Taking an Integrated Systems Approach for Energy Savings
Developing
and Promoting the Integration of High-Performance Envelope and Lighting Technologies
The practice of window and lighting systems design in commercial buildings is typically a non-interactive process. Architects, who are responsible for the shell of the building, rarely explore the full integration of the solar heat and daylight-admitting window system with their lighting and mechanical system consultants.
Survey data reveals the shortcomings of the resulting built product in terms of energy efficiency and comfort. In a recent study of federal buildings in the Pacific Northwest, 55-65% of office workers had complaints regarding thermal or visual discomfort due to the envelope design, despite the provision of space-conditioning.
Energy-efficient electric lighting, glazing, and daylighting control technologies have the potential to significantly reduce the peak demand and total electricity use of commercial buildings - if these technologies are designed as integrated systems and the process is supported by appropriate design tools. Since lighting and cooling in commercial buildings constitute the largest portion of energy use and peak electrical demand, promotion of such integrated systems could become a cost-effective option for owners and utilities.
As an additional significant benefit, although difficult to quantify, these integrated systems can also provide higher quality work environments that are more comfortable for the occupants and also provide owners with higher value space.
Approach
In 1991, the California Institute for Energy Efficiency, a consortium of California utilities and agencies, began support of this multi-phase R&D program, which has focused on bringing together viable envelope, daylighting, and lighting solutions from traditionally disparate disciplines. As such, the approach differs substantially from conventional research in that it cuts across traditional narrow areas of building research and is intended to directly lead to near-term solutions for commercial buildings. Prototype designs have been exposed to more complex and realistic environmental conditions as research has progressed; e.g., field tests versus simulations, in-situ building installations versus scale models. Development of paper-based design guidelines have been initiated; the transition to computer-based design tools will be made in the next phase of work.
Accomplishments
Two integrated systems have been developed for cooling-load dominated commercial buildings: 1) dynamic systems and 2) advanced optical systems. Dynamic systems, such as automated venetian blinds (functional precursors to the switchable electrochromic glazings) with a dimmable electric lighting system, actively balance daylighting and thermal heat gains while addressing comfort issues. Advanced optical systems, such as light shelves and light pipes, passively extend the depth of daylighting penetration to approximately 10 m beyond a conventional sidelight window, and distribute daylight more uniformly to achieve a higher level of visual comfort.
Dynamic Systems
DOE-2 simulations of an automated venetian blind with daylighting controls indicate that 16-26% total energy savings can be attained with the blind system compared to a conventional insulated window system in Los Angeles. These savings have been corroborated with outdoor field test data gathered this past year in a 1:3 reduced-scale office module. If the blinds are operated to block direct sun and optimize interior daylight levels, a lighting energy savings of 37 - 71% is attained on clear sunny days over a fixed blind system for south to southwest-facing windows. These savings were accomplished using as-is or modified commercial lighting products or prototype solutions. On the cooling side of the equation, results from the Mobile Window Thermal Test Facility (MoWiTT) indicated that the blind system with a less optimal control algorithm was more than twice as effective at reducing solar heat gains under clear sky conditions as a static unshaded bronze glazing, while providing approximately the same level of useful daylight.
Advanced Optical Systems
Using measured bi-directional illuminance data in combination with mathematical algorithms, the daylight output of several advanced optical technologies was shown to be significantly more effective at distributing useful daylight than conventional technologies. For example, the south-facing lightshelf produced daylight illuminance levels that were two to four times greater than a conventional flat light shelf at a depth of 8.38 m from the window wall, during clear sky conditions from 9:30-14:30, February to October. Cooling loads were of minor concern since the daylighting aperture was 40% smaller in area than the base case light shelf.
A prototype skylight system, a derivative of the light-redirecting concepts of the basic perimeter daylighting systems, was designed, installed, and demonstrated at full-scale at the Palm Springs Chamber of Commerce, in collaboration with Southern California Edison (SCE). The design was highly effective at distributing daylight throughout the entire room cavity and produced a uniform workplane illuminance throughout a partly cloudy winter day. Practical experience gained working with the contractor, 3M, and SCE led to further refinement of the underlying conceptual designs and a greater understanding of the practical issues surrounding fabrication and construction. Occupant feedback has also been useful in refining the design concept.
Design Tools
Successful implementation of these integrated systems will require better design data and tools. As a first step, we are developing a twelve-section daylighting design guideline that provides a quick and easy reference to integrated design principles. The approach has been tailored to the architectural design process, from programming though building occupancy, in a series of concise how-to bullets and supporting reference material. Design guidelines will need to be expanded to computer-based tools, to put a decision- making capability in the hands of the architect and engineer. We expect to build these new capabilities into versions of the Building Design Advisor (BDA) and PowerDOE design advice modules to be described in future articles.
References
Beltrán, L.O., E.S. Lee, K.M. Papamichael, S.E. Selkowitz. "The Design and Evaluation of Three Advanced Daylighting Systems: Light Shelves, Light Pipes and Skylights." Proceedings of the Solar '94, Golden Opportunities for Solar Prosperity, American Solar Energy Society, Inc., June 25-30, 1994, San Jose, CA. LBL Report 34458, Lawrence Berkeley Laboratory, Berkeley, CA.
Lee, E.S., S.E. Selkowitz, F.M. Rubinstein, J.H. Klems, L.O. Beltrán, D.L. DiBartolomeo, R. Sullivan. 1994. "Developing Integrated Envelope and Lighting Systems for New Commercial Buildings." Proceedings of the Solar '94, Golden Opportunities for Solar Prosperity, American Solar Energy Society, Inc., June 25-30, 1994, San Jose, CA. LBL Report 35412, Lawrence Berkeley Laboratory, Berkeley, CA.
Contact
Eleanor Lee
(510) 486-4997
Fax (510) 486-4089
e-mail: ESLee@lbl.gov