Dust Collection Pressure-Flow Calculation Program

[Thomas Wilson]

ust collection sizing is one of those Goldilocks problem. Size the duct too big and the dust settles out in the big ducts. Size it too small and the pressure losses are too great and there is not enough flow at the tool to collect the dust. I wrote a Matlab program to calculate the intersection of the fan performance curve and the duct system pressure loss curve. This is a standard engineering problem for predicting the flow and flow velocity. . I just programmed it up. I used the most accepted pipe friction factor formula (an explicit version of Colebrook) and loss coefficients from ASHRAE for the fittings. It is a Matlab program. The user inputs are just the lengths of various diameters and types of pipe and the numbers of fittings. The list is not extensive but enough for almost any small shop. The list can be readily extended. The same sort of too much or too little applies to the dust collector itself. I intend the program as a design tool for my own use but the activity on this topic on the forum suggests others might be interested.

What is different about may program? Most duct calculators online only calculate the system loss for a given flow (given as input by the user). This is not what you really want to know. What you want is the system flow given the system design. To find the actual operating point for the flow you would have to iterate manually between the fan head curve and the loss calculation. My program has the iteration built in.

I have all the correlations and data built-in. You just input the configuration data and run the code. I have checked my calculations against other data sources and correlations so it is reasonably reliable.

I use form loss coefficients for fittings rather than equivalent length. This form loss method is the textbook recommended approach.

I also have a separate version that does a main duct with two active branches. I created this version for my Sawstop with the over arm guard. It be useful for any tool that has two collection points, like router tables with collection box below the table and connection on the fence above or a bandsaw with a small nozzle right at the blade and another connected to the housing for the lower wheel. It would also work for two tools operating simultaneously

I have provided a method for including special terms that are present in dust collection systems but are not readily available from handbooks. This includes a way to model the losses in the cyclone and filter and entrance loss coefficients specifically for woodworking tools. I have not fully populated this cability with data but I have bought a hot wire anemometer and a manometer (Testo brand) to measure them experimentally. I have just embarked on this part of the calculator. Oneida may have seen me coming with this idea. Since I bought my system, they discontinued publishing the data that I used to estimate the flow losses in the cyclone and filter.

If anyone is interested in acquiring the coding, I will polish up the comments and put it on the Mathworks File Exchange. It is free but with no warranty or guarantee. I would say using the coding requires basic Matlab skills because you enter your data in the Matlab script and have to edit the source file to do so. And gyou would benefit from a general undergraduate-level knowledge of flow in pipes. Not too much because the coding is all done. You just have to understand the meaning of the labeling on the results.

Or, if you just want to discuss this kind of stuff, I am always available to listen or to explain or both.

TW

[Larry Frank]

It would be good to show an example of a system and how the programs works.

[Thomas Wilson]

It would be good to show an example of a system and how the programs works.

The calculation does what I need but does not make much of a graphical show. Glitz takes time. I put this up because there are two other posts asking questions that a design calculation would answer. If there were enthusiastic interest from fellow Matlab-using-woodworkers, then I would put forth the effort to produce the show. Frankly, interest seems lukewarm to nonexistent. My post was a trail balloon to connect with like-minded people. I will wait to see more interest. Also, I have some mouse-related tendinitis which means I should limit screen time.

[Paul Biggs]

Hi Thomas, I would be very interested in this if you are willing to share it? It would help me hugely. You don't need to worry about tidying it up and comments etc I'm sure I would be able to figure it out I've got a fair bit of MATLAB experience.

[Thomas Wilson]

Hi Thomas, I would be very interested in this if you are willing to share it? It would help me hugely. You don't need to worry about tidying it up and comments etc I'm sure I would be able to figure it out I've got a fair bit of MATLAB experience.

Hi Paul,

Sorry. I have dropped out of the SawmillCreek forum so I had not seen your request until today. I am willing to share the program. Are you thinking of making a commercial product? I would love to see that happen. There is so much myth and mystery and anecdotal information parading as fact that a little engineering could help clean up.

I would stipulate that my computational kernel remain public access so I could share it with anyone who asks or could write up the methods in my blog. You would be free to use, modify, write about,and sell if you wish.

I can send you the model file. I have not run it in several years so I am a bit rusty. Would you share an email address that you would like to receive the model file. Good luck.

Thomas

[David Frech]

Hello Thomas,
I would also like to try out your Matlab application. I'm starting the journey from Harbor Freight to ??? for dust collection and it would be nice to see what's needed.
Thanks

[Thomas Wilson]

Hi David,
I am traveling right now and left my laptop at home. I meant to load it but forgot. When I am back at my home base on next Tuesday, I think I can add a public folder with the files to my google drive or Apple iCloud so that it will be accessible to all. I also intend to write up the methods I used in the calculation and explain why I chose them. This will be easier if I can find the spiral notebook where I wrote it down originally. I will put links here when the files are loaded.

One of the difficulties with duct collector modeling is coming up withe data to model the fan, cyclone, and filter. Most people would appreciate some help getting the data they need for their system from available sources and instruction on putting it in the correct form for the calculation. I will work on that.

TW

[Chris Parks]

Hi David,
I am traveling right now and left my laptop at home. I meant to load it but forgot. When I am back at my home base on next Tuesday, I think I can add a public folder with the files to my google drive or Apple iCloud so that it will be accessible to all. I also intend to write up the methods I used in the calculation and explain why I chose them. This will be easier if I can find the spiral notebook where I wrote it down originally. I will put links here when the files are loaded.

One of the difficulties with duct collector modeling is coming up withe data to model the fan, cyclone, and filter. Most people would appreciate some help getting the data they need for their system from available sources and instruction on putting it in the correct form for the calculation. I will work on that.

TW

Have a look at the Australian WW forum, it has the best collection of data in the world for hobbyists all done by a physics professor with real numbers. The mods don't allow any direct links to other fora but try this, first hit in this search.

australian woodworking forum - Google Search

[Thomas Wilson]

Have a look at the Australian WW forum, it has the best collection of data in the world for hobbyists all done by a physics professor with real numbers. The mods don't allow any direct links to other fora but try this, first hit in this search.

australian woodworking forum - Google Search

Hey Chris,
You have mentioned the dust collection information on the Australian forum many times in the past and I have looked at it. I am aware of BobL’s posts there. I could not find the data I need. Perhaps you can help. I wanted fan curves for commonly used impellers in cyclone dust collectors and the brand association. If some has the specific impeller, impeller type can be determined from measured physical dimensions. I also need measured specific loss coefficients (loss per unit area) of filter media for brands of filters. I have something I use for this but it is not brand specific. And, cyclone loss coefficients for brand specific cyclones. With these data, I can construct a pressure-flow model of cyclone even if the manufacturer only reports fan-only maximum flow data for the fan (the big flow number people misunderstand as actual flow).

Oneida and Grizzly and maybe others give a graph of pressure versus flow for the full dust collector assembly (cyclone, fan, filter) which are measured directly on an actual system. If available, I digitize those graphs manually and use that function in the computation. When that is not available, I fall back on an approximation that combines flow characteristics of the individual components. That is what I am looking for.

I know you work in the dust collectior business so you may know of good sources of data. Finding it for me would be very helpful.

Thanks very much.

[Chris Parks]

Thomas, I personally don't worry about fan curves because I know what works for a hobbyist WW who wants to install a ducted system though I must admit my approach has changed in the recent past.

6" duct, 15" impeller at 60hz with all ports on the machines opened up top 6" is my go to recipe as it simply works.

The bigger the impeller means that it can be run slower reducing noise. I am largely out of the retail market now but if someone came to me wanting a DE ducted system I would get a 17" impeller made and run it at 40hz via a VFD. A Clearvue would work with the unit being no larger than a 15" so there is no downside from my POV and the running noise both in the workshop and at the exhaust is far lower.

I would not install a ducted system using single phase for a bet as a VFD adds speed control and other advantages such as remote starting on machine start very simply.

There is a company in the US whose name escapes me that has fan curves on their website and someone else might recall their name for you. The main problem with ducted systems in not the fan curve but the cheap inadequate dust extraction machines that retailers sell to people using horsepower as the selection criteria. Don't buy anything with less than a 14" impeller and forget HP altogether. If the retailer can't tell you what size impeller it has don't buy it as you are simply wasting money and not getting the performance you need for good fine dust control. Personally I don't see the need for a hobbyist needing fan curve information because to utilise it would mean a custom impeller being made. Another problem with DE is people try to over think it when Bill Pentz has already done that and arrived at the 15" / 6" recipe years ago and his website is simply over the top with information that is only useful to those who want to build their own cyclone.

Bob Loss on the Oz forum has provided information over the years with good basic explanations that anyone can understand and put simply it is the best repository for DE information in the world for anyone who wants to expand their knowledge. He has a fundamental professional background in designing clean rooms for research labs and he tried and proved stuff no one else has done previously and debunked stuff like using 2 x 45 degree bends with good solid demonstrations of why it does not work any better than a single bend and why using air speed meters is a waste of time. Anyone putting up a ducted system will be helped by a few hours reading the information he has published.

To sum up, forget fan curves and buy using impeller size as the criteria and use 3 phase which is very easy to do using a VFD. The bigger the impeller the slower you can run it but it most probably tops out at 17" for a hobby workshop. In the US where basement workshops are common the slower speed means lower noise levels which must be a plus. For anyone making a cyclone making a 17" impeller will cost about the same as a 15/16" one, been there and done that.

[Larry Frank]

I kind of agree with Chris. Oneida does publish its fan curves. I actually measured a fan curve for my Oneida Super Dust Gorilla with 15" impeller and 5 hp The data I got using a hot wire anemometer was close to the Oneida curve. It was interesting but not very useful. I find running with 6" DWV pipe and 15" impeller works very well.

Doing all the calculations is interesting but not very useful for most hobby woodworkers.

Also, the Aussie forum is worth a visit. BobL makes a great contribution to the dust extraction subject.

[Jim Becker]

The advantage to having actual fan curves available is to ascertain that the vendor's product can actually perform in real world conditions and I agree that there's no need for keen analysis for most small shop solutions. Vendors who publish the fan curves publically are saying that their machine will perform in a certain way over varying conditions. Vendors who simply say in their marketing material some big CFM number without providing a fan curve that shows the conditions where that CFM is possible are um...just marketing.

[Chris Parks]

The advantage to having actual fan curves available is to ascertain that the vendor's product can actually perform in real world conditions and I agree that there's no need for keen analysis for most small shop solutions. Vendors who publish the fan curves publically are saying that their machine will perform in a certain way over varying conditions. Vendors who simply say in their marketing material some big CFM number without providing a fan curve that shows the conditions where that CFM is possible are um...just marketing.

Apart from Oneida and Clearvue the whole retail end of DE is just marketing BS. There is no way that the average woodworker can check fan curve performance with any accuracy AFAIK due to a number of factors and the big one is how do you control the speed? and then that brings in the factor of how the duct runs and design affect the air flow. Different legs of the ducting will always have different flow rates and the whole thing is like herding 100 cats. I am yet to be convinced that the fan curve means anything to a WW and how knowing it is an advantage. The best thing to do when checking air flow is set up a manometer close to the DE inlet and using that maximise each duct run with the machine in the system. It is the total air flow we are trying to maximise not a piece of open duct.

Very few systems are designed optimally due to most users being reluctant to open up machine ports to 6" for some reason. If the ports are not opened up the airflow in the duct is governed by the maximum air flow of the 4" port which is abysmal compared to a 6" port. I find it strange that those same people would modify a car without hesitation.

Bandsaws get singled out for poor dust extraction but that is easily fixed by allowing air into the cabinet because you can't extract air from a closed cabinet so the debris accumulate in the cabinet instead of being extracted. I leave the cabinet door ajar on mine all the time with a small piece of wood holding it open and the air flow collects all the debris leaving a clean cabinet.

[Jim Becker]

Apart from Oneida and Clearvue the whole retail end of DE is just marketing BS. There is no way that the average woodworker can check fan curve performance with any accuracy AFAIK due to a number of factors...

True, but since there are almost no other DC vendors that provide the fan curve other than Harvey, there's nothing to check. To simplify my earlier point, these companies actually publish the data so if one is comparing the "general CFM figure" for their systems it's likely accurate. For the rest of the mass market, nope, like those 1.5 and 2 hp DCs that claim 1200 or 1500+ CFM and neglect to say that those numbers are about at the point where the unit goes up in flames because it has no ductwork attached.

I absolutely agree with many of your other points, too, the most important one is that in order to have enough volume of air to move the dust and chips, it has to actually come from somewhere. It's not "suction"...it's air flow.

[Larry Frank]

The comments about opening up machine ports to 6" is an interesting one for me. It takes a lot of work and skill to do a good neat job of opening up a port. I also wonder if it hurts the resale value. If a really good job is done, probably not.

I have considered opening the ports on my saw and other tools. For completeness, I have a 5 hp Oneida Super Dust Gorilla which has plenty of capacity. With the standard 4" ports, the dust collection is very good on my Sawstop, planer, bandsaw, and Supermax sander. I considered that any improvement that I might get from 6" ports would have been very small and could not justify the effort and costs.

With a different dust collector, perhaps things might be different.