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Green & Sustainable Construction

Building Program for Green Design

The building program is a document conveying the conditions and requirements of a project. Along with specifying the number of square feet of different types of space (office, assembly, laboratory, etc.) and the need to meet code requirements, the program should state clear and quantitative sustainability performance goals. For example, the building program may specify a desired LEED level (Silver, Gold, Platinum), or it may specify a maximum dollar amount per square foot per year operating cost. Other goals frequently described in the program relate to achievement of a project that is beautiful, safe, reliable, or comfortable, or that provides superior air and light quality.

Some organizations, such as federal agencies, have developed their own architectural guidelines regarding sustainability that would be referred to in the building program. The building program would also document the energy-related needs of users—a critical first step in designing systems to meet those needs efficiently, and an indicator of the suitability of various renewable energy sources.

Goal-setting should be considered a team activity. Team members must proceed with a keen awareness of, and commitment to, project goals. This is much more likely to happen if they have a sense of control by sharing in setting goals and also in determining how success will be measured. If a goal is stated very generally, as “to minimize life cycle cost through sustainable design principles,” it would be difficult to judge whether it was met in the end. This is why a more quantitative goal could be more useful.

Energy performance goals can be set with different objectives. Annual energy use per gross square foot (BTU/SF/year) is a common metric among federal projects because that is the way progress toward statutory goals is tracked. Shortcomings of BTU/SF/year as a measurement standard are that BTUs supplied by different fuels have different costs, and there is no differentiation between time-of-use or demand rates.

Another option is to specify an energy use goal as a certain percentage less than that required by code. For example, a goal might be to use 25% less energy than allowed by 10CFR434/435 for federal projects, ASHRAE 90.1 for commercial buildings, or the California Title 24 energy efficiency standards. A useful metric is annual operating costs ($/year), which accounts for costs of different fuels and time-of-use and demand savings, and integrates well as a figure of merit with all other annual costs, such as operation, maintenance, water, and disposal.

It is important to use the same yardstick to measure performance as was used to set the goal in the first place. Disputes often arise when goals set using a computer model are compared to actual utility bills. There are many variables, including schedules, occupancy, and plug loads, that affect energy use after a building is occupied. These are outside of the designer’s control. Although the performance of the building will ultimately be evaluated by measuring the actual resource use (such as utility bills) of the completed building, the performance of the design team should be evaluated by simulating the final design with the same computer program and uncontrolled parameters (weather file, utility rates, occupancy, schedules, plug loads) that were used to set the goal.

How are the energy goals set before anyone knows what the building looks like? One approach is to model a default building in the shape of a shoebox with the same floor area and number of floors, the same occupancy schedules, and the same kinds of space (office, circulation, kitchen, meeting rooms, storage, etc.) as called for in the building program. First, a reference case is defined to serve as a benchmark with which the performance of the evolving design will be compared. For the reference case shoebox model, the properties of walls, roofs, windows, and mechanical systems are the minimum required by applicable codes. The annual energy performance of the reference case shoebox model is evaluated using climate data and utility rates for the site. Then a suite of energy-efficiency measures is modeled using the shoebox to determine which strategies are most effective. For example, if evaporative cooling is effective on the shoebox model, it is likely to be effective for the actual design. Measures are evaluated in combination with each other to account for interactions.

The shoebox model with the most cost-effective package of measures implemented provides an estimate of what should be achievable in the design, but the goal is usually set above this level. For example, a reference case might be 100 KBTU/SF/year, the shoebox with all ideal cost-effective measures implemented might be 30 KBTU/SF/year, and the actual goal for the project might be set at 40 KBTU/SF/year, a reasonable goal for the design team. The Energy-10 computer program has been developed especially to implement this pre-design analysis and to aid in setting energy-use goals.

Andy Walker, PhD, PE, the author of this article, is senior engineer at the National Renewable Energy Laboratory.This article was adapted from Green Building: Project Planning & Cost Estimating, 3rd Edition, available through RSMeans.


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