Stephen Selkowitz

Thermal and daylighting performance of an automated venetian blind and lighting system in a full-scale private office

Abstract Dynamic envelope/lighting systems have the potential to optimize the perimeter zone energy balance between daylight admission and solar heat gain rejection on a real-time basis, and to increase occupant comfort. Two side-by-side full-scale offices in Oakland, California were built to further develop and test this concept. An automated venetian blind was operated in synchronization with a dimmable electric lighting system to block direct sun, provide the design workplane illuminance, and maximize view. The research program encompassed system design refinements, energy measurements, and human factors tests. In this study, we present lighting energy and cooling load data that were monitored in this facility over the course of a year. Significant energy savings and peak demand reductions were attained with the automated Venetian blind/lighting system compared to a static venetian blind with the same dimmable electric lighting system. Correlations between key weather parameters and cooling and lighting were used to illustrate how the dynamic system was able to simultaneously achieve optimization between lighting and cooling end uses under the full range of weather conditions of this sunny, moderate climate. Energy efficiency estimates were conservative since experience shows that conventional daylighting control systems and manually operated shading devices are rarely used effectively in real world applications.

Office worker response to an automated Venetian blind and electric lighting system: a pilot study

Abstract A prototype integrated, dynamic building envelope and lighting system designed to optimize daylight admission and solar heat gain rejection on a real-time basis in a commercial office building is evaluated. Office worker response to the system and occupant-based modifications to the control system are investigated to determine if the design and operation of the prototype system can be improved. Key findings from the study are: (1) the prototype integrated envelope and lighting system is ready for field testing, (2) most office workers (N= 14) were satisfied with the system, and (3) there were few complaints. Additional studies are needed to explain how illuminance distribution, lighting quality, and room design can affect workplane illuminance preferences.

Advancement of Electrochromic Windows

Arnold Schwarzenegger Governor ADVANCEMENT OF ELECTROCHROMIC WINDOWS Prepared For: California Energy Commission Public Interest Energy Research Program Prepared By: Lawrence Berkeley National Laboratory April 2006 CEC-500-2006-052 PIER F INAL P ROJECT R EPORT

The design and evaluation of integrated envelope and lighting control strategies for commercial buildings

This study investigates control strategies for coordinating the variable solar-optical properties of a dynamic building envelope system with a daylight controlled electric lighting system to reduce electricity consumption and increase comfort in the perimeter zone of commercial buildings. Control strategy design can be based on either simple, instantaneous measured data, or on complex, predictive algorithms that estimate the energy consumption for a selected operating state of the dynamic envelope and lighting system. The potential benefits of optimizing the operation of a dynamic envelope and lighting system are (1) significant reductions in electrical energy end-uses - lighting, and cooling due to solar and lighting heat gains - over that achieved by conventional static envelope and lighting systems, (2) significant reductions in peak demand, and (3) increased occupant visual and thermal comfort. The DOE-2 building energy simulation program was used to model two dynamic envelope and lighting systems, an automated venetian blind and an electrochromic glazing system, and their control strategies under a range of building conditions. The energy performance of simple control strategies are compared to the optimum performance of a theoretical envelope and lighting system to determine the maximum potential benefit of using more complex, predictive control algorithms. Results indicate that (1) predictive control algorithms may significantly increase the energy-efficiency of systems with non-optimal solar-optical properties such as the automated venetian blind, and (2) simpler, non-predictive control strategies may suffice for more advanced envelope systems 1 incorporating spectrally selective, narrow-band electrochromic coatings.

Advanced Optical Daylighting Systems: Light Shelves and Light Pipes

We present two perimeter daylighting systems that passively redirect beam sunlight further from the window wall using special optical films, an optimized geometry, and a small glazing aperture. The objectives of these systems are (1) to increase daylight illuminance levels at 4.6-9.1 m (15-30 ft) from the window aperture with minimum solar heat gains and (2) to improve the uniformity of the daylighting luminance gradient across the room under variable solar conditions throughout the year. The designs were developed through a series of computer-assisted ray-tracing studies, laser visualization techniques, and photometric measurements and observations using physical scale models. Bi-directional illuminance measurements in combination with analytical routines were then used to simulate daylight performance for any solar position, and were incorporated into the DOE-2.1E building energy analysis computer program to evaluate energy savings. Results show increased daylight levels and an improved luminance gradient throughout the year compared to conventional daylighting systems.

High-performance commercial building façades

There is a significant and growing interest in the use of highly-glazed facades in commercial buildings. Large portions of the facade or even the entire facade are glazed with relatively high transmittance glazing systems, and typically with some form of sun control as well. With origins in Europe the trend is expanding to other regions, including the United States. A subset of these designs employ a second layer creating a double envelope system, which can then accommodate additional venting and ventilation practices. The stated rationale for use of the these design approaches varies but often includes a connection to occupant benefits as well as sustainable design associated with daylighting and energy savings. As with many architectural trends, understanding the reality of building performance in the field as compared to design intent is often difficult to ascertain. We have been particularly interested in this emerging trend because prior simulation studies have shown that it should be technically possible to produce an all-glass facade with excellent performance although it is not a simple challenge. The published solutions are varied enough and sufficiently complex that we undertook a year-long international review of advanced facades to better understand the capabilities and limitations of existing systems and the tools and processes used to create them. This is also intended to create a framework for addressing the missing tools, technologies, processes and data bases that will be needed to turn the promise of advanced facades into realities. This summary, available as a PDF file and a web site, reports those findings.

The Effect of Venetian Blinds on Daylight Photoelectric Control Performance

Abstract We investigate how a venetian blind, a common but optically-complex fenestration system, contributes to the unreliable performance of daylighting control systems. Using a fully instrumented, full-scale testbed facility, we monitored the daylighting performance of a modified closed-loop proportional photoelectric control system in a private office over the course of a year. The ratio of workplane illuminance from daylight to photosensor signal is characterized in terms of solar condition and venetian blind angle. Variations in this ratio causes actual illuminance levels to be periodically insufficient. This type of characterization can be used by the installer to determine whether the initial control adjustments made during commissioning will lead to reliable performance under most daylight conditions. Commissioning guidelines are given with caution, based on our observations from this specific case study. We quantified the effect of variability in this ratio on control performance. With a middle-of-the-road gain constant, monitored workplane illuminance levels did not fall below 90% of the design setpoint for 91% of the year. When discrepancies occurred, differences between the daylight correlation and measured conditions were the primary cause of insufficient illuminance at the workplane. This performance is not applicable to commercially-available closed-loop proportional systems because 1) typical systems are rarely commissioned properly upon installation, and 2) off-the-shelf systems combine the photosensor’s response to daylight and electric light into one gain parameter. Even though the prototype system was subject to the same discrepancies in the daylight correlation fit as commercially-available systems, performance was substantially improved because the prototype was able to separate the electric lighting contribution to workplane illuminance from the daylighting contribution, at no added cost. Commissioning should accommodate the effect of the fenestration system, since variations in luminance distributions produced by the window are the primary cause of unreliable performance.

The energy-savings potential of electrochromic windows in the US commercial buildings sector

Completed April 30, 2004. LBNL-54966. The Energy-Savings Potential of Electrochromic Windows in the US Commercial Buildings Sector E.S. Lee * , M. Yazdanian, S.E. Selkowitz Building Technologies Program, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Mailstop 90-3111, 1 Cyclotron Road, Berkeley, CA 94720, USA Abstract Switchable electrochromic (EC) windows have been projected to significantly reduce the energy use of buildings nationwide. This study quantifies the potential impact of electrochromic windows on US primary energy use in the commercial building sector and also provides a broader database of energy use and peak demand savings for perimeter zones than that given in previous LBNL simulation studies. The DOE-2.1E building simulation program was used to predict the annual energy use of a three-storey prototypical commercial office building located in five US climates and 16 California climate zones. The energy performance of an electrochromic window controlled to maintain daylight illuminance at a prescribed setpoint level is compared to conventional and the best available commercial windows as well as windows defined by the ASHRAE 90.1-1999 and California Title 24-2005 Prescriptive Standards. Perimeter zone energy use and peak demand savings data by orientation, window size, and climate are given for windows with interior shading, attached shading, and horizon obstructions (to simulate an urban environment). Perimeter zone primary energy use is reduced by 10-20% in east, south, and west zones in most climates if the commercial building has a large window-to-wall area ratio of 0.60 compared to a spectrally selective low-e window with daylighting controls and no interior or exterior shading. Peak demand for the same condition is reduced by 20-30%. The emerging electrochromic window with daylighting controls is projected to save approximately 91.5-97.3 10 12 Btu in the year 2030 compared to a spectrally selective low- E window with manually-controlled interior shades and no daylighting controls if it reaches a 40% market penetration level in that year. Keywords: Building energy-efficiency, electrochromic windows, daylighting controls, primary energy use, peak demand. 1. Introduction In 2002, the US Department of Energy (DOE) worked with members of the window industry to create a roadmap that helped define the technologies and tools that will be needed to create and sell the next generation of windows in the 21 st century [1]. Window industry executives identified a new generation of dynamic, responsive “Smart Windows” as the number one top priority. Smart windows include chromogenic glazings that can be reversibly switched from a clear to a transparent, colored state by means of a small applied voltage, resulting in thermal and optical properties that can be dynamically controlled. “Smart windows” incorporating electrochromic glazings could reduce peak electric loads significantly in many commercial buildings and provide added daylighting benefits throughout the US, as well as improve Corresponding author. Tel.: +1-510-486-4997; fax: +1-510-486-4089. Email address: eslee@lbl.gov (E.S.Lee).

A Design Guide for Early-Market Electrochromic Windows

Switchable variable-tint electrochromic (EC) windows preserve view out while modulating transmitted light, glare, and solar heat gains. Consumers will require objective information on the risks and benefits of this emerging technology as it enters the market in 2006. This guide provides such information and data derived from a wide variety of simulations, laboratory tests, and a 2.5-year field test of prototype large-area EC windows evaluated under outdoor sun and sky conditions. This design guide is provided to architects, engineers, building owners, and others interested in electrochromic windows. The design guide provides basic information about what is an electrochromic window, what it looks like, how fast does it switch, and what current product offerings are. The guide also provides information on performance benefits if more mature product offerings were available.

A computer-based daylight systems design tool

Currently numbers like illuminance or glare index are used for the evaluation of daylight system designs. We propose to use photorealistic pictures in addition to numbers as a way to assess the quality of a design solution. This is necessary since numbers-based performance criteria, that are currently in use, are either not sufficient to evaluate performance, or they require expert knowledge for interpretation. The paper discusses the implications and ramifications of this approach.