Explaination of Same size Fan RPM with different Air Flow and Static Pressure 1

[kshenq85]

Hi all,

I would like to seek for some explanation regarding using the same fan size but different requirement of air flow and static pressure.

Here are the info.
Fan Size : 315 (Double Inlet Forward Curve Fan)

For Fan A
Air Flow : 12100 CMH
Total Static : 931 Pa

Fan B
Air Flow : 9630 CMH
Total Static : 930 Pa

Looking at the fan curve, they seems to share the same RPM even though the air flow and static pressure is different.

But how can I explain this in layman terms so that it would not complicate the understanding of the customer.

Please help. Thanks.

Best Regards,
kshenq85

 

[cry22]

Then they must have different wheel diameter, or different sheave.

 

[ScottyUK]

Are the fans identical, or are they just the same frame size? Post links to the fan datasheets.

 

[capliard]

The customer needs to know those fans at their above-stated point of operation do not deliver the same air power. For B delivers about 30% less air at same pressure.

Those fans cannot be exactly the same. They can look the same but aren't.




Ingenieur Minier. QuTbec, Canada.

 

[willard3]

They are not the same fan by definition.

 

[dbill74]

What is "315"? Diameter/model number/something else?
Are these fans installed already or are you trying to specify something for a new installation?

 

[kshenq85]

The fans are the same. The 315 is the size of the of the fan.
In short, the fans are exactly the same.

I have attached the Fan Size 315 Technical Datasheet for your reference. Thanks.

 

[kshenq85]

Sorry, I have missed out the file

 

[dbill74]

On the fan curve you provided, each bold black line is a separate fan curve and is a function of the blade geometry, fan construction and motor. In your example, you have a 1.5 kW motor (the 1.5 bold line).

What you don't see on the provided graph is the system curve. This is a function of the distribution system, A.K.A. the ductwork. This curve is going to have an exponential look to it starting at 0 pressure, 0 air flow and curving up to the right. Every system curve is different because it is based on physical properties of the ductwork. These properties include things such as the length of runs, inside dimensions of the ductwork, shape of the ductwork and material of the ductwork.

If you were to plot the system curve on the fan curve, the point where the 2 curves meet is your operating point. Where the fan reaches a balance between the amount of air and pressure it is imparting and the resistance from the ductwork.

The ductwork for Fan A has less resistance allowing a larger volume of air. Fan B's ductwork might have slightly smaller ductwork creating more resistance and thus less air is able to get through. You may also want to note that there is about a 10% difference in efficiency between the 2 fans.