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Green Building Bible, Fourth Edition
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    • CommentAuthorXT600
    • CommentTimeJan 11th 2018
     
    I've yet to decide how to ventilate my house (1760 mid terrace) but will probably not go with MVHR due to there being two chimneys with unsealed woodburners downstairs. I guess a PIV system may work better. However,I'm currently fitting some new stud walls upstairs and considering putting in a 50mm pipe (which will fit down through the studwork) from the loft space to the downstairs room. Would this pipe be any use with an MVHR system should I change future plans or is it too small? All the systems I've seen use much larger diameter ducts.
    • CommentAuthorsnyggapa
    • CommentTimeJan 11th 2018
     
    smallest I have seen is semi flexible 75mm outside diameter, about 60mm internal. sometimes you use two 75mm pipes to keep the noise down - I would guess that 50mm would be very noisy (higher velocity air movement)
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 11th 2018
     
    Seems a bit small to be, it only has 0.002m^2 area.
    A litre is 0.001m^3
    So to shift 1 litre per second you need a air flow speed of 5 m/s, which is 11 MPH.
    It may whistle a bit.
    • CommentAuthorXT600
    • CommentTimeJan 11th 2018
     
    I could probably stretch to 75mm, will take out most of the studwork but do-able. I've had several lengths of 50mm wastpipe I've been trying to find a home for ages :-)
    • CommentAuthorDarylP
    • CommentTimeJan 12th 2018
     
    use the semi-rigid oval? ....designed for this sort of job........ :-)
    :cool:
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 12th 2018
     
    Posted By: XT600I could probably stretch to 75mm
    That will give you a windspeed of 5 MPH to move 1 litre a second.

    How much air are you looking to shift?
    • CommentAuthortony
    • CommentTimeJan 12th 2018
     
    Why not try rectangular plastic duct say 100x50 ?
    • CommentAuthorXT600
    • CommentTimeJan 12th 2018
     
    <blockquote><cite>Posted By: SteamyTea</cite><blockquote><cite>Posted By: XT600</cite>I could probably stretch to 75mm</blockquote>That will give you a windspeed of 5 MPH to move 1 litre a second.

    How much air are you looking to shift?</blockquote>

    I've no idea. When the wind blows through my open keyhole I can feel the draught from some distance, so a 75mm hole seems massive in that respect! :-)
    • CommentAuthorXT600
    • CommentTimeJan 12th 2018
     
    <blockquote><cite>Posted By: tony</cite>Why not try rectangular plastic duct say 100x50 ?</blockquote>

    Good idea, worth considering thanks...
    • CommentAuthorgoodevans
    • CommentTimeJan 12th 2018
     
    For MVHR in a kitchen would require 10 l/s - a 50mm pipe requires a flow speed of 5m/s for that capacity (Steamy is a factor of 10 out in his calcs I think). The flow speed needs to be down to less than 2m/s ideally.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 13th 2018
     
    <blockquote><cite>Posted By: goodevans</cite>(Steamy is a factor of 10 out in his calcs I think)</blockquote>Could well be

    Pi x 0.025^2 = 0.001963m^2

    Litre = 0.001m^3

    Flow rate = V / Pipe Area

    0.001 / 0.001963 = 0.509

    So yes, I must have got an extra zero in somewhere (or left one out I think)

    So a flow rate of 10 l/s will be 5.1 m/s which is 11 MPH, which is still fast.
    •  
      CommentAuthordjh
    • CommentTimeJan 13th 2018 edited
     
    For laminar flow - which you need for quiet operation - the flow velocity profile is parabolic not uniform. So you need to double the peak speed. So a 50 mm pipe is way too small for 10 l/s.

    See e.g. https://www.pipeflowcalculations.com/pipe-valve-fitting-flow/flow-in-pipes.php
    • CommentAuthorXT600
    • CommentTimeJan 13th 2018
     
    Am I barking up the wrong tree even considering MVHR with the existence of two woodburners? (one of these is inset into the original surround, so I don't see myself ever changing them for direct air supply versions)

    I've been looking at a simple piv system but not sure I like the idea of very cold air being pushed into the house, or the idea of a 400w heater heating this air ...
    • CommentAuthortony
    • CommentTimeJan 14th 2018
     
    PIV should be banned, like you say it pushes cold air into the house,

    It does work in terms of no mould or condensation, probably would make wood burner glow red.

    The bad thing about it is that it continuously pushed warm air out through all gaps and cracks!
    • CommentAuthorXT600
    • CommentTimeJan 14th 2018
     
    <blockquote><cite>Posted By: tony</cite>PIV should be banned, like you say it pushes cold air into the house,

    It does work in terms of no mould or condensation, probably would make wood burner glow red.

    The bad thing about it is that it continuously pushed warm air out through all gaps and cracks!</blockquote>

    The other thing about PIV is they normally get put in the landing ceiling, so how does that help circulate air around the bedrooms?
    I'm wondering whether I could modify a PIV output by splitting it and ducting the air into each bedroom and also one downstairs. That way the air will have a small chance to warm up a little as it gets pushed around the duct. It will also get to where its needed rather than one icy blast from the landing!
    • CommentAuthortony
    • CommentTime7 days ago
     
    And the bedrooms would become very cold and more noisy
    • CommentAuthorgravelld
    • CommentTime7 days ago
     
    Posted By: XT600The other thing about PIV is they normally get put in the landing ceiling, so how does that help circulate air around the bedrooms?
    The bedrooms have trickle vents which is where the positive pressure is pushed out.
    • CommentAuthorXT600
    • CommentTime3 days ago edited
     
    <blockquote><cite>Posted By: gravelld</cite><blockquote><cite>Posted By: XT600</cite>The other thing about PIV is they normally get put in the landing ceiling, so how does that help circulate air around the bedrooms?
    </blockquote>The bedrooms have trickle vents which is where the positive pressure is pushed out.</blockquote>

    My bedrooms are now highly insulated and airtight apart from gaps left under the doors. The windows are triple glazed without air vents. This is to reduce traffic noise from the road, and to avoid pollution from the road side. My plan is to push fresh air into the rooms from the loftspace, which will circulate through the room, under the doors, and leave through the 'open' chimneys downstairs. The issue now is to decide how to control the amount of air pushed into the bedrooms, without introducing extra noise :-)
    • CommentAuthorXT600
    • CommentTime3 days ago
     
    Does anyone know if I can get a 100mm filter box with some washable filters to try out?
    •  
      CommentAuthordjh
    • CommentTime3 days ago
     
    Make a box out of cardboard or hardboard etc and tape it in place? Filter material from http://www.fairair.eu/en/
    • CommentAuthorDarylP
    • CommentTime2 days ago
     
    http://www.justfans.co.uk/duct-mounted-panel-filter-495-495-22mm-p-2146.html ?
    • CommentAuthorXT600
    • CommentTime2 days ago
     
    Thanks for the links guys, will take a look at them.
    Do you think that by using in-line filters in each room duct this will help avoid noise transference between rooms?
    •  
      CommentAuthordjh
    • CommentTime2 days ago edited
     
    Posted By: XT600Do you think that by using in-line filters in each room duct this will help avoid noise transference between rooms?

    No, not really. You need attenuators for that purpose.
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