@conference {60094, title = {Potential energy savings with exterior shades in large office buildings and the impact of discomfort glare}, booktitle = {Fourth BEST Conference Building Enclosure Science \& Technology (BEST4)}, year = {2015}, month = {04/2015}, address = {Kansas City, Missouri}, abstract = {

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.

}, author = {Sabine Hoffmann and Eleanor S. Lee} } @techreport {60935, title = {A Pilot Demonstration of Electrochromic and Thermochromic Windows in the Denver Federal Center, Building 41, Denver, Colorado}, year = {2013}, note = {

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

}, month = {07/2013}, abstract = {

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.

}, keywords = {building controls, daylighting, Demand Side Management, electrochromic, energy-efficiency, Smart windows, switchable windows, Thermochromic, Window}, url = {http://gsa.gov/portal/content/187967}, author = {Eleanor S. Lee and Luis L. Fernandes and Howdy Goudey and Jacob C. Jonsson and Dragan C. Curcija and Xiufeng Pang and Dennis L. DiBartolomeo and Sabine Hoffmann} }