Regular Characteristics And Spatial Distribution Of Heat Flow And Heat Transfer Coefficients On The External Surface Of Buildings

Heat flow density is an important parameter in the field of building thermal engineering.Through the measurement of heat flow,the gain and loss of heat during the actual operation of the building and the cause of the formation of the thermal environment can be analyzed.When the surface temperature and air temperature are determined,the heat flux density of the building surface can be characterized by the surface heat transfer coefficient.Among them,the surface heat transfer coefficient of the exterior protection structure is an important physical parameter for the heat exchange between the exterior protection structure and the outdoor,and its value has an important impact on the building energy consumption.The heat flow and heat transfer coefficient of building exterior surface are affected by many factors of outdoor environment and enclosure structure.The heat flow and heat transfer coefficient of actual building surface are dynamic changes.At present,the method of taking fixed value for heat transfer coefficient in China’s building thermal energy saving standard does not reflect many actual heat transfer conditions.It is necessary to test the actual building on site to get the actual building The relationship between heat flow and heat transfer coefficient and key influencing factors provides a new value method for heat transfer coefficient,a practical measurement basis for relevant calculation theory,and a support for accurate prediction of building thermal environment and energy consumption.To sum up,this paper uses the method of field measurement to test and study a variety of working conditions of an external heat preservation and heating building in Xi’an,obtains the distribution law and spatial distribution characteristics of heat flow and heat exchange coefficient of the actual building,and on this basis,uses the method of numerical simulation to discuss the influence of heat exchange coefficient on thermal design.The main work and results of this study are as follows:(1)Based on the direct heat balance method,the radiation and convective heat transfer coefficients of the building’s external surface are measured in the field,and the curves of radiation,convective and total heat flow,convective and radiant heat transfer coefficients of the external wall are obtained.The results show that the radiative and convective heat transfer coefficients of the outer wall are 2.19～11.32 W/(m~2·K)and0.15～6.58 W/(m~2·K);the average proportion of radiant heat flow of external wall to total heat flow is 80%;the value of convective heat transfer coefficient is very small in the low wind speed area of urban center,which needs to be reconsidered;for the natural wind with low wind speed,the relationship between convective heat transfer coefficient and wind speed and turbulence is given,and it is found that the correlation between convective heat transfer coefficient and turbulence is better.(2)By using the method of field test,the heat flow and heat transfer coefficient of building surface under five different working conditions are studied.The main test data are the outdoor air temperature,the external surface temperature,the internal surface temperature,the indoor air temperature,the external surface heat flow density and the internal surface heat flow density.The difference of the external surface heat flow and heat transfer coefficient caused by the building orientation is analyzed.Then,we choose three angles to analyze the interior and exterior surfaces of the South exterior wall,the interior and exterior surfaces of the South exterior window and the interior and exterior surfaces of the roof,that is,the heavy vertical envelope,the light vertical envelope and the heavy horizontal envelope.After that,the roof,the South exterior wall and the South exterior window surface are tested and analyzed.In addition,the exterior window is selected as light-weight enclosure and the exterior wall as heavy enclosure.The surface heat flow and heat transfer coefficient of the South exterior wall and the South exterior window are analyzed.At last,the heat flow and heat transfer coefficient of the North exterior wall,the North exterior window,the East exterior wall,the South exterior wall,the South exterior window and the interior and exterior surfaces of the roof are tested and calculated,and the distribution frequency of the heat transfer coefficient of the interior and exterior surfaces of different parts of the enclosure structure is calculated,and the maximum distribution frequency range of the heat transfer coefficient is obtained.According to the heat flow situation of different directions,the design calculation and analysis of equal heat flow for the most buildings are carried out.(3)This paper analyzes the influence of the heat transfer coefficient of the outer surface on the heat transfer coefficient of the heavy,light and single-layer glass windows,and indicates that for the light steel and single-layer glass windows,the value of the surface heat transfer coefficient should be refined according to the outdoor wind speed and seasonal changes,so as to increase the reliability of the energy-saving design of the building.After that,a simplified calculation method is used to calculate the change percentage of heat storage and the total heat storage in June,July and August under different surface heat transfer coefficients.Finally,through the design builder building simulation software,select different heat transfer coefficient models to analyze the energy consumption of the measured buildings.The actual building surface heat flow and heat transfer coefficient obtained in this study reflect the actual thermal situation of the operating building,and summarize the change rule of the surface heat flow and heat transfer coefficient under the influence of various working conditions.The obtained surface heat flow and heat transfer coefficient provide a reference for its value.In the actual thermal design application,due to the influence of the change of the heat transfer coefficient,the heat transfer coefficient is obtained for the enclosure The influence of structure,heat storage ventilation and building energy consumption,the recommended values of heat transfer coefficient in these cases are given.