TRNSYS (pronounced "tran-sis") is a dynamic thermal simulation software developed by the University of Wisconsin. It is thus used for the simulation of transient systems. It can therefore be used to evaluate the performance of thermal or electrical energy systems, but it can also be used to model other types of dynamic systems. The software is developed in FORTRAN code. Kernel and Libraries of Components The software is characterised by its computational routine and its extensive library of components. The first part is based on a powerful kernel that can read and run input files, iteratively solve the system, determine convergences and display the system variables via a graphical interface. The second part of TRNSYS consists of an extensive library of components, each of which allows the simulation of the performance of a specific part of a system. The standard TRNSYS library consists of approximately 150 models, ranging from a single pump to multi-zone building models, wind turbines, electrolysers, weather data processors and basic HVAC equipment.