Green Building Forum - MVHR design principals Tue, 19 Dec 2023 08:22:39 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301225#Comment_301225 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301225#Comment_301225 Mon, 17 Apr 2023 18:51:35 +0100 adamsmith
We are about to have our first airtight test done, if the results are good we would like to go ahead with MVHR self-installation.

Does anyone have any particular radial systems they would recommend? Due to us having limited space it does need to be a radial system.

Also are there any design principles that need to be followed I’m thinking based on my current understanding:

• Extraction only for (WC, ensuite, and bathroom)
• Supply only for small rooms (study, living room)
• X2 supply and extraction for 60m2 kitchen/ lounge/ diner
• X1 supply x1 extraction in the largest master bedroom
• X1 supply for medium size bedrooms

Attached is our construction drawing, any advice is really appreciated]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301228#Comment_301228 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301228#Comment_301228 Mon, 17 Apr 2023 20:24:53 +0100 djh Posted By: adamsmithWe are about to have our first airtight test done, if the results are good we would like to go ahead with MVHR self-installation.Hello. Good luck with the test. What stage is the build at?
Does anyone have any particular radial systems they would recommend? Due to us having limited space it does need to be a radial system.
I'm very happy with our Ubbink system using the AE35 ducts and a previous generation of their distribution boxes. We have a Brink Renovent Excellent MVHR unit but the duct system will work with other units. I liked that the ducts were easy to feed through our metal web joists, and easy to set up and plug together at both ends. The flow restrictors on the distribution boxes make everything very simple. The biggest grief is wrangling all the ducts into one place to connect them to the distribution boxes.

Where will your ducts run? Where will you fit the MVHR unit? Where will the intake and exhaust ducts penetrate the building? Which way is north, BTW?
Also are there any design principles that need to be followed I’m thinking based on my current understanding:
• Extraction only for (WC, ensuite, and bathroom)
• Supply only for small rooms (study, living room)
• X2 supply and extraction for 60m2 kitchen/ lounge/ diner
• X1 supply x1 extraction in the largest master bedroom
• X1 supply for medium size bedrooms
The basic principle is extract from all 'wet' rooms and supply to all 'habitable' rooms. You get to choose which e.g. a plant room is maybe based on how the system balances. You'll need an extract in the kitchen and a supply in the living/dining area. You'll need a supply in bedrooms and extract in the en-suite. The MVHR system designer will calculate flow rates and number of terminals etc (Companies like CVC Direct offer this service). The general idea is to put the terminals as far from the door as possible. Don't forget you need undercuts (or hidden overcuts) on all doors. And obviously you won't want all the extractors if you're going for airtight + MVHR.

There's a good guide at http://www.passivhaustrust.org.uk/UserFiles/File/Technical%20Papers/2018%20MVHR%20Good%20Practice%20Guide%20rev%201.1.pdf and there's various other guides on manufacturers' sites.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301233#Comment_301233 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301233#Comment_301233 Tue, 18 Apr 2023 07:21:22 +0100 borpin
Unit is connected to distribution boxes and then semi rigid ducting to outlet/inlet points.

Vents are in the roof but there is a residue left from the exhaust vent, so if doing it again, I'd definitely raise the exhaust vent above the surface of the roof by possibly 300mm.

Use insulated ducting from/to outside (preferably rigid not flexible).

I have retrofitted an additional filter box on the inlet side to catch some of the 'crud' before it hits the primary filter.

Think about likelihood of freezing.

Condensation drain (if required).

Monitor CO2 in someway (either supplier sensor - usually expensive, or cheaper one from China and an ESP device). My experience is it is a more important factor than humidity on deciding ventilation rates.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301235#Comment_301235 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301235#Comment_301235 Tue, 18 Apr 2023 10:15:17 +0100 adamsmith
Your build is at the first fix stage, all stuff work and electrics in, first fix plumbing to go, ducting fit, then we can start drylining. We have a chalet bungalow, and have insulated/ airtight, from soffit to ridge so feel its worth testing at this stage to see how much more we need to close up, or how much we need to use the internal layer for airtight (hopefully as little as possible)!

The unit is going under the eves next to the main bathroom upstairs, duct runs through the first-floor joists/ eves/ small loft space above the rafter ties. Where the unit is being positioned under the eves it will make access to the atmosphere very easy, the plan is to go straight out the roof with the inlet and outlets (with them spaced appropriately. The Ducts will exit on the south roof elevation.

I'll have to take a look at the Ubbink system using the AE35 ducts, looks very good. I'll get in contact with as many design companies as possible and see how the designs compare. At this stage, it looks like the ducting runs are going to be the main snag, but nothing that can't be got over!

Thanks everyone for the Advice







:bigsmile:]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301238#Comment_301238 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301238#Comment_301238 Tue, 18 Apr 2023 11:05:22 +0100 djh Posted By: adamsmithThe unit is going under the eves next to the main bathroom upstairs, duct runs through the first-floor joists/ eves/ small loft space above the rafter ties.Sounds good. Don't forget you'll need easy access to the MVHR unit to clean or change the filters every few months. What type of joists do you have? - if they are solid it will be quite difficult to route ducts through them. You'll also need significant space for the distribution boxes and all the ducts around them.

As borpin says, use insulated ducts for the intake and exhaust, assuming the MVHR is within the thermal envelope. Use a dry trap such as HepVO for the condensation drain since water is likely to evaporate from a wet trap.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301240#Comment_301240 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301240#Comment_301240 Tue, 18 Apr 2023 11:32:53 +0100 revor MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301242#Comment_301242 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301242#Comment_301242 Wed, 19 Apr 2023 05:51:10 +0100 cjard MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301246#Comment_301246 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301246#Comment_301246 Wed, 19 Apr 2023 11:01:25 +0100 Mike1 Posted By: cjardTake the opportunity to install a central vacuum system alsoIf you're asthmatic it's no doubt a very good idea. But otherwise why lug around a coil of hose around when you could use a rechargeable (or robot) vacuum instead?]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301249#Comment_301249 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301249#Comment_301249 Wed, 19 Apr 2023 14:51:19 +0100 borpin Posted By: adamsmithThe unit is going under the eves next to the main bathroom upstairs, duct runs through the first-floor joists/ eves/ small loft space above the rafter ties.You generally need good access to the unit, a big door that opens so beware! Also, it does produce some noise that may be noticeable close to a bedroom at night.

Don't underestimate the difficulty in threading the semi-rigid ducts and fitting the outlets!]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301250#Comment_301250 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301250#Comment_301250 Wed, 19 Apr 2023 15:55:23 +0100 Artiglio Again as above don’t underestimate the amount of room needed to get wverything connected and leave space for maintenance. Glad i decided to do it and performance can only improve once other half of house is finished.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301251#Comment_301251 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301251#Comment_301251 Wed, 19 Apr 2023 16:39:07 +0100 Simon Still
Depending on where your unit is located relative to all the rooms a branched system probably takes up less space (the manifold units aren't small and the radial pipes take up a lot of space once they start to come together.). Disadvantage is supposed to be sound leakage between rooms.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301252#Comment_301252 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301252#Comment_301252 Wed, 19 Apr 2023 16:58:09 +0100 Dominic Cooney
It resulted in some very short pipe runs of less than a metre!

The insulated inlet & outlet ducts also ran in the floor void and out of the back wall.

I put a lot of effort into sound reduction measures in the walls and ceiling of the utility/plant room.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301253#Comment_301253 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301253#Comment_301253 Wed, 19 Apr 2023 17:04:45 +0100 Dominic Cooney
All the downstairs rooms are absolutely fine because the vents are either in the ceiling or on the wall close to the ceiling.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301254#Comment_301254 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301254#Comment_301254 Wed, 19 Apr 2023 18:41:09 +0100 djh Posted By: Dominic CooneyThe one thing I would have done differently is put the supply vent to each bedroom higher up the wall or even on the ceiling. They are about halfway up the wall, which I thought would be fine and made it a hell of a lot easier for me in terms of installation (it meant that I didn't have to get past a chord in the roof timbers), but now that it is finished and the beds are in place they have ended up a bit too low down the walls.All our upstairs bedrooms have the vents in the floor (under the bed in one case :). So the duct just runs amongst the joists and terminates in a box in the same space. The extract vents in the wetrooms are mounted in the internal stud walls, about 2.3 m off the floor. In the plant room I didn't actually fit a vent/terminal, I just brought the duct out into the space and used airtightness tape over the end to adjust the opening to the correct m³/hr.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301256#Comment_301256 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301256#Comment_301256 Wed, 19 Apr 2023 20:25:15 +0100 Dominic Cooney Posted By: djhvents in the floor

What a good idea. Although I can almost guarantee that if we had done this, they would have been in the wrong place, e.g. under a wardrobe or something! It was hard enough trying to get enough electrical sockets in the right place, we always seem to end up with the furniture in other places than we initially thought.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301258#Comment_301258 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301258#Comment_301258 Wed, 19 Apr 2023 20:36:47 +0100 djh MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301265#Comment_301265 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301265#Comment_301265 Thu, 20 Apr 2023 08:40:05 +0100 GreenPaddy
re. roof exhaust/intake, consider the intake blockage with snow, and also the intake should have a leaf/insect mesh - access to clean. These need cleaning a couple of times a year.

I always route the exhaust through the roof, but the intake through a wall, or a soffit. Also provides the separation you rightly mentioned.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301272#Comment_301272 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301272#Comment_301272 Thu, 20 Apr 2023 11:19:24 +0100 djh
The roof generally has reduced pressure, whilst a wall may have reduced or increased pressure depending on which way the wind is blowing.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301275#Comment_301275 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301275#Comment_301275 Thu, 20 Apr 2023 11:42:41 +0100 Peter_in_Hungary Posted By: djhThe idea of having both intake and exhaust together but separated on the same wall (or both on the roof) is to balance dynamic pressures when the wind blows. So both experience the same additional pressure, or the same reduced pressure, and thus the MVHR doesn't really notice and doesn't have to draw extra power for its fans.
My understanding = yes]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301317#Comment_301317 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301317#Comment_301317 Mon, 24 Apr 2023 07:43:18 +0100 borpin Posted By: GreenPaddythe intake should have a leaf/insect meshI have a wire guard to prevent birds, but the larger crap was drawn in, hence my additional pre-filter which works really well (but filter needs replacing 3-4 times a year).]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301326#Comment_301326 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301326#Comment_301326 Mon, 24 Apr 2023 12:33:48 +0100 djh Posted By: borpin
Posted By: GreenPaddythe intake should have a leaf/insect mesh
I have a wire guard to prevent birds, but the larger crap was drawn in, hence my additional pre-filter which works really well (but filter needs replacing 3-4 times a year).Same here. I didn't want an insect mesh on the intake (or exhaust) because then I would somehow need to clean it regularly, so I have a washable g3 filter at the MVHR intake that collects all the insects.]]> MVHR design principals http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301341#Comment_301341 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17816&Focus=301341#Comment_301341 Tue, 25 Apr 2023 09:12:28 +0100 Simon Still Something like this on a flat roof (and the roofer has run the membrane to a level where it can't be removed)
https://www.u-buy.co.uk/product/GIA2G4O-round-roof-rain-cap-hvac-vent-galvanized-steel-all-weather-rain-cap-roof-top-round-roof-vent-with-ru

the incoming filter picks up some flies but maybe there are huge numbers more in the incoming pipe run.

My relatives unit (rural, sheep grazing in next field) had a vast number of dead flies in it but they're desiccated and they're on the 'dirty' side of the filter so dont' see that they're doing any harm. (I mean a couple of pints of dead flies - not sure they'd swept it out properly for a while and there was a 'trench' ahead of the filter completely filled with fly bodies. And quite a few live ones flew out when I opened the unit....]]>