APPLYING DAYLIGHT GLARE PROBABILITY (DGP) SIMULATIONS TO WINDOWS WITH FABRIC SHADES AND AUTO-SHADE POSITION CONTROL
Open Access
- Author:
- Aljuhani, Abdulrahman Eid
- Graduate Program:
- Architectural Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 15, 2023
- Committee Members:
- Richard Mistrick, Chair & Dissertation Advisor
Julian Wang, Major Field Member
Greg Pavlak, Major Field Member
Ute Poerschke, Outside Unit & Field Member
James Freihaut, Program Head/Chair - Keywords:
- Daylight Glare Probability
DGP
Daylight Simulations
Automated Shading Control
Fabric Shades
Radiance
Spatial Daylight Autonomy
sDA
frads
Glare source
Glare protection
DGP calculation
Vertical illuminance - Abstract:
- Several research studies have focused on developing metrics to evaluate and quantify discomfort glare from daylighting apertures in buildings. Proposed glare models were analyzed by other studies to assess the performance of these glare models, with the Daylight Glare Probability (DGP) model shown to have the best agreement to actual occupant assessments. The target of this study is to understand the impacts of different shade transmittance properties on the calculated DGP value, to develop a simpler image-based DGP calculation method for hourly annual simulations, and to study the implementation of DGP for automated shade position control. 12 combinations of specular and diffuse transmittance for fabric shades were applied in a parametric study of the shade's impact on the calculated DGP. Different window orientations and view directions were applied as well as a detailed study of the contributions of the two main terms in the equation for DGP. This study showed that the value of the contrast term increases sharply when the received amount of light at the observer is low. At higher levels, the contrast contribution to the DGP increases very little and the saturation effect elevates the DGP value at a slightly higher rate. When the sun is not visible, the DGP is generally low with no glare risk. Lowering the shades to cover more of the window increases glare protection, whereas increasing the openness factor mainly increases the DGP values with slight DGP increases when increasing the diffuse transmittance factor. Simulations of DGP generally require the creation of an HDR image for a viewing condition and computing the DGP value using the Evalglare tool. This study provides a new method that conducts simulations faster and with more accuracy than existing methods. For the proposed faster DGP simulation method, three images are required: a relatively small 3-Phase image (200X200 image size), the same 3-Phase image size with only the sun’s direct effect, and a 1500X1500 rpict image with only the sun’s direct effect. The sun glare source and the vertical illuminance in the 3-Phase image of the sun effect are subtracted from the list of glare sources and from the vertical illuminance obtained from the 3-Phase image. Then, a new vertical illuminance is computed which includes the contribution from the rpict direct sunlight image, and details on the solar disk glare source, if present, are added to the list of glare sources in the field of view. The DGP equation is then processed with these revised input parameters. The presence of the sun in the window or shade and the sun's size are critical factors in defining the correct sun contribution in the scene. The rpict image must be large enough to provide a correct number of pixels to characterize the correct sun size in steradians, and appropriate parameters must be entered into the rpict command line. Based on the climates of both Boston, MA and Denver, CO, annual daylight simulations with 5-Phase approach were conducted using frads. Automated shade controls were set for several viewing directions with South, East, and North façades across six fabric shades with different openness (O) and diffuse transmittance (D) percentages (O1-D5, O3-D5, O5-D5, O1-D10, O3-D10, and O5-D10). The automated shade control in this study requires selecting the shade occlusion position that limits DGP to 35% or less and provides the highest level of daylight. If all shade positions provide higher DGPs than 35%, the shade position with the lowest DGP is selected. When the FOV contains windows and the space is oriented to either South or East, the visibility of the sun and the transmittance of the shades increase the level of automated shade occlusion, including many hours with 75% and 100% shade occlusion positions. Increasing the number of clear skies with South and East façade orientations increases 75% and 100% shade occlusion hours such as Denver’s skies compared to Boston’s skies. The increase of the daylight level or the transmittance properties when viewing windows of the South or East facade increases the sDA values and increasing the shade’s diffuse transmittance factor with a clear sky has more influence in increasing the sDA than the openness factor. The different shade occlusion positions applied in the auto-shade control significantly increase the achieved sDA compared to the default sDA method that uses only two shade positions: shades up and full shades down. Including a high reflectance desk in the FOV which the sun can strike causes an increase in the 75% occlusion hours and a decline in 0%-occlusion hours of the auto-shade control. Obstructing the horizon with a highly reflective building for an East façade reflects the late day sunlight to the East façade, increasing the 75% and 100% occlusion hours as well as the sDA values more in Denver than Boston since Denver has clearer sky conditions. The North façade experiences a high glare issue when a high reflectance opposing building exists with no noticeable change in the influence of the number of clear skies on the sDA values.