Rule-based control of air-flow in air-conditioning systems

摘要

Outdoor air is often used for cooling the interiors of buildings to reduce the energy consumption of their HVAC systems. Outdoor air may also be used for heating, but this is less common. In both cases, the coils of the central air-handling unit are switched off, so that the temperature of the air that is supplied to the building is controlled by mixing the return air with the incoming fresh air. Successful control of the temperature of the supply air is very much dependent on the flow control afforded by the inlet, bypass, and return dampers. A linear relationship is desirable between the position of the actuators and the air-flows, or, even better, the position of the actuators and the temperature of the supply air. Unfortunately, good control is seldom achieved in practice due to poor design, resulting from incorrect sizing of the dampers or modifications to the original design of the ductwork, coupled with the usual practice of using the output from a single PI controller to adjust the position of all three dampers. The paper describes ways of overcoming these problems, chiefly the use of rule-based methods.