by Chris Baker, AIA, PE, BEMP, LEED AP BD+C, The Weidt Group
Nine major cities in the United States now require building owners to benchmark and disclose the energy consumption of their buildings.i Several states also benchmark all state-funded facilities.ii The Environmental Protection Agency has found that between 2008 and 2011, on more than 35,000 buildings with monitored energy consumption, average energy reduction was 2.4% per year and more than 7% over the 3-year period.iii It may be true that you cannot manage what you do not measure, but measurement is not enough. Measuring and reporting a building’s energy consumption is only half of the challenge. Simply ranking buildings by their energy consumption per square foot is not even enough. To be useful, a measurement needs comparison to some benchmark to determine if it is satisfactory or needs improvement.
For example, a building using 100 kBtu/sf of energy would be doing quite well if it was an intensive research laboratory and quite poorly if it was a warehouse. Even within a given building type, there can be wide variations due to occupancy density, the occupant’s equipment, or the amount of data center load. A very efficient building with 20% of its floor area used as a data center will use more energy than an inefficient building without a data center.
Energy Star is a good starting point and provides benchmarking comparison for several types of buildings, but this standard does not yet exist for all building types. In Minnesota alone, nearly 75% of public buildings are ineligible for benchmarking by Energy Star because of their designated type of use. This is because Energy Star is based on statistical analysis of the Commercial Building Energy Consumption Survey (CBECS), and there are 16 building types for which there are a large enough population of buildings sampled to provide statistically significant benchmarks.
Source: Institute for Market Transformation
An alternative to Energy Star’s statistical benchmarking is to use model-based benchmarking. With model-based benchmarking, an energy model of an equivalent building, but with standard operations and physical parameters set to the current energy code, establishes a unique benchmark for each building. Buildings with different uses can then be compared via the ratio between their energy use and the benchmark energy use. So a building using 1.2 times the benchmark energy use would indicate opportunity for energy use reduction, while a building using 0.70 times the benchmarked energy use would indicate it is performing relatively well compared to the benchmark. Model-based benchmarking provides a consistent method that can be applied across all building use types. This allows a state or local government to compare the energy use of a fire station to that of a library and determine which one would benefit more from an intervention.
The real value of comparing a building’s energy consumption to a benchmark is to determine which buildings will benefit the most from energy efficiency improvements. Research by Lawrence Berkley National Laboratory, a U.S. Department of Energy lab managed by the University of California, has shown that by targeting energy retrofits with benchmarking, there is twice as much energy savings per dollar spent. If your benchmarking only applies to a portion of the portfolio of buildings, you have an incomplete picture of where the best opportunities are located.
Model-based benchmarking provides a consistent way to judge the relative savings opportunities across a broad range of building types. This allows energy efficiency to be an even better financial and sustainability opportunity. In Minnesota, for instance, B3 Benchmarking, a model-based benchmarking tool, has identified the 23% of state buildings that have a cumulative potential savings of $31 million per year if they were brought up to the energy performance of a typical new building in the state.
Posted on: May 8th, 2014