Project Description

The U.S. Environmental Protection Agency National Computer Center demonstrates that a green building can compete financially with a conventional building. Completed within conventional budget constraints, the Computer Center achieved a LEED-NC Silver rating in early 2005.

To offset some of the environmental impact of the building's massive quantity of data-processing equipment, a significant portion of the roof is covered with a photovoltaic array. Besides generating electricity, this "solar roof" also assists in mitigating unwanted radiant heat gain. The remaining roof area is covered by a reflective, white, Energy Star compliant membrane.

A large amount of south-facing, vertical glass allows daylight into office spaces and provides passive solar gain for winter heating. A central atrium provides direct daylighting in the lobby and indirect daylighting in offices directly facing the lobby. Indoor air quality is monitored by carbon dioxide sensors, and ventilation is adjusted as needed. Printing and copying rooms have dedicated ventilation. The preservation of natural site features was an important priority in determining the building site. In addition, ten acres were designated permanent open space. Approximately 82%, by weight, of all construction waste was sorted and recycled. A design-build approach was adopted as the best method for assuring that the design intent would be achieved. This is particularly important when considering the design's many nontraditional features. Conspicuous barriers were erected during construction to protect site features, such as stands of trees, that were to be preserved.

Sustainable Features

• A "solar roof" covers an area of approximately 15,000 square feet. The solar roof consists of a 94-kilowatt (peak) photovoltaic (PV) array made up of 2,185 individual tiles. Each tile is a stacked composite made up of a layer of rigid polystyrene foam insulation board, a wiring chase and airspace, and a PV module. Each tile interlocks with adjacent tiles and rests on top of the membrane-covered roof deck with no mechanical penetrations.

• The output of the PV array offsets approximately 5% of the building's electricity consumption, which is estimated to be approximately twice that of a conventional office building of equivalent size, due to the large demand from data-processing equipment.

• The flat roof is covered by a highly reflective, Energy Star compliant, white membrane (reinforced thermoplastic polyolefin) that reduces unwanted heat during the cooling season.

• A duct system is installed in the building for heating and cooling distribution and for ventilation. An economizer provides additional cooling efficiency by introducing outside air when conditions are suitable. A building automation system controls all of the heating, cooling, and ventilation functions and it is programmed for nighttime setback of these functions and lighting. Carbon-dioxide sensors control the amount of ventilation, so that the introduction of fresh air and the exhaust of stale air occur when most needed, namely during high levels of building occupancy. Variable-frequency-drive pumps and blowers are used on water and air distribution systems.

• Many of the office spaces are located on the front (south) side of the building to take advantage of passive solar thermal gain and daylighting. An extensive amount of vertical glass is used, and summer shading is provided by externally mounted aluminum shading structures. A central, two-story atrium provides direct daylighting for the lobby and indirect daylighting for those offices directly adjacent to the lobby. The atrium also provides passive solar heating in the winter.

• Space heating is provided by a natural-gas fired boiler that supplies hot water to heating coils. The building has no installed chiller; instead, it is linked, via underground piping, to a central water-chiller system that serves multiple buildings on the Research Triangle Park campus.

• High-efficiency fluorescent lighting is used throughout the building, in combination with occupancy sensors, to prevent lighting empty rooms.

• In 2004, the EPA entered into a three-year agreement with an energy services company for the purchase of 100 million kilowatt hours worth of green power in the form of renewable energy certificates. These certificates support biomass power generation from paper pulp facilities. This agreement offsets all of the electricity used by the entire Research Triangle Park campus.

• A building automation system controls and optimizes heating, cooling, and ventilating functions while also managing fire safety, lighting, and security in the building. The system is also able to track maintenance intervals and provide equipment-malfunction alarms.