo of keeping-plants-and-occasionally-
opening-a-window.

~~~
Animats
If the windows and the HVAC aren't talking, you end up trying to heat or air
condition the outside world. This is both futile and expensive.

Also, it takes about eight trees to absorb the CO2 emitted by one human. The
contribution of houseplants is tiny. Especially since they usually don't get
full sunlight.

~~~
user5994461
>>> If the windows and the HVAC aren't talking, you end up trying to heat or
air condition the outside world. This is both futile and expensive.

That's an argument to be made to the hotel or office owner. The user has no
control on the HVAC and is forced to open the window or turn on electric
heaters to cancel it.

------
Hasz
If you're interested in a hardware solution, I've used the MH-Z19 CO2 sensor
to great results. It's an NDIR (read:not electrochemical) sensor with a UART
interface and temperature compensation. It will report up to 5000ppm and comes
factory calibrated.

It's also $20 in singles from China. Coupled with whatever microcontroller you
want, it's totally possible to have a distributed net of CO2 sensors for a low
cost per node.

That being said, it's a ton of work and this is an excellent solution with
much quicker results.

~~~
tga
Just wanted to add that Tasmota[0] (one of the open source firmwares for
ESP8266 controllers) seems to already support MH-Z19 sensors.

This cuts down on the work if all you want is to measure your CO2 level: you
can get a $3 Wemos and a sensor, (solder pins, figure out the sensor
connector), flash Tasmota, and you'll have it already reporting on MQTT over
wifi. I would argue it's even easier than installing and maintaining Linux on
a RPi.

[0] [https://github.com/arendst/Sonoff-
Tasmota](https://github.com/arendst/Sonoff-Tasmota)

------
enra
I was looking in to a indoor quality monitor, and seems like for $80, you
could just buy this which connects to homekit [https://www.amazon.com/Elgato-
Eve-Room-technology-Bluetooth/...](https://www.amazon.com/Elgato-Eve-Room-
technology-Bluetooth/dp/B01M2YTIBC/)

~~~
seanp2k2
Came here to say something similar. I expected an actual circuit build (of
which there are many), but this is just plugging in a USB data logging CO2
monitor (which is $116 on Amazon right now, but apparently the normal price is
~$70 USD) and using it with Prometheus. I've done something similar wrapping
[https://github.com/merbanan/rtl_433](https://github.com/merbanan/rtl_433) to
pick up temp / humidity monitoring data from sensors around my home, then
stuffing the results into InfluxDB and using Kapacitor for alerting (sends me
an email when my freezer gets too hot) + Chronograf for graphing. It took an
evening of reading docs and messing around to get it all working, and I'd
recommend Ding I Y if it sounds cool -- you'll very likely learn something.
Note that you could do the same with an ELK stack or Sensu or Nagios or
whatever you want to play with.

~~~
tga
What kind of 433MHz temperature+humidity sensors are you using? What kind of
battery life do you get from them in the freezer?

~~~
seanp2k2
They’re all Acurite sensors with lithium batteries (Energizer ultimate
lithium, available at Target on sale sometimes and other places). The one in
the freezer is a “00592TXR” and lasts ~9 months in there IIRC (lithium cells
do much better with cold temps than alkaline). I also have a few model 06044
which are small temp + humidity sensors with a display. These also have good
battery life. Lastly, Acurite makes a smart hub to log to their cloud, model
09150M. I haven’t set it up yet, but it basically does the same stuff:
[https://www.myacurite.com/#/login](https://www.myacurite.com/#/login)

Here’s the kind of stuff it can do: [https://www.acurite.com/access-my-
acurite-remote-monitoring....](https://www.acurite.com/access-my-acurite-
remote-monitoring.html)

I’ve also had an Acurite display with some segments of digits that looked
funky depnending on viewing angle. It was usable but kind of bugged me. I
contacted them and they RMAd it quickly and easily for me (they just sent a
new unit). For this reason, their easy availability on Amazon, the reliability
and battery life I’ve had with half a dozen of their sensors deployed in and
outdoors, I’ll keep buying them when I need this type of thing in the future.
They don’t ever lock up or need fiddling with, so they’re kind of boring in
that they just keep working until the batteries go flat. The widespread open
source support is also certainly nice :)

~~~
tga
Thanks, that's encouraging! I was worried they might not last that long,
especially at low temperatures.

I am using a Sonoff RF Bridge[0] to talk to 433MHz sensors. It is also
supported by Tasmota[1].

[0] [https://www.itead.cc/sonoff-rf-
bridge-433.html](https://www.itead.cc/sonoff-rf-bridge-433.html) [1]
[https://github.com/arendst/Sonoff-Tasmota/wiki/Sonoff-RF-
Bri...](https://github.com/arendst/Sonoff-Tasmota/wiki/Sonoff-RF-Bridge-433)

------
rootusrootus
I'm sure it's just a coincidence, but Amazon just bumped the price of that
sensor up by almost $40. Perhaps that is a proxy for how popular this article
is and how quickly Amazon notices the trend.

------
rubicon33
Honest question - Why would one want to monitor CO₂ in their office?

~~~
pcr0
Elevated CO2 levels have a noticeable impact on human cognitive ability.
Indoor environments obviously have higher CO2 levels vs outdoor, but certain
offices may have worse than typical indoor levels due to poor ventilation.

[https://thinkprogress.org/exclusive-elevated-co2-levels-
dire...](https://thinkprogress.org/exclusive-elevated-co2-levels-directly-
affect-human-cognition-new-harvard-study-shows-2748e7378941/)

~~~
rubicon33
Interesting, I had no idea. Do you think it's worth getting a CO2 monitor for
a home office? I don't usually have the windows open since it's cold out. Is
one person enough to elevate a small 10x10 office to cognitive impairing
levels?

~~~
Shank
It’s a small investment and probably worth it if you already suspect bad
ventilation. Within seconds of plugging a CO2 monitor into my bedroom outlet,
the monitor was registering 1200ppm — and that was without any humans in it
prior.

------
gregmac
Do the huge corresponding drops in CO2 and temperature at 11pm and 9am mean
that the "solution" was to open a window or door for ~15 minutes a couple
times a day?

Seems like a simple solution, other than there's a good half-hour of sub-17
degree temperatures right at the start of the workday, which isn't exactly a
great motivator to start working. Unless you are skilled at typing with winter
gloves on, I guess.

------
ksec
Well $80 dollar is affordable but certainly isn't low cost to me. Why are all
Co2 Monitor cost so much?

And on the subject, do we have O2 level monitor as well?

------
thismyusername
What do you guys think about ozone? I know its banned in California from what
I've heard. But I hear it kills a lot of bad compounds like mold. I could be
wrong though, would love to hear you guys opinion on it.

------
tandav
In almost every office I was there was a poor ventilation. I have extremely
high co2 ppm in my university labs. I try to always open windows where it
possible.

------
zokier
> we were now able to optimize HVAC settings in our office (Well, we mainly
> complained to our facility management).

Time to go shop some plants?

~~~
sannee
A random google link says that you would need hundreds of plants per person to
get sufficient oxygen production [1].

And during night, the plants would just produce CO2, which would presumably
get accumulated, making the whole situation worse.

[1] - [https://io9.gizmodo.com/5955071/how-many-plants-would-you-
ne...](https://io9.gizmodo.com/5955071/how-many-plants-would-you-need-to-
generate-oxygen-for-yourself-in-an-airlock)

~~~
ThePadawan
Another random google link says it could be as little as four shoulder-height
areca palms: [http://www.secrets-of-longevity-in-humans.com/oxygen-
produci...](http://www.secrets-of-longevity-in-humans.com/oxygen-producing-
plants.html)

------
kayoone
i am looking for something similar but for particulate matter instead of co2
like PM2.5. I am also looking for a solution that would work mobile, eg. on a
bike. Any help greatly appreciated!

~~~
stroebjo
There is a project in Germany which monitors particulate matter. They provide
a guide how to build a sensor using a SDS011 and a ESP8266:
[http://luftdaten.info/en/construction-
manual/](http://luftdaten.info/en/construction-manual/)

Not sure if/how this would work mobile, though.

