MVHR Design help!

[Tosh]

I need to order my ducting asap and have used a xls kindly shared by others on the forum. I've input the numbers but would be grateful for some sanity check and interpretation. Do the numbers I've input look correct e.g. 'air quality adj'? What size unit does all this info tell me I need? Anything else that doesn't look right to the well trained eye?

 

I do have a design from BPC and they said I need a 580m3/h unit. They also used twin 75mm ducting to most outlets but I'd prefer to go larger and with less runs as our plant room is on the Grd Fl at one end of the house. I must admit I struggled to get much help when I quizzed them about the design. I got the impression that they didn't want to share too much info for whatever reason. Any advice appreciated 🙂

 

[ToughButterCup]

Every MVHR company I talked to could not / did not want to see the point that I made to each of them - very politely. There is a conflict of interest inherant in the way systems are designed and marketed.

 

The supplier designs the system.

 

The only way round the issue is to ask another (2?) companies to quote for the same job.

Compare and contrast, post here and we'll confuse you some more 😑

[JohnMo]

55 minutes ago, Tosh said:

design from BPC and they said I need a 580m3/h unit.

Two things to consider when buying an MVHR unit, based on sizing.

 

Normally the bigger the better, they make less noise for a given flow rate than a small unit only just big enough. The other is allowing for turndown, once you have it commissioned and build signed off, as you may want to reduce flows especially if a few people live in the house. So all things considered a unit that has your duty point in the middle of the units capacity range, us about right.

 

Your lounge also needs a good flow rate as it normally has plenty of people in it.

[Tosh]

31 minutes ago, ToughButterCup said:

Compare and contrast, post here and we'll confuse you some more 😑

Being confused is easy; my appetite to learn is ok, its the understanding thats getting harder as I get older 🤣

 

26 minutes ago, JohnMo said:

Your lounge also needs a good flow rate as it normally has plenty of people in it.

 

Yes I was pondering over that one. I'll tweek the adj figures.

 

But what size unit do those calculations show i need? Would it be 2 x 263m3/h i.e. is the theory that if it was on full boost then it would need to up the supply as well? I'm not trying to penny pinch (cough cough) between units but just want some figures of my own as a basis to have some sensible conversations, if thats possible, with suppliers.

[Marvin]

Hi @Tosh

 

It would really help if you showed us the layout.

 

Usually you require 1 inlet any non wet room and one outlet on any wet room (wet rooms are loos showers kitchens, bathrooms, shower rooms and any room with a supply of water including utility rooms). However with larger or longer rooms you may need an inlet and outlet.

 

I see nothing exceptional after looking at the design

[Marvin]

48 minutes ago, Tosh said:

But what size unit do those calculations show i need? Would it be 2 x 263m3/h i.e. is the theory that if it was on full boost then it would need to up the supply as well? I'm not trying to penny pinch (cough cough) between units but just want some figures of my own as a basis to have some sensible conversations, if that's possible, with suppliers.

AS I understand it (having an MVHR for the last 6 years) In theory the MVHR unit pulls and pushes at the same time, your property being air tight.... , and therefore the flow rate refers to the flow of air through the building not the input or output.

[Coanda]

8 minutes ago, Marvin said:

AS I understand it (having an MVHR for the last 6 years) In theory the MVHR unit pulls and pushes at the same time, your property being air tight.... , and therefore the flow rate refers to the flow of air through the building not the input or output.

If there's a flow through the building of x m3  doesn't it follow that there must x m3 coming in and x m3 going out or am I missing something?

[Marvin]

HI @Coanda You are quite right, however the same 263m3 air flow unit will do both: the same push of air in, as the push of air out at the same time...... otherwise the building would blow up like a ballon... 😂

 

So this would be one 263m3 unit....

Edited December 8, 2023 by Marvin

[Marvin]

Hi @Tosh

 

I think that the red crosses are showing that the volume of air required at the indicated room outlet would have to travel too fast down the size of pipe suggested. 

 

This refers to the extract ducts.

[Tosh]

21 minutes ago, Marvin said:

It would really help if you showed us the layout.

Here's the layout that BPC sent back to me.

A couple of points:

 

• we have no ceiling space on the first floor hence why the valves are positioned on walls;
• there is a ceiling void above the landing but stops at the gallery which I can some ducts but not sure if thats preferable to just feeding from below and up into each room throught the studs (oval ubbink?). The sitting room/gallery is not a closed room. The door is an error on the drawing, it has a balustrade to the hallway/stairs void. 
• the xls I've populated dismisses the extract outlet on the large void as I read somewhere on the forum that all this would do is pull smells from kitchen?

 

[Tosh]

28 minutes ago, Marvin said:

So this would be one 263m3 unit....

Gosh thats quite a difference to the 580 m3/h unit BPC recommended.  What do you think BPC would've based their sizing on? When I spoke to them they just kept saying 'its based on the drawings you sent us' which obviously wasn't very helpful! Well not me at least..

[Marvin]

21 minutes ago, Tosh said:

Gosh thats quite a difference to the 580 m3/h unit BPC recommended.  What do you think BPC would've based their sizing on? When I spoke to them they just kept saying 'its based on the drawings you sent us' which obviously wasn't very helpful! Well not me at least..

Hi @Tosh  Who is the manufacturer, what is the type of MVHR??

 

Ah... It depends what type of unit your installing. Your layout shows 2 separate units?? Is the light blue thing the MVHR and the boxes manifolds?  Or are the fan units in the blue and green boxes...???

Edited December 8, 2023 by Marvin

[Tosh]

Hi @Marvin yes just a single unit (their options below). Yes the light blue is the MVHR unit. Green is supply manifold. Red extract manifold. TBH I'm more geared to other units atm but thats another story. However I'm still trying to get my head around these units of circa 600 m3/h and the calculations in my spreadsheet which would indicate a unit of circa 260m3/h?

 

 

 

[Chanmenie]

Could someone point me to the spreadsheet or share a link please.