# Re: [EnergyPlus_Support] VFD for fans

```Hello,
The way specific variable speed fan models account for their energy
consumption for a given flow rate is by Fan Delta Pressure, efficiency, fan
curves, etc.  All of these are found in the InputOutput Reference document
for the Fan:Simple:Variable Volume object.  The input changes that are
necessary to model different variable volume fans of the same size and
efficiency is with the fan curves which are specified by a curve fit with
the 5 coefficients specified as input.  I have included Table 18 and the
description of the fan coefficient fields from the IO Ref doc.  To model
your VFD drive you would have to fit that fans curve and enter the 5
coefficient fit in for your fan.

What I would do is take the Variable Speed Motor coefficients and plot them
with a spreadsheet program.  Then compare them to the VFD fan curves that
you are trying to model.  Then either fit the curve for the VFD drive or
adjust the coefficients for the variable speed motor until that curve
represents the VFD drive's fan curve.  Compare these to the existing
variable speed motor fan curve to determine that it represents the fan you
are trying to simulate.  Then enter the new coefficients for that fan.

Thanks Richard Liesen

Table 18.  Fan Coefficient Values
Type of Fan              Fan Coeff. 1   Fan Coeff.  2   Fan Coeff.  3   Fan
Coeff. 4    Fan Coeff. 5
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
Var. Speed
Motor    0.0015302446       0.0052080574     1.1086242       -0.11635563 0.000

Field:  FanCoefficient 1
The constant coefficient (C1) in a fourth order polynomial curve giving the
fraction of full load power (PLF) as a function of flow fraction (FF). Flow
fraction is the air mass flow rate divided by the maximum air mass flow
rate. The curve is:
PLF = C1 + C2. FF + C3. FF2 + C4. FF3 + C5. FF4

Field:  FanCoefficient 2
The linear coefficient (C2) in a fourth order polynomial curve giving the
fraction of full load power (PLF) as a function of flow fraction (FF). Flow
fraction is the air mass flow rate divided by the maximum air mass flow
rate. The curve is:
PLF = C1 + C2. FF + C3. FF2 + C4. FF3 + C5. FF4

Field:  FanCoefficient 3
The quadratic coefficient (C3) in a fourth order polynomial curve giving
the fraction of full load power (PLF) as a function of flow fraction (FF).
Flow fraction is the air mass flow rate divided by the maximum air mass
flow rate. The curve is:
PLF = C1 + C2. FF + C3. FF2 + C4. FF3 + C5. FF4

Field:  FanCoefficient 4
The cubic coefficient (C1) in a fourth order polynomial curve giving the
fraction of full load power (PLF) as a function of flow fraction (FF). Flow
fraction is the air mass flow rate divided by the maximum air mass flow
rate. The curve is:
PLF = C1 + C2. FF + C3. FF2 + C4. FF3 + C5. FF4

Field:  FanCoefficient 5
The coefficient C5 in a fourth order polynomial curve giving the fraction
of full load power (PLF) as a function of flow fraction (FF). Flow fraction
is the air mass flow rate divided by the maximum air mass flow rate. The
curve is:
PLF = C1 + C2. FF + C3. FF2 + C4. FF3 + C5. FF4

At 09:11 AM 6/16/2004, you wrote:
>I uploaded a idf file to the folder "Files".
>
>The file name is: Chesapeake_DXVAV_SA55.IDF, it's under my ID:
>liao_lucia and posted on 06/06/2004. In which there are 2 fans of
>SIMPLE:Variable Volume.
>
>I talked to the facility guy and found out that they upgraded the
>fans with VFDs (variable frequency drive). How can my model reflect
>the change ?
>
>Thanks.
>
>Lucia
>
>
>
>
>
>
>The primary EnergyPlus web site is found at:
>http://www.energyplus.gov
>
>The group web site is:
>http://groups.yahoo.com/group/EnergyPlus_Support/
>
>Attachments are not allowed -- please post any files to the appropriate
>folder in the Files area of the Support Web Site.
>
>
>
>
>

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```