VA-89-01-2 -- Response of Self-Tuning Single-Loop Digital Controllers to a Computer-Simulated Heating Coil PDF

One approach to providing standardized control equipment for heating, ventilating, and air-conditioning (HVAC) systems is through one or more interohangeab/e single-loop digital controllers (SLDC). Many commeroia/ SLDC combine the well-known combination of proportional, integral, and derivative control with serf-tuning and/or adaptive control capabilities./n anticipation of the future need to subject SLDC to reproducible tests, an exerciser simulating a hot water air-heating coil was programmed on a personal computer and the response of four different commercial SLDC with manually initiated self-tuning control capabilities was tested. While ff is too early to make general conclusions, three out of four SLDC studied provided stable, responsive control for the simulated heating coil. All four controllers used open-loop step-response characteristics for self-tuning, and the dynamic response to disturbances varied: (1) one controller, which used a 0% to 100% to 0% control signal cycle for self-tuning, failed to obtain stable control parameters; (2) a second controller, which used a current value to 100% to 0% control signal cycle for self.tuning, provided the most desirable control under load disturbances; and (3) the two remaining controllers, which used a single control signal step change for self-tuning, provided superior control under setpoint disturbances.