The Blue Ridge Parkway Destination Center blends state-of-the-art computational analysis with state-of-the-shelf passive solar design. The Center’s mission is to orient visitors to the history, culture and resources of the Parkway and surrounding region, while demonstrating high-performance, ecological design. Located near Asheville, N.C., the facility includes exhibit space reflecting the heritage and development of the Parkway, as well as spaces for regional orientation and visitor information. A digital-immersive theater showing a high-definition film of the Parkway is a feature attraction.

Since most of the Parkway is experienced by car, creating an intimate experience with the woods, as well as allowing for the famous views, was an important design criterion. Nestled into a hill, the building evokes a “tree-house-like” atmosphere that allows visitors to experience the majestic vistas and surrounding woodlands for which the Parkway is known. The facility’s optimized passive solar design, along with a mix of other strategies, is projected to reduce energy use by 75 percent.

Climatic Response

Natural ventilation reduces the building’s cooling load in the swing seasons. Photo by Jonathan Hillyer/Atlanta.

The design was developed in direct response to regional climatic conditions. Climate analysis and preliminary energy modeling were part of the schematic design process. The summer design temperature in Asheville is 87 degrees Fahrenheit (F), and the winter design temperature is 19 F. There are 4,512 heating degree days and 748 cooling degree days, with fairly strong solar radiation in winter. In this heating-dominated climate, the use of passive solar provided an opportunity for significant energy savings. A mild cooling season with low nighttime temperatures allows for natural ventilation and passive nighttime cooling. Daylighting and energy recovery provided additional opportunities to reduce energy use.

Ideal passive solar orientation would have the building elongated along the east-west axis, but existing site topography required that the building be oriented 30 degrees west of south to minimize grading and protect existing vegetation. To maximize solar harvesting with this orientation, the south façade was segmented to form a saw-toothed plan, forming a row of south-facing passive solar Trombe walls (named for Felix Trombe, the French engineer who popularized the use of high-mass solar collectors in the 1960s). The Trombe walls were integrated into the design of the building, serving as structure, exhibit areas, daylighting elements, air distribution (both for the active HVAC system and the passive Trombe walls), and an intimate space to view the surrounding woods. The Trombe wall segments are interspersed with east-facing windows that provide instantaneous heat gain on winter mornings.

Visitors can experience the surrounding woods through the Trombe walls. Photo by Jonathan Hillyer/Atlanta.

Each Trombe wall consists of eight-inch concrete providing thermal mass, with a six-inch air-gap and a curtain wall system with insulated glazing. The sun heats the wall, causing heated air to rise in the air space. The heated air is directed into the building through vents at the top of the wall, passively drawing cooler air into the vents at the base of the wall to be heated in turn. At night, dampers close off the walls, preventing reverse thermo-siphoning (i.e., cold air from the cavity falling and entering the building at night), while heat stored in the mass walls is released throughout the night. In summer, the walls are vented at night, allowing for passive cooling.

Initial energy modeling for this project in DOE-2.2 (eQUEST v3.6) showed that space heating accounted for 65 percent of the overall building energy use, while lighting, fans and space cooling accounted for 28 percent of the other loads. Another study model, run without any HVAC system, showed that the Trombe walls added approximately 8 degrees F to a conventional high- mass building with optimized orientation, and approximately 30 degrees F to exterior dry bulb temperatures, while reducing the summer daytime temperatures even without night flushing. Unfortunately, conventional energy modeling software (like eQUEST) has some shortcomings when it comes to predicting thermal comfort from passive elements.

Enlarge this picture CFD overlay on building section showing warm air pluming out of the Trombe wall. Courtesy of Lord, Aeck & Sargent.

Passively conditioned buildings have greater variations in air temperatures and, more importantly, in surface temperatures. This results in a wider variation of comfort conditions. Conventional energy modeling programs cannot accurately represent these subtle variations in conditions. Furthermore, it was necessary to model the effects of thermal lag due to thermal mass in the building as well as thermal driven buoyancies. In order to attain a full-field solution that would be sensitive to subtle differences in Mean Radiant Temperature (MRT), air temperature, and thermal buoyancy, it was determined that computational fluid dynamics (CFD) would be necessary to fully asses the performance of the building in passive mode. CFD modeling, which was constructed in partnership with Pennsylvania State University’s Applied Research Laboratory (ARL), allowed the team to study snapshots of the building at different times of the day and year.

The CFD simulations show that the Trombe walls provide significant benefit to the building in winter, keeping the building at 30 to 40 degrees F above the outside temperature even at night. The fall simulation showed the building attaining comfort conditions completely passively. The only area of concern was the performance in summer, but with shading and night venting, the cooling load will be reduced. We estimate that the Trombe walls contribute an annual energy savings of 128.5 MBTU/yr, which is around 35 percent of the building’s heating load.

Enlarge this picture Cutaway through Trombe wall showing the integration of passive and active strategies. Courtesy of Lord, Aeck & Sargent.

Utilizing data from the different analyses, the design team selected the following mix of strategies to optimize the Center’s performance in addition to the passive solar Trombe walls:

• Increased roof and wall insulation, and 100 percent planted roof to reduce heat transfer through the building skin.
• High-performance glazing utilizing thermally broken aluminum frames.
• Appropriate orientation and external overhangs and shading devices to allow sunlight in the building in winter while blocking it in the summer. While external shades are important, good orientation is the best shading strategy.
• High-efficiency HVAC system with an energy recovery wheel for the entire building. This was a viable energy saving strategy due to the large winter heating loads and the facility’s large ventilation loads. The building also uses a 98 percent efficient modulating boiler and underfloor air distribution in the theater space.
• Radiant heating, which allows for efficient heating of the high ceiling spaces. The exhibit hall, lower floor lobby, marketing area and restrooms all have hydronic radiant heating in the floor. In spaces with high ceilings, radiant floors maintain comfort without having to heat the volume of air to the same degree as an air side system. The radiant floor reduces both heating and fan loads.
• Ceiling fans. The CFD simulation showed that warm air would stratify in the high ceiling spaces. Ceiling fans in the building move the stratified warm air back down to occupants.
• Daylight harvesting coupled with efficient lighting design (0.8W/ft2) reduced the lighting loads by 78 percent. Lighting power density is reduced using T8s and T5s and metal halide lamps. Lights are controlled with daylight and occupancy sensors that turn off the lights when the daylight is sufficient, or when the building is unoccupied.
• Natural ventilation reduces the building’s cooling load in the swing seasons.

This integrated design approach, leveraging sophisticated quantitative analysis, yielded a design with a 75 percent reduction in energy use over an ASHRAE 90.1-1999 base building. This reduction was achieved by integrating energy modeling into the design process, and using dynamic analysis tools like CFD to analyze the passive performance of the building. The CFD simulations show the Trombe walls contributing toward passive survivability by keeping the building only slightly below the comfort zone, even under extreme conditions. The building offsets its carbon footprint through the purchase of green-e certified renewable energy. Completed in January 2008, the building is tracking LEED Gold certification and is currently under review by the U.S. Green Building Council. The design team is currently working with Georgia Tech to monitor the performance of the Trombe walls.

Blue Ridge Parkway Destination Center

Location: Asheville, N.C.

Size: Two stories, 12,000 square feet

Completed: January 2008

Certification: targeting LEED Gold

Sustainable Design Strategies: passive solar system to heat the building including vented Trombe walls, an energy recovery unit, hydronic radiant heated flooring, a 10,000-square-foot green roof, lighting and occupancy sensors, daylighting and operable windows, a stormwater runoff system that captures rainwater for use on-site, and proper building siting to optimize passive solar strategies and views of nature.

Project team: Blue Ridge Parkway, the Southeast Region of the National Park Service, and the Denver Service Center; Lord, Aeck & Sargent, Inc.; Van Sickle & Rolleri Ltd.; The Jaeger Co.; Rocky Mountain Institute Built Environment Team; Newcomb & Boyd; Palmer Engineering Co., Inc.; Long Engineering, Inc.; Waveguide Consulting; Applied Research Laboratory at The Pennsylvania State University; Perry Bartsch Jr. Construction Co.