Measurement And Simulation Of Outdoor Thermal Environment For Urban Residential District Planning

With urbanization process accelerating, residential communities mushroomed over our country, however outdoor thermal environment is deteriorated because of taking no account of thermal environment during settlement planning period. Meanwhile, outdoor thermal environment and our daily life are closely bounded up. Therefore in order to build favorable outdoor thermal environment of residential community, optimized thermal environment measures are required at the beginning of settlement planning period, which would help reduce building energy consumption.At present, relevant researches conducted by domestic and foreign scholars are mainly focused on macro study of urban thermal island and urban wind field, which have achieved a series of results. However, urban thermal environment is influenced by factors such as solar radiation, building distribution, terrain, water bodies, greening and different kinds of underlying surfaces and each factor associates with others, which hinders quantitative researches on such influence factors. At micro level, researches on urban settlement thermal environment are rare and lack developed theoretical studies. Therefore this article focused on residential community, conducting field test and simulation on micro-thermal environment.Firstly, selecting a building complex in Reading University, which contains four types of construction layout(Street Canyon Type (point 1,2); Semi-enclosed type (point 3); Garden Type (point 4,5); Open Type (point 6)), to arrange 6 fixed test points. Though remote monitor and mobile observation, we measured atmosphere dry bulb temperature, relative humidity, wind speed, horizontal solar radiation, underlying surface temperature and building surface temperature of the 6 fixed points at all seasons. The result shows that different observation points of building layout have different influence factors of wind speed and asphalt pavement surface temperature has a closer correlation with atmosphere dry bulb temperature than solar radiation does and this correlation differs from each point. By means of establishing thermal balance equation of lawn and multi-factor regression, we concluded that linear regression equation of lawn energy differs in different construction layout and lawn temperature influence factors varies. Outdoor thermal environment measure can be applied as boundary conditions for following numerical simulation as well as simulation verification.Secondly, based on zero equation, building air flow and heat transfer model of building complex and applied 3D coupled solution to solve problems of residential community outdoor air flow and heat transfer. Factors such as solar radiation, long wave radiation, latent heat exchange between air and greenings and water bodies, anthropogenic heat, heat exchange between buildings and humidity exchange between air and underlying surfaces, are under consideration in the physical model. Meanwhile this paper selected walls, roofs, air, greenings and water as study objects respectively and established a heat balance equation to conduct coupled solutions. In order to accelerate computation and reduce hardware requirements for computer simulation, we calculated the received solar radiation amount of underlying surface and building surface, surface temperatures of underlying surfaces and building walls, roofs, and finally air flow field and dry bulb temperature by the SIMPLE algorithm of collocated grid and SLUR scan algorithm. Specifically, this article made 3 steps to simulate outdoor thermal environment computation: 1. Establishing a mathematical model of urban outdoor thermal environment. 2. Calculating sky view factor (SVF) of underlying surface, sun direct radiation, diffuse radiation, short-wave radiation, reflected radiation heat, and then classifying and recording data. 3. Inputting results of second step as the condition of air flow and heat transfer to simulate computation.Finally, taking a building complex in Reading University as example to conduct simulation and analysis to confirm the physical model. Using thermal parameters of the building envelop and different underlying surface, meteorological data of Reading University, indoor setting temperature, air conditioning calculated temperature in summer as initial condition to simulate. Comparing simulated data and measured data, the result shows that they have similar variation and within tolerance range, which verify the air flow and heat transfer model of urban settlement to be reasonable.This work lays a practical and theoretical foundation of numerical simulation for optimizing urban residential thermal environment, which is expected to be widely applied at early stage of urban settlement planning.