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Following on from some discussion in my blog:

 

we are experiencing some fan noise transmission through our radial ducting to individual room valves, only really noticeable on normal ventilation rates at night when the house is silent, but certainly noticeable during the day when the MVHR is on boost.

 

Experience of other members suggest a silencer would greatly assist in reducing the transmission of any fan noise, and I'm pleased to say having contacted my supplier (BPC) they are going to send me a silencer.  I'm also planning to build my own using some acoustic foam that I've purchased.

 

I'll do a comparison test in due course to see which silencer works best.

 

One of the things Gary from BPC suggested was that there may be an air imbalance in the MVHR unit, and I thought it would be helpful to explore how we all go about balancing our systems.

 

I borrowed and airflow LCA301 meter (with hood) from my builder and used that to measure the air flow at each room terminal, adjusting each individual room terminal as required to meet the flow rates specified by BPC.  I know some members have distribution boxes that allow the adjustment to be made by way of restrictor rings in the distribution box.

 

I balanced the system and set fan speeds so that the supply and extract air flow rates were the same.  The cumulative supply / extract rates were equal to each other (or at least as close as I could get them to be).  However, thinking back to previous builds and advice, and one which was professionally commissioned, there was always a difference in the supply and extract air flow rates of up to 10%.  Has anyone else done this? I'm not convinced this is the best approach as you end up over or under pressurizing the house.

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Only just starting to play with ours. It's been running now since yesterday afternoon. At the moment with no terminals fitted, just the bare ceiling "plenum" units.

 

No silencer fitted yet and really the only noise is from the mvhr unit itself. Even on boost there's not much noise to speak of from the terminals, just the noise from the unit in the plant room. There's no door on the plant room yes so whether it would be audible in the adjacent bedroom is unknown.

 

I wonder how much difference fitting the teminals make? anything that restricts the flow and causes turbulance can create noise. My thinking is to start with all the terminals almost fully open and work from there to try and ballance the system with as little obstruction to airflow as possible.

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Most of the noise will probably come from the point where the flow is restricted, which is one reason why HB+ put the restrictors inside the plenums, rather than down at the terminals.  Our terminals are not adjustable, they are fixed, full flow, and the flow regulation is by fitting restrictor discs inside the plenums, at each duct connection point.  It was a PITA to balance, because of all the running around, but it does mean there's no flow noise from the terminals, even on those runs that are throttled right down.

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Following this thread with interest. Just got my ducting diagram from BPC and apart from a few tweaks it is all looking good. We are using the Vent Axia like a few on BH and it seems quite straight forward to install as a DIY? My only concern will be the cooling mode but I am sure somebody will already have completed this on their build?

TIA

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1 hour ago, ProDave said:

I wonder how much difference fitting the teminals make? anything that restricts the flow and causes turbulance can create noise. My thinking is to start with all the terminals almost fully open and work from there to try and balance the system with as little obstruction to airflow as possible.

 

1 hour ago, JSHarris said:

Most of the noise will probably come from the point where the flow is restricted, which is one reason why HB+ put the restrictors inside the plenums, rather than down at the terminals.  Our terminals are not adjustable, they are fixed, full flow, and the flow regulation is by fitting restrictor discs inside the plenums, at each duct connection point.  It was a PITA to balance, because of all the running around, but it does mean there's no flow noise from the terminals, even on those runs that are throttled right down.

 

It's fan noise that's the problem for me rather than air flow noise (forcing air through a small opening).  When I remove the adjustable terminal cover, fan noise increases. 

 

 

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Discounting two very short runs to the vestibule and cupboard containing our DHW, no nothing under 5 metres.

 

I'll see if I can borrow a decibel meter so I can put some numbers to the problem.

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I found that fan noise was the only noise we had, and it was very effectively fixed by adding silencers to the short ducts from the MVHR to the plenums.  The noise was certainly more pronounced from the very short ducts than the longer ones, so there seems little doubt that the ducts themselves absorb a fair bit of sound.

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@JSHarris I do wonder if the addition of a small disc of acoustic foam to the inner of the valves would have a similar effect as most of these fans are cage fans so the sound wave is within the duct - adding an absorption layer at the end would stop the reflected sound. 

 

I plan to do a  similar thing with foam sound panels on the outside of a false wall to dampen the external road and rail noise into a bedroom. 

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It may do.  

 

The silencers I made are a mix of expansion and absorption silencers, larger chambers lined with acoustic foam to absorb the sound.  They work by slowing the air flow velocity down, which allows the sound to be better absorbed by the larger exposed area of foam (technically it's converted to heat which is then dissipated, before someone mentions the law of conservation of energy...........).

Edited by JSHarris
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Anyone with a BPC system. Does the systems they supply use disks in the plenums or terminals or do they screw down the air valves. I have not yet got all ny equipment and would prefer to use a disc based system.

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58 minutes ago, dogman said:

Anyone with a BPC system. Does the systems they supply use disks in the plenums or terminals or do they screw down the air valves. I have not yet got all ny equipment and would prefer to use a disc based system.

 

You screw the terminals in each vent to increase / decrease air flow.

 

That said, I've not got round to doing mine and been in the house since September.

 

Will probably need to do this to get BC sign off.. 

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1 minute ago, Bitpipe said:

[...] That said, I've not got round to doing mine and been in the house since September.

 

Will probably need to do this to get BC sign off.. 

 

.... just in case the BC turns up with a flow meter to check ..??

 

In reality, how many BCOs check that the commissioning has been done correctly ..?!

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13 minutes ago, PeterW said:

 

.... just in case the BC turns up with a flow meter to check ..??

 

In reality, how many BCOs check that the commissioning has been done correctly ..?!

 

All you need is a certificate. This should do it :D IMG_1097.thumb.PNG.dcdbabed066ad0aba6e69cf8b5a896ea.PNG

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  • 1 month later...
On 11/06/2017 at 18:01, JSHarris said:

I did a proper report for BC

 

Although i dont think i'll need a report, would anyone have a template of a report i could use just in case asked (plan on balancing mine in a few weeks)

 

(for Northern Ireland regs if possible)

 

i do have the flow rates that BPC gave me which i would copy and paste over some elses.

 

thanks

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A copy would be great thanks (even if you uploaded to your mayfly website as i did look there first - sure i seen a copy before but couldnt find it when i seached(maybe it was on ebuild)). and i'll have a read through the link too.

 

thanks

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I can stick up on my website later easily enough.  I didn't follow that guidance note, as I hadn't found it when I did my measurements, but building control were fine with what I produced, which was really just ticking off all the bits of Part F that applied, with some measured data.

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44 minutes ago, JSHarris said:

I have a copy of the report I did on my other PC, that I can upload later, but there is a lot of useful info in this guidance note: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/456656/domestic_ventilation_compliance_guide_2010.pdf

 

Link above is to the old version of the Domestic Ventilation Compliance Guide - there is a 2013 version effective from April 2014.

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6 hours ago, readiescards said:

Is there a link to the updated versions that can be posted here? I , and maybe others, would fine useful please

 

There doesn't seem to be a newer version available online, the one I linked to is still the only one on the government web site AFAICS.  There is a newer, more general, guide to compliance with domestic building regs, but that seems to have very little detail in it: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/453968/domestic_building_services_compliance_guide.pdf

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