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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorborpin
    • CommentTimeNov 25th 2019
    I started measuring and recording CO2 levels recently using a number of different MHZ devices.

    Whilst they are not all consistent for various reasons, what I have noticed is that the CO2 readings seem to rise when the room is heated (electric heater / hairdryer) and when the humidity rises.

    Is there a scientific explanation for this?


    • CommentAuthorjfb
    • CommentTimeNov 25th 2019
    I am afraid I cant answer your question but I am interested in which sensors you have. Do you have a link to the MHZ devices you have?
    • CommentAuthorborpin
    • CommentTimeNov 25th 2019 edited
    From AliExpress;

    MHZ19B https://www.aliexpress.com/item/32371956420.html - remember to specify the sensitivity
    MHZ16 https://www.aliexpress.com/item/32606345110.html - I use this inside my MVHR unit

    https://www.aliexpress.com/item/32529101036.html - ESP8266 board for hooking them up to.


    https://eu.banggood.com/Wholesale-Warehouse-2pcs-75-x-54-x-27mm-DIY-Plastic-Project-Housing-Electronic-Junction-Case-Power-Supply-Box-wp-Eu-1063302.html?akmClientCountry=GB&rmmds=myorder - Case

    Easy enough to setup. I've used both Tasmota and ESPHome plus a bit of Node-red. Currently happier with Tasmota as the WiFi seems to be more stable.

    I am happier with the 0-5000ppm versions than the 0-2000ppm sensor. The latter one seems to find it hard to get the baseline (about 400ppm) right.
    • CommentAuthortony
    • CommentTimeNov 25th 2019
    Proxy CO2 detectors are cheap, real CO2 detectors expensive.
    • CommentAuthorborpin
    • CommentTimeNov 25th 2019 edited
    Posted By: tonyProxy CO2 detectors are cheap, real CO2 detectors expensive.

    for the price these are pretty good. I feel the readings are where I'd expect them to be.
    • CommentAuthorLF
    • CommentTimeNov 25th 2019
    I was going to ask about temperature compensation but top links show it is included.
    How big are the spikes ?

    Unit states +/- 50 ppm accuracy
    Is the voltage supply to it stable ?

    Could it be MV runs harder and it is dragging slugs of laden gas from from somewhere or a dead leg in the ducting system that starts getting emptied or something ?

    CO2 will be released from water as temperature is increased

    Good luck
    • CommentAuthortony
    • CommentTimeNov 25th 2019
    Don’t breathe either 🙂
    • CommentAuthorborpin
    • CommentTimeNov 25th 2019
    Posted By: LFCO2 will be released from water as temperature is increased
    Ah that could be it. It isn't massive, it is just noticeable - Chemistry was never my strong point :bigsmile:

    The increase is seen mostly in the bedroom sensor but doesn't really translate through to the MVHR unit.

    It would also explain why the CO2 level in the MVHR never drops to background levels as the HR bit will be heating the air and as I have already noted the RH of that air never goes below 75%.

    I'll know more when the bypass goes on in the summer!
    • CommentAuthorborpin
    • CommentTimeNov 25th 2019
    Posted By: tonyDon’t breathe either
    Noticeable that I can identify when the rooms are occupied as the CO2 rises (unsurprisingly!).
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