air cleaner motor from box fan? - Woodworking Talk - Woodworkers Forum
Reply
 
Thread Tools Display Modes
post #1 of 28 Old 07-09-2011, 10:16 AM Thread Starter
Senior Member
 
wilbwworker's Avatar
 
Join Date: Jan 2011
Posts: 141
View wilbwworker's Photo Album My Photos
air cleaner motor from box fan?

Hi guys I have a 12 x 20 foot shop with a peaked roof. It is completely open inside all the way to the roof. I have calculated the cubic footage to 2400 cubic feet. This is not a large area.

Currently for an air filter I use an 18' box fan with a filter attached to the back. Pretty low tech I know but better than nothing. As I am preparing to build an air cleaner I am wondering why I can't use the same fan and motor inside of the box I am building?

I don't know the velocity or size of the motor and there are no markings on it. I checked last night. However it would seem to me that in such a small space I can change the air pretty quickly with that fan.

Can I just take it apart from the housing and mount both the blades and the motor inside a box with some HEPA filters before the fan?

I am having some trouble finding a squirrel cage fan and this occured to me last night as I was working in the shp.

Western MA
wilbwworker is offline  
Sponsored Links
Advertisement
 
post #2 of 28 Old 07-09-2011, 10:28 AM
where's my table saw?
 
woodnthings's Avatar
 
Join Date: Jan 2009
Location: SE, Michigan
Posts: 26,216
View woodnthings's Photo Album My Photos
just off the top of my head

The squirrel cage motors/blowers are meant to operate with a restriction. The motor in a box fan isn't. If you restrict it somewhat probably not an issue...but possibly it may overheat inside that box, and it will be difficult to know. FIRE?
Personally i would leave the fan intact, just rotate it so the switches can be reached easily and make a 1/4" or so open box on the sides. Then you can add several filters across the draw end maybe with strips to retain them. It's worth a try but keep an eye on it for heat. bill

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
woodnthings is online now  
The Following User Says Thank You to woodnthings For This Useful Post:
BWSmith (07-12-2011)
post #3 of 28 Old 07-09-2011, 10:48 AM
SS user
 
Gene Howe's Avatar
 
Join Date: Feb 2009
Location: Snowflake, AZ
Posts: 2,690
View Gene Howe's Photo Album My Photos
I'd hold out for a squirrel cage!
Surely, there are HVAC folks around who usually have a pile of them "out back". Mine came from my own furnace after a retrofit AC unit was installed. The installer said they sell used ones for $10.00 and that $ goes towards Friday's beer for the crew.
Gene Howe is offline  
Sponsored Links
Advertisement
 
post #4 of 28 Old 07-09-2011, 12:04 PM
Member
 
Join Date: Dec 2010
Location: Colorado, USA
Posts: 39
View wmodavis's Photo Album My Photos
How do you fit an eighteen foot box fan in your 12 foot shop? That's a big fan!
wmodavis is offline  
post #5 of 28 Old 07-09-2011, 12:36 PM Thread Starter
Senior Member
 
wilbwworker's Avatar
 
Join Date: Jan 2011
Posts: 141
View wilbwworker's Photo Album My Photos
har har

That fan is huge! I have it installed by the Jolly Green Giant!

Western MA
wilbwworker is offline  
post #6 of 28 Old 07-11-2011, 09:08 PM
Nic
Junior Member
 
Join Date: Jul 2011
Posts: 1
View Nic's Photo Album My Photos
http://www.surpluscenter.com/electri...tname=electric - check here for squirrel cage fans.
Nic is offline  
post #7 of 28 Old 07-12-2011, 01:30 PM Thread Starter
Senior Member
 
wilbwworker's Avatar
 
Join Date: Jan 2011
Posts: 141
View wilbwworker's Photo Album My Photos
Thanks Nic, That is a handy place to go. My next question is how big of a blower do I need? I have calculated my cubic feet around 2400. How big should I buy?

Western MA
wilbwworker is offline  
post #8 of 28 Old 07-12-2011, 02:23 PM
where's my table saw?
 
woodnthings's Avatar
 
Join Date: Jan 2009
Location: SE, Michigan
Posts: 26,216
View woodnthings's Photo Album My Photos
I checked that site

And none of those squirrel cage blowers are large enough for your space.
Based on these specs at the bottom (1044 CFM max) you might want to get something like this: http://www.amazon.com/708620B-AFS-1000B-Filtration-Electrostatic-Pre-Filter/dp/B00004R9LO
If you search shop air filtration units you'll find that www.Grizzly.com www.pennstateindustries .com and other make similar units.

If you want to make one I suggest a visit to your local and hopefully friendly furnace repair or heating and cooling store where they will have a take off blower from a furnace. I got one for $40.00 with 3 speeds... and don't forget to ask which color wires go where. You can get a 4 position rotary switch to select each speed. A box of plywood to surrond the blower and some furnace filters will give you a good start. Buy the filters first and make the box to suit that size...slightly bigger than the blower unit....
Who knows, their sheet metal guy might just bend up a cover for you at a reasonable cost and a few donuts thrown in. It's surprising what happens when you show up in person and have a good attitude.
Search home or shop built air filtration units for more info. bill

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 07-12-2011 at 08:06 PM.
woodnthings is online now  
post #9 of 28 Old 07-12-2011, 03:54 PM
Thumb Nailer
 
dbhost's Avatar
 
Join Date: Jan 2008
Location: League City, Texas. A.K.A. Hurricane Alley
Posts: 2,454
View dbhost's Photo Album My Photos
FWIW, if you are going to go the buy it route instead of build it, I can certainly feel good about recommending the Grizzly G0572. I hear great things about the Jet as well. Haven't seen any posts about the PSI units, but they are so simple it is kind of hard to screw them up.

Interested in my woodworking, workshop and whatnot? See http://daves-workshop.blogspot.com, want to see my other interests such as hunting, fishing, off roading, and camping? See http://wildersport-outdoors.blogspot.com
dbhost is offline  
post #10 of 28 Old 07-12-2011, 04:43 PM Thread Starter
Senior Member
 
wilbwworker's Avatar
 
Join Date: Jan 2011
Posts: 141
View wilbwworker's Photo Album My Photos
No way am I buying it. I can't afford it. I have to build it myself..... so my question still is this:

What size blower do I need?

I saw a fan on that website that would move 500 cfm. By my rudimentary math skills if I bought and installed that one wouldn't I change the air like every five minutes?

I know it isn't a squirrel cage but would that work?

Western MA
wilbwworker is offline  
post #11 of 28 Old 07-12-2011, 08:15 PM
where's my table saw?
 
woodnthings's Avatar
 
Join Date: Jan 2009
Location: SE, Michigan
Posts: 26,216
View woodnthings's Photo Album My Photos
I don't think the CFM specs are on furnace blowers

If you want to build one the cheapest way, is get a used furnace blower. Make sure it will work on 120 V as some are 220v motors!
You probably have less than $100.00 if you get a used furnace blower, a rotary switch and make a plywood box...1/2" will do. Cut the end off an extension cord for a power cord.
Make a top and bottom identical.
Make a left and right side with a space for the filters.
Make a frame for the filters.....wire it up, turn it on.
Take pix, post here! bill

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 07-12-2011 at 09:41 PM.
woodnthings is online now  
post #12 of 28 Old 07-12-2011, 08:34 PM Thread Starter
Senior Member
 
wilbwworker's Avatar
 
Join Date: Jan 2011
Posts: 141
View wilbwworker's Photo Album My Photos
OKay but do I need a certain size blower? Or will anyone of them do?

Western MA
wilbwworker is offline  
post #13 of 28 Old 07-12-2011, 08:52 PM
In History is the Future
 
firemedic's Avatar
 
Join Date: Dec 2010
Location: South Louisiana - Gonzales
Posts: 6,423
View firemedic's Photo Album My Photos
Quote:
Originally Posted by wilbwworker
OKay but do I need a certain size blower? Or will anyone of them do?
I picked up a 1/3 hp blower for $30 from my AC... Man does it move some air. I haven't put it in a box yet, but the plan is similar to what your doing. You probably don't need one that big, but you definitely don't need one bigger than that...

~tom ...it's better to remain silent and be thought a fool than to open one's mouth and remove all doubt...
firemedic is offline  
post #14 of 28 Old 07-12-2011, 10:16 PM
In History is the Future
 
firemedic's Avatar
 
Join Date: Dec 2010
Location: South Louisiana - Gonzales
Posts: 6,423
View firemedic's Photo Album My Photos
Or you could always go this route:

http://www.chiefsupply.com/3092-Temp...c-Blowers.aspx

:)

~tom ...it's better to remain silent and be thought a fool than to open one's mouth and remove all doubt...
firemedic is offline  
post #15 of 28 Old 07-12-2011, 10:23 PM
where's my table saw?
 
woodnthings's Avatar
 
Join Date: Jan 2009
Location: SE, Michigan
Posts: 26,216
View woodnthings's Photo Album My Photos
This one will do

Quote:
Originally Posted by wilbwworker View Post
OKay but do I need a certain size blower? Or will anyone of them do?
http://cgi.ebay.com/FURNACE-SQUIRREL...item2a0d2fcfbe
Perfect! size and voltage is correct. bill
Others are listed below...

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
woodnthings is online now  
post #16 of 28 Old 08-22-2011, 06:19 PM
Junior Member
 
Join Date: Aug 2011
Posts: 8
View darrollr's Photo Album My Photos
Lets learn from each other!

I built an ambient air cleaner/purifier system like you are talking about a couple years ago for use in my 24’x24’ garage. I've had great luck with it so far but am now looking to update it some since I have a much bigger shop now and need more filtration. I am a welder and use it to get rid of the smoke, gases, fumes, dust, etc.

I have researched many sites and many existing machines and come up with what I think is a great solution but am looking for someone with more knowhow to tell me if my calculations are correct. It can be very daunting trying to understand all that is involved in creating an efficient air cleaner/purifier. There are so many calculations and variables involved; it is hard for me to wrap my head around it all.

I will post some pics later. For starters I built a box with a 13.5”, 1/10th HP, 1320CFM attic fan. The fan is mounted in the top facing the ceiling. This way the clean air is distributed using the "Coanda Aerodynamic Principle." The air hits the ceiling and is distributed across the shop ceiling and away from the intake/return filters. I made my box so that all four sides have filters. Leaving a space between the fan and the filters assures that the entire area of the filters will be used. Good filters require significant backpressure, which means tight sealing to prevent bypassing. There are currently 4 stages of filtering. Each side of the box has four 20”x20” filters in series. That is a total of 16 filters. I do not remember the micron rating or the cost for all of the filters.

These are the filters:
4" merv 12 pleated filter with 226.66 Square Ft. of filter media, and an initial resistance of 0.15 @ 300 FPM,
1" merv 9 carbon activated filter with 33.33 Square Ft. of filter media, and an initial resistance of 0.218 @ 300 FPM,
1" merv 8 electrostatic washable filter with 33.33 Square Ft. of filter media, and an initial resistance of 0.32 @ 300 FPM,
1" merv 2 cheap Fiberglass furnace filter prefilter, (I will not use this type again, it doesn’t do enough good to justify using it. I am replacing it with 1” MERV 4 Cut-N-Fit Blue Natural Fiber furnace filter with 33.33 Square Ft. of filter media, and an initial resistance of 0.125 @ 300 FPM.
I plan to make a 5th washable prefilter out of fine mesh fiberglass window screen, just to catch the large debris.

I know that this is a lot of filters, but it is my understanding that you want to have a low static pressure for the machine to work properly. And in my opinion, the more filtering, and the more types of filtering, the better.

My combined total Square Feet of filter media for the 16 filters is = 1306.6

My total initial resistance of filter media for the 16 filters is =? I am not sure how to add these up!

The idea behind a proper air filtration system is to exchange the greatest amount of air in the shortest duration while at the same time keeping the velocity slow enough so as not to disturb settled dust in other parts of the space. Another important issue is to avoid negating the 'arrestiveness' of the filter by having too much air being drawn through the filter and thereby drawing the dust through the filter. Arrestiveness is defined as the ability to retain particulate without it being drawn through the filter. So, the idea here is to move enough air to trap the dust at the source by using the proper amount of airflow and, of course, using the proper filters.

In the grand scheme of air handling, any fan is able to exchange a certain volume of air in a certain amount of time and is expressed in (CFM) or cubic feet per minute.
All of the air which enters the air cleaner/purifier system enters through the return air filter. The filter must be theoretically sized according to the cfm (cubic feet per minute) requirement of the system. A filter that is too small will cause a number of problems. The filter will clog very rapidly if undersized and reduce air flow. Air velocity also becomes critical with reduced size and dirt will pass through instead of staying in the filter. The system is trying to draw in the designed air quantity and if the filter will not allow flow, air will be drawn in from any possible crack. Every system, no matter how air tight you construct it, will have small cracks through which dirty, warm air will enter the system as static pressure increases. A large surface area filter will negate the effect of these cracks by having a lower static pressure and lower air velocity.

The airflow resistance of a filter and the fan pressure required to overcome it depend on how fast the air is moving and how long and narrow the paths are. Friction along air paths creates resistance to airflow. Fans must develop enough pressure to overcome this resistance and move air through the filter.
Airflow resistance and fan pressure are usually expressed in inches of water column (in. water, or in. H2O). This term comes from gages called u-tube manometers that are sometimes used to measure pressure.
Propeller fans normally can't generate more than about 2 in. water pressure. They are most commonly used for exhausting air from attics or overhead spaces, or general air circulation.
Tube-axial and vane-axial fans are the most common types used for HVAC. They are relatively inexpensive and fairly efficient when static pressure is less than about 4 in. water. The main disadvantage of these fans is that they are very noisy.
The maximum allowable filter velocity is 300 feet per minute (fpm) on disposable filters. For best results, the recommended minimum filter surface area is 2.00 cubic feet per minute (cfm) per square inch of filter area. Using 2.00 cfm per square inch the velocity of air across the filter will not exceed 300 fpm.

Example: 2000 (CFM) ÷ 200 in. water = 1000 square inches of filter media.
Fan Performance

Because of the way fan impellers (blades or rotors) are designed, the amount of air they can move decreases as the pressure they are working against increases. The airflow vs. pressure information for a particular fan is called the fan performance data. Performance depends on the size, shape, and speed of the impeller, and the size of the motor driving it. Performance differs widely among brands and models, even for fans with the same size motor.
Access to fan performance data is essential for selecting fans and for determining airflow provided by existing fans. Most manufacturers sell fans that have been tested using procedures specified by the Air Movement and Control Association International, Inc. (AMCA). The manufacturers can provide you with performance data in the form of tables or graphs. Avoid fans for which AMCA data is not available.

Selecting Fans
Calculate total airflow needed

The first step in selecting a fan is to determine the total airflow it must provide.
Estimate static pressure
The next step in selecting a fan is to estimate the pressure the fan will be operating against.
Estimating fan power requirements
Fans are usually described by the horsepower (hp) rating of the motor used to drive the impeller. It's helpful when selecting fans to estimate the power requirement first so you know where to start looking in the manufacturer's catalog.
Fan motor size depends on the total airflow being delivered, the pressure developed, and the impeller's efficiency. Impeller efficiencies generally range from 40% to 65%. If we assume an average value of 60%, we can use the following formula to estimate the fan power requirement.
Fan power (hp) = airflow (cfm) x static pressure (in. water) ÷ 3814
Example, Fan power = 7325 cfm x 2.4 in. water ÷ 3814 = 4.6 hp.

Selecting the best fan available
The most critical factor is whether the fan can provide enough airflow at the expected operating pressure. Start by looking at performance data for a fan having a motor rated just under the power value you calculated. If this fan provides more than enough airflow, look at the next size smaller. If your first pick is too small, try the next size larger.
darrollr is offline  
The Following User Says Thank You to darrollr For This Useful Post:
Shop Dad (01-02-2012)
post #18 of 28 Old 08-22-2011, 06:20 PM
Junior Member
 
Join Date: Aug 2011
Posts: 8
View darrollr's Photo Album My Photos
Questions I have:
1. Do I need a gap between each filter and if so, how big?
2. How can I determine the Merv rating of my filter unit with all of the filters combined?
3. What is the combined initial resistance of my filters? (AKA: Airflow Restriction, Airflow Resistance, Negative Pressure, Pressure Drop, etc.)
4. Do I have enough or not enough initial resistance for my fan?
5. Do I have too much area of filter media for my fan?
6. Is my fan adequate?
7. Any advise at all?

Things I want to implement on my new ambient air cleaner/purifier:
1. Build it out of 24 gauge galvanized sheet metal. This will cut down on weight and make a nicer enclosure.
2. Add a fluorescent light to the bottom of the box to better illuminate my work area.
3. Install a pressure gauge on my new box to tell when to clean/replace the filters. As the filters get clogged more negative pressure builds inside the box. Here is the type of gauge I plan to use.
http://www.amazon.com/Dwyer-Mark-Model-Inclined-Manometer/dp/B003NUVVV6/ref=pd_sim_sbs_hi_1

4. Add plug in receptacles for easy access at my work area.
5. Add power switch with timer.
6. I may use furnace filter gasket tape to better seal the filters.

Last edited by darrollr; 08-22-2011 at 06:22 PM. Reason: Updated Link
darrollr is offline  
post #19 of 28 Old 08-22-2011, 06:35 PM
Senior Member
 
Join Date: Jul 2008
Location: Florida Panhandle
Posts: 11,960
View GeorgeC's Photo Album My Photos
I would just install an exhaust fan up near the peak of the roof. That was it can be both a cooling fan and exhaust the dust to the outside.

Of course in the dead of winter you might not want that fan running.

George
GeorgeC is offline  
post #20 of 28 Old 08-22-2011, 07:39 PM
Junior Member
 
Join Date: Aug 2011
Posts: 8
View darrollr's Photo Album My Photos
My shop is a conditioned space so I dont want to push my heated or cooled outside. Plus I live in Oklahoma and it is 100+ and high humidity, so I dont want to pull that hot humid air inside. I also dont have any windows so the air would have to come in from an open door which would also let in uninvited pests.
darrollr is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Woodworking Talk - Woodworkers Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
DIY air cleaner/filter Gene Howe Tips, Tricks, & Homemade Jigs 32 07-23-2011 09:36 AM
Blade Cleaner ( Oven Cleaner ). Woodsphere General Woodworking Discussion 5 04-08-2011 12:34 AM
Ambient air cleaner help please. xphnmn Dust Collection 6 04-08-2011 12:10 AM
Have a good Cab't cleaner? Leatherneck General Woodworking Discussion 12 06-17-2010 07:15 PM
Air cleaner opinions chubbyhubby Power Tools & Machinery 4 04-01-2010 06:31 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome