Thread: Bastardising a room air cleaner into an enclosure.... ideas?

I can't see a problem with this idea especially if you can use alternate/cheaper size filters. Ordinarily I'd like to see something a little finer as the final filter but once it's conditioned it should be OK as it is continually scrubbing air. The most critical thing is to get an air tight seal between the fan and the filter so that all the air from the fan is forced through the filter and does not bypass the filter and just cycle back into the shed. If you draw something up I am happy to comment on it.

It's a pity we can't find a cheap source of squirrel cage motors so serious HEPA room air filters could be made from scratch. There used to be a company in SA called PREECE fans that made really beaut 1000 CFM squirrel cage fans for about $300 but i have not been able to track these down. There are some 400 and 500 CFM fans on Ebay but they are on the small side. The only 1000 CFM ones I see on ebay are from the US so they get pretty expensive.

FWIW we used to make our own fan, prefilter and final HEPA filter enclosures for the labs at work using the PREECE fans.
The sizes of filter area ranged from 300 x 300, to 600 x 1200 mm
The main issue we had with the commercial enclosures were they were made of epoxy coated steel and in the slightly corrosive atmosphere of the labs they would eventually rust so we made them out of epoxy painted ply or in the cleaner labs Polypropylene/HDPE. The 1200 x 600 commercial units also cost about $3500 each and we needed quite a few of them whereas we could buy the parts for about 1/3rd of the price and I got quite quick at making the enclosures.

Below, the corrugated paper things in the plastic boxes are the 1200 x 600 HEPAs and the fan unit is on the LHS inside a plastic box with a speed controller underneath it. The HEPA filtered air would be pushed by fans down over the central bench and go down to the floor and over to and up the false walls. The far end is a fume hood with a 1200 x 600 HEPA above it. I built this entire lab from scratch plumbing, electrical, air flow etc
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After 2000 we found an NZ company that was importing thickly Powder coated HEPA Filter enclosures fitted with fans and Filters from the US and if we ordered more than 2 dozen we could get them for an amazing price. I think we paid around $700 each for the basic 1200 x 600mm size and $900 for teh super high efficiency units, and if they died or corroded we just replaced them - not many did - I think we lost 3 in about 10 years. In the end we purchased around 70 of these units to fit out a very large lab.

In 2008 a fire in one of the labs resulted in the severe contamination of a lab, one HEPA filter enclosure, and 14 HEPA filters. I offered the 14 smoke contaminated filters for free on the forums and only one member came and picked up two.
I scored the HEPA filter enclosure and 3 HEPA filters before they all ended up in the skip. I cleaned up the smoke HEPA damaged enclosure and tested the filters and they still worked fine and now have that unit in my shed. This unit is so efficient I cannot measure it's actual efficiency - the work particle detector detects ZERO particles over a 4 hour measuring period.

Hepa1.jpg

Absolutely incredible. I'd kill for something like those.

The Jet has a big squirrel cage in it. I'll take a photo.

This is beginning to sound like a plan! Let's find a monster HEPA filter!



edit: made a few contacts. Plans progressing. Found two good suppliers for ~MERV8 pre-filters and ~600x600 HEPA's in a few depths. Centrifugal fans and motors next!

Perhaps I can take a cue from the HVAC and hydroponics industries?

Squirrel cages with motors are fairly hard to come by, it seems. A few in China, hardly any here. Weird.

These might fit the bill though (in the 12" model): https://www.ebay.com.au/itm/4-5-6-8-...t/223498981102

This colossus is apparently 1/3HP.

Its just under 10" wide and the "inlet" appears to be about 8".

The grill at the end offends me mightily.

Originally Posted by woodPixel

Perhaps I can take a cue from the HVAC and hydroponics industries?

Squirrel cages with motors are fairly hard to come by, it seems. A few in China, hardly any here. Weird.

These might fit the bill though (in the 12" model): https://www.ebay.com.au/itm/4-5-6-8-...t/223498981102

Before using one I'd like to know the static pressure the fan can generate. Those fans are meant for ventilation wth nothing in their path way hence have a limited resistance capability.

Ive written to the fan dudes.

Originally Posted by woodPixel

This colossus is apparently 1/3HP.

Its just under 10" wide and the "inlet" appears to be about 8".

The grill at the end offends me mightily.

That's similar t0 the one I have ventilating my spray booth/welding bay fume hood.
Fan.jpg

And a bit bigger than the one I have as a general exhaust fan at my roofline above my TS.
IMG_5180.jpg

I got both of these out of skips at work about 5 and 6 years ago - they were quite beat up and corroded and I had to rebalance the fans.
They are both nominally 1/3rd HP, and both have speed controllers.
The blue one is a 3P motor and that grey box attached to it is a used 1HP VFD I bought for $70.
I can run this one at up to 70Hz where it moves heaps of air but not for too long as the motor gets hot even with all the air rushing past - good for a quick general vent of the shed.
At the other end of the scale at say 40 or 35 Hz its whisper quiet and still moves lots of air.

BTW along with the blue one in the skip there were 4 more of these fans in various states of health, one was badly crushed and beyond repair. I took two and gave one to a mate.

That "skip" you often refer to sounds like a bloody Aladdin's cave of wonders!

Is this chart any use for static pressures? It is for that eBay link above.

I wouldnt mind a motor with a speed knob... I need to Brush Up on my motors

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Thanks for the info.

Hummmm . . . .830 Pa for the 12" thats about 3.5" WC - that's a bit on the light side. It will be fine for clean filters but it will lose CFM as the filter blocks up.

Can you measure the static pressure on your squirrel cage fan.
Make up a U-tube manometer and block off the exit and measure the pressure?

I know you guys don't do much with central heating thus the scarcity of squirrel cage fans but you do have ducted central air conditioning don't you? Wouldn't one of those contractors have fans from old units they've replaced or have you come up with weird ways of cooling too?

Pete

Originally Posted by QC Inspector

I know you guys don't do much with central heating thus the scarcity of squirrel cage fans but you do have ducted central air conditioning don't you? Wouldn't one of those contractors have fans from old units they've replaced or have you come up with weird ways of cooling too?
Pete

Many Australian houses use ducted evaporative AC which uses a large axial fan. These work very well in dry areas although refrigerated AC is becoming more popular especially in the more humid areas.
In terms of refrigerated AC, many homes use a couple of what are called split systems that service one or several rooms (we have over about 10 years installed 4 of these at our place!) and these are more common that fully ducted systems.
For some time many fans in domestic an commercial fully ducted refrigerated air conditioners have had a low profile like that shown below so they fit in the limited spaces found in modern Australian ceilings.
The units usually contain two smaller/low profile squirrel cage fans driven by one motor (3) and integrated into an enclosure with a heat exchanger (1) and VFD (2) etc.
Because they contain a substantial heat exchanger (1) and VFD(2), even in a used state they tend to command prices much greater than the value of their fans
The shape of the enclosures are also not that conducive to commonly sized filters or being modified to suit a room air filter.
Enclosures to suit more common filter sizes are often located elsewhere in the ducting.

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Thanks Bob. The other thought I just had when looking at your illustration is kitchen range hoods. The one installed in our home has a squirrel cage fan and can move up to 600 cfm continuously and 800 cfm for a few minutes. I guess the only advantage to a cold climate is the piles of old fan assemblies at our disposal.

Pete

Originally Posted by QC Inspector

Thanks Bob. The other thought I just had when looking at your illustration is kitchen range hoods. The one installed in our home has a squirrel cage fan and can move up to 600 cfm continuously and 800 cfm for a few minutes. I guess the only advantage to a cold climate is the piles of old fan assemblies at our disposal.

Pete

Yeah - I've looked at a few. Like most fans their CFM claims are unreliable and the one we have here are usually Axial fans that have very little static pressure as the typical filters they pull cooking fume through are quite coarse.

I should add that Evaporative AC fans make excellent shed ventilation fans. Evap AC fans typical provide ducted air for a whole house so they move HUGE amounts of air and are not expensive to run. One of the least dusty DIY sheds I have assessed is a smallish shed with a house sized EVAP AC fan - it was a bit of a gale at full speed but it was a very low dust environment.

Originally Posted by BobL

Yeah - I've looked at a few. Like most fans their CFM claims are unreliable and the one we have here are usually Axial fans that have very little static pressure as the typical filters they pull cooking fume through are quite coarse.

shortest job I ever had was working ??? with an outfit that cleaned the fans/pipework etc for maccas, hungry jacks etc. You get into full cover overall, eye protection and air canister for fresh?? air then crawl into the pipework and scrap the shoit out. I last 3.2 hours and told them where to put it.

That was 25 years ago and Ive never had fast food since.