MVHR Active Carbon Filter

[Ultima357]

Having lived with MVHR for 9 months I have just completed a DIY active carbon filter as my neighbours just like stinky bonfires too much. Whilst you can easily shut it off when you're at home, it is a horrible surprise to come home to find your home smelling like a bonfire. 

 

So I began to research active carbon filters and found those commercially available ones were stupidly expensive and the cost of replacing the filters was also the best part of an arm too. I began therefore at the actual active carbon filter and found that these are many and varied and a huge range of costs. Looking at what I had room to install I decided to get as large a filter as possible and at reasonable cost. I chose one designed for plant nurseries as they are both compact and low cost and got one rated at 600m3/hr with an estimated 3 year life. Again I found a variety of prices but being an experiment, I decided on one costing just over £40 delivered. You can find similar for up to 3 times this. 

 

Pictures show the construction of a 450 x 400 x 400mm box in 12mm mdf mainly, just the end out with 18mm to give a greater rigidity for the filter mount/seal. Installed it today and already tested tonight as just had to shut windows due to stinking bonfire again! Running at 220m3/hr currently with no smell whatsoever. Well pleased. Total cost less than £70 for materials. Being retired I don't count my labour. 

 

Monitoring the MVHR it has given some additional load/back pressure as expected, increasing the input fan speed by between 50rpm and 500rpm depending on m3/hr selected. The higher rate when running at 330m3/hr. At 100m3/hr its around 150rpm up. MVHR is Brink Flair 400. 

 

If this continues to perform, I might go for a higher cost filter with less back pressure when I replace it or see if I could squeeze two of these in parallel into the space I have. Should be possible. Just another 30 quid for more mdf and a few more hours making it. I rebated and glued joints to keep it airtight apart from the lid which is rebated and just screwed down. 

 

Hope this might inspire others to give it a go. Filter from Future Gardens, Assasin 600m3/hr. MDF from wherever you can get it. Just two quarter sheets. Plus a few hours design and sawdust making on my cnc router table but could be done using a hand router and table saw if you have a good eye for square and straight edges... ?

[PeterW]

Nice idea - that MDF needs a couple of good coats of decent eggshell or gloss to stop it absorbing moisture though. 

[dpmiller]

what weight is the filter, and what size of granule? First one gives a clue about how much you can adsorb, second is related to flow restriction and rate of adsorption.

 

/ used to spend a lot of time working on duct-free fume cupboards...

[Nick Laslett]

15 hours ago, Ultima357 said:

Having lived with MVHR for 9 months I have just completed a DIY active carbon filter as my neighbours just like stinky bonfires too much. Whilst you can easily shut it off when you're at home, it is a horrible surprise to come home to find your home smelling like a bonfire. …*snip

 

Thank you for highlighting this. I’m still a long way from finishing my build, but this issue with MVHR sucking in bonfire smoke seems like a potential problem for some sites. This is a potential downside to MVHR that needs to be flagged up during the design stage, so that it can be planned around. 

[Ultima357]

Sorry for late reply everyone. I set it to flag me on responses but it didn't! Anyway, as for data on how much carbon granules are in it, there is no data on it, but it weighs circa 3 to 4kg and I'd guess the housing being aluminium will be only 500gm of this. There are similar carbon filters such as Carboair which have more data and are probably better. Of course more expensive too and as I am experimenting I choose a low cost item to start with. Typically they filter :-

 

 

Pesticides/herbicides 0.001nm

Paint pigment 1-5nm

Odours/Diterpenes 1-10nm

Mould spores 10-30nm

Plant spores 3-40nm

Common dusts 30-600nm

Plant pollens 10-1000nm

 The active carbon bed is 50mm thick.

 

I coated the mdf with two coats of external grade water based clear lacquer to seal it. It's situated on the house supply side so shouldn't get overly moist. 

 

As for planning one in at the start, I'd say just give yourself enough room and go my route. The branded mvhr filters are very expensive and I would expect they sting you for replacement filters. As mine is rated for 600m3/h with a life of 12 to 18 months, and I generally run at just 100m3/h, I'm expecting a life of at least 2 years. Time will tell but it's on the prefiltered side so only dealing with the smells, not too much dust, so should be OK. Maybe when it's time to replace I'll use a more expensive version with less back pressure or put a couple of these in parallel in a larger box. I need to make fitting a replacement easier for sure but it's in and working well. 

 

 

[dpmiller]

you can always stick it in the oven and bake the odours back out again...

[SteamyTea]

16 hours ago, dpmiller said:

you can always stick it in the oven and bake the odours back out again...

Or report neighbours to the council.

[Ultima357]

On 09/08/2021 at 11:14, SteamyTea said:

Or report neighbours to the council.

Smoke is a very difficult thing to track down sometimes. Tonight we have a countryside scent outside, local pig farm by the smell, thankfully the filter is doing the job! 

[Ultima357]

Final comment. Having lived with it for several weeks I can now say it works fantastically well. Yesterday, someone close by was burning rubbish including rubber by the smell of it. Quickly closed doors and windows (it was a nice warm sunny day) and result, absolutely no smell inside. Outside was purgatory! So if you're considering this, based on my experience I'd unreservedly recommend doing it. 

[CalvinHobbes]

Very impressed! Have made a note of this for our build. Thank you.

[Ultima357]

Update to this filter. After proof of concept with the low cost and relatively low volume flow filter, I have now rebuilt the whole unit using a much larger filter rated at 2400cu m/hr. The reduced back pressure means the fan works at lower rpm whilst maintaining the throughput and at maximum 330cu m/hr of the MVHR there is very little difference between the in and out fans rpm wise. Given the flow rating of the filter (Phresh 600 x 300), I'm expecting a lot of years service before any need to replace it. 

[SteamyTea]

11 hours ago, Ultima357 said:

I have now rebuilt the whole unit using a much larger filter rated at 2400cu m/hr.

Good stuff.  Do you have pictures and prices?

[Ultima357]

No unfortunately I built it in a hurry and didn't take photos and it's a bit too warm to go up the attic at the moment. The filter I bought from Future Gardens https://www.futuregarden.co.uk/phresh-premium-filters. It's the 600 x 315 @£188. The cabinet housing I used 15mm mdf and used one and a half sheets. The two sheets cost just under £80 these days with cuts as required so I could get it all in my car. Fortunately I have a CNC router table so able to accurately cut out the required holes and rebates for jointing, so all in around £250. The filter is quite a beast as the 315 refers to the inlet diameter and its around 440mm diameter overall and weighs in at around 18kg if I remember correctly. Basically it's a big box with raised plinth inside across 2/3rds of the depth to hold the filter and provide the appropriate airway flow. Mounted it vertically as that was all I had space for.