Reserve Base Reaches for the Sky
The innovative design of a new training facility supports net zero energy aspirations at Parks Reserve Forces Training Area, Calif.
By Bari Ewing, P.E., CEM, BEMP, LEED AP BD+C, and Bobby Morris, AIA, NCARB, LEED AP BD+C, M.SAME
Axonometric view of the U.S. Army Reserve Training Center at Parks Reserve Forces Training Area, Calif., illustrating passive design strategies: shading (green and gray), natural ventilation (blue) and thermal mass (red). Images courtesy Mason & Hanger
New federal buildings must meet extremely rigorous energy efficiency and sustainability standards. The design of the U.S. Army Reserve Training Center at Parks Reserve Forces Training Area in Dublin, Calif., illustrates just how demanding these standards have become.
The design team developed solutions so that the new Training Center could meet, and sometimes even exceed, these stringent requirements. The Army Reserve also desired that the building satisfy requirements for LEED Silver. The result is an innovative combination of passive energy systems with radiant flooring, natural ventilation, walls and windows designed to facilitate natural ventilation, moisture resistance and daylighting.
The architects and engineers introduced these solutions to the project’s stakeholders during a sustainability charrette. The sustainability charrette continued for two days, followed six weeks later by a design charrette. Sessions fostered detailed discussions of all aspects of the building’s design. At the conclusion, stakeholders at every level agreed that the proposed design would satisfy their requirements while simultaneously facilitating the base’s goal of moving toward a net zero future of zero net energy consumption and zero annual carbon emissions. The project’s many stakeholders included office workers expecting a bright, comfortable workspace; maintenance workers, who wanted a facility that was easy to maintain; the U.S. Army Corps of Engineers (USACE), the client authorizing compensation; and the officers up the chain of command making funding decisions about the project.
What made the project’s innovate design possible is the regional climate. Parks Reserve Forces Training Area’s location in Northern California, outside San Francisco, features moderate temperatures, plenty of sun and a consistently strong breeze—more than 16-mph. The region’s climate makes it possible to use a combination of energy producing technologies, including passive cooling and heating, solar heating, solar hot water, radiant flooring and natural ventilation; all these are key features for developing a passive energy conservation strategy. However, because a massive solar array is being installed adjacent to the Army Reserve Training Center, plans for additional solar energy generation were unnecessary. The building’s passive solar and other energy reducing methods will facilitate the base’s overall net zero energy goal.
Axonometric section showing the thermal mass wall (red) receiving solar gain through atrium glazing.
The design team also had to factor in how occupants would deal with a different way of working. For the Training Center’s low energy design to work, office occupants would need to accept a different layout of their working spaces. For natural ventilation, for example, the space requires an open office design to facilitate the flow of air. In the Army Reserve, an individual’s rank determines the amount of square feet of office space he or she will be allotted. This often involves privacy walls. The new plan necessitates changing attitudes about going from a traditional closed office environment to occupying a spacious, open office environment—one without walls.
The overall building would use a split design, with a single story on one side and three stories on the other. The shorter side would employ a conventional heating and cooling system because there are no air intakes on the first floor of military structures. The taller side would implement passive systems by using a massive atrium wall made of heat-trapping concrete to help heat the office area as well as drive the natural ventilation and cooling through buoyancy.
The charrette also presented the concept of dual control systems: one for the microclimate and one for the macroclimate. Direct digital controls (DDCs) would control the macro system by opening and closing windows based on variables present in the indoor and outdoor climates. Occupants control the microclimate by allowing users working within a 10-ft radius of a window to open it manually. The passive heating and cooling systems ensure that manually operated windows do not waste electricity used to power conventional heating and cooling systems.
As part of its agenda, the charrette elicited questions from Army Reserve stakeholders about which elements of the design they had concern about, such as the manually operated windows and the building’s required level of maintenance. Since the taller side of the building does not include a mechanical HVAC system, manually opening windows would not endanger the passive energy concept by wasting electricity or natural gas. As for maintenance, the design would produce a building that was very easy to clean and repair. There would be no mechanical system to maintain, and the concrete flooring and finishes would have a much longer life than carpet or even tile.
USACE requires a lifecycle cost analysis of any component or system that costs more than 1 percent of a project’s cost. The lifecycle cost analysis of the radiant floor heating system involved comparing costs of radiant flooring to three other heating methods. Radiant flooring integrates hot water coils that radiate heat under the floor—this results in no forced air and no ceiling required to hide ductwork. The comparisons included variable air volume boxes with hot water reheat to provide heated air to each zone; geothermal, using a water-to-water heat pump for low temperature hot water and radiant heat; and the simple device of an electric fan coil unit. Lifecycle cost comparisons included first cost, annualized maintenance cost and annual energy cost. While geothermal compared closely to radiant floor heating in its annual cost of energy, the total lifecycle cost of the radiant floor method, at $953,075, was more than $200,000 less than the next lowest lifecycle cost comparison, the simple electric fan coil unit. In addition to the clear cost advantage, radiant heating was an ideal choice for the facility’s abundant natural ventilation as it allows spaces to be free of fans and ductwork.
A passive energy efficient building contains a delicately balanced, interdependent network of components. If something in the heating system changes, something else will change in response. A design must create and preserve this balance. An example of such a balance is the quality of the windows chosen for the facility. These allow more solar heat transfer than accepted standards recommend. Heat transfer into the building is its source of heat. The engineers first created an energy model to test the concept with windows carrying various heat-transfer ratings and then specified the windows with the rating that worked best. During the summer, exterior shades are used to block the higher sunlight, effectively disabling the heat transfer effect.
CHALLENGES AND OPPORTUNITIES
Computational Fluid Dynamics model of plan view indicating air flow, speed and temperature throughout the Training Center.
Fleshing out the design after the charrette required solutions to technical and design challenges. Technical challenges involved controlling the wind coming into the building and designing a natural ventilation system. Design challenges included sizing the wall areas correctly, finding moisture-resistant finishes and designing the daylighting controls.
Department of Defense structures must adhere to an anti-terrorism design protocol that requires air intakes to be at least 10-ft high, as a defense against chemical and biological attacks. Since manually operated windows can act as air intakes, the split-level design places no operable windows on the first floor and uses first floor space on the taller side for storage. The single story side contains offices, hence the need for conventional heating and cooling there.
At first, the designers assumed that orienting the building at a right angle to the wind was the best way to implement a natural ventilation system. However, modeling that building orientation showed that the ventilating breeze could be strong enough to blow papers off desks. Engineers then used the modeling system to test different rotations away from a perpendicular orientation. They discovered that at a rotation of 15° the ventilation system worked, and the windows still received plenty of winter sun for solar heating.
To design a natural ventilation system, engineers modeled an empty rectangular box and tested the ventilation produced by various shapes of roofs. Through this approach they determined that a mono-slope roof allowed outside air flowing in through several low windows to move through the entire space and exhaust high up on the other side of the building. The warmer interior air heated the incoming air, causing it to rise. At the top of the building, the ventilation stream followed the path of least resistance through the exhaust openings so it could continue to rise. As an added benefit, the ventilation system helps to condition the inside air by picking up heat and removing it during the warm Dublin summers.
Computational Fluid Dynamics model of plan view indicating air flow, speed and temperature throughout the Training Center.
To design ventilation for the winter (that is, without open windows) the engineers worked with the number and placement of the intakes and trickle vents near and through the floor. Minimal ventilation is required due to the radiant floor heating. Engineers also molded an airflow that maintained comfortable temperatures in the various spaces and kept out rain and air currents that were too strong.
The moderate climate enabled the designers to use money saved on the wall construction with less insulation to invest in a greater number of windows. In this climate, the outside temperatures are similar or close to the temperature goal inside the building. So while most building designs must minimize heat transfer through the walls, that cost was unnecessary. The wall design is just tight enough to comply with the building code without exceeding it.
Moisture resistant finishes were important in the design because the natural ventilation system can introduce moisture into the building, especially when it is humid or raining. The concrete flooring resists moisture as do the modular aluminum framing and glazing systems in the specification for the small number of private offices in the facility.
The facility’s open design for most of the office space, and the transparent glazing used for the private offices, provide clear views of the floor and allow natural light in. Due to the extensive use of glass walls, separate fire and smoke alarms were not needed in each individual office, but only in the main areas. The concept both saves the expense that would normally go into a more elaborate fire and life safety system and eliminates the cost of maintaining such a system.
The lifecycle cost of efficient lighting methods is aided significantly by the use of daylighting. The high-glazing percentage reduces lighting energy needs with windows that allow for greater light transmittance. Natural ventilation further reduces energy consumption in this climate, and in addition, sensors on the lighting system turn off the lights when sufficient natural illumination fills the building. The first cost of daylighting methods for this building was $41,875, with an energy savings $2,856 and a simple payback in 14.66 years.
Reaching for the lofty goal of achieving zero net energy cost for Parks Reserve Forces Training Area, the Army Reserve has moved toward that aim by approving a predominantly passive energy design for its new Training Center. Using combinations of passive energy technologies, including passive cooling and heating, solar heating, radiant flooring, daylighting and natural ventilation, the new facility will lead the way for other bases to create energy efficient environments—and meet, and exceed, rigorous federal standards.