This paper describes a procedure for deriving a dynamic model of an HVAC system that consists of a zone, heating coil, cooling and dehumidifying coil, humidifier, ductwork, fan, and mixing box. In particular, the interest is centered on control strategies to reduce energy consumption and improving the quality of the indoor environment. Indoor temperature and humidity may be maintained at set point values by an air-handling unit using a PID control action. The PID parameters must be carefully tuned to produce less oscillatory responses. The timing technique, using the Ziegler-Nichols rule, is investigated from a practical viewpoint. Simulation results showing the open loop and the closed loop responses of indoor temperature and humidity ratio are given. The results show that the system is capable of controlling the disturbance efficiently within a small period of time and with less error. The dynamic model can be especially useful for control strategies that require knowledge of the dynamic characteristics of HVAC systems. © 2004 Elsevier Ltd. All rights reserved.