Balancing MVHR system

[ADLIan]

Apologies - got my Guides mixed up. It was the Domestic Building Services Guide that was updated in 2013 not the Ventilation Guide (still at 2010 version)

[Jeremy Harris]

@JamieM, attached is the report I drew up, but it's worth noting that it doesn't follow what's in the guidance note, as at the time that I wrote it up I hadn't found the guidance (it wasn't easy to find at that time as it is now).  BC accepted it without any questions; I got the feeling that they just ticked a box that it had been done without looking at it closely..................

Mechanical Ventilation and Heat Recovery system Test Report.pdf

[DundeeDancer]

I'm looking to have a MVHR system installed into my apartment and I have drawn up my own design but I have no idea if it really would be a balanced system and what really makes it balanced.  Wondering who and how much a MVHR designer would charge to take my design and prove it works or show the weak points/failings.  I take it these designers have air flow modelling systems that should show up system flaws?  Any recommendations on a designers to use most welcome.

 

Thanks, DD.

 

 

[JamieM]

i went with BPC (as did many on here) and gave them my plans and they drew up the ducting plan for me and gave me a price for the parts required-> MHRV unit, ducting etc.  They calculated the flow rate for supply or extract needed for each room. it needs balanced (as far as i am aware) so the total supply matched the total extact.  i think the exast and intake ducts that enter/exit your property need to be at least a certain distance apart (maybe 1.5m but i'd need to check) and preferable on the same side of the building (unlike yours in your sketch). i think if they are on different sides the wind can affect it.

 

BPC didnt charge for the plan they gave me. (wouild highly recommend them as a company)

[DundeeDancer]

Yes I've already been in contact with BPC and they gave me a price for 2 different MVHR units and some prices for ducting.  No plan though, I'll give them a nudge maybe they were going through a busy period. The Paul supplier in Rosyth is also catching my eye https://www.paulheatrecovery.co.uk/ will see if they can propose anything as well hopefully at reasonable designer fees.

[Jeremy Harris]

The plan is easy to draw up, but any system will need to be checked to ensure the flow rates as-installed are both sensible and meet the requirements.  As an example, I calculated the resistance of every length of ducting, bend and fitting in our system, to ensure that the Part F requirements would be met.  When I measured the actual flow rates they were barking mad, massively exceeding the Part F requirements in some rooms, and overall the system was way out of balance in terms of the extract matching the fresh air feed.

 

No designer of any radial duct system is going to be able to calculate the flow rates to the degree needed to make the system perform at its best, all anyone can do is make sure that it is designed so that there is little or no risk of the key flow rates for Part F (the extract rooms and the whole house ventilation rate) being lower than the requirements after installation.

 

I tried hard to make sure that I had an equal flow resistance on both the extract side and the fresh air feed side, by detailed calculation, but then found that the installation screwed up all the theoretical calculations.  This wasn't because I deviated from the plan, it was just because small variations in curvature in semi-rigid ducting have a disproportionately large impact on resistance.  This is largely down to the relatively small diameter of semi-rigid ducting, with larger diameter rigid ducting, with known radius fixed bends, you can calculate the flow rates far more accurately.

 

Frankly you can design a semi-rigid system very well using some simple rules of thumb; what I did by doing a lot of detailed calculations was a total waste of time and effort.  What's worse, I should have realised that there would be a large disparity between theory and practice, as it was blindingly obvious after the event..................

[vfrdave]

On 7/20/2017 at 11:06, JamieM said:

i went with BPC (as did many on here) and gave them my plans and they drew up the ducting plan for me and gave me a price for the parts required-> MHRV unit, ducting etc.  They calculated the flow rate for supply or extract needed for each room. it needs balanced (as far as i am aware) so the total supply matched the total extact.  i think the exast and intake ducts that enter/exit your property need to be at least a certain distance apart (maybe 1.5m but i'd need to check) and preferable on the same side of the building (unlike yours in your sketch). i think if they are on different sides the wind can affect it.

 

BPC didnt charge for the plan they gave me. (wouild highly recommend them as a company)

Hi @JamieM did you install the system yourself?

[JamieM]

17 minutes ago, vfrdave said:

Hi @JamieM did you install the system yourself?

yes, me and my woman did it.

 

still need to adjust the flow rates but waiting for the plumber and spark to connect the drain and electricity before i can do that. (trying to get them to do it this week)