The ability to accurately measure and compare the energy use of commercial buildings is critical to improving their performance and increasing standards of efficiency. The compilation of performance data for the purposes of comparison and analysis will ensure new benchmarks. Recent building codes, such as the 2012 International Energy Conservation Code (IECC) are aiming to increase energy efficiency in new buildings by 30% over the 2006 edition and 17% over the 2009 edition. In addition, policies, such as the Better Buildings Initiative are prompting partners in the private and public sectors to make America’s buildings 20% more efficient over the next decade. Therefore, data collection is proving vital to gauging baselines of energy consumption and establishing benchmarks.
Although energy modeling, particularly when performed during the design phase, can be instrumental in making decisions regarding design, it can sometimes prove unreliable for predictive metrics. For instance, in 2008, Washington, D.C.-based U.S. Green Building Council (USGBC) commissioned a study from the New Buildings Institute (NBI), White Salmon, Wash., which compared design intent to the actual performance of 121 buildings certified under the Leadership in Energy and Environmental Design (LEED) New Construction (NC) ratings system. The study found that data reported by more than half the buildings deviated by more than 25% from design predictions, with 30% performing significantly better than predicted and 25% performing significantly worse.
A study released last November by NBI and developed jointly with Ecotope, Seattle, summarizes the extent to which operations and occupant behavior impact a building’s energy use compared to design characteristics. “Sensitivity Analysis: Comparing the Impact of Design, Operation, and Tenant Behavior on Building Energy Performance” also makes recommendations for design teams, owners, and operators on what they can do to ensure the full potential for energy savings from efficiency measures is realized — and provides a broad perspective on how buildings use energy and what aspects of building energy performance deserve more attention in design, operation, and policy strategies. Most significantly, the study suggests that although the market generally assigns responsibility for building energy performance to the design team for aspects such as envelope, HVAC system, and lighting system features, operational and tenant practices have a significant impact on building energy use.
For example, decisions about the efficiency levels of the lighting and controls systems are fully under the purview of the designers, according to the report, but the ultimate effectiveness of the lighting controls is more in the hands of building operators and occupants. “The perception that energy performance is relatively set once the building is designed and constructed is not valid,” explained NBI Technical Director Mark Frankel, an author of the report. “In fact, a significant percentage of building energy use is driven directly by operational and occupant habits that are completely independent of building design, and, in many cases, these post-design characteristics can have a larger impact on total energy use than many common variations in the design of the building itself.”
Therefore, while computer modeling of buildings built to the 2012 IECC shows on average more than 30% better energy efficiency than those built to the ASHRAE 90.1-2004 model code, the real-world performance of the buildings (once they’re built and occupied) may not meet that level. The effect of occupant behavior, in particular, on energy use is difficult to predict. Despite being built to correct specifications, buildings may not perform as well as their modeled estimates because of end-users’ unpredictable energy use. As a result, the new code contains language requiring proof of commissioning once the certificate of occupancy is issued, which may also be used for compliance reporting after building occupancy.