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A Study Of The Thermal And Energy Performance Of A Partitioned Gravity--Driven Cooling Window

Posted on:2024-01-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:L LiFull Text:PDF
GTID:1522307319464144Subject:Heating, Gas Supply, Ventilation and Air Conditioning Engineering
Abstract/Summary:PDF Full Text Request
External windows are an important part of the building envelope,providing aesthetics,indoor and outdoor separation,lighting,ventilation and other functions for the building,while having an important effect on the energy consumption of the HVAC system and carbon emissions of the building.Therefore,research on energy-saving technology of external windows is of great significance to reduce building energy consumption and achieve carbon peaking and carbon neutrality goals.This dissertation proposes a novel energy-saving external window technology,called partitioned gravity-driven cooling window(GDC window).The window has the characteristics of multiple glasses,embedded pipes,circulation air in cavity,and enhanced cooling of pipes,which can utilize low-grade cold source,reduce the heat gain of the external windows in summer,thereby reducing the cooling load of the HVAC system.This dissertation studies the heat transfer and energy-saving characteristics of GDC window,and the main research contents and conclusions are as follows.(1)A theoretical model of GDC window is developed by using the analytical method,and the mathematical expression of gravity-driven potential for the airflow circulation in the cavity of GDC window is also derived.The principle of GDC window can be explained from a theoretical view according to the theoretical model,and the influencing trend of the main parameters of GDC window are also analyzed to guide subsequent numerical research.Through the analysis of the four parameters(the solar radiation intensity,the thermal resistance of the separation layer,the water temperature and the airflow circulation resistance coefficient in the cavity),it is found that the four parameters have an important influence on the gravity-driven potential of GDC window and the strengthened cooling effect of the pipes.(2)A numerical model of GDC window is developed by using the method of computational fluid dynamics,which can used to calculate the flow and heat transfer results.In the numerical model,the open optic software WINDOW is used to calculate the optical parameters of GDC window.An experimental platform is designed for the validation of numerical model,experiments under different conditions are carried out.The accuracy of the numerical model of GDC window is verified by comparing the experimental measurement data with the simulated data.(3)The flow and thermal characteristics of GDC window are studied using the numerical model.Firstly,the effects of the structural features of GDC window are studied,and the results show that the three main features of GDC window(cavity partition,air circulation flow,and utilization of high-temperature cold source)have positive effect on the strengthened cooling of the pipes and reduction of heat gain.Then,the main structural parameters of GDC window,the thermal resistance of the separation layer,optical parameters of venetian blinds,water temperature are quantitatively analyzed for their influence on thermal performance of GDC window,and the results showed that 1)The window height,outer cavity thickness,blinds width,fin height,and the number of pipes have a monotonous effect on the pipes’ cooling load and the heat gain of GDC window,2)There is an optimal value for the fin spacing,3)The thermal resistance of the separation layer begins to have an obvious impact on the pipes’ cooling load and the heat gain of GDC window after it increases to a certain value,4)The increase of the inclination angle of the blinds or the decrease of the solar reflectance on the surface of the blinds is beneficial to reduce the total heat gain of GDC window,5)The reduction of the water temperature is beneficial to increase the pipes’ cooling load and reduce the heat gain of GDC window.Even using a high-temperature cold water higher than the indoor temperature,the GDC window can still have a good energy-saving effect.(4)Using the data generated by the numerical model,empirical models of GDC window are developed by using linear regression and Gaussian process regression,which can be used to quickly calculate the pipes’ cooling load and heat gain of GDC window.Input parameters for the empirical model include solar radiation,outdoor air temperature,and the water temperature.The two empirical models are evaluated by K-fold cross-validation,and the results show that the Gaussian process regression model was superior to the linear regression model.(5)Based on the empirical model obtained by Gaussian process regression and the software WINDOW,the energy-saving characteristics of GDC window in cooling season of four climate zones(hot summer and warm winter,hot summer and cold winter,cold and severe cold zone)are firstly studied.Then,the energy-saving characteristics of GDC window combined with natural cold source and mechanical cold sources of different temperatures are analyzed.Finally,a case study of GDC window utilizing the direct evaporative cooling water in different climate zones are performed.The main conclusions include 1)The cooling load reduction of GDC window in different orientations in different climate zones are relatively close.When the water temperature is 25℃,the cooling load reduction rates of GDC window are about 49%and 61%respectively compared with blinds window and the inner blinds window,2)When natural cold source is used,the energy-saving rate of GDC window increases with the decrease of the water temperature.Taking the south window in Wuhan as an example,when using a free high-temperature cold source at 15℃ and 30℃,the energy saving rate of GDC window than the built-in blinds window and the inner blinds window are 68.8,37.8%and 75.8,51.8%,respectively,3)When a mechanical cold source is used,the energy-saving rate of GDC window increases with the increase of the water temperature,but the increase gradually decreases.Taking Wuhan south window as an example,when the mechanical cold source is 15,20,and 25℃,the energy-saving rate of GDC window than the built-in blinds window and the inner blinds window are 16.9,29.2,34.1%and 35.5,45.1,48.9%,4)When the direct evaporative cooling water is used,GDC window has a better energy-saving effects in cities with lower wet bulb temperatures in the cooling season.Arranged from high to low wet bulb temperatures,the energy saving rate of GDC window than the built-in blinds window and the inner blinds window are 38.7,40.1,42.9,43.2%and 52.6,53.5,56.6,57.5%,respectively,in the four cities of Guangzhou,Wuhan,Beijing,and Harbin.The study of this dissertation provides the method and data basis for the subsequent in-depth research and practical application of GDC window.At the same time,the relevant quantitative analysis results show that GDC window has practical significance,which is potential to improve building energy efficiency and reduce carbon emission by utilization of low-grade energy.
Keywords/Search Tags:Building energy efficiency, Low carbon technology, Low--grade energy utilization, Multiple glazing window, Gravity--driven cooling
PDF Full Text Request
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