Study On The Control Optimization And Overall Performance Of Electrochromic Windows

The visible transmittance of electrochromic windows can be adjusted by applying a voltage.Therefore,in office building applications,this feature can be used to reduce the cooling load of the building during the cooling period,and to avoid glare and improve the visual comfort of the room;while in the heating period,it can replace the shading device to block glare,reduce heat load and lighting energy consumption,and has obvious flexibility.However,the control strategy of electrochromic windows also has some problems to be solved.The change in transmittance of electrochromic windows affects natural daylighting and dire ct sunlight,which in turn affects lighting energy consumption and air conditioning energy consumption.Therefore,in order to determine the control strategy of electrochromic windows to meet the visual comfort of the room and minimize the energy consum ption of the building,this paper focuses on two commonly used control strategies —Ccontrol–1(based on outdoor horizontal illumination to control the state change of electrochromic windows)and Control–2(based on window incident solar radiance to control the state change of electrochromic windows),a new control strategy,partition control,is proposed to separate the electrochromic windows separately to prevent glare caused by direct sunlight when the sun appears in the view of human eyes.Taking Changsha as an example,this study uses EnergyPlus to establish a comprehensive model of heat transfer and lighting for electrochromic windows,and taking an optimization of the control threshold of three strategies with GenOpt to minimize the energy consumption of buildings lowest.And finally using EnergPlus to comprehensively simulate the electrochromic windows of the three control strategies with optimal control thresholds,compared with ordinary double–air clear window and Low–e window,and analyzed the energy saving potential and impact on visual comfort of electrochromic windows.Combined with the electrochromic window control of the three control strategies output by EnergyPlus,the HoneybeePlus— a daylighting simulation tool,was used to simulate the three kinds of control strategies of the electrochromic window and the ordinary double–layer hollow window.And then the results were compared and analyzed.In order to meet the indoor visual comfort and completely eliminate the glare phenomenon,the control strategy under the optimal control threshold is optimized with the daylight glare value(DGI)less than 22,and under the control states with the lowest energy consumption of the three control strategies,an electrochromic window control method that satisfies visual comfort are obtained.Finally,comprehensive analysis of the comprehensive performance of electrochromic windows using various control strategies is carried out in terms of energy saving potential and visual comfort.The main conclusions of this paper are as follows:(1)From the perspective of building energy conservation,in the Changsha area,the electrochromic windows of the three control strategies reduce the annual building energy consumption by 54.46 kWh,49.68 kWh and 55.71 kWh,the energy saving ratios are 14.77%,14.33% and 16.07%,compared to the ordinary double–air clear window;With 25.88 kWh,25.1kWh and 31.13 kWh the energy saving and 8.16%,7.92%,9.82% energy saving ratios compared to Low–e window respectively.Therefore,when using the third control strategy(Control–3),electrochromic windows have the most obvious effect on reducing building energy consumption.(2)From the perspective of daylighting,electrochromic windows use the first two control strategies to make more use of natural lighting,and the lighting energy consumption is lower,but correspondingly it will increase glare and reduce visual comfort;When the electrochromic window takes the partition control strategy,although daylight is reduced,useful daylight is more than the first two control strategies,and it also significantly reduces glare and improves the visual comfort environment.Therefore,electrochromic windows use a partition control strategy to improve visual comfort more effectively.(3)The control strategies of Control–1 and Control–3 are further optimized wit h the aim of visual comfort under the control threshold of the lowest energy consumption.That is,when DGI>22,make the state of the window to switch one step to the coloring state Under the condition that all the optimized control strategies satisfy the visual comfort,the energy saving potential is 32.05% and 36.74% compared with the ordinary window with the shading system,respectively;In terms of natural daylighting,the optimized electrochromic window can be used more effectively for natural daylighting,which avoids glare and reduces the need for artificial lighting,the efficiency of Control–3 is the best.It can be obtained that,through the control mode of Control–3,the electrochromic window has the best comprehensive performance under the condition of satisfying visual comfort.The research methods and results of this paper can provide theoretical basis and reference for the use and control of electrochromic windows in other climate regions in China.It is of great significance for the future research of smart window control.