Back in 2007, the Energy Engineering Program at the University of Massachusetts Lowell completed a study of the actual energy performance of 19 green buildings across the Bay State. The study was funded by the Massachusetts Renewable Energy Trust and identified 13 schools which were certified under the LEED-based Massachusetts Collaborative for High Performance Schools Criteria, as well as 6 buildings that had earned LEED certification. The study compared energy consumption as predicted during the design phase and actual occupancy post-construction; buildings included in the study provided at least one year of occupancy data. The authors also interviewed individual project teams and energy modelers and conducted occupancy surveys in evaluating the effectiveness of various types of efficiency measures. All of the buildings received design or construction grants from the Massachusetts Technology Collaborative, which provided the prediction data that project teams had submitted in connection with their funding applications.
Although the study concluded that these 19 green buildings were consuming (on average) 40 percent more energy than predicted, all of the buildings were consuming less than a building designed to Massachusetts baseline building codes. The disparity in predicted versus actual energy consumption is probably not surprising, but the study did identify a number of issues common across the buildings which resonate with many of the technical and operational provisions of documents like the Model Green Lease. I think it is therefore worthwhile to review the study both from a green leasing perspective, but also in terms of LEED, particularly because the Lowell study has not been referenced in many of the recent articles discussing the ongoing LEED performance gap.
Among other factors, the study identified the following as accounting for the disparity in predicted versus actual performance:
- The predictive energy models used during the design phase were created based on the incremental amounts of projected energy savings from each of the proposed systems and efficiency measures which, according to the energy modelers interviewed for the study, did not account for the building’s performance in its entirety once those systems were installed and operational;
- By nature, predictive energy modeling does not account for the behavior of building operators and occupants with respect to their use of plug loads, occupancy levels, and operating hours (but note the importance of green leasing practices in this context);
- Design and materials changes during the construction phase on account of budget constraints (which emphasizes the need for ongoing construction counsel); and
- Some of the buildings suffered from increased energy consumption during the initial months of occupancy due to incompletely installed or commissioned systems, which the study concluded stemmed from contractors who incorrectly set the systems initially, as well as occupants who did not understand how to use the systems.
In addition to suggesting that these specific design and construction factors may impact green building performance, I think it is also important to note that the authors identified a “frustration” in stakeholders over the observed energy performance gulf. The study suggests that the gap be bridged through “communicating uncertainties in design predictions” and “better training in the use of the technologies in the buildings;” the former is a marketing and construction contracts issue which we’ve frequently discussed in the context of LEED, while the latter can be addressed through the use of various types of green lease provisions.
Although the study itself is somewhat dated, I do think that it emphasizes two important points. First, LEED building performance has been a question mark for quite some time, and will likely remain a critical issue for the foreseeable future, particularly while industry stakeholders continue to grapple with addressing the foregoing building performance factors through risk management strategies, construction contracts, and green lease provisions. Second, it confirms the unpredictable nature of energy modeling and importance for project teams to manage their clients’ expectations when discussing the opportunities presented by green building and other sustainable construction practices.
- Barrientos, J., U. Bhattacharjee, T. Martinez, and J. Duffy, 2007, “Green Buildings in Massachusetts: Comparison between Actual and Predicted Energy Performance,” Proceedings Annual Meeting American Solar Energy Society