MVHR newbie.. help needed

[Savage87]

Hello everyone, I'm Alex, I moved in to my victorian mid terrace 7 years ago and I have been gradually been refurbishing it over the years and now I'm at the last stage doing the kitchen up. Most of the work has been done by myself apart from the plastering, which I have tried but it's not for me

 

I'm looking to get a MHVR unit into the loft and use a radial ducting system throughout the house. This forum has helped a lot, I've been reading loads of topics but I still have a couple of questions that I don't have ansers to.

 

I had a couple of quotes in for the unit but I'm leaning towards the Domus HRXE (possibly the HRXE-H), I can really afford to spend more than 1000 pounds for the unit and this would be under budget. If someone has a better idea, I am listening.

https://www.domusventilation.co.uk/ventilation-solutions/fan-range/mechanical-ventilation-heat-recovery-mvhr/hrxe

 

I have looked at several units to see the fan settings/speeds/flow rate so I can choose wisely but I don't really understand how to read these charts. I calculated that I need a minimum extract of 52.5m3/h (48m3*0.3*3.6).

Would this be enough for setting 3, 13.5l/s extract?

Does the volume flow rate reffers to only extract or both supply and extract combined?

What are the Pascals all about?

 

Floor area = 90sqm total of which ground floor is 44sqm and first floor 46sqm

Extract volume = 48.64m3 (kitchen/bathroom/toilet/under stairs cupboard)

Supply volume = 125.72m2 (living+3bedrooms)

 

When it comes to the ductwork, I'm been told that a rigid system is better, but the semirigid works as well.

Currently looking at the Airflow Pro semi rigid system. What do you guys this, is this ok?

 

My wife has only one requirement, that the system is quiet.

My understanding is that once you increase the air velocity above 2.5m/s that's when it starts to get noisy.

I was looking at the charts for the 75mm duct https://www.ribaproductselector.com/Docs/9/00139/external/COL285316.pdf on page 4 and it shows that 2.5m/s air velocity it can carry 28m3/h at 2.2Pa/m resistance. The longest pipe lenght that I need to fit is 9m.

The extract for the kitchen needs flow rate of 28m3/h based on the volume of the room and I'm a bit worried, would I need to run 2 ducts to the kitchen?

Does anyone know what is the maximum lenght of pipe that I can fit before I get into trouble?

 

Enough question for now.

I've attached my floor plan.

Any help is much appreciated!

This is a DIY project, the same as the rest of the house

 

 

[PeterW]

Welcome 

 

if you don’t have to hit building Regs / SAP then have a look at these systems from Boulder 
 

https://www.ventilationmegastore.co.uk/product/dhv-25n-unit/

 

@Nickfromwales used to have a couple of contacts I think there

[Nickfromwales]

7 hours ago, PeterW said:

Welcome 

 

if you don’t have to hit building Regs / SAP then have a look at these systems from Boulder 
 

https://www.ventilationmegastore.co.uk/product/dhv-25n-unit/

 

@Nickfromwales used to have a couple of contacts I think there

Yup. Speak to Byron.

Just beware asking for designs as a member here had less than good results when they designed their UFH layout. 
They may have their ducks in a row now though as that was a while back. 
I used to buy all my UFH pipe and consumables from them, quite competitive. 

[jfb]

2 pipes to kitchen.

Make sure you have a sound attenuator on the supply side before the manifold. Easy to build yourself with some OSB and rockwool RWA45 (or something similar) or buy.

Noise comes from the machine itself and through the ducting (loudest).

[Jeremy Harris]

I'd be inclined to consider fitting silencers on both the room supply and room extract sides, close to the MVHR unit, as we found that we had significant noise coming into our utility room and downstairs WC from the fairly short duct runs between those rooms and the plenum chamber.

 

I know that one well-known supplier only chooses to supply a single silencer for the room supply side, but I'm not convinced that's the best option.  Some MVHR units are significantly noisier than others, too, so it's well worth looking at the specs and considering where you'll fit the thing.  Longer duct runs tend to attenuate duct noise, but you can then get flow noise if the ducts aren't sized correctly (if opting to use a radial duct system then you might possibly need double duct runs to some terminals).

 

Definitely a good idea to look at where to fit silencers during the initial installation.  I didn't, and ended up making silencers out of OSB and acoustic foam, that were a custom shape to fit in the restricted spaces I had left.  With hindsight, I could have made room for ready made silencers just by positioning some of the ducts differently, but this was near-impossible to do after second fix.

[vivienz]

Be cautious about where in the loft you put the unit. Ours is in our loft space, directly above the en suite to our bedroom and even on a low flow speed it sounds like a ship's engine. Additional sound proofing may have made a difference but our contractor didn't finish the job so I will see if we can get it done as a retrofit and report back with any improvements.  Much of the noise from ours is from the MVHR unit itself rather than the ducts and vents - these are compratively quiet.

[Jeremy Harris]

28 minutes ago, vivienz said:

Be cautious about where in the loft you put the unit. Ours is in our loft space, directly above the en suite to our bedroom and even on a low flow speed it sounds like a ship's engine. Additional sound proofing may have made a difference but our contractor didn't finish the job so I will see if we can get it done as a retrofit and report back with any improvements.  Much of the noise from ours is from the MVHR unit itself rather than the ducts and vents - these are compratively quiet.

 

 

Good point, but as I mentioned above, it's also worth looking carefully at the specification of the MVHR, especially for the larger sized units.  Some can be a great deal noisier than others.  In some cases, where the location pretty much has to be above a habitable room, it maybe worth paying a bit more to get a quieter unit. 

 

For example, a unit that's 3dB noisier than another will be twice as noisy, as each 3dB is a doubling in noise level, something that may not be obvious when looking at the spec.  The bottom line is that you often get what you pay for in terms of both noise and efficiency.

[jfb]

1 hour ago, JSHarris said:

For example, a unit that's 3dB noisier than another will be twice as noisy, as each 3dB is a doubling in noise level, something that may not be obvious when looking at the spec.

is that right? Seems a bit small an increase. I thought it was nearer 6-10db to double perceived volume.

[Jeremy Harris]

5 minutes ago, jfb said:

is that right? Seems a bit small an increase. I thought it was nearer 6-10db to double perceived volume.

 

 

Yes: https://pulsarinstruments.com/en/post/understanding-3db-rule

 

It's why people will often agree to save some money by, say, getting a 30dB MVHR over a 27dB MVHR, without realising that the 30dB one is twice as noisy.

[jack]

18 minutes ago, JSHarris said:

Yes: https://pulsarinstruments.com/en/post/understanding-3db-rule

 

It's why people will often agree to save some money by, say, getting a 30dB MVHR over a 27dB MVHR, without realising that the 30dB one is twice as noisy.

 

1 hour ago, JSHarris said:

For example, a unit that's 3dB noisier than another will be twice as noisy, as each 3dB is a doubling in noise level, something that may not be obvious when looking at the spec.  The bottom line is that you often get what you pay for in terms of both noise and efficiency.

 

3dB is a doubling in the amount of energy, but the difference in perceived volume will not be anything like double. Most people can barely perceive a 3dB change in an ordinary setting.

 

@jfb is right. Doubling of perceived volume takes a roughly 10dB increase (depends on the type of noise and other factors).

[Jeremy Harris]

35 minutes ago, jack said:

 

 

3dB is a doubling in the amount of energy, but the difference in perceived volume will not be anything like double. Most people can barely perceive a 3dB change in an ordinary setting.

 

@jfb is right. Doubling of perceived volume takes a roughly 10dB increase (depends on the type of noise and other factors).

 

 

Depends a very great deal on perception and sound energy level, though.  At very low noise levels, like in a bedroom at night, then our hearing tends to be far more sensitive to small changes in sound energy than it does for loud noises.  I can certainly very easily  hear a 1dB difference at levels down around 30dB(A), but I can't really hear a 1dB difference up around 70 to 80dB(A) at all (I struggle to hear a 2 or 3dB change at around 80dB(A).

 

As most people can detect a 1dB level change at low levels fairly easily, I'd suggest that, for MVHR, aiming to get a unit that's a few dB quieter than another, if it's going to be located in a noise-sensitive area, like above a bedroom, would still be a very worthwhile thing to aim for.  There's nothing worse than deciding to save a few pounds by opting for what seems, on paper, to be a slightly noisier unit, only to later find that the noise level is higher than expected. 

 

When we were looking around, it seemed that some of the Brink units were amongst the quietest.  Not cheap, but probably worth the additional cost if noise was a potential concern for the best location for the unit.  I opted to locate the MVHR at first floor level, tucked away in a reasonably well soundproofed room (I lined it with acoustic foam, a bit like a studio), as I knew that the unit we'd chosen was likely to be a bit more noisy than some that are available.

[SteamyTea]

14 hours ago, Savage87 said:

Does the volume flow rate reffers to only extract or both supply and extract combined?

What are the Pascals all about?

That chart has me confused too, and judging by the replies, no one else wants to take it on.

Possibly best asking the manufacturer/supplier to tell you what it is about.

[joth]

Regardless of perceived noise levels, measuring noise and comparing figures across manufacturers looks like another can of worms (reminds me of comparing bike lights -- every manufacturer claims brighter AND longer battery life than everyone else).

 

e.g. taking some well regarded, comparable models:

Zehnder Q350 https://www.zehnder.co.uk/download/19868/118402/en_uk-42893_0.pdf

Brink 300 https://irp-cdn.multiscreensite.com/404d9e8c/files/uploaded/Renovent Excellent 300(Plus) Technical Sheet BrinkHRV.pdf

 

Zehnder claims 16 dbA vs 30 dbA for the Brink, on their respective lowest speeds (150 m3/h vs 90). So to the novice that means  on lowest setting, the Brink is 2^((30-16)/3), or 25 times louder?

This is most likely because Zehnder measure at 3m distance but Brink don't state what distance.  I have to admit, like with ASHP, I've thus far not really analysed any of this in detail and just relied on picking a major brand manufacturer that states they have the the quietest model so probably comparably good to next one.

 

[Ed Davies]

14 hours ago, Savage87 said:

 

Isn't this table mixing up air change rates needed for normal background operation (around 0.4 ac/h) and the boost conditions needed in the “wet” rooms which will also only need around 0.4 ac/h most of the time?

 

Depending on whether the system goes to boost if somebody gets up in the night the sound levels when on boost are much less important than for normal operation.

[Jeremy Harris]

1 hour ago, joth said:

Regardless of perceived noise levels, measuring noise and comparing figures across manufacturers looks like another can of worms (reminds me of comparing bike lights -- every manufacturer claims brighter AND longer battery life than everyone else).

 

e.g. taking some well regarded, comparable models:

Zehnder Q350 https://www.zehnder.co.uk/download/19868/118402/en_uk-42893_0.pdf

Brink 300 https://irp-cdn.multiscreensite.com/404d9e8c/files/uploaded/Renovent Excellent 300(Plus) Technical Sheet BrinkHRV.pdf

 

Zehnder claims 16 dbA vs 30 dbA for the Brink, on their respective lowest speeds (150 m3/h vs 90). So to the novice that means  on lowest setting, the Brink is 2^((30-16)/3), or 25 times louder?

This is most likely because Zehnder measure at 3m distance but Brink don't state what distance.  I have to admit, like with ASHP, I've thus far not really analysed any of this in detail and just relied on picking a major brand manufacturer that states they have the the quietest model so probably comparably good to next one.

 

 

 

Sadly I think you're right, in that it seems that manufacturers don't make it easy to compare noise levels realistically.  We did go and see two or three houses with MVHR fitted, and this gave us a fairly good feel for how noisy different units were, at least in that particular installation. 

 

The quietest one we heard was a Brink, fitted in a top half of a hot press.  It was noticeably a lot quieter than other units when stood next to it.  The noisiest one we heard was a Paul, although that was mounted in a larger space, so it may well be that the sound level from it wasn't that much higher, but just seemed to be, as it was less enclosed.

 

My daftest decision was knowing that the combined MVHR and heat pump unit we'd chosen was a bit noisy, choosing (sensibly) to mount it on a vibration isolators (well, they are Mini exhaust mounting bobbins...) but then choosing not to fit silencers initially.  From when we were looking around it was clear that most of the MVHR units that included a heat pump were noisier than those without, which isn't really a problem if the unit is mounted somewhere where the noise isn't going to be a problem.  I'd definitely not want our Genvex mounted in the loft space above a habitable room, though it's fine tucked away at the back of our services room (or at least, it's fine now that I've fitted silencers).

[joth]

21 minutes ago, JSHarris said:

Sadly I think you're right, in that it seems that manufacturers don't make it easy to compare noise levels realistically

Perhaps partially answering my own question, for Passivhaus certified components the PHI database provides numbers that seem more comparable (presumably measured through a common protocol)

https://database.passivehouse.com/en/components/list/ventilation_small

 

This puts just 4 dB between those units I listed although it looks like the Brink Flair 325 if the newer/better comparison, 1.5 dB quieter than the Zehnder 

 

Edited October 23, 2019 by joth

[Nickfromwales]

3 hours ago, JSHarris said:

 

 

Good point, but as I mentioned above, it's also worth looking carefully at the specification of the MVHR, especially for the larger sized units.  Some can be a great deal noisier than others.  In some cases, where the location pretty much has to be above a habitable room, it maybe worth paying a bit more to get a quieter unit. 

 

For example, a unit that's 3dB noisier than another will be twice as noisy, as each 3dB is a doubling in noise level, something that may not be obvious when looking at the spec.  The bottom line is that you often get what you pay for in terms of both noise and efficiency.

Indeed. 
I recall some time ago having a conversation with a client where she baulked at paying the higher amount for a PH certified heat & cool MVHR unit ( sub 30db ) and staying “I’m not  paying that it’s unjustifiable. I’ll have the cheaper unit and put up with it” so exactly the case of “you get what you pay for”.

Can’t have a champagne job on lemonade money, sorry.  ?

 

Probably good to note here that retrospectively ‘silencing’ a cheap MVHR unit with bolt-on silencers is nonsense, as that does nothing to attenuate the noise from the MVHR unit itself. That only reduces audibility at the supply and extract terminals, so if the audibility at the terminals is acceptable then you’re stuck with the decision to purchase a cheaper / noisier unit.

Also;
It’s easy to tell if your MVHR installer has fitted the required ( primary ) silencer. It’s usually a large silver foil flexible section coming off the MVHR unit ‘fresh’ aka ‘supply’ outlet off the unit. They are lined with a fluffy material that immediately absorbs sound and stops it getting to the rooms as nuisance ‘noise’. If you have one of those, then you have a technically complete installation. Buying other bolt-ons at that stage will be utterly pointless. 

[Nickfromwales]

1 hour ago, JSHarris said:

The quietest one we heard was a Brink, fitted in a top half of a hot press.  It was noticeably a lot quieter than other units when stood next to it.  The noisiest one we heard was a Paul, although that was mounted in a larger space, so it may well be that the sound level from it wasn't that much higher, but just seemed to be, as it was less enclosed.

I only fit Brink now, excellent products. I can heartily recommend CVC ventilation for supply of the Brink stuff. They have their own in house PH certified specialist and their design services are spot on.

[vivienz]

2 hours ago, JSHarris said:

My daftest decision was knowing that the combined MVHR and heat pump unit we'd chosen was a bit noisy, choosing (sensibly) to mount it on a vibration isolators (well, they are Mini exhaust mounting bobbins...) but then choosing not to fit silencers initially.  From when we were looking around it was clear that most of the MVHR units that included a heat pump were noisier than those without, which isn't really a problem if the unit is mounted somewhere where the noise isn't going to be a problem.  I'd definitely not want our Genvex mounted in the loft space above a habitable room, though it's fine tucked away at the back of our services room (or at least, it's fine now that I've fitted silencers).

 

I think that this is the problem we have. I agreed to have the unit fitted into the loft space with the assurances that it would have anti-vibration installed and be as acoustically isolated as possible but this was never done. Hopefully a retro- fit will help reduce the vibration to some degree.

[Jeremy Harris]

16 minutes ago, vivienz said:

 

I think that this is the problem we have. I agreed to have the unit fitted into the loft space with the assurances that it would have anti-vibration installed and be as acoustically isolated as possible but this was never done. Hopefully a retro- fit will help reduce the vibration to some degree.

 

 

Depends really on how the noise is being transmitted.  Some units are just inherently much noisier than others, and anti-vibration mounts may well make little or no difference, they may even make things worse if the noise comes from the case itself, by allowing it to resonate a bit.

 

If the sound is coming from the case of the unit, which was what seemed to be the source with one of those we looked at years ago (pretty sure it was a Paul unit), then the only real fix is either to change it for a quieter unit or, perhaps, try and fit some acoustic insulation around it.  There's no guarantee that fitting additional acoustic insulation around will get the noise level down to an acceptable level, though, especially if the unit is just inherently noisy, as some can be.  I lined our services room with acoustic foam, in a bid to reduce the sound level, and that does seem to help a bit, in that it seems to absorb a fair bit of the sound coming from the MVHR, but it doesn't exactly make the unit silent. 

[vivienz]

Thanks, Jeremy. I will need to look at the potential solutions that can be fitted, but in due course as we are decirating our old house right now to get it on the market. Hopefully, I can find something that will improve matters and bring it up to the promised standard. Another one for the snagging list for the new place!

[Jeremy Harris]

24 minutes ago, vivienz said:

Thanks, Jeremy. I will need to look at the potential solutions that can be fitted, but in due course as we are decirating our old house right now to get it on the market. Hopefully, I can find something that will improve matters and bring it up to the promised standard. Another one for the snagging list for the new place!

 

 

Might be worth checking to make sure that the MVHR is actually OK and to spec as far as noise goes.  I remember reading somewhere (may have been on Ebuild years ago) of someone that had a problem with noise from an MVHR that was due to a faulty fan, or maybe fan bearing.  Noise from something like that might well be worse when the unit's running at a higher fan speed, so that may be something to check. 

 

Although the manufacturers can be a bit creative when it comes to things like sound levels, our Genvex is at the noisy end of the spectrum for these things, as this excerpt from the manual shows:

 

 

The key figures here are the ones that cannot easily be silenced, the left column that gives the sound level 1m in front of the unit.  The duct noise is really neither here nor there, as the silencers will remove most of that.  Even with silencers and additional insulation I would still very definitely not want to have a unit like this in a loft space above a bedroom! 

 

As a guide, you don't want anything louder than about 30dB(A) in a noise-sensitive location.  If the choice of location is limited, then it's best to choose the quietest model you can find, rather than rely on trying to reduce the noise by additional insulation, etc, although the downside of that is that it may cost more.

 

[dpmiller]

6 hours ago, SteamyTea said:

That chart has me confused too, and judging by the replies, no one else wants to take it on.

Possibly best asking the manufacturer/supplier to tell you what it is about.

 

Available flow rate wrt restriction @ different fan speed settings.

[Oz07]

20 hours ago, PeterW said:

Welcome 

 

if you don’t have to hit building Regs / SAP then have a look at these systems from Boulder 
 

https://www.ventilationmegastore.co.uk/product/dhv-25n-unit/

 

@Nickfromwales used to have a couple of contacts I think there

Why excluding building regs for this unit?

 

Is there a way to follow these threads on this forum?

[Ed Davies]

21 hours ago, Savage87 said:

What are the Pascals all about?

 

They're documentation is not explicit on the subject but I'd assume it's the pressure difference the fan is blowing against. That'll be made up of the any pressure differences between the indoor and outdoor air and the resistances to the flow of the ducts and terminals. If the system's at all properly set up then the duct and terminal resistances should dominate but it could go badly wrong if, say, the inlet and exhaust ducts went to opposite sides of the house on a windy day. What's not clear to me is whether that graph is for both the supply and extract paths together or for just one path. Of course, the pressure caused by resistance in the ducts and terminals depends on the flow rate: the higher the flow the greater the pressure difference.