Engineering Equation Solver (EES) is a commercial software package used for solution of systems of simultaneous non-linear equations. It provides many useful specialised functions and equations for the solution of thermodynamics and heat transfer problems, making it a useful and widely-used program for mechanical engineers working in these fields.

The program is developed by F-Chart Software, a commercial spin-off of Prof Sanford A Klein from Department of Mechanical Engineering
University of Wisconsin-Madison.

EES is included as attached software for a number of undergraduate thermodynamics, heat-transfer and fluid mechanics textbooks from McGraw-Hill.

It integrates closely with the dynamic system simulation package TRNSYS

TRNSYS

TRNSYS is a simulation program primarily used in the fields of renewable energy engineering and building simulation for passive as well as active solar design. TRNSYS is a commercial software package developed at the University of Wisconsin...

, by some of the same authors.