THE IMPACT OF OVERHANG LENGTH, WINDOW ORIENTATION, AND CLIMATE ON SPATIAL DAYLIGHT AUTONOMY (SDA) AND ANNUAL SUNLIGHT EXPOSURE (ASE) FOR A CLASSROOM

Open Access
Author:
Ai, Qi
Graduate Program:
Architectural Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 10, 2016
Committee Members:
  • Richard George Mistrick, Thesis Advisor
Keywords:
  • Daylighting
  • Annual Sunlight Exposure
  • Spatial Daylight Autonomy
  • overhang
  • Window orientation
  • climate
Abstract:
Daylighting has advantages in energy savings when integrated with electric lighting, and it has visual discomfort issues like electric lighting as well. To better deploy daylighting, IES LM-83-12 proposed two metrics: Spatial Daylight Autonomy (sDA300/50%) and Annual Sunlight Exposure (ASE1000, 250h) to evaluate the daylight conditions in a space. sDA300/50% indicates the sufficiency of daylight inside a room and the ASE1000, 250h shows the potential risks of visual discomfort. The LEED V4 criteria introduced the application of spatial daylight autonomy and annual sunlight exposure for the evaluation of daylight credits. In order to have a better perspective on sDA and ASE, conventional metrics such as Daylight Factor (DF), Daylight Autonomy (DA), Useful Daylight Illuminance (UDI) and continuous Daylight Autonomy (cDA) were reviewed and compared with the two new metrics. This research was designed to investigate the sDA300/50% and the ASE1000, 250h of a classroom with dimensions of 33 feet × 30 feet × 10 feet excluding furniture and partitions. 6 selected cities were grouped by 3 latitudes. 8 façade orientations were applied in 45° steps. Overhang lengths ranging from 0 feet (non-overhang) to 4 feet (with a 5 feet overhang added to the ASE1000, 250h simulations), shading devices like roller shades and blinds, and climate (indicated by the sunshine hours) were included in this research as variables. The non-GUI advanced version of DAYSIMps and other program scripts were implemented in the simulations. ASE1000, 250h does not account for shading devices so there is no difference between roller shades and blind conditions for this metric. sDA300/50% was studied for the roller shades with 5% VLT and horizontal blinds were modeled in two different approaches (a translucent material with 20% VLT distribution and real geometry with 80% reflectance) per IES LM-83. The simulation results of ASE1000, 250h, are dependent on the solar angles determined by the latitudes, window orientations, and the overhang length. The climate also affects the ASE results because of the sunshine hours throughout a year. The sDA denotes mainly the diffuse light penetration inside a space. The sDA300/50% results are impacted by the shading on/off hours and the climate. The shading devices were lowered if the direct sunlight covered more than 2% of the work plane area. The shading options are impacted by the window orientations, overhang lengths, and climate. Recommendations were provided to help designers improve the daylight performance inside the classroom. The directions of north, northeast, and northwest are the preferred orientations for achieving low ASE values. The longer overhang helps to increase the sDA in south, southwest, southeast, west and east facing and lowers the ASE only slightly on these orientations, but it still high. Adjustments to the overhang or aperture sizes can be made according to the climate to achieve better daylight performance and budget savings. As expected, the blinds have better sDA300/50% than the 5% VLT roller shades due to their higher transmittance. Further studies to comprehensively evaluate daylight conditions and energy savings in total building energy are encouraged.