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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthoradamsmith
    • CommentTimeApr 17th 2023
     
    Hello,

    We are about to have our first airtight test done, if the results are good we would like to go ahead with MVHR self-installation.

    Does anyone have any particular radial systems they would recommend? Due to us having limited space it does need to be a radial system.

    Also are there any design principles that need to be followed I’m thinking based on my current understanding:

    • Extraction only for (WC, ensuite, and bathroom)
    • Supply only for small rooms (study, living room)
    • X2 supply and extraction for 60m2 kitchen/ lounge/ diner
    • X1 supply x1 extraction in the largest master bedroom
    • X1 supply for medium size bedrooms

    Attached is our construction drawing, any advice is really appreciated
    •  
      CommentAuthordjh
    • CommentTimeApr 17th 2023 edited
     
    Posted By: adamsmithWe are about to have our first airtight test done, if the results are good we would like to go ahead with MVHR self-installation.
    Hello. Good luck with the test. What stage is the build at?
    Does anyone have any particular radial systems they would recommend? Due to us having limited space it does need to be a radial system.
    I'm very happy with our Ubbink system using the AE35 ducts and a previous generation of their distribution boxes. We have a Brink Renovent Excellent MVHR unit but the duct system will work with other units. I liked that the ducts were easy to feed through our metal web joists, and easy to set up and plug together at both ends. The flow restrictors on the distribution boxes make everything very simple. The biggest grief is wrangling all the ducts into one place to connect them to the distribution boxes.

    Where will your ducts run? Where will you fit the MVHR unit? Where will the intake and exhaust ducts penetrate the building? Which way is north, BTW?
    Also are there any design principles that need to be followed I’m thinking based on my current understanding:
    • Extraction only for (WC, ensuite, and bathroom)
    • Supply only for small rooms (study, living room)
    • X2 supply and extraction for 60m2 kitchen/ lounge/ diner
    • X1 supply x1 extraction in the largest master bedroom
    • X1 supply for medium size bedrooms
    The basic principle is extract from all 'wet' rooms and supply to all 'habitable' rooms. You get to choose which e.g. a plant room is maybe based on how the system balances. You'll need an extract in the kitchen and a supply in the living/dining area. You'll need a supply in bedrooms and extract in the en-suite. The MVHR system designer will calculate flow rates and number of terminals etc (Companies like CVC Direct offer this service). The general idea is to put the terminals as far from the door as possible. Don't forget you need undercuts (or hidden overcuts) on all doors. And obviously you won't want all the extractors if you're going for airtight + MVHR.

    There's a good guide at http://www.passivhaustrust.org.uk/UserFiles/File/Technical%20Papers/2018%20MVHR%20Good%20Practice%20Guide%20rev%201.1.pdf and there's various other guides on manufacturers' sites.
    • CommentAuthorborpin
    • CommentTimeApr 18th 2023 edited
     
    I currently have a Komfovent Unit from BPC. Very pleased with it especially as I can connect to the MODBUS interface and collect the data and control it via HomeAssistant.

    Unit is connected to distribution boxes and then semi rigid ducting to outlet/inlet points.

    Vents are in the roof but there is a residue left from the exhaust vent, so if doing it again, I'd definitely raise the exhaust vent above the surface of the roof by possibly 300mm.

    Use insulated ducting from/to outside (preferably rigid not flexible).

    I have retrofitted an additional filter box on the inlet side to catch some of the 'crud' before it hits the primary filter.

    Think about likelihood of freezing.

    Condensation drain (if required).

    Monitor CO2 in someway (either supplier sensor - usually expensive, or cheaper one from China and an ESP device). My experience is it is a more important factor than humidity on deciding ventilation rates.
    • CommentAuthoradamsmith
    • CommentTimeApr 18th 2023
     
    Thanks, DJH,

    Your build is at the first fix stage, all stuff work and electrics in, first fix plumbing to go, ducting fit, then we can start drylining. We have a chalet bungalow, and have insulated/ airtight, from soffit to ridge so feel its worth testing at this stage to see how much more we need to close up, or how much we need to use the internal layer for airtight (hopefully as little as possible)!

    The unit is going under the eves next to the main bathroom upstairs, duct runs through the first-floor joists/ eves/ small loft space above the rafter ties. Where the unit is being positioned under the eves it will make access to the atmosphere very easy, the plan is to go straight out the roof with the inlet and outlets (with them spaced appropriately. The Ducts will exit on the south roof elevation.

    I'll have to take a look at the Ubbink system using the AE35 ducts, looks very good. I'll get in contact with as many design companies as possible and see how the designs compare. At this stage, it looks like the ducting runs are going to be the main snag, but nothing that can't be got over!

    Thanks everyone for the Advice







    :bigsmile:
    •  
      CommentAuthordjh
    • CommentTimeApr 18th 2023
     
    Posted By: adamsmithThe unit is going under the eves next to the main bathroom upstairs, duct runs through the first-floor joists/ eves/ small loft space above the rafter ties.
    Sounds good. Don't forget you'll need easy access to the MVHR unit to clean or change the filters every few months. What type of joists do you have? - if they are solid it will be quite difficult to route ducts through them. You'll also need significant space for the distribution boxes and all the ducts around them.

    As borpin says, use insulated ducts for the intake and exhaust, assuming the MVHR is within the thermal envelope. Use a dry trap such as HepVO for the condensation drain since water is likely to evaporate from a wet trap.
    • CommentAuthorrevor
    • CommentTimeApr 18th 2023
     
    How are you arranging your kitchen extraction. It is not a good idea to extract direct into the MVHR .What we did was fit a ceiling recirculation extractor fan and direct the exhaust via duct into the kitchen about a couple of metres from the MVHR extract valve. Next to the cooker I fitted a boost switch to switch the MVHR to boost. It works very well.
    • CommentAuthorcjard
    • CommentTimeApr 19th 2023
     
    Take the opportunity to install a central vacuum system also
    • CommentAuthorMike1
    • CommentTimeApr 19th 2023
     
    Posted By: cjardTake the opportunity to install a central vacuum system also
    If you're asthmatic it's no doubt a very good idea. But otherwise why lug around a coil of hose around when you could use a rechargeable (or robot) vacuum instead?
    • CommentAuthorborpin
    • CommentTimeApr 19th 2023
     
    Posted By: adamsmithThe unit is going under the eves next to the main bathroom upstairs, duct runs through the first-floor joists/ eves/ small loft space above the rafter ties.
    You generally need good access to the unit, a big door that opens so beware! Also, it does produce some noise that may be noticeable close to a bedroom at night.

    Don't underestimate the difficulty in threading the semi-rigid ducts and fitting the outlets!
    • CommentAuthorArtiglio
    • CommentTimeApr 19th 2023
     
    I decided on mvhr quite late into the project ( well after layout had been decided) this compromised the positions of inlet/outlets and duct runs. In addition I couldn’t get ducts to join the two sections of the house ( barn/ later oast) so have ended up with two systems. First in the oast is up and running and works well with the exception of extraction in the kitchen, which doesn’t really cope with stronger cooking smells or when there’r things boiling. As above i fitted a recirculating hood and am modifying how i cook. Last resort will be an extractor for the days it doesn’t cope, if need be.
    Again as above don’t underestimate the amount of room needed to get wverything connected and leave space for maintenance. Glad i decided to do it and performance can only improve once other half of house is finished.
  1.  
    I know radial systems are all the rage now (it's what we fitted) but I was at a relatives recently and their MVHR (An incredibly solid industrial looking Genvex) seems to be branched.

    Depending on where your unit is located relative to all the rooms a branched system probably takes up less space (the manifold units aren't small and the radial pipes take up a lot of space once they start to come together.). Disadvantage is supposed to be sound leakage between rooms.
  2.  
    I absolutely squeezed ours in to a barn conversion, including chiselling away a floor joist (additional support is provided by block walls) so that the manifolds would fit into the floor void above the utility/plant room.

    It resulted in some very short pipe runs of less than a metre!

    The insulated inlet & outlet ducts also ran in the floor void and out of the back wall.

    I put a lot of effort into sound reduction measures in the walls and ceiling of the utility/plant room.
      MVHR manifolds.jpg
  3.  
    The one thing I would have done differently is put the supply vent to each bedroom higher up the wall or even on the ceiling. They are about halfway up the wall, which I thought would be fine and made it a hell of a lot easier for me in terms of installation (it meant that I didn't have to get past a chord in the roof timbers), but now that it is finished and the beds are in place they have ended up a bit too low down the walls.

    All the downstairs rooms are absolutely fine because the vents are either in the ceiling or on the wall close to the ceiling.
      MVHR room vent.jpg
    •  
      CommentAuthordjh
    • CommentTimeApr 19th 2023
     
    Posted By: Dominic CooneyThe one thing I would have done differently is put the supply vent to each bedroom higher up the wall or even on the ceiling. They are about halfway up the wall, which I thought would be fine and made it a hell of a lot easier for me in terms of installation (it meant that I didn't have to get past a chord in the roof timbers), but now that it is finished and the beds are in place they have ended up a bit too low down the walls.
    All our upstairs bedrooms have the vents in the floor (under the bed in one case :). So the duct just runs amongst the joists and terminates in a box in the same space. The extract vents in the wetrooms are mounted in the internal stud walls, about 2.3 m off the floor. In the plant room I didn't actually fit a vent/terminal, I just brought the duct out into the space and used airtightness tape over the end to adjust the opening to the correct m³/hr.
  4.  
    Posted By: djhvents in the floor


    What a good idea. Although I can almost guarantee that if we had done this, they would have been in the wrong place, e.g. under a wardrobe or something! It was hard enough trying to get enough electrical sockets in the right place, we always seem to end up with the furniture in other places than we initially thought.
    •  
      CommentAuthordjh
    • CommentTimeApr 19th 2023
     
    I see that GBS don't like terminals in the floor (draughts from supply terminals and dust into extract terminals) but we haven't noticed any draughts. As long as the wardrobe has some short legs it would be OK - air doesn't need much space to move through. Tell me about sockets! My principle was to put at least a double socket on every bit of 'disconnected' wall, and one near each corner and door on longer sections. But there are still some places where we've ended up running extension leads because the sockets aren't in the right place etc.
    • CommentAuthorGreenPaddy
    • CommentTimeApr 20th 2023
     
    Adam,

    re. roof exhaust/intake, consider the intake blockage with snow, and also the intake should have a leaf/insect mesh - access to clean. These need cleaning a couple of times a year.

    I always route the exhaust through the roof, but the intake through a wall, or a soffit. Also provides the separation you rightly mentioned.
    •  
      CommentAuthordjh
    • CommentTimeApr 20th 2023
     
    The idea of having both intake and exhaust together but separated on the same wall (or both on the roof) is to balance dynamic pressures when the wind blows. So both experience the same additional pressure, or the same reduced pressure, and thus the MVHR doesn't really notice and doesn't have to draw extra power for its fans.

    The roof generally has reduced pressure, whilst a wall may have reduced or increased pressure depending on which way the wind is blowing.
  5.  
    Posted By: djhThe idea of having both intake and exhaust together but separated on the same wall (or both on the roof) is to balance dynamic pressures when the wind blows. So both experience the same additional pressure, or the same reduced pressure, and thus the MVHR doesn't really notice and doesn't have to draw extra power for its fans.

    My understanding = yes
    • CommentAuthorborpin
    • CommentTimeApr 24th 2023
     
    Posted By: GreenPaddythe intake should have a leaf/insect mesh
    I have a wire guard to prevent birds, but the larger crap was drawn in, hence my additional pre-filter which works really well (but filter needs replacing 3-4 times a year).
    •  
      CommentAuthordjh
    • CommentTimeApr 24th 2023
     
    Posted By: borpin
    Posted By: GreenPaddythe intake should have a leaf/insect mesh
    I have a wire guard to prevent birds, but the larger crap was drawn in, hence my additional pre-filter which works really well (but filter needs replacing 3-4 times a year).
    Same here. I didn't want an insect mesh on the intake (or exhaust) because then I would somehow need to clean it regularly, so I have a washable g3 filter at the MVHR intake that collects all the insects.
    • CommentAuthorSimon Still
    • CommentTimeApr 25th 2023 edited
     
    Same here - the vents on mine probably have 5-10mm holes so isn't going to stop flies.
    Something like this on a flat roof (and the roofer has run the membrane to a level where it can't be removed)
    https://www.u-buy.co.uk/product/GIA2G4O-round-roof-rain-cap-hvac-vent-galvanized-steel-all-weather-rain-cap-roof-top-round-roof-vent-with-ru

    the incoming filter picks up some flies but maybe there are huge numbers more in the incoming pipe run.

    My relatives unit (rural, sheep grazing in next field) had a vast number of dead flies in it but they're desiccated and they're on the 'dirty' side of the filter so dont' see that they're doing any harm. (I mean a couple of pints of dead flies - not sure they'd swept it out properly for a while and there was a 'trench' ahead of the filter completely filled with fly bodies. And quite a few live ones flew out when I opened the unit....
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