Energy efficiency analysis and modeling of a multiple-chiller plant for process industries

Abstract

This document presents the results of the research project through experimental investigation and analysis. Typical operational behaviour and problems occurring at a multiple-chiller plant ( e.g: low performances of the chillers, inappropriate sequence of operating the chillers) resulted in the need to develop some physical system models that are used as a design and performance evaluation tool for energy intensive process industries. Basic mathematical simulation models have been used to understand the performance behaviour of the refrigeration and heat pump systems for more than three decades. Development of this approach has been helping to improve system operation and reduce energy consumption. The objectives of the research project are to encourage energy conservation and identify appropriate energy efficiency measures as well as develop some physical simulation system models for energy intensive process industries through plant investigation, experimental system analysis and system modeling simulation. To achieve these objectives, the study has focused on developing some simulation programs, in particular, for refrigeration plants in such industries. The study can bring sustainable benefits to the practice of energy use in process industries in three main aspects: 1. The study has reduced energy consumption and operation costs in the participating industries as well as impacting on their respective environments. 2. · Physical simulation system models with different configurations and varying complexity are developed to understand the behaviour of industrial refrigeration systems typically used in these industries, in terms of part load efficiency and potential operating problems under different conditions such as, steady state, part load and transient state conditions as well as under intervention of the capacity control system. 3. The physical simulation system models are used as the design and performance evaluation tool to explore prospective configurations of hardware in terms of improving system operation, retrofitting the plants and control strategies leading to energy savings. The research project undertaken through plant investigation, experimental system analysis and system modeling simulation is presented in the nine following chapters. The experimental investigations have evaluated the performance of the multiple-chiller plant at a process facility in New Zealand and revealed some major problems leading to operating the plant inefficiently. The experimental analysis has also suggested some recommendations in terms of demand load estimation methods, plant configurations and control strategies. The · advantages and disadvantages of different modeling strategies and approaches have been critically reviewed and applied to develop some physical simulation system models of different configurations and varying complexities. These simulation programs include the steady-state simulation system models with one-zone, three-zone and local heat transfer integration approach heat exchanger models, and transient simulation system model of an oil injected screw chiller as well as the design and rating performance models for wet cooling towers applicable to the refrigeration plant. In addition, different simulation system models have been developed for different chillers due to the variation in the configurations of the multiple-chiller plant at a process facility. These developed simulation system models can predict performance parameters under both steady state and transient start up conditions as well as under the intervention of the capacity control system. The developed system models are used as the design and performance evaluation tool for retrofitting the refrigeration plant and for investigation of different control strategies to improve the performance and reliability of the multiple-chiller plant.