Volume 10, Number 3, September 2005
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People spend over 90% of their time indoors and, as a result, receive little exposure to bright light. Research suggests that a higher light exposure than that typically experienced indoors could improve health and well-being. To be sustainable, however, these light exposures need to come from energy-efficient sources, of which daylight is one.
Being able to control direct sunlight is an important aspect of successful daylighting, and translucent fibreglass daylight sandwich panels offer one possible solution, with the potential to provide high levels of diffuse light that would be considered by occupants as providing good lighting quality.
|Figure 1. East room translucent sandwich panel installation. The photo was taken at noon on a sunny, mostly clear-sky day.|
IRC researchers conducted an experiment in which temporary office workers spent one day in an enclosed office with a translucent sandwich panel installation (Figure 1) and another day in an enclosed office that had a traditional window with a perforated roller blind (Figure 2). The work consisted of a set of tasks simulating regular office work and the filling out of questionnaires about satisfaction, mood and the office environment, including lighting. Lighting and supplemental electric heating energy use were also monitored.
|Figure 2. West room window and roller-blind installation with blind down. The photo was taken at noon on a sunny, mostly clear-sky day.|
When combined with a daylight-linked lighting-control system, the office with the translucent sandwich panel system consumed 29% less energy for lighting than the office with the window and blind. Average light levels in the translucent sandwich panel room were 2.6 times greater, and light exposure in the 450 – 470 nanometres (nm) range of the spectrum (which is thought to include the key wavelengths for potential health effects) was approximately eight times greater. Both rooms were judged to be equally satisfactory work environments with good overall lighting quality; however, there was a slight tendency to judge the East room as having more bothersome glare in the morning, and people preferred the view offered by the larger window in the West room. Supplemental heating energy use was in line with expectations based on the insulating properties (U-values) of the two façades.
A related IRC project developed and validated an optical model for daylight simulation of the translucent sandwich panel using illuminance measurements collected in IRC's full-scale daylighting test rooms (shown in Figure 1). The transmittance properties of the panels were derived from integrating measurements from two different sources. The resulting, validated optical model (see Figure 3) of the translucent panel can easily be plugged into daylight simulation software, such as Radiance and IRC's Daysim (http://www.nrc-cnrc.gc.ca/ci-ic/article/v8n1-4), to provide an annual daylight analysis of buildings that feature these panels.
|Figure 3. Comparison of measured and simulated illuminances on the desk plane in the East room for a sunny day. The simulation is based on the translucent sandwich panel model.|
Such an analysis is shown for the experimental installation at IRC (Figure 4). It demonstrates that the translucent panel can effectively deliver more useful daylight levels to the East room than the window and blind combination can to the West room. This finding confirms that the East room receives more annual daylight than the West one, which explains the lighting energy savings observed during the light exposure experiment. The optical model developed in this project can be adopted for comparable translucent materials once the required transmittance properties have been determined.
|Figure 4. Comparison of the percentages of the annual occupied time (i.e., Mon.–Fri. from 8:30 to 16:30) in the East and West rooms during which time a minimum illuminance level of 450 lux is maintained by daylight.|
A detailed tutorial for those unfamiliar with simulation techniques was also developed as part of this project to encourage more widespread adoption of integrated design using daylight (http://www.nrc-cnrc.gc.ca/eng/ibp/irc/about/daysim.html).
IRC conducted this research with financial support from the Keller Companies, Inc./Kalwall Corporation. For more information, please contact Dr. Jennifer Veitch at (613) 993-9671, fax (613) 954-3733, or e-mail firstname.lastname@example.org. The simulation model and tutorial are available at http://www.nrc-cnrc.gc.ca/eng/ibp/irc/about/daysim.html.