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    • CommentAuthordelprado
    • CommentTimeJul 14th 2017
     
    I still can't find a solution to this problem. You go to all the expense and effort of air sealing, very good windows, but how do I get fresh air in without hearing the neighbours retarded dog?
    • CommentAuthorbarney
    • CommentTimeJul 14th 2017
     
    You use in line acoustic attenuators on supply and extract upstream and downstream of you fan units with maybe a bit of duct lining on the ducts leading to/from the fans to the outside world

    You can also use plenums with offset inlets and outlets (again, with or without linings)

    It's not possible to get "silent" and you really wouldn't like it anyway. No point going any further than the other weakest elements of your construction (be that walls, windows, doors etc

    Work out the worst Rw value you have and then match the vent system to that (probably converted to an NR value in octave bands)

    Regards

    Barney
    •  
      CommentAuthordjh
    • CommentTimeJul 14th 2017
     
    The intake and exhaust vents of our system overlook the pen where the neighbour puts their dogs sometimes (maybe 10 m away straightline). We don't hear the dogs (actually just one of them that sometimes barks) via the MVHR. We do hear it through the triple glazed windows, but at much reduced volume. The neighbour maybe 100 m away across the road in a normal house complains more.

    We have short, foam-insulated ducts to the MVHR unit, then shortish, foam-insulated ducts to the supply and extract noise-insulated distribution boxes, then semi-rigid ducts to the rooms. The supply duct between MVHR and distribution box does include an attenuator. But I think not having rigid ducts anywhere helps quite a bit.
    • CommentAuthordelprado
    • CommentTimeJul 17th 2017
     
    Thank boy both.

    DJH that is a fantastic testimony! And a barking dog is what I am looking to sort out!

    To move it forward, can someone whisper to me a company I can reliably consult to look seriously at the design?

    Thanks
    • CommentAuthorbarney
    • CommentTimeJul 17th 2017
     
    Rigid circular ducts will transmit noise far more effectively than square or rectangular sections as the duct wall is effectively much stiffer in the former

    Semi rigid ducts are quite effective as some frequencies

    Careful arrangement of bends has a reasonable effect

    Personally, I would go with Caice or IAC Acoustics for attenuators in any ducted system (both before and after the fans) on supply and extract

    Regards

    Barney
  1.  
    <blockquote><cite>Posted By: djh</cite>We have short, foam-insulated ducts to the MVHR unit, then shortish, foam-insulated ducts to the supply and extract noise-insulated distribution boxes, then semi-rigid ducts to the rooms. The supply duct between MVHR and distribution box does include an attenuator. But I think not having rigid ducts anywhere helps quite a bit.</blockquote>

    Can you explain what you mean by 'foam insulated ducts'?

    I've got semi rigid to the rooms but just used insulated flexi duct (foil/fibreglass/foil) between the manifold boxes and the fan unit. I've never been aware of any outside noise coming through the ducts (you'd always hear it through the windows first) but less fan noise, esp on boost, would be nice. It's not really a problem but can definitely hear when the boost is on in bed at night.
    •  
      CommentAuthordjh
    • CommentTimeJul 17th 2017
     
    The insulated ducts are these: http://www.ubbink.co.uk/products/ventilation-ductwork/insulated-ductwork.aspx
    and the semi-rigid we used are: http://www.ubbink.co.uk/products/ventilation-ductwork/Air-Excellent-Semi-Rigid-Ductwork/Semi-Circular.aspx (AE35SC)

    The distribution boxes were an earlier version than the product shown but operate similarly. We bought everything from Passivhaus Store and they also designed the system to the passivhaus criteria, which include noise levels. The fans are just audible at full speed but we don't use that setting anyway.
  2.  
    My setup sounds very similar to Simon's and I did not do anything special to dampen noise in the system.

    My neighbour has a dog and I do hear it bark through the 3G windows, but I have never been aware of hearing noise through the MVHR ducts.

    As per Simon's comment we can also hear the unit running when it was on boost (it is worst in some rooms than others).
    • CommentAuthordelprado
    • CommentTimeJul 18th 2017
     
    What is the explanation of the silence through the ducts? You have a 6 or 8 inch hole to the outside and you hear nothing, and yet you hear through a window which is air tight?
    • CommentAuthorbarney
    • CommentTimeJul 18th 2017
     
    Ducts are quite good at soaking up "noise" at certain frequencies due to the material, shape, etc

    A widow can only attenuate due to reflection, mass and stiffness - and whilst glass is quite good, in reasonable pane sizes it's not high mass nor very stiff, it simply vibrates due to sound waves impinging on it, sets up vibration in the air gap between the panes, which in turn excites the inner pane, which excites the air adjacent to it and you hear the sound

    You'd need a mid pane gap of about 100mm or so and with absorption material in the "cheeks" if you want to provide really good attenuation of sound - but that's less good thermally as you get quite big convection currents in a gap of that width

    Regards

    Barney
    • CommentAuthorCX23882
    • CommentTimeJul 18th 2017
     
    I fitted a 1.2m long duct attenuator from Ductstore.co.uk, to my Drimaster PIV unit. It absolutely works to cut noise. Whilst the Drimaster is inaudible outside the loft on my "normal" speed setting, when it is on boost, its fan bearing noise level can be a bit more than what I find acceptable.

    The only thing I'm unsure about is how much it affects flow through the duct. The attenuator has a perforated surface inside, so it's no longer smooth for that length of "duct". I doubt it matters much for the Drimaster since it's intended to be used with flexi ducting, but where things are a bit more finely tuned as with MVHR, I'd want to check.

    As for windows, I think the best bet is fitting secondary glazing a far distance from existing double glazing. That way you have optimal gap in the double glazing for thermal, and optimal gap between double and secondary for acoustic. I'm currently considering a "heavy duty" SG system that takes sealed units. I'm so tired of yappy dogs whilst trying to concentrate on work.
    •  
      CommentAuthordjh
    • CommentTimeJul 18th 2017
     
    As Barney and CX23882 say, a large gap between the layers of glazing is best for acoustic purposes. The mnormal gaps are best just for thermal purposes. For acoustic glazing it is also normal to use different thicknesses of glass in the different panes, so they resonate at different frequencies.

    The best I ever saw was a radio studio in Hilversum, in the Netherlands. It had ten-layer glazing as it was built directly above a major roundabout.
  3.  
    Ah, Hilversum... Reminds me of the station selector on my old wireless....
    • CommentAuthordelprado
    • CommentTimeJul 30th 2017
     
    I spoke to green building store and they wont specify me something as my house is not a passiv house (basically).

    Can anyone recommend another supplier?
    •  
      CommentAuthorfostertom
    • CommentTimeJul 30th 2017 edited
     
    Posted By: Nick ParsonsAh, Hilversum... Reminds me of the station selector on my old wireless....
    I discovered the other day that exotic Bayreuth on the old dial meant Beirut - at that time the prosperous Monte Carlo of the eastern Med.
  4.  
    Oh! Not this one? - ''Bayreuth is a sizeable town in northern Bavaria, Germany, on the Red Main river in a valley between the Franconian Jura and the Fichtelgebirge Mountains.''
    •  
      CommentAuthorfostertom
    • CommentTimeJul 30th 2017
     
    Oh - but from Beirut Wiki: "Beirut (Arabic: بيروت‎‎ Bayrūt About this sound pronunciation (help·info), French: Beyrouth) is the capital and largest city of Lebanon. "
  5.  
    I'll have to tune in the wireless and see what I hear!
    •  
      CommentAuthordjh
    • CommentTimeJul 30th 2017
     
    The radio station in Bayreuth only operated a long time ago, when such wirelesses were made, if I understand correctly. Nowadays the area is covered by Bayerischer Rundfunk.
  6.  
    Yes, I was thinking of tuning in in a historical sense!
  7.  
    Suppliers -

    I sourced my kit through www.bpcventilation.com Good service and keen pricing. When they made a mistake in what they sent out it was sorted quickly and easily, as were extra parts I needed.


    Silencers - Looks like one of these is might help my system.
    https://www.bpcventilation.com/attenuator-silencer
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