With growing energy needs to run equipment and more complex HVAC and lighting systems in today's commercial buildings, architects and engineers can only go so far in delivering on energy efficiency. A new study by New Buildings Institute (NBI) summarizes the extent to which operations and occupant behavior impact a building's energy use compared to design characteristics.

The study, which was developed jointly with Ecotope in Seattle, Wash., 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. NBI is a national, nonprofit organization working to improve the energy performance of commercial buildings. Ecotope provides research, design and analysis for projects targeting deep energy efficiency outcomes.

The study, Sensitivity Analysis: Comparing the Impact of Design, Operation, and Tenant Behavior on Building Energy Performance, 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 very 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, however 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," explains 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," Frankel said.

Among the study's key findings:

-Building envelope, HVAC and lighting systems are the primary areas where the design team can impact building efficiency. Best practices in envelope and lighting design can save at least 40 percent of total building energy use; poor practices can increase energy use by about 90 percent in all climate zones. When the effects of HVAC system selection are added, best design practices can lead to about a 50 percent savings, and worst practices can lead to a 60-210 percent increase in energy use, depending on climate.

-Best practices in building operations are shown to reduce energy use 10-20 percent across all climate zones. Poor practices in this area can increase energy use 30-60 percent or more. The design team may be able to limit these loads by incorporating features such as metering and control strategies, as well as involving building operations staff in the design process, commissioning and start-up procedures.

-The behavior of occupants also has a significant impact on overall energy use, though tenants are seldom in a position to recognize their direct effect. The installation of submetering and energy-use "dashboards" can help building tenants understand and reduce their energy use.

-The design team has the largest potential impact on total building energy use, and many of the design decisions made about building features also determine the degree to which operators, and to a lesser degree tenants, can successfully manage their own behaviors to achieve efficient building performance.

-After occupancy, operations and tenant behavior have a much greater potential to adversely impact energy use than to improve upon the original design characteristics.

-The study offers important insights into the impact of various measures in different climates and suggests there are a range of climate-driven performance features that are not fully recognized in current design practice, or in the energy codes that regulate these features.