(continued)

The Photovoltaic System

Zion National Park is located in a remote area of southern Utah, where electrical power is not always reliable. So the NPS required an uninterrupted power system (UPS) for the building.

Because the battery storage and electrical components were already a part of the UPS, designers could easily convert it into a photovoltaic (PV) system by adding a PV array. PV panels on the south roof (7,200 watts) provide approximately 30 percent of the electricity needed.

Some of the energy is stored in batteries. When the utility company cannot provide power, the batteries fuel the cool towers, window controllers, cash registers, and computers. The reliance on daylighting and the lack of air-conditioning have greatly reduced the electrical loads.

Using photovoltaics in combination with utility power provides a highly reliable power source. Excess power is sold back to the power company.

Optimized Overhangs

Daylighting and solar radiation enter the Zion National Park Visitor Center through the windows. The length and position of the window overhangs were determined based on the Zion Canyon latitude and weather patterns.

During the summer, when it is undesirable for the sun's heat to enter the building, overhangs shade the windows. When the sun is low in the winter, it shines under the overhangs and into the building to provide solar heat.

Trombe Walls

A south-facing Trombe wall provides most of the heating for the Zion Visitor Center. Heat from the sun is trapped between a pane of high-transmittance, patterned glass and a black selective coating. A masonry wall stores heat for release into the building later in the day.

Winter surface temperatures in the Trombe wall often reach 100 degrees Fahrenheit (38 degrees Celsius). This warm surface provides radiant comfort to visitors. Overhangs on the roof prevent the high summer sun from hitting the wall.

Thermal Mass Flooring

During the winter, the sun shines directly onto the visitor center's concrete floor, which absorbs and stores the heat. The warm floor helps heat the building and maintain occupant comfort, even after sunset. Other massive materials, such as brick and stone, also store the sun's heat and add mass to a building's interior.

The stone walls of the canyon itself demonstrate how massive materials store heat. The rock walls remain warm on cool nights after the sun has warmed them on sunny days. During the summer, the walls are cool in the morning after the previous day's heat was released during the night.

Lighting

The primary source of light in the visitor center is daylight, which enters through the clerestory and other windows. Overhangs shade the south-facing windows from direct sunlight during the summer.

The building configuration shades most of the west-facing windows and only diffuse light enters the north-facing windows. This design maximizes the amount of daylighting entering the space while minimizing glare and heat from direct sunlight.

When there is not enough daylight, the building's energy management computer adjusts electric light levels to provide only the amount of additional light required. Only energy-efficient fluorescent lamps (T-8) and high-intensity discharge lamps are used in the building.

Natural Ventilation

Reducing the solar heat gain in the summer significantly lowers the building's cooling load, so the building can often be kept cool solely through natural ventilation.

A natural stack effect induces air movement through the building when the clerestory windows are open. The building's energy management computer automatically opens these windows when cooling is needed. Ventilation air enters the building though open doors and manually operated windows on the north and west walls and above the south-facing Trombe wall.

Passive Down-Draft Cool Towers

When natural ventilation is not enough, cool towers help bring the temperature down. Water is pumped over pads located at the top of each tower. This water evaporates, cooling the air. The cool, dense air "falls" through the towers and exits through the large openings at their base.

The energy management computer controls these openings and can direct cool air into the building or out onto the patio. The only energy required for the towers is a fractional horsepower pump that circulates water over the pads. No fans are needed. Measured flow is approximately 8000 cubic feet per minute (3.8 cubic meter per second) for each tower.

Energy-Efficient Landscaping

Water from Utah's Virgin River is diverted into historic irrigation ditches located throughout the complex. The ditches run through the complex providing most of the water for the cottonwood trees and other foliage. Using this water saves energy because of water treatment and pumping costs of the potable water supply.

Energy-efficient landscaping also includes shade structures outside the building and existing trees, which create a display area that extends the space of the visitor center. These outdoor "rooms" for permanent displays allow for a smaller building design as well as lower capital and operation costs.

Federal Government Role

In the 1980s, severe budget cuts in U.S. federal funding for energy-sensitive projects placed unwelcome limitations on research and architectural experimentation. So it is especially heartening to see such a building emerge from the efforts of U.S. federal agencies.

The Zion Canyon Visitor and Transportation Center building should draw the attention of architects once again to the opportunity to reduce fossil fuel consumption and pollution. It also demonstrates how buildings need not be barriers between occupants and their surroundings.

It will be interesting to see if such energy awareness can be maintained even if federal leadership in the U.S. returns to the attitude of environmental neglect seen in the 1980s. Visitors to Zion Canyon who learn about this harmonious built environment can further the cause by sharing its enthusiasm for practical sustainability.

B.J. Novitski is managing editor of ArchitectureWeek and author of Rendering Real and Imagined Buildings.

The building was designed to blend in with its desert site. Photo: Larry Kilborn A section through the visitor center shows the operation of the cooltowers, the window overhangs, the natural ventilation, and the Trombe walls. Image: James Crockett, NPS Architectural drawings of the Zion Canyon Visitor Center display energy-efficient features and materials. Image: James Crockett, NPS The photovoltaic panels on the roof provide more electricity than the building needs. Photo: Paul Torcellini, NREL Excess electricity is sold back to the power grid. Image: National Renewable Energy Laboratory A section through the visitor center shows the operation of the cooltowers, the window overhangs, the natural ventilation, and the Trombe walls. Image: James Crockett, NPS Overhangs help keep the building cool by blocking direct solar gain when the sun is high on the summer. When the sun is low in the winter, it can shine under the overhangs and into the building. Image: National Renewable Energy Laboratory The interior of the center is largely illuminated by daylighting. Photo: Larry Kilborn   Click on thumbnail images to view full-size pictures.