MVHR plans sanity check and good units with pollen filters

[mistake_not]

Hi all.

 

Spent a good while reading others posts, and am now planning my own MVHR retrofit installation as part a whole range of works.  However, I know I will have missed (at least) one thing, so grateful for a sanity check on my thinking.

 

My current plan is a MVHR unit in the loft, running pipework radially. To help with allergies I want to use a unit that has at least a F7 filter, so was looking at the Zehnder Q350. Quick questions on it:

 

• Is it likely to be quieter / less vibration noise if I attach it to a gable wall, or joists?
• The unit looks good, but should I be looking at something else instead?
• I plan to use BPC 90mm semi-rigid radial pipe as it seems easy to install, and should provide minimal pressure loss and be quiet. I can drop pipes down to the ground floor relatively easily via some boxing in and use of wardrobe corners.

 

My house layout is as per the two images attached. I have added planned exhaust and supply locations to the diagrams (exhaust in red, supply in green).  Total floor areas is approx 190m2. I have the following calculations (from Part L and PassivHouse tables) for amount of air needed, and again welcome folks pointing out the likely errors.

 

Room	Supply m3	Extract m3
kitchen	20	67
Living room	47
Office	20
WC		35
utility		29
gym	29
family bathroom		45
en suite		40
master bedroom	40
spare bedroom	20
small bedroom 1	20
small bedroom 2	20
total	216	216

 

Some very basic pressure loss calculations put the longest and most bendy pipe run at less than 50PA (supply), so think I am fine on that front. 

 

Thanks in advance for any that help 🙂

Edited December 7 by mistake_not

[JohnMo]

I have never seen a good reason to have a supply in an extract area - kitchen. I would supply more to the gym instead.

9 minutes ago, mistake_not said:

Some very basic pressure loss calculations

You need to calculate the most onerous run, not all of them. You need to calculate from MVHR to and including the terminal.

 

11 minutes ago, mistake_not said:

F7 filter

Nothing wrong with F7, although I have never had any issues with just G4.

 

Map where the air travels to and from, do you have the whole area covered, with flow going through hallway and stairs.

[Benpointer]

Not an expert but from our experience of 15 years with full-house MVHR I'd say three things:  

1. We installed the unit in our service cupboard - noise has never been an issue in normal operation they are very quiet.
2. Putting the unit in the loft will be a PITA when you have to change filters (every three months or so in our experience) put it in the airing cuboard if it will fit, or anywhere where you can easily get to it.
3. Your inlet and exhaust locations look good to me.

[Benpointer]

3 minutes ago, JohnMo said:

I have never seen a good reason to have a supply in an extract area - kitchen. I would supply more to the gym instead.

 

We did a very similar supply and extract in our kitchen diner (6.1m x 5.3m) and it worked very well.

[JohnMo]

2 minutes ago, Benpointer said:

We did a very similar supply and extract in our kitchen diner (6.1m x 5.3m) and it worked very well.

Not saying it doesn't work, but travel path can be quite short and it's better to wash through general areas also - gym is under ventilated anyway

[Benpointer]

42 minutes ago, JohnMo said:

Not saying it doesn't work, but travel path can be quite short and it's better to wash through general areas also - gym is under ventilated anyway

Depends if it ever gets used 😉

[Mike]

4 hours ago, mistake_not said:

Is it likely to be quieter / less vibration noise if I attach it to a gable wall, or joists?

Zehnder (always?) recommend fixing to a wall with a minimum mass of 200 kg/m², so go for the gable wall (if it must be in the loft). However anti-vibration mounts are available if that's not feasible.

[Russdl]

7 hours ago, mistake_not said:

Is it likely to be quieter / less vibration noise if I attach it to a gable wall, or joists?

 

FWIW. We have a Brink Flair, so not a dissimilar model to the Zehnder. Ours is sat in a warm loft space on a block of EPS without any kind of fixings. The MVHR has never moved and never transmitted any perceivable vibration. 

[shuff27]

I have a Zehnder Q350, it's a good quality unit & runs quietly but it's also bulky & heavy.  Mine's in the GF utilty room - I wouldn't fancy trying to get it into the loft!

 

BTW, why does your GF floor plan have so many internal doors?  I counted 11 which seems an inefficient use of space (my house which is a similar size has 4 on GF).  Re MVHR, could you not reconfigure the utility room to fit in the unit there?

[JohnMo]

2 hours ago, shuff27 said:

why does your GF floor plan have so many internal doors?  I

There are 6 sets of doors inside/outside in kitchen alone. Ditch at least one door to hall.

 

From outside to utility 2x doors, ditch the internal one and the wall and make utility bigger. Same with front door.

 

If you are airtight (MVHR would suggest you are) you don't need double doors.

[mistake_not]

All, thanks for the advice so far. To address some of the comments:

 

What would an appropriate supply requirement be for the gym? It does get used (6+ times a week) but only for weight training. My thought is we open a window when training as supplying sufficient air would be hard. Also we keep the gym / utility colder, so keeping supply and extractor from those 2 balanced and therefore eliminating flow to and from the rest of the house seemed to make sense. But yes could easily increase flow and exhaust from those to areas.

 

Otherwise simple airflow modelling has enough going through hall and landing. Also without supply to the kitchen / diner I get no flow through that bit of the kitchen.

 

Agree unit in loft is a pain - even more because I would have to widen the hatch to get it up there. Unfortunately airing cupboard is full, but will see if I could get a sensible ducting run from utility. 

 

Anyone got any thoughts on ducting? Specifically is the 90mm semi-rigid ducting worth it? 

 

 

[JohnMo]

1 hour ago, mistake_not said:

balanced and therefore eliminating flow to and from the rest of the house seemed to make sense

Your MVHR will not move heat easily.

 

1 hour ago, mistake_not said:

Also without supply to the kitchen / diner I get no flow through that bit of the kitchen

That is why you need map where the air is likely to go. It will go the shortest route possible, but you need to manipulate flow paths to make it go a long way.

 

If you a coanda extract in the kitchen the air is actually taken from many meters away not near the extract, same with supply 

 

https://www.zehnder.co.uk/en/indoor-ventilation/solutions/air-distribution/zehnder-comfovalve-luna-e125

[mistake_not]

30 minutes ago, JohnMo said:

That is why you need map where the air is likely to go. It will go the shortest route possible, but you need to manipulate flow paths to make it go a long way.

Know of any air flow modelling software? CFD might be overkill!

 

That vent looks good thanks. Annoyingly our kitchen diner will have a steel beam down the middle where the rear wall used to be, which would likely disrupt this approach.

[Nickfromwales]

1 hour ago, mistake_not said:

That vent looks good thanks. Annoyingly our kitchen diner will have a steel beam down the middle where the rear wall used to be, which would likely disrupt this approach.

You can have penetrations made in the steel before it’s installed. I do this all the time on my M&E installs, very simple to achieve. 

[mistake_not]

1 minute ago, Nickfromwales said:

You can have penetrations made in the steel before it’s installed. I do this all the time on my M&E installs, very simple to achieve. 

 

Are those penetrations to allow airflow around a room, or for ducting to go through? I need flow around a room if I was to use a coandra extract (I think).

[JohnMo]

1 hour ago, mistake_not said:

Know of any air flow modelling software? CFD might be overkill!

Just do it on paper, if a point supplies 47 - lounge, where is likely to go, always the shortest routes first. So basically to the 67 extract from kitchen. Now where is the other 20 coming from? So what areas do you miss?

[mistake_not]

12 minutes ago, JohnMo said:

Just do it on paper, if a point supplies 47 - lounge, where is likely to go, always the shortest routes first. So basically to the 67 extract from kitchen. Now where is the other 20 coming from? So what areas do you miss?

 

I did all this originally. The only bit that was missed was half the kitchen diner, so I added another supply to the kitchen which is shown in the design you see.

 

So specifically, the other 20 comes from the living room, though might pull from office as well.

 

The only element that may not be covered is the stairs.

[Nickfromwales]

41 minutes ago, mistake_not said:

 

Are those penetrations to allow airflow around a room, or for ducting to go through? I need flow around a room if I was to use a coandra extract (I think).

Anything you want / need basically. But for ducts and small bore services for my needs mostly. 
 

Can be letterbox shaped for transfer grilles I’m sure. 

[mistake_not]

I might have "nerd sniped" myself and done some 3D CAD and CFD....

 

This run is using the following table for air supply and exhaust:

 

Room	Supply m3	Extract m3
kitchen		100 (2 locations)
Living room	45
Office	25
WC		30
utility		30
gym	45
family bathroom		30
en suite		30
master bedroom	35
spare bedroom	30
small bedroom 1	20
small bedroom 2	20
total	220	220

 

 

Definitely some issues with the CAD, but just playing for now.  Not quite sure what I am aiming for though; do I want the longest possible runs between supply and exhaust, best coverage of the whole house with no "dead" zones, or just lowest main air age. Obviously no dead zones seems like a good start point.

 

If folks want to interrogate more you can create your own SimScale account (for free) and copy the project and play (or just look properly at my results): https://www.simscale.com/workbench/?pid=1479988443212465839&mi=run%3A100%2Csimulation%3A99&mt=SIMULATION_RUN

 

 

 

Edited December 16 by mistake_not