Discusses good control of heating, ventilating and air conditioning systems as the best way to improve energy efficiency in air conditioned buildings. Looks at the Human Science Building at the University of Pretoria in this light. Simulations were performed using QUICKcontrol, a new software tool. Control methods investigated included air bypass, reset control, setback control, improved start-stop times, economiser control and carbon dioxide control. Sixty percent savings were predicted in HVAC power consumption, giving a payback period of nine months.