Fadec Posted yesterday at 13:19 Posted yesterday at 13:19 Hi all I have a dilemma which is playing on my mind and hope you can be of some help. All bedroom doors to the landing in a home with an MVHR system often need a 10mm undercut gap at the bottom to allow for airflow between rooms. This is to ensure proper ventilation. Every bedroom has an en-suite bathroom with a door with the 10mm gap with a return extraction pipe back to the Mvhr manifold, so was thinking that the main bedroom doors to the landing might not need the 10mm gap as the airflow path would be satisfactory between the bedrooms and its own bathroom. That’s the first thing but the other thing is I am actually going to put extraction vents In the landing because of the heat that is generated in the whole house settles in this area, my thinking is it would be good to circulate that heat in the winter but also in the summer to get rid of the heat when the unit is in summer bypass mode. So because I need this extra function with the landing extraction should I put the 10mm gap on the bedroom doors to the landing because the airflow path from the bedroom can now go 2 ways to the ensuite bathrooms and the landings. Thanks in advance..
JohnMo Posted yesterday at 13:41 Posted yesterday at 13:41 13 minutes ago, Fadec said: main bedroom doors to the landing might not need the 10mm gap Is the airflow to bedrooms and ensuite the same - if not you need an under cut 15 minutes ago, Fadec said: going to put extraction vents In the landing because of the heat that is generated in the whole house settles in this area Could be a waste of time. Why not just a big supply there instead. But then - No supply to bedrooms and obviously extract in the ensuites. It would need to sized to at least match all the ensuites and any bathroom upstairs. The bedrooms then get through flow on the way the extract points. You need door under cuts. It's a valid system and is called cascade ventilation. The issue with the extract in the hall is where does it gets it's flow from. You either over ventilation the bedrooms or from down stairs? MVHR is rubbish at moving heat around, flow rates are too low and air has a low heat capacity.
Fadec Posted yesterday at 17:55 Author Posted yesterday at 17:55 4 hours ago, Fadec said: Hi all I have a dilemma which is playing on my mind and hope you can be of some help. All bedroom doors to the landing in a home with an MVHR system often need a 10mm undercut gap at the bottom to allow for airflow between rooms. This is to ensure proper ventilation. Every bedroom has an en-suite bathroom with a door with the 10mm gap with a return extraction pipe back to the Mvhr manifold, so was thinking that the main bedroom doors to the landing might not need the 10mm gap as the airflow path would be satisfactory between the bedrooms and its own bathroom. That’s the first thing but the other thing is I am actually going to put extraction vents In the landing because of the heat that is generated in the whole house settles in this area, my thinking is it would be good to circulate that heat in the winter but also in the summer to get rid of the heat when the unit is in summer bypass mode. So because I need this extra function with the landing extraction should I put the 10mm gap on the bedroom doors to the landing because the airflow path from the bedroom can now go 2 ways to the ensuite bathrooms and the landings. Thanks in advance..
Fadec Posted yesterday at 18:04 Author Posted yesterday at 18:04 Hi thanks for the response, where the stairs are on the downstairs plan at the top of the plan the square box that surrounds is open to the upstairs and all the blue circles at the right hand side of the house is the supply valves so the cool air would be provided from that side.
JohnMo Posted yesterday at 18:40 Posted yesterday at 18:40 Your trying way to hard One supply or extract to each room is normally all that's needed. 3 in a dining room is not required. 2x extract in utility? Why 3 in kitchen? Why MVHR does not move heat about, it's a ventilation system. The very max you can move is 10W per m² of floor area with a heater running at about 70 degs. I would concentrate on looking at your heating system and look to move to a low temperature system.
Fadec Posted yesterday at 20:47 Author Posted yesterday at 20:47 Thanks John, because of the run lengths from the attic to the Kitchen/utility and Dining room. The lengths are 17m to 20m from the manifolds and the transmission of air is in 75mm flexible pipes/ducting. There are many bends to get around the steelwork so I guess it would be easier to reduce the airflow rate on the plenum valves when setting up.
dpmiller Posted yesterday at 21:01 Posted yesterday at 21:01 you generally put two hoses into the plenum of one inlet/outlet if the duct run is long
JohnMo Posted yesterday at 21:14 Posted yesterday at 21:14 25 minutes ago, Fadec said: Thanks John, because of the run lengths from the attic to the Kitchen/utility and Dining room. The lengths are 17m to 20m from the manifolds and the transmission of air is in 75mm flexible pipe s/ducting. There are many bends to get around the steelwork so I guess it would be easier to reduce the airflow rate on the plenum valves when setting up. Use a double or triple duct plenum, then you can run as many ducts as you need to one terminal. 1
Fadec Posted yesterday at 21:24 Author Posted yesterday at 21:24 Thanks I have some plenums around the house with 2 pipes like the ones shown above from BPC. In the dining room I had plenums some left over so I used 3 plenums with 1 pipe going to each of them just to use them.
Nickfromwales Posted 22 hours ago Posted 22 hours ago 10 hours ago, JohnMo said: The bedrooms then get through flow on the way the extract points. You need door under cuts. It's a valid system and is called cascade ventilation. I’d never design for that amount of stale humid air being pulled through a bedroom into its respective en-suite. Bedrooms get a fresh air supply, and need to be able to have that air flow across the room, divisible here by some being extracted at the gallery at the top of the landing, and some by the en-suite. @Fadec, the 3x plenums in the dining is OTT, but if you are at peace with 3 crying warts then technically it’s the better solution as when on boost this will give the lowest level of audibility by far. Why not go for a linear plaster-in unit with all 3 ducts going to it? Me personally, I’m not a fan of how utilitarian these basic air valves look, in a domestic setting, but that may bother me more than it bothers you. Que sera. Utility and living, please just do 2 ducts > 1 plenum, and reduce the ceiling clutter; if only to help my ocd.
JohnMo Posted 16 hours ago Posted 16 hours ago 5 hours ago, Nickfromwales said: design for that amount of stale humid air Not even sure where that comes from, humidity air in a wet room, yes, stale in a whole house ventilation system running 24/7? Stale air just doesn't occur. Seeing the layout with bedroom and ensuite doors next to one another the through flow scheme is not going to work anyway. Too much of a short cut for air travel. What I was proposing is no different from a Brink Multi flow system, or a Passivhaus Cascade system, promoted by them for retrofits. Or systems like FreshR or Blu Martin.
Fadec Posted 15 hours ago Author Posted 15 hours ago 6 hours ago, Nickfromwales said: I’d never design for that amount of stale humid air being pulled through a bedroom into its respective en-suite. Bedrooms get a fresh air supply, and need to be able to have that air flow across the room, divisible here by some being extracted at the gallery at the top of the landing, and some by the en-suite. @Fadec, the 3x plenums in the dining is OTT, but if you are at peace with 3 crying warts then technically it’s the better solution as when on boost this will give the lowest level of audibility by far. Why not go for a linear plaster-in unit with all 3 ducts going to it? Me personally, I’m not a fan of how utilitarian these basic air valves look, in a domestic setting, but that may bother me more than it bothers you. Que sera. Utility and living, please just do 2 ducts > 1 plenum, and reduce the ceiling clutter; if only to help my ocd.
Fadec Posted 15 hours ago Author Posted 15 hours ago Hi Nick thanks for the reply, In all the bedrooms upstairs there is 1 fresh supply plenum in each of the rooms with 2 x 75mm pipes I read that if you positive pressure with more air than what would be extracted so the ensuites for every bedroom have 1 extract plenum with 1 x 75mm pipe and that they are nearer to the extract manifold. Plus as mentioned earlier we could put the 10mm gap under the bedrooms doors to the landing for that alternative path. Good to hear that the dining room will be okay, I was worried a bit that I was putting 3 plenums with 1 pipe to each but will be less audible sounds it could be a good move considering they are main living spaces. I have ordered the plastered in version for those 3 as aesthetically it will look better, picture below. The utility has 1 plenum with 2 pipes but not much transfer of air into it as there is no direct door from the landing into it only the kitchen door which is bothering me a little. the dining room has 2 plenums with 1 pipe each so the same as the dining area will have a lower noise at boost.
Fadec Posted 12 hours ago Author Posted 12 hours ago 3 hours ago, JohnMo said: Not even sure where that comes from, humidity air in a wet room, yes, stale in a whole house ventilation system running 24/7? Stale air just doesn't occur. Seeing the layout with bedroom and ensuite doors next to one another the through flow scheme is not going to work anyway. Too much of a short cut for air travel. What I was proposing is no different from a Brink Multi flow system, or a Passivhaus Cascade system, promoted by them for retrofits. Or systems like FreshR or Blu Martin. The system is more or less in place what’s left is the attic pipe manifolds which are in situ plus the alterations for the up stairs landing extract manifold that I’m going to feed into the extract line and have the ability to manually/automatically vari with a motor controlled Bellimo valve. So the cascade system looks to be different with no pipes and a route I can’t take.
Nickfromwales Posted 12 hours ago Posted 12 hours ago 2 hours ago, JohnMo said: Not even sure where that comes from, humidity air in a wet room, yes, stale in a whole house ventilation system running 24/7? Stale air just doesn't occur If hot air rises and accumulates at the head of the stairs, it’ll be less than fresh air there, plus it has been stated that the concern is it’ll be ‘hot’, so not air I’d choose to transfer to the en-suite with the bedroom being used as transfer. Areas do stagnate, as airflow in vaulted areas and thoroughfares aren’t usually addressed in MVHR designs, hence why for a next potential project with 2 storey gallery aspects I’ll be looking at push/pull in the high (and vaulted) aspects; this will be to shift the air and recover as much of the heat that has risen there as is practicable. There’s no reason to cascade here, when putting fresh air into habitable rooms is (afaic) such a far better solution, and the opportunity exists to do so. Retrofit or get-out-of-jail solutions shouldn’t be used if it’s a new project, and where a full MVHR system can be designed and installed to achieve the absolute best outcome. 1 hour ago, Fadec said: Plus as mentioned earlier we could put the 10mm gap under the bedrooms doors to the landing for that alternative path. There’s no ‘could’ you need to do the undercuts if you want the system to function properly. The airflow is dictated by the rates set during commissioning, and they won’t be set up so the input to the bedrooms are equal to the extracts in the respective en-suites. The idea would be for airflow to make its way to / from spaces via the path of least resistance, so it can function as per design. 1
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