Evaporative cooling: A nationwide low-energy alternative

Traditional direct evaporative coolers operate by humidifying air, making them suitable in the 40% of the United States with hot, arid summers. These methods can save 60%-80% of first cost and power and maintenance costs compared to refrigerated cooling there. However, new indirect evaporative coolers that cool air without humidifying it can have direct evaporative second stages and thus achieve comfort in our moderately humid areas that constitute perhaps another 40% of our country. Such indirect coolers with small refrigerative second stages can create comfort throughout most of our high humidity zones make up perhaps 20% of our total overheated summer area, mostly shorelines and the lower Mississippi Valley. Until mass production of two-stage coolers is achieved, in the moderate and high humidity zones these related two-stage coolers may cost more than conventional air-conditioning units but should save about 40%-50% and 20%-25%, respectively, in maintenance and power costs. These savings increase where extra ventilation is needed, where summer peak demands create power price penalties, and where the indirect first stages can also recapture waste heat in winter. Today, favored by long-run power costs and other trends, evaporative air-conditioning clearly deserves greater use almost everywhere.