Compensation of manual reset to offset thermal loads change for air-conditioning system

PI controllers have been commonly used in air-conditioning systems. Among PID controllers, the D action is frequently switched off for the simple reason that it is difficult to tune properly. In some situations, it is possible to estimate thermal loads (or disturbances) before they will enter the plant. It is then natural to offset the thermal loads before they affect the control output. A typical example is a certain system for air-conditioned space in which an outdoor thermometer detects sudden weather changes and the occupant roughly anticipates the thermal loads changes. Disturbances can be offset by the compensation of the manual reset. This control strategy can be called a variety of feed-forward. The objective of this paper is to introduce the compensation strategy of the manual reset for air-conditioning systems and to compare this strategy with a traditional PI control strategy. Simulation results obtained from representative thermal loads are presented to demonstrate that PD control based on the compensation method leads to more stable operation in comparison to the traditional PI control.