Investigations On The Influence Of Building Envelope On Indoor Thermal Environment In Summer And The Way Of Energy-saving Cooling In Buildings

Buildings in cold areas of China need to meet the load of winter heating and summer air conditioning,so the energy consumption of buildings is usually large.Carrying out research on the law of building HVAC energy consumption and building energy-saving technology is of great scientific value and engineering practical significance for the in-depth promotion and realization of China’s "double carbon"strategic goal in the construction field.Based on the summer statistical meteorological conditions in Jinan as the simulation to calculate the environmental conditions,a two-dimensional room physical model and a mathematical model of indoor and outdoor environmental heat transfer of typical building structures in cold areas are established,and the change laws and influencing factors of the indoor environment in summer are numerically studied based on this model.Establish a closed room heat transfer model to eliminate other room temperature influencing factors such as permeability air volume,change the thermal conductivity of the peripheral parapet wall,compare the change law of the wall and the indoor temperature,and obtain the influence law and physical mechanism of the thermal conductivity of the building wall on the wall temperature and room temperature:The thermal resistance of the existing building exterior wall in China’s cold areas can basically completely block the transfer of indoor and outdoor heat through the wall in summer,and the transmission of environmental radiation by the external windows in building maintenance is the main determinant of summer room temperature.The physical mechanism of the influence of the thermal conductivity of the wall material on room temperature is more reflected in the speed and amount of heat that the wall absorbs and releases to the room alternately on the day and night,and superimposes the influence of the window through radiation,thereby affecting the fluctuation peak and trough of the room temperature in the 24-hour period of a day;The smaller the wall thermal conductivity,the lower the summer indoor night temperature valley value and the average temperature throughout the day in Jinan.Due to the influence of the wall to the room suction and exothermic process,the wall thermal conductivity is one of the determinants of the temperature of the thermal balance state of the room,which has a certain degree of influence on the potential air conditioning energy consumption of the room in summer,and the thermal conductivity of the north and south walls has a difference in the degree of influence on the room temperature.When the thermal conductivity of the north and south walls is changed at the same time,the influence of the temperature change of the north wall on the thermal comfort of the human body is greater than that of the south wall,so when designing the building,priority can be given to the optimization of the thermal conductivity of the north wall to obtain the summer building energy saving effect.Maintaining other conditions unchanged,changing the specific heat capacity of the outer wall of the house is compared to the change of the indoor environment,and the influence law and physical mechanism of the specific heat capacity of the wall on the wall temperature distribution and room temperature are obtained:The specific heat capacity of the wall has a positive impact on the stability of the indoor temperature,and the specific heat capacity of the wall material increases the amount of heat that the wall absorbs and releases alternately in the day and evening to enter the room,thereby"shaving the peak and filling the valley" for the fluctuation of the room temperature in the 24-hour period of a day.Compared with the change of the thermal conductivity of the wall,the change of the specific heat capacity of the wall has a greater impact on the energy consumption of air conditioning in summer.In this paper,the heat capacity change ranges from 10.88 W/m2 to 13.32 W/m2 during the day.Optimize the specific heat capacity value of the north and south walls respectively,and it is possible to obtain better air conditioning energy-saving effects;When the average specific heat capacity of the wall is greater than 5430 J/(kg·K)later,the change of indoor human thermal comfort index(PMV)is no longer significant with the increase of the specific heat capacity of the wall,and it can be inferred that the wall specific calorific value of the optimal PMV value exists under fixed meteorological conditions.Different from the change of the thermal conductivity of the wall,and the specific heat capacity of the north and south exterior walls are changed at the same time,the influence of the south wall and the north wall on the thermal comfort of the human body is basically the same.Because of the transformation of the wall suction and exothermic process,the interior of the wall produces two turns in the direction of heat flow in one day,and in this steering process,the walls with different specific heat capacity and thermal conductivity will cause certain room temperature differences.In addition to affecting the heat flow of the wall suction and exothermic,the specific heat of the wall also affects the speed of heat transfer in the wall and the steering cycle of the heat flow.Keep the wall structure unchanged,and compare the three energy-saving external windows of the high-permeability low-radiation glass window.the comprehensive sunshade window that eliminates direct sunlight radiation but retains the scattered radiation,and the sun-shaded low-radiation glass window on the indoor thermal environment.The results show that the three kinds of energy-saving external windows can effectively improve the indoor thermal environment in summer,and the comprehensive sunshade window and the shading type low-radiation glass window can greatly reduce the indoor temperature,and the room temperature can be maintained in the human thermal comfort state during the summer room in Jinan from 21:00 to 9:00 the next day without using additional cooling methods.Compared with ordinary glass windows,high-transmittance low-emissivity glass windows,integrated sunshade windows and shading low-emissivity glass windows can significantly save the potential air conditioning load of summer rooms,and the potential air conditioning load of summer rooms of 11.24 W/m2、30.44 W/m2 and 33.68 W/m2 can be saved under the model conditions of this article.Select the typical wall structure,establish the open ventilation room model,and compare the impact of the natural permeation wind throughout the day with the indoor natural wind in the morning from 0:00 to 6:00 in the morning,the indoor natural air in the morning from 0:00 to 6:00 in the morning,and the light air conditioning refrigeration and ventilation in the rest of the period on the indoor environment.The results show that in the summer of Jinan,the natural wind strategy of changing the wind from the outside to the indoor from the outside to the outside is 6 to 7 times per hour during the 0:00 to 6:00 a.m.period in the summer has a significant effect on the cooling of the built environment,and the strategy can reduce the room temperature by more than 3 K during the day.In the absence of other infiltration heat indoors,when the natural air in the early morning combined with the cooling measures of mild air conditioning refrigeration and ventilation in the rest of the time is adopted,the energy consumption per unit area building refrigeration is only 6.94 W/m2,which can significantly reduce the indoor air and wall temperature,and meet the indoor environment to meet the requirements of human thermal comfort.