Efficient venetian blind control strategies considering daylight utilization and glare protection

This paper presents the development of new venetian blind control strategies considering daylight provision, lighting energy use and visual comfort. A hybrid ray-tracing and radiosity method is used to calculate transmission through the window-blind system and interior illuminance distributions taking into account specular and diffuse material properties. Work plane illuminances are used to extract daylighting metrics, while directional light distribution and respective luminance values are used to calculate glare potential. Four types of control strategies were evaluated – a cut-off angle control, a daylight-redirecting control, and two glare protection control modes. Using the common “cut-off” angle may result in a strong second reflection that might significantly affect visual discomfort depending on view direction and profile angle. Proper rotation of the tilt angle and consideration of specular characteristics can minimize this effect and redistribute daylight deeper into the space, although glare problems cannot be eliminated in some cases. Moreover, two additional control strategies were developed based on glare probability and sky conditions: the first is a model-based control derived from real time glare simulation results. The second is a “simplified” control that uses pre-calculated correlations between glare probability and transmitted illuminance to establish binary set points that can be used in model-predictive control algorithms.A detailed daylighting analysis was performed in order to evaluate set points for blind control actions, annual daylighting metrics, lighting energy use and daylight glare probability and duration. Different room sizes, glazing properties, blind material characteristics and orientations were studied. The results showed that diffuse blinds do not reduce the risk of glare when light redirection is desired; double-sided slats with a diffuse top and a specular bottom surface are better in this regard. Fixed angles at 60° or higher provide satisfactory results for most cases, although there is a penalty in daylighting efficiency. The two glare protection control algorithms proved to be efficient in providing high daylight autonomy values without the risk of glare for all studied cases.     

内置百叶中空玻璃的热工能性及适应性研究

对内置可调百叶中空玻璃的热工性能进行了计算后,分析了百叶状态、百叶颜色及间层填充气体对其热工性能的影响,并进一步研究了其在夏热冬暖地区的适应性。     

基于隔热采光性能的建筑百叶综合节能效果研究

本文兼顾隔热以及采光性能,研究了建筑百叶对室内制冷能耗和照明能耗的综合影响,并提出光热综合能耗来全面评估其节能性。依据软件模拟无遮阳、45°以及90°开启百叶三类模型在夏季典型日的制冷负荷与所需光通量,计算出建筑窗体引起的光热综合能耗。结果表明：夏季在使用光效较低的灯具时,90°开启百叶比无遮阳情况节能13%,而使用光效高的灯具时,90°开启百叶比无遮阳情况节能29%,但45°开启百叶的节能效果与其相差不大。当根据室外光热环境对百叶进行合理控制时,光热综合能耗将会更小,节能率高达40%。     

百叶外遮阳太阳散射辐射计算模型及程序实现

窗户外部的遮阳系统可以减少进入室内的太阳辐射得热量。目前,在计算遮阳系统对太阳辐射的遮挡作用时,仅仅从几何角度上考虑遮阳构件对直射辐射的减少作用,没有考虑对散射辐射的影响,但在实际中,遮阳构件的存在,对散射辐射的影响不能忽略,特别是对于百叶类型的遮阳构造,由于其布置较为紧密,对直射辐射遮挡较多,进入室内的太阳辐射主要为散射辐射,因此建立详细的散射辐射计算模型,可以正确反映和评估其遮阳效果,并为计算遮阳构件对建筑能耗的影响提供基础。通过分析散射辐射入射到百叶遮阳板上的光学特性,建立用于计算太阳散射辐射透过和反射的数学模型,并根据该模型得到用于计算机编程的算法。该模型和算法可以应用于不同的百叶遮阳系统,为建筑能耗模拟中考虑百叶遮阳板对空调能耗的影响提供理论基础。     

An empirical correlation for free convection in a window with a between-panes louvred blind

An empirical correlation for free convection in a double-glazed window with an enclosed Venetian blind is developed. The correlation makes use of an existing model from the literature (called the reduced slat length model) for the pure conduction asymptote. Published experimental data for night-time conditions (i.e. with no solar irradiation) are used to characterize the average Nusselt number at higher Rayleigh numbers. The asymptote blending method of Churchill and Usagi is used to combine these results into an empirical correlation that spans the full range of variables for which experimental data are currently available. The correlation is applicable to all common fill gases, and predicts the effects of Rayleigh number, slat angle and blind-to-enclosure width ratio on the average Nusselt number. The use of the correlation to predict the U-value of this complex fenestration is demonstrated. The results compare well with published measurements.     

44°百叶窗冲模设计的改进

在百叶窗冲制过程中,由于弯曲和拉延变形,材料在局部上的内应力作用,使板料产生翘曲而翻塌.改进后的结构,消除了内应力的作用,不仅使产品符合要求,而且提高了模具寿命.