Silencers for mvhr

[mistake_not]

Putting together my mvhr system, and want a sanity check on silencers. For context I'm planning a radial system.

 

The questions:

 - where do you place them. I assume I only need 2, each fitted between the unit and the supply / exhaust manifolds.

- anyone had experience of the semi flexible BPC ones? If so any good? There also look like there are some ok ridgid ones from other suppliers.

 

And before anyone says, yes aware I need to factor in pressure losses etc 🙂

[Nickfromwales]

Yes to location, and direct off unit / before manifold ✔️ 

 

Do not use the flexible attenuators (flexi duct) as they’re just a cheap rubbish solution in comparison to using the rigid attenuators. 
 

I oversize these to max out on the acoustic benefits, but this obvs depends on a) how the design pressures would otherwise affect the audibility and by how much you then need to arrest it, and b) the length of the attenuator that you then need to do so.

 

On a previous MVHR install the client wanted a lot of cooling to the 4 upstairs bedrooms, rear of the house with loads of glazing facing absolute south. After the explanation, that they would need elevated fan speed to effect cooling via MVHR, they opted to beef these up and we put 1000mm long ones in vs the usual 500(?)mm ones.

 

One of the other ways to cheat this problem is to do what I do and jump up one size of unit to get the bigger ports / ducting; if a 325 unit will suffice I oversize to a 400 as this gives you much lower fan speeds and pressure, but also you jump from 150mm ducts to 180mm ones, further benefitting the occupants. 
 

This (imo) promotes longevity, as the fan is doing a much easier job, but also the longer heat stays in the heat exchanger the better the heat recovery should be (unless someone tells me different?).

 

Budget MVHR doesn’t always work well, more just that it “functions” to tick a box. One of the places I wouldn’t skimp, certainly not with a flexible ‘silencer’! 

[mistake_not]

Awesome thanks for the detailed reply. Yeah was skeptical, hence the question. I got BPC to do a design, and they specced the semi flexible ones, didn't like the idea, so sought wisdom here. Thanks for validating my thoughts!

 

Yes have oversized unit: it's capable of 375m3, but my max requirements from BR are approx 170, so hopefully running quiet.

 

I'll probably try and get the 900mm version of these in then: https://www.blauberg.co.uk/blauberg-attenuating-silencer-duct-mounted

 

 

[Conor]

If you are tight for room, prioritise the supply side rather than the extract. I only had room for one and put it on the supply side, all silent. I used the 150mm cylindrical ones from Lindab. They are huge.

[Nick Laslett]

I brought all of my MVHR ducting direct from Lindab. Here is the silencer page. They discount these list prices. 
 

https://www.lindab.co.uk/Products/ventilation/Sound-attenuation/?sort=popularity&display=16&page=1

 

They have a lot of configuration options. They have a double rubber gasket making for an easier seal. 
 

My MVHR system is still not commissioned, but I have 500mm long silencers. I would have gone with 900mm, but had height restrictions. For before the manifold I went with 200mm diameter, just seemed easier to overspec the system. From the manifold I went with the 90mm/76mm spiral ducting. Like @Nickfromwales suggests, don’t skimp on the MVHR components, it is going to be in place for a very long time. 

 

Robin Clevett was a big influence on my choice of Lindab. He did a very good promotional video on their system. 
 

https://youtu.be/0EQ-pJmPZ-M

 

Edited March 15 by Nick Laslett