@techreport {57096, title = {Annual daylighting performance of a passive optical light shelf in sidelit perimeter zones of commercial buildings}, year = {2013}, abstract = {

Sunlight redirecting systems have the potential to significantly offset electric lighting energy use in deep perimeter zones of buildings where the windows are subject to high daylight availability. New Radiance modeling tools have recently been developed and validated, enabling accurate and timely simulation analysis of the annual energy and comfort performance of these optically-complex, anisotropic systems. A parametric study was conducted using these tools to evaluate the performance of a commercially-available passive optical light shelf (OLS) in a 17.4 m deep (57 ft), south-facing open plan office zone in three climates. Daylighting efficiency, discomfort glare, and lighting energy savings with continuous dimming and bi-level switching controls were determined at varying depths within the zone. The OLS decreased lighting energy use significantly throughout the depth of the space and achieved these savings with minimal discomfort glare in the area near the window. Annual lighting energy use intensity was reduced to 1.71-1.82 kWh/ft2-yr (22-27\%) over the full depth of the perimeter zone across the three climates modeled (Phoenix, Washington DC, and Minneapolis) compared to a non-daylit zone at 2.34 kWh/ft2-yr. There was a greater occurrence of discomfort glare (3-7\% during daytime work hours) if the occupant was in a seated view position looking at the window from the back of the room. The system is passive, needing no adjustment during the day and over the seasons and can be used as a retrofit measure in existing buildings. These results are encouraging and demonstrate how the primary daylit sidelit area can be extended well beyond the defined limits provided by the newly adopted ASHRAE 90.1-2010 code (i.e., 1.0 times the head height of the window).

}, keywords = {bidirectional scattering distribution functions, buildings energy efficiency, daylighting, Radiance simulations}, author = {Andrew McNeil and Eleanor S. Lee} } @article {57097, title = {Empirical Assessment of a Prismatic Daylight-Redirecting Window Film in a Full-Scale Office Testbed}, journal = {LEUKOS: The Journal of the Illuminating Engineering Society of North America}, volume = {10}, year = {2013}, note = {

Illuminating Engineering Society (IES) Annual Conference 2013
Huntington Beach, CA,
26 - 29 October 2013

}, month = {10/2013}, pages = {19-45}, address = {Huntington Beach, California}, abstract = {

Daylight redirecting systems with vertical windows have the potential to offset lighting energy use in deep perimeter zones. Microstructured prismatic window films can be manufactured using low-cost, roll-to-roll fabrication methods and adhered to the inside surface of existing windows as a retrofit measure or installed as a replacement insulating glass unit in the clerestory portion of the window wall. A clear film patterned with linear, 50-250 micrometer high, four-sided asymmetrical prisms was fabricated and installed in the south-facing, clerestory low-e, clear glazed windows of a full-scale testbed facility. Views through the film were distorted. The film was evaluated in a sunny climate over a two-year period to gauge daylighting and visual comfort performance. The daylighting aperture was small (window-to-wall ratio of 0.18) and the lower windows were blocked off to isolate the evaluation to the window film. Workplane illuminance measurements were made in the 4.6 m (15 ft) deep room furnished as a private office. Analysis of discomfort glare was conducted using high dynamic range imaging coupled with the evalglare software tool, which computes the daylight glare= probability and other metrics used to evaluate visual discomfort.

The window film was found to result in perceptible levels of discomfort glare on clear sunny days from the most conservative view point in the rear of the room looking toward the window. Daylight illuminance levels at the rear of the room were significantly increased above the reference window condition, which was defined as the same glazed clerestory window but with an interior Venetian blind (slat angle set to the cut-off angle), for the equinox to winter solstice period on clear sunny days. For partly cloudy and overcast sky conditions, daylight levels were improved slightly. To reduce glare, the daylighting film was coupled with a diffusing film in an insulating glazing unit. The diffusing film retained the directionality of the redirected light= spreading it within a small range of outgoing angles. This solution was found to reduce glare to imperceptible levels while retaining for the most part the illuminance levels achieved solely by the daylighting film.

}, keywords = {buildings energy efficiency, daylighting, microstructure film, prismatic film, windows}, doi = {10.1080/15502724.2014.837345}, author = {Anothai Thanachareonkit and Eleanor S. Lee and Andrew McNeil} } @article {57039, title = {An empirical study of a full-scale polymer thermochromic window and its implications on material science development objectives}, journal = {Solar Energy Materials and Solar Cells}, volume = {116}, year = {2013}, month = {09/2013}, pages = {14-26}, chapter = {14}, abstract = {

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{\textdegree}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.

}, keywords = {buildings energy efficiency, Solar control, Thermochromic, windows}, doi = {10.1016/j.solmat.2013.03.043}, author = {Eleanor S. Lee and Xiufeng Pang and Sabine Hoffmann and Howdy Goudey and Anothai Thanachareonkit} } @article {55431, title = {End User Impacts of Automated Electrochromic Windows in a Pilot Retrofit Application}, journal = {Energy and Buildings}, volume = {47}, year = {2012}, month = {04/2012}, pages = {267-284}, chapter = {267}, abstract = {

Automated electrochromic (EC) windows, advanced thermally-improved window frames, and a dimmable lighting system were installed in a single, west-facing conference room in Washington DC. The EC windows were commercially-available, tungsten-oxide switchable devices, modulated automatically between either fully clear or fully tinted transparent states to control solar gains, daylight, and discomfort glare. Occupants were permitted to manually override the automated EC controls. The system was monitored over a 15-month period under normal occupied conditions. The last six months were used in the analysis. Manual override data were analyzed to assess the EC control system design and user satisfaction with EC operations. Energy and comfort were evaluated using both monitored data and simulations.

Of the 328 meetings that occurred over the six month period, the automatic system was manually overridden on 14 or 4\% of the meetings for reasons other than demonstration purposes. When overridden, occupants appeared to have switched the individual zones with deliberation, using a combination of clear and tinted zones and the interior Venetian blinds to produce the desired interior environment. Monitored weekday lighting energy savings were 91\% compared to the existing lighting system, which was less efficient, had a higher illuminance setpoint, and no controls. Annual performance was estimated using EnergyPlus, where the existing condition met the ASHRAE 90.1-2007 prescriptive requirements except for a higher window U-value. Annual energy savings were 48\% while peak demand savings were 35\%.

}, keywords = {buildings energy efficiency, control systems, daylighting, Electrochromic windows, Integrated systems, Intelligent buildings}, doi = {10.1016/j.enbuild.2011.12.003}, author = {Eleanor S. Lee and Erin S. Claybaugh and Marc LaFrance} } @article {3184, title = {A validation of the Radiance three-phase simulation method for modeling annual daylight performance of optically-complex fenestration systems}, journal = {Journal of Building Performance Simulation}, volume = {April 2012}, year = {2012}, month = {05/2012}, keywords = {bidirectional scattering distribution functions, buildings energy efficiency, daylighting, radiance, validation}, doi = {10.1080/19401493.2012.671852}, author = {Andrew McNeil and Eleanor S. Lee} }