My dust extraction plans - please comment

[fobos8]

Hi all

I mainly do site work but have started to do more joinery from home. I have just bought a 12" planer thicknesser so need to sort out some serious dust extraction. Over the coming years I plan to get a decent table saw and probably other machines.

I have read the Bill Pentz website. My plans for a system are as follows;

6" ducting with the main run going through hole in garage wall to lean to shed outside which contains a 3hp, 12" impellor, 3000m3/hour chip extractor. The filter will not trap fine dust so as not to reduce airlow. The shed will be built so its well vented.

I realise that cold air will be sucked outside when I have the extractor switched on but I thinks its a small price to pay.

Would anyone like to comment on my plans in case I've missed the point on something.


Many thanks, Andrew

 

[OLD]

If you have a wood burning stove it will smoke when the extractor runs .

 

[Chems]

Is 6inch really necessary for the home workshop?

 

[woodsworth]

Any time you are taking air outside of the shop new air needs to replace it. When i was in the Tin/forced air furnace trade we used to make up air units for commercial applications and apartment blocks. In your situation i would pipe it outside into a cyclone and back in through a filter. That way you have the noise in an insulated box outside, where you can empty the container without contaminating the shop and you won't loose air from your shop as you will be filtering it back in. The filters will last a lot longer as cyclones are very effective at removing small particles if designed properly.

 

[ondablade]

Hi Andrew. The hard air flow numbers below rely on interpreting/guesstimating from Bill Pentz's table at middle of this page: http://billpentz.com/woodworking/cyclone/DCBasics.cfm

Presumably you are exhausting outside to avoid the need to fit a cyclone and fine filters. The cooling effect of drawing in outside air will depend i guess on the temperature of that air, the starting temperature and volume of your shop, and the cfm rate for how long/often the air is being dumped.

One way of looking at it is how fast the air in your shop will be replaced by outside air - divide the volume of the shop in cubic ft (length X breadth X height in ft). So volume in cubic feet/1100 = rough time in minutes to replace the air the shop. (pardon if i'm being too picky)

You can estimate the heat loss in kW using the formula:

Heat loss in Btu/hr = 1.08 X cfm X (room temp deg F - outside air temp deg F)

3412 Btu/hr = 1kW, so divide the answer by 3412 to get the answer in KW.

You probably have a fair feel for how quickly you shop would warm up on say 2kW of heating, so this would give some feel for how fast it might cool.

While i'm fitting a cyclone and HEPA filters that's my plan too - no point clogging your filters if exhausting is causing nobody any problem, and the outside air temperature and humidity conditions allow. That said my shop is fairly large at 8.5X5.5M with a loft overhead. (a decent hot air reservoir) I will have an 8in branch to exhaust outside fitted with a blast gate - when closed it will divert all of the air through the filters.

According to Bill's test tables a 12 inch impeller delivers around 880cfm on 10ft of flex hose with filters and a cyclone. (the high number is the result of a very short hose compared to most ducted installations, add more ducting and it rapidly goes south) He's presumably on 3450rpm 60Hz US motors so you will lose a bit by going to 50Hz in the UK. On the other hand he reckons that 3hp will deliver 1100cfm on a 13 inch impeller, so you have a bit more power. (but check your rpm is 2850)

It's possibly unlikely that the motor is oversized (as in there is less impeller than the motor can handle) on a commercial dust system, and while it probably doesn't do the 3,000m3/hr (1760cfm) on any realistic duct set up it could well do some more than the 880 cfm Bill quotes for a 12 in impeller. (this draws only around 1.5hp) Your coarse filters and no cyclone will save some pressure drop too, as will using smooth ducting as opposed to flex hose per Bill's test. (hose has 3 - 4 X the pressure drop per unit length as galvanised duct.

880cfm is not quite enough to do a really good job he says (it meets chip collection rather than fine dust collection needs), but depending on how you figure the pros and cons above you could easily end up around 1100cfm which if achieved he reckons is fine.

It'd be important to carefully think through the ducting and hose arrangements to minimise the lengths and avoid leaks and restrictions - especially of flexible hose. Also to make sure the machine hoods are not restrictive. i.e. have free area equal to at least 6 in duct. Bill's 10ft of flex hose should be equivalent to about 30ft or a bit more of galvanised ducting - so it'd probably be best to get as far under this as possible.

One test that should i think give a ball park indication of where you are on CFM would be to check the current being drawn by the fan motor while the system is in use and work it back to hp. (240 X amps)/1000 = kW. (approx) Then kW/0.746 = hp.

If it's less than about 2.2hp (as you restrict the intake on a fan the power drawn reduces) it's probably getting a tiny bit marginal on cfm to do the full-on dust clearance job.

Please pardon the mixing of units... :lol:

 

[ondablade]

PS On smoking of stoves OLD. I've been thinking of installing a waste/dust burning stove, and wondered about that.

I suppose if exhausting outside the effect would be minimised if you made sure to have lots of air intake area (open door???? ), but i'm not sure how feasible or effective that might be.

Do dust systems generally cause problems with stoves if filtered and set up to recirculate air inside the building? I'm guessing it would only take a small disturbance in pressure to upset the draught in any flue...

 

[OLD]

I have a smaller version of your proposal (1hp 100mm) and i have to open the door about 25mm, its easy to forget as it takes a short time before it starts smoking.

 

[dickm]

Don't know if it's relevant, but we have a forced ventilation system in the house (with heat recovery unit) extracting from the kitchen end of the open plan and blowing into the living end. Even with a 4" pipe leading direct to the hearth from outside, our previous woodstove was a pig to manage if the ventilation was on. But our current Morso doesn't seem so fussy.

 

[Finial]

I don't think 6 inch ducting is over the top at all. Bigger would be better for a 3 hp motor.

I would think twice about venting outside. the extractor won't run just when the machines are running. You will be lucky if it catches all the dust at source, but if you leave it on it acts like an air cleaner. Then the heat loss will be really noticeable. So fit the filter, with or without a cyclone. You can get extractors with filter cleaning and the suction will still be strong if the ducting is reasonable. You could leave it off in summer and vent outside then.

Remember machine noise could be a problem to neighbours either from the extractor itself or from the air inlets in the main shop, and the fine dust also if not filtered.

 

[ondablade]

The minimum airflow you need on a 6 inch duct is around 800cfm - this to get the 4,000fpm needed for good conveying of dust and chips, especially up a vertical leg.

On venting outside Finial. I think too that unless Andrew can restrict his fan running to short periods that it's likely to get cold (and also possibly too humid for his wood) in winter. That said some talk of working in conditions around zero degrees, so i guess it's horses for courses.

The big practical issue as above is that if in winter the incoming average 70% RH air is not heated to something above 60 deg F the RH in the shop (which determines the equilibrium moisture content your timber will head for) will set the timber on its way to something above the 8 or 9% moisture said to be ideal for cabinet work. (70%RH delivers around 17% MC ) It takes a long time to reach equilibrium moisture content, but the bigger issue is perhaps that the resulting (fairly quickly arising) inequalities in moisture content (as the moisture works its way into the wood from the outside surfaces) through your timer may cause cracking and warping.

That depending on the sort of work you do and your methods may or may not be an issue for you...

 

[fobos8]

my intention would be to extract only when machining. There's no point in having it on at any other time.

Thanks for the points about stoves - hadn't thought about that.

....... so to avoid the heat loss of having the whole dust extraction system outside can somebody explain in idiots terms how I set up a system which separates the big chips into a bucket inside and sends the fine dust outside?

 

[fobos8]

.........have just realised that by sending the fine dust outside that it be sending the warm shop outside so will be the same as having the machine outside.

What other options are there for meeting the specifications prescribed by Bill Pentz. I have no engineering knowhow whatsoever so cannot make something myself. The ClearVue system some have mentioned does't have a 50Hz motor so cannot be used in UK.

Have noticed that there are some Cyclone systems available with the neccessary airflow (>800 cfm ) but the filters don't seem to have the 300sq feet recommended by Pentz. This one http://www.axminster.co.uk/product-Axminster-Plus-Axminster-Plus-UB-3100ECK-Cyclone-Extractor-795045.htm only has 9m2.

What other choice do I have in the UK than to put a chip collector outside if I want to meet the Pentz spec?

 

[Chems]

clearview are closing, you might be able to get a cheap on sent over. That and a good filter is what you need to keep your warm air in.

 

[ondablade]

The most economic option Andrew if you don't want to shove your warm air outside and replace it with cold is as Chems says to recirculate it within the building. This means as before that it becomes necessary to filter the dust out to a very high standard or you just end up with a dust distribution system.

The high quality filters this entails require (by current methods anyway) an effective cyclone to avoid filter blinding and overly frequent replacement.

This is only speculating, but you could i guess heat your incoming air to replace what you exhaust, but using the formula above 1,100cfm raised from freezing to 60 deg F is a heating load of about 10kW.

Expensive if run for any time, but (thinking aloud in Heath Robinson mode) perhaps do-able as a part of a larger heating solution with a wood stove or even a heat exchanger (large aluminium truck radiator set in a hole in the wall, it'd probably draw no significant heat if you stopped air flowing through it when the fan was off !) fed from you central heating system?

Your suggestion is good thinking as a possible route to minimising dust system costs - a short hose, no cyclone or filters and exhausting outside is if you can get away with it is one way of maximising the air shifted with the smallest possible blower. The question is whether or not it makes sense in the total picture.

Apart from comfort it might well be do-able for much of the year. If you are doing e.g. traditional oak beams where some splitting and movement is not an issue, then there's no obvious problem either.

A lot hangs on whether your blower has enough puff. It might be a good move to take some ammeter readings to figure out what HP it's drawing as above before spending on trying to upgrade the system.

You have to make your own call on the DIY route as a means of getting to a more robust spec system, but it's not that very difficult and there's lots of info about.

Maybe as Chems says you could buy one cheaply from Ed..

PS I didn't know Clear Vue were closing Chems, but checking after your post i see that Ed has a notice up on his site. It's a pity. I hope he's genuinely retiring as his margins cannot have been all that large at the prices he was charging.

I got some of their 6inch moulded Lexan blast gates (they look and feel great) for my system only last week.

 

[fobos8]

Ian

Thanks for your indepth reply.

As you say I've got choices; the external system I mentioned or having an internal system with a great cyclone, great impeller and motor and great filter.

I've got no intention to build diy the second option - its way out of my league - i just know it is.

Your right there is potentially a problem from an external system that of drawing humid air into the workshop. I can't see a way of measuring how much of a problem it would be other than just trying it.

I could get an internal stysem like this one http://www.axminster.co.uk/product-...-Plus-UB-3100ECK-Cyclone-Extractor-795045.htm but I'm sure on the Pentz site he recommends 300 sq ft filters. Are there any available that I can fit to this machine?

 

[DaveL]

While the size of the filters on the Axminster machine are smaller than Bill recommends, it does have 'automatic filter cleaning for consistent performance', which should help to overcome the smaller size.
All of the filters will need cleaning in time, having bigger filters makes the effects of the clogging slower and lengthens the time between cleans.
I don't think it will be easy to fit bigger filters as the machine is quite compact for a dust collector of that spec.

 

[OLD]

My suggestion would be stick to original proposal and have a vent back to the shop from the lean to at high level, looking at my situation very little dust would find its way back.
Also note if you open up the air input to the stove its much less likely to smoke

 

[ondablade]

Hi Andrew. I honestly can't say for sure. Looking at the Axminster spec it should probably at 3hp have enough grunt to shift enough air to meet Bill's numbers if the hose and duct runs are kept short.

A lot hangs on how efficient the cyclone is, in that it determines how much junk gets to the filters. They mutter about 0.2 micron in the spec., but quote no spec for the filters but as Dave says maybe the shaker would help. It'd be interesting to ask for a filter spec.

It's no problem to buy HEPA (99.99% eff @ 0.3 micron) filters in the UK, so you could if needed probably upgrade. Donaldson Filtration (the local branch of a mjor international outfit) in the North do a 12 3/4 X 26 in approx cartridge for £120, and there are a few others around i have info for too although i don't know what spec their stuff is.

Looking at the unit it's conceivable that you could fit two filters side by side with a bit of modification. If it doesn't need to be mobile then a second stacked cartridge like the Clear Vue layout might be an option by raising it a bit higher off the ground.

Failing that less filter area very probably means you have to change filters more often, but one at a time instead of two - it may not increase your cost of filters very much. (anybody got any experience?)

That's about as far as i can take it Andrew, bear in mind i'm speaking as much from past HVAC experience as of use of the Pentz system...

 

[fobos8]

Hi Ian

Thanks again. There's a lot to consider. If I upgaraged the filter so a larger area it will definateley affect airflow so I doubt I'd get the 3,700 on the spec for the original filter.

Gonna sleep on it.

Cheers, Andrew

 

[croy5199]

I have a Dust Extractor from Bill Pentz, but due to workshop size constraints, never used it.
It comes with the cyclone, the impeller, some 6" gates. I also purchased a 2KW AEG singly phase 240VAC motor locally for it. Offers around £500. onco will be considered.
Call Roy on 0773420 6952