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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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General: Health issues with passive houses?

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      CommentAuthorSteamyTea
    • CommentTimeOct 9th 2016 edited
     
    Posted By: fostertomWow, I thought worldwide atmospheric CO2 had only just peaked thro 400.
    The growing season is over, so tends to be rising until the spring.
    http://www.esrl.noaa.gov/gmd/ccgg/trends/weekly.html

    I am intrigued as to why the readings are so high in an unused room. Could one of you (Ed or CX) put on in an outdoor building (shed or garage) and see what the readings are.
    • CommentAuthorEd Davies
    • CommentTimeOct 9th 2016 edited
     
    Though COâ‚‚ is well-mixed through the atmosphere on a period of a few years it varies quite widely from place to place and with time of year and on shorter timescales. Even on the top of Mauna Loa they have to do a fair amount of averaging to get a clean signal and some days are rejected from the data as they're too variable.

    I am a bit surprised that it's so high here as we're at (well, just passed) the global low-point for the year at the end of the northern hemisphere growing season so you'd expect NH concentrations to be comparatively low to bring the global average down. However, looking at charts of the world COâ‚‚ distribution it seems to be right. This is something I want to find out more about but suspect it's because COâ‚‚ is produced mostly on the northern hemisphere land but absorbed by the southern hemisphere ocean. Not sure about that, though.
    • CommentAuthorEd Davies
    • CommentTimeOct 9th 2016 edited
     
    Posted By: SteamyTeaCould one of you (Ed or CX) put on in an outdoor building (shed or garage) and see what the readings are.
    Just put it in the shed to try that while I'm out today but the WiFi doesn't seem to reach which is a pity but not too surprising with two heavy stone walls in between. Might try something a bit more complicated later but have other things to do today.

    These are the toys, by the way. Black box: USB power bank; grey box: USB hub to draw enough power that the power bank stays switched on; white box: COâ‚‚ monitor.
      dsc02066-small.jpg
    • CommentAuthorCX23882
    • CommentTimeOct 9th 2016 edited
     
    My wi-fi range doesn't quite reach the garage, so it'll be a couple of days before I can rig up another access point.

    I left it in the bedroom last night - door open, 1 occupant, window trickle vent open (with Drimaster PIV unit in the hallway ceiling):
    - before going to bed 780ppm
    - 30 minutes after going to bed, it quickly climbed to 1100ppm
    - throughout the night, fluctuating between 1100 and 1300
    - quick fall off to 900ppm within 15 minutes of getting up
    - left the house for 2 hours, and bedroom levels slowly dropped to around 550ppm
    - changed the bedding in the bedroom - quickly rose to 1000ppm within 30 minutes of being in there
    - moved it to the utility room, which I haven't been in, and got 650ppm.

    As an experiment, I've hung it out of a ground floor, road-facing window. CO2 settled at around 500ppm.
  5.  
    All - Calibration, Calibration, Calibration. How do you know your unit is accurate - have you sent it off to a NAMAS accredited cal lab? Have you a cal cert?

    Just pointing this out.

    I work in the pharmaceutucal industry and it is ferocious for insisting that measuring devices are properly accurate and calibrated. If they aren't, you really are flailing around in the dark... IMHO its always a good idea to distrust readings from instruments until you have build up a good set of data. Cheap stuff off Ebay can be horribly wrong....
    •  
      CommentAuthordjh
    • CommentTimeOct 9th 2016
     
    Posted By: dimengineerAll - Calibration, Calibration, Calibration. How do you know your unit is accurate

    Hire a calibrated meter for a week (about £60 IIRC) and use that to [approximately] calibrate your own.
    • CommentAuthorEd Davies
    • CommentTimeOct 9th 2016 edited
     
    Yes, calibration is worth thinking about - one reason I shared my numbers was to see if they were plausible compared with anybody else's. However, high levels of absolute accuracy really aren't needed for tuning and experimenting around a house - so long as the averaged figures are reasonably stable and consistent (not too affected by temperature, humidity, voltage or whatever) and in the right general ball park that's good enough.
    • CommentAuthortony
    • CommentTimeOct 9th 2016
     
    I am wondering if you are measuring things with adsorption at the same wavelengths as CO2 which would include a lot of organic compounds.

    How does the meter measure, is it an optical device?
    • CommentAuthorRobL
    • CommentTimeOct 9th 2016
     
    Most CO2 meters for home use have ABC - Automatic Background Calibration. That is, over a period of a week or so, they find their lowest reading and assume that it actually represents 400ppm. The actual readings are all offset, taking the lowest measurement as a 1 point calibraton.
    The assumption for most CO2 sensors is that over a few days they will sometimes be left in an unoccupied room, and so get a reasonable background reading.
    If this is the type of calibration, then it can't give a useful background level of CO2, as it will always give around 400ppm as the answer.
    We have a CO2 meter too - the numbers I see here seem ok. Ours normally says 500-1100ppm, easily over 1000ppm if breathing on the unit itself. By 2000ppm air feels "stuffy" to me, YMMV.
    • CommentAuthorEd Davies
    • CommentTimeOct 9th 2016
     
    “Most CO2 meters for home use have ABC…”

    Yep, but that's a selling point of these sensors; they don't need that background low level.

    http://shop.vair-monitor.com/index.php?rt=product/product&product_id=130
    http://www.figaro.co.jp/en/product/feature/cdm7160.html

    “We have a CO2 meter too - the numbers I see here seem ok.”

    Ta, good to know.
  11.  
    Posted By: RobLMost CO2 meters for home use have ABC - Automatic Background Calibration.
    Yup mine does, took me a while to realise it had never experienced a proper outside level and had crept big time. I had to leave it outside hooked up for a week to get it back to normal. Good for "it's gone up 1000ppm" not for "Oh look it's 550, so it must be the local power stn or the approaching Ice Age"
    • CommentAuthorborpin
    • CommentTimeOct 21st 2016
     
    I have just got my sensor (went missing as delivery address country was down as Ukraine but he happily sent another out) and surprised how high the indoor values were (6-700) but reading this thread, that seems fairly normal. Checked outside values and about 460 which is reasonable. calibration may be an idea but it is relative values you are most interested in so a variation of 10% is acceptable IMHO.

    Going to turn up the MVHR though and perhaps actually check the air flows properly. Next I need to automate increasing the MVHR wrt CO2 :bigsmile:
    • CommentAuthorjfb
    • CommentTimeNov 15th 2016
     
    question regarding these CO2 monitors: how do you access the CO2 readings via wifi? I mean is there a bit of software it comes with or you download? I'm presuming it doesn't have the reading on the box itself?

    cheers
    • CommentAuthorEd Davies
    • CommentTimeNov 15th 2016
     
    It's more of a push rather than pull thing: the COâ‚‚ monitor can send the readings to your computer in various ways. In normal operation the monitor is switched off most of the time to save power and isn't even signed on to the router so you can't access it, not even ping it. It just wakes up for a second or two when a reading needs to be taken and sent.

    To configure it you plug it into a USB port on your computer where it appears as a serial port. There's a Chromium app which does the setting which works well (when you chose the right one [¹]).

    The main protocols it can use to push the readings are making an HTTP request with the values in the URL (usually as query parameters) or via the MQTT prototcol [²]. There are tabs in the configuration app to set up well known public “cloud” services for this or you can point it at your own computer's web or MQTT server.

    [¹] http://forum.vair-monitor.com/showthread.php?tid=1 :shamed:

    [²] https://en.wikipedia.org/wiki/MQTT
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 16th 2016
     
    I was over at our old mate JSH's place today. He has a CO2 meter sitting in his livingroom.
    Was reading 418ppm when we went to look at it.
    He made the unit himself.
    • CommentAuthorGotanewlife
    • CommentTimeNov 16th 2016 edited
     
    Posted By: SteamyTeaHe made the unit himself.
    Obviously and probably a little helicopter to take the unit around the house automatically and log all the data :shamed:
    • CommentAuthorjfb
    • CommentTimeNov 17th 2016
     
    thanks - i wrote to the developer as well as he seems to have discontinued the vAir model which has a display of current CO2 levels (which I would quite like) and he mentioned that he had been thinking of adding a display to the v3 monitor - 'WOuld this be better for you?'. Seems helpful!
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 17th 2016
     
    Posted By: Gotanewlifea little helicopter
    I did spy a drone too :wink:
    • CommentAuthorborpin
    • CommentTimeNov 19th 2016
     
    Posted By: SteamyTeaI was over at our old mate JSH's place today. He has a CO2 meter sitting in his livingroom. Was reading 418ppm when we went to look at it. He made the unit himself.
    I got one of the sensors he bought from him a while ago but never used it.

    However, those units need calibrating regularly (one of the reasons I never used it) and that level suggest it needs calibrating as it is below the normal background levels outside. I have my sensor outside now and it is reading 450 which is (I gather) about right so unless JSH has managed to develop a CO2 capture device....
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 19th 2016
     
    No idea, just looked at what it was showing in the room.

    I wonder if a lime plaster, which can absorb CO2 in some situations, lowers internal levels.
    Just a thought that, I know very little about chemistry and want to know even less.

    “All science is either physics or stamp collecting.” Rutherford
    • CommentAuthortony
    • CommentTimeNov 20th 2016
     
    Yes, lime does absorb CO2 but so slowly that in a ventilated house there will be no appreciable depletion of the levels.
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 20th 2016
     
    Yes, that was my feeling.
    • CommentAuthorgyrogear
    • CommentTimeNov 20th 2016
     
    Lager absorbs lime, though...

    gg

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