Wednesday, October 7, 2009

How much energy do green buildings really save?

LEED continues to receive considerable attention in the media since it is the country's leading green building certification program. However, questions about the program's true effectiveness are beginning to surface. A recent New York Times article (August 31, 2009, "Some Buildings Not Living Up to Green Label") reported that a LEED-certified Federal Building in downtown Youngstown, Ohio was "hardly a model of energy efficiency." In fact, according to an environmental assessment conducted last year, the building reportedly did not even score high enough to qualify for the Energy Star label. This is not really "news" as the U.S. Green Building Council (USGBC) that administers the LEED program in a study last year of 121 new buildings certified through 2006 itself found that more than half (53%) did not qualify for the Energy Star label and 15% scored below 30, meaning that they used more energy per square foot than at least 70% of comparable buildings. One of the problems appears to be where the LEED points come from. The General Services Administration, which owns the Youngstown building, indicated in the Times article that points were "racked up for things like native landscaping rather than structural energy-saving features." The inferrence clearly is that perhaps the LEED criteria need re-visiting.

Interestingly, the USGBC also found from its own research that a quarter of the new buildings that have been certified do not save as much energy as their designs predicted, probably because the energy models used to predict how much energy a planned building will consume are inexact. Clearly, much still needs to be done to develop a comprehensive database of modelled versus actual building energy use information. Such a database would unquestionably improve building energy performance models.

LEED assigns credits before a building has been operated, but the only real way to know how a building is performing is to collect energy use data over time. Fortunately, as of this year the LEED program will require all newly constructed buildings to provide energy and water bills for the first five years of operation as a condition for certification.

The Canadian National Research Council also recently published an interesting study by Guy Newsham, Sandra Mancini and Benjamin Birt in August (Report NRCC-51142) that added more fuel to the fire. Their analysis of 100 LEED-certified buildings found that while LEED buildings used 18-39% less energy per square foot than their conventional counterparts in the CBECS database, 28-35% of LEED buildings used more energy. In addition, the measured energy performance of LEED buildings had little correlation with the certification level of the building or the number of energy credits achieved by the building at the time of design. This clearly presents a problem for building owners and operators who are not realizing the energy performance they were expecting.

These problems and issues have the potential to raise questions about the credibility of green building rating systems. This would be unfortunate as it could jeopardize the overall societal benefits that still accompany these rating systems. The fundamental problem in my view is that we are not giving sufficient recognition to the fact that there is a large variability between buildings (even between the same types of buildings in the same geographic location) and to do true comparisons at a statistically meaningful confidence level requires a much larger dataset than currently exists. As such, many of the comparisons (particularly against the relatively small CBECS dataset) leave much to be desired, and may in fact do more harm than good as they can be misleading. Unfortunately, the media, as expected, will often pick up the newsworthy conclusions of a just-published study, but fail to note any of the limiting conditions upon which the conclusions were drawn. As such, a top priority of our industry should be to build a much larger and more complete (and transparent) building energy performance dataset against which statistically significant energy consumption benchmarking can be done.


jr said...

Before we throw the baby out with the bath water, let's remeber that LEED is not just about energy effeciency in operations. It also includes practices that address water use, and other sustainable practices that address embodied energy. On the other hand, it is truly disheartening to see higher energy use and under-performing systems.

Mark said...

Most of the 'performance gap' between models and reality can be attributed to the assumptions that go into the models. We can model the envelope and systems reasonably well, it is humans that don't conform to our models.

The value of additional data collection is to understand how plug and process loads and actual schedules drive energy use.

If the rating systems are to accurately portray energy use, then they need to be based on real performance data and not design intent. The USGBC's Building Performance Initiative hopefully will address this issue.

Mark Stetz P.E. CMVP
Stetz Consulting LLC

joelmckellar said...

This is the first well balanced consideration of the issues behind the LEED energy use reports that I've seen! One thing I'd like to add is that before June 2007, LEED did not require buildings to do anything more than meet that ASHRAE 90.1 baseline with regards to energy use. That has since been changed to more stringent energy reduction requirements, and I suspect that future studies of buildings registered after that point will show much more robust savings.

cameron.ware said...

I hope this article gains momentum and is passed around to increase awareness of this growing problem -- before lack of action hurts the value and intention of LEED.

The latest round of LEED point definitions redefined (increased) points awarded to the thermal envelope and the use of highly efficient systems such as Insulated Concrete Form for walls or more energy efficient roof systems, etc. However, much more work in the LEED definition is necessary to award -- the corresponding reduction in A/C tonnage required for a given building as well as the corresponding reduction in amperage to the building which ultimately translates into cost and energy savings.

It will be up to our engineers and architects to be open to the thinking necessary to get by the status-quo.

Lot's of eyes are on the two net-zero energy schools now under construction in Kentucky. I would imagine if they are successful LEED points in this regard will be revisited again.

rbicknese said...

The good news is that LEED is causing people to look much more closely at the performance of buildings and causing performance to improve, increasing the transformation of the building industry to a greener and more energy efficient level. This performance is relative. It is not and never was intended to be absolute.

LEED Energy Optimization credits are tied to meeting either prescriptive standards or performance standards, the last based on energy modeling. Energy models are too often viewed as predictions of performance. THAT IS A MISTAKE that has lead to a great deal of misunderstanding. Energy models should be viewed as indicators of relative performance.

Actual energy performance will be influenced heavily by two human factors that models have difficulty quantifying: 1. Variations in occupant use, and 2. Variations in the quality of building construction, and installation and calibration of systems.

We have all come to rely on EPA ratings for automobile fuel efficiency as an indicator of a car's performance. But what percentage of people actually achieves the exact EPA rating? Not very many! We can understand that lead-footed teen-aged drivers will not achieve as high of a miles per gallon rating that easy-going drivers will achieve. Likewise, the ways buildings are used affect the amount of energy they consume.
Energy modeling systems are acceptable for LEED compliance (in part) if actual results consistently fall within something like 6-7% of modeled performance. (I apologize for being less precise on that number than I would prefer). Even so that range does not account for variables in use between modeled and actual use. Modelers understand this on both counts but for some reason critics of performance ratings do not. We would be better served by modeling systems if they offered a range of performance rather than a single number. I suspect modeling systems will continue to improve, especially to account for variables in use.

I think we can all understand that if R-16 is used in the energy model as the insulating value of a wall assembly (after taking into account typical thermal short circuits through building materials) but the contractor leaves gaps in the insulation, and/or does a poor job sealing penetrations in that wall, the performance will suffer. The poorer the installation is, the poorer the performance will be. Likewise if HVAC equipment is not properly commissioned performance will suffer.

LEED requires Fundamental Commissioning of Energy Systems as a prerequisite. It also offers additional credit for Enhanced Commissioning, but does not require it. Furthermore energy monitoring is an additional optional credit. Monitoring provides feedback for improving energy systems performance.

As an example of some connections between modeling, commissioning, use and monitoring I offer the Bick i-building (intelligent building) in St. Louis, Missouri. My firm was the architect and LEED consultant. The building is LEED-NC Gold certified and achieved the Fundamental Energy Systems prerequisite. After 4-5 months of operation the building was using more energy than modeling suggested. Through a careful review and analysis of data gathered through their monitoring system the Bick Group made adjustments in their systems that improved performance approximately 10% ABOVE that suggested by modeling. The Bick Group has been reaping those savings and all the other green benefits that LEED helped them achieve for over 3 years. Perhaps even better the building is a delightful and enriching place to be due in no small part to its superior indoor air quality and thermal comfort , and dynamic and effective daylighting.

LEED continues to raise the bar on building performance and the benchmarks it relies on with fairly aggressive increases in minimum performance levels. But again, that is the point; market transformation to a better way for people, the planet and prosperity. Onward and upward!

Ralph Bicknese
hellmuth + bicknese architects
Saint Louis, Missouri

Poor Richard said...

I'm concerned that most of the discussion here and debate in the industry completely misses the point. That is: LEED is a DESIGN/CONSTRUCTION oriented program.

The ACTUAL energy use of any building has to do with proper day to day operation, adjustment and "continuous commissioning" of the buildings.

Without competent facility management staffing, a LEED Platinum building could become an inefficient energy hog and/or IAQ disaster in a very short time.

A perfect design and flawless installation are great but they are NEVER substitutes for proper day to day building operations.

Poor Richard