Traditional direct-evaporative coolers operate by humidifying air, so produce comfort only in the arid, say, 40% of U.S. hot-summer areas, but save 60%-80% of first cost, power and maintenance compared to refrigerated cooling there.

However, new indirect-evaporative coolers which cool air dry can have directevaporative second stages and thus achieve comfort in our moderately-humid areas, perhaps another 40% of our territory which justifies seasonal cooling.

And such indirect coolers with small refrigerative second stages can create comfort throughout most of our high-humidity zones comprising perhaps 20% of our total overheated summer area, mostly shorelines and the lower Mississippi Valley.

Until mass production is achieved in the moderate and high humidity zones, the related two-stage coolers may represent slightly greater investments than conventional air conditioning 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, with long-run power costs and other trends favoring it, evaporative air conditioning clearly deserves greater use almost everywhere.

Units: Dual