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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.

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  1.  
    Posted By: WillInAberdeenSure this could be automated and then optimised.

    With perhaps a RH sensor and switch in series with a timer to prevent ventilation when you don't want it.
    • CommentAuthorEd Davies
    • CommentTimeMar 28th 2022
     
    This optimisation is very much the sort of thing I want to play with.

    When I said “humidity” earlier it was in reference to the desired temperature, i.e., separate from the IAQ aspect of humidity. For reasons which seem back to front to me, a given temperature seems to feel warmer if the air is dry. Personally, I'd expect humid air to feel warmer as there's less heat loss from the skin via evaporation but whatever.

    Anyway, I think part of the optimisation scheme is planning ahead for the building fabric humidity depending on the season and the forecast weather. If you know that next week you're going to have a hard time getting rid of water vapour efficiently then it makes sense this week to run the house at the lower end of the comfortable humidity range in order to dry out some buffer space. And vice-versa.

    Also, if the house is dried out then the humidity becomes higher there'll be a small release of heat from the associated condensation. Anybody remember the Dutch cat litter thread?
    •  
      CommentAuthordjh
    • CommentTimeMar 28th 2022 edited
     
    Posted By: Ed DaviesIt seems to me that the time you want to use “summer” bypass and/or more ventilation than is needed for IAQ is anytime the outside air temperature is in the direction you want to move the indoor temperature. I.e., when either:

    a) the indoor air is cooler than desired and the outdoor air is warmer than the indoor air currently is or

    b) the indoor air is warmer than desired and the outdoor air is cooler than the indoor air currently is.

    Am I missing something?
    I think that's true but practically speaking only case (b) matters and that's exactly what our summer bypass does. Case (a) never happens because it never gets cooler inside than outside. edit: just to clarify the last bit about case (a) I mean never at a time when you want it warmer inside. i.e. it only happens in summer.

    Case (b) is also the time when you might open some windows. In our case we have usable windows upstairs on the east and west walls and windows downstairs on those two walls plus a patio door on the south wall. So breeze and/or stack effect means we almost always get cross ventilation. All have got fly screens; we sometimes also open other doors and windows when there are few insects or dust.

    It'd be difficult to automate opening doors and windows, because apart from requiring significant power there are security concerns. We don't seem to have problems with humidity management - I don't take special actions to control it most of the time. I'm generally happy to let the MVHR just do its thing most of the time. In particular I don't touch it when we open or shut windows. It doesn't care.
    • CommentAuthorJonti
    • CommentTimeMar 29th 2022
     
    Ed,

    whilst I do not now I did live in a house with one for 18 months. My experience was that whilst the air quality was better than without it in a house with the windows shut it was not the same as airing. I also had the misfortune to live there during a two day power cut and with only the doors that could be opened in 32C heat it was not a pleasant experience.

    Just to be clear, I think the positives of a MVHR do outweigh the negatives but I would still want the option to open windows and feel a MVHR system should be developed to accommodate this.
    • CommentAuthorEd Davies
    • CommentTimeMar 29th 2022
     
    Jonti, interesting comparison, thanks. But: “…but I would still want the option to open windows and feel a MVHR system should be developed to accommodate this.” Surely anywhere residential would have opening windows, at least for fire escape? And can't you at least turn off the MHRV to “accommodate” this if there's any problematic interaction (I can't see why there would be)? As DJH says “In particular I don't touch it when we open or shut windows. It doesn't care.”
    • CommentAuthorborpin
    • CommentTimeMar 29th 2022 edited
     
    Posted By: djhI'm generally happy to let the MVHR just do its thing most of the time. In particular I don't touch it when we open or shut windows. It doesn't care.
    Well no, but if it then decides to do something that consumes more energy, you should care (I do).
    •  
      CommentAuthordjh
    • CommentTimeMar 29th 2022
     
    Posted By: borpin
    Posted By: djhI'm generally happy to let the MVHR just do its thing most of the time. In particular I don't touch it when we open or shut windows. It doesn't care.
    Well no, but if it then decides to do something that consumes more energy, you should care (I do).
    All it's going to do is carry on doing what I've told it to do. Yes, if there's a strong wind blowing it will have to use a bit more power to maintain the flowrates, but (a) it's not very much in the grand scheme of things and (b) the windows are normally open when (i) it's not terribly windy and (ii) the sun is shining so the power is coming from our PV system. (not at night, though). So whilst there might be a theoretical issue to consider it doesn't meet my threshold for practical action.
    • CommentAuthorJonti
    • CommentTimeMar 29th 2022
     
    Ed,

    where I was was a rented, 4 room one storey house which had a door front and back but none of the windows opened. It was actually written into the rental contract that the door were not to be left open and we were told this was due to the MVHR system.
    • CommentAuthorborpin
    • CommentTimeJun 9th 2022 edited
     
    My odyssey with this unit continues. I'll reiterate, these devices do not always do what you think they do. Unless you measure and review the data, you just don't know!

    I have been playing with the Eco mode (I think DJH mentioned it somewhere) and it produces interesting results. It does seem to be the best for summer operation, but I cannot quite work out exactly what logic it is using and I'm sure there is a bug as the Heat Recovery suddenly decides to switch off for no discernable reason. I reached out to Komfovent who did respond, but did not appear to understand the issue (or didn't want to).

    The Eco options appear to work against themselves sometimes e.g. Constant Heat Recovery v Free Cooling - There is an inherent issue there. If you look at the ModBus document it refers to this as "Free Cooling & Heating" - not the same thing! Logically, I would expect that between the Min and Max supply values, it would recover heat below the maximum; cool above the maximum; heat below the minimum, but it doesn't do that!

    I have expanded my EmonCMS monitoring and my HA template to control and report on the Eco Mode. I have also automated increasing the ventilation rate when there are more people home.

    If I take the figures on Heat Recovery at face value, it appears that since end of Feb I have recovered 2,165 kWh of energy for the consumption of 222kWh. That is a pretty good return. At price cap prices, that is £600 saved. True, not all that energy 'needed' to be saved as the internal temperature rose above the minimum, but interesting nevertheless.

    I would recommend this unit, but the control cannot be left to the unit itself for maximum efficiency.
      Eco Options.png
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