Crunch time for MVHR install - not sure about best attenuation strategy?

[MikeSharp01]

We are just about to put the MVHR unit  in and hook it up to all the ductwork and the outside world. We have a Titon HRV4.25 Q Plus B2 (with the aura controller) and I am not sure what attenuation strategy I should use. I have read loads of stuff on here and elsewhere and also spoke to the technical team at Titon (can't praise them (him) enough) and he suggested using two of their 1m semi flexible attenuators although I know some on here advise against these devices. I had intended to put the attenuation into the distribution boxes, so after the unit in supply and before it on extract, which I will custom make, based on ideas shown elsewhere here, to fit the space and allow maintenance but his suggestion - which will be the other side of the unit on the connections to the outside, has some advantages eg getting fitted in the space /lined up. I do want to to be as quiet as I can get away with. Any thoughts.

[JohnMo]

14 hours ago, MikeSharp01 said:

Titon (can't praise them (him) enough)

Same view as myself

 

14 hours ago, MikeSharp01 said:

he suggested using two of their 1m semi flexible attenuators

That is what I am using. Installed between MVHR unit and distribution plenums. You have to have at full stretch and then they are fine, not sagging or loose. I have just plain steel distribution plenums and no further attenuation. No issues - don't over think it.

 

Install filter G3/4 cones in the extract terminals, these add to the noise attenuation anyway. But install before commissioning to keep all the dust out of the ducts.

[MikeSharp01]

59 minutes ago, JohnMo said:

That is what I am using. Installed between MVHR unit and distribution plenums.

With us there is no room for them before the distribution plenums so they will need to go on the other side between the titon and the outside air but I do have room inside the DIY plenums for some foam etc. Not sure what the effect of having the attenuator on the external connections is though. 

 

[Simon R]

16 hours ago, MikeSharp01 said:

I do want to to be as quiet as I can get away with. Any thoughts.

Mike, you may like to consider using these. Mr Harris put me on to them, the idea is that you keep the air velocity down to a minimum in the tubes by installing these restrictors at the plenum. You pop out the restrictor rings as required. It's a bit of a fiddle as it's an iterative process as you balance out the flows. 

[MikeSharp01]

1 hour ago, Simon R said:

you may like to consider using these. Mr Harris put me on to them, the idea is that you keep the air velocity down to a minimum in the tubes by installing these restrictors at the plenum. You pop out the restrictor rings as required. It's a bit of a fiddle as it's an iterative process as you balance out the flows. 

Thanks. Good plan - I will get some when the balancing starts.

[joe90]

18 hours ago, MikeSharp01 said:

do want to to be as quiet as I can get away with. Any thoughts.

Again I did this at the manifold to reduce noise at the rooms, if worked very well.

[jack]

On 04/09/2024 at 12:50, MikeSharp01 said:

With us there is no room for them before the distribution plenums so they will need to go on the other side between the titon and the outside air but I do have room inside the DIY plenums for some foam etc. Not sure what the effect of having the attenuator on the external connections is though. 

 

 

The sounds are from the unit itself and airflow within the system, particularly through any throttle points. I doubt putting an attenuator between the unit and the outside will have any impact on the noise at the internal inlets/outlets.

 

On 04/09/2024 at 13:54, Simon R said:

Mike, you may like to consider using these. Mr Harris put me on to them, the idea is that you keep the air velocity down to a minimum in the tubes by installing these restrictors at the plenum. You pop out the restrictor rings as required. It's a bit of a fiddle as it's an iterative process as you balance out the flows. 

These are the standard approach with Ubbink (Brink) manifolds. The designer told us the right number of rings to pop out and everything was close enough that we needed only slight adjustments on the room vents in a couple of places to get everything balanced.

 

I don't know whether there's a way of estimating the number of rings to pop out for other systems.

[Dave Jones]

who designed it, set flow rates etc ?

 

Ours has a couple massive silencers on the unit itself and another 6 or so box silencers throughout the house. Cant hear anything with ear next to the plenum on boost.

 

 

[MikeSharp01]

 

 

1 hour ago, jack said:

The sounds are from the unit itself and airflow within the system, particularly through any throttle points. I doubt putting an attenuator between the unit and the outside will have any impact on the noise at the internal inlets/outlets.

On ours I designed it and have set the flow rates. I am using the attenuators to give me flexibility, of the pipes, as much as sound attenuation. The main distribution box will have its own silencer and the two other distribution boxes will  also be baffled and internally covered in acoustic foam so I am hopeful it won't be too noisy - I also have a until that has the twice the capacity needed even for boost so am expecting it to run at about 20-25% of its capacity most of the time which should keep the noise down. I can then also use a high boost for cooling via a heat battery in the bedroom distribution feed - which will be noisy but then so are fan coil units of my acquaintance.

[Nick Laslett]

Maybe I’m being hugely naive, but as I have designed and installed my MVHR gear, I was not expecting noise to be much of an issue. 
 

I fitted 600mm Lindab box silencers on the house supply and extract sides, I would have liked to have used the 1m models, but did not have the room. I asked Paul Heat Recover if the ComfoPost had any sound attenuating properties, they said it didn’t, but basic physics tells me that it must have some effect, whether positive or negative because the air path is changed. 
 

I went with the semi-flexible ducts from a manifold, as this was meant to be better for sound transmission between rooms. 
 

The anecdotal evidence based on the BuildHub community back into 2019, when I was specifying all this stuff, was that MVHRs pushed the air at such a low rate, that noise would not be a problem. How noisy is my unit going to be?
 

I’m still ages away from commissioning the unit, although I could run it without the plenums just to get a general feel. Building work is still going on upstairs. Anyway I will report back on this post at some future date, with any tales of woe and regrets. 

[Simon R]

On 16/09/2024 at 12:28, jack said:

don't know whether there's a way of estimating the number of rings to pop out for other systems.

I just estimated based on room air volume requirement. The largest flow with no restrictor, then the others as a percentage of the largest flow ( I didn't use restrictors in any of the returns). Using pi r2 to calculate the rings to remove. This works out at approximately 70,55,36,19,16% which is a reasonable starting point. Having done this measure the flows with the room restrictors fully open. If the flow was too low then remove another ring to get to the right sort of volume +-20%.  As changing each restrictor affects the pressure in the system you may need to repeat the process. I would not bother trying to be too exact, it really is a diminishing returns exercise I called quits when within 20%. Once you get to this point you can then adjust the MVHR fan speed to get the required flow in the room with the largest. The other rooms should also be correct at this point.

After setting up this way I found that in practice I could run the MVHR at a lower fan speed and still have a comfortable environment (almost silent).