Ventilation: getting started with MVHR

1 to 30 of 73

- CommentAuthorMarkyP
- CommentTimeNov 29th 2016 edited
I've taken the decision to incorporate some sort of ventilation and heat recovery into my renovation and extension. I have designed and built for air tightness which includes the renovated section and I'm reasonably confident a good air tightness level will be achieved. I have the building currently stripped back to the bones in most places and wont again have such a good chance to lay the infrastructure for a ventilation system. I'm a bit overwhelmed by the myriad of systems and options out there, are there any good resources to help get me started? I understand the principles of MHVR but could do with reading more about detailed design considerations, installation, and tuning and I dont know where to start in terms of choosing a system manufacturer. I'm self-managing my project and doing loads DIY, I would consider seriously installing and commissioning the MHVR myself.

I am planning to contact Fresh-R with a copy of my drawings and ask if they can provide a written installation proposal for their product and data on how it would meet UK regs. I'm prepared to explore this option, and discuss with my BCO who so far has been pragmatic and reasonable. I find the idea of a ductless system appealing but will also be looking hard at the tried and tested ducted approach as well. Up front cost will be a significant factor in choice.
- CommentAuthordjh
- CommentTimeNov 29th 2016 edited
In terms of ducted systems, there are two approaches that I think are sensible. One is the traditional branched rigid ducting and the other is radial semi-rigid ducting together with plenums/distribution boxes.

I have semi-rigid ducting and I think it was a good choice. It is simpler to install and commission because the balancing is designed in from the start rather than added at commissioning by adjustment. Either type needs a significant amount of space to run the ducts in and enough space not only for the MVHR unit but also to run all the ducts that connect to it.

The detailed design in my case was done by the supplier. The notion is that fresh air is supplied to habitable rooms (living, dining, bedrooms etc) and extracted from kitchens, bathrooms etc. The total extract must add up to the same as the total supply, which can mean tweaking some of the individual rates a bit to make it all add up. Duct flow resistance is an important factor in the flow rates achieved, and minimising duct speed is an important factor in reducing noise.

In terms of particular brands of unit, there are various factors. Overall size is one - make sure you can achieve the building regs rates, ideally with a good deal of spare capacity. Running an MVHR flat out makes a lot more noise. Some manufacturers are better than others, both in terms of quality and also the accuracy of their specs. Obviously they also tend to cost more.

The UK has a database, known as the SAP Q appendix:
http://www.ncm-pcdb.org.uk/sap/pcdbsearch.jsp?mvType=3&brand=&model=&modelQualifier=&pid=34
It lists MVHR units and their SFP (specific fan power) and efficiency, which are the two most important performance indicators. You want low SFP and high efficiency. If a device isn't listed, don't buy it. The database seems to be fairly awkward to use.

PHI also has a database: http://database.passivehouse.com/en/components/list/ventilation_small or http://database.passivehouse.com/en/components/list/ventilation_big
The PHI tests the units more stringently so the list of products is not so large and not so cheap, but the database is a bit easier to use.
- CommentAuthorGreenfish
- CommentTimeNov 29th 2016
Give yourself plenty of time to get responses back from suppliers, many are surpisingly slow given they are in business to sell kit. But sort out a house plan that you can provide, and examine what they come back with very carefully.

What is your floor area? If > 100sqm then the 0.3 l/s per sqm regs requirement will dominate. I found that a number of the system providers over looked that detail when offering a MVHR unit, just using a number of rooms kind of estimate for unit suitability. If you feel that you do want to operate at the reg flow rate, then you need a unit that can deliver this with ease as DJH said.

I have a radial semi-rigid ducting based system (that works more by luck than judgement), but I have to wonder if I would have been better off with a ridgid one that was *accurately designed*
- CommentAuthorbarney
- CommentTimeNov 29th 2016
Assuming the designer does know what he's doing, a designed system isn't that accurate either - basically design values minus 0% and plus 20% (to allow for unknowns on resistance) - basically it's the commissioning that's important (be that static regain plenums, dampers and/or fan speed adjustment)

If DIY takes your fancy, a friend of mine put in a heat exchanger from VES (Ecobox, I think) and then added the in line fans as separate items (with a pollen filter as a further lose item). That gives you plenty of scope to get it to fit - we used round PVC ducts

Not the peak of efficiency, but mouse quiet and does the job perfectly well. Balancing was by a combination of throttling valves on extract and speed control on the fans - he runs the house slightly over pressure on supply (ie the "house" is slightly positive to external

Regards

Barney
- CommentAuthorGotanewlife
- CommentTimeNov 29th 2016 edited
I have designed and fitted 2 systems entirely DIY in a deep renovation with no previous experience. Sounds so grand doesn't it! In fact, it was dead easy. One was based around an Aircycle 2 the other a much smaller VUS 100P. For the smaller system, just one sucking in the kitchen and 2 blowing in the bedrooms, using a design service would have been utterly pointless - it really was a piece of doddle. The other one had some really nasty routing some of which became more complicated once the pilot holes were drilled and the exact juxtaposition of different elements was discovered. Also the location of the unit itself was important to me and was 'tight' getting the 4 pipes out in a sensible way was seriously taxing. Simply no way on earth a design service could have helped. I used a couple of in-line attenuators and lots of common sense and attention to detail to minimise the niose. For the airflow I used a couple of iris valves for coarse control. Whilst i have an anemometer I never actually got around to properly commissioning it - it seems to work brilliantly as does the other one. I got some help from this Forum but really I just think the novelty of MVHR is being used as a way to print money.

In short unless you require proper sign off DIY it!!!!!
- CommentAuthordjh
- CommentTimeNov 29th 2016
Posted By: GotanewlifeIn short unless you require proper sign off DIY it!!!!!

DIY is fine. UK regs require you to submit the commissioning certificate to building control.
- CommentAuthorEd Davies
- CommentTimeNov 29th 2016 edited
Posted By: djh: â€œUK regs require you to submit the commissioning certificate to building control.â€

I think you mean English regs. Not Scottish:

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14159#CommentBody_238388

No idea about Wales or NI. (Writes the quarter-Irish Englishman with a Welsh surname living in Scotland.)
- CommentAuthorMarkyP
- CommentTimeNov 30th 2016
many thanks for the comments, very helpful.

I have a few questions:

1. what are the factors to consider when choosing a rigid, semi-rigid or flexible duct system? wouldnt a rigid system have a smooth bore and therefore create less resistance to airflow or less turbulence? less noise?
2. I have a wood burner, is there any prospect of the MHVR system distributing heat from the sitting room to other parts of the house? Air recovered from the sitting room at times the wood burner is running will be very warm. I assume I now need to consider a dedicated air supply for the wood burner?
3. noise is a worry, my wife sleeps with one eye open so any sort of background whirring or hum will no doubt be a problem. What should I be doing to absolutely minimise the background noise? I see above suggestions to oversize the unit to avoid running it too hard. Anything else?
4. what would be the relative merits of branched or radial duct systems?
5. does every ventilated room require both input and extract? or can you have an inbound airflow in a common space like a hallway, and extract in occupied rooms, creating a net airflow into the rooms via gaps under doors?
6. I'm in England, could I commission the system myself and submit the paper work and satisfy building control?
- CommentAuthorringi
- CommentTimeNov 30th 2016 edited
Posted By: MarkyP1. what are the factors to consider when choosing a rigid, semi-rigid or flexible duct system? wouldnt a rigid system have a smooth bore and therefore create less resistance to airflow or less turbulence? less noise?

Cost and layout of the building. Rigid is best if it works for your building, otherwise one of the expensive new radial systems with smooth semi-rigid ducts. The cheap flexible ducts (with a spiral of wire) are the worse, and must be installed very carefully so they are not compressed at bend, or with insulation etc.

Posted By: MarkyPI have a wood burner, is there any prospect of the MHVR system distributing heat from the sitting room to other parts of the house?

MHVR moves too little air to transport much heat, therefore assume MHVR will not move any heat about.

Posted By: MarkyPnoise is a worry, my wife sleeps with one eye open so any sort of background whirring or hum will no doubt be a problem. What should I be doing to absolutely minimise the background noise? I see above suggestions to oversize the unit to avoid running it too hard. Anything else?

Also consider noise from other rooms, you can get Sound Attenuators, it is normal to fit one on the output of the MHVR unit (going into the home), but you could also fit one on the duct going to your bedroom to reduce noise form other rooms.

Radial systems claim to have less issues with noise between rooms.

Posted By: MarkyPdoes every ventilated room require both input and extract? or can you have an inbound airflow in a common space like a hallway, and extract in occupied rooms, creating a net airflow into the rooms via gaps under doors?

Best to extract from wet rooms like the kitchen and bathroom, then spread the inputs about so as to get a flow of air in all your rooms. However just extracting from wet rooms with an inbound airflow in a common space like a hallway is still 100 times better the what most homes have.

Posted By: MarkyPI'm in England, could I commission the system myself and submit the paper work and satisfy building control?

Why are you telling BC you are putting a system in?
- CommentAuthordjh
- CommentTimeNov 30th 2016
Posted By: MarkyP1. what are the factors to consider when choosing a rigid, semi-rigid or flexible duct system? wouldnt a rigid system have a smooth bore and therefore create less resistance to airflow or less turbulence? less noise?

IMHO:
- do NOT use flexible ducting. It is grossly inferior.
- semi-rigid is easy to DIY and performs as well as rigid, providing it is properly sized. It is smooth bored. It shouldn't need balancing because that is designed in.
- rigid is the traditional form. I don't have first-hand experience but I think it is more difficult to design and install and commission. I also suspect it may be cheaper.

I have a wood burner, is there any prospect of the MHVR system distributing heat from the sitting room to other parts of the house?

Not really. An MVHR system does not move anything like the quantity of air of a forced air heating system, and the air temperature of the source (sitting room air) is nowhere near as hot as a furnace.

Air recovered from the sitting room at times the wood burner is running will be very warm. I assume I now need to consider a dedicated air supply for the wood burner?

I don't know the rules but I believe you need an air supply if the house is reasonably airtight. A ducted supply is also more thermally efficient.

noise is a worry, my wife sleeps with one eye open so any sort of background whirring or hum will no doubt be a problem. What should I be doing to absolutely minimise the background noise? I see above suggestions to oversize the unit to avoid running it too hard. Anything else?

My wife wakes up at the least provocation. The MVHR doesn't bother her at all. Apart from minimising duct speed and the number of bends, and adding attenuators where appropriate, the main thing to think about is the location of the MVHR unit. It needs to be as acoustically isolated as possible, so in a closed room/cupboard somewhere. Note that the manufacturer requires a minimum density for the wall it is fastened to that basically means masonry, not studwork. Since I have no masonry, I used extra OSB, tile backer boards and acoustic membrane on the stud wall. So in my case if you know what you're listening for and where to stand, you can hear the unit, but only just.

does every ventilated room require both input and extract? or can you have an inbound airflow in a common space like a hallway, and extract in occupied rooms, creating a net airflow into the rooms via gaps under doors?

No, 'habitable' rooms have a supply valve, 'wet' rooms have an extract valve. Ideally there's a similar number of each. You need to think about how the air will flow from the supply valves to the extract valves, ideally crossing through as much of the rooms as possible. Hallways don't usually have terminals, they're mostly on the path from a supply valve in a habitable room to an extract valve in a bathroom.

I'm in England, could I commission the system myself and submit the paper work and satisfy building control?

Yes, that's what I did. You will need to rent the calibrated flow meter.
- CommentAuthordjh
- CommentTimeNov 30th 2016
Posted By: ringiRadial systems claim to have less issues with noise between rooms.

Radial systems simply don't have issues with noise between rooms. The crosstalk is way below noise via other paths.
- CommentAuthorMarkyP
- CommentTimeNov 30th 2016 edited
Posted By: ringi
Why are you telling BC you are putting a system in?

it's a large scale project - big extension and complete upgrade of the existing structure so BC are visting regularly to inspect lots of other aspects. I wont invite attention to the MVHR but I think it's likely they will spot it, then it's down to the amount of interest it generates with the BCO. But good to know that if they request a commissioning report I can produce it myself.

Posted By: djh
No, 'habitable' rooms have a supply valve, 'wet' rooms have an extract valve. Ideally there's a similar number of each. You need to think about how the air will flow from the supply valves to the extract valves, ideally crossing through as much of the rooms as possible. Hallways don't usually have terminals, they're mostly on the path from a supply valve in a habitable room to an extract valve in a bathroom.

what about extraction over a cooker? Is the extraction rate adequate and is there some manual override or boost for when you have a few pots boiling away? is a cooker hood filter adequate to prevent grease building up in the extract ducting back to the MVHR unit?
- CommentAuthordjh
- CommentTimeNov 30th 2016
Posted By: MarkyPwhat about extraction over a cooker? Is the extraction rate adequate and is there some manual override or boost for when you have a few pots boiling away? is a cooker hood filter adequate to prevent grease building up in the extract ducting back to the MVHR unit?

You need to decide whether you care most about extraction of cooking smells (with consequent loss of heat) or about thermal performance.*

The last thing you want is grease etc from cooking going into the MVHR extract, so you need an independent cooker hood, well away from the kitchen extract valve. The hood can extract to outside, or it can just filter the grease and smells somewhat and recirculate the air.

I have a recirculating hood and our kitchen extract valve has stayed clean so far, although I'm considering fitting an extra grease filter to it, as belt and braces. Everything will depend on your own behaviour, preferences and tolerances, so you'll need to make up your own mind which way to go.

* Although ISTR there is at least one heat recovery cooker hood (Berbel?) Loads of dosh, I expect.
- CommentAuthorjoe90
- CommentTimeNov 30th 2016
Having read extensively here and other places I have decided on a recirculating cooker hood with grease filters and MVHR extract the other side of the kitchen ( for stale air or smells only).
- CommentAuthorRobL
- CommentTimeNov 30th 2016
We have a diy fitted MVHR, and also a wood burner. The lounge with the woodburner has an MVHR supply, which ensures a "fight" does not occur between MVHR & stove.
Noise was an issue for my wife too - our solution is:
MVHR location in loft, far away from master bedroom, above the bathroom.
Pipes to MVHR are short lengths of preinsulated sound absorbing ones, so that fan noise is attenuated - and it's much easier to install with flexi pipes used here.
All other pipes are very wide bore solid ones - 6inch or 10 inch diameter, so that the airspeed is low.

Result: On normal setting, I can't hear it in the bedroom, but can faintly in the bathroom.
On boost, I can faintly hear it in the bedroom, and a low rumble in the bathroom, which is easily dominated by the shower.

There's a grease trap in the kitchen MVHR extract, and we still have the original cooker hood blower extract, which goes outside. This one has been fitted with a one way flap, so it does nothing expect for the rare occasion it's used.
- CommentAuthorVictorianeco
- CommentTimeNov 30th 2016
Best value one stop shop for ducting and grilles?
- CommentAuthorringi
- CommentTimeNov 30th 2016
For plastic ducts https://www.bes.co.uk/products/180.asp you may wish to get them to send you a paper caterlog, as their website is a pain.
- CommentAuthorringi
- CommentTimeNov 30th 2016
Posted By: RobLMVHR location in loft

I hang mine from a purlin so it does not touch the ceiling joists, I used a bit of OSB to create a "wall" it could be screwed to.
- CommentAuthorVictorianeco
- CommentTimeNov 30th 2016
Can't find any semi rigid sucting on that site ringi?
- CommentAuthorringi
- CommentTimeNov 30th 2016
I got the rigid plastic ducting from them, they make not do the more "modem" systems.
- CommentAuthorbarney
- CommentTimeNov 30th 2016
I'd start here:

https://www.roofingsuperstore.co.uk/user/u/files/lindab-in-domo-brochure.pdf

Keep in mind that a lot of what is sold as semi ridged ducting is basically twin wall services ducting

Examples here:

http://www.naylor.co.uk/wp-content/uploads/2012/12/NEWDuctnAccessRevised1703111.pdf

Look for MetroFlex

Regards

Barney
- CommentAuthorringi
- CommentTimeNov 30th 2016
The price of the semi ridged ducting has come down a LOT since I put in our MVHR at these prices it looks like one of the best option.
- CommentAuthorringi
- CommentTimeNov 30th 2016
Posted By: djh
Posted By: ringiRadial systems claim to have less issues with noise between rooms.

Radial systems simply don't have issues with noise between rooms. The crosstalk is way below noise via other paths.

That depends on the design of the connecting box between the ducts and how good the sound insulation is on your doors etc....
- CommentAuthorEasyBuilder
- CommentTimeNov 30th 2016
A tip from another thread. Exterior terminals for intake and exhaust will need mesh to stop spiders entering and blocking the pipes with cobwebs, and other crud from clogging the MVHR filter. The mesh will need to be cleaned periodically, so itâ€™s a good idea to position the terminals within easy reach.
- CommentAuthordjh
- CommentTimeNov 30th 2016
Posted By: ringi
Radial systems simply don't have issues with noise between rooms. The crosstalk is way below noise via other paths.

That depends on the design of the connecting box between the ducts and

I'd be interested to see the design of one that does have problems .... it might be useful to people to know to avoid that brand!

how good the sound insulation is on your doors etc....

That's 'another path' - nothing to do with the ducts.
- CommentAuthordjh
- CommentTimeNov 30th 2016 edited
FWIW, I used the AE35 system http://www.ubbink.co.uk/products/ventilation-ductwork/air-distribution/Semi-rigid-ductwork.aspx

CVC sell a competitive system - http://cvcdirect.co.uk/Whole%20House%20Ventilation/hbductsystemsfro.html - I note they claim a smooth internal lining but that's not what the image shows, so I'd double check.
- CommentAuthordjh
- CommentTimeNov 30th 2016 edited
Posted By: EasyBuilderA tip from another thread. Exterior terminals for intake and exhaust will need mesh to stop spiders entering and blocking the pipes with cobwebs, and other crud from clogging the MVHR filter. The mesh will need to be cleaned periodically, so itâ€™s a good idea to position the terminals within easy reach.

The last sentence is critical. If the terminals are not easily accessible, then it's probably easier just to clean the crud from the MVHR filter, as I do as part of their regular cleaning. Insects don't affect the exhaust so much, because there's a continuous breeze coming out of it.
- CommentAuthorringi
- CommentTimeNov 30th 2016
Posted By: djh
Posted By: ringi
Radial systems simply don't have issues with noise between rooms. The crosstalk is way below noise via other paths.

That depends on the design of the connecting box between the ducts and

I'd be interested to see the design of one that does have problems .... it might be useful to people to know to avoid that brand!

Some of the cheaper ones have ducts connected opposite each other and are no more then a metal box. The better ones have all the out going ducts on the same side and sound absorbing surfaces on the inside.
- CommentAuthordjh
- CommentTimeDec 1st 2016
Posted By: ringiSome of the cheaper ones have ducts connected opposite each other and are no more then a metal box.

Ah, thanks. I'd no idea such things existed. Even so, the system will have a lot less crosstalk than a branched rigid system, other things being equal.
- CommentAuthorbarney
- CommentTimeDec 1st 2016
Not necessarily - SPL will tend to divide in the ratio of volume flow rate at "T's" and duct diameter is critical to what frequency is propagated

Circular ducts are the worst for attenuation as the wall is very stiff in comparison to square or rectangular sections

A radial system is effective when the plenum box is the right size and acoustically lined - more effective when inlets and outlets are "offset" across the plenum - but a T and Branch system can perform very well without adding additional cross talk attenuators depending on layout

Regards

Barney

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Ventilation: getting started with MVHR