03492nas a2200253 4500008003900000245009000039210006900129260001200198300000700210520268100217653003002898653003102928653001602959653002002975653001202995100002403007700002103031700001903052700002303071700003103094700001803125700002103143856007403164 2014 d00aAngular selective window systems: Assessment of technical potential for energy saving0 aAngular selective window systems Assessment of technical potenti c01/2014 a363 a

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 façade 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.

10aangular selective systems10aBuilding energy-efficiency10adaylighting10aShading Systems10awindows1 aFernandes, Luis, L.1 aLee, Eleanor, S.1 aMcNeil, Andrew1 aJonsson, Jacob, C.1 aNouidui, Thierry, Stephane1 aPang, Xiufeng1 aHoffmann, Sabine uhttps://facades.lbl.gov/publications/angular-selective-window-systems02421nas a2200205 4500008003900000245011400039210006900153260001200222300001200234490000700246520171800253653003101971653001602002653002902018100002402047700002102071700002902092700001902121856007502140 2014 d00aMonitored lighting energy savings from dimmable lighting controls in The New York Times Headquarters Building0 aMonitored lighting energy savings from dimmable lighting control c01/2014 a498-5140 v683 a

Digital addressable, dimmable lighting controls were introduced to the US market in the early 2000s with the promise of facilitating capture of potential energy savings with greater flexibility over their historic, typically unreliable, analog counterpart. The New York Times Company installed this emerging technology, after having tested the system thoroughly prior to procurement, in their new building in New York, New York. Four years after full occupancy in 2007, the owner agreed to participate in a post-occupancy monitored evaluation of the dimmable lighting system to verify actual performance in the field. Annual lighting energy savings from daylighting, setpoint tuning and occupancy controls were determined for the daylit, open-plan office areas on three typical floors (6, 11, and 20th floors) of the 51-story high-rise tower. Energy savings were calculated from ballast control signal and occupancy data recorded by the manufacturer's lighting control system. The ballast data were calibrated with independent measurements of lighting energy consumption. Savings from dimming controls (daylighting and setpoint tuning) were 12.6 kWh/m2-yr (1.17 kWh/ft2-yr) for the daylit spaces on the three floors overall, or 20%, relative to ASHRAE 90.1-2007. Compared to the prescriptive code in effect at the time of the building's construction (ASHRAE 90.1-2001), savings were 21.0 kWh/m2-yr (1.95 kWh/ft2-yr) or 28%. Annual lighting energy use with all lighting control strategies was 33.9 kWh/m2-yr (3.15 kWh/ft2-yr) in the daylit, open plan zones on average for the three floors. A simple payback analysis was conducted.

10aBuilding energy-efficiency10adaylighting10alighting control systems1 aFernandes, Luis, L.1 aLee, Eleanor, S.1 aDiBartolomeo, Dennis, L.1 aMcNeil, Andrew uhttps://facades.lbl.gov/publications/monitored-lighting-energy-savings02177nas a2200205 4500008003900000245012200039210006900161260001200230300000900242490000700251520147200258653003101730653002501761653001601786653002701802100002401829700002101853700002201874856007501896 2013 d00aLighting energy savings potential of split-pane electrochromic windows controlled for daylighting with visual comfort0 aLighting energy savings potential of splitpane electrochromic wi c06/2013 a8-200 v613 a

A simulation study was conducted to evaluate lighting energy savings of split-pane electrochromic (EC) windows controlled to satisfy key visual comfort parameters. Using the Radiance lighting simulation software, interior illuminance and luminance levels were computed for a south-facing private office illuminated by a window split into two independently-controlled EC panes. The transmittance of these was optimized hourly for a workplane illuminance target while meeting visual comfort constraints, using a least-squares algorithm with linear inequality constraints. Blinds were successively deployed until visual comfort criteria were satisfied. The energy performance of electrochromics proved to be highly dependent on how blinds were controlled. With hourly blind position adjustments, electrochromics showed significantly higher (62% and 53%, respectively without and with overhang)lighting energy consumption than clear glass. With a control algorithm designed to better approximate realistic manual control by an occupant, electrochromics achieved significant savings (48% and 37%, respectively without and with overhang). In all cases, energy consumption decreased when the workplace illuminance target was increased. In addition, the fraction of time during which the occupant had an unobstructed view of the outside was significantly greater with electrochromics: 10 months out of the year versus a handful of days for the reference case.

10aBuilding energy-efficiency10aControl optimization10adaylighting10aElectrochromic windows1 aFernandes, Luis, L.1 aLee, Eleanor, S.1 aWard, Gregory, J. uhttps://facades.lbl.gov/publications/lighting-energy-savings-potential