MVHR DiY install?

[gc100]

Hi,

 

Probably a dumb question but can I install the MVHR rather than using an installer? I know building control want details of the MVHR being used but does that mean I need to use an official installer?

 

I'm looking at a quote of £8,744 + VAT from the installer:

1 x Zehnder ComfoAir Q 350- MVHR unit

2 x ComfoWell Manifolds (including sound attenuators)

Radial Pipework – Zehnder ComfoTube (smooth interior)

12 x Standard – Supply/Extract Lindab Airy Vents (round/metallic/white)

2 x External Wall Grilles Controllers – ComfoSense C67 remote display

Labour & Commissioning

 

From a rough online search the materials cost about £3000! unless I'm horribly mistaken but I don't think so. That leaves £5700 for the 'install and commissioning'

 

Is there any reason I could not do it, or the builder for that matter?

 

 

[Jeremy Harris]

Yes, several here have done DIY install and commissioning.  Not a difficult job, but the commissioning and balancing is a bit tedious.  Better to DIY simple and tedious stuff, IMHO, rather than pay someone a lot of cash.

 

I probably spent around three or four days on the MVHR installation and commissioning.

[gc100]

Thanks @JSHarris. What exactly is involved in the commissioning and balancing? Where could I go to find detailed information about this?

 

I've have a further requirement that I want to install an A/C unit and reuse the same ducts if possible and there is no installers my part of the country who have any experience or can do it.

[dnb]

19 minutes ago, gc100 said:

I want to install an A/C unit and reuse the same ducts

I am aiming to do much the same. I have located very few people with any experience of this at all. It would be interesting to compare notes.

 

My A/C supplier can see nothing wrong with the approach, believes it will become more common in the future, and will supply me all the bits and commission the bits I can't do, but will not underwrite my system design.

[Jeremy Harris]

Commissioning is mainly getting the system balanced.  There are a couple of airflow meters in the forum tool loan scheme for doing the flow measurement at each terminal.  The process is a bit iterative, but really just needs patience, going around every ceiling terminal, measuring the flow rate and then adjusting it up and down to get the required extract rates from specified rooms (kitchen, bathroom, WC, utility, as in building regs), making sure the sum of the fresh air supply equals the sum of the extracts and also that the total background ventilation rate meets the figure in building regs.

 

Forget about trying to run air conditioning via MVHR, the flow rate is way too low to make any useful difference. We have an MVHR that cools the air, but it's not very effective in warm weather at all.

[gc100]

4 minutes ago, dnb said:

I am aiming to do much the same. I have located very few people with any experience of this at all. It would be interesting to compare notes.

 

My A/C supplier can see nothing wrong with the approach, believes it will become more common in the future, and will supply me all the bits and commission the bits I can't do, but will not underwrite my system design.

 

Ah let me know how you get on, I'm only just looking into this aspect - I need to find a local A/C supplier who is willing to work with me on this.

[gc100]

3 minutes ago, JSHarris said:

Commissioning is mainly getting the system balanced.  There are a couple of airflow meters in the forum tool loan scheme for doing the flow measurement at each terminal.  The process is a bit iterative, but really just needs patience, going around every ceiling terminal, measuring the flow rate and then adjusting it up and down to get the required extract rates from specified rooms (kitchen, bathroom, WC, utility, as in building regs), making sure the sum of the fresh air supply equals the sum of the extracts and also that the total background ventilation rate meets the figure in building regs.

 

Thanks. How do you adjust the flow rates? Is this done in the plenums? Whats the difference between 'total background ventilation rate' vs ' total airflow in/out?

[dnb]

Approved document F (a riviting bedtime read) containst the details of exactly how much ventilation is required and defines the terms.

 

Remember that the A/C is recirculating the air within the house, and the MVHR is exchanging it with air from outside. So it's not a case of dual purposing all ducts. Some will only be required for one job. I will turn my house plan document into a simplified schematic (it's difficult to follow over 3 floors) to illustrate what I mean.  There are some games to be played with summer bypass on the MVHR too.

 

I should say my plan involves a Mitsubishi Electric 5kW ducted A/C unit and an MVHR unit.

Edited August 22, 2019 by dnb

[Jeremy Harris]

Just now, gc100 said:

 

Thanks. How do you adjust the flow rates? Is this done in the plenums? Whats the difference between 'total background ventilation rate' vs ' total airflow in/out?

 

 

Adjustment depends on the parts chosen.  Ours uses throttle plates fitted in the distribution plenums to throttle down each duct, other systems may use adjustable ceiling terminals.  Adjustable ceiling terminals may possibly be slightly noisier, as the flow velocity ends up increasing, but they are a lot easier to adjust.  The throttle plates are a PITA to adjust, but in theory reduce flow noise, because the local velocity increase they create is in the plenum chamber, so well away from the rooms.

 

The total background rate often dominates, and is the rate that the system needs to deliver when on its normal setting.  The total airflow in and out should be equal and can either be the background rate or any other setting.  In addition, the system needs to be able to achieve the required extract rates for the kitchen, bathrooms, WC and utility room.  Often this rate may be met in background ventilation mode.

[dnb]

1 minute ago, JSHarris said:

The total background rate often dominates

Yep. If I strictly followed ADF I would turn the MVHR down to achieve the purge rate!

[mvincentd]

August 2017 I was quoted £4750 for design & supply of Comfoair q350 based system + £350 to commission ( I believe the designing element represented £350).  My ducting system is a bit different so i'd think you probably can just go out and buy your materials for £3000ish.

The Comfocool system was quoted at £9500...it not only required the addition of the Comfocool unit but also using all pre-insulated ducting and using the larger q600 mvhr.....for the sake of some not particularly effective cooling.

I installed it all myself and am currently running it 'uncommissioned'....i'm expecting to fork out the £350 commissioning fee just to buy off the feeling that I might not have set it up to get the best out of it, but if you're not at all bamboozled by this document then I reckon you can do it all yourself.

ComfoAir_Q_2018_(merged).pdf

[MikeSharp01]

9 hours ago, JSHarris said:

Forget about trying to run air conditioning via MVHR, the flow rate is way too low to make any useful difference.

A few days back I dimly recall you discussing taking a chilled water feed from your ASHP to provide upstairs summer cooling via the MVHR just to push the upstairs temp down a little on the hottest days. So not full AC but a contribution to cooling would you recommend this where you have a reversible ASHP.

[Jeremy Harris]

Just now, MikeSharp01 said:

A few days back I dimly recall you discussing taking a chilled water feed from your ASHP to provide upstairs summer cooling via the MVHR just to push the upstairs temp down a little on the hottest days. So not full AC but a contribution to cooling would you recommend this where you have a reversible ASHP.

 

 

Yes, I did, but ideally not using the MVHR, but using separate fan coil units.  The snags with using the MVHR are that the air flow rate is low, so not much heat can be moved, and it is always cooling warm air from outside in hot weather, whereas it's more efficient to just recirculate partially cooled air from inside for cooling. 

 

I do wish that I'd run pipes from the downstairs UFH up to the bedrooms, along with condensate drains, as I could then have fitted a couple of fan coil units that could cool the bedrooms down, in much the same way as the split air con I recently fitted (that also recirculates air).

[Gone West]

11 hours ago, gc100 said:

Is there any reason I could not do it, or the builder for that matter?

It's pretty straightforward. My blog has details of how we installed our MVHR and commissioned it.

[gc100]

So just to be clear : does the 'commissioning' need to be signed of by any 3rd party?

[Jeremy Harris]

1 minute ago, gc100 said:

So just to be clear : does the 'commissioning' need to be signed of by any 3rd party?

 

No, there's no need for any third party involvement.  I wrote a brief report covering it for building control, but frankly they weren't interested in it at all, so I think I may as well not have bothered.

[gc100]

12 hours ago, dnb said:

Approved document F (a riviting bedtime read) containst the details of exactly how much ventilation is required and defines the terms.

 

Remember that the A/C is recirculating the air within the house, and the MVHR is exchanging it with air from outside. So it's not a case of dual purposing all ducts. Some will only be required for one job. I will turn my house plan document into a simplified schematic (it's difficult to follow over 3 floors) to illustrate what I mean.  There are some games to be played with summer bypass on the MVHR too.

 

I should say my plan involves a Mitsubishi Electric 5kW ducted A/C unit and an MVHR unit.

 

Hi @dnb,

 

Where would I find Approved document F please? 

 

I did read with interest your thread here and was looking at your design - is this the final one? It seems you are 'pushing' (for want of a better word) cooled air from the A/C into the hallway and then also the central plenum for distribution. The return to the A/C seems to be coming from the MVHR and the plenum  - can you run the MVHR at the same time or will there be too much draw for the MVHR, or will the draw just be reversed from the plenum?

 

My house is a simple single story design

 

 

 

The central corridor will have a false ceiling whereby I'm planning to run all the MVHR ducts to the rooms. Im actually planning to put the MVHR in the garage and not the boot room as shown just to save some space.

 

 

 

 

 

[Jeremy Harris]

6 minutes ago, gc100 said:

Where would I find Approved document F please? 

 

 

https://www.gov.uk/government/publications/ventilation-approved-document-f

[joth]

The garage would not normally be recommended place for the MVHR as it's outside the thermal envelope: it works more efficiently to have it inside the envelope. 

[joth]

13 hours ago, gc100 said:

That leaves £5700 for the 'install and commissioning'

 

Fwiw I'd first look into doing the install DIY as that's the bulk of the cost and very easy to learn to do, then get in someone experienced to commission it. Green building store  recommend this approach (saying DIY install is often better than paying e.g. a builder to do it, as generally the DIYer will take their time and follow the design more accurately)

There's certainly an argument for learning to do the commissioning so you can maintain and adjust it if needed in future too, but for for a few hundred pounds I'd prefer to know it was at least initially all running correctly.

 

 

[gc100]

Yes makes sense indeed thanks. I suspect finding someone willing to commission/check it over as its just the installers who do this so can't see them being motivated. However I think I'll have to end up doing it, as the labour rate is just too crazy. 

 

If only I could do the same for the ASHP!!

Edited August 23, 2019 by gc100

[joth]

On a sample of 2, Green building store and Enhabit were both very happy to quote for design, supply and commissioning. Neither seemed particularly interested in doing the install work.

If you have a radial topology the install is very simple. However looking at you linear layout a trunk and branch might be more efficient. Still not terribly complex to install from what GBS said. 

[Jeremy Harris]

26 minutes ago, joth said:

 

Fwiw I'd first look into doing the install DIY as that's the bulk of the cost and very easy to learn to do, then get in someone experienced to commission it. Green building store  recommend this approach (saying DIY install is often better than paying e.g. a builder to do it, as generally the DIYer will take their time and follow the design more accurately)

There's certainly an argument for learning to do the commissioning so you can maintain and adjust it if needed in future too, but for for a few hundred pounds I'd prefer to know it was at least initially all running correctly.

 

 

 

That assumes that a "professional" undertaking system commissioning would actually do a competent job.  I doubt that would be the case, TBH.  Commissioning is pretty easy, but a bit tedious, and from the limited evidence I've seen of badly setup MVHR systems I really doubt whether many are set up properly.  At least if you do it yourself (not at all hard; easier than the installation work) then you can be confident that it's working properly.

 

As an example, take a look at this thread, where @lizzie had problems with her MVHR being very badly commissioned initially:

 

 

[Bitpipe]

1 hour ago, gc100 said:

Yes makes sense indeed thanks. I suspect finding someone willing to commission/check it over as its just the installers who do this so can't see them being motivated. However I think I'll have to end up doing it, as the labour rate is just too crazy. 

 

If only I could do the same for the ASHP!!

 

Let's be clear - your building inspector will look for a bit of paper that says the MVHR installation is compliant with Part F.

 

This paper can be complete fiction or the result of a highly skilled calibration exercise - it does not need to be issued by a professional / qualified person. BC will never check that its correct (doing so would be impractical anyway).

 

Now, as the inhabitant of the house you have a legitimate concern that the system is working properly.

 

You can either pay someone to do this or do it yourself - depends what you think your time is worth.

 

If you go as far as installing the system yourself then this last step is pretty trivial - commissioning sounds complicated but essentially it means turning it on and balancing the intake / extract airflow at plenums plus setting the fan speed at the unit to deliver the min / boost airflow.

 

Now, I installed my system DIY and it was almost 2 years later when I bothered to check that it was balanced (needed to create that bit of paper for the BCO). 

 

So I borrowed the measuring tool from the forum, read the posts that explained what to do, ran around and took measurements, tweaked plenums and fan speeds, measured again and satisfied myself that it was good enough - wrote it all down and gave bit of paper to BCO who never mentioned it again. A few hours work including tea breaks.

 

TBH - there was no noticeable difference at all before and after (even the measurements were only 15% or so out initially) so how you could ever tell that a paid installer had really done their job correctly is beyond me. Airflow from MVHR is very low by design.

 

What's more important with a MVHR system is regular cleaning and replacement of the filters - put reminders in your calendar as it's easily forgotten once you're busy with normal life again

[Gone West]

44 minutes ago, Bitpipe said:

Let's be clear - your building inspector will look for a bit of paper that says the MVHR installation is compliant with Part F.

That wasn't the case for me. I had all the results ready to show him for building regs. compliance and he wasn't interested. So after setting it all up for SAP, which he wasn't interested in, I set it up again for PH rates which it's been running at for eighteen months without problems.