Optimizing the Design of Chilled Water Plants in Large Commercial Buildings

Abstract

Design of chilled water plants has very large impact on building energy use and energy operating cost. The chapter proposes procedures and analysis techniques for energy efficiency design of chilled water plants. The approach that leads to optimal design variables can achieve a significant saving in cooling cost. The optimal variables include piping sizing, chilled water temperature difference, and chilled water supply temperature. The objective function is the total cooling energy cost. The proposed design method depends on detailed cooling load analysis, head and energy calculations, and optimization solver. The pump head calculations including piping, all fittings, valves, and devices are achieved by using the Darcy–Weisbach Equation and given flow parameters. The energy calculations are done by using generic chiller, fan, and pump models. The method is tested on an existing office two-storey building with a packaged air-cooled chiller. A whole building energy simulation model is used to generate the hourly cooling loads, and then the optimal design variables are found to minimize the total energy cost. The testing results show this approach will achieve better results than rules-of-thumb or traditional design procedures. The cooling energy saving could be up to 10 % depending on particular projects.

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