Methodology for determining the optimal operating strategies for a chilled-water-storage system—Part I: Theoretical model

Abstract

This article proposes a new methodology for determining the optimal operating strategies for a chilled-water storage system under a time-of-use electricity rate structure. It is based on a new classification of operating strategies and an investigation of multiple search paths. Each operating strategy consists of a control strategy and the maximum number of chillers running during the off-peak and on-peak periods. For each month, the operating strategy with the lowest monthly billing cost and minimal water level higher than the set-point is selected as the optimal operating strategy for the current month. A system model is developed to simulate the tank water level at the end of each time step and the system total power during each time step. This model includes six sub-models: plant, thermal energy storage tank, loop, chiller, control strategy, and nonplant power. This method considers the interaction among plant, tank, and loop, and it is easy for users to apply it to different projects, modify individual models, or implement new sub-models. The final results will be a table showing the monthly control strategy and maximal number of chillers staged-on during the off-peak and on-peak periods, an operation schedule that is easy for the operators to follow.

Acknowledgments

Zhiqin Zhang, is PhD Student and Research Assistant. William D. Turner, PhD, PE, is Professor. Qiang Chen, PE, Associate Member ASHRAE, is Research Engineer. Chen Xu, PE, Associate Member ASHRAE, is Project Manager. Song Deng, PE, Member ASHRAE, is Associate Director.