conditioning (HVAC) loads, and plug loads. Data were tabulated every 15 minutes and the data were used to calibrate the computer simulation models. Among the study findings were the following:

  • All of the buildings used much less energy on an annualized basis than comparable code-compliant buildings. Three of the buildings had net source energy savings of more than 50 percent. Three of the buildings had energy cost savings that exceeded 50 percent. Overall, net source energy savings ranged from 77 to 22 percent, and energy cost savings ranged from 67 to 12 percent.
  • Site energy use was 25 to 62 percent less than the baselines. Site energy costs were 12 to 67 percent less than the baselines.
  • Each building’s actual energy use was greater than the energy use predicted by models. Factors cited for this included occupant behavior and their acceptance of systems; higher plug loads than modeled; temperature controls set higher in actuality than in modeling; changes between the buildings as they were designed and as they were constructed.
  • Creating energy cost goals during design and verifying the costs are difficult due to instability in energy prices.
  • Caution must be exercised in comparing the initial predictions, analysis, and actual data because these numbers can vary greatly.
  • Measurable goals must be defined that can be used throughout the design process. Setting the goal can drive the project and can result in good performance against that metric.
  • Achieving and maintaining high performance of the building requires a constant effort, which is absent in most buildings. Continually tracking building performance is expensive and requires motivated, trained staff. However, advances in metering technology, computerized communications, and automated controls offer hope for the future.

Evaluating the Energy Performance of the First Generation of LEED-Certified Commercial Buildings

R. Diamond, M. Optiz, T. Hicks, B. Von Neida, and S. Herrera. Lawrence Berkeley National Laboratory: Berkeley, Calif. 2006.

This study by Diamond et al. presented an early analysis of the actual energy performance of 21 LEED-certified buildings that were certified between December 2001 and August 2005. The study does not indicate what certification levels had been achieved by individual buildings.

The study compared the modeled energy use for LEED-NC-certified buildings (data taken from the submissions required for LEED certification) against actual utility bills for the first year of operation (utility billing data were collected from 2003 to 2005). Modeled energy data were collected for both the as-designed building and the base-case building. The authors note the study is “only a preliminary guide to how LEED buildings in general are performing as a group” due to a range of issues. The issues included the sample size, the wide variation in building type (libraries, offices, multifamily, mixed use, laboratories) and building size (from 6,100 square feet to 412,000 square feet); 14 buildings were owned by the federal government, certified as LEED-NC, and located across the country; 7 buildings were commercial and concentrated mostly in the Pacific Northwest.

For the 18 buildings for which the authors had both simulated whole building design and actual purchased energy, the actual consumption was 28 percent lower than the base-case. However, there was significant variation among individual buildings, with some being more energy efficient than predicted, and some being less efficient. The actual energy use in the federal buildings was lower than the modeled

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