Design And Optimization Of A Double-tank Solar Water Heating Syste

Dual-tank solar water heating system with two large tanks is often used in places of large water demand and stringent water quality situation.The study of the traditional single-tank solar water heating systems is fairly wide at home and abroad at present about the system structure,thermal analyses,and working conditions in order to improve solar water heating system performance and increase collection efficiency,but there are few studies for dual-tank solar water heating system.Therefore,this paper focused on the research of the relationship between the water level in dual water tanks and pipe diameter,thermal stratification,matching methods and the other aspects,meanwhile summarized and optimized the results,so as to have theoretical guiding significance in engineering design for a dual-tank solar water heating system.In order to solve the problem of overflow and other issues in tanks resulting from improper design of dual-tank solar water heating systems,the paper based on the forced circulation dual-tank solar water heating system,a function was given about the relationship between the maximum possible difference of the water level in dual water tanks and pipe diameter,through the analyses of the change of water level in system operation.Meanwhile,with an example calculated and analyzed,the size ofthe reserved space,the connecting pipe diameter and the height positions of openings of the related pipes were offered.Using CFD software for numerical simulation,temperature stratification of thermal storage tanks for dual-tank solar water heating systems was studied.Many numerical simulations were carried out with different factors including inlet water velocity,intake position height,inlet water temperature and other factors;the analyses of these factors on thermal performance was obtained.At the same time,the changes in temperature stratification taking the actual situation into account were given.According to the different types of dual-tank solar water heating systems,the studies of the relationships between the solar collector and the two tanks about matching methods and connection methods were simulated,by the way of statistics and comparison of simulated time,the system comprchensive heat efficiency,the average temperature of the available hot water,the proportion of the available hot water,the utilization of the heat input.Comprehensive analyses and the recommendations were given in the optimal way to match the area and connection mode.A discussion about the influence of the thermal performance of dual-tank solar water heating systems under different conditions about solar radiation intensity was made.