Center for the Built Environment
Impact of Fixed Exterior Shading on Daylighting: A Case Study of the David Brower Center
- Author(s): Zelenay, Krystyna
- et al.
Commercial buildings in the U.S. consumed 18% of primary energy and 36% of the nation's electricity in 2006 (U.S. Department of Energy, 2011). According to the 2003 Commercial Buildings Energy Consumption Survey (CBECS), heating, cooling and lighting account for 36%, 8% and 21%, respectively, of the total energy consumed in the commercial building sector (Energy Information Administration [EIA], 2008). In response to increasing concerns over global warming, a number of initiatives to reduce energy used by U.S. buildings have taken form over the course of the past decade, including the development of voluntary rating systems such as the Leadership in Energy and Environmental Design (LEED) rating system of the U.S. Green Building Council (USGBC) and the Energy Star rating system of the U.S. Environmental Protection Agency. Yet despite significant efforts on behalf of a range of public and government organizations progress has been slow (Scofield, 2009).
One of the essential components in low-energy buildings is the building envelope. Window systems are critical to occupant comfort and well-being, but frequently bring a high level of complexity to the design process due to the inherent difficulty of striking a balance between occupant comfort needs, building energy use, project budget and a range of other considerations. While windows provide a way to introduce daylight and views, fenestration design must be carefully assessed in terms of daylighting, visual comfort, heat gain and heat loss. A number of studies suggest that without proper solar and lighting control, occupants are likely to draw shades or blinds when visual or thermal comfort thresholds are exceeded (Figure 1) and that blinds are likely to remain closed for extended periods of time, negating the potential benefits of having the window in the first place (Galasiu & Veitch, 2006; Inkarojrit, 2008). Automated controls provide a way to control facade systems, as is the case with automated shading, however they provide their own set of challenges – added operational complexity and cost, and the need for maintaining additional controls and components (Heschong Mahone Group [HMG], 2008; Zelenay, Perepelitza & Lehrer, 2011). In contrast, fixed window elements, such as fixed exterior shading, may offer less opportunity for selective control of daylighting and solar heat gain, however the risk of faulty system operation, experienced with automated systems that are improperly commissioned or maintained, is eliminated.
While exterior shading systems offer significant benefit in terms of solar control and occupant thermal comfort and are quite common in Europe, they are not typically implemented on U.S. buildings (Perepelitza 2010 Zelenay et al., 2011). The prevalence of exterior shading systems in Europe can be explained by higher energy prices, stricter building codes, and higher expectations regarding the quality of the working environment and construction (Yudelson, 2009). Owner and design team concerns about operation and maintenance of and high cost of systems are the main factors impeding the widespread adoption of these systems in the U.S. (Lee, Selkowitz, Bazjanac, Inkarojrit, & Kohler, 2002; Lee & Selkowitz, 2005; HMG, 2008; Zelenay et al., 2011).
In light of the fact that exterior shading is uncommon in the U.S., the question of why fixed exterior louvers were implemented at the David Brower Center, a four-story mixed-use building in Berkeley, California, is a compelling one (Figure 2). The building, situated in a dense urban neighborhood in downtown Berkeley (Figure 3), was designed by the San Francisco-based firm Daniel Solomon Design Partners (formerly Solomon E.T.C.) in collaboration with Tipping Mar + Associates (structural engineer), Integral Group (mechanical engineer formerly Rumsey Engineers), and Loisos + Ubbelohde (daylighting and facade consultant).