fan curve estimation

[Cheetos]

Hi, guys, for a centrifugal fan curve, you have 2 end points (0 CFM, Max SP) and (Max CFM, 0 SP). I though I could use the Bernoulli equation to verify it, but it's not working. Maybe someone can shed light on what I'm missing. Max SP + 1/2 density * (0 CFM/area)^2 = 0 SP + 1/2 * density * (Max CFM/area)^2

I thought the total energy transferred by the fan should be the same at any point along the fan curve. At 0 CFM, all the energy is converted into pressure head, and at max CFM, all the energy is converted into kinetic energy. The only thing I can think of is, for Max CFM case, the air in the centrifugal fan has to turn 90 degr, so in addition to full kinetic energy at the outlet, maybe some of the energy is converted during the 90 degr turn?

 

[MintJulep]

Are you using absolute pressure?

 

[miningman]

where is your consideration of fan efficiency??

 

[nuuvox000]

At maximum pressure you'll have more electrical energy converted to waste heat from the motor. So miningman is right about efficiency, you need to consider that.

 

[Cheetos]

Thanks guys for the feedback. I definitely did not consider fan efficiency.

 

[EnergyProfessional]

won't be accurate, but look at curves of similar fans. Manufacturers, like Greenheck, have software where the curves can show all kind of data.

 

[Cheetos]

Thanks guys. One thing I'm trying to figure out is whether it is possible to estimate both end points of the fan curve based on RPM and fan geometry. I'm trying to do a very rough estimate of the fan performance. If I can get both end points, I can draw a straight line, and based on my system resistance, I can estimate where my operating point is.

Is it possible to derive equations to estimate those points or should I just follow @EnergyProfessional's suggestion and research from vendors? With that as a baseline, I can use fan laws to estimate my performance.