Fan curves

saisanthoshm88 · January 15, 2013, 01:10

Every fan manufacturer provides a fan curve with in the product manual but in reality the fan curve is different for different systems.

The manufacturer is completely unaware of the kind of system into which the fan shall be installed so in what ways is the fan curve provided by the manufacturer useful to the customer.

Could some one please provide a clarification on this.

singer1812 · January 15, 2013, 12:32

Look up "Fan Laws" on google.....

saisanthoshm88 · January 16, 2013, 04:20

Fan laws as I'm aware of are only useful to predict the performance of a geometrically similar fan from the original fan curve.

But I'm talking about a situation where the actual system into which the fan is installed is physically different from the system in which the laboratory tests are performed by the manufacturer to get the fan curve.

Because as far as I know the fan curves are obtained by the manufacturer by testing the fan in a fully ducted condition and while in reality the fan shall operate in a totally different physical system so how is the fan curve provided by the manufacturer useful in that case.

As a CFD analyst my intention would be to use the fan curve in simulating the fan performance and not at all to have it as any selection criteria.

sainath.s@tdps.co.in · January 16, 2013, 05:43

As I explained u earlier to the message, Do u have the load characteristics of the machine where you are going to install the fan?

Your point is valid that the fan is tested in a ducted channel and its characteristics will vary when placed inside the system.

You need to plot a similar curve for your machine. Super impose both the curves. The point at which the curves intersect is the operating point of the fan.

Also make considerations for the corrections that need to be done for the temperature and density because the manufacturer would have tested the fan at a particular temperature.

singer1812 · January 16, 2013, 10:35

If you are looking to select a fan, run your system at various flow rates.

You dont need a fan selected to do this, but perhaps you have a space claim that you want the fan to fit in, and with that model a good inlet and exit area (of the fan) that is similiar to a typical fan you might use (this will keep total pressure for the fan at approximately the same as the actual fan).

You can then map this total pressure system curve onto the any fan curve of your choice as Sainath said.

I dont think that this is a bad way of doing things, and will probably size your fan selection reasonably well.

January 15, 2013, 01:10	Fan curves	#1
saisanthoshm88 Senior Member --------- Join Date: Oct 2010 Posts: 303 Rep Power: 18	Every fan manufacturer provides a fan curve with in the product manual but in reality the fan curve is different for different systems. The manufacturer is completely unaware of the kind of system into which the fan shall be installed so in what ways is the fan curve provided by the manufacturer useful to the customer. Could some one please provide a clarification on this. __________________ Best regards, Santhosh.

January 16, 2013, 04:20		#3
saisanthoshm88 Senior Member --------- Join Date: Oct 2010 Posts: 303 Rep Power: 18	Fan laws as I'm aware of are only useful to predict the performance of a geometrically similar fan from the original fan curve. But I'm talking about a situation where the actual system into which the fan is installed is physically different from the system in which the laboratory tests are performed by the manufacturer to get the fan curve. Because as far as I know the fan curves are obtained by the manufacturer by testing the fan in a fully ducted condition and while in reality the fan shall operate in a totally different physical system so how is the fan curve provided by the manufacturer useful in that case. As a CFD analyst my intention would be to use the fan curve in simulating the fan performance and not at all to have it as any selection criteria. __________________ Best regards, Santhosh.

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January 15, 2013, 12:32		#2
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	Look up "Fan Laws" on google.....

January 16, 2013, 05:43		#4
sainath.s@tdps.co.in New Member Sainath Join Date: Mar 2012 Posts: 27 Rep Power: 14	As I explained u earlier to the message, Do u have the load characteristics of the machine where you are going to install the fan? Your point is valid that the fan is tested in a ducted channel and its characteristics will vary when placed inside the system. You need to plot a similar curve for your machine. Super impose both the curves. The point at which the curves intersect is the operating point of the fan. Also make considerations for the corrections that need to be done for the temperature and density because the manufacturer would have tested the fan at a particular temperature.

January 16, 2013, 10:35		#5
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	If you are looking to select a fan, run your system at various flow rates. You dont need a fan selected to do this, but perhaps you have a space claim that you want the fan to fit in, and with that model a good inlet and exit area (of the fan) that is similiar to a typical fan you might use (this will keep total pressure for the fan at approximately the same as the actual fan). You can then map this total pressure system curve onto the any fan curve of your choice as Sainath said. I dont think that this is a bad way of doing things, and will probably size your fan selection reasonably well.