Stones Posted June 11, 2017 Share Posted June 11, 2017 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. Link to comment Share on other sites More sharing options...
ProDave Posted June 11, 2017 Share Posted June 11, 2017 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. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 11, 2017 Share Posted June 11, 2017 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. 1 Link to comment Share on other sites More sharing options...
Pete Posted June 11, 2017 Share Posted June 11, 2017 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 Link to comment Share on other sites More sharing options...
Stones Posted June 11, 2017 Author Share Posted June 11, 2017 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. Link to comment Share on other sites More sharing options...
ProDave Posted June 11, 2017 Share Posted June 11, 2017 Do you have particularly short runs of duct? My shortest inlet duct is about 6 mertres and I cannot hear the fan noise even if I get on a stepladder and put my ear to the terminal. Link to comment Share on other sites More sharing options...
Stones Posted June 11, 2017 Author Share Posted June 11, 2017 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. Link to comment Share on other sites More sharing options...
PeterW Posted June 11, 2017 Share Posted June 11, 2017 BPC do an acoustic vent which may help you https://www.bpcventilation.com/125mm-metal-acoustic-supply-valve 1 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 11, 2017 Share Posted June 11, 2017 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. Link to comment Share on other sites More sharing options...
PeterW Posted June 11, 2017 Share Posted June 11, 2017 @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. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 11, 2017 Share Posted June 11, 2017 (edited) 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 June 11, 2017 by JSHarris 1 Link to comment Share on other sites More sharing options...
dogman Posted June 11, 2017 Share Posted June 11, 2017 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. Link to comment Share on other sites More sharing options...
Bitpipe Posted June 11, 2017 Share Posted June 11, 2017 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.. 1 Link to comment Share on other sites More sharing options...
PeterW Posted June 11, 2017 Share Posted June 11, 2017 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 ..?! Link to comment Share on other sites More sharing options...
Barney12 Posted June 11, 2017 Share Posted June 11, 2017 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 4 Link to comment Share on other sites More sharing options...
PeterW Posted June 11, 2017 Share Posted June 11, 2017 I reckon our local council would accept that ..!! I'm on my third "street naming officer" who is basically asking me to do her job ..... Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 11, 2017 Share Posted June 11, 2017 I did a proper report for BC, only because the regs seemed to require a commissioning report. I don't think it was even glanced at by BC............. Link to comment Share on other sites More sharing options...
JamieM Posted July 19, 2017 Share Posted July 19, 2017 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 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted July 19, 2017 Share Posted July 19, 2017 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 1 Link to comment Share on other sites More sharing options...
JamieM Posted July 19, 2017 Share Posted July 19, 2017 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 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted July 19, 2017 Share Posted July 19, 2017 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. 1 Link to comment Share on other sites More sharing options...
ADLIan Posted July 19, 2017 Share Posted July 19, 2017 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. 1 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted July 19, 2017 Share Posted July 19, 2017 Well spotted, I just copied the link from my blog, which is now out of date - I should have checked. Link to comment Share on other sites More sharing options...
readiescards Posted July 20, 2017 Share Posted July 20, 2017 Is there a link to the updated versions that can be posted here? I , and maybe others, would fine useful please Link to comment Share on other sites More sharing options...
Jeremy Harris Posted July 20, 2017 Share Posted July 20, 2017 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 1 Link to comment Share on other sites More sharing options...
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