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    • CommentAuthorGotanewlife
    • CommentTimeApr 23rd 2017 edited
     
    Really good info. Really. But now do it again with the window being opened in another room, preferably at the end of a corridor on the same floor, that would represent a FreshR type scenario.
    • CommentAuthorlineweight
    • CommentTimeApr 23rd 2017 edited
     
    Posted By: GotanewlifeReally good info. Really. But now do it again with the window being opened in another room, preferably at the end of a corridor on the same floor, that would represent a FreshR type scenario.

    The window I've been using to do these tests is exactly in the location where I'd put the unit. So for my particular case, it does represent that scenario.
  1.  
    OK but that is for one room, were you not hoping the unit would have an effect beyond that room. Obviously I started reading this thread half way through. Sorry.
    • CommentAuthorlineweight
    • CommentTimeApr 24th 2017
     
    Posted By: GotanewlifeOK but that is for one room, were you not hoping the unit would have an effect beyond that room. Obviously I started reading this thread half way through. Sorry.


    If you have a look back through the thread I think you'll find the answer to your question. Yes I am hoping the unit can have an effect throughout the whole flat. However, I live in a smallish 2 bed flat, not a 10 bed mansion so it seems feasible. The Fresh-R or Blumartin units seem able to turn over a sufficient quantity of air for that volume of space. There is of course the question of whether it will reach the points furthest from the unit, hence the tests described just above (which, ignoring the effect of bedroom doors, represent measurements taken at just about the furthest possible distance from the unit).

    A couple of pages back you'll see my tests of what happens in one of the bedroom looking at what goes on with the door open or shut. With the oor shut there is not enough air exchanged with the rest of the flat to keep the CO2 levels reasonably low. Therefore I'll likely be looking as some kind of cascade ventilation system where a standalone fan moves air in/out of the bedroom(s) from the hallway where the unit will be located.
    • CommentAuthorgravelld
    • CommentTimeApr 24th 2017
     
    Thanks for the write-ups @lineweight. Really interesting info.

    The stark thing for me though is that it isn't that controlled, and you cannot really derive what a Fresh-R type device might achieve because you're completely dependent of the vagaries of pressure - external (wind, aspect, all sorts of things) and internal (stack effect). And all varying over time periods of course.

    I don't understand how "There is of course the question of whether it will reach the points furthest from the unit, hence the tests described just above" - how these tests represent anything in that regard?
    • CommentAuthorlineweight
    • CommentTimeApr 24th 2017 edited
     
    I agree, I can't fully derive what a Fresh-R type device would achieve, because I would be dependent on what rate of air exchange its control system decides to provide given different CO2 concentrations and so on.

    Also, I don't know how to calculate what a window, open by X mm, is equivalent to, in terms of an in-wall unit providing a certain rate of air exchange.

    What I can however derive - I think - is that if I provide adequate access to fresh air at a certain position in my flat, then it does seem that in the largest room its benefits will reach the parts of that room which are furthest from the unit, without any additional forced air circulation.

    This is because my last set of measurements were taken with the sensor placed at the point which is furthest from where the unit would be. The unit would be where the window currently is - the window that I was opening to varying degrees in my tests.

    I agree there are lots of vagaries to do with wind and stack effect and so on, which would apply both during my tests and when a Fresh-R unit was installed. I'm unfortunately limited in what I can do about this. All I can say is that all my tests were done on days that weren't particularly windy. Also, the effect of opening the window is very clear in the results; the effect I feel is strong enough that it's not so marginal as to be overwhelmed by variations in conditions. I wouldn't claim to be able to prove that to you objectively though, with the results I have. I can say that when I repeat the tests at different times, the results are fairly consistent. The graphs shows the results of four tests I did when I left things undisturbed for several hours afterwards. There were other occasions where I did it and then opened other windows within an hour or so, because I didn't feel like sitting in a stuffy room. On those occasions the peak values, and the slope of the first part of the graph following them, were fairly similar to those seen in the full-duration tests.
    • CommentAuthorgravelld
    • CommentTimeApr 24th 2017
     
    Ok, I see, yes I agree with that. And I can also understand how you want to do some form of experimentation to begin to grok the situation.

    I think there are some rules of thumb out there how open windows relate to air permeability but I can't remember them and I'm not sure if they are of much use anyway.

    I wonder if anyone has built an air tight house, then installed ventilation which open to measure different levels of natural ventilation, while somehow not impeding natural ventilation, and perform these types of CO2, RH etc measurements? This isn't the same thing as just running MVHR at different levels, because the varying effects of natural pressure aren't being measured. It would have to be averaged over a time period of course to account for time based differences.
    • CommentAuthorlineweight
    • CommentTimeApr 24th 2017
     
    One thing that occurred to me was whether this kind of CO2 test could be an alternative way of testing airtightness. Where for whatever reason a blower test was impractical, or too expensive. You would somehow produce a certain level of CO2 and then measure its rate of decline.

    Probably too many variables to make it meaningful.

    In my case, the fact that opening a window just a crack produced a significant effect, makes me think that the airtightness I've achieved must be - with the help of some motivated reasoning - "fairly good".
    • CommentAuthorEd Davies
    • CommentTimeApr 24th 2017
     
    Posted By: lineweightAll I can say is that all my tests were done on days that weren't particularly windy.
    This and the rest of that paragraph are very useful to help understand how significant your tests were. Thanks.

    One thing that occurred to me was whether this kind of CO2 test could be an alternative way of testing airtightness. …

    Probably too many variables to make it meaningful.
    Yes, probably too many variable for an individual test. But monitoring a house over a long period to get its time-constants for temperature, humidity, CO₂, etc, is, I think, likely to be much more interesting. Sort of a long-term and more systematic version of:

    On those occasions the peak values, and the slope of the first part of the graph following them, were fairly similar to those seen in the full-duration tests.
    It frustrates me no end to see all these graphs people produce of temperature, etc, against time. That's interesting as a first look but not really helpful for understanding. Scatter plots and correlations of appropriate variables might be more illuminating though we see them so rarely that it's hard to say.
    • CommentAuthorlineweight
    • CommentTimeApr 24th 2017 edited
     
    Posted By: Ed DaviesIt frustrates me no end to see all these graphs people produce of temperature, etc, against time. That's interesting as a first look but not really helpful for understanding. Scatter plots and correlations of appropriate variables might be more illuminating though we see them so rarely that it's hard to say.


    Maybe that kind of data will become more easily obtainable with an increase in home automation systems.

    Doing my tests, the sensor records CO2 levels, but I have to manually record things like: how many people were in the room, when did I start/stop cooking, when did I open and close windows, etc etc. That's labour-intensive and prone to error/gaps. In a house where these things are recorded automatically with occupancy sensors and so on, the kind of scatter plot data you describe would be much easier to produce. I agree it would be much more interesting and informative.

    Of course you still have the problem that no two houses are really the same, and where they differ, it can be in a multitude of ways, so comparing between buildings would still be very tricky.
    • CommentAuthorlineweight
    • CommentTimeMay 5th 2017 edited
     
    Another unit dredged up in my ongoing researches

    https://www.airflow.com/Product-Detail/residential%5Fheat%5Frecover2/Duplexvent-Basic-Line/90000400/Duplexvent-UNO-DV40

    up to 150m3/hr but minimum appears to be 60m3/hr, much higher than the other units I've looked at. I want something which can ramp down to a lower rate than that I think.

    not entirely clear what it monitors... RH? CO2?
    • CommentAuthorGotanewlife
    • CommentTimeMay 5th 2017 edited
     
    Au contraire, it is entirely clear what it monitors - nothing!

    This is very expensive for what it is. Any standard compact MVHR can be plumbed into a cupboard without any pipes other than 2 stubs to outside. The one I have has reduced fan speed frost protection (but mine is adjustable for temp), mine has 3 speeds but mine isn't wireless. Neither can be controlled by an external sensor. Mine is quietish yours is very slightly quieter, notionally, but still too loud IMO to be left out on display as suggested by its mirror finish SS coating. In short, apart from the wireless gimmick the only thing you are getting for the extra £650 is a post heater. :devil::devil:

    DIY a std one into a cupboard on an outside wall, you'll get a better result niose wide, more controllability and save money! External pipes just finish in 90 ss bull nose vent things will be more effective, and internally you get to choose the best inlet and outlet positions rather than being fixed by the unit and you can have much larger vents.
    :smile::smile:

    I parallel wired this into my unit's boost switch input and it is extremely effective and dead cheap - (also for sale in UK)

    https://www.amazon.co.uk/gp/product/B00GNT1NJY/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=A2I0KD4PFXY56D

    There is a thread on it.
  2.  
    Gotanewlife

    I agree it seems expensive for what it is.

    I have already been looking at quite a few "standard" units as you suggest. For various reasons (other design changes since starting this thread) an in-wall unit might not actually make much sense for me after all, although I still intend to install with very minimal ducting.

    There are a few in the £600-800 ish price range which monitor RH but not CO2.

    I am keen on CO2 being part of the control setup.

    Some of these units have a boost switch input and - again as you suggest - I could wire a CO2 sensor into this.

    eg.either of these fit that bill

    https://brookvent.co.uk/heat-recovery-ventilation-systems/

    (and in contrast to Vent-Axia, Nuaire and the like, their technical help involves a knowledgable person you can get straight through to!)

    The only thing with that approach is that ideally, I'd like to be able to control the fan speed proportionally to the CO2 level (instead of an all-or-nothing approach).

    One that *appears* to fit that bill (but costing an extra £600) is this

    https://www.vent-axia.com/range/lo-carbon-sentinel-kinetic

    That would be using a 0-10v output CO2 sensor.



    The other thing I'm after, to sort of match what the Fresh-R, Blumartin etc can do, is a unit that I can choose to set the "trickle" rate as low as I want on. Many units won't let you set it lower than about 50 m3/hr it seems.

    Both of the units I've mentioned above allow setting it right down to nearly 0%.
    • CommentAuthorlineweight
    • CommentTimeMay 17th 2017 edited
     
    I have found this:

    https://www.heatraesadia.com/products/heating-and-ventilation/mechanical-ventilation-and-heat-recovery/advance-and-advance-plus.htm

    which is starting to look like my favourite. Unit is about £800. It has various add on sensors, including CO2, and what looks like a sensible and fairly comprehensive control system. SFP looks good. As far as I can make out the "trickle" rate can be set down to 25m3/hr - not quite as low as I'd like ideally but better than most others.

    The CO2 sensor is pricey at around £380. However, is compensated for by the low price of the unit itself. It seems like the lowest a CO2 sensor is going to cost, as a DIY-type arrangement, is around £100. Unlike the Vent Axia Sentinel mentioned above it doesn't look like this unit has DIY friendly control inputs. However, realistically, the time spent faffing around with semi-unofficial DIY arrangements has a price in itself.

    If I go for it I will report back.
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