A Case Study on Condenser Water Supply Temperature Optimization with a District Cooling Plant

Abstract

District cooling (DC) continues to proliferate due to increasing global cooling demands and economies of scale benefits; however, most district-scale modeling has focused on heating, and to the best of our knowledge, researchers have yet to model cooling plants featuring waterside economizers in DC settings. With the Modelica Buildings library expanding its capabilities to district scale, this study is one of the first to demonstrate how the open-source models can be used for detailed energy and control analysis of a DC plant. For a real-world case study, we developed and calibrated high-fidelity models for a DC system central plant at a college campus in Colorado, USA, and we optimized the condenser water supply temperature (CWST) setpoint for a DC plant across multiple time horizons using the Optimization library in Dymola. Results indicate that annual CWST optimization saves 4.7% annual plant energy, with less than 1% of additional energy savings gained through daily optimization. This confirms previous studies' findings that high frequency CWST optimizations are not necessary for the studied system.

Modelica-based modeling and simulation of district cooling systems: A case study

“…Further, we also evaluate and present the numerical performance (i.e., the scalability) of a detailed plant model connected to complete districts of several sizes, which is important to understand the capabilities and limitations of large Modelica models for DC analysis. Lastly, this paper's case study extends our previous work on the campus's central plant [20] by presenting a systematic methodology in modeling and simulation of an existing DC system, adding models for the distribution network with individual building loads, improving the central plant models, and extending the impact analysis to include financial and carbon savings.…”

“…The plant's hierarchical control is implemented through a Supervisory Control and Data Acquisition system; at top Master Control level, the plant operates in either MC mode (running the chillers only) or FC mode (running the WSE only). Further details about the mechanical and control system configurations, including system schematics and nominal information for the plant equipment, can be found in [20].…”

Modelica-Based Modeling and Simulation of District Cooling Systems: A Case Study

“…The plant's hierarchical control is implemented through a Supervisory Control and Data Acquisition system; at top Master Control level, the plant operates in either MC mode (running the chillers only) or FC mode (running the WSE only). Further details about the mechanical and control system configurations, including system schematics and nominal information for the plant equipment, can be found in [27].…”

“…The detailed central plant model represents the physics of the real mechanical and control systems. Modelica diagrams and model details about the central plant can be found in [27].…”

“…These contributions are presented using a validated model of an actual DC system at a satellite campus of the University of Colorado Boulder. Based on our previous work on this campus's central plant [27], this study presents a systematic methodology in modeling the DC system, adds models for the distribution network with individual building loads, and improves the central plant models. In addition, several energy efficiency measures that do not require capital investment are explored, including control setpoint optimization, assessing the effectiveness of the nonintegrated WSE, and adjusting pump setpoints.…”