Cooling a 58,000-sq.-ft. glass atrium is a challenge in itself, but doing so in a desert environment where temperatures can reach 122 F is more problematic. That's what consulting engineer Ove Arup & Partners, New York City, were faced with in the Sandra Day O'Connor United States Courthouse in Phoenix.
With the aid of digital modeling, the firm's engineers decided to use a passive evaporative-cooling technique, rather than refrigeration. Evaporative cooling is accomplished by spraying a fine mist across a current of warm, dry air. As the water is absorbed, its humidity increases while its temperature decreases.
In the courthouse, hot air is pulled in through openings in the top of the atrium just below its roof. The air is pulled across the atrium until it meets the sixth-floor wall of the courthouse block, where nozzles above the gallery spray a fine mist of water. The moisture is absorbed into the air, cooling it, but also making it heavier. The air descends to the atrium floor. As it descends, exhaust air from the enclosed spaces and overflow air from the air-conditioned gallery balconies provide further cooling. The air then flows back outside through openings several feet above the ground floor.
Combined with other climate-control techniques such as the use of various shading devices, the system keeps the temperature 20 degrees cooler than outside on summer days. A temperature of 73 F is maintained throughout most of the year.