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Using REFPROP .FLD files


The National Institute of Standards and Technology (NIST) has developed REFPROP (also called NIST Standard Reference Database 23), which provides high accuracy property data for pure refrigerants and refrigerant mixtures. REFPROP is the most authoritative source of pure fluid property data.  REFPROP also provides high accuracy data for refrigerant mixtures, ammonia-water, and most mixtures of organic fluids. The Professional license of EES can access the property data provided by REFPROP with the EES_REFPROP interface


The coefficients in the equations REFPROP uses to calculate property data for pure fluids are provided in .FLD files.  These files are contained in the Fluids folder within the REFPROP directory, e.g., C:\Program Files (x86)\REFPROP\Fluids.  Each file provides information for a separate fluid.  For example, CO2.FLD provides the necessary information for carbon dioxide.


EES can read .FLD files developed for REFPROP version 10 using the $INCLUDE directive.  For example, the following directive will read the REFPROP .FDL file for carbon dioxide.


$INCLUDE C:\Program Files (x86)\REFPROP\Fluids\CO2.fld 


After executing this directive, EES is able to provide thermodynamic property information for the fluid, in the same manner as for built-in fluids.  The fluid name used in EES property functions is the file name (without the .FLD) appended with _rp.  For example,


$INCLUDE C:\Program Files (x86)\REFPROP\Fluids\CO2.fld 

$UnitSystem SI K kP kJ mass

h_f=enthalpy(CO2_rp,T=250 [K],x=0)

h_g=enthalpy(CO2_rp,T=250 [K],x=1)


will return the specific enthalpy of saturated liquid and vapor for carbon dioxide at 250 K.  The fluid name can be provided using a string variable, e.g., F$='CO2_rp'.



1.  The values returned by EES in this manner will not be exactly the same as those provided by REFPROP.  EES uses the coefficients in the .FLD file for its own property calculations, which are similar but not identical to those in REFPROP.  The differences should be minor.

2.  Viscosity and thermal conductivity are estimated using a corresponding states method based on propane as the reference fluid.  Values should be considered approximate.  Surface tension data are not available.

3.  Online help listing the source and applicable ranges of property information is not provided for fluids entered with .FLD files.  Please use the REFPROP program to view this information.

4.  The default reference states for specific enthalpy and specific entropy provided in the .FDL file may be changed in EES using the $Reference directive, e.g., $Reference CO2_rp IIR



See also:  Fluid Property Information 

 EES_REFPROP interface

 $INCLUDE directive