2009 - Daylight Symposium
THE REALIZED SAVINGS RATIO: MEASURED VERSUS PREDICTED ENERGY SAVINGS FOR DAYLIGHT HARVESTING by Lisa Heschong
Architect & Founding partner
Heschong Mahone Group (HMG)
One of the important benefits of daylighting is a corresponding reduction in building electric lighting energy use. Properly designed and installed automatic photocontrols in a daylit space should provide reliable energy savings. The Heschong Mahone Group undertook two studies to compare achieved savings from photocontrol installations against engineering predictions. The first study looked at a variety of 34 “toplit” spaces, and the second study included 123 “sidelit” spaces, all of which included photocontrols. Monitored savings due to operation of the photocontrols (excluding the effects of other types of automatic controls and manual operation) were compared to estimates for each system using the whole building energy simulation tool eQuest (DOE2.1). For toplit spaces overall, a “Realized Savings Ratio” of 98% was found. For sidelit spaces the ratio was much lower, with one half of the systems found to be not functional, and those that were functional only producing one half of the expected savings. This paper will report on our methodology and findings, including system characteristics associated with greater success or failure, and implications for improving the success of daylighting energy savings.
Lisa Heschong is a principal of Heschong Mahone Group and a licensed architect who has divided her professional practice between energy research, writing and building design. As a researcher, she led the project teams, which analyzed the impacts of daylighting on human performance for the Daylighting and Productivity Studies funded through PG&E and CEC. She also led the team that analyzed baseline lighting characteristics and created a computer model of lighting energy use for the State of California Energy Commission . As a writer, she worked with Lawrence Berkeley Laboratories to synthesize their research into Residential Windows: A Guide to New Technologies and Energy Performance (WW Norton). She also is author of Thermal Delight in Architecture (MIT Press), a co-author of the Advanced Lighting Guidelines, the CHPS Best Practices Manual, and the Skylighting Guidelines, all web-based publications. As a lighting expert, she has developed the successful web-based training program for the Federal Energy Management Program (FEMP) and conducted workshops across the country for DOE.
As an architect, Ms. Heschong has managed projects to design high-rise office buildings, K-12 schools, and residences. She has consulted on numerous school designs through the Bright Schools program of the California Energy Commission, and reviewed school proposals for the Office of Public School Construction. She also taught studio design at the Architecture Department of the University of California at Berkeley.