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    • CommentAuthorRobL
    • CommentTimeMar 30th 2017
     
    You might be able to add on a different CO2 sensor - how about this one (digikey link, other suppliers are available):

    https://www.digikey.co.uk/products/en/sensors-transducers/gas-sensors/530?k=co2+sensor&k=&pkeyword=co2+sensor&pv71=810&pv71=944&FV=fff4001e%2Cfff8028f&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

    £123, 0-10v linear output over 0-2000ppm CO2, 18-36v supply. It looks compatible with our vent-axia sentinel plus so far as I can see.
    • CommentAuthorlineweight
    • CommentTimeMar 30th 2017 edited
     
    Posted By: RobLYou might be able to add on a different CO2 sensor - how about this one (digikey link, other suppliers are available):

    https://www.digikey.co.uk/products/en/sensors-transducers/gas-sensors/530?k=co2+sensor&k=&pkeyword=co2+sensor&pv71=810&pv71=944&FV=fff4001e%2Cfff8028f&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25" rel="nofollow" >https://www.digikey.co.uk/products/en/sensors-transducers/gas-sensors/530?k=co2+sensor&k=&pkeyword=co2+sensor&pv71=810&pv71=944&FV=fff4001e%2Cfff8028f&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

    £123, 0-10v linear output over 0-2000ppm CO2, 18-36v supply. It looks compatible with our vent-axia sentinel plus so far as I can see.


    Thanks...this may be going a bit beyond my technical know-how though.

    Unless you can suggest some reasonably accessible reading that would help me understand how this would work.
    •  
      CommentAuthordjh
    • CommentTimeMar 30th 2017
     
    Posted By: lineweightIs your Brink unit a whole house / ducted system?

    Yes, it's a Renovent Excellent 300. I don't know how big your flat is but I'd be wary of running any unit too close to its capacity. The noise and power requirements both go up dramatically.

    Conventional wisdom says a two bedroom flat needs at least three supply points and two extracts, so I'll be interested to follow the story. (2 bedrooms & a living room supply, bathroom & kitchen extract). I haven't seen anything yet that convinces me anything other that a mass airflow achieves sufficient ventilation. I don't have any personal experience of any of the 'ductless' systems, nor have I seen any independent studies of in situ CO2 levels etc in dwellings.
    • CommentAuthorlineweight
    • CommentTimeMar 30th 2017
     
    I've got myself a CO2 monitor and am doing some measurements (pre-MVHR) which I'll use when I make my decision as to what exactly to install.

    Will post a summary of what I gather from those measurements here in a bit when I've collected a bit more.

    An early observation is that CO2 levels spike and vary much more obviously than humidity levels, at least here in my flat.
    •  
      CommentAuthordjh
    • CommentTimeMar 30th 2017
     
    Posted By: lineweightAn early observation is that CO2 levels spike and vary much more obviously than humidity levels, at least here in my flat.

    i think I agree with that but it occurs to me to ask what the response time of the two sensors is? I think humidity sensors tend to be fairly slow.
    • CommentAuthorlineweight
    • CommentTimeMar 30th 2017 edited
     
    Posted By: djh
    Posted By: lineweightAn early observation is that CO2 levels spike and vary much more obviously than humidity levels, at least here in my flat.

    i think I agree with that but it occurs to me to ask what the response time of the two sensors is? I think humidity sensors tend to be fairly slow.


    I don't know and not sure if that info is available. I am using one of these:

    https://www.netatmo.com/product/weather/weatherstation/specifications

    I do have another humidity sensor that i can check it against though.

    In any case what I'm partly interested in is: when the air feels stuffy does it correlate with raised humidity or raised CO2 levels? And so far it seems to correlate much more obviously with CO2 levels. So I think I'd rather a system that was looking at CO2 levels, when it was deciding whether to ventilate, than one that was only looking at humidity.
  1.  
    Some observations on what happens overnight in an approx 8.5 m2 bedroom with airtight construction, window closed with no trickle vents.

    In each case the CO2 levels are around the baseline of 400-500 at the beginning of the night (ie. before anyone goes to bed). I've indicated the peak CO2 levels during the night, as well as the difference in RH, comparing beginning of the night with its highest level during the night.

    The door has a brush seal around 3 sides but a small gap underneath. So when the door is closed, there's an approx. 20mm x 800mm gap underneath.

    In all cases, no other windows open in other parts of the flat during the night.

    Night 1: 2 people, door closed
    Peak CO2 1433ppm
    RH 51 / 61

    Night 2: 2 people, door closed
    Peak CO2 1705ppm
    RH 55 / 58

    Night 3: 1 person, door closed
    Peak CO2 1314ppm
    RH 55 / 57

    Night 4: 1 person, door closed
    Peak CO2 1610ppm
    RH 58 / 60

    Night 5: 1 person, door open 400mm throughout
    Peak CO2 741ppm
    RH 57 / 57

    Night 6: 2 people, door open 400mm throughout
    Peak CO2 875ppm
    RH 55 / 57

    Night 7: 2 people, door open 50mm throughout
    Peak CO2 1069
    RH 55 / 55


    What I take away from this is:
    - having the door open has quite a significant effect on CO2 levels
    - just having the door open, so the air in the room can exchange with the air in the rest if the flat, seems to control CO2 quite satisfactorily
    - suggests that having a "cascade" system where the bedroom door is closed but a fan moves air in/out of the bedroom from the general volume of the flat during the night ought to work fine - ie. not necessary to have the room independently ventilated to the outside air.
    - aside from what seems to be an anomalous result on night 1, the RH doesn't really change much at all
    - any sensor-activated fan in this room ought to work from a CO2 sensor rather than a humidity sensor.

    I'm now going to spend a few days watching what happens in a living/kitchen area - with the sensor placed at the opposite end of the space from where I'd put a single-space MVHR unit. I'll open/close a window at that MVHR location (but nowhere else) to try and simulate the introduction of fresh air at that point without anything actively circulating it.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 3rd 2017 edited
     
    Valuable.

    Posted By: lineweight- just having the door open, so the air in the room can exchange with the air in the rest if the flat, seems to control CO2 quite satisfactorily
    So why would we go to the elaboration of
    Posted By: lineweight- suggests that having a "cascade" system where the bedroom door is closed but a fan moves air in/out of the bedroom from the general volume of the flat during the night ought to work fine
    The latter allows the door to be closed, for privacy - but why not a non-vision hole in the wall, serving same purpose (no fan reqd)?
    • CommentAuthorgravelld
    • CommentTimeApr 3rd 2017
     
    Thanks for the ref to that new product @lineweight
  2.  
    Posted By: fostertomThe latter allows the door to be closed, for privacy - but why not a non-vision hole in the wall, serving same purpose (no fan reqd)?


    The "hole" would need to be soundproofed to the same level that can be achieved with an inter-room transfer fan.

    I'd suggest this for privacy reasons in certain circumstances!

    That might be easily achievable - I'm not sure.

    In my particular case, the arrangement I'm leaning towards might also use that transfer fan as a means of circulating air around the whole flat generally. How important I judge that to be might depend on the results I get from my next set of measurements.
  3.  
    Posted By: gravelldThanks for the ref to that new product @lineweight


    Maybe consider adding the Xpelair Muro to your list too.

    It appears to have a CO2 sensor as part of its controls - either integral to the unit or placed remotely.

    Around the £700 mark - but maximum flow rate of around 50m3 instead of around 100m3.

    Two of them would still be a fair bit cheaper than the Blumartin or Fresh_R as far as I can see.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 3rd 2017
     
    Posted By: lineweightThe "hole" would need to be soundproofed to the same level that can be achieved with an inter-room transfer fan
    That cd be done without including a fan.

    Posted By: lineweightHow important I judge that to be might depend on the results I get from my next set of measurements
    Looking forward to that.
    • CommentAuthorringi
    • CommentTimeApr 3rd 2017
     
    Sound proofing veneration holes is easy, there are lots of plans on the internet showing who to it for recording studios. (but you may then need fans, as all the designs make the air take a complex path with many bends.)

    But it still allows smoke to get past the door, so you can’t do it if you require fire doors for any reason.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 3rd 2017
     
    Posted By: ringiit still allows smoke to get past the door
    The right intumescent insert will block the hole solid - but like intumescent fire doors, only when flame or v hot air gets to it - until then the smoke is free to pass.
    •  
      CommentAuthordjh
    • CommentTimeApr 3rd 2017
     
    Posted By: ringiSound proofing veneration holes is easy

    Is that so the priest can't hear you, or so you can't hear him?
  4.  
  5.  
    ''Is that so the priest can't hear you, or so you can't hear him?''

    Thanks djh! I managed to hold back. I think it's an ecclesiastical auto-correct!
    •  
      CommentAuthorSteamyTea
    • CommentTimeApr 4th 2017
     
    Posted By: lineweightwhen the air feels stuffy does it correlate with raised humidity or raised CO2 levels?
    Our old mate Damon HD recorded the levels in a local school. When I looked at the data, there was a good correlation between RH and CO2 levels when the room was occupied.
    A school classroom is not a house though (30 kids in a box). So may only be valid for that situation.
    Correlation is not causation.
    • CommentAuthorgravelld
    • CommentTimeApr 4th 2017
     
    Posted By: lineweight
    Maybe consider adding the Xpelair Muro to your list too.
    Thanks, but that looks like a single room unit - I need a system for a house (unless I missed something detailing how multiple units can work together).
  6.  
    Posted By: gravelld
    Posted By: lineweight
    Maybe consider adding the Xpelair Muro to your list too.
    Thanks, but that looks like a single room unit - I need a system for a house (unless I missed something detailing how multiple units can work together).


    Well, I don't see why you couldn't use them in the same way that you might use the Fresh-R or Blumartin or Nexxt units - have more than one throughout the building, perhaps in conjunction with some cascade/inter-room ventilation. Obviously you'd need more of them, because of their lower capacity, and it may or may not make any sense according to the size and layout of the house.
    • CommentAuthorgravelld
    • CommentTimeApr 5th 2017
     
    I've wondered that, but without manufacturer support I'd be nervous spending still significant capital.

    For example, they'd have to be balanced right? I know some SRHRV are not...
    • CommentAuthorlineweight
    • CommentTimeApr 5th 2017 edited
     
    Posted By: gravelld
    For example, they'd have to be balanced right? I know some SRHRV are not...


    Can you expand on that?
    • CommentAuthorgravelld
    • CommentTimeApr 5th 2017
     
    Well if they over or under pressurise... what would that mean? Extra losses through the fabric?
  7.  
    Posted By: gravelldWell if they over or under pressurise... what would that mean? Extra losses through the fabric?


    I was meaning more, how do you know some are not balanced right?

    I don't see any particular reason to suspect the Muro one, say, of not being properly balanced, any more than, say the Blumartin or other systems that don't rely on ducting.
    • CommentAuthorgravelld
    • CommentTimeApr 5th 2017
     
    If you look in the archives I remember discussion of some of the VA units being slightly unbalanced.

    The units designed to work together I assumed were net balanced when set up, but maybe I'm wrong.

    Also you have crossflow to consider; these are in theory designed in by system designers for the ductless systems, but how to design it in for multiple SRHRV units? Again I assume there are no such designers for these units.
    • CommentAuthorlineweight
    • CommentTimeApr 5th 2017 edited
     
    In the Lunos system where the units work in sync to push/pull air alternately, obviously they need to know what each other are doing.

    But I'd have thought that if a SRHRV unit or a "ductless" unit (as far as I can see, they are essentially the same thing; it's just the capacity that is different) is set up properly balanced, then it shouldn't have any effect on the balancing of another unit elsewhere - they don't need to communicate with each other, they just have to both be balanced. But maybe it is more complex than that?

    Not sure exactly what crossflow would mean in the context of two ductless units... they don't work by actively moving air across the building but just rely on gas diffusion and general air movement through convection etc - as far as I can tell.
    •  
      CommentAuthordjh
    • CommentTimeApr 5th 2017
     
    I seem to remember that some SRHVR units have a greater outflow than inflow as a cheap way to avoid the need for a frost pre-heater or other technique to avoid freeze up in cold conditions. Maybe that is what gravelld is thinking of.
    • CommentAuthorgravelld
    • CommentTimeApr 6th 2017
     
    Yes, I think that's it. Different units may/will vary of course.
    • CommentAuthorlineweight
    • CommentTimeApr 12th 2017 edited
     
    Some more measurements.

    This time I am looking at an open plan living/kitchen/work area, about 4m x 7m so a volume of perhaps 70 m3, although it's slightly more complicated than that because an open stairwell rises into it from below.

    The table below lists measurements taken during periods when this space is occupied by one person (me!) mainly sedentary (I work from home). The two windows are approximately at opposite corners of the room. "Rear window" is near the stairwell and it pretty much at the position where I plan to install a MVHR unit. It's around 6m distant from where I'm generally sitting. "Front window" on the other hand is about 2m from where I'm sitting, and the sensor is placed about half way between me and this window (so about 1m away).

    I was interested to see the effect on CO2 levels of having either window open. Situations with both windows open are not really of interest because then it can be assumed there's a crossdraft. I wanted to see what effect having a window open has on CO2 levels, without any active circulation of air.

    "C" means closed, "O" means open, "full" = fully open, 200 = open with a 200mm wide gap, 50 = open with a 50mm wide gap.

    I've noted the values that the CO2 ppm ranges between in each situation.

    Observations:

    - clear difference between having no windows open and one window open fully. Although the CO2 levels are not that bad with everything closed, they are just edging over the undesirable 1000 level. Can probably assume it would get worse with more people in the room.
    - with the rear window fully open, even though it's 6 or 7m away from the sensor and there's no active cross ventilation, the levels are kept pretty close to what they'd be with no-one in the room.
    - decreasing the open area of that window does seem to have an impact. But even having it open just a little bit (50mm gap along the bottom and top - it's a centre pivot velux) seems to have a noticeable effect and keeps the levels below 1000ppm.
    - perhaps not surprisingly, because it's only 1m from the sensor, opening the front window just a little bit, is enough to keep the levels at pretty much what they'd be with no-one in the room
    - not included in table, but I've also been measuring humidity and it doesn't really do anything exciting, staying at a relatively low level regardless. This is similar to my observations in the bedroom.

    I've also been measuring whilst cooking has been going on. This produces much starker increases, in both CO2 and humidity. With all windows closed CO2 went up to 4600ppm on one occasion. However, I'm going to do some more measurements before posting these, because not all cooking sessions are the same, so I'm going to do some more controlled experiments now. Will post those results in due course.
      Screen Shot 2017-04-12 at 20.12.49.jpg
    • CommentAuthorlineweight
    • CommentTimeApr 23rd 2017 edited
     
    If anyone is interested here is what happens in the same room as described in my previous post, if I deliberately raise CO2 levels by turning the gas hobs in the kitchen on.

    In each case, I turned all the hobs on for 10 minutes, then turned them all off, and recorded what happened to the CO2 levels, as recorded at the sensor, on the other side of the room, over the following hours.

    The different lines represent different degrees to which I opened the window: fully closed, open just a very little bit (15mm gap), open a bit more (50mm gap) and open more again (200mm gap). All other windows in the room remained clsed throughout.

    With the window closed, you can see the levels take quite a while to level off. In fact, they don't reach what might be considered a "comfortable" level of under 1000ppm for at least 5 hours.

    Opening the window just a very small bit has a noticeable impact, both in terms of the peak it spikes at, and the time it takes to level off.

    Opening it by 50mm more has more of an effect.

    Opening it by 200mm reduces the spike to a negligible size.

    An inconsistency between the red and orange lines is that for the red one, I did the experiment and left the room overnight, whereas for the orange one, I returned to the room about an hour and a half afterwards, and this explains the bump in that line.

    NB all of these are with just one window open - no active air movement or cross-ventilation - with the window concerned being around 6m away from the sensor and on the other side of the room. To me, this seems to demonstrate that the CO2 will diffuse away quite quickly, as long as the internal air has a point of contact with the fresh air outside.
      Screen Shot 2017-04-23 at 16.20.29.jpg
   
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