Robust optimal design of district cooling systems and individual cooling systems considering uncertainty and reliability

Pao Yue-kong Library Electronic Theses Database

Robust optimal design of district cooling systems and individual cooling systems considering uncertainty and reliability

 

Author: Gang, Wenjie
Title: Robust optimal design of district cooling systems and individual cooling systems considering uncertainty and reliability
Degree: Ph.D.
Year: 2016
Subject: Air conditioning.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xxvii, 213 pages : color illustrations
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2890600
URI: http://theses.lib.polyu.edu.hk/handle/200/8471
Abstract: This thesis attempts to answer the following questions which are not well answered in existing studies: - Are district cooling systems energy efficient when compared with conventional individual cooling systems and what is the performance of district cooling systems coupled with different technologies in subtropical areas? - How to obtain a cooling system (either district cooling system or individual cooling system) that can offer the best performance under uncertainty? - How to obtain a cooling system (either district cooling system or individual cooling system) that can offer the best performance when uncertainty or failures of equipment arise? District cooling system is widely used but its performance is rarely reported. The system performance compared with the individual cooling system determines its future application. Performance assessment of district cooling systems is conducted by comparing with individual cooling systems in subtropical areas. Characteristics of district cooling systems are summarized after quantitative energy performance analysis. Measures to handle the additional peak electricity load due to developing a new area and using district cooling systems are assessed. Application of ice storage systems in the district cooling system is evaluated under different tariffs and design strategies. The performance of the district cooling system integrated with PHES is analyzed. The operation costs of the district cooling system with and without combined cooling, heating and power system are compared. Comments and suggestions are summarized for the application of district cooling systems in the subtropical area. Information or data used in the system design at planning and design stages are often very different from that when the system is in operation. Such difference is taken as uncertainty. Uncertainty exists widely in the design process of district cooling systems and individual cooling systems. It will affect the design options but is not sufficiently investigated yet. To ensure that the cooling systems perform well in operation eventually, uncertainty-based optimal design methods are proposed. The performance of the cooling systems using the proposed methods is compared with that using the conventional design method. An optimal design method concerning uncertainty is developed based on mini-max regret theory. It achieves the optimal design considering uncertainty. Without the needs of probability distribution assumptions and introducing new models, this method can determine the uncertainty-based optimal cooling systems very effectively. By comparing the regrets of each design option, the uncertainty-based optimal cooling system can be identified, which is associated with the minimum maximum regret. The method is demonstrated in the design of the chiller plant and chilled water system of a building.
By quantifying the uncertainty at planning and design stages, an uncertainty-based optimal design method is proposed and its application steps are introduced. Uncertainties in the outdoor weather, building design/construction and indoor conditions are concerned. Strategies to deal with the variables containing uncertainties are introduced. Based on the peak cooling load distribution, the capacity of the cooling systems can be determined with quantified risks. Based on the distribution of the annual energy consumption or cost, the configuration of the cooling systems can be selected with quantified confidence. The uncertainty-based optimal method is implemented in a district cooling system and an individual cooling system in Hong Kong respectively. By using the uncertainty-based optimal design method, stake holders can make decisions with quantified confidence. The components or sub-systems in a cooling system cannot be always available due to failures or maintenance. A robust optimal design method considering both uncertainty and reliability is proposed. The robust optimal design can maintain the good performance under uncertainty or failures of components in the cooling system. Steps to realize the robust optimal design method are presented. The availability risk cost is introduced to account for the losses caused by the unmet cooling load. By taking the total annual cost including the capital cost, operation cost and availability risk cost as the objective, the robust optimal cooling system can be achieved. The proposed method is demonstrated in both the district cooling system and individual cooling system. Performance of the cooling systems using the robust optimal design is compared with that using the conventional design method, uncertainty-based design method and reliability-based design method. The impacts of uncertainty on the design of district cooling systems and individual cooling system are compared. The influential factors for cooling loads of the district cooling system and individual cooling system are identified. Similarities and differences are summarized. Then the impacts of both uncertainty and reliability on the design of the district cooling system and individual cooling system are also assessed and compared.

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