A Study On The Effect Of Natural Ventilation At Night On The Indoor Thermal Characteristics Of Office Buildings And Their Energy Saving Potential In Hefei

With the development of society,people’s living standards are gradually improving,the demand for energy is increasing rapidly as well.Among them,building energy consumption accounts for the largest proportion of energy consumption in the whole society.Therefore,how to reduce the energy consumption of buildings has become one of the urgent problems in our country at this stage.Scholars at home and abroad have done a great deal of research on how to reduce the energy consumption of buildings through natural ventilation,but most experts and scholars have simply studied the design scheme of natural ventilation and the feasibility of natural ventilation to reduce the energy consumption of buildings,and there is less research on the effect of natural ventilation on indoor thermal characteristics of buildings and their energy-saving potential.As a result,the analysis and study of indoor thermal characteristics and its energy-saving potential of natural ventilation has a certain reference value in reducing the energy consumption of buildings.Based on the outdoor meteorological parameters of Hefei in the hot and cold summer and winter,this paper explores the analysis of the impact of night-time natural ventilation on indoor thermal environment and its energy-saving potential in office buildings in Hefei area.First of all,this paper introduces the characteristic analysis of heat storage in the building wall.The temperature of outdoor in Hefei is measured in practice,and the equation of outdoor temperature change is obtained by the least square fitting.The steps and principles of Fluent for simulation as well as calculation are introduced in detail.By virtue of the Fluent,the model is not only established,but also the boundary conditions and parameters of the wall are set.Besides,the equation of outdoor temperature change is imported into Fluent for simulation,calculation and analysis.It is found that the wall temperature change is more latency than the outdoor temperature change due to the heat storage reason,and there is a temperature difference in various parts of the wall.Unexpectedly,the temperature change law of the inner wall is basically the same as the change law of outdoor temperature.Secondly,on the basis of the heat storage characteristics of the wall,the simulation and calculation is carried out to explore the effect of natural ventilation on indoor thermal environment at night.In order to realize the goal,it is necessary to reset the boundary conditions in Fluent and add natural ventilation.In the software,natural ventilation time is from 21:00 to 9:00 the next day,lasting a total of 12 hours.By taking the center of the room as the standard point of temperature monitoring,12 hours of natural ventilation will be simulated and calculated when the room environment temperature changes.The indoor ambient temperature under 12 hours of natural ventilation and the indoor ambient temperature without natural ventilation will be compared and analyzed.After that,the temperature and velocity cloud map with representative time points will be selected,and the cloud map will be compared and analyzed by comparison and analysis of the temperature and velocity cloud map at various moments,which helps to obtain the effect of natural ventilation on the indoor thermal environment at night.The finding,that during 12 hours of natural ventilation,the initial ventilation of the indoor ambient temperature is improved best,is proven.As time goes by,the ventilation effect gradually goes down,and there is phenomenon that air flow rate from center point of a room reaches zero.After ventilating for 12 hours,the room temperature overall goes down by about 6 degrees.Next,on the basis of 12 hours of night ventilation,taking the actual situation into account is relatively important.Because of the possibility of overtime of employees in office buildings,natural ventilation throughout the night might not go on smoothly.Therefore,under the direction of natural ventilation for 12 hours,the time for natural ventilation is divided into three time blocks,respectively,from 21:00 to the next day 1:00,the next day 1:00 to the next day 5:00,the next day 5:00 to the next day 9:00 each time period for ventilation 4 hours.Each of them lasts four hours.During the process of the observation,it is concluded that the night ventilation effect is the best in the period from 1:00 on the next day to 5:00 the next day,followed by the 21:00-1:00 period of the next day,and the worst is in the period of 5:00-9:00 the next day.In accordance with the above order,the temperature decreases by 7 degrees,6 degrees and 4 degrees respectively.Then,the paper explores the energy-saving potential of natural ventilation at night by building a practical building model.Based on DeST-C software,an office building model on the ground is built,which consists of four floors.The first layer is 3.9 meters in height,and the rest of them are 3.6 meters.What’s more,the building is 57.0 meters in length,the width is 9.4 meters,and the construction area is 2143.2 meters.According to the viewpoints of this paper,the first step is to simulate and calculate how much the energy consumption of buildings is when there is no natural ventilation at night,which is regarded as the basis item of energy consumption analysis.Afterwards,the window opening time is set with four window ventilation schemes.The first scheme is from 21:00 to the next day 6:00.The second one is from 21:00 to 1:00 the next day.The third one is from 1:00 to 5:00 the next day,and the last one is from 3:00 to 6:00 the next day,through which building energy consumption can be obtained.Compared with the energy consumption of buildings without natural ventilation at night,the ventilation time will be slightly adjusted here as the officers have to get to the office before 8 am.The cold,hot load and energy-saving ratio of natural ventilation at night at different times are obtained by comparison analysis.The energy-saving effect of natural ventilation at night under four different cases is as follows,scheme1> scheme 2>scheme3> scheme4,and energy saving ratio of the total load is 3.27%,1.6%,2.86% and 2.74% respectively.Finally,it is concluded that,under the condition of all-night natural ventilation,its indoor thermal ambient temperature is optimal and the energy saving potential is optimal.If there is no natural ventilation throughout the night,the next day 1:00 to the next day 5:00 for the natural ventilation is pretty beneficial to the improvement of its indoor thermal environment,and the energy saving potential is best.