REFPROP 9.1 is a reliable workhorse, but it is aging. If you encounter persistent issues, consider:
With careful attention to compatibility mode and environment variables, REFPROP 9.1 will continue to serve as an accurate and indispensable tool for thermodynamic calculations for years to come.
This guide applies to REFPROP Version 9.1 (circa 2013). For the latest updates, please visit the official NIST REFPROP website.
Installing NIST REFPROP 9.1 typically involves the base software installation on Windows followed by linking the Dynamic Link Library (DLL) to applications like Excel, MATLAB, or Python. 1. Core Software Installation (Windows) REFPROP 9.1 is a licensed software provided by NIST. Run the Installer
: Use the executable provided with your purchase (often via CD-ROM or digital download). Default Directory : By default, it installs to C:\Program Files (x86)\REFPROP refprop 91 install
. It is highly recommended to keep this path, as many third-party wrappers look for it there by default. Verification : After installation, open the REFPROP.EXE
(Graphical User Interface) to ensure the fluid files and mixture models load correctly. National Institute of Standards and Technology (.gov) 2. Linking to Microsoft Excel
The most common use case for version 9.1 is within Excel via the Locate the Add-in REFPROP.XLS in your installation folder. Save a copy as REFPROP.XLA REFPROP.XLAM to your local "Add-ins" folder. Set Trusted Locations Open Excel and go to File > Options > Trust Center > Trust Center Settings Trusted Locations and add the folder C:\Program Files (x86)\REFPROP Activate the Add-in File > Options > Add-Ins In the "Manage" dropdown at the bottom, select Excel Add-ins (or browse to find the file if it's not listed). Fixing DLL Links : If functions return errors, press to open the Visual Basic Editor. Check if the path to REFPROP.DLL in the module matches your actual installation path. National Institute of Standards and Technology (.gov) 3. Installation on macOS
Because REFPROP is a Windows-based Fortran program, macOS users must use a wrapper. Directory Setup : Create a folder named /Users/$USER/Library/Group Containers/UBF8T346G9.Office/ Copy Files : Copy your folders (must be capitalized) and the librefprop.dylib file into this new folder. Excel Setup REFPRP91.XLA REFPROP 9
file specifically designed for Mac, which can be found in the NIST REFPROP-wrappers GitHub 4. Troubleshooting Common Issues Missing Fluids : Ensure the subdirectories are present in the main REFPROP folder. Path Environment Variable : If calling REFPROP from Python or MATLAB, adding C:\Program Files (x86)\REFPROP to your Windows System Environment Variables (Path) often resolves "DLL not found" errors. 32-bit vs 64-bit
: Ensure your Excel version (32 or 64-bit) matches the DLL version you are calling. REFPROP 9.1 typically provides both REFPROP.DLL (32-bit) and REFPRP64.DLL CoolProp can't load REFPROP v10 mixtures on Debian 9 #1829
Before beginning the installation, ensure the following:
Cause: Missing Visual Basic runtime components on newer Windows versions.
Solution: Download the VB6 runtime library from Microsoft (if still available) or copy MSCOMCTL.OCX from a working older PC. Then run: With careful attention to compatibility mode and environment
regsvr32 C:\Windows\SysWOW64\MSCOMCTL.OCX
Run Command Prompt as administrator.
Unlike freeware, REFPROP requires a paid license. For version 9.1, you need:
Important note for 2025: NIST no longer sells new licenses for version 9.1. You can only install it if you purchased it before the version was superseded. If you lack a legitimate installer and license, consider purchasing the current version from NIST or using the free NIST REFPROP web API.
REFPROP 9.1 uses environment variables to locate its fluid data (fluids\, mixtures\). Sometimes the installer does not set this correctly.