TRNSYS (pronounced ‘tran-sis’), commercially available since 1975, is a flexible tool designed to simulate the transient performance of thermal energy systems. TRNSYS’s beginnings can be found in a joint project between the University of Wisconsin – Madison Solar Energy Lab and the University of Colorado Solar Energy Applications Lab. In the 1970’s a house was built in Colorado to study emerging solar energy technologies. The University of Wisconsin contributed by writing a Fortran program to predict the energy use in the building. Toward the very end of the project, when the Fortran programming graduate student was writing his thesis, a simple modification was made to the backup heating system in the house. Reworking the Fortran program took an inordinately long 8 weeks, delaying the student’s graduation. In subsequent work, the University of Wisconsin developed a method of describing each component of and energy system as a Fortran subroutine having inputs and outputs. Anyone with a Fortran compiler could use the basic component format to model new technologies and quickly incorporate them into the TRNSYS library. Describing a complex energy system in TRNSYS, therefore, was reduced to a process of choosing the system components and hooking them together.

More than 25 years later, TRNSYS is a well respected energy simulation tool under continual development by a joint team made up of the Solar Energy Laboratory (SEL) at the University of Wisconsin – Madison, The Centre Scientifique et Technique du Bâtiment (CSTB) in Sophia Antipolis, France, Transsolar Energietechnik GmBH in Stuttgart, Germany and Thermal Energy Systems Specialists (TESS) in Madison, Wisconsin. TRNSYS currently boasts a graphical interface, a library of 80 standard components, add on libraries offering over 300 other components, a world wide user base and distributors in France, Germany, Spain, Sweden, Luxembourg, the US and Japan.

We at TESS have created this website to keep you informed about TRNSYS, its capabilities, its distributors and its users. There is also a lot of information contained in these pages and we are always pleased to hear from you if you have questions about where to find something particular.