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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorgravelld
    • CommentTimeFeb 13th 2015 edited
     
    Can we make a list of the reasons that MVHR is "difficult" to retrofit?

    I see this phrase or meme cast about a lot in green building circles. But what does it actually mean?

    I don't really see what's "difficult" in running a few ducts around your house. Maybe some plasterboard has to come down. You might have to scramble around in the loft a bit. At worst you have to run them inside the living space and do some boxing in!

    So what's "difficult" about it? Is it just a collective failure of ambition?
    • CommentAuthorsnyggapa
    • CommentTimeFeb 13th 2015
     
    in addition to the above - which can be "easy" as long as you don't care about aesthetics - is achieving the correct level of airtightness in an old building to make it worthwhile

    -Steve
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 13th 2015
     
    Yes, airtightness and everything is in the way.
    • CommentAuthorringi
    • CommentTimeFeb 13th 2015
     
    A MVHR is well worth while for quality of life regardless of the level of airtightness.

    But the MVHR will not save any energy without good airtightness.

    If you got good airtightness now, retro-fitting a MVHR may damage it...
    • CommentAuthortony
    • CommentTimeFeb 13th 2015
     
    Airtightness is irrelevant when there is no wind, hardly with light wing and very relavent when is windy.

    Relying on airleakege for ventilation is a wrong aproach, build tight ventilate right.


    Retrofit in a bungalow or the upstairs of a house is a piece of cheese, holes in ceiling with a pad saw and run ducts to a box and main in and out to outside. To get to the ground flooe drop down a cupbuard or in a corner and case the duct in. good design, use a bit of a bulkhead in the hallway to feed several rooms etc

    It id doable

    Reasons why not

    Hassle
    Expense
    no percieved gain
    joists in the way
    noise
    lac of skills
    flat roofs
    loft hatch too small
    difficult to get ducts into floor void
    pipes and wires in the way
    • CommentAuthorgravelld
    • CommentTimeFeb 13th 2015
     
    That's the kind of thing I'm getting at Tony - what are the specific problems and how can they be counteracted (or argued against)?
    • CommentAuthorringi
    • CommentTimeFeb 13th 2015
     
    I also hid the issue that no one would do a design for me that took into amount tanks in the loft etc. All the duct layouts done as part of a "free" design service were unworkable in real life.

    Install quotes were also very unreasonable and had so many "get outs" that I could not predict how many add-ons I would be charged for on the day.

    Therefore I did my own layout and install, but most people would not be that brave.
    • CommentAuthorHollyBush
    • CommentTimeFeb 13th 2015
     
    I guess when things get tricky is it appropriate to miss some rooms out and assume you get 80% of the benefit from just doing the most used rooms?

    Then I also presume you can through single room HR into the mix, and finally the Breathing Window...
    • CommentAuthoralexc
    • CommentTimeFeb 13th 2015
     
    Building on tony.

    Download an installation guide from a MVHR.

    You read items along lines of:
    install 1m long silencer between MVHR and air inlet.
    Do not let it freeze
    Do not use flexable pipe if (you do want max effiency, min noise levels)
    put it in some wooden case, or find space somewhere so that the noise of the machine is seperated from living/sleeping quarters
    Max sure the device sited such that it does not cause vibration through to other places.
    making sure the pipes are sealed(you buy pipe with internal rubber seals that slot together. probs more expensive)
    If the device has a screen, make sure its visible/easy to see somehow.
    Do not install in bathroom

    The above is in the install guides I have read. Lost list of do nots.
    I have thought its more that its another thing that may go wrong, and wahts wrong with opening the woindow.
    • CommentAuthorgravelld
    • CommentTimeFeb 13th 2015
     
    What do you do about joists in the way? Run ducting over the top and ensure insulation is deep enough over it?

    Why would running ducts in the floor void be necessary? It's in my head that normally the unit is in the loft, ducts in loft and ceiling voids... and in living area as needs be.
    • CommentAuthoratomicbisf
    • CommentTimeFeb 14th 2015
     
    Posted By: gravelldWhat do you do about joists in the way? Run ducting over the top and ensure insulation is deep enough over it?

    Why would running ducts in the floor void be necessary? It's in my head that normally the unit is in the loft, ducts in loft and ceiling voids... and in living area as needs be.


    Ducts in floor voids may be necessary in a house with more than one storey to get between the loft and the ground or lower floor.

    I found it can be a little tricky, but with a little imagination I've done it without any of the ducts being visible or boxed in.

    So far I've run a duct down inside a stud wall from the loft, coming out under the bath then used various 45 and 90 degree bends to run it along under the bath but above the floor before it goes through the floor to a grille on the kitchen ceiling. Getting it between vertical studs in the wall and then missing the steel floor beams, timber noggins and pipes made it a little convoluted but with a bit of effort it's far from insurmountable.

    Between the two main bedrooms there is no wall, just a set of built in cupboards which should be ideal for ducts.

    I guess it does depend a lot on the house construction.

    Ed
  1.  
    Posted By: atomicbisfI guess it does depend a lot on the house construction.
    Tell me about it!! Solid stone walls, incl central main wall, beam and block floors. But have fitted upstairs though....
    • CommentAuthorgravelld
    • CommentTimeFeb 14th 2015 edited
     
    Posted By: atomicbisf
    Ducts in floor voids may be necessary in a house with more than one storey to get between the loft and the ground or lower floor.

    Sorry, misinterpreted that as ground floor void.

    Posted By: atomicbisfSo far I've run a duct down inside a stud wall from the loft, coming out under the bath then used various 45 and 90 degree bends to run it along under the bath but above the floor before it goes through the floor to a grille on the kitchen ceiling. Getting it between vertical studs in the wall and then missing the steel floor beams, timber noggins and pipes made it a little convoluted but with a bit of effort it's far from insurmountable.

    ...

    I guess it does depend a lot on the house construction.
    Yes, and the unknown - although in a BISF house maybe a bit more about the construction can be assumed but you still don't know what's been done since construction.
    • CommentAuthorPaul_B
    • CommentTimeFeb 14th 2015
     
    I plan on retrofitting MVHR at some point in the future as DIY project. I am fortunate in that the house has built in wardrobes so I can hide the boxing in of the pipework to drop from loft to ground floor. The other option would be to increase the current boxing for the two soil pipes so that the MVHR can sit next to the soil pipe, I can add insulation and make use of the existing framework of the boxing.

    Question, if you need to run pipes perpendicular to the joist and cut a hole through them can the joist be strengthened to take account of the hole by putting metal plating above and below the hole on either side of the joist? If so what sort of calculations would need to be done to determine length, thickness, number of bolts?

    Paul
  2.  
    Well I think you've answered the OP question right there Paul :sad:
    • CommentAuthorShevek
    • CommentTimeFeb 15th 2015
     
    The other way to do this is to run PVHR, such as Ventive, for each room and run everything vertically up to the roof, either via a chimney or wherever you can find a good spot to go vertically. Beats MVHR in my opinion.
    • CommentAuthorEd Davies
    • CommentTimeFeb 15th 2015
     
    Whatever the arguments for P vs M HRV, surely passive means you're more constrained on the duct runs so it'll be harder to retrofit. If you can fit PHRV then you can fit MHRV but not necessarily vice-versa.
    • CommentAuthorSwarm
    • CommentTimeFeb 15th 2015
     
    Is PVHR tried and tested? How about effectiveness and ease of install vs MVHR?

    I have a central chimney feeding two fires, one on each of the two lower floors of a three storey house. I was going to install MVHR and remove the fires and chimney but now you have got me thinking.
    • CommentAuthortony
    • CommentTimeFeb 15th 2015
     
    M recovers energy from the exhausted air
    P does not!
    • CommentAuthorandyman99
    • CommentTimeFeb 15th 2015
     
    Reasons why not

    Need for building control approval?
    • CommentAuthorGotanewlife
    • CommentTimeFeb 16th 2015 edited
     
    Each of my MVHR fans are individually controllable in trickle and boost (ie I set 4 fans speeds). In my retrofit scenario my MVHR will (when I set it up sometime!) be set in an overpressure 'balance' - best of both worlds! Minimising cold air entering through leaky bits and hence reducing condensation.

    I reckon I can make an adequate void for MVHR ducting by creating a false ceiling in one room and that, coupled with a built in cupboard, will allow retrofit MVHR, albeit all other rooms will have suboptimal outlet/inlet placements. Still way better than vast amounts of boxing in otherwise required.
    • CommentAuthorEd Davies
    • CommentTimeFeb 16th 2015 edited
     
    Posted By: tony:

    “M recovers energy from the exhausted air
    P does not!”

    So you're saying that Ventive are being misleading when they call their system ”Passive Ventilation with Heat Recovery (PVHR)”?

    http://www.ventive.co.uk/passive-ventilation-heat-recovery/
    • CommentAuthortony
    • CommentTimeFeb 16th 2015
     
    They claim up to 95% heat recovery but I cant see it or anything close in normal operation and would wonder how it could do any good when it is windy.

    May be I should say P can recover some heat but has no controls.
    • CommentAuthorPaul_B
    • CommentTimeFeb 16th 2015 edited
     
    Posted By: Paul_B...Question, if you need to run pipes perpendicular to the joist and cut a hole through them can the joist be strengthened to take account of the hole by putting metal plating above and below the hole on either side of the joist? If so what sort of calculations would need to be done to determine length, thickness, number of bolts?


    Anyone able to comment on my question?
    • CommentAuthoratomicbisf
    • CommentTimeFeb 16th 2015
     
    Posted By: Paul_B
    Posted By: Paul_B...Question, if you need to run pipes perpendicular to the joist and cut a hole through them can the joist be strengthened to take account of the hole by putting metal plating above and below the hole on either side of the joist? If so what sort of calculations would need to be done to determine length, thickness, number of bolts?


    Anyone able to comment on my question?


    I would think it could, but surely MVHR ducts are too large to go through joists?

    Here's some of mine, under a bath, so you can see I've had to be a bit 'creative' to get it from the wall through the floor.

    Ed
  3.  
    Short answer no.

    If you really really really needed to put a large hole through a wooden joist, you would prob have to use 2 lengths of steel C sections clamped on either side with bolts through the steels and joist, with a hole cut through the steels on either side of the hole in the joist. exact solution depends on size and position of hole and joist

    not worth it
  4.  
    <blockquote><cite>Posted By: atomicbisf</cite><blockquote><cite>Posted By: Paul_B</cite><blockquote><cite>Posted By: Paul_B</cite>...Question, if you need to run pipes perpendicular to the joist and cut a hole through them can the joist be strengthened to take account of the hole by putting metal plating above and below the hole on either side of the joist? If so what sort of calculations would need to be done to determine length, thickness, number of bolts?
    </blockquote>

    Anyone able to comment on my question?</blockquote>

    I would think it could, but surely MVHR ducts are too large to go through joists?

    Here's some of mine, under a bath, so you can see I've had to be a bit 'creative' to get it from the wall through the floor.

    Ed<div id="Attachments_219663" class="Attachments"><ul><div><img alt="DSC_0050.JPG" src="/forum114/extensions/InlineImages/image.php?AttachmentID=5687"></img></div></ul></div></blockquote>

    Are you sure you will be able to tighten the compression joint on that U bend under the bath once its in place?? :confused:
  5.  
    I've retrofitted many ducted MVHR systems during Passive House renovation projects, its like pulling teeth!
    Its twice as difficult as fitting ducted MVHR in a new build and never worth the effort, you end up having to redecorate every room and fan consumption goes through the roof with all the bends and spaghetti ductwork!
    The payback for MVHR in a new build is 40-50 years, its probably double that in a renovation project, better to spend the money on extra insulation and open the windows for fresh air.
    I was glad when we discovered the simple, effective solution!
  6.  
    Posted By: Viking HouseI was glad when we discovered the simple, effective solution!
    What would that be then I wonder? :bigsmile::bigsmile:
    Posted By: Viking Housenever worth the effort,

    Thing is, MVHR in a retrofit is not about payback, so I disagree: in fact it is always worth the effort.
  7.  
    Posted By: bot de pailleAre you sure you will be able to tighten the compression joint on that U bend under the bath once its in place??http:///forum114/extensions/Vanillacons/smilies/standard/confused.gif" alt=":confused:" title=":confused:" >

    There will always be a way, awkward, painful, time-consuming but a solution there will be. Worst case raise the whole bath........:cry:
   
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