Collecting More Data Isn't the Answer
By Larry Spielvogel, P.E.
The U.S. Green Building Council's Aug. 26 press release about its Building Performance Initiative implies that a large-scale collection of energy data from LEED buildings will improve energy performance. This suggests a response to escalating criticism about the actual energy use of LEED-certified buildings compared with all others. Why do few published stories about these buildings include metered energy and water use data? If these buildings can waste energy efficiently, perhaps one answer is not to include those measures that allow that to happen.
The reality is that neither predicted nor actual measured energy use determines whether a building is energy efficient. Nor does energy use alone determine whether a building meets or exceeds all required or desired criteria or provide the accountability necessary to achieve those results.
I have been collecting and evaluating detailed metered and measured building energy performance data for 40 years. Collecting the data is one thing, even if done completely and correctly. However, evaluating the data and then making comparisons among buildings is something else. Buildings alone do not use energy. The occupants, operators and systems do.
In an extreme case, look at apartment buildings where each apartment is identical, and the metered energy use per apartment can easily vary by two or three to one, or more. Individually metered floors in office buildings occupied by the same company or tenant also can vary by two or three to one.
The functions in a building can also have a major influence on building energy use. The presence of a laundry in a hotel or hospital can make a 25 to 50 percent difference in total building energy use per bed, room or square foot compared with an identical building on the same street.
Buildings with intermittent occupancy present similar dilemmas. How does one estimate, predict or compare the energy data for two identical churches on the same block built at the same time when one is only occupied for a few hours each Sunday and on some holidays and the other is occupied most days of the week?
Comparing metered energy use to modeled energy data is not a valid measurement of anything. If the modeling and estimating methods were sufficiently accurate, utility companies would not require the use of meters.
Some articles I wrote 25 years ago show apartment by apartment or office floor by office floor metered energy-use data in the same building. For another good example, look at the range of energy data for any given building type shown in the statistically significant quadrennial CBECS reports, collected at a cost in eight figures.
That reminds me of an energy research project 35 years ago during the 1970’s energy crisis. The U.S. Postal Service spent hundreds of thousand of dollars instrumenting and recording the detailed energy use in a large postal facility. The conclusion was that they could collect lots of data.
The answer in evaluating and comparing energy data is using professional judgment and experience. That involves knowing and understanding not only the energy use and particulars of the subject building, but also the energy use and particulars of comparable buildings in the area. Comparing the energy use of a suburban office building in Boston with suburban office buildings in Providence without knowing the particulars is not likely to be meaningful or conclusive. This is much like the commercial real-estate appraisal profession.
Larry Spielvogel is principal of L. G. Spielvogel Inc., King of Prussia, Pa.