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Heating and cooling: MVHR duct size question

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  1.  
    • CommentAuthorwoodgnome
    • CommentTimeJul 18th 2015 edited
     
    I am about to start first fix of my MVHR. BPC plans show the 75mm airflex ducts terminating at the distribution boxes in my plant room in the garage (radial system)
    There is then about 1m to MVHR unit, which is 150mm rigid.
    If i put the distribution boxes about 8m further away from MVHR, nearer the supply/ extract points and ran the supplied 150mm rigid from here to the MVHR would it make a difference to performance.
    Reason for this is that I could then put the distribution boxes in the living room loft area and it will be lot easier to put 2 x 150 ducts through the wall into garage and plant room and insulate to the MVHR, than running 16....yes, 16 x 75mm airflex ducts through the wall.
    Should have called BPC but didn't think about it till today and want to crack on this weekend.
    Cheers
    • CommentAuthorDarylP
    • CommentTimeJul 19th 2015
     
    woodgnome,

    If you can extend the 150mm rigid in a straight line, it won't make much difference in terms of back pressure & system efficiency.
    Howeve, if the 150mm has 90s or 45s, you might want to look at enlarging this section to 200mm dia?

    Good luck
    :smile:
    • CommentAuthorwoodgnome
    • CommentTimeJul 19th 2015 edited
     
    Cheers
    I have decided to keep it as origina Plan, because if I put the distribution boxes in the living room loft area I won't be able to get at them once the ceiling is on and plastered. The only way round would be a hatch in the living room ceiling, which will look pants...
    If I did extend the 150mm ductwork it would have several 90deg bends.

    While I'm on the subject, how much difference is there between balancing the system using the room supply and extract valves as opposed to restrictor rings in the distribution box...is there a noticeable difference in noise?
    •  
      CommentAuthordjh
    • CommentTimeJul 20th 2015
     
    Is the garage heated? You need to insulate all ducts unless they are passing through heated spaces.

    Posted By: woodgnomeWhile I'm on the subject, how much difference is there between balancing the system using the room supply and extract valves as opposed to restrictor rings in the distribution box...is there a noticeable difference in noise?

    I can't answer your question, but isn't your system designed one way or the other? Deciding whether or not to use restrictor rings isn't the sort of decision to take on the hoof.
    • CommentAuthorDarylP
    • CommentTimeJul 20th 2015
     
    ..personally, we install the 'blue' system with RRs in the plenums, where given the choice.

    I am not totally sure of the reason(s) why, but it seems quieter than the adjustable inlet/extract valve method.
    Perhaps because there is less speeding up / slowing down of the air mass at the valve-end? (not well explained I know...:shamed:)
    • CommentAuthorbarney
    • CommentTimeJul 20th 2015
     
    Having the volume control device away from the terminal will:

    1 - give better regulation as you have a significant number of diameters of straight pipe after the VCD to allow flow to straighten

    2 - be quieter in operation as the "shearing" noise is further from the occupants and attenuated by the duct

    Regards

    Barney
    • CommentAuthorwoodgnome
    • CommentTimeJul 20th 2015 edited
     
    Djh
    Garage not insulated but plant room will be. Ducts not in plant room will be insulated.



    Posted By: DarylP..personally, we install the 'blue' system with RRs in the plenums, where given the choice.

    I am not totally sure of the reason(s) why, but it seems quieter than the adjustable inlet/extract valve method.
    Perhaps because there is less speeding up / slowing down of the air mass at the valve-end? (not well explained I know...https:///newforum/extensions/Vanillacons/smilies/standard/shamed.gif" alt=":shamed:" title=":shamed:" >)


    That's what I have recently found out, so I might have to have a re think.

    Barney

    Thanks

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