Thread: Room air filter - Yes or no?

OH and another

Rather than buying an air filter .... buy another dust extractor, so that it can be located closer to the machines/s and have a shorter duct run.

cheers

Originally Posted by soundman

This will change the air in the workshop and reduce the dust load in the air faster than early anything else.

Assuming his shed is 2.7m high internally his shed volume is 194 m^3 or 6800 cuft. To achieve 20 room changes per hour will require 2270 CFM of extraction so he will indeed need a big fan. This is not unreachable in practice but I would not do this with just one fan as it will not be able to efficiently exhaust the fine dust.

Venting using a single exhaust fan in a large shed often ends up creating a preferential flow path, usually exhausting as much fresh air as dusty air and can even result in scattering dust to all parts of the shed before it is exhausted. Single exhaust fans can create what are known as dead zones in a shed from which dust can take much longer to remove.

The shape of the shed plays a big part in determining how effective exhaust fans operate. In long narrow sheds the fan and inlets should be located on the opposite shorter walls . On large sheds several fans and air inlets may be needed to avoid dead zones. I have tested this using particle counters in my L shaped shed. Even with 2800 CFM of exhaust extraction in my 42m^2 shed the air in the short section of the "L" part of the shed remains dustier for longer than the rest.

The most effective/efficient way to reduce the dust load in a shed is to grab as much of the dust at source as possible and exhaust it outside the shed by locating the DC outside the shed.

Well I have gone cold on the RAF idea. I understand your comments on the cfm ratings, I think I read another of your and your analogy of cfm ratings and vehicle manufacturers fuel consumption claims.
In regards Soundman's comments about rearranging my workshop unfortunately that isn't really practical for the combination saw. The router and bandsaw are mobile so can be easily moved though t he bandsaw position is dictated by the size of the timber I am using at the time.
Looking at the Timbecon catalogue there is virtually nothing in the way of 6" fittings so I presume that means pvc pipe and fittings.
To save me re-inventing the wheel can you suggest any websites or similar showing good setups so that I can get some good ideas, particularly in regards takeoff points.
Thanks to all for the helpful comments and info

Again Bob and as usual a whole pile of unnecessary complication .... a room air filter will have all the same problems of an extractor fan probably more and a whole lot less air flow.

IF a large portion of the shed is occupied with other things, ( particularly if it is the other end) we don't need to worry too much about that volume ...... place the large fan near the working area and have a little thaught about controlling the air flow by opening what ever doors and windows to advantage.

At one time I had the fan unit out of a Cardifiar .... it was a low reving 3 foot diameter fan .... let me tell you it shifted some air. ... 20 room changes a hour ... PFT ....... it would empty my shed of dust or smoke in about 3 minutes .... and that includes the dead spots ... the majority is gone in about 30 seconds ...... Remember I play with smoke machines.

A mate of mine picked up a bunch of these at auction ... he had a couple of these in a much bigger shed ....... well placed and running in summer gave a steady breeze thru his shed.

Exhaust fans large enough and well placed are realistic and effective.

Another long term member of this forum has a 2 foot ( 600mm) industrial extraction fan in the gable end of his shed ....... he will assure you it shifts whatever dust or fumes out of his shed very effectively ..... and yes he can control the airflow by opening doors and windows so the air flows where it should.

Now did I not say ....... right at the beginning of my post ......that getting dust extractors outside the shed was the most effective way of reducing dust inside the shed.

Remember there is pretty much NO tool that has 100% effective dust extraction, so no matter what plumbing you do, then there are the fumes that come from glues and finish products, you must have some sort of ventilation.

cheers

Again ..... going 6 inch makes a whole pile of extra work and expense. .... by the time you do all that you could buy another dust extractor and take the shortest run across the ground to outside the shed ..... some guys have even trenched and saved themselves 75%
of the length of going overhead or more

Go price a length of 100mm against a length of 150mm ...... and sit down before you hear the prices of the 6 inch fittings.

4 inch PVC can be made to fit all the commonly available 4 inch dust extraction hardware.

a bucket of boiling water will soften PVC and it can be stretched or compressed with hose clamps to fit pretty much anything close to that size.

All the standard plastic dust extraction hardware is PVC and will glue into 4 inch pipe with standard plumbers PVC glue .... remember softening the pipe to fit first.

some of the guys use toilet pan collars as plug in 4 inch connections.

There are a lot of people on this forum with systems built on 100mm PVC pipe ...... as long as you keep the duct lengths short and keep as few as absolutely possible bends it is perfectly adequate.

Unless you have a lot of time and money, building a fully plumbed 6 inch system is a waste of time .... Yeh I know a few who have done it.

multiple dust extractors and shorter lengths of pipe in my opinion is far more doable

Oh and forget the cyclone thing too ...... I was involved in the first flush of cyclone building on this forum way back in the early 2000s ....... unless you have plenty of power and plenty of money, 4 and 6 inch cyclones are a waste of time and money ..... oh and the space.

BTW .... look at the back history on this forum and there will be plenty of pictures and discussion .... a lot of it that predates BobL.
Go back far enough and you may see pictures of my saw bench and my mini cyclone that I still use.

cheers


cheers

Originally Posted by BobL

Originally Posted by Huon pine fan

In regards to a question I asked earlier about having a remote stop/start, is it simply a matter of removing the switch from the machine and then running a lead from the unit to an appropriate place inside the shed where the switch would be remounted?

Yes

I’m in the process of doing this, but I need four core cabtyre in order to do it - live, neutral, earth and an extra wire for the coil to hold the switch closed.

Originally Posted by soundman

let me tell you it shifted some air. ... 20 room changes a hour ... PFT ....... it would empty my shed of dust or smoke in about 3 minutes

PFT? 20 changes per hour is every 3 minutes.

Originally Posted by soundman

shed of dust or smoke in about 3 minutes .... and that includes the dead spots ... the majority is gone in about 30 seconds ...... Remember I play with smoke machines.

"Play" might be the operative word here.
I use 4 particle counters (that can actually measure dust levels even when it can't be seen) including access to two pro level counters that I access from my place of former employment. I have been using the pro instruments since 1978.
You simply cannot tell by looking at at any dust especially smoke when you think its all gone there is still a lot of small stuff around.
During the last few months in Perth there have been several smoke alerts from prescribed burnoffs and I have monitored their progress with my particle counters.
The detectors can detect smoke well before it can be smelled and seen. This showed me that judgments based on anything that can be seen are a waste of time.

RE: 20 room changes per hour emptying a room in 3 minutes
It just doesn't work like that. Ventilation works at best on a half emptying principle.
The first room change removes AT BEST half the dust in the room, Assuming NO MORE DUST has been added, the next room change empties another half of the remaining dust, and the next room change removes another half etc.
So the sequence goes 1/2, 1/4, 1.8, 1/16, etc
20 room changes per hour is at best andin practice about 10 room changes per hour and remember that assumes that no more dust is generated during this time.

20 room changes per hour is actually less than desirable but it works for small sheds but the "Fannage" required for large DIY sheds become impractical because of things like the noise and power requirements. There are quiet low powered high volume fans out there that use squirrel cages but these cost $$.

Originally Posted by FenceFurniture

PFT? 20 changes per hour is every 3 minutes.

Yeh how about you quote the entire sentence ........ complete air change in about 30 sec .... dust and smoke will always hang around in corners longer.

Originally Posted by BobL

"Play" might be the operative word here.
I use 4 particle counters (that can actually measure dust levels even when it can't be seen) including access to two pro level counters that I access from my place of former employment. I have been using the pro instruments since 1978.
You simply cannot tell by looking at at any dust especially smoke when you think its all gone there is still a lot of small stuff around.
During the last few months in Perth there have been several smoke alerts from prescribed burnoffs and I have monitored their progress with my particle counters.
The detectors can detect smoke well before it can be smelled and seen. This showed me that judgments based on anything that can be seen are a waste of time.

RE: 20 room changes per hour emptying a room in 3 minutes
It just doesn't work like that. Ventilation works at best on a half emptying principle.
The first room change removes AT BEST half the dust in the room, Assuming NO MORE DUST has been added, the next room change empties another half of the remaining dust, and the next room change removes another half etc.
So the sequence goes 1/2, 1/4, 1.8, 1/16, etc
20 room changes per hour is at best andin practice about 10 room changes per hour and remember that assumes that no more dust is generated during this time.

20 room changes per hour is actually less than desirable but it works for small sheds but the "Fannage" required for large DIY sheds become impractical because of things like the noise and power requirements. There are quiet low powered high volume fans out there that use squirrel cages but these cost $$.

Bla Bla Bla ......Yeh Yeh you can bang on all you like about unachievable targets and beat your chest about how much you know and what instruments you have.

Truth of the matter is that the vast majority of home workshops will NEVER come close to those rediculous expectations.... because for one reason or the other it simply is not achievable. ... mostly cost.

Truth of the matter is the vast majority of commercial workshops NEVER come close to those rediculous expectations.

However, taking a workshop from having dust everywhere to a reasonably managed situation where it is not unpleasant and some light PPE will do the job, is quite reasable, affordable and easy enough to do.

AND YES I can tell by looking, that there is not a thick film of dust on every horizontal surface, yes I can tell by looking that there are not piles of dust on the floor, yes I can tell by looking that there is way more dust being captured before than after.
I can tell by looking that there is no longer, dust all over my clothes and in my hair after a day in the workshop.

For most people, they don't need to instruments to see a clearly and dramaticaly improved situation.

For most people that use other than the very latest, high cost industrial equipment, That is pretty much all of us, the dust capture at source will be so poor, that regardless of what else they do they will never achieve the reduculous targets you keep banging on about.

cheers

Originally Posted by soundman

let me tell you it shifted some air. ... 20 room changes a hour ... PFT ....... it would empty my shed of dust or smoke in about 3 minutes

Ah well, it's a little ambiguous you see. What you meant was "PFT - gone" but it can also be read as "PFT - that's nothing" or "PFT - so what?". That's why I queried it.