@techreport {58592, title = {Angular selective window systems: Assessment of technical potential for energy saving}, year = {2014}, note = {

Submitted to Energy and Buildings, May 27, 2014

}, month = {01/2014}, pages = {36}, type = {DOE / CEC PIER Technical Report}, abstract = {

Static angular selective shading systems block or filter direct sunlight and admit daylight within a specific range of incident solar angles. They can potentially deliver energy efficient performance within the typical 4.6-m (15-ft) deep perimeter zone of buildings when tailored to a specific fa{\c c}ade orientation and latitude. The objective of this study is to quantify the technical potential of these systems to reduce energy use and peak demand in commercial buildings, specifically: a) achieve 30-50\% reductions in perimeter zone energy use vs. ASHRAE 90.1-2004, b) constrain peak window loads to less than 43 W/m2-floor (4 W/ft2-floor), and c) to the extent possible, admit useful daylight in the perimeter zone without exceeding the peak solar load constraint. Three distinctly different commercial shading systems were evaluated: a micro-perforated screen, a tubular shading structure (double- and triple-paned configurations), and an expanded metal mesh. This evaluation was performed mainly through computer simulation for a multitude of scenarios, including multiple climates (Chicago, Illinois and Houston, Texas), window-to-wall ratios (0.15-0.60), building codes (ASHRAE 90.1-2004 and 2010) and lighting control configurations (with and without daylighting controls). Angular selective shading systems are optically complex and cannot be modeled accurately using conventional simulation tools, prompting the development of unique versions of the EnergyPlus, Radiance and Window simulation tools. Results show significant potential reductions in perimeter zone energy use, with the best commercially-available system reaching 28\% and 47\% savings, relative to ASHRAE 90.1- 2004 and respectively without and with daylighting controls, on south facades in Chicago with WWR=0.45, while constraining peak window heat gains to under 43 W/m2-floor, and enabling significant savings from daylighting controls. Results suggest that it is possible that existing systems can be improved to more consistently achieve 30-50\% energy savings. Level of angular selectivity, spectral selectivity of low-e coatings and thermal conductance of the angle-selective layer were identified as critical factors for the performance of angular selective systems. Static, angular selective shading systems offer a potentially low-cost option to significantly reduce window heat gains and control glare from visibility of the sun orb, while permitting the admission of useful daylight and access to views to the outdoors. This type of system shows significant potential to contribute towards net-zero energy goals in both new and retrofit construction.

}, keywords = {angular selective systems, Building energy-efficiency, daylighting, Shading Systems, windows}, author = {Luis L. Fernandes and Eleanor S. Lee and Andrew McNeil and Jacob C. Jonsson and Thierry Stephane Nouidui and Xiufeng Pang and Sabine Hoffmann} } @article {57094, title = {Acceleration of the matrix multiplication of Radiance three phase daylighting simulations with parallel computing on heterogeneous hardware of personal computer}, journal = {Journal of Building Performance Simulation}, year = {2013}, abstract = {

Building designers are increasingly relying on complex fenestration systems to reduce energy consumed for lighting and HVAC in low energy buildings. Radiance, a lighting simulation program, has been used to conduct daylighting simulations for complex fenestration systems. Depending on the configurations, the simulation can take hours or even days using a personal computer. This paper describes how to accelerate the matrix multiplication portion of a Radiance three-phase daylight simulation by conducting parallel computing on heterogeneous hardware of a personal computer. The algorithm was optimized and the computational part was implemented in parallel using OpenCL. The speed of new approach was evaluated using various daylighting simulation cases on a multicore central processing unit and a graphics processing unit. Based on the measurements and analysis of the time usage for the Radiance daylighting simulation, further speedups can be achieved by using fast I/O devices and storing the data in a binary format.

}, keywords = {daylighting simulation, graphics processing unit, multicore central processing unit, OpenCL, parallel computing}, doi = {10.1080/19401493.2013.795193}, author = {Wangda Zuo and Andrew McNeil and Michael Wetter and Eleanor S. Lee} } @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} } @techreport {58288, title = {Automated Production of Optimization-Based Control Logics for Dynamic Fa{\c c}ade Systems, with Experimental Application to Two-Zone External Venetian Blinds}, year = {2013}, month = {09/2013}, type = {CEC PIER Technical Report}, author = {Brian E. Coffey and Andrew McNeil and Thierry Stephane Nouidui and Eleanor S. Lee} } @conference {3385, title = {Acceleration of Radiance for Lighting Simulation by using Parallel Computing with OpenCL}, booktitle = {12th International Conference of the International Building Performance Simulation Association (Building Simulation 2011)}, year = {2011}, month = {11/2011}, pages = {p. 110-117}, address = {Sydney, Australia}, abstract = {

This study attempted to accelerate annual daylighting simulations for fenestration systems in Radiance ray-tracing program. The algorithm was optimized to reduce both the redundant data input/output operations and floating-point operations. To further accelerate the simulation speed, calculation for matrices multiplications was implemented in parallel on a graphics processing unit using OpenCL, a cross-platform parallel programming language. Numerical experiments show that combination of above measures can speed up the annual daylighting simulations 101.7 times or 28.6 times when sky vector has 146 or 2306 elements, respectively.

}, author = {Wangda Zuo and Andrew McNeil and Michael Wetter and Eleanor S. Lee} }