Pre filter between MVHR vents and MVHR unit

[JohnMo]

47 minutes ago, Russdl said:

A sheet of PIR or similar fits the first 4 criteria but falls down on the last.

But does it fail if you add local reinforcements (metal or wood) in local stress areas. You can make strong corners by using dowels, and even screw in to dowels etc.

 

An idea here

 

[Nick Laslett]

Why not just buy some armaflex sheets and glue this to the exterior of the existing box? This is what I did with the galvanised steel filter box from Zehnder. 
 

Funnily enough just stepped out of my place, to be passed by farm vehicle moving manure. On Sunday, next door had a bonfire. 
 

So glad I’ve got a pre-filter for all these country smells. 

Edited July 22 by Nick Laslett

[Russdl]

@JohnMo thats interesting, thanks for the link.

@Nick Laslett that would prove difficult to get an airtight seal on the current boxes.

 

I was thinking I could do with something like a ply backed PIR - which of course I've now discovered does exist!

 

As I have a sheet of insulation left over from the garage build I think I'll experiment with the local reinforcement idea, or maybe make my own PIR backed plywood sections, or perhaps a combination of the two.

 

What would be the best way of adhering foil backed insulation to plywood?

[JohnMo]

7 minutes ago, Russdl said:

What would be the best way of adhering foil backed insulation to plywood?

Spray foam, allow to flash off and not stick fingers when touching and squish together (dampen surface first). Bit like foaming plasterboard to the wall.

 

Or you can use double sided tape, the decent scrim stuff used for sticking vapour membrane together.

[Mike]

3 hours ago, Russdl said:

To that end I'm going to be remaking them but what material should I use?

If you're willing to forego the DIY & the 90° bend, you may be able to buy them.

 

The Zehnder IsoBox, for example, is made from EPP, has a DN160 connection & can take a pre-filter, a carbon filter, or both. Or a DIY filter, I guess. Paul used to sell them in the UK.

 

I guess that other manufactures may make similar for larger ducts.

 

 

 

Edited July 22 by Mike

[Mike]

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Edited July 22 by Mike
double post

[Russdl]

Thanks @Mike, everything was originally built around replacing a 90° bend so that if I screwed it up I could remove my Heath Robinson filter and refit the 90° bend - so the 90° change of flow direction is one of the few certainties.

 

However, I could refit the original 90 and cut out a bit of the straight duct flow for one of those boxes you linked to. I've never seen those before but I suspect they don't give them away - or the filters? I'll take a look.

[SteamyTea]

On 07/08/2023 at 07:27, Russdl said:

Also the power draw 67W before 34W after. 

When I did my toolmaking apprenticeship, we combined machine amperage and an assigned tool life so we knew when to change the work bits.

Mayne you can do something similar, say 4 months and 50W.

[Mike]

3 hours ago, Russdl said:

Thanks @Mike, everything was originally built around replacing a 90° bend so that if I screwed it up I could remove my Heath Robinson filter and refit the 90° bend - so the 90° change of flow direction is one of the few certainties.

 

However, I could refit the original 90 and cut out a bit of the straight duct flow for one of those boxes you linked to.

A good idea :)

 

The best price I found was €85, carbon filter included, from https://www.econology.fr/zehnder-comfosystems-caisson-filtrant-isobox-dn-160-filtre-a-pollen.html, but there's not going to be as much competition in the UK market.

[Russdl]

As expected, they don’t give them away!
 

As I’ve got some bits and bobs lying around I’ll go with rebuild and if that fails reconsider the pro version. 

[Jolo]

Hi all,

 

New member here. I read this thread with interest, as my new MVHR F7 filter became black with muck and flies in just a few weeks (ugh). 

 

After failing to find an insulated box for sale anywhere (I'd have thought they'd be popular!), I ended up buying a metal filter box from an online retailer (actually ended up with two, silly story) and, as expected, it became misty with condensation as soon as the outside temperature dropped. So thanks to @Nick Laslett's advice I bought a square metre of 19mm-thick Armaflex AF self-adhesive insulation and covered the box in that. It's not pretty but it does work really well, the outside of the insulation doesn't feel cold at all, even though the metal box inside is.

 

One question I had for @Russdl while looking at the photo of the grime-covered filter was, have you considered putting it in the box at 45 degrees? From the photo it looks like nearly all the air flow across the mesh is through a circle which is against the duct that's behind it. But with the mesh at 45 degrees you'd have a much larger air flow surface area (the diagonal of the side of the box, by the width of the box) which should mean less pressure drop, and a longer time before it becomes clogged. (Just my 2p's worth - I wish I had space for such a big pre-filter!)

[Russdl]

2 hours ago, Jolo said:

have you considered putting it in the box at 45 degrees? From the photo it looks like nearly all the air flow across the mesh is through a circle which is against the duct that's behind it. But with the mesh at 45 degrees you'd have a much larger air flow surface area

As it happens, that is exactly what I did during the mid life refurb!

 

 

 

It is so much better, shame I couldn’t work it/you weren’t available when I made the Mk1!

 

I’ve also increased the insulation and air tightness with some left over bits and pieces. My pre filter material is now some fine mesh muslin material that costs pence and works like a charm. 

[Jolo]

3 hours ago, Russdl said:

It is so much better, shame I couldn’t work it/you weren’t available when I made the Mk1!

 

Great minds think alike, eh! I can't claim credit for the idea though, I saw it on a YouTube video where a guy in the US was replacing his MVHR unit and he happened to have a pre-filter box with a diagonal filter, which he also explained. 

 

The cloth you've used as a filter is interesting... I might try something like that instead of buying more G3 material. Though the stuff that my filter box came with is so thin, I doubt it causes too much pressure drop, the F7 in the main unit probably causes far more.

 

Your box now has some serious insulation on it!!

[Russdl]

1 hour ago, Jolo said:

Your box now has some serious insulation on it!!

And I think very necessary.
 

Previously it was just some thin foam on the inside (and not very well attached, definitely not airtight).
 

I’m hoping the new set up will improve performance thermally, waiting for some proper cold days so I can check the temperature of the boxes, the Mk1 was definitely getting cool last winter.