Research On Key Design Parameters Of Solar Hot Water System

Energy shortage, environment pollution and climate warming has become the main contradiction which constrains China’s economic and social sustainable development, exploitation and using of new energy resources, such as solar energy, is being taken more and more attention. Right now, some key design parameters related to engineering design of SWHS subsist stated disfigurement and deficiency. The research was in process combined with the formulating of Sichuan province engineering construction local standards "Evaluation standard for solar water heating system of civil buildings", absorbing domestic and foreign relevant research achievements and engineering experiences, doing research and optimization for related design parameters. The results of this study will be realistically meaningful and important to taking advantage of SWHS, reducing auxiliary energy consumption and improving reliability and economic of the system.First, a simplified calculation model for SWHS was studied by dynamic theoretical calculation method, a similar simulation model based on TRNSYS which was used to validate the veracity of the calculating model.Secondly, influence of the collector area, volume of tank and the flow rate of the circulating pump on the change rule of the optimum tilt angle is analysized by simplified calculation model with the principle of changing a single variable, comparing with two other factors, the collector area has a greater impact on the change of the tilt angle. On this basis, the collector area was determined by the reasonable solar fraction and the optimum tilt angle matching with the collector area was based on the minimum auxiliary heat consumption throughout the year, three typical cities which have significant seasonal differences between solar radiation and hot water load were used as examples in simulative calculation. Results show that, the design of collector area and optimum tilt angle are mainly affected by the seasonality of the solar radiation and heating load, for the SWHS with heat collection and water supply occurring in different time periods. The optimum tilt angle increases with the increasing of collector area when the solar radiation shows the contrary change tendency with the heating load. The optimum tilt angle is almost unchanged when the solar radiation shows the similar change tendency with the heating load.In addition, A double-water tank SWHS assisted by Gas-fired boiler simulation model based on TRNSYS was built, combining the characteristic of living water, the corresponding control strategy is proposed, so as to meet the requirement of outlet point. By means of simulation model, the main design parameters of SWHS are optimized, analysing the the relationship between the change of design parameters and its influence on the operating mode of system. Results show that, when solar collector area is given, the optimum consumption of the solar collection system circulating pump is reduced with increasing volume of the tanks; when volume of the double-water tank is given, the optimum consumption of the solar collection system circulating pump increases with increasing solar collector area; No matter what form of the changing areas or volumes, the optimum consumption of the load side circulating pump; Choosing appropriate power auxiliary heating boiler satisfies both economy and water supply reliability; Compared with volume of the tanks, solar collector area has more effect on solar fracrion. Similar with simplified model, the optimum tilt angle increases with the increasing of collector area in given area; And the optimum volume proportion of double tanks is determined.Finally, in order to select solar fraction more comprehensively and scientifically, a multi-level evaluation model based on the consideration of economy, energy efficiency, environmental protection, system safety and maintenance, water supply reliability was established. By adopting the idea of integrated evaluating, the TOPSIS ranking method based on gray relation analysis was applied, and the model could be used to select the optimal solar fraction, with minimum relative similarity degree as the evaluation criteria, and a living computation example was presented. The model is used to provide a new method and approach for the design and evaluation for practical engineering.