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    •  
      CommentAuthordjh
    • CommentTimeMay 24th 2016
     
    A couple of weeks ago, I hired a CO2 monitor for a few days just to see what actually happens inside our house. The most interesting result I got is from our ensuite, which has an extract valve, and which has a single door opening to our bedroom that has a supply valve.

    You can see a single spike of humidity to 87% and of CO2 to 1020 ppm. That was when I took a shower with the door closed (the door frame has a slot to allow ventilation air past). You can see how fast the readings come back down as soon as I opened the door. My wife took a shower shortly afterwards but she leaves the door slightly open so there isn't another spike.

    CO2 climbs a bit overnight and then starts coming down after I get up - I don't use the ensuite in the morning. There's another blip when my wife gets up.
      ensuite.png
  1.  
    Would 1 person in a small room be enough to spike CO2 that much?
    •  
      CommentAuthordjh
    • CommentTimeMay 24th 2016
     
    Posted By: Simon StillWould 1 person in a small room be enough to spike CO2 that much?

    You got me! I had the Leicester football team and the elephants from Whipsnade in there with me. :boogie:

    The room is 2 m square and 2.4-3.2 m high.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 24th 2016
     
    Just randomly thinking here, but could the CO2 be coming out the hot water. Warmer water can hold more CO2 (though it turns it to acid), so as the water cools rapidly (it has a large surface area to volume ratio in a shower) some dissolved CO2 comes out.
    I may be talking out my rear end, or that may be the problem.

    Our old mate Damon HD did some research into this, I think the data is on his website.
    •  
      CommentAuthordjh
    • CommentTimeMay 24th 2016
     
    So some back of the envelope numbers.

    Background CO2 outdoors is apparently 380 ppm or so.
    Background CO2 in our house seems to be about 450 ppm.
    450 ppm = 810 mg/m³ I think.

    A person breathes out about 1 kg CO2 per day (which doesn't contribute to global warming since it is produced from plants that were eaten). Which is 694 mg/min.

    My shower seems to have taken 11 minutes in total (i.e. door was closed for that period) so the total CO2 exhaled is 7639 mg.

    The volume of the room is about 12 m³, so that's 637 mg/m³ of extra CO2
    810+637 = 1447 mg/m³ or 803 ppm

    So either the room is smaller or I was breathing heavily :cry: Or my arithmetic has gone astray.
    •  
      CommentAuthordjh
    • CommentTimeMay 24th 2016
     
    Posted By: SteamyTeaJust randomly thinking here, but could the CO2 be coming out the hot water. Warmer water can hold more CO2

    Well it can but it didn't - ten seconds before it sprayed out the shower head, it was cold water in the main.

    I may be talking out my rear end, or that may be the problem.

    Our old mate Damon HD did some research into this, I think the data is on his website.

    DHD did research on your rear end? :devil:
    • CommentAuthorEd Davies
    • CommentTimeMay 24th 2016 edited
     
    Posted By: SteamyTea: “Warmer water can hold more CO2”

    Are you sure? Normally gases come out of solution as water warms. One of the global warming feedbacks is considered to be increased atmospheric CO₂ as the sea water warms, isn't it?

    Playing with these equations [¹] in gnuplot shows a decreased solubility with increased temperature for CO₂ over the range 0 to 50 °C unless I've messed up.

    [1] https://en.wikipedia.org/wiki/Henry%27s_law#Temperature_dependence
  2.  
    You don't need to do any maths, CO2 sensors will spike with someone standing next to them and show similar readings to what you are getting. Your wife probably completely ignored the thing and you probably looked over at it because you were aware it was there and breathed in its direction a few times.....

    Sensor placement is crucial and avoiding putting them in direct line of folk breathing next to them. In a very small room you would need to be even more careful.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 24th 2016 edited
     
    Posted By: Ed DaviesAre you sure? Normally gases come out of solution as water warms.
    Your dead right, I realised as I was driving to work I had it the wrong way around.
    •  
      CommentAuthordjh
    • CommentTimeMay 24th 2016
     
    Posted By: willie.macleodCO2 sensors will spike with someone standing next to them and show similar readings to what you are getting.

    Indeed. That became obvious as soon as I turned the thing on. The ensuite was the third room I got to so I'd had a bit of practice.

    Your wife probably completely ignored the thing and you probably looked over at it because you were aware it was there and breathed in its direction a few times.....

    Sensor placement is crucial and avoiding putting them in direct line of folk breathing next to them. In a very small room you would need to be even more careful.

    Good advice. I'm fairly sure the data is realistic. It has a real-time display as well as logging so it was easy to see any induced spikes.
    •  
      CommentAuthorfostertom
    • CommentTimeMay 25th 2016
     
    Posted By: Ed DaviesAre you sure? Normally gases come out of solution as water warms
    But wouldn't warm water be a better solvent, and if prevented from off-gassing (enclosed in pipe) could be carrying more CO2 until released to fresh air?
    • CommentAuthorEd Davies
    • CommentTimeMay 25th 2016
     
    I don't think this is actually relevant to this thread but, no, my understanding is that warmer water does not dissolve most gasses better. It's not like it's having to break chemical bonds in order to dissolve them in the way it would getting solids off your plate when you're washing up. I don't know if this is the right way to think of it but perhaps it's that the warmer temperature helps drive the gasses out of solution.
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