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# fan:VariableVolume: fan law and nodes, EnergyPlus

I need to incorporate a fan law in a model with the Fan:VariableVolume object, how do I do it? and how do I define the input and output nodes in the model?

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@mcdemarchi it sounds like you're using EnergyPlus, but can you confirm that? If so, please mention EnergyPlus in your question title and/or body, as well as add the energyplus tag so that others can provide better help.

( 2022-09-09 15:49:24 -0500 )edit

Thanks for the observation. I use Energy Plus.

( 2022-09-12 11:32:51 -0500 )edit

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In the Fan:VariableVolume object are coefficients for how power varies with flow. Set up these coefficients to provide a cubed output of power versus flow. At a flow fraction of 1, this curve output should be 1. At a flow fraction of 0.5 this curve output should be 0.125. Set coefficient 4 = 1 and the others = 0. Note that Coeff 1 = constant, Coeff 2 = flow fraction, Coeff 3 = flow fraction^2, Coeff 4 = flow fraction^3 and Coeff 5 = flow fraction ^4. So for an ideal fan only Coeff 4 is used.

Fan:VariableVolume,

N8 , \field Fan Power Coefficient 1
\note all Fan Power Coefficients should not be 0.0 or no fan power will be consumed.
\note Fan Power Coefficents are specified as function of full flow rate/power
\note Equation:
N9 , \field Fan Power Coefficient 2
N10, \field Fan Power Coefficient 3
N11, \field Fan Power Coefficient 4
N12, \field Fan Power Coefficient 5

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Thanks for your reply. To confirm, I sent you the curve of the fan that I must program and what I understood that I must do. The fan curve is: (Flow, Pressure) (45210, 0) (42940, 10) (40400, 20) (38250, 30) (36020, 40) (33150, 50) (30030, 60) (26050, 70) I understand that I have to transform the flow and pressure to values between 0 and 1, which would be: (Flow, Pressure) (1, 0) (0.95, 0.143) (0.894, 0.286) (0.846, 0.429) (0.797, 0.571) (0.733, 0.714) (0.664, 0.857) (0.576, 1) and calculate the coefficients for this Flow-Pressure pair. Is it so?

( 2022-09-13 07:45:03 -0500 )edit

You want a fan power ratio as a function of air flow ratio. This would be at constant external static pressure (Pressure Rise input field). it looks like you have provided flow rate and pressure. You need to convert these to a flow ratio (e.g., Flow = 45210 / max flow = 45210 = 1.0, and Flow = 26050 / max flow = 45210 = 0.5762, which appears to be what you have done) and a POWER consumption ratio, (e.g., Flow Rate * DeltaPress / (FanEff * RhoAir) divided by max power), and then curve fit power ratio as a function of flow ratio.

( 2022-09-13 18:42:04 -0500 )edit

 // Simple Variable Volume Fan - default values from DOE-2 // Type of Fan Coeff1 Coeff2 Coeff3 Coeff4 Coeff5 // INLET VANE DAMPERS 0.35071223 0.30850535 -0.54137364 0.87198823 0.000 // DISCHARGE DAMPERS 0.37073425 0.97250253 -0.34240761 0.000 0.000 // VARIABLE SPEED MOTOR 0.0015302446 0.0052080574 1.1086242 -0.11635563 0.000 

( 2022-09-13 18:42:25 -0500 )edit