New NRC report asks “Do green buildings outperform conventional buildings?”
The National Research Council (NRC) has released a new comprehensive post-occupancy investigative report on the performance of “green” and “conventional” office buildings. The study included occupant surveys and physical building and energy use data collected from 24 buildings (12 green, 12 conventional) across Canada and the northern U.S, and also refers to NRC’s previously-published work on energy analysis.
Occupants completed a questionnaire with items related to environmental satisfaction, job satisfaction and organizational commitment, health and well-being, environmental attitudes, and commuting behaviour. In total, the NRC recorded valid surveys from 2,545 occupants, and in addition conducted on-site physical measurements at each building; collected data at a sample of workstations on prevailing thermal conditions, air quality, acoustics, and lighting; and recorded workstation size, ceiling height, window access and shading, electric lighting system, and surface finishes.
In looking at energy performance, the NRC conducted a re-analysis of data gathered by the New Buildings Institute on one year of data from 100 LEED-certified commercial buildings in North America. Each green building was “twinned” with a similar conventional building from the U.S. commercial building stock. They also collected monthly utility data from the 24 buildings in the field study sample, where available.
From analysis of their original post-occupancy field study data, and re-analysis of extant datasets on LEED/conventional building energy use, NRC concluded (among other findings) that:
- Green buildings exhibited superior indoor environment performance compared to similar conventional buildings. Outcomes that were better in green buildings included: environmental satisfaction; satisfaction with thermal conditions; satisfaction with view to the outside; aesthetic appearance; disturbance from HVAC (heating, ventilation and air conditioning) noise; workplace image; night-time sleep quality; mood; physical symptoms; and reduced number of airborne particulates.
- Green building rating systems might benefit from further attention in several areas, including: consideration of a LEED credit related to acoustic performance; a greater focus on reducing airborne particulates; enhanced support for the interdisciplinary design process; development of post-occupancy evaluation protocols, and their integration into on-going certification systems.
- On average, LEED buildings exhibited lower total energy use intensity than similar conventional buildings. A specific case study from our own field study dataset confirmed the potential for substantial energy use intensity reductions through a green building renovation. However, many individual LEED buildings did not meet energy performance expectations. Further, there was little correlation between the number of LEED energy credits obtained during design and the resulting energy performance.