Green buildings deliver better indoor environment quality and energy efficiency than otherwise similar conventional buildings according to post-occupancy evaluation research in office buildings.
The number of buildings with green credentials is growing rapidly, and an increasing number of jurisdictions require green features in new buildings. However, in most cases these buildings are judged on their greenness at the time of their design, and there has been little follow-up to determine whether post-occupancy performance meets expectations.
While there have been numerous studies, they have been limited by small samples and narrow scopes. Given the lack of objective and measured data, NRC and its collaborators set out to directly compare green and otherwise similar conventional buildings in indoor environment quality and energy efficiency.
Indoor environment quality
NRC, collaborating with industry, conducted an original field study focused on indoor environment quality. Pairs of buildings were sought—one green and one conventional—that were as similar as possible (e.g., of similar size and age, in the same climate zone, with a similar employer, and occupants doing similar work). This provides confidence that any differences in the measured outcomes are due to greenness rather than other factors. The 12 pairs of office buildings chosen were in Canada and the northern US. Most green buildings were LEED certified to some level, or on the path to LEED certification, though some were judged green by other criteria. Data were collected between May 2010 and October 2011.
On-site physical measurements were made using a custom-built, mobile, integrated-sensor platform, referred to colloquially as the NICE Cart (National Research Council Indoor Climate Evaluator), see photo.
The NICE Cart took a detailed snapshot of indoor environment conditions over a 10-15 minute period at representative workstation locations within a building during normal working hours. These measurements included temperature, air speed, relative humidity, carbon dioxide, respirable particles concentration, light levels, and sound (ambient levels and speech privacy).
The NRC researcher manually recorded other important workstation characteristics. This was supplemented by a structured interview with the building manager/operator. The NICE Cart measurements were collected in a single 2-4 day visit at each building. In total, 974 measurements were taken across the 24 buildings.
Building occupants completed a confidential online questionnaire addressing elements that green buildings are said to influence, including: environmental satisfaction, job satisfaction and organizational commitment, health and well-being, environmental attitudes, and commuting. Questionnaire data from a building were collected in a three-week period around the dates of the NICE Cart measurements at the location. In total, 2545 occupants completed the questionnaire.
In general, all buildings provided indoor environment conditions that were within recommended practice on physical measures and satisfactory to occupants based on questionnaire responses (except for satisfaction with speech privacy, which was unsatisfactory, on average, in both green and conventional buildings).
There were many results that were not statistically significantly different between green and conventional buildings. However, when there were statistically significant differences, green buildings were favoured on 12 outcomes and performed less well on only one. This consistent trend suggests that overall, green buildings do provide superior indoor environment quality. However, this might not be true for every individual green building.
NRC conducted a re-analysis of energy data from LEED-certified buildings collected and shared by the New Buildings Institute and the US Green Buildings Council. NRC re-analysis showed that, on average, LEED buildings used 18-39% less energy per floor area than their conventional counterparts. However, about one-third of individual LEED buildings used more energy than their conventional counterparts. Further, the measured energy performance of LEED buildings had little correlation with the number of energy credits achieved at design time.
- National Research Council Canada
- Natural Resources Canada Program of Energy Research and Development (PERD)
- Governments of Alberta, Manitoba, Nova Scotia, New Brunswick, Ontario, and Saskatchewan
- Fonds en efficacité énergétique de Gaz Métro (Energy efficiency fund for Gaz Métro customers)
- BC Hydro
- Haworth Inc.
- Jim H. McClung Lighting Research Foundation Inc.
- University of Idaho – Integrated Design Lab
- Public Works and Government Services Canada
Overall, it appears that LEED buildings do save energy, and that a general program of building green can be expected to reduce energy use by upwards of 20%. However, the disappointing energy performance of individual LEED buildings might be a problem for the owner/operators of these buildings, who are not realizing the energy savings that they presumably expected. Further, the energy-related credits that people are striving for seem to have little relation to measured energy performance. These factors might raise questions for the credibility of green building rating systems, which could jeopardize the overall societal benefits.
The superior performance of green buildings is good news for a society that is increasingly facilitating their development. There are some aspects of green building performance that need to be improved, and some claims that still need to be validated. This is likely no surprise to serious green building advocates. In this context, research such as this is a necessary part of evolving the green building process from good to better.