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Participant

Join Date: May 2010
Posts: 4

Blower CFM And Horse Power

05/04/2010 7:14 PM

I have a customer who purchased a used supply fan, the fan unit does not have a name plate for model number, I have found the manufacturer who is Mc Quay. I need to determine the horsepower of the motor that will be needed to drive the fan.

Specs i have.

inlet 16" diam x 2

exhaust 46" x 43"

centrifugal fan

blower wheel: 34" diam x 12" wide x 2

Blower shaft 2-1/2"

number of blades on each blower wheel: 10

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Pathfinder Tags: blower CFM fan horsepower
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Guru

Join Date: Oct 2008
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#1

Re: Blower CFM and horse power

05/04/2010 7:17 PM

Have you not searched?

www.AirDistributors.com

There are tons of these at Search GlobalSpec

Just enter McQuay.

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Participant

Join Date: May 2010
Posts: 4
#2

Re: Blower CFM And Horse Power

05/04/2010 10:00 PM

Yes i have been to Mc Quay's web site and they do not have any supply fans only, they have fan coil units but we dont have the refrigeration part of it, I called Mc Quay and was told they needed the part number to look up the fan curves.

thanks

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Guru
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#3

Re: Blower CFM And Horse Power

05/05/2010 2:56 AM

The shaft power required by any fluid mover is the pressure rise multiplied by the volumetric flowrate divided by the efficiency.

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Guru
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#4
In reply to #3

Re: Blower CFM And Horse Power

05/05/2010 8:50 AM

I think this formula has to multiplied by some constant.

power delivered by a fan/blower= K*P*V

I don remember the value of K and relevant units of P and V

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Guru

Join Date: Jul 2005
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#5
In reply to #4

Re: Blower CFM And Horse Power

05/05/2010 3:31 PM

No, PWSlack's formula is fine. If P is in Pa, V in m3/s, it gives power in watt.

OP was titled Blower CFM And Horse Power, but doesn't mention CFM (or pressure rise). I'm having trouble picturing this fan. Are there 2 off 16" suctions? Even if so, area is small compared with discharge 46" x 43". The other data - impeller dimensions, shaft dia. etc aren't much help in estimating power. Fan speed is not given.

Cheers..........Codey

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Guru
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#8
In reply to #5

Re: Blower CFM And Horse Power

05/06/2010 6:59 AM

Yes that formula by PS is right,I was messing output watt with the input in CFM and inches of Water. Thanks for correcting.

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Active Contributor

Join Date: Feb 2009
Location: Chicago
Posts: 11
#6

Re: Blower CFM And Horse Power

05/05/2010 11:50 PM

You really need to get the fan curve from the manufacturer. A good photo or drawing should help but the hardest part will be getting tech support to assist since they are so far removed from the situation.

Centrifugal fans come in a variety of "styles" (squirrel cage, paddle wheel, etc....) and within each style you can have variations in fan blade design that makes it is impossible solve your problem even if you could provide the rest of the needed information like flow rate, system resistance, s.p. and then you still need to know max tip speed so you don't wick 'er up to much.

Perhaps a box of doughnuts sent to McQuay will help.

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Anonymous Poster
#7

Re: Blower CFM And Horse Power

05/06/2010 2:10 AM

Dear member

1. size of the motor required will depend on at what speed u r going to run the fan to deliver the required air flow against the load.

2,Select an available motor say 5/10 kw motor and couple it to the fan with a VFD and start from very low speed increase it while continuously measuring the airflow and power consumption.

3. with in 1 or 2 trials u can finalize the motor size and fan speed.

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Power-User

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#9

Re: Blower CFM And Horse Power

05/06/2010 10:43 AM

It's a 30,00 cfm nominal. if it's a free air exhaust you will need 30 hp to be safe. whomever reccomended the vfd was correct. you would usually see either 16 or 18" on the driven sheave and the normal on the drive would be 5-6". I use alot of Lenze vfd's but they are almost all equal in everything but price. if you want bulletproof go for ABB. I would take it to 60Hz or FLA whichever comes first and back it down to whatever the users requirements are. 30 HP 4poles should do 30,000 at 2.0 TSP.

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Power-User

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#10

Re: Blower CFM And Horse Power

05/06/2010 10:54 AM

sorry i didn't check your static, if your specs are right you won't get much over 21,000 cfm with 30 hp. get the cfm and static requirement and i can give you the hp. if you have money in this i would check the bearings first and go the 900 bucks for a dynanmic balance at start-up. you shaft can't take anymore hp unless you use the vfd for soft start.

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Active Contributor

Join Date: Feb 2009
Location: Chicago
Posts: 11
#11
In reply to #10

Re: Blower CFM And Horse Power

05/06/2010 2:29 PM

So did you "come down from the mountain" with this advice?

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Participant

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#12
In reply to #10

Re: Blower CFM And Horse Power

05/10/2010 10:17 PM

Thanks Everyone,

I have done a little more research and figured that it would take around a 25hp motor and from what ConwayMech said helps confirm my calcs. Sorry if there wasn't a lot of info but it is all that i had to go with. I am installing a VFD on the motor for soft start and control of the motor, Right now the customer just wants it to run constantly but i am trying to work on them to install temp sensors and a control system to maintain the temp in the tower. If they run it in the winter here they will cool off the hydraulics to much and have issues.

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Users who posted comments:

Anonymous Poster (1); Codemaster (1); CONWAYMECH (2); lyn (1); PWSlack (1); rakesh_semwal (2); snax (2); Volts480 (2)

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