Wanted: More Energy-Efficient LEED BuildingsLevon Whyte for Zondits, July 9, 2014
Developed by the US Green Building Council (USGBC) in March 2000, The Leadership in Energy and Environmental Design (LEED) is a set of rating systems for the design, construction, operation, and maintenance of green buildings, homes, and neighborhoods. It seeks to encourage and recognize sustainable building strategies that utilize resources efficiently and are environmentally responsible.
According to the USGBC, buildings built to meet the LEED benchmark cost less to operate and can save building owners as much as 40% in water and energy costs. To receive LEED certification building projects must satisfy prerequisites and earn points to achieve different levels of certification. (You can read more about the LEED certification process in this Zondits article by Max Twogood).
As of March 2012 there were approximately 12,000 LEED-certified buildings across the world. In the same year, 41% of all nonresidential new constructions were green, as compared to 2% of all nonresidential buildings in 2005. While it is certainly encouraging to see this growing trend towards sustainable building practices, it raises the question: How many of these new green buildings, and more specifically, LEED New Construction (NC) buildings, are achieving the energy savings they claim?
The first major study seeking answers to this question was documented by the New Buildings Institute (NBI) in their 2008 paper “Energy Performance of LEED for New Construction Buildings.” In it, Turner et al. analyzed the measured energy performance of 121 LEED NC buildings to non-LEED building stock. According to their results, on average (the median value) LEED buildings use 25%‒30% less energy per square foot than the national average. The study also revealed that, on average, buildings achieved the savings predicted by their respective energy models used in the LEED submittal process. (In the LEED-NC rating, under the Energy and Atmosphere category, points are awarded based on the energy savings predicted through the building’s energy model). For both of these metrics, however, the data points from which the averages were derived display a large degree of scatter. For example, while on average the buildings achieved the energy predicted, more than half of the projects deviate by more than 25% from their design projections, with 30% significantly better and 25% significantly worse, as shown in the graph below.
This means that there are buildings currently touting Gold or Platinum LEED energy efficiency that are actually consuming up to 50% more than the code baseline. This should be cause for concern.
After the release of the NBI study there was some controversy on how the NBI interpreted the data and how they presented their findings. For this reason additional papers (Scofield et al. and Newsham et al.) were released that sought to address areas where it was thought the NBI had not been accurate enough in interpreting the data collected. One issue was that the median energy usage intensity (EUI) for the LEED-NC buildings was what was being compared to the national average EUI, which is not necessarily a consistent comparison. There were also concerns about new LEED NC buildings being compared to the stock of existing US buildings regardless of their age. It was suggested by Henry Gifford, NYC mechanical engineer and building scientist, in his paper that the LEED buildings should have been compared to non-LEED buildings constructed during the same time frame. The majority of buildings in the national average are much older and already far less efficient than newer non-LEED buildings, and thus the baseline becomes skewed. In making corrections to the results from NBI to compensate for these very valid concerns, Gifford posits that the buildings actually consume 29% more energy than the CBECS mean for new buildings.
Now, while all studies done so far are as not as comprehensive as researchers would desire, (a number of challenges are faced when gathering data post-project, including building managers’ reluctance to provide energy usage data for fear of the removal of their LEED certification) they all highlight the fact that the LEED-NC certification process could benefit from revision to improve the consistency of results.
So, then, what changes can be made to achieve better results in energy efficiency in the LEED system? One suggestion is to focus on improving energy modeling across the industry. LEED points are predicated on the amount of energy saved as predicted by the energy models, and, thus, if models are inaccurate then buildings, when constructed, will not meet their projected energy savings. Improvement in modeling can be achieved through implementing a formal feedback program within the LEED program, between the building modelers and building owners. Post-project building performance data, provided by the building owners, can help modelers in identifying what modeling strategies work in predicting building performances and what approaches are not reliable. Over time, energy modeling best practices will be identified, documented, and standardized. This will begin the process of closing the gap between predicted and actual performance.
Additional scrutiny to the energy models submitted to LEED is another recommendation to improve the accuracy of predicted energy savings. As I know from my experience with energy model review, it can be quite easy to overlook errors in an energy model that can result in large corrections in projected savings. There are also situations where new and emerging HVAC systems, such as variable refrigerant flow (VRF) are proposed as an energy efficiency measure, yet mainstream modeling software has not been updated to ably represent the system. As such, modelers have to attempt “workarounds” in the current software to compensate for this. At times, the product of the workaround is a good representation of the system, but it takes a keen eye and someone who is very familiar with the new technology and the modeling software to approve the model. It is therefore essential for LEED to ensure that review personnel consistently deliver comprehensive assessments of models and that these individuals are provided with the most up-to-date training and resources to keep abreast of new developments in building energy efficiency.
A final proposal to effectively remedy this situation would be to provide LEED certification one year after the buildings have been commissioned. This way, both the building owners and LEED would be certain of the building performance not only in the Energy and Atmosphere category but in other measureable categories, such as Indoor Environmental Quality and Water Efficiency. I expect, though, that this suggestion would receive some opposition. Building owners may be reluctant to pay for the LEED certification process (up to $150,000 in additional costs) knowing that there is a possibility that they may not get the level of certification they set out to achieve (if any level of certification at all) because the building does not perform as expected. For this reason LEED would also be opposed to this suggestion, as the more building owners are reluctant to apply to LEED the slower business becomes.
I believe, however, that it is better for building owners to know for a fact that their certified LEED buildings are saving them energy and money (providing a return on investment). It is not worthwhile to simply have a nice plaque on a building if the building is actually consuming more energy than what was budgeted for. Such a building costs the owner more in the long run—far more than the process it took to get the plaque on the building. Additionally, LEED certification post-construction also prevents any false advertisement to the public. As it stands today, a building plaque that says LEED Platinum may very well be mis-LEED-ing.