MVHR ducts and manifold

[Apple]

Hi. Left it to the last second, roof going on and need to get an MVHR system. Original spec was couple of drimasters but living in house with one and it creates a very noticeable cold draft. In previous house most the extraction points and chimney were blocked up due to drafts and noise of them flapping in the wind (never had any condensation). So hoping MVHR will be better.

Due to costs going to be doing a self install but have quotes for 2 competing systems. One is radial and the other is a branch system. It’s a 2 storey with a concrete first floor so the branch system is looking attractive to minimise hole size required thru the slab and the block walls on flat holding them up. However the radial system of continuous pipe to every duct and the ease of install is appealing although realise still need the big ducting to get to them.

Reading the forums a few have installed both systems in different builds, did you have a preference?

The house is kinda a T shape with a bit joining them in middle. Both radial and branch designs have system installed in hotpress on one side but this will cause quite long pipe runs to the valves and the for the external supply and exhaust. Considering moving unit into attic. This would make very short external runs and then have separate ducts for both sides of the house with each downstair manifolds installed between ceiling and slab. Not sure though how the system would be balanced if the rings are in the manifolds as they will be plastered over. Am I missing something, do you need to leave a hatch or can it be balanced at the valve? Can’t take all the individual radial pipes from the attic, hole would be too big. 
What’s the consequences of going for the 90mm over 75mm radial ducts? There is quite an increase in airflow versus the increase in price.
 

[Conor]

Need to see a drawing, floor area, required flow rates etc.

 

In the meantime, I've a hybrid system. MVHR, 125mm ducts to each floor (three floors in total), then a 6 port manifold serving each floor. Keeps almost all of the 80mm runs to the valves under 10m, and meant only two cuts through the slabs at 125mm each.

[Apple]

Ventilation GF.pdfVentilation FF.pdfApologies for delay getting back. Your hybrid system sounds very interesting. I’ve attached one location guide for radial ducts. I moved the ground floor manifold trying to get better location but it was above the island originally. I was thinking of hybrid system 4 distribution boxes for the supply, 2 for upstairs and 2 down and this would make shorter runs and smaller holes in walls. Had got to point where after all that was thinking a simple branch system would be easiest.
 

[JohnMo]

Few comments

 

Lots of bedrooms and not much living space.

 

Be careful of over ventilation it's nearly as bad as under ventilation, can dry out the air a lot in cold weather and wasteful energy wise.

 

Kitchen diner, why so many supply and extract points, your kitchen needs around 47m3/h, so one extract is more than capable of that. Same for a few of the bedrooms that have multiple outlets - no need (you are ventilating based on the areas likely number of people), you just need one supply point that will wash across the room.

 

Locate supply and extracts as far from doors and openable windows as possible so there is no short circuiting of air flow.

 

First start with the flow required for each room, the flow for wet areas will be extraction, for dry rooms supply. Some areas will flow through instead of direct supply air, for example corridors and stairs. You need to be supplying and extracting the same amounts.

 

You need to map the way the air will move around the house, so supplying x m3/H, where does it go, does the flow path purge all the air. For example a couple of rooms around the kitchen area will have zero flow with the current scheme.

[Apple]

Thanks.

That was design from online seller. Had some concerns over it but didn’t know enough when first got it. Learning process, going to spend the weekend doing the calculations.

Are there any recommended templates? Was gonna copy some of the previous posts as a starting point.
Was concerned about the amount of exhaust in kitchen, utility and Qc with no supply for them.

The amount of ducts in that design wouldn't be possible, the access holes needed would be to big.

[JohnMo]

You really don't want supply and exhaust in the same room, you need the air to move around the house,the longer the travel paths the better. So think in terms of supply in the far corner of a room (from door) and extract in another room again in the far corner. Longest flow path is good, short flow path bad.