Carbon Air Filter

[MikeGrahamT21]

Hi,

 

Everywhere I ask about MVHR and outdoor smoke, everyone seems to recommend a carbon air pre-filter to remove the smell and any organic particles. They are stupidly expensive!

 

I have come across these though: http://www.carboair.co.uk/carboair-100-200-660

Seem to go for anything between 100 and 300 on ebay, which is much more palatable. 

Not sure they are designed for this purpose, but as long as the air intake can be located inside our ventilated roof space, I don't see an issue bolting this onto an MVHR duct.

 

What do you think? Would it work? And would having the air intake inside ventilated roof space be suitable? Having the intake inside would increase summer temperatures though, so that maybe needs a bit of thinking about. I suppose I could house this in a sealed container, which also has a duct to the outside world.

Edited February 15, 2018 by MikeGrahamT21

[richi]

16 minutes ago, MikeGrahamT21 said:

I have come across these though: http://www.carboair.co.uk/carboair-100-200-660

"CarboAir™ 100 has been developed to filter very high concentrations of VOCs from larger grow rooms."

Do I detect a wink-wink in that sentence?

 

Anyway, I'm sure @JSHarris will be along in a moment to outline a homebrew solution containing fish-tank granules 

[Jeremy Harris]

It seems that a fair few of these odour-reducing filter manufacturers have sprung up from the need to ventilate indoor cannabis farms without letting the distinctive, and rather strong, odour escape..............

 

Making a home brew carbon filter with fish-tank granules should be really easy.  The cross sectional area needs to be large, as the granules will restrict flow, so I would suggest trying to find a carbon granule based recirculating cooker hood cartridge, as large as you can find, and then make a case to house it inline with the fresh air feed to the rooms (not on the intake side of the MVHR, on the fresh air outlet side, so it has the benefit of being warmed up and pre-filtered).

 

If you include an ozone generator before the carbon filter you may well be able to extend the life of the granules before they need changing/regenerating.

 

All told not a hard thing to DIY, and it would have the added advantage of acting as a silencer on the fresh air feed side, too.

 

Fish tank granules are cheap when bought in bulk, I still have around 5 or 6 kg of them from the 10kg I bought years ago to replenish our cooker hood filter.

[Ian]

I once designed a large new-build curry factory located right next to a lot of housing. All extracts from the food production areas were filtered through an externally located shipping container that was fitted with racks of carbon.

Edited February 15, 2018 by Ian

[Jeremy Harris]

I love the idea of a shipping container being used as a giant filter!

[Ian]

@MikeGrahamT21

The filters in the link you provided look very similar in shape to ones I've got at home on a reverse osmosis water unit:

http://www.ro-man.com/shop/large-diameter-carbon-filters

[Cpd]

2 hours ago, MikeGrahamT21 said:

Not sure they are designed for this purpose, but as long as the air intake can be located inside our ventilated roof space, I don't see an issue bolting this onto an MVHR duct.

 

What do you think? Would it work? And would having the air intake inside ventilated roof space be suitable?

This has been talked about before, from what i remember you want both the intake and exhaust to be on the same building face. So both on a wall and separated by a few meters to prevent contamination, so exhaust downwind of intake. The reason i think is to help with balancing the system as if your intake is in the roof and your exhaust on a wall exposed to winds there will be a pressure difference. Also if I remember correctly you dont want to be sucking in cold wet air into your roof space. Sure someone will correct me if i am wrong. I wanted to do the same thing but have been warned against it, would be good to get clarity. 

[Jeremy Harris]

@Cpd, spot on, for all those reasons.  I'm having to move our external intake with a short length of externally mounted ducting, just to get around the wind-induced imbalance, which is a significant issue.  At the moment we have the exhaust facing away from the prevailing wind and the intake at righ angles to it, which is far from ideal.  Had I realised the impact this would have I'd have not fitted the intake terminal where it is.

[dpmiller]

You need a fair old area of enclosure to stop carbon granules being terribly restrictive, from my fumecupboard experience. Does mean dear, but also means plenty of storage capacity.

 

http://www.carbonfiltersdirect.com/

are my supplier of chioce for carbon cassettes if anyone fancies building a housing around one.

[PeterW]

Can someone explain to thicko here as to why you couldn’t use this stuff ..?? 

 

http://www.finest-filters.co.uk/diy-activated-carbon-foam-18-x-12?gclid=EAIaIQobChMI_puvjeKo2QIVTrHtCh08_g4wEAQYASABEgKsSPD_BwE

 

If you put this into a 12” square filter casing with the gap in the middle filled with granules, would it work ..??

 

Or have I been at the product @JSHarris eluded to..?! 

[Jeremy Harris]

I'm not sure, it depends on its resistance to air flow.  In my head I had visions of using two sheets of fine wire mesh, maybe around 1m square, separated by a gap of around 10mm, which was filled with carbon granules.  That's pretty much how our old cooker hood filter is made up, although the wire mesh either side has a thin layer of non-woven fluffy filter stuff that helps keep the carbon granules in place.

[PeterW]

http://www.ducting-express.co.uk/store/index.php?route=product/category&path=61_202

 

What about these ..??

 

 

[Jeremy Harris]

3 minutes ago, PeterW said:

http://www.ducting-express.co.uk/store/index.php?route=product/category&path=61_202

 

What about these ..??

 

 

 

They look like they would do the job, especially as it looks as if they are designed for things like spray booths, so will presumably have a pretty high capacity for VOCs.  I wonder what sort of flow resistance they have?  MVHR probably needs a more free-flowing filter than something like a spray booth, with it's higher flow rate/greater available dynamic pressure.  Might need some experiments to see what sort of pressure drop you get across one.

 

I've been thinking that a long, thin, carbon granule panel filter might be a good option.  If you made up a long box, with a rectangular carbon granule filter fitted as a divider down the centre, then fed air in at one end, on one side, and took air out at the other end on the other side, I have a feeing that the air would have a longer exposure time to the carbon, yet not be overly restrictive.

[MikeGrahamT21]

23 hours ago, richi said:

"CarboAir™ 100 has been developed to filter very high concentrations of VOCs from larger grow rooms."

Do I detect a wink-wink in that sentence?

 

Anyway, I'm sure @JSHarris will be along in a moment to outline a homebrew solution containing fish-tank granules 

Yeah I did think about cannabis myself when I read that lol!

[MikeGrahamT21]

Thank you for all of the replies, very useful links too. The CarboAir ones seem to be pretty high flow, but I suppose i'd have to match it correctly with whatever MVHR unit I end up with.

 

I suppose the most important question, would it get rid of the smoke smell, and would an F7 (can you get F7 filters?) filter remove the harmful particles?

 

Just trying to keep the dream of MVHR alive, what with all the neighbours who seem to love burning things round here all the time!

[Jeremy Harris]

3 minutes ago, MikeGrahamT21 said:

Thank you for all of the replies, very useful links too. The CarboAir ones seem to be pretty high flow, but I suppose i'd have to match it correctly with whatever MVHR unit I end up with.

 

I suppose the most important question, would it get rid of the smoke smell, and would an F7 (can you get F7 filters?) filter remove the harmful particles?

 

Just trying to keep the dream of MVHR alive, what with all the neighbours who seem to love burning things round here all the time!

 

I may get time tonight to do a sketch of a design that I think might work OK, and that could easily be a DIY project.  I've been giving this some thought overnight, as we could do with something to help keep bonfire smoke out.  Twice this week I've had to turn the MVHR off, because a couple of neighbours decided to break the "bonfire ban".  It's only a seasonally issue, really, but is still a nuisance if you don't happen to notice until the house is already smelling of smoke.

 

Watch this space, as I should be able to post up my early sketches either tonight or tomorrow, depending on the weather and if I get deflected off to do some other task............

 

None of the available filters will take take out PM2.5s, but carbon may well adsorb them, I think.

[MikeGrahamT21]

1 hour ago, JSHarris said:

 

I may get time tonight to do a sketch of a design that I think might work OK, and that could easily be a DIY project.  I've been giving this some thought overnight, as we could do with something to help keep bonfire smoke out.  Twice this week I've had to turn the MVHR off, because a couple of neighbours decided to break the "bonfire ban".  It's only a seasonally issue, really, but is still a nuisance if you don't happen to notice until the house is already smelling of smoke.

 

Watch this space, as I should be able to post up my early sketches either tonight or tomorrow, depending on the weather and if I get deflected off to do some other task............

 

None of the available filters will take take out PM2.5s, but carbon may well adsorb them, I think.

That would be brilliant, look forward to seeing what you come up with :-)

 

Yeah a lot advertise that they take out PM2.5 in some way or other.

[MikeGrahamT21]

56 minutes ago, richi said:

Here's the one I just bought for my Berstrøm recirculating hood (it just came with some useless foam filters): amzn.to/2EMVzoM -- seems well made, but no idea yet if it's actually removing any smell!

Yeah i've got a spare one something like that laying around somewhere, it did remove the smells, but it choked the hood so much, that it barely moved any air, so I took it off, think our hood is just massively underpowered.

[Jeremy Harris]

20 minutes ago, MikeGrahamT21 said:

That would be brilliant, look forward to seeing what you come up with :-)

 

Yeah a lot advertise that they take out PM2.5 in some way or other.

 

In theory they might, as the spec for F7 is > 1µ, I believe, but they seem to rely on stuff that small sticking to the filter, rather than actually being positively filtered out, I think.  This seems to be a general principle with a lot of air filtration, AFAICS, in that in order to reduce the flow resistance the manufacturers rely on the filter capturing smaller particles by some sort of attraction between the particle and the filter material, maybe by shaping the filter to force a velocity change over it's surface (that's a random guess!).  I've had a close look at the F7 filters on our unit, and to the naked eye they look coarser than the 5µ filter in our water system.  Not very scientific at all, but intriguing as a comparison.

[PeterW]

Wonder if using an ion type “spike” generator would be enough to get any smoke particles to bond to a carbon foam filter..?? I know they normally need quite low flows but could it work ..?

[Jeremy Harris]

13 hours ago, PeterW said:

Wonder if using an ion type “spike” generator would be enough to get any smoke particles to bond to a carbon foam filter..?? I know they normally need quite low flows but could it work ..?

 

 

It might help, but I've a feeling that an ozone generator ahead of the carbon filter might work a bit better, for a few reasons.  The chances are that the sort of particulates in bonfire and wood smoke will oxidise fairly well, plus most corona discharge ozone generators are also powerful ionisation sources, to, so will tend to work like an ionisation generator (which is really just a very low amplitude corona discharge).  Ozone will also tend to make the carbon last longer, as it will oxidise pretty much any volatile that the carbon adsorbs.  The trick would be getting the right amount of ozone at the right times.  That could be something as simple as a manual switch, that's operated whenever there's smoke around, if the smoke is only an infrequent issue.

[MikeGrahamT21]

One thing I've never found out, is Ozone good or Bad? You hear both sides on the net

[Jeremy Harris]

1 hour ago, MikeGrahamT21 said:

One thing I've never found out, is Ozone good or Bad? You hear both sides on the net

 

Both!

 

On the good side:

 

As a very powerful oxidising agent it's probably one of, if not the, best way to disinfect water, as it kills pretty much all bugs, cysts etc in seconds, much more quickly that chlorine, and best of all it has no harmful breakdown products.  The main alternative, chlorine stays in sealed water systems and also produces harmful breakdown and reaction products, like chloramines.

 

As a means of removing odours, when used at very low concentrations, it is safe and useful, again because it leaves no harmful residuals behind.

 

As a bleaching agent (from oxidation) ozone has the same advantages as it does for water disinfection, but the concentration needed is greater.

 

As a means of disinfecting sealed rooms and both removing persistent odours and killing pretty much anything in the room (bugs etc) then it can be very effective, as it breaks down quickly (in around 30 mins) to oxygen when the ozone generator is turned off,  This makes it safer in most respect than other forms of fumigation.

 

As a protective layer in the upper atmosphere it allows life to survive on our planet, by being one of the major filters against harmful ultraviolet radiation from the sun.

 

On the bad side:

 

It causes irritation to our nose, eyes, lungs etc at quite low concentrations - as a general rule if you can smell it the concentration is bordering on that which may cause irritation.  The irritation from low concentrations goes away, with no lasting damage, soon after the source of exposure is removed.

 

At high concentrations it can very quickly cause serious damage to any mucous membrane it is exposed to, and may lead to long-lasting damage to the nose, airways, lungs and eyes in particular.  At a high enough concentration it can kill, mainly as a consequence of this sort of damage.

 

On balance:

 

If used carefully it can be very useful as a chemical free disinfectant, that leaves no residuals behind, and can also be very useful in removing volatile odour molecules.  You can smell it at concentrations that are below those that cause harm, so that makes it hard to accidentally suffer the harmful effects.  In general I think that, used sensibly, ozone has a place in disinfection, bleaching and odour control and some types of fumigation.

[MikeGrahamT21]

Never knew that, a very useful thing indeed!

[MikeGrahamT21]

@JSHarris Did you manage to come up with a plan for something like this?

 

I've emailed a few more MVHR suppliers, again all say carbon filters, but again none of them can guarantee that it will even work, and at £800, its a lot of money to gamble on.

 

I did have a thought on making any sort of carbon filter last longer, and that was to put a manual bypass, so that when the heating season is over, we can effectively bypass the carbon filter, since we don't live in a high pollution area anyway, but other than that, i'm still in the no-go camp for MVHR, which is still extremely annoying. Its a good job i've got a lot of improvements to make before i get to this stage lol!

 

Reading a few bits online seems to suggest electrostatic will remove the majority of the smoke, which will be the ozone you spoke about. Looking on ebay these type units are really cheap to buy, and I'm guessing you'd just put the carbon brushes into the MVHR ducting and silicone them in?

Edited May 4, 2018 by MikeGrahamT21