Variable Window Shading Strategies and Occupant Impressions of Thermal Comfort, Visual Comfort and Productivity

Presented by: Dr. Julia Day

Relevance / Problem / Context High-performance building strategies have the potential to greatly reduce energy use and positively impact building occupants (Edwards & Torcellini, 2002). For example, daylighting has been found to increase occupant productivity, increase overall satisfaction, and to ultimately, save energy costs associated with electric lighting use. Many studies have also shown how occupant performance can be affected by the quality of light in a space, and occupants with access to natural daylight perform better when compared to those who only have access to electric light (Heerwagen, 2000; Heschong et al., 2002). In addition, access to natural daylight within the office space has been proven as advantageous to building occupants’ psychological and physiological health (Heschong, 2002). However, sustainable design strategies, such as daylighting, can also lead to negative effects with regard to building occupants if they are not thoughtfully designed. Daylight is a dynamic light source that changes on a daily basis, so an understanding of daylight controls, shading options, and seasonal and diurnal patterns of the sun are crucial to its overall success (Day, Theodorson, & Van den Wymelenberg, 2012). If daylighting designs are poorly conceived (or if control is not provided) it may lead to issues such as glare, headaches, eye strain or migraines. Method / Findings This research presents the results of a large-scale NSF study, which included both field measurements and surveys of three large commercial office buildings in Charlotte, North Carolina. Each building had a different type of shading strategy: roller shades, automated blinds, and electrochromic glazing, respectively. Physical data collection included temperature, relative humidity, light measurements, and high dynamic range (HDR) photography. Results indicated that some of the shading strategies worked better for controlling glare than others. In addition, online surveys were sent to each of the buildings to assess occupant’s subjective thermal and visual comfort perceptions. In total, 5,031 surveys were sent to the three buildings, and 1,068 occupants participated in the survey for a response rate of 21.2%. The survey was open for two weeks, and two reminders were sent to participants, in addition to the initial survey deployment. This presentation will primarily focus on the survey responses, which include both closed-ended and open-ended questions. The open-ended survey responses revealed many of the reasons why occupants were satisfied (or not satisfied) with their interior environments. For example, responses included statements such as: “Although in a cube, just being close to a large window helps keep me connected to the world outside. I can look outside to clear my mind or relieve tension. In the past, only officers had windows so this makes me feel special and happy when I come in,” and “I don't sit near windows due to the glare on the computer screen, and eye strain if facing windows. In fact, I sit as far away and parallel to any windows for that reason).” Similar to the literature, many occupants enjoyed the daylighting for reasons such as the connection with the outdoors, while others disliked the daylight in the space due to glare and poor control options. Other complaints were related to the thermal performance of the various shading options rather than visual comfort. Advancement of design knowledge Thermal and visual comfort are issues that arise repeatedly in a wide array of multi-disciplinary research and literature, and the findings of this study echo much of the literature: (1) it is difficult to provide comfort to all occupants, (2) an integrated design process is important, and (3) designers need to better understand how design moves affect building occupants. It is important that interior designers understand daylighting strategies, shading, and corresponding human perceptions of comfort.

References:

  • Day, J., Theodorson, J., & Van Den Wymelenberg, K. G. (2012). Understanding controls, behaviors and satisfaction in the daylit perimeter office: A daylight design case study. Journal of Interior Design, 31(1), 17–34.
  • Edwards, L., & Torcellini, P. (2002). A literature review of the effects of natural light on building occupants (No. NREL/TP-550-30769) (pp. 1–54). National Renewable Energy Laboratory.
  • Heerwagen, J. H., & Heerwagen, D. R. (1986). Lighting and psychological comfort. Lighting Design and Application, 16(4), 47–51.
  • Heschong, L., Wright, R. L., & Okura, S. (2002). Daylighting impacts on human performance in school. Journal of the Illuminating Engineering Society, 31(2), 101–111.
  • Heschong, L. (2002). Daylighting and human performance. ASHRAE journal, 44(6), 65-67.