The myriad commitments created by the Energy Policy Act of 2005, Executive Order 13423—Strengthening Federal Environmental, Energy, and Transportation Management and the Energy Independence and Security Act of 2007 are driving the design and construction of Department of Defense (DOD) facilities to Leadership in Energy and Environmental Design (LEED) Silver, or higher, levels of certification. Sustainability goals that include lifecycle costs, long-term maintenance and operation, and thresholds of reduction in energy intensity and water consumption are all crucial in the successful design and construction of DOD facilities.
Three critically important strategies in meeting these goals are incorporating sustainability as a project goal from the beginning; using energy modeling to assist in determining appropriate materials and systems; and considering the building holistically when targeting reductions in the energy budget.
The earlier major design decisions are made, the smaller the financial impact. This is particularly true in focusing on sustainability, as changes often have significant impact on the energy budget. These same changes, if made later in the design process, can negatively impact the project budget.
A prime example of solid early decision making is the Tyndall Air Force Base, Fla., Fitness Center & Energy Demonstration Project. Construction of the $18.5 million, 75,278-ft2 fitness center is nearing completion, and it is anticipated that it will exceed its LEED Silver target by achieving LEED Platinum. The two-story building features a full-sized gymnasium, two intramural basketball courts, three racquetball courts, a cardiovascular/weight room, two group exercise rooms and a wellness center. A charrette was held daily early in the design process to address methods of minimizing energy and water use while maximizing indoor air quality and achieving LEED certification.
Simple changes to the original design paid big dividends in the energy budget. The original design oriented the long sides of the rectangular floor plan east and west. By simply rotating the building, the team was able to drastically reduce direct sunlight and solar heat gain. Exterior slatted sun shades on the south-facing windows permit users of the facility serene views of the Gulf of Mexico and beaches while limiting solar gain. The building is projected to use 34 percent less energy annually than a comparable non-LEED building, with at least half of the savings attributed to passive elements. This means Tyndall Air Force Base will pay 40 percent less in annual energy costs for the fitness center than a comparable facility.
David Strain, Air Force Team Leader and Project Manager for the U.S. Army Corps of Engineers Mobile District, valued the decisions made early in the facility design. Strain said the key to designing and constructing a LEED-certified project is recognizing “that it does require time and money to take the extra steps, but as long as you budget for it from the outset and have buy-in from the entire team, including subcontractors, you will achieve LEED certification successfully. We’re paying premiums for long-term energy savings, but given that we are responsible for the long-term costs of the facility, unlike developers in the private sector, reasonable payback on the investment makes good sense.”
The fitness center’s large, north-facing windows allow indirect north daylight into the center. Photo sensors will measure available daylight and maintain light levels by dimming the artificial light systems, resulting not only in reduced lighting demand, but also a reduced HVAC load, which reduced construction costs. The lighting power density for the building is approximately 23 percent below the maximum allowed by ASHRAE 90.1-2004 standards, yet still provides adequate illumination for all of the spaces. The design also includes three north-facing clerestory windows in the gymnasium, running the width of the space and introducing abundant levels of natural light.
The fitness center design includes a three-stage domestic hot water system which incorporates a solar collector heating system, a second tank that recovers condenser heat from the one-third-capacity air-cooled chiller and a high-efficiency hot water boiler, should demand exceed the first two “free” systems.
Modeling for Success
The second strategy for satisfying sustainability-related mandates is using energy modeling software to evaluate building systems and materials. Key information about the building, including geographic location, size and the functions it will perform, are used to develop an energy budget. Making large-scale design decisions early and committing to them helps determine the energy use from the outset. Using energy modeling as early as pre-program verification provides design-build teams competing for DOD projects with a manageable process to determine strategies that will comply with the cost and energy models simultaneously, increasing the likelihood of team success.
The Global Hawk hangar project at U.S. Naval Air Station Sigonella, Italy, where the climate is comparable to that in the southern U.S., provided a unique proposition for a design team from U.S.-based RLF Architects and Engineers. The facility, which includes a 46,000-ft2 hangar bay, was required to achieve a 30 percent energy reduction over an equivalent building constructed to ASHRAE 90.1-2004 standards to comply with the Energy Policy Act of 2005. This was a particularly challenging goal for a facility that is essentially an open bay as aircraft are rolled in and out.
Managed by the Naval Facilities Engineering Command Norfolk District, the hangar requires nearly a clean-room atmosphere to protect the expensive and complex electronics that control the unmanned reconnaissance aircraft. Preliminary thought by the design team was that a chilled water system had the greatest potential for achieving the energy goals; however, following an energy modeling study, it was apparent that the most efficient system was a simple air-cooled split DX system, which would require no energy to move chilled water. Because Global Hawks fly during the day, the hangar doors are seldom open during the heat of the day, a key factor in energy model’s projections.
The Big Picture
The third key to improving energy performance in a building is to reduce energy demand. The use of an energy model identifies the major users of energy, enabling the design team to focus its efforts. Typically, for commercial and institutional buildings, lighting, process loads and ventilation consume the majority of a building’s energy. In most cases, the building envelope has a relatively small impact on energy use. When evaluating the envelope, the most significant thermal envelope element usually is fenestration. In the north, the major issues are thermal conductivity, positioning and sizing for passive thermal gain in the winter. In the south, the effect of direct solar radiation heating the building contents must be addressed.
Successful project teams seek to reduce a building’s energy demand first and defer decisions on the HVAC systems once they have reduced the load that the HVAC system has to address. Suppose, for instance, a 30,000-ft2 building design with greater than necessary internal lighting, lots of direct south-, east- and west-facing glass with poor solar heat gain performance. This building might have a peak load of 100-T of air conditioning. To make up for that high demand, the mechanical engineer will design a very high-efficiency—and relatively expensive—HVAC system, operating at 0.7-kW/T. The peak load for the HVAC system will draw 70-kW of electrical power.
Take that same building, change its orientation, add external shading, reduce the internal lighting power density, add daylight harvesting for the spaces with exterior exposure and use high-performance solar heat gain performance glass. These changes could reduce the peak air conditioning load to as little as 70-T, immediately saving money. Instead of using extremely high-efficiency (and high-cost) equipment, the mechanical design might call for a system efficiency of 0.9-kW/T. The HVAC system peak power demand drops to 63-kW, resulting in savings in both initial and operating costs.
Kim Shinn, P.E., LEED AP, is Principal and Mechanical Engineer, TLC Engineering.