Introduction to HVAC Control Systems

This chapter provides an introduction to heating, ventilating, and air-conditioning HVAC systems. The ultimate aim of every HVAC system and its controls is to provide a comfortable environment suitable for the process that is occurring in the facility. In most cases, the HVAC system's purpose is to provide thermal comfort for a building's occupants to create a more productive atmosphere or to make a space more inviting to customers. This chapter also introduces the concept of a control loop, the basic building block of all control systems, and the various control strategies and algorithms used in control loops. In a control loop information flows in a circle from the sensor (the speedometer) measuring the controlled variable to the controller, where the current value of the controlled variable is compared to the desired value or set point. The controller then makes a control decision and passes that on to the controlled device and to the process plant. This then has an effect on the current value or control point of the controlled variable, starting the process all over again.