Research On Building Heating Technology Of Solar Air Collector In Tibet

Building energy-saving technology is the content of the"Building Technology"direction in the"Master’s Program for Civil Engineering and Water Conservancy"of Tibet University.Energy saving building technology is an important newly developing research interests and content in terms of building technologies.The current thesis designs,develops,and tests a pure solar air-heating collection system in Lhasa,Tibet,rich in solar energy resources.The research work includes building heating principle of the pure solar air collection system,structural designing of the heat collection system,development of the heat collection chambers,and final efficiency testing of the pure solar air heat collection systems and other works.Solar air collector is a device that uses solar energy to heat air and can be used for heating,hot water supply,and other aspects.Compared with traditional solar water heaters,solar air collectors have a wider range of applications and higher energy utilization efficiency.In high-altitude areas like Tibet,solar air collectors can effectively solve heating and hot water supply problems,reduce dependence on traditional energy,and also reduce environmental pollution and resource waste.Therefore,the research and development of solar air collectors in Tibet has important practical significance and application value.The developed pure solar air heat collection system is mainly consists of a solar fan,a heat collection chamber,a solar tracking system,a gas pipeline,and related brackets.The solar global irradiance during the test period were measured by using the CMP-11 global radiometer(measuring wavelength range285-2800nm)made by Kipp&Zonen company of the Netherlands.The light transmittance of the covers used for the solar air collectors was tested by using the Canadian Spectrafy SIM-G solar spectrometer(wavelength 280-1200nm,accuracy0.1nm).The temperature of the inlet and outlet of the collector chambers were tested by using professional thermometers.The size of a single solar air collector is 2000mm in length,940mm in width,and 124mm in height;Metal partitions were used inside the individual collector to divide the chamber into four equal parts,each chamber was internally perforated and connected,allowing the cold air blown in from the air inlet to gradually heat up the four collector chambers.In order to increase the temperature of the gas in the chambers,grid shaped metal wires were installed at a certain slope inside the four chambers(to increase the contact probability between the air and the collector grid).In order to blow cold air into the collector chamber from the air inlet,we utilized a solar or conventional power fan with an air blowing rate of 150m~3/h.A total of 4 sets of solar air collectors with the same size were developed in this research work.In the testing and research work,conducted tests and research on the heat collection performance for the single-chamber,double-chamber,three-chamber,and four-chamber collectors respectively.The heat collection performance of the developed collectors was tested under actual natural light conditions in Lhasa during summer and winter time.The heat collection performance of a single chamber solar air collector was tested under natural sunlight at the Najin Campus of Tibet University in Lhasa(91.18°E,29.65°N,elevation3660 meters)in the summer of June 2022.In the test on June 2,the variation range of total solar irradiance in Lhasa was about161.8-1588W/m~2.The average ambient temperature(inlet temperature)22.5℃of the collector in the tracking sun mode was heated by the single collector,made the average temperature of hot gas at the outlet reached about 68℃,the highest temperature at the outlet of the collector on that day reached 85℃,close to the boiling point of Lhasa water of 86℃,indicating that the system has high heat collection performance,with a maximum heat collection efficiency of 36%,and a hot air flow rate of 150m~3/h at the outlet.In early March 2023,performance tests were conducted for single-chamber,double-chamber,three-chamber,and four-chamber collector systems under actual sunlight.In winter,under the sunshine of Lhasa,the maximum temperature at the outlet for the single-chamber collector reached 77℃,with an efficiency of34%;The double-chamber reached 79℃,with an efficiency of 42%;The three-chamber reached 83℃,with an efficiency of 40%;The four-chamber collector reached 85℃with a 47%efficiency.Although the number of chambers connections does not increase the outlet temperature much,it can improve the stability of the outlet temperature.During the test,it is found that the outlet temperature of the collectors is very sensitive to the change of solar irradiance,i.e.it is very sensitive to the change of weather.If appropriate insulation measures are taken for the collectors,the outlet temperature will be correspondingly more stable.The developed pure solar air collector is composed of a metal shell and an organic glass cover,without the use of glass vacuum tubes.It is designed to adapt to the climate characteristics of Tibet,such as large temperature differences between day and night,cold winters,and strong sandstorms.Vacuum tube glass collectors are prone to breakage and have a short lifespan under the climatic conditions of Tibet.Therefore,this collector has practical application value in terms of performance.Due to limited time and effort during master’s research work,the main research and testing work was carried out on the developed heat collection system,further improvement and efficiency of the collector will be still required detailed research work.The specific areas that need to be improved in the future are mainly included insulation measures for the collectors,sealing of the collector chambers,and material optimization.The current thesis also studies designs of integrating the solar air collectors with buildings.