Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.
Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
 Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




Ventilation: DIY Balancing of MVHR

Bottom of Page

1 to 30 of 33

  1. <
  2. 1
  3. 2
  4. >
    • CommentAuthorGreenfish
    • CommentTimeOct 17th 2014 edited
     
    MVHR in my new build has been commissioned (by the plumber that fitted it, with a certified anemometer). However at building regs flow levels it is too noisy so I want to fiddle with it to try an improve things without totally messing it up. To be honest the plumber had never done MVHR before so I have doubts that it is perfect anyway. With hindsight it could have done with some "design" considering air velocity at each vent etc. before it was fitted, but we are well past that point. Manufacturer (Polypipe) specified the system, plumber fitted it, I stupidly thought everyone else knew what they were doing.... Those room vents most closed are the most noisey, the flow being choaked at the vent and whistles and whooshes, and I would like to adjust that.

    Anyway having read the previous thread covering DIY balancing http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=6681, I have bought a small handheld anemometer and made myself a cardboard cone. Having run around taking measurents at each vent I get consistent air speeds (m/s) over time, and the expected ratio between normal and boost, but when I calculate the flows (l/s) I get values that are half or less the flows that the calibrated meter recorded. Is there more to the calculation than I realise? Is the hobby anemometer just not upto the job? What should I do with my velocities to get a volume flow? Do I need a length of straight ducting on the end of the cone to smooth the flow?

    Advice anyone?
    • CommentAuthortony
    • CommentTimeOct 17th 2014
     
    try turning down the fan speeds or fit something that van set the lower, mine go in 1% steps from 0 to 100%
    • CommentAuthorEd Davies
    • CommentTimeOct 17th 2014
     
    AFAIK, simple velocity times area should do, just πr²v. Doesn't account for the low velocity near the sides of the pipe, of course, but I don't think that'll make too much difference as long as the pipe you're measuring in is wide enough. Do you want to post more details of what you've done to see if we can spot any slips?

    Perhaps the plumber got it wrong and you have too high airflow hence the noise.
    • CommentAuthorGreenfish
    • CommentTimeOct 17th 2014 edited
     
    The regs, based on floor area, want a normal total flow of 65l/s. At this level the whole house throbs, especially where the vents/terminals are throttling the flow. The centres vibrate even when tightened in place, I now understand that noise is unsurprizng given that the air velocity in several vents is exceeding 3m/s. The design solution would have been either larger vents or more vents/ducts serving each room. Too late for that.

    Yes I can turn the fan down, did that while the plummer and calibrated anemometer were still in the house. Set the fan so that boost was 65l/s, and normal under half that. Only measured final flow at one vent to assess the fan speed change, no marks on the fan itself just a pot to turn. Worked alongside the plummer, don't think we got it wrong on the day.

    Over the summer we were still making dust (sanding for painting etc.) so left the commissioned MVHR off and opened the windows. Only now do we have the MVHR running and I am dissatisfied with the results, some vents still whine horribly during boost (turn up the music someone is in the shower), bathroom not clear quick enough etc. I am hoping I can balance it more intelligently now and get a better setup, rather than turn it off so much I have to open the windows to demist the bathroom.

    OK, here is what I have. This anemometer http://www.amazon.co.uk/dp/B009MO86V0/ref=pe_385721_51767431_TE_dp_1 stuck in a slot cut into the side of a plastic cup with the bottom cut off. Then a cadrboard cone extending the cone of the cup into a 200mm diameter top that I hold against the ceiling. Lots of tape to seal things. Assuming πr²v, and a 25mm diameter cup/cone bottom I multiply the displayed speed (m/s) by 0.49 to get a flow in l/s.

    The one vent measured at the current fan speed on commissioning day read 3.5l/s normally, 8l/s on boost. With my homemade kit I now read 3.1m/s and 6.4m/s which I convert to flows 1.5l/s and 3.1l/s respectively. Considering all the vents overall flow adds up to around 10l/s each way, 20l/s in boost, not the 30l/s and 64l/s I was expecting. Seems that I need a conversion factor of 3 on my kit. Spot any errors?
    • CommentAuthorEd Davies
    • CommentTimeOct 17th 2014
     
    Given the numbers, I agree with your arithmetic.

    But according to that Amazon page the anemometer is 45 mm across so it looks like the fan is about 30 mm across. If you're only blowing a 25 mm wide airstream over it it'll underread by a factor of 1.44. Using 30 mm as the diameter (not strictly right but possibly better) I'd make the airflows 2.2 and 4.52 l/s respectively. Not quite you're original numbers but a move in the right direction, at least.

    But I'm still confused as that doesn't really correspond with sticking a 45 mm wide thing through a slot cut in the side of a 25 mm diameter tube.
    • CommentAuthorGreenfish
    • CommentTimeOct 17th 2014
     
    You may have found my mistake, thanks Ed. The anemometer is 45mm across, so is the bottom of the cup/cone. The fan opening is 25mm diameter, I have been using that as my "tube" diameter because that is the area of air that can leave the apparatus. Should I use 45mm instead? Could be that the ring thinkness is invalidating my results? The profressional anemometer had only a narrow frame, no bunted end to the cone. Thoughts?
    • CommentAuthorEd Davies
    • CommentTimeOct 17th 2014
     
    When I was thinking about this before I was looking at anemometers like this one:

    http://www.amazon.co.uk/Skywatch-Xplorer-1/dp/B00102DBB2/ref=sr_1_4?s=sports&ie=UTF8&qid=1413552515&sr=1-4

    with a fairly small fan with not much structure round it.

    Still, if you are ducting all the air through the anemometer and 25 mm is the fan diameter then I can't see what would be wrong with your original numbers except that the calibration of the device will be for the free air flow which results in a given flow through the fan within the ring - the ring will increase the flow through the fan a bit but it's difficult to say how much as in free air some air will also spill round the sides. Hence the preference for one without much of a ring.

    The other measurement method used is to time how long it takes to fill a volume, say a bin liner. Bit of a nuisance when trying to set up your MHRV but maybe useful to calibrate your anemometer.
    • CommentAuthorGotanewlife
    • CommentTimeOct 17th 2014 edited
     
    Good Lord Greenfish are we related or something!! I have just bought the same maonometer in order to balance my newly installed MVHR - a couple of days ago I even drafted a thread with the same title!! I DIY'ed my MVHR and hence I put in silencers and I used several flexible joiners too. What I also did was fit a pair of iris dampers at what I judged to be critical points - I have not played much yet but the noise out of the vents didn't seem to change at all no matter how closed the iris damper a few meters upstream was. Perhaps you can retro-fit? I have also just bought a 3m2 roll of some foam stuff bonded to a thin layer of lead (£20/m2 - owch) - a product for noise reduction of pipes (meant to add coment to the soil pipe thread) - not used yet. I am pretty sure that when I went overboard on noise insulation of the pipes as they leave the MVHR unit, there was a noticeable reduction in noise at the vents, which I imagine was caused by damping the pipes so preventing noise vibration propagating. Everything is still open/unfinished so can't do/say much more at present. Link to a few pics here:

    https://www.dropbox.com/sh/4eu3fyp49iqiug3/AAAJSlZ3QDVibqPSpxIiR8aLa?dl=0
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 17th 2014
     
    • CommentAuthorGreenfish
    • CommentTimeOct 17th 2014
     
    Happy that my homemade kit could be used to adjust vents in a balanced way, but so wanting to get some absolute values out of it I have done some experiments. I think the issue was funneling the flow through a 25mm apature. The anemometer was intended to be held in open space (measure the wind), so not sure if that has something to do with it. Anyway I took the cup off my cone and added padding around the big end to help the seal at the ceiling. Flow now collected and directed out through a 60mm circle while I hold the anemometer over the opening - some air passes around the outside of the anemometer. The speeds when converted to flows now match the comissioned day values. Hey!

    Anyone else done this witha biy of DIY kit?
    • CommentAuthorEd Davies
    • CommentTimeOct 17th 2014 edited
     
    Excellent - it's nice to know that it matches and it's also a useful lesson about the airflow spilling round the sides.

    80 mm circle would give 0.5 litres/second for each 0.1 m/s airspeed.
    113 mm circle would give 1 litre/second for each 0.1 m/s airspeed.

    Edit to add: but then your 60 mm is about right for 1 m³/hour.
  12.  
    Thanks Greenfish! However, a picture would really help!!!!! I have yet to make my cone etc so benefitting from all your hard work would be coool. Ta in anticipation

    PS - can you not access some of the shortest branches 'somewhere' in order to fit some dampers (doesn't have to be the expensive iris ones of course...)
  13.  
    Posted By: GreenfishAnyone else done this witha biy of DIY kit?


    Yes, I used the "cardboard + eBay anemometer/flow meter" method when commissioning my MVHR. After balancing the readings worked out very close to what I was expecting from the unit. I don't see the point of a calibrated instrument for a DIY install.
    • CommentAuthorGreenfish
    • CommentTimeOct 18th 2014 edited
     
    OK Gotanewlife here are some pictures. Original with cup so air only leaving through vanes - small exit 25mm seems to cause trouble. Then the upgrade no cup and air can flow around the outside of anemometer which gives good measurements. However the setup is sensitive to how far the anemometer is from the exit.
      cone02.jpg
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 18th 2014
     
  16.  
    Taeverso, I reckon my Blue Peter days will come in handy!

    Further to your original problem, on trickle (of unknown level but already dramatically improved air quality and I haven't even fitted the condensate drain yet or done any balancing) I just tried closing an exit valve and the noise level went DOWN, in other words the noise I can hear is from the fans not from air movement. It is still not too late for me to fit an attenuator in what will be our masterbedroom (204x60 format attenuator 1m or 0.5m).

    Better just do some gross subjective tests on yours before you spend ages tinkering; it may be that reducing the fan speeds a bit won't actually help much and you might need to start looking at some other strategies - is ALL of your system now inaccessible?
    • CommentAuthorGreenfish
    • CommentTimeOct 19th 2014 edited
     
    Posted By: SteamyTeaCan see why they use a hot wire meter now.
    But mine didn't cost £160!

    Posted By: GotanewlifeTaeverso, I reckon my Blue Peter days will come in handy!
    Wonderful training.

    Details that you can't see under the tape: loops of plastic top and bottom (salvaged from electric cable conduit) to stiffen the cone. Wide end has padding (5mm flooring underly) for a better seal when pushed against the ceiling. You need to take care with anemometer position to get accurate absolute values, otherwise as long as it is same each time the relative values (per vent) are ok but the calculated flow is incorrect. Good luck.

    Going to start another thread regarding noise and making the best of what I have now I can do measurements.
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 19th 2014
     
    Posted By: GreenfishBut mine didn't cost £160!
    Was just an example.


    Posted By: GreenfishGoing to start another thread regarding noise and making the best of what I have now I can do measurements.
    My android phone has a noise meter, not sure how good it is.
    In the 'olden days', twin carburettors on cars where partly set up with a stethoscope (and a vacuum gauge).
    • CommentAuthorborpin
    • CommentTimeOct 19th 2014
     
    Posted By: SteamyTeaIn the 'olden days', twin carburettors on cars where partly set up with a stethoscope (and a vacuum gauge).
    Ah, Triumph Spitfire, twin SU carbs - sitting on the wheel trying to get the %^$£ things balanced - those were the days ....
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 19th 2014
     
    I never managed too (on the MGB), did you?
  21.  
    I used a bit of tube to hear the hissing when balancing the twin Strombergs on my Imp Sport. Those where the days....
  22.  
    Ohh oh, I don't think I need a stethoscope to hear the whine of a diverging thread....
    •  
      CommentAuthordjh
    • CommentTimeOct 19th 2014
     
    Posted By: borpin
    Posted By: SteamyTeaIn the 'olden days', twin carburettors on cars where partly set up with a stethoscope (and a vacuum gauge).
    Ah, Triumph Spitfire, twin SU carbs - sitting on the wheel trying to get the %^$£ things balanced - those were the days ....

    Hmm, I remember balancing my Spit involved sitting on the wheel and a lot of driving up and down a straight bit of road but I don't remember any stethoscopes. Must have been the poor man's way.
    • CommentAuthorEd Davies
    • CommentTimeOct 19th 2014 edited
     
    Stop it.

    PS: maybe better if we just all whisperize the off-topic stuff?
    • CommentAuthorwookey
    • CommentTimeNov 23rd 2015
     
    Is the building control man going to want to actually check the airflow values at outlets, or even just check they are operating? I see talk of a the 2010 regs requiring a comissioning certificate. Is that a standard form - I've not found one yet? But can I just fill that in and give it to the BC to show due diligence?
    • CommentAuthorDarylP
    • CommentTimeNov 23rd 2015
     
    Wookey,

    The Brink kits have an 'installation confirmation' checklist at the back of the manual, detailing flow-rates at the valves.
    BC accept this.

    Cheers :smile:
    • CommentAuthorGreenfish
    • CommentTimeNov 23rd 2015
     
    Posted By: wookeyIs the building control man going to want to actually check the airflow values at outlets, or even just check they are operating? I see talk of a the 2010 regs requiring a comissioning certificate. Is that a standard form - I've not found one yet? But can I just fill that in and give it to the BC to show due diligence?


    Still not had BC sign off, but probably not the slowest completion ever :)

    When I first spoke to BC about this it was a grey area. He wanted it tested and certified by a competent person, but could not tell me what qualified as "competent". My plumber, that did the install (his first and so far only MVHR), hired a calibrated and certified anemometer, balanced the system and completed the paperwork proforma that came with it. That is my certificate that I will eventually show to BC.

    In effect it turns the points in Part F into a checksheet, and he signed as a competent tradesman. I hope the BC will be happy!

    I have found a comparable commissioning certificate online here

    https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&ved=0ahUKEwiOz6eDrabJAhULshQKHbY-B24QFgheMAw&url=ftp%3A%2F%2Fhost213-123-201-144.in-addr.btopenworld.com%2FPROJECTS%2FScoble%2520Farm%2FMowbray%2FNHBC%2FCommissioning%2520Certificate%2520MVHR.pdf&usg=AFQjCNEgcyk8c-S7bqEUBZc92Jzc2frBIA&cad=rja

    So I am assuming that what I have is standard. Hope that helps.
    •  
      CommentAuthordjh
    • CommentTimeNov 23rd 2015
     
    Posted By: wookeyI see talk of a the 2010 regs requiring a comissioning certificate. Is that a standard form - I've not found one yet?

    The form is apparently section 5 of the Domestic Ventilation Compliance Guide 2010 which is available online.
    • CommentAuthorwookey
    • CommentTimeNov 25th 2015
     
    Aha. cheers for tracking that down djh.

    Greenfish - how long ago did you start? I'm coming up to 4 years soon I think, which is moderately slow for a 1-room extension and garage reroofing. The BC seems to to have given up sending reminders this year.
    • CommentAuthorGreenfish
    • CommentTimeNov 25th 2015
     
    Posted By: wookeyGreenfish - how long ago did you start? I'm coming up to 4 years soon I think, which is moderately slow for a 1-room extension and garage reroofing. The BC seems to to have given up sending reminders this year.


    Previous site owner "broke ground" 3 years ago just in time to meet pp, and created a muddy hole. Construction of new house started seriously March 2013, we were weather tight by Oct, the builders left site April 2014 (plastering was done by Feb) leaving us to "finish off". Saving money doing things like decoration, skirting, flooring, tiling etc. was fine, but it is slow. Some major landscaping was needed, had help with that in Aug 2014 (no more clay pile!). But the time just flown while we faff around with built in furnature etc., and other life issues get in the way. We are here most of the time now, but many of our belongings and furnature are still in the old house, got too used to living without them and are moving in slow motion. If we got our act together we could complete, all the main certificates (air test, HETAS etc.) are in place. But then we have decided to have an ASHP installed, and might was well get it zero VAT. BC did email a year ago, so hope they are still waiting.

1 to 30 of 33

  1. <
  2. 1
  3. 2
  4. >
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press