Category Archives: energy modeling

Building performance investigation doesn’t pay – yet

Today I was working away on trendlogs for the under-performing LEED building, trying to figure out why air-handling units were misbehaving in various ways, when my boss startled me. “Stop working on that!”, he exclaimed. “We have to watch the budget REALLY closely on this one!” Considering that we were only 8 hours into the project, this was rather unexpected. We clearly have an exceptionally small budget to bring this complicated 150,000sf building into line with its energy model – and this is a building that has gotten the best that money can buy from the very beginning.

So if THIS privileged building isn’t worth more study, even to save thousands of dollars a year and to gain its last (necessary) M&V point, where do the thousands of other green building hopefuls find incentives for maintaining their performance goals? That is, before a dramatic energy crisis solves the problem for us?

Since we’re already discussing LEED issues, a closer look at the LEED v.3 Minimum Requirements is worthwhile, and is mildly encouraging. For new construction and major renovations, Item 6 reads:

6. Must Commit to Sharing Whole-Building Energy and Water Usage Data
All certified projects must commit to sharing with USGBC and/or GBCI all available actual whole-project energy and water usage data for a period of at least 5 years. This period starts on the date that the LEED project begins typical physical occupancy if certifying under New Construction, Core & Shell, Schools, or Commercial Interiors, or the date that the building is awarded certification if certifying under Existing Buildings: Operations & Maintenance. Sharing this data includes supplying information on a regular basis in a free, accessible, and secure online tool or, if necessary, taking any action to authorize the collection of information directly from service or utility providers. This commitment must carry forward if the building or space changes ownership or lessee.

While this commitment is still technically voluntary, certification can be withdrawn for failure to comply. Still, the performance is not required to reach or, apparently, to even approach the performance originally predicted. Even to gain Monitoring & Verification points, it is only necessary to “Provide a process for corrective action if the results of the M&V plan indicate that energy savings are not being achieved.”

The issue of confidentiality was also broached, and real estate lawyers are already taking note. Apparently the ugly jungle of building design lawsuits has just added a fertile patch of soil. Regrettably, this has potential to delay further the all-important transfer of information from real buildings back to the design community.

Meanwhile, I was immediately reassigned to a new project: construction of a DOE2.2 energy model for a large ambitious new building, not so very different in program from the troubled LEED building. It’s in schematic design, of course, which means that a large number of important details are completely absent. Energy models are valuable tools, and this model-building exercise will surely be a useful guide for the architects. Unfortunately, it will surely not predict the actual energy performance. But it sure does have a nice big budget.


Nature calls

On September 10, the prestigious journal Nature published a commentary entitled Overrated Ratings”, in which it criticizes the LEED green building award system for falling short in promoting design of low-energy buildings.

“…as is well known in the building research community but not outside it,” the editors write, “neither LEED nor any other such rating is a reliable guide to energy performance. Labelled buildings often perform no better in energy terms than the general building stock, and sometimes worse.”

Sometimes WORSE. How is that possible? True, the original LEED system weighted energy performance rather lightly, giving nearly equal weight to site design, water and waste management, and green materials. But these should not be causing the energy use to be occasionally WORSE than average, especially since the energy performance of every LEED building must be modeled if it is to gain energy points.

Here, unfortunately, is the problem, as the editors continue: “most ratings assess a building’s energy performance using theoretical projections from engineers’ models, but don’t measure its real, post-occupancy performance, which often can be much poorer.”


My colleagues and I have just begun work on a project with this exact problem. The building was awarded LEED Gold two years ago, in part through energy points gained with a careful, thorough DOE2.2 model that used the best information available at the time (i.e., pre-occupancy). Two years later, this beautiful building is using about 50% more energy per year than modeled. Fifty percent. This is not the kind of error that results from occupants squeezing a few more people into a space than projected, or cranking the thermostats up a few degrees. This is a sign of pervasive use of building spaces and systems in ways very, very different than intended by the owner, designed by the architects and engineers, and yes, simulated by the modelers.

Why are we doing this? Because, thank goodness, LEED 2.2 had a “Monitoring and Verification” point that this building needed to keep its Gold label. The teeth are sharper in LEED v.3.

We don’t know what the problems are, yet, though we have some preliminary ideas. We believe they will be relatively easy to identify, though we fear that some of them result from conflict between design intents and occupants’ reality. Most of all, though, we hope that this effort will become part of a new, larger, and sustained national effort to evaluate the performance of not just LEED buildings, but all new green buildings, and vast numbers of green-ing existing buildings as well.