Studies On The Thermal Environment And Natural Ventilation Of Industrial Membrane Structure Building In Summer

With the increasingly stringent control of environmental pollution in China,the environmental protection department has mandated that open-air storage yards must be completely closed in order to fundamentally solve the problem of dust pollution.In recent years,due to its unique advantages such as excellent economy,strong adaptability and durability,and good self-cleaning,new closed membrane structure buildings have been more and more applied in industrial storage yards,warehouse buildings and other fields.It can effectively control dust pollution,greatly improve and protect the environment.However,the thermal inertia of such buildings is very small,resulting in serious indoor thermal environment problems.For example,the work area average temperature of the summer can reach more than 47.5℃ in Xi’an,affecting the physical and mental health of the staff.At present,there are few reports on the study of the internal thermal environment and ventilation of industrial membrane buildings in the world..In view of this,this paper aims to improve its internal thermal environment and natural ventilation effect,as follows:Firstly,the new membrane structure building form and membrane material type were obtained through field research.In order to solve the problem that the optical properties and thermal parameters of membrane materials are seriously missing and difficult to obtain,common membrane materials samples were collected and their photothermal properties were tested.The variations of the solar transmittance,absorptivity and reflectivity of the membrane materials with the wavelength of spectrum under different substrate,coating,color and gram weight studied experimentally,and the optical characteristic parameters are given.Based on the measured data combined with the thermal theory calculation,the multiple regression function of heat transfer coefficient of membrane surface under the combined action of wind speed,emissivity and surface temperature is proposed,which may provides the necessary data support for the thermal calculation of the membrane building.Secondly,the indoor thermal environment characteristics and influence parameters of industrial membrane building were studied experimentally.The test results show that light and thin semi-transparent membrane material is extremely sensitive to solar radiation and outdoor environmental changes.It is difficult to rely on the thermal resistance of the membrane material itself to reduce the impact of outdoor thermal disturbance,and there is a ’greenhouse effect ’during the day and a inverse greenhouse’at night.Based on the experimental test and theoretical analysis of heat transfer,the heat transfer model of the semi-transparent membrane building envelope was established.The heat transfer characteristics of membrane structure under the periodic changes of outdoor air temperature and solar radiation were studied,and the heat gain calculation method of membrane structure building was proposed.The results show that not only the solar radiation heat plays a decisive role in the thermal performance of the membrane,but also the long-wave radiation heat transfer cannot be ignored.Indoor heat gain solar radiation heat gain accounts for about 75%of the total heat gain(absorbed heat gain accounts for 83%of solar radiation heat gain,transmitted heat gain accounts for 17%of solar radiation heat gain),outdoor long-wave radiation heat gain accounts for about 18.76%of the total heat gain,indoor long-wave radiation heat gain accounts for about 5.93%of the total heat gain.Compared with the heat gain calculation model of the curved membrane structure building,the maximum heat gain calculated by the horizontal projection method is 24.8%smaller.It can provide a theoretical basis for studying the distribution law of internal thermal environment.Thirdly,the characteristics and distribution of thermal environment in membrane buildings under the conditions of no material,no self-heating material(such as mineral powder)and self-heating material(such as coal)were studied by experiment and simulation..The test shows that under the condition of high indoor air temperature and radiation irradiation,when the surface temperature of the internal heat source is 50℃,the average temperature of the working area in summer is 47.5℃,and the temperature difference between the working area and the outdoor environment can reach 12.4℃.There is a bad internal thermal environment.The indoor thermal environment model of membrane building was established and the accuracy was verified by experimental data.The variation of Grashof number Gr,dimensionless temperature Θ and radiation convection ratio ψ of heat dissipation material were studied under different heat dissipation intensity,different material surface temperature and different surface emissivity.When the material surface emissivity ε≥ 0.39 and the surface temperature is within 70℃,the radiation convection ratio ψ≥ 0.5,the influence of the radiation effect on the internal thermal environment characteristics cannot be ignored.Finally,based on the calculated fluid dynamics,the indoor ventilation airflow organization model of membrane building was established and the accuracy was verified by experimental data.The variation of indoor thermal environment of industrial membrane buildings under different ventilation conditions under the combined action of solar radiation heat and radiant heat of heat dissipation material was simulated.The variation law of internal velocity field,temperature field and their characteristic parameters were obtained under the parameters of variable inlet and outlet layout,area and height from the ground..The results show that the average temperature of the working area is 31.6℃,the ventilation rate is 56.22 kg/s,and the wind speed of the material surface is 0.4-0.6 m/s,which will not cause dust on the surface of the indoor material.When the dimensionless equivalent effective orifice area A/H~2 of the inlet and outlet is changed,adjusting the dimensionless A/H~2 of the inlet is more conducive to reducing the temperature of the working area,and the optimal range is 0.34～0.45.Inlet installation height should not be higher than 0.75 m,fresh air can better flow through the working area,building ventilation effect is better.In this paper,the heat transfer characteristics of semitransparent membrane structure under the periodic change of outdoor air temperature and solar radiation were studied,which can provide theoretical support for the heat transfer analysis of curved membrane building and the engineering calculation of heat gain.In addition,the characteristics of indoor thermal environment under the coupling of solar radiation and radiant heat of heat dissipation material,as well as the variation of internal velocity field,temperature field and its characteristic parameters under the parameters of variable air outlet and heat source have been studied.It can provide a theoretical basis for solving the problems of poor internal thermal environment and poor ventilation effect,and contributes to the popularization and application of industrial membrane buildings.