Interest in simulation of the performance of HVAC components and systems has increased considerably in recent years, generated by the possibility of producing integrated plant/building models for energy studies, and investigating the performance of operational plant with a view to improving the design of installed systems. The paper presents an overview of the various approaches to this simulation problem in three sections: component models, linking protocols (networking) and methods for solving the component model equation sets. Probable avenues of future development in both research and design oriented applications are discussed.