Center for the Built Environment

This paper describes the development of new control logic for starting and stopping energy-intensive equipment in buildings such as staged air-conditioning units. The concept is to use pulse-width modulation (PWM) instead of level-crossing logic. A finite state machine is used to handle the case where a single unit has multiple stages of operation. An optimized coordinator determines the phase of the PWM signals of each unit so that peak demand for power is minimized over each PWM period. Control logic for the PWM function was developed so that the phase could be manipulated by the coordinator.

Computer simulations were used to assess the performance of the new strategy and to compare it to level-crossing logic. The following five metrics were used to assess the performance: 1) magnitude of the control error, 2) start/stop frequency, 3) average power consumption, 4) standard deviation of the power consumption, 5) peak power consumption. The computer simulations showed that the new strategy could reduce peak power consumption by 20% relative to level-crossing logic. The computer simulations also showed that the new strategy increased the magnitude of the space temperature control error by 11% and increased the number of start/stop operations by 27% relative to level-crossing logic.