Fundamentals of Control Systems

Abstract

The purpose of automatic controls is to modulate the capacity of HVAC equipment to satisfy the heating and cooling requirements of a building and to monitor and control safely the operation of HVAC systems. This type of control traditionally has been performed by pneumatic and electric control systems. Today, microprocessors are taking the place of conventional controllers and are rapidly becoming the preferred automatic control method for building HVAC systems. Because of the declining cost of semiconductor chips and the proven reliability of microprocessor-based controllers, direct digital control (DDC) systems now compare favorably against conventional control methods in both functional and economic terms. DDC, however, is not the answer to every automatic control problem. A solid grounding in control system fundamentals is necessary before one can fully understand how to best apply direct digital controllers to common control system designs. Because DDC systems are typically used in combination with other types of control systems, control system fundamentals are now reviewed.