Research On The Influence Of Clearness Index On Heat Gain Of Flat Roof In Typical Areas Of Jiangxi Province

With the enhancement of China's comprehensive strength and the rise of national life and consumption level,the proportion of building energy consumption in disposable energy consumption is also increasing year by year.At the same time,the public's demand for comfort and suitability of the building environment is getting higher and higher,which leads to the increase of the quantity and usage of air-conditioning equipment in all kinds of buildings year by year,making the energy consumption of HVAC equipment account for about 50%of the building energy consumption in recent years.Therefore,on the basis of guaranteeing indoor comfort,controlling building energy consumption is a key content of building energy saving.Accurate calculation of HVAC energy consumption under different weather conditions is the basis of precise design and regulation of HVAC system to reduce HVAC energy consumption.In order to study the actual detailed heat transfer of building horizontal envelope under various weather conditions,the concept of clearness index is introduced to represent various weather conditions.By using 1stOpt software,the relationship between outdoor temperature parameters and clearness index was found in Nanchang area and Ganzhou area of Jiangxi Province during June to September in summer and December to February in winter.The regression equations of clearness index and daily maximum temperature,and the regression equations of clearness index and daily range in winter and summer in Nanchang City and Ganzhou City of Jiangxi Province are obtained respectively.The determinant coefficients of the regression equations are still large when there are many samples.The results show that for both Nanchang and Ganzhou,the relationship between the maximum outdoor temperature and daily range in winter and summer and the clearness index is obvious.On the one hand,the above regression equation makes up for the lack of some radiation data of meteorological stations in Jiangxi.In the subsequent in-depth analysis of solar energy resources,it provides a reliable mathematical model and data support.On the other hand,the obtained regression equation is based on the measured data over the past years.Under the conditions of different clearness index calculated by the regression equation,the change of air temperature outside is closer to reality.As the boundary condition of the follow-up simulation study,the simulation results can be closer to the real situation.Fluent 14.5 software was used to simulate the specific heat transfer process of horizontal building envelopes in Nanchang and Ganzhou cities of Jiangxi Province under different conditions of clearness index.The influence of the clearness index on the average temperature,heat transfer flux,heat storage of each structural layer of the building's horizontal envelope,and the total net heat gain of the roof's external surface is analyzed,and the relationship between the clearness index and the total net heat gain of the roof's external surface is obtained.At the same time,the actual distribution frequencies of the clearness indices in Nanchang and Ganzhou during the past 30 years are analyzed,and the heat transfer and energy consumption of the horizontal envelopes in the two cities in winter and summer are calculated.Summer situation,Nanchang area:June:2.44×10³KJ·m^-2.July:3.18×10³KJ·m^-2.August:2.85×10³KJ·m^-2.September:2.36×10³KJ·m^-2.Summer typical day in Nanchang area:5.30×10³KJ·m^-2.Ganzhou area:June:2.91×10³KJ·m^-2.July:3.76×10³KJ·m^-2.August:2.77×10³KJ·m^-2.September:2.19×10³KJ·m^-2.Typical Summer Days in Ganzhou Region:4.39×10³KJ·m^-2.Winter situation,Nanchang area:December:-0.28×10³KJ·m^-2.January:-0.65×10³KJ·m^-2.February:0.04×10³KJ·m^-2.Typical winter days in Nanchang area:-0.48×10³KJ·m^-2.Ganzhou area:December:0.032×10³KJ·m^-2.January:-0.351×10³KJ·m^-2.February:0.132×10³KJ·m^-2.Typical Winter Days in Ganzhou Region:-0.11×10³KJ·m^-2.It is found that the total net heat gain under actual weather conditions is significantly different from the total net heat gain of the horizontal envelope structure calculated under typical day weather conditions.If the air conditioning load calculated under the most adverse weather conditions is used to control the air conditioning equipment,it will cause a great waste of energy.The correction coefficients of the total net heat gain of the roof in each month are given according to the calculation results of typical day weather conditions.Summer situation:June to September in Nanchang:0.46,0.60,0.54,0.45.Summer in Ganzhou:0.66,0.86,0.63 and 0.49.Winter conditions:winter in Nanchang:December to February:0.58,1.35,-0.083.Winter in Ganzhou area from December to February:-0.29,3.19,-1.2.Therefore,the research results will provide basic data and theoretical guidance for building energy conservation in Jiangxi.