Hey,
I´m moving into a new home that is equipped with a central ventilation system and I am going to control it via HA. Goal is to set values for Humidity and CO2. At first I thought about the MH-Z1X ESP route but now I´ve just discovered pretty cheap ready to use units on Ali.
I find it somehow strange that these devices are cheaper than a DIY CO2 module and I´d guess that they are not that accurate but as long as they are +/-100 ppm I´m fine with it.
Any experience? Maybe someone already verified the accuracy of those things.
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The world of sensors and the quality of the data they provide is a real wild west! I’ve spend too much time and money trying to ‘get a good solution’ in many sensor domains, and I am pretty sure I continue to be far from a solution.
That said, at my current state (read that as drawer full of devices).
For CO2, I am using the Aranet4 bluetooth units, link below. They are pricey, but on my rant, they defend their solutions with at least some research.
For temperature and humidity, I have stayed in the ‘low cost zone’ and have found that Bluetooth Low Energy devices that report ‘often’ seem to be the best route. Example device below.
Among the challenges is finding product that you can still buy, the changes in the availability of these low cost devices is a really challenge. If you find something that ‘works’, quickly buy a number of them to allow your project to run for a while. This is often a problem. I have some very good devices, that are no longer sold.
So my input based on my experience:
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Companies that will defend their solutions with some effort in the research front. This comment is ‘tongue and cheek’, however perhaps some strong reality… when you ‘take the cover off’ all these devices and find the same sensor, you have to question your cost vs. quality decisions soooooo much! However, so far, what I am using, I continue to think I have made good choices.
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Ease of getting the data from the sensor in a open aka ‘hackable’ way. Bluetooth so far is the winner here.
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Device readings update rate. This is a real ‘black box’ for many sensors. So far again, many Bluetooth Low energy devices seems to come out on top here.
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Battery life. From my experience, devices that are not ‘plugged into the wall’. Bluetooth devices win, because they last a long time, use low cost and powerful batteries and do not emphasize lasting for say 50 years vs. sending data at ‘useful’ intervals (a zigbee problem for home automation projects)
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My work, that continues to work for 2 years…however there are a number of BLE sensor collection projects that as well seem to be working very well:
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From another pov… the idea behind CO2 sensors is to protect you against…well … you guessed it. Connectivity to any (!) system should be sub to that. My main question (living in France) is… which of the dozens of offerings is actually working as designed. I bought 2, one triggered for whatever reason multiple times and had to throw it away…the other one did not trigger so far…but that raises a question : is it actually doing something?? I second the "wild west’ comment above and before all, regardless of where you want to connect it to, it should protect you … no bother discussing after you died 
It might take some effort to die from a high level of CO2. @vingerha are you confusing CO and CO2? Different problems.
Indeed…meant CO… so applicable comment but not in this topic
@daKazze, the following may answer your question? The quality of the CO2 “guestimations” seems very poor: Notes on Tuya Air Quality Sensors (Electronics, Home Automation) — Kaspars Dambis
I know this post is pretty old, but for anyone coming here with the same question, CO2 sensors MUST have a NDIR sensor inside for an accurate measure, any other CO2 sensors are just crap estimations that are basically useless
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