Describes a versatile personal computer program which accurately models seven basic types of variable air volume control systems and is easily extended to many subtypes within each of these seven major configurations. Presents results of sample runs with a prototypical building which show the strong dependence of ventilation and pressurisation performance on fan and damper sizing.KEYWORDS: Computer programs, controls, air conditioning, buildings, pressurisation, variable volume air conditioning, ventilation, performance, fans, sizing outdoor air, dampers.