Thermal Performance Of Evacuated Tube Solar Water Heater And Medium Temperature Solar Collector

With the continuous development of urbanization in China, the proportion of building energy consumption in the total energy consumption is increasing gradually. To promote sustainable development, it is an effective way to save energy and reduce emission by the popularization and application of solar thermal technology in civil buildings. In this thesis,modelling and experiments have been performed on the thermal performance of typical evacuated tubular domestic solar water heater(ETDSWH) and medium temperature evacuated tubular solar collector(MTETSC), the evaluation method research on the application effect of solar thermal system in civil buildings has also been performed.Firstly, the main influence factors on the thermal performance of ETDSWH are decided theoretically. Then the test method and device for thermal performance of ETDSWH are developed. With the device, effects of parameters, including the water volume per aperture area, tube center distance, tube length, insulation thickness and others, on the thermal performance of ETDSWH are investigated by experiments. Experiment results show that the water volume per aperture area has the most significant effect. It is found that the daily useful energy increased by 0.53~1.56MJ/m2 and the daily average collection efficiency increased by 3.1%~9.2% within the increase of the water volume per aperture area by 10kg/m2. Using the results, well effects are obtained in the optimization of ETDSWH, which proves that the experimental research results can be useful in the design and application of ETDSWH.Secondly, based on energy balance equations, the mathematical models for the MTETSC have been developed to predict its thermal performance. With Matlab programming, iterative method for solving the models is accomplished. Then test device for the thermal performance of MTETSC is designed and assembled. Using this test device, experiments haves been performed on a MTETSC sample. Results show that the deviation between the simulated and tested intercept efficiency is 5.9%, for the heat loss coefficient is 5.6%. The models have been verified by the experiment result. And it is applicable to the thermal performance research.With the validated model, it is found that the radiation heat transfer between the absorb plate and external tube plays a key role in the heat loss of MTETSC. To improve the thermal performance, the heat shield under the absorb plate is introduced into the MTETSC. According to the test results, the efficiency curve is η=0.7763-1.8617T*. Comparing with the MTETSC without heat shield, the intercept efficiency increases by 7.2% and the heat loss coefficient decreases by 50.9%. The MTETSC with heat shield has significant improvement on the thermal performance.In addition, regarding the technical, economic and environmental factors, the evaluation methods on the application effect of solar thermal system has been proposed and applicated in demonstration projects. It can be used in the designing and optimizing of the solar thermal system to promote its application.