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Measuring RH and CO2


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I'm resuming the design work on my mvhr and want to get a sense as to the current situation with RH and CO2 in our home. Ivev renovated extensively and we are pretty well air tight and we are having some condensation issues in a few places so keen to get a baseline before i do any work. Are there any suggestions for meters to measure these? Looking for plug and play ideally. 

Edited by MarkyP
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39 minutes ago, SteamyTea said:

probably because it does not have a real CO2 sensor, but one that measures H and then makes assumptions.

How does that assumption work?  We can have a spell of really wet weather and the RH goes up. How does that mean the CO2 level also goes up?

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On 20/12/2019 at 10:15, joth said:

Looks like the MH-Z19 is popular with  Home Assistant users.  £20 from amazon or half that from AliExpress

https://www.open-homeautomation.com/2016/08/24/monitor-co2-levels-in-your-house/

https://esphome.io/components/sensor/mhz19.html

 

 

 

Well that turned out to be a fun Sunday project. I hooked the MH-Z19 up to an ESP2866 (D1 mini) just about within my soldering ability, flashed ESPHome which has a bundled driver for this sensor and the readings appeared in Home Assistant first time. £20 not including the machine that's running HA.

As an aside, I did a clean install of home assistant too, using the Hassio docker distribution this time, and goodness it's come along a long way even since May when it looks like I last tried it. 

 

 

 

Screenshot_20200203-073709.png

IMG_20200202_122207.jpg

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30 minutes ago, joth said:

Well that turned out to be a fun Sunday project. I hooked the MH-Z19 up to an ESP2866 (D1 mini) just about within my soldering ability, flashed ESPHome which has a bundled driver for this sensor and the readings appeared in Home Assistant first time. £20 not including the machine that's running HA.

As an aside, I did a clean install of home assistant too, using the Hassio docker distribution this time, and goodness it's come along a long way even since May when it looks like I last tried it. 


Its soooo frustrating being a Luddite..... I would love a working Co2 monitor and recorder but both the above information and the links to the hardware just leave me completely bamboozled why you just can’t buy a semi decent one that is plug and play for sensible money is very frustrating.  Ok rant over. @joth Well done mate, your like an alchemist in my eyes. 

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Well I am a Luddite so fir my conservatory I bought this on Ebay for a few quid ( a damp soggy feb day in Devon hence the high humidity). I was wanting a Co2 monitor to see how effective the MVHR was but convinced by others that RH was a good indicator of Co2. 
 

I have always thought that running the MVHR 24/7 was not needed (especially in summer when doors and windows are open). I have a humidity stat that I have yet to connect to the MVHR to kick the unit to boost after baths/shower/cooking, I am now thinking of installing a second one to switch the MVHR on when the RH and associated Co2 level get above a threshold that requires the house to be ventilated.

65476FBE-CAD3-42AF-BA7D-490B7F6728B4.jpeg

Edited by joe90
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3000 ppmv, ouch!

 

I've said it before on here but I'm a bit sceptical about those MH-Z19s as they calibrate by assuming that the CO₂ will go down to 400 ppmv at regular intervals. I'm not sure that assumption is sound. Here's the CO₂ level in my bedroom since the beginning of November. I was away for a long weekend at the beginning of that month and the CO₂ did get down to about 410 ppmv then but hasn't really done so very often or for long since.

 

You can turn off that calibration (the HA software referenced above does that) but then you need to take it outside once in a while to calibrate it. I'm not sure how long a while is OK and what effect temperature has on that. Assuming 400 ppmv as the baseline is not something which is likely to be valid long term, either.

 

My data was measured with a vAir monitor containing a CDM7160 sensor which, AIUI, is similar in principle to the MH-Z19 but has a separate internal path through a calibration chamber to compare against.

co2.png

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I have temp and humidity sensors and I take on board what folk say about Co2 following RH but I live so close to the sea on the west coast of Scotland where for the last two months its  rained nearly EVERY bloody day...... RH is always high.... and I just want to be able to clearly record and monitor Co2 as I am trying various different approaches to ventilation in about 4 different buildings. I just find it frustrating that it’s not easy...... unless your an computer and engineering alchemist!

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Our experience is that CO2 doesn't track RH at all well in this house.  It did in our old house, but that was less well ventilated and often had much higher CO2 levels, in particular.  External RH variation seems to dominate the internal RH here,  whereas at our old house I think that the apparent correlation between RH and CO2 concentration may have been because both were largely driven by occupant expired air.

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When I looked at @DamonHD's data it matched well. 

It was s school though.

I am pretty sure that there is a seasonal variation in CO2. This is because the major landmass is in the northern hemisphere, so goes down during the growing season.

https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide

But only seems to be about 5ppm, so probably less that the cheap sensors accuracy.

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6 hours ago, Ed Davies said:

3000 ppmv, ouch!

 

I've said it before on here but I'm a bit sceptical about those MH-Z19s as they calibrate by assuming that the CO₂ will go down to 400 ppmv at regular intervals. I'm not sure that assumption is sound. Here's the CO₂ level in my bedroom since the beginning of November. I was away for a long weekend at the beginning of that month and the CO₂ did get down to about 410 ppmv then but hasn't really done so very often or for long since.

 

You can turn off that calibration (the HA software referenced above does that) but then you need to take it outside once in a while to calibrate it. I'm not sure how long a while is OK and what effect temperature has on that. Assuming 400 ppmv as the baseline is not something which is likely to be valid long term, either.

 

 

Quite. I do indeed have that auto-calibration disabled and so also pretty skeptical about the absolute figures on it. I'll try leaving it for a few days and see.

https://www.circuits.dk/testing-mh-z19-ndir-co2-sensor-module/ suggests it does include a reference gas chamber (nitrogen) but knowing quality control on these things it could be quite hit and miss anyway.

For data logging it's still useful to see variation through the day and from one day to the next even if the absolute numbers aren't correct, and certainly could be enough for triggering an MVHR boost.

 

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