industrial wood shop DC

[Clymber]

As an amateur woodworker on the side, I was pleased when my next work assignment was to design a dust collection system for an industrial wood shop (Maybe this will inspire me to move beyond the shop vac in my garage). However, since I am new to the HVAC design world, I've got a few questions.

Apparently this will be a basic woodworking shop. No finishing, just multiple BS, DP, TS(3), RAS, and a surface planer.

My basic idea is a cyclone separator for the big stuff followed by a cartridge-type DC. Obviously the fan should be sized for all equipment operating at once. However, instead of a mega-sized constant speed blower, are variable-speed devices used?

I'm envisioning a flow or pressure measuring device linked to a variable speed drive on the fan. Airflow would vary based on demand. Automatic blast gates on individual equipment would open when the equipment is started and vice versa.

Does anybody have experience with similar systems or is it easier just to keep the basic CV system?

I would also expect that the DC equipment would be located outside and fresh air make-up would be required to cover the exhaust stream(independent of the conditioned air). Is this right?

TIA.

 

[cme]

no vsd

use the industrial hygenists handbook

you have to keep the air velocity high enough so you convey it into the collector

4000 fpm seems to ring a bell (dry dust)

you should be at 12" on the fan

i use torit mfr in the past, with "sock" after-filters and silencer, check codes for recirc restrictions due to combustible wood dust, its been some time since i eng one

there are mfr's for high pressure flex hose used where needed at the equipment, i dont have the url handy

 

[Clymber]

Thanks, cme. VSD is out the window. I stumbled across the website for ONEIDA AIR SYSTEMS, which has a good alternative. If 2 or 3 machines are attached to each DC, I can filter the air and return it to the space. If it doesn't leave the building, I won't have to worry about make-up air.

Thanks for the help.

 

[cme]

Give them a few floor cleanouts too

 

[quark]

This link gives you good deal of information about dust extraction system in woodwork shops. An excel spreadsheet for the design of cyclone separator is also included.

http://billpentz.com//woodworking/cyclone/index.cfm

Intalling multiple DCs is a better idea than going for vfd control. I strongly opine that a switch is a better energy saving device.

As wood dust is in the infinite list of carcinogens, you may rethink about your option of recirculation. Anyhow, you can use enthalpy wheels or runaround loops to tap the energy.

Regards,

 

[ChrisConley]

Clymber,

I have a technical handbook from N.R.Murphy, which gives recommended extraction numbers for equipment as well as recommended duct velocities for conveying sawdust, chips, wet or dry.

I recommend checking out there website and ordering the manual (it was free).

http://nrmurphy.com/

My two cents is that constant volume systems are easiest to control, and maintaining duct velocity (3800-4200 fpm for sawdust) is almost impossible with a VFD.

We tend to specify the combination cyclone/filtration unit. With a terylene filter.

Other concerns are fire protection related. Check your local codes if a sprinkler protection of the unit is required. Fan should be AMCA class A.

 

[walkes]

An additional thought:

You can probably size the unit for some diversity. 70% of the machines operating then isolating the additional extraction runs with blast gates.

 

[lilliput1]

Make sure there is no way the unit can run with all the inlets close or you will cavitate the fan. I worked on a turbine fan vacuum system used to catch metal shavings from aircraft riveting operation and the system had a modulating control valve at the end that maintained a minimum pressure in the system. Trouble was it was noisy as hell. Had to put (3) silencers in series to get noise level down to 80 dbA.

 

[Clymber]

thanks for all the advice, guys. Looks like I'm ready to get this underway.

 

[cme]

Oh ..... Ground the ductwork

 

[dpoppeli]

Don't use plastic duct. That pretty much eliminates any grounding issues.

I doubt you could cavitate duct at pressures seen in a typical woodworking system since the duct will have to be strong enough to take the occasional wood-block careening through the system anyway. Blocking off all the inlets is probably undesirable jsut form the noise standpoint but it does get pretty efficient that way with lower motor amps pulled.

Oneida seems to know what they are talking about and appear to have reasonable prices.

A varibale-pitch drive might be nice to allow a balancing of the system without multiple sheave and belt changes. This limits you to lower HP systems.

An initial flow measurement is handly to ensure you're at a minimum conveying velocity. Too high jsut wastes energy, too low... well. This can be done with a $50 Grainger magnehelic and a pitot tube. Reuse the magnehelic on your afterfilter to indicate when it needs to be cleaned.

 

[darkvibe]

Just some random toughts from reading this.... Don't forget a duct leakage test in the specs. Heavy and wet sawdust has a transport velocity of 4000-4500 fps in the handbook. Ive done similar systems and used a blast gate in each drop and a bleed-in damper at the end of the header.