Despite many challenges, “the RSF building will perform better than most of today’s energy efficient buildings and use less than half the energy used by a similar building built to code for the same budget.”
The U.S. Department of Energy’s Research Support Facility (RSF), located on the National Renewable Energy Laboratory (NREL) campus in Golden, Colorado, will be one of the nation’s most energy efficient office buildings—in fact it will be the nation’s largest net-zero energy building. Through this project, the U.S. Department of Energy (DOE) will establish a new benchmark for large-scale, sustainable commercial building design.
Despite its large size—222,000 square feet supporting over 800 employees—the RSF will produce as much energy as it consumes in a year. To achieve this net-zero energy status, the RSF offers many leading-edge features:
- Advanced windows that actually open
- A distinctive “lazy-H” shape with narrow wings to take advantage of daylighting
- A subterranean “thermal labyrinth” that mimics a cave to help heat the building
- Photovoltaic panels on the building’s roof and parking areas
- Appropriate window shading
- Advanced light-reflecting devices that direct daylight to achieve 100% workspace daylighting.
While all of these are important to this building’s extremely low energy use, the key factor in the success of the RSF was the performance-based focus of the exhaustive request for proposals (RFP). Long before the first sketch was made, the RFP set out a series of criteria the building should meet. Included in the criteria was an initial energy use target of 25,000 Btu per square foot per year (or 25 kBtu/ft2/year). This focus on energy performance guided all of the design discussions and feature decisions.
Working together, DOE and NREL developed a suite of performance goals to ensure that the RSF could become a model building. A principal goal in the RFP, energy use intensity, is rarely quantified in a building contract, even when a project is designed to be a green building. The entire RFP is available to review by visiting NREL’s Web site.
“It was critical to set the energy efficiency requirement during the initial RFP. The architects, engineers, and contractors all needed to buy into that goal before accepting the project,” said Jeff Baker, Director of Laboratory Operations at the DOE Golden Field Office.
“To work toward this kind of low energy goal, a whole building integrated design approach is mandatory,” Baker said. “All design decisions then are made with this target in mind. This encouraged the team to consider how all of the building components and systems would work together early on.”
Determining the Appropriate Goal
An energy use target of 25 kBtu/ft2/year is very aggressive. By comparison, office buildings built over the past 30 years typically use three times more energy than the RSF. Even by new construction standards, 25 kBtu/ft2/year is approximately 50% more energy efficient than the commercial energy code issued by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), 90.1-2004.
To determine the appropriate goal, researchers from NREL’s Buildings Research and Development program performed computer simulations using tools such as EnergyPlus. They also collected data from high-performance buildings nationwide to create an energy specification that could be met within a typical project budget, yet set an ambitious new energy efficiency benchmark for the nation.
In addition, the simulations pointed the way toward key strategies needed to meet the aggressive energy goal, such as the orientation, glazing areas, and the 60-foot-wide building wings to enhance daylighting and natural ventilation. The design-build team further developed these strategies and also introduced many of their own ideas. “Once we set the energy target, the rest of the design cascaded from that number,” said Ron Judkoff, Principal Program Manager for Building Energy Research at NREL.
Key Steps to Energy Efficiency
Architects and engineers incorporated many strategies and technologies that combine to save energy by emphasizing daylighting and natural ventilation. In addition to the orientation and overall design of the RSF, other key energy-efficiency strategies involve the building’s largest and most pervasive systems:
- Triple-glazed windows individually fitted with exterior overhanging shades and side-fins to reduce interior heat gain, heat loss, and glare, while allowing for daylighting.
- Light-reflecting devices that push the daylight deeper into the office spaces.
- Insulated precast concrete walls for passive climate control, including transpired solar collectors for heating.
- Also for climate control, a dynamic network of automatically controlled windows, evaporative cooling, radiant heating and cooling, exhaust air energy recovery, and heat recovery from the data center.
Achieving low energy use also required looking at common office features differently:
- Reducing kitchenettes from 1 for every 15 employees to every 20 employees.
- Using internet-tied telephones rather than standard models.
- Favoring laptop computers over PC workstations.
- Installing more energy-efficient elevators including energy recapture.
- Choosing highly reflective interior paint to enhance daylighting.
- Shutting off lights at night.
- Designing workstations with low walls for daylighting and natural airflow.
- Eliminating individual faxes, scanners, and personal printers and utilizing high efficiency Multifunction Devices.
Reaching the Energy Goal
The RFP required an energy use intensity of 25 kBtu/ft2/year at a standard occupant space density of 650 occupants in a 220,000 ft2 building. This energy use intensity target accounted for all energy use in the building, including the occupant’s portion of the data center and all plug loads. The RFP allowed some adjustment to this target if the space could be used more efficiently and could accommodate more people. During the design process, the team was able to fit 824 occupants into the building. More people require more energy, and so the energy use target was increased to 31.8 kBtu/ft2/year based on the RFP’s space density normalization procedure.
Additionally, because the data center is sized to serve the entire campus and not just the RSF, an additional energy allowance was added to reflect the exception to the project. Given these changes, the current projected RSF energy use intensity, including the full data center for all of NREL, is 35.1 kBtu/ft2/year. Despite these challenges, the RSF will perform better than most of today’s energy efficient buildings and use less than half the energy used by a similar building built to code for the same budget.
Comparison of Buildings Energy Use Intensity
Average U.S. office building:
ASHRAE 2004 code for new commercial space: 55 kBtu/ft2/year
Chesapeake Bay Foundation, Maryland: 40 kBtu/ft2/year
BigHorn Home Improvement Center, Colorado: 40 kBtu/ft2/year
RSF: 35.1 kBtu/ft2/yr, including the data center for the entire NREL campus
Design-Build Helps to Deliver at a Competitive Cost
The design-build approach required the team to find creative solutions to the RSF’s performance challenges and to accept responsibility for the building’s actual performance. The firm-fixed price contract required the team to be more responsible for the overall project cost. Because of the effectiveness of design-build, the construction cost of this high-performance building will be a market-competitive price of about $259 per square foot.
Spreading the Word
DOE would like to see more U.S. commercial buildings built like the RSF. To achieve this, DOE will share information on the project’s unique design-build strategy and key documents, including the RFP, with industry. Additionally, DOE will provide details about the RSF’s innovative features.
According to the Buildings Energy Data Book, in 2006 commercial buildings accounted for 18% of U.S. primary energy consumption. “DOE expects the RSF project to help reduce the nation’s energy consumption by changing the way commercial buildings are designed and built,” said Baker. The lessons learned with the RSF will help get the nation moving down this critical path.