MVHR newbie.. help needed

[PeterW]

5 minutes ago, Oz07 said:

Why excluding building regs for this unit?

 

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

These units are not on the SAP register so score really poorly with the basic 75% efficiency from memory which can affect your BRegs approval. 
 

And to follow, just click the “Notify me of replies” slider at the bottom of the reply box. 

[Oz07]

Thanks @PeterW

My current project has a passive ventilation strategy i.e. trickle vents but i'm bashing a MVHR unit in. Surely this will improve sap score regardless or could it have the effect of making it worse?

Are they a generic cheap unit?

[PeterW]

They are a generic unit but as they don’t want to spend several thousand pounds having them certified, then they don’t have them done. 
 

They are a very close copy of a Mitsubishi unit, and to be honest probably share a lot of components ...! 

[Oz07]

cheers

[Savage87]

14 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

 

Thanks @everyone for your quick replies! I'm impressed. I appreciate all your help and I understand that your advice comes with no liability!

Any input is good input, I won't just rely on the answers I get on this topic, I will do further research as well and I will take full responsability for this project!

 

@PeterW I had a quick look at the Boulder units and I think the Domus unit is better (I hope I am right ).

Also you mentioned about hitting building regs. Do I have a choice? I am under the impression that I need to hit the minimum targets.

The main reason I want to put the MVHR unit is because of air quality, I don't have any damp/condensation problems. All the house is insulated, floors, walls and loft and I live on a main busy road and each time I open the windows I'm thinking that a lot of pollution is coming in as well.

 

@Nickfromwales I have already done my own underfloor heating for the whole of the ground floor. It's been running for a couple of years and I have no problems with it

Like I said above, I will take full responsability if anything goes wrong

 

@jfb I was thinking that I need 2 ducts going to the kitchen, I was kind of hoping that I needed 1.

 

@JSHarris I will fit some silencers on the supply, the extract I don't think I'm too worried about. It's the bedrooms and the living room that will need to be silent.

The last think I want is the wife constantly saying that she can hear noise from the air vents.

I kind of have to fit the unit in the loft, as I tried conving my wife to put on the landing and building a cupboard for it but she doesn't want it.

My loft is unheated but I have more than 300mm of loft insulation and all of it is overboarded with chipboard on a railing system https://www.amazon.co.uk/LoftZone-8x8USAVE-StoreFloor-Loft-Decking/dp/B00SX0VNT6 . I'm hoping this will keep the noise in the loft.

The duct runs won't be that long as this isn't a big house. I'm hoping that I can keep the unit on low so it produces the minimum amount of noise.

 

@vivienz the unit will be above our bedroom but like I said earlier, I'm hoping that the loft insulation and boarding will do a good job.

 

@joth I had a quote recommending the Zender ComfoAir 200. Which is a good unit but a bit pricey and I do understand that I need to spend more to get a better unit. I'm hoping to spend less than 1000 pounds on it.

 

@Ed Davies I got this chart from another topic and used it for my house. The chart was done this way just so I can balance the supply and extract. The extract side isn't enough to satisfy building regs (minimum extract flow rates from the kitchen (13l/s), bathrooms (8l/s), utility room (8l/s) and WC (6l/s)) in normal operation mode, so I will need to set the boost to meet the minimum flow. If something is wrong please let me know.

The system shouldn't be used in boost mode in the night time, as you said, it will be a lot louder.

 

 

 

 

 

 

[PeterW]

It’s more about the SAP score for a new build rather than the flow rates. You have to meet the minimum extract rates for BRegs, the rest is academic if it’s a retrofit. 

[Savage87]

3 hours ago, JSHarris said:

 

 

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.

 

 

I've seen these charts on a lot of units but I do not fully understand them. I do understand that the lower the number in dB the quitter it is.

I don't know that the different frequencies are all about..

 

Looking at the Domus HRXE Breakout sound performance chart it says that it really quiet on speeds 1 and 2. I'm planning to run it on speed 2 for normal operation mode.

 

Edited October 23, 2019 by Savage87
chart added

[Jeremy Harris]

If fitting MVHR in a cold loft then it may well need installing in an insulated box, with good access for the regular filter changes etc.  The ducts in the cold areas will also need insulating well.

[Savage87]

8 minutes ago, PeterW said:

It’s more about the SAP score for a new build rather than the flow rates. You have to meet the minimum extract rates for BRegs, the rest is academic if it’s a retrofit. 

 

To balance the system out, I can only meet BRegs on boost and I understand that this is acceptable.

[Savage87]

3 minutes ago, JSHarris said:

If fitting MVHR in a cold loft then it may well need installing in an insulated box, with good access for the regular filter changes etc.  The ducts in the cold areas will also need insulating well.

 

Thanks for letting me know. What I'm planning to do is insulate the loft below the rafters, alternatively I will insulate all the ducts in the cold areas to avoid condensation.

[NSS]

@Savage87, forgive me if I've missed something earlier in the thread, but have you had an air test on the property? If not, it may be worth doing so before even considering installing MVHR as, if the airtightness is not great, you may find that no MVHR unit is going to work efficiently.

[Jeremy Harris]

5 minutes ago, Savage87 said:

 

To balance the system out, I can only meet BRegs on boost and I understand that this is acceptable.

 

 

There are two building regs requirements to meet.  The first is that the whole dwelling continuous background ventilation rate has to meet or exceed 0.3l/s/m² of total floor area.  This needs to be on the normal ventilation setting, not boost.  The other requirement is the extract rate from designated rooms, 13l/s from the kitchen, 8l/s from bathrooms and utility rooms, and 6l/s from WCs.  This can be on boost, but in all probability the requirement to meet the whole dwelling ventilation rate on the normal setting will dominate.

 

The system must be balanced at the continuous ventilation rate, but can be allowed to go out of balance a bit at the boost rate if that's unavoidable.

[Savage87]

2 minutes ago, NSS said:

@Savage87, forgive me if I've missed something earlier in the thread, but have you had an air test on the property? If not, it may be worth doing so before even considering installing MVHR as, if the airtightness is not great, you may find that no MVHR unit is going to work efficiently.

 

Thanks for bringing this up. I haven't had an air tightness test done. I would like to get one done. As is stands, I'm hoping there's not much leakage in the house as everything is insulated, I have double glazing, the 2 chimneys have been sealed of, so I'm hoping this will bring the values down to an acceptable level. If I do the test and the values are high I will try to seal everything of as best I can.

 

I understand that this is really important but I'm also looking to get fresh filtered air in the house without having to open the windows.

 

My wife brought an important question up. If the unit has in theory 90% heat recovery and you change the air in the whole house every couple of hours, wouldn't this mean that you have to use the heating more often?

For example, if it's 23 degrees in the house and in 2-3 hours it might go down by 2-3 degrees because of the constant ventilation wouldn't the heating kick in more often just to keep the desired temperature?

I didn't know how answer this question and I hope some has a good answer

[Jeremy Harris]

Bear in mind that relatively well-insulated new builds sometimes (often, I suspect) struggle to meet the building regs airtightness requirement, and for MVHR to give any useful energy saving you probably need to be about half the air leakage rate  that  building regs require, and to get the best from MVHR you really need to be a fair bit less.

 

I fitted decent double glazing to our old house, added loads of loft insulation, had cavity wall insulation installed and spent ages going around sealing up all the dozens of tiny air leaks, mainly around the internal wall to ceiling joints (these were invisible to the naked eye, but leaked badly).  I made a home made blower to check for air leaks, which worked well.  I estimated that I managed to get the airtightness down to about 15 ACH at 50 Pa, so around 15 times worse than needed to get MVHR to work well.  I'm not convinced that I could have improved the airtightness much more, without ripping the ceilings down and replacing them, as there were just too many places where air was leaking.  I even had serious air leaks at every electrical fitting, as the cables were chased into the walls, but there were air leaks behind the plastered over cable capping.

[NSS]

11 minutes ago, Savage87 said:

 

Thanks for bringing this up. I haven't had an air tightness test done. I would like to get one done. As is stands, I'm hoping there's not much leakage in the house as everything is insulated, I have double glazing, the 2 chimneys have been sealed of, so I'm hoping this will bring the values down to an acceptable level. If I do the test and the values are high I will try to seal everything of as best I can.

 

I understand that this is really important but I'm also looking to get fresh filtered air in the house without having to open the windows.

 

My wife brought an important question up. If the unit has in theory 90% heat recovery and you change the air in the whole house every couple of hours, wouldn't this mean that you have to use the heating more often?

For example, if it's 23 degrees in the house and in 2-3 hours it might go down by 2-3 degrees because of the constant ventilation wouldn't the heating kick in more often just to keep the desired temperature?

I didn't know how answer this question and I hope some has a good answer

I'd really get that air test done before going any further.

[SteamyTea]

It is well worth making your own blower if you can as when a house is tested, there is not enough time to find all the leaks.

And the leaks are very obvious.  No need to get hippy @joe90 with his josh sticks, but I will travel for 200 Marlboro and petrol money.

Edited October 24, 2019 by SteamyTea

[jack]

8 hours ago, JSHarris said:

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).

 

A 1dB difference is detectable in A/B testing, sure, but it will make zero practical difference to perceived loudness between two potential real world installations.

 

My point was - and remains - that 3dB doesn't involve a perceived doubling of loudness. Nothing like it, in fact.

 

8 hours ago, joth said:

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?

 

It takes a 10dB increase for the perceived volume to double. In this case, the difference is 14dB, which is a little more than a factor of two in terms of perceived volume.

 

What's probably of greater interest, and impossible to know without listening to the units in the flesh, is the spectrum of the noise. Some types of noise are perceptually far more intrusive than others. White or pink noise, for example, tend to very quickly fade into the background. Indeed, some people use white or pink noise generators to help them sleep. It's spectral peaks like case resonances, bearing rumble, "beats" from fans, and the like that people find annoying. It's therefore possible that two units with the same dBA figures could have noticeably different levels of perceived noise. 

 

7 hours ago, joth said:

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.

 

We have the Brink Excellent 400. It's fine now it's boxed in, but I was very surprised at how noisy the unit itself was on boost when it was out in the open. To be fair, it's pushing a huge amount of air around at that setting, the noise of which I think would be very hard to suppress. We get very little sound through the vents though, even on 100% power. 

 

8 hours ago, JSHarris said:

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.

 

Was this in a house in Totnes, by any chance? 

[Jeremy Harris]

1 minute ago, jack said:

Was this in a house in Totnes, by any chance? 

 

No, it was in Ireland, when we were over there looking at other MBC builds.

[jack]

1 hour ago, Savage87 said:

My wife brought an important question up. If the unit has in theory 90% heat recovery and you change the air in the whole house every couple of hours, wouldn't this mean that you have to use the heating more often?

 

More often than what though? You need fresh air one way or the other. You can bring it in with or without heat exchange. Using heat exchange means less energy consumption for a given rate of ventilation.

 

1 minute ago, JSHarris said:

No, it was in Ireland, when we were over there looking at other MBC builds.

 

Interesting, because a Paul unit installed in Totnes was also the loudest MVHR I've ever heard.  

[Jeremy Harris]

12 minutes ago, jack said:

Interesting, because a Paul unit installed in Totnes was also the loudest MVHR I've ever heard.  

 

 

That's probably a useful confirmation that these units are a bit noisy, then.  Mind you, the Brink unit we saw/heard in Ireland was the quietest one I've heard, it really was very, very quiet, even standing inches in front of it, with it at about head level.

[Savage87]

 

@JSHarris From the chart that I produced on my first post the values in bold

14.78 + 14.82 l/s = 29.6l/s this is for the continuous background ventilation rate which exceeds 0.3l/s/m2 ( 90 x 0.3 = 27l/s) have I calculated this correctly?

The extract rate from designated rooms are shown in l/s below and I can't acheive under normal operation mode, but will be able on boost

 

@NSSI would love to get this done now but the house isn't at it's best at the moment. The kitchin is back to brickwork. I also need to get a window replaced.

I will also look into the homemade blower idea.. Thanks!

 

@JSHarris WOW, that's impressive. This is the extent that I'm willing to go to as well. I have replaced all the ceiling, nearly all of them have been plastered, apart from the spare bedroom which is yet to be plastered, and I have coving on them as well, the hatch to the loft is airtight. The electrical outlets might have some leaking but I'm willing to put the work in to make it better.

 

@jack ... More often than the current state of the house, where you have to open the windows for a couple of hours to get fresh air in.

For example, I still have radiators upstairs and in the morning we open the windows upstairs for half a day and that's it. Downstairs we don't open the windows that much and the heat stays in for longer. With the MVHR unit I would have colder air coming in more frequently, does this make sense?

 

Edited October 23, 2019 by Savage87

[Jeremy Harris]

Looks like the whole dwelling background ventilation rate is the same as the required extract rate for the kitchen + bathroom + WC, then. 

 

The kitchen needs 13l/s, the bathroom 8l/s and the WC 6l/s, so 27l/s for extract, and if the net internal floor area is 90m², then the whole dwelling continuous background ventilation rate is also 27l/s.  It's often the case that the whole dwelling continuous rate ends up being the thing that determines the ventilation rate needed, which is handy, as it saves having to mess about considering the impact of boost settings, as boost isn't needed to comply with the regs and everything can be set at the background rate.

 

To put things in perspective, I reckon I managed to get our old house pretty well sealed, but it was around 15 ACH at 50 Pa at a guess.  Our new build is far from being the most airtight here, but it came in at 0.43 ACH during the air test, so around 35 times more airtight.

[NSS]

22 minutes ago, JSHarris said:

 

 

That's probably a useful confirmation that these units are a bit noisy, then.  Mind you, the Brink unit we saw/heard in Ireland was the quietest one I've heard, it really was very, very quiet, even standing inches in front of it, with it at about head level.

Or maybe it's just down to how well (or otherwise) it's been installed. As I've said elsewhere, we have a  PAUL Novus 300 and you cannot hear it running in any room in the house, even on boost. Sure, if I go out to the plant room, which sits within the footprint of the house but is only accessible from the attached garage), you can hear it running, but none of that noise (or at least none that is discernable) is transmitted through the ducting to the inside.

[Jeremy Harris]

9 minutes ago, NSS said:

Or maybe it's just down to how well (or otherwise) it's been installed. As I've said elsewhere, we have a  PAUL Novus 300 and you cannot hear it running in any room in the house, even on boost. Sure, if I go out to the plant room, which sits within the footprint of the house but is only accessible from the attached garage), you can hear it running, but none of that noise (or at least none that is discernable) is transmitted through the ducting to the inside.

 

 

May well be.  Just to be clear, this wasn't duct/flow noise, as far as I could tell all the MVHR units we looked at in our tour around were silent in the rooms (hard to be sure, as we were being shown around during the day).

 

The Paul unit seemed noisy when stood in the loft space/unfinished room where it was located - this was noise coming from the case of the unit, not from the ducts or terminals.  The Brink was in the top half of a hot press, so about head height, and seemed very quiet when stood next to it.  Similarly, our Genvex can definitely be heard when standing in our services room, much like the Paul unit, especially if I'm in there when it's running on full boost, with the compressor running.  It can't be heard outside that room, but as I mentioned, I'd not really want to site such a unit in the loft space above a bedroom, as I doubt that it could be silenced well enough to prevent the noise being a bit intrusive.

[Savage87]

@JSHarris I hope I understand what you said in your last post. Do the above figures match with what your were saying?