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While the primary role of window attachments is often to moderate glare and solar heat gains, they are also able to provide additional daylight to interior spaces. For this purpose, a variety of daylight-redirecting window systems have been developed over the past 150 years. Fixed reflective systems (slats/light shelves) or prismatic systems that rely on total internal reflection work well under specific solar conditions, but generally sacrifice performance over a much wider range of incident solar angles and sky conditions. Dynamic systems - typically reflective slats - are more responsive to sun angles but have not been able to achieve optimal performance for glare and daylight redirection efficiency. A previous investigation into an adjustable, reflective blind concept first conceived of in the late 1970s showed promise but was not reduced to practice due to lack of adequate simulation and analysis tools. In this paper, this concept is further developed and its energy and visual comfort performance evaluated for four mid-latitude, temperate climates using ray-tracing simulation techniques. Results indicate significant potential lighting energy savings when compared with conventional automated reflective blinds (2.1–4.9 kWh/(m2·a), or 14%–42%, depending on climate and orientation) or, especially, manually-operated matte white venetian blinds (1.4–7.9 kWh/(m2·a), or 9%–54%, depending on climate and orientation), while maintaining acceptable or better visual comfort conditions throughout the interior space.

A novel semi-transparent building integrated photovoltaic (BIPV) laminate was developed and introduced in this paper. It was produced by cutting standard mono-crystalline silicon solar cells into small strips and then making electrical connections between each strip before laminating the cells between two layers of glass. The overall energy performance and energy saving potential of the BIPV insulated glass unit (IGU) under real world conditions were identified through a side by side comparative study. Compared to the reference IGU, the BIPV IGU had lower solar heat gain coefficient (SHGC) but much higher U-factor. The average HVAC electricity saving of the BIPV IGU was about 10% relative to the reference IGU. Daylighting measurement and analysis were carried out to evaluate the trade-offs associated with the BIPV IGU between daylight, glare, and lighting energy use. The results indicated that the BIPV IGU is better than the reference IGU in reducing discomfort glare. However, if the most conservative viewpoint near the window is used for the assessment, a lower transmittance BIPV IGU is required to bring the overall discomfort levels below the perceptible level. Lastly, the net energy saving potential associated with the novel BIPV IGU was identified based on the power, thermal and daylighting performance. On average, the BIPV IGU saved 16.8% of the total electricity use of the room. Further studies and improvement on the energy conversion efficiency of solar cells, the optimal transmittance as well as the thermal properties would make this technology more energy-efficient and affordable.

The researchers developed a new generation of high-performance façade systems and supporting design and management tools to support industry in meeting California’s greenhouse gas reduction targets, reduce energy consumption, and enable an adaptable response to minimize real-time demands on the electricity grid. The project resulted in five outcomes: (1) The research team developed an R-5, 1-inch thick, triplepane, insulating glass unit with a novel low-conductance aluminum frame. This technology can help significantly reduce residential cooling and heating loads, particularly during the evening. (2) The team developed a prototype of a windowintegrated local ventilation and energy recovery device that provides clean, dry fresh air through the façade with minimal energy requirements. (3) A daylight-redirecting louver system was prototyped to redirect sunlight 15–40 feet from the window. Simulations estimated that lighting energy use could be reduced by 35–54 percent without glare. (4) A control system incorporating physics-based equations and a mathematical solver was prototyped and field tested to demonstrate feasibility. Simulations estimated that total electricity costs could be reduced by 9-28 percent on sunny summer days through adaptive control of operable shading and daylighting components and the thermostat compared to state-of-the-art automatic façade controls in commercial building perimeter zones. (5) Supporting models and tools needed by industry for technology R&D and market transformation activities were validated. Attaining California’s clean energy goals require making a fundamental shift from today’s ad-hoc assemblages of static components to turnkey, intelligent, responsive, integrated building façade systems. These systems offered significant reductions in energy use, peak demand, and operating cost in California.

Exterior shades are the most effective way to control solar load in buildings. Twelve different coplanar shades with different geometry, material properties, and cut-off angles were investigated for two California climates: the moderate San Francisco Bay Area climate and a hot and dry Southern California climate. The presented results distinguish themselves from other simulation studies by a newly developed method that combines three research-grade software programs (Radiance, EnergyPlus, and Window 7) to calculate heat transfer, daylight, and glare resulting from optically-complex fenestration systems more accurately. Simulations were run for a case with constant electric lighting and a case with daylighting controls for a prototypical, internal load dominated office building. In the case of daylighting controls, the choice of slat angle and solar cut-off angle of a fixed exterior slat shading system is non trivial. An optimum slat angle was identified for the considered cases. Material properties (e.g., solar and visible reflectance) did not affect energy use if constant electric lighting was assumed, but they did have a significant influence on energy use intensity (EUI) when daylighting controls were assumed. Energy use increased substantially when an additional interior shade was used for glare control.

Switchable electrochromic (EC) windows are part of a new class of dynamic, energy-efficienttechnologies that enable real-time, active load management in response to weather conditions andthe unique operating conditions of individual buildings. Owners can now specify a solid-statetechnology that reacts to various stimuli like the skin of a living entity. The technology can becontrolled to address multiple criteria to achieve a more optimal energy-efficient and comfortableindoor environment than one with static or manually operated technologies. Inputs can includedata on outdoor solar conditions, utility rates, occupancy status, heating, ventilation, and airconditioning (HVAC), or operating emergency or security mode. The outputs then dictate how theEC window is controlled, whether as a self-contained autonomous unit that achieves specific zonalobjectives or as a part of an integrated system designed to address whole building, campus and gridrelated goals. Since windows typically have a 30-year life, these dynamic qualities enable thebuilding to be adaptable and more resilient as the environmental, operating and economic contextevolves.

The U.S. General Services Administration (GSA) Public Buildings Service (PBS) has jurisdiction, custody or control over 105 land ports of entry throughout the United States, 35 of which are located along the southern border. At these facilities, one of the critical functions of windows is to provide border control personnel with direct visual contact with the surrounding environment. This also can be done through surveillance cameras, but the high value that U.S. Customs and Border Protection (CPB) officers place on direct visual contact can be encapsulated in the following statement by a senior officer regarding this project: “nothing replaces line of sight.” In sunny conditions, however, outdoor visibility can be severely compromised by glare, especially when the orb of the sun is in the field of view. This often leads to the deployment of operable shading devices, such as Venetian blinds. While these devices address the glare, they obstruct the view of the surroundings, negating the visual security benefits of the windows.

As rapid growth in the construction industry continues to occur in China, the increased demand for a higherstandard living is driving significant growth in energy use and demand across the country. Building codesand standards have been implemented to head off this trend, tightening prescriptive requirements forfenestration component measures using methods similar to the US model energy code American Society ofHeating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 90.1. The objective of this study is to(a) provide an overview of applicable code requirements and current efforts within China to enablecharacterization and comparison of window and shading products, and (b) quantify the load reduction andenergy savings potential of several key advanced window and shading systems, given the divergent viewson how space conditioning requirements will be met in the future.System-level heating and cooling loads and energy use performance were evaluated for a code-compliantlarge office building using the EnergyPlus building energy simulation program. Commercially-available,highly-insulating, low-emittance windows were found to produce 24-66% lower perimeter zone HVACelectricity use compared to the mandated energy-efficiency standard in force (GB 50189-2005) in coldclimates like Beijing. Low-e windows with operable exterior shading produced up to 30-80% reductions inperimeter zone HVAC electricity use in Beijing and 18-38% reductions in Shanghai compared to thestandard. The economic context of China is unique since the cost of labor and materials for the buildingindustry is so low. Broad deployment of these commercially available technologies with the propersupporting infrastructure for design, specification, and verification in the field would enable significantreductions in energy use and greenhouse gas emissions in the near term.