Good HVAC control is often the most cost-effective option to improve the energy efficiency of a building. However the effect of changing the control strategy (i.e. effect on indoor comfort and energy consumption) is usually the most difficult to predict. To achieve this more easily, a new simulation tool, QUICKcontrol, was developed. In this paper, the new tool is used to investigate the energy savings potential in the Engineering Tower Building (ETB) of the University of Pretoria. The influence of reset control, economizer cycle combined with CO2 control on the outside air ventilation rate and better system start-stop times were investigated. The simulation models were firstly verified with actual measurements obtained from the existing system to confirm their accuracy for realistic control retrofit simulations. With the aid of the integrated simulation tool it was possible to predict savings of 491 MWh per year (34% building energy saving) by implementing these control strategies. These control strategies can be implemented in the building with a direct payback period of less than 9 months.