Redefining Efficiency

Redefining Efficiency

Joe David

Contemporary architectural practice faces many issues regarding the environmental impact of construction and land development. In an effort to respond to a growing public demand for environmentally focused design, architectural firms have looked to LEED to provide a means to evaluate their environmental design strategies. Current program guidelines require extensive energy modeling during the Design Development phase of a project, testing a model of the proposed design against a prescriptive code ‘baseline’. This has lead to the widespread recognition of buildings for integration of innovative energy efficiency strategies, but is primarily based on modeling completed during the pre-construction phase. The disconnect between ‘projected’ and ‘actual’ energy footprints illustrate the growing need for post-occupancy testing and monitoring as a way to accurately quantify and evaluate a building’s actual environmental impact.

LEED

The United States Green Building Council’s Leadership in Energy and Environmental “is a third-party certification program and the nationally accepted benchmark for the design, construction and operation of high performance green buildings” (usgbc.org). Since its inception in 1998, LEED has become the most recognized source for verification of a environmentally focused design. According to a recent article in Fast Company, the program has been adopted by “22 states, and 75 localities” as requirement for new construction. With over 14,000 certified buildings to date, it has succeed in marketing the concept of ‘green’ design to a the general public.

Within the LEED program lies the heavily weighted ‘Energy and Atmosphere, credit one: optimized energy performance’. This credit is a major source of the widespread introduction of energy modeling to the contemporary architectural practice over the past decade. For all buildings over 20,000 sf in the LEED program, energy modeling is mandatory. For buildings that are smaller, the alternatives are heavy in documentation and hand calculations - making energy modeling a more desirable choice for an architecture firm with schedule restrictions or a healthy budget.

Regardless of the modeling software, engineer, or building - an energy model is only useful if it can be compared to a baseline. Energy savings measured through energy modeling are established by first creating a baseline model, a version of the building with the lowest quality envelope, fenestration, and highest electrical loads allowable by a given standard, and then measuring the energy savings made in the proposed building design. In the case of LEED, the standard is ASHRAE 90.1 or local code, whichever is more stringent. Points are scored by the percentage of energy saved with the proposed building over the baseline model. It becomes critical for the score of the project that the energy gap between the two models is as large as possible - in the LEED program, there is no advantage to submitting a “conservative” model.

LEED has provided incentive for designers and clients to consider the energy footprints of their buildings during the design phase of a project. The inclusion energy efficient appliances, more substantial insulation, better glazing, and comprehensive modeling have become staples of a LEED building. Frequently however, critical analysis of the energy systems stops there. A certificate of compliance is awarded based on the projected savings demonstrated by an energy model. A building can receive LEED status without ever submitting a utility bill to reinforce the results of the model. Despite the rigor of the modeling process, and the experience of many top engineers, too many factors are variable - primarily the use patterns of occupant; often an unknown tenant.

Comparison and Prediction

Energy models consider hundreds of variables in their calculation of a space. Anything from solar orientation, climate, occupant schedule, to lighting is factored into the calculation. The reality is that if any of these variables are slightly off, the predicted energy demand of the building will also be incorrect. The odds are high that most variables will have some discrepancy from the built project or actual operating trends; even if a modeled at R-30 and built to specification, imperfections in the material or gaps in the assembly will cause variance. As a result, a model with a 20-30% accuracy from the actual operating values is considered to be successful.

The occupant is a major source of the disconnect between modeled and actual energy data. Nobody can predict their own future, needless to say, an engineer can’t predict with absolute certainty how an owner or tenant will operate a building. A building may be designed to the highest standards of efficiency, but the results are invalidated if an owner decides to buy a larger TV and stereo system to outfit their new home. Changing work schedules, annual climate trends, and plug loads can all quickly cancel energy saved in the building envelope design. Despite the precision of our modeling tools, there is no way to accurately predict the future uses of a building.

By considering the value of energy modeling beyond the context of LEED, the tool becomes increasingly useful to a design team during pre-construction. The strength in modeling lies in its ability to compare the impact of design factors with known values and consequences. For example, instead of predicting an absolute value, a model can be used to explore the impact of adding another layer of insulation to a wall. By manipulating one factor at a time, such as better insulation vs. thermally broken glazing, the design team can make informed decisions about where to invest time and money. The advantage of using an energy model is the ability to accurately compare the performance of multiple design iterations of the same project. By analyzing multiple solutions side by side, a designer can say ‘we decided to use window x on the south facade because it performed better than the same building with window y’. An energy model should be used to determine the delta between various schemes, not predict an absolute energy value.

Local Examples

With eighty-five LEED certified buildings to date in the Seattle area (usgbc.org), the majority opting for energy modeling during design, there is a wealth of energy data that has been collected on new construction in our community. Additionally, all buildings in the area are connected to gas and electricity meters, which provide actual fuel consumption data. Often, the modeled value is used purely to achieve a LEED score, and then filed away - while the building owner is left with an ‘efficient’ building that operates at a completely different value.

The City of Seattle has mandated that all new construction meets LEED Silver standards. This means that within our city there a number of public buildings that have both an energy model and accessible energy records. The 2005 Seattle PI article ‘Seattle's new City Hall is an energy hog’ brought light to the disconnect between ‘projected’ and ‘actual’ energy consumption in Seattle. The article outlines how the new city hall (BCJ arch and Bassetti arch), completed in 2004, used significantly more energy than its larger predecessor. According the the article “the new building uses 7,045 kilowatt-hours of energy on average per day, compared with 5,940 kilowatt-hours per day in the old place.” The building received a LEED gold rating. Although the program promoted environmentally focused daylighting and material strategies in the building, its current method of energy calculation failed. The Seattle City hall begins to illustrate the difficulty of designing energy efficiency for a large, undefined, user group.

The Alley 24 project (NBBJ arch, Flack + Kurtz eng.) was completed in 2006 in the South Lake Union district of Seattle. From the outset, the entire design team rigorously pursued the goal of energy efficiency. Energy modeling projected an Energy Use Index value of 42.8 (kBtu/sqft/yr) for the building. The EUI value is an effective way to quantify the energy consumption of any building, regardless of its fuel type. This value is well below the Commercial Building Energy Consumption Survey average value of 60 kBtu /sqft/yr, which compares similar buildings in the same climatic region. After the first year of operation, the actual EUI was 45.8. The design team attributes this strong correlation to a widespread understanding by the tenants (who happen to be the architects) of how to efficiently operate the building.

By comparing the two examples, it becomes clear that operational trends by the occupant ultimately determine how effective energy efficiency strategies will be in reducing a building’s environmental footprint.

Alternatives

Energy efficiency should be defined by actual energy consumption. Emphasis should be placed on first year energy consumption - building owners seeking LEED would provide utility documentation following the first year of occupancy. This would free the energy modeling process from the burden of generating ‘hard values’ and allow the model to used as a tool for iterative comparison. Additionally, it would hold all members at all levels of the building accountable for efficiency. The design team would seek to design a building that is easily operated and well detailed. The construction team would be motivated to construct a building that performs well. The owner / tenant group will be educated as to how to operate their building. Ultimately, more people will be engaged in the process of energy conservation - and energy consumption will actually be reduced. With engagement at all levels; design, construction, and occupancy, the disconnect between projected and actual will be closed. Post occupancy data will be the best evaluative tool that a contemporary design firm will have in promoting environmentally focused design.

Energy modeling is a critical tool in determining the role contemporary architecture plays in the future of our environment. It is important that we understand the tool’s strength as a comparative calculator, rather than a prediction of the future. We need to look less at the ‘projected’ energy values from energy models, and focus our attention on how changes in the building envelope and orientation effect the efficiency of the building. Because energy values are highly dependent on user groups - it is impossible to accurately predict building performance. However, it is possible make educated decisions about how material combinations will perform in specific locations. Current energy assessment for new construction places too much emphasis on the energy model, and would achieve far more by focusing on the actual amount of carbon footprint of our built environment.

Sources

Kamenetz, Anya. "The Green Standard?". Fast Company December, 19 2007:

"LEED Projects & Case Studies Directory". United States Green Building Council. December 2009 <www.usgbc.org/LEED>.

Mulady, Kathy. "Seattle's new City Hall is an energy hog". Seattle Post Intelligencer July 5, 2005: 1-2.

NBBJ Architects, "Alley 24". AIA code GREEN Sept. 20, 2007: 1-16.

Rosenbaum, Marc. "Understand the Energy Modeling Process". The Pittsburg Papers 2003: 1-6.