The basic functional goal of incorporating window and lighting systems in commercial buildings is to give occupants an adequate level of daylight or electric lighting to perform visual tasks productively. Occupant surveys reveal some of the shortcomings of conventional design practice and broaden the definition of an acceptable office environment. In a study of office workers in the Pacific Northwest region, slightly more than 40% of the occupants said the sunlight in their offices was too bright at least some of the time, and 60% of the occupants said the window was a primary source of glare and interfered with their work. Yet more than 50% of the occupants in several Tokyo high- rise office buildings preferred to have seats nearer the window, citing the brightness, outside view, wide visual range, and open feeling as advantages.
Traditional approaches to creating energy-efficient buildings involve selecting from long lists of efficient components. By taking an integrated systems approach to combining disparate building envelope and lighting components, we can attain greater energy savings can be attained and improved occupant comfort compared to conventional energy-efficient design practice. This integrated systems approach is the basis for a multiyear project, supported by the California Institute for Energy Efficiency and DOE, to develop and promote advanced building systems integrating high-performance envelope and lighting technologies. Since the illumination and cooling of commercial buildings account for the largest portion of peak electrical demand, these integrated systems can become a cost-effective DSM option for utilities.
For commercial office buildings in moderate climates, choosing glazing materials to optimize energy use and electric demand may be viewed as a trade-off between lowering the solar heat gain coefficient to reduce cooling while maintaining the visual transmission of the glass to capture daylight savings. However, harnessing daylight in a building poses a significant technical challenge because of the great variability in daylight intensity. Achieving higher energy savings under these conditions requires looking beyond static systems to dynamic systems that respond to changing climatic or occupant conditions. By linking a dimmable electric lighting system with daylighting sensors to a fenestration system that can automatically modify the transmission of daylight, we can get real-time control of the cooling and lighting energy balance while addressing glare and thermal comfort.
"Smart" electrochromic glazings now under development offer the best long- term potential for dynamic control. The technology consists of a multilayered, thin-film device that changes from a clear to an increasingly dark, colored state when low-voltage current is applied. By using electrochromic glazings in a curtain wall, we can dynamically alter daylight levels and visual privacy in the space and control thermal energy flows in the entire building envelope.
We are investigating this concept using an automated blind system (Figure 1) as a substitute for electrochromic glazings, working toward a responsive system that can be linked to the building HVAC system by a network of sensors and operated by intelligent energy management controls. Currently, the position of the blind system is coupled actively to variable external and internal conditions-the sun going behind a cloud or changing functional needs in a room, for example. The system could accommodate preferences for controlling view, glare, privacy, and task lighting levels when the space was occupied, and could switch to a minimum energy consumption mode whenever the occupant left the office.
Figure 1. This "smart" automated venetian blind system has been designed to respond to changing solar conditions and access to view in real-time by using a network of sensors and an intelligent computer control system to operate the slat angle of the blinds. In this field test, we are comparing the thermal performance of the smart system (left) to a static tinted glazing system (right) using the Mobile Window Thermal Test (MoWiTT) facility.
Conventional windows provide daylight in the outer 10 to 12 feet of a perimeter space. New daylighting technologies extend the daylit area by redirecting sunlight further from the glazing aperture, reducing electric lighting and cooling energy within a larger floor area. The challenge of successful daylighting design is to collect sunlight from a source that varies in both intensity and position and to distribute the luminous flux comfortably with minimal glare and thermal impacts.
The system we have been developing consists of a window wall divided into an upper daylighting and a lower view aperture. The lower view aperture incorporates spectrally selective glazing with a shading device to control glare, direct sun, heat gains, and view for those occupants adjacent to the window. The upper daylighting aperture incorporates a prototype light shelf or light-pipe technology to redirect or transport direct sunlight to depths of 9.28 m (30 ft) from the window wall; supplemental daylight is contributed from the lower view window for the first 4.57 m (15 ft) from the window (Figure 2). These technologies use a customized geometry developed for the solar path at a given latitude and unique reflective films to control the redirection of daylight.
Figure 2. South-facing light shelf: (a) Section along centerline of room, and (b) detail of light shelf reflectors.
Realizing the full energy-saving potential of envelope and lighting technologies for commercial buildings means designing and packaging them as integrated systems, supported by appropriate design tools. The focus of the third phase of research is deployment, conducted along the lines initiated in earlier phases of research-through showcase demonstration projects in partnership with California utility sponsors-and evaluation in an occupied testbed office building. By demonstrating the conceptual designs and prototype technologies, we hope to accelerate their adoption by building professionals. We are also working to establish manufacturer-utility partnerships to foster the commercialization of products.
To develop a preliminary assessment of how an integrated, dynamic envelope and lighting system would perform, we conducted a series of building simulation tests modeling both conventional glazings and automated blind systems. The DOE-2 energy simulation program helped us understand the performance of various control strategies. The initial results show that automated systems with motorized blinds that are adjusted continuously to maintain desired light levels and block direct sun provide substantial energy and demand savings compared to conventional static glazing design solutions.
In a second study, field measurements were taken in the outdoor Mobile Window Thermal Test (MoWiTT) facility (see Figure 1 and Center Research Facility article). Side-by-side measurements were made of the thermal performance of conventional tinted glass compared to a spectrally selective glazing with an automated venetian blind. Solar sensors and a smart controller kept the blinds tilted at the optimum angle throughout the day. The automated blind with photocell controls showed a 50% reduction in total solar and lighting heat gains for a south-facing window (Figure 3).
Figure 3. Results from the MoWiTT facility for a clear day indicate that the automatically controlled interior blind coupled with a selective glazing system (B) was more than twice as effective at reducing solar heat gain as a commonly used nonoperable system, single-tinted (bronze) glazing (A), while providing approximately the same electric light energy savings. The large differences in the heat flow between the two samples were driven principally by the admittance of direct sun into the base-case chamber.
With Southern California Edison, we applied our project results to the problem of providing daylight in a windowless office at the Palm Springs Chamber of Commerce. In addition to using advanced, commercially available envelope and lighting technologies throughout the building, we designed a skylight prototype to split and redirect incoming daylight to the ceiling plane in two separate windowless internal offices (Figure 4A). We gained considerable experience working with the manufacturer of special optical films, the building contractor, the architect, and the utility. Occupants reported that the skylight provides lively, bright, and uniform daylight throughout the space (Figure 4).
Figure 4. The reflector system used in the prototype skylight for the Palm Springs Chamber of Commerce was designed to split the incoming daylight flux and redirect it to the ceiling plane of two separate rooms (Figure 4a). The installed skylight (above) yielded excellent illuminance uniformity on the workplane and brightened typically dark wall and ceiling surfaces.
The testbed demonstration approach is designed to help make the transition from Phase I and II scale model prototypes, reduced-scale field tests, and building energy simulations to a more robust technology solution suitable for larger building applications. It is both an R&D facility to help answer research questions and a limited proof-of-concept test, designed to eliminate practical "bugs" from an innovative building system. Side-by-side energy and environmental quality comparisons of prototype versus conventional design will prove the design. Negotiations are under way to form a partnership with Pacific Gas & Electric and a major U.S. commercial developer and owner of a 24-story commercial office building in downtown Oakland, California.
Efforts in 1995 will focus on deployment, getting industry feedback on demonstrations of the two prototypes, and continued work on tools for integrated design, including quick, accessible reference materials.
Building Technologies Program
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