Development and Investigation of Outdoor Swimming Pool Heating Systems for Winter Application


Student thesis: Doctoral Thesis

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Awarding Institution
Award date2 Aug 2019


Swimming is one of the most popular sports in subtropical regions like Hong Kong and the Greater Bay Area of China, and thus in these regions there are many outdoor swimming pools owned by governments, propriety owners and hotels. In summer, the water temperature of outdoor swimming pools can be easily maintained at the comfort level of 28oC without any heat input. However, there is always a heavy heat demand for maintaining the water temperature within the comfortable range in winter. This will lead to very high operating costs if electrical or gas boilers are used, especially for outdoor pools. Hence, many outdoor swimming pools are closed during the winter, which results in the waste of facilities and spaces. Advanced heating techniques including solar collectors, heat pumps and heat storage technology have been developed for outdoor swimming pools. Developing an integrated heating system with solar collector/heat pump and phase change material (PCM) is an effective means to reduce the operating cost of the system. However, detailed investigations of the feasibility analysis, design optimization and operation optimization of the low-cost heating systems are still lack. Hence, this thesis presented the systematic development of two low-cost outdoor swimming pool heating systems: air-source heat pumps (ASHPs)-based heating system and solar collector-integrated ASHPs-based heating system, which included the development of the ASHPs-based heating system, optimal design of the PCM storage tank, feasibility analysis of the ASHPs-based heating system, development, multi-criteria design optimization, feasibility analysis and demand-based control of the solar collector-integrated ASHPs-based heating system.

Firstly, an ASHPs-based heating system for outdoor swimming pools was developed. In this system, ASHPs were used to collect heat from the ambient air. With the assistant of a PCM storage tank, heat collection was scheduled to the on-peak period. Thus, the head demand of outdoor swimming pools during their open period was fulfilled by the PCM storage tank. The sizing principle and the control strategy of the system were introduced. The design of the PCM storage tank was also optimized to reduce the volume of the PCM storage tank. In the optimization, the effect of critical design variables on the volume of the PCM storage tank was analyzed, based on which the optimal design variables were identified.

Secondly, the feasibility analysis of the proposed ASHPs-based heating system was conducted. A simulation platform was constructed using MATLAB and TRNSYS, which was used to generate the operating data of the heating system. Using these data, the feasibility was evaluated by analyzing the control performance, reliability performance, energy performance and economic performance. Case studies were carried out to show the feasibility of the proposed outdoor swimming pool heating system for use in winter in subtropical weather conditions by comparing with a conventional heating system.

Thirdly, solar collectors were integrated into the ASHPs-based heating system in order to use the heat collected from the solar irradiation and further reduce the operating cost. The sizing strategy for the main components including ASHPs, PCM storage tank, and solar collector, was developed, which considered the coupling between the two heat sources. To obtain better overall performance of the system, a multi-criteria design optimization method was developed to improve the system design, which considered the dissatisfied percentage of thermal comfort, initial cost, operating cost, and energy use.

Finally, the feasibility analysis and demand-based control of the proposed solar collector-integrated ASHPs-based heating system were performed. Once again, a simulation platform was constructed to simulate the operation of the whole system and generate data for the feasibility analysis. To improve the energy efficiency and reduce the operating cost, a demand-based control strategy was developed to control the charging process of the PCM storage tank. To access the efficiency of the demand-based control, the performance of the proposed control strategy was compared with a traditional control strategy.

    Research areas

  • Outdoor swimming pool, Phase change material, Low-cost heating, Feasibility analysis, Design optimization