TY - JOUR T1 - Balancing daylight, glare, and energy-efficiency goals: An evaluation of exterior coplanar shading systems using complex fenestration modeling tools JF - Energy and Buildings Y1 - 2016/01// SP - 279 EP - 298 A1 - Sabine Hoffmann A1 - Eleanor S. Lee A1 - Andrew McNeil A1 - Luis L. Fernandes A1 - Dragan Vidanovic A1 - Anothai Thanachareonkit KW - Complex fenestration systems KW - Discomfort Glare KW - Energy Plus KW - Energy Use Intensity KW - Exterior shades KW - Glare Control KW - radiance AB - 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. VL - 112 U2 - LBNL-1005092 DO - 10.1016/j.enbuild.2015.12.009 ER - TY - Generic T1 - Discomfort glare with complex fenestration systems and the impact on energy use when using daylighting control T2 - 10th International Conference on Advanced Building Skins Y1 - 2015/11// A1 - Sabine Hoffmann A1 - Andrew McNeil A1 - Eleanor S. Lee A1 - Raghuram Kalyanam KW - building simulation KW - Complex fenestration systems KW - daylighting control KW - Discomfort Glare KW - Energy Use Intensity KW - radiance JF - 10th International Conference on Advanced Building Skins CY - Bern, Switzerland U2 - LBNL-1005094 ER - TY - CONF T1 - Potential energy savings with exterior shades in large office buildings and the impact of discomfort glare T2 - Fourth BEST Conference Building Enclosure Science & Technology (BEST4) Y1 - 2015/04// A1 - Sabine Hoffmann A1 - Eleanor S. Lee AB - Exterior shades are highly efficient for reducing solar load in commercial buildings. Their impact on net energy use depends on the annual energy balance of heating, cooling, fan and lighting energy. This paper discusses the overall energy use intensity of various external shading systems for a prototypical large office building split into the different types of energy use and for different orientations and window sizes. Lighting energy was calculated for a constant lighting power as well as for dimmed lighting fixtures (daylighting control).In Section 3, slat angles and solar cut-off angles were varied for fixed exterior slat shading systems. While the most light-blocking shades performed best for the case without daylighting controls, the optimum cut-off angle with daylighting controls was found to be 30 deg for the office building prototype used in Chicago and Houston. For large window-to-wall (WWR) ratios, window related annual energy use could be reduced by at least 70 % without daylighting control and by a minimum of 86 % with daylighting control in average over all orientations.The occurrence of discomfort glare was is considered in Section 4 of the paper, which looks at the performance of commercially available exterior shading systems when an interior shade is used in addition to the exterior shade during hours when occupants would experience discomfort glare. Glare control impacts overall energy use intensity significantly for exterior shades with high transmittance, especially when daylighting controls are used. In these cases, exterior shades are only beneficial for window-to-wall areas ≥ 45% in the hot Houston climate. For smaller windows and in a heating/cooling climate like Chicago, exterior shades can increase energy consumption. JF - Fourth BEST Conference Building Enclosure Science & Technology (BEST4) CY - Kansas City, Missouri U2 - LBNL-187170 ER - TY - RPRT T1 - Angular selective window systems: Assessment of technical potential for energy saving Y1 - 2014/01// SP - 36 A1 - Luis L. Fernandes A1 - Eleanor S. Lee A1 - Andrew McNeil A1 - Jacob C. Jonsson A1 - Thierry Stephane Nouidui A1 - Xiufeng Pang A1 - Sabine Hoffmann KW - angular selective systems KW - Building energy-efficiency KW - daylighting KW - Shading Systems KW - windows AB - Static angular selective shading systems block or filter direct sunlight and admit daylight within a specific range of incident solar angles. They can potentially deliver energy efficient performance within the typical 4.6-m (15-ft) deep perimeter zone of buildings when tailored to a specific façade orientation and latitude. The objective of this study is to quantify the technical potential of these systems to reduce energy use and peak demand in commercial buildings, specifically: a) achieve 30-50% reductions in perimeter zone energy use vs. ASHRAE 90.1-2004, b) constrain peak window loads to less than 43 W/m2-floor (4 W/ft2-floor), and c) to the extent possible, admit useful daylight in the perimeter zone without exceeding the peak solar load constraint. Three distinctly different commercial shading systems were evaluated: a micro-perforated screen, a tubular shading structure (double- and triple-paned configurations), and an expanded metal mesh. This evaluation was performed mainly through computer simulation for a multitude of scenarios, including multiple climates (Chicago, Illinois and Houston, Texas), window-to-wall ratios (0.15-0.60), building codes (ASHRAE 90.1-2004 and 2010) and lighting control configurations (with and without daylighting controls). Angular selective shading systems are optically complex and cannot be modeled accurately using conventional simulation tools, prompting the development of unique versions of the EnergyPlus, Radiance and Window simulation tools. Results show significant potential reductions in perimeter zone energy use, with the best commercially-available system reaching 28% and 47% savings, relative to ASHRAE 90.1- 2004 and respectively without and with daylighting controls, on south facades in Chicago with WWR=0.45, while constraining peak window heat gains to under 43 W/m2-floor, and enabling significant savings from daylighting controls. Results suggest that it is possible that existing systems can be improved to more consistently achieve 30-50% energy savings. Level of angular selectivity, spectral selectivity of low-e coatings and thermal conductance of the angle-selective layer were identified as critical factors for the performance of angular selective systems. Static, angular selective shading systems offer a potentially low-cost option to significantly reduce window heat gains and control glare from visibility of the sun orb, while permitting the admission of useful daylight and access to views to the outdoors. This type of system shows significant potential to contribute towards net-zero energy goals in both new and retrofit construction. N1 -

Submitted to Energy and Buildings, May 27, 2014

U2 - LBNL-187060 ER - TY - RPRT T1 - High Performance Building Façade Solutions-Phase II Y1 - 2014/03// A1 - Eleanor S. Lee A1 - Brian E. Coffey A1 - Luis L. Fernandes A1 - Sabine Hoffmann A1 - Andrew McNeil A1 - Anothai Thanachareonkit A1 - Gregory J. Ward KW - automated shading KW - between-pane shading KW - bidirectional scattering distribution functions KW - building energy simulation tools KW - Complex fenestration systems KW - daylighting KW - daylighting simulation tools KW - electrochromics KW - exterior shading KW - goniophotometer KW - light shelves KW - microprismatic films KW - model predictive controls KW - motorized shading KW - shading KW - solar-optical properties KW - switchable windows KW - thermochromics KW - virtual prototyping KW - window heat transfer AB - The High Performance Building Façade Solutions–Phase II project was initiated through the California Energy Commission’s Public Interest Energy Research (PIER) program in July 2010 to support industry’s development and deployment of both incremental and breakthrough façade technologies in partnership with the U.S. Department of Energy (DOE). The objective of this three-year project was to develop, or support the development and deployment of, promising near-term and emerging zero net energy building façade technologies for solar control and daylighting, addressing two of the largest end uses in California commercial buildings: cooling and lighting. In partnership with industry (such as manufacturers), three classes of technologies were investigated: daylighting systems, angular-selective shading systems, and dynamic façade systems. Commercially available and emerging prototype technologies were developed and evaluated using laboratory tests. Simulations, full-scale outdoor tests in the Advanced Window Testbed, and demonstration projects quantified energy and peak electric demand reductions and occupant satisfaction, acceptance, and comfort associated with the resultant indoor environment. Several new technologies were developed using virtual prototyping tools. Integrated control systems were developed using model predictive controls. Simulation tools were developed to model operable complex fenestration systems such as shades and microprismatic films. A schematic design tool called COMFEN was developed to facilitate evaluation of these advanced technologies in the early design phase. All three classes of technologies resulted in significant reductions in perimeter zone energy use and peak electric demand, providing viable options that can support California’s long-term goal of achieving zero net energy use in the next decade. U2 - LBNL-1004337 ER - TY - JOUR T1 - An empirical study of a full-scale polymer thermochromic window and its implications on material science development objectives JF - Solar Energy Materials and Solar Cells Y1 - 2013/09// SP - 14 EP - 26 A1 - Eleanor S. Lee A1 - Xiufeng Pang A1 - Sabine Hoffmann A1 - Howdy Goudey A1 - Anothai Thanachareonkit KW - buildings energy efficiency KW - Solar control KW - Thermochromic KW - windows AB - Large-area polymer thermochromic (TC) laminated windows were evaluated in a full-scale testbed office. The TC interlayer film exhibited thermochromism through a ligand exchange process, producing a change in solar absorption primarily in the visible range while maintaining transparent, undistorted views through the material. The film had a broad switching temperature range and when combined to make an insulating window unit had center-of-glass properties of Tsol=0.12-0.03, Tvis=0.28-0.03 for a glass temperature range of 24-75°C. Field test measurements enabled characterization of switching as a function of incident solar irradiance and outdoor air temperature, illustrating how radiation influences glass temperature and thus effectively lowers the critical switching temperature of TC devices. This was further supported by EnergyPlus building energy simulations. Both empirical and simulation data were used to illustrate how the ideal critical switching temperature or temperature range for TC devices should be based on zone heat balance, not ambient air temperature. Annual energy use data are given to illustrate the energy savings potential of this type of thermochromic. Based on observations in the field,a broad switching temperature range was found to be useful in ensuring a uniform appearance when incident irradiance is non-uniform across the facade. As indicated in prior research, a high visible transmittance in both the switched and unswitched state is also desirable to enable reduction of lighting energy use and enhance indoor environmental quality. VL - 116 U2 - LBNL-6376E DO - 10.1016/j.solmat.2013.03.043 ER - TY - RPRT T1 - A Pilot Demonstration of Electrochromic and Thermochromic Windows in the Denver Federal Center, Building 41, Denver, Colorado Y1 - 2013/07// A1 - Eleanor S. Lee A1 - Luis L. Fernandes A1 - Howdy Goudey A1 - Jacob C. Jonsson A1 - Dragan C. Curcija A1 - Xiufeng Pang A1 - Dennis L. DiBartolomeo A1 - Sabine Hoffmann KW - building controls KW - daylighting KW - Demand Side Management KW - electrochromic KW - energy-efficiency KW - Smart windows KW - switchable windows KW - Thermochromic KW - Window AB - Chromogenic glazing materials are emerging technologies that tint reversibly from a clear to dark tinted state either passively in response to environmental conditions or actively in response to a command from a switch or building automation system. Switchable coatings on glass manage solar radiation and visible light while enabling unobstructed views to the outdoors. Building energy simulations estimate that actively controlled, near-term chromogenic glazings can reduce perimeter zone heating, ventilation, and air- conditioning (HVAC) and lighting energy use by 10-20% and reduce peak electricity demand by 20-30%, achieving energy use levels that are lower than an opaque, insulated wall.This project demonstrates the use of two types of chromogenic windows: thermochromic and electrochromic windows. By 2013, these windows will begin production in the U.S. by multiple vendors at high-volume manufacturing plants, enabling lower cost and larger area window products to be specified. Both technologies are in the late R&D stage of development, where cost reductions and performance improvements are underway. Electrochromic windows have been installed in numerous buildings over the past four years, but monitored energy-efficiency performance has been independently evaluated in very limited applications. Thermochromic windows have been installed in one other building with an independent evaluation, but results have not yet been made public. UR - http://gsa.gov/portal/content/187967 N1 -

Completed September 30, 2012, released March 30, 2014.

U2 - LBNL-1005095 ER -