The purpose of heating, ventilation, and air conditioning (HVAC) controls is to provide comfort in laboratories, clean rooms, warehouses, offices, and manufacturing spaces. The term airhandler refers to the total system, including fans, heat-exchanger coils, dampers, ducts, and instruments. The system operates as follows: Outside air is admitted by the outside air damper and is then mixed with the return air from the return air damper. A substantial source of inefficiency in conventional HVAC control systems is the uncoordinated arrangement of temperature controllers. Two or three separate temperature control loops in series are not uncommon. The airhandler is just one of the industrial unit operations. The process of air conditioning is similar to all other industrial processes. Fully exploiting state-of-the-art instrumentation and control results in dramatic improvements. The control and optimization strategies can be implemented by pneumatic or electronic instruments and controlled by analog or digital systems.