Cooling towers, evaporative condensers, and closed-circuit coolers are widely used in comfort cooling, process cooling, and in industrial refrigeration systems. These devices exhibit very good heat rejection efficiency, low first costs, and they are available in a wide array of sizes and configurations, making their specification and selection relatively easy. Their unparalleled performance comes from evaporative cooling, which means the inside of the interior portions of the equipment are being constantly exposed to aerated water for the majority of its operating time. It is critical to choose the right materials of construction, not only for protecting the equipment investment and maintaining the maximum efficiency, but also for safety and structural integrity. The common materials used in packaged evaporative cooling devices are galvanized steel {hot dipped galvanized carbon steel (HDG), as well as hot-mill-galvanized carbon steel (HMG)} and 300 series stainless steel (SS). Galvanized steel has been, and still is, the dominant material, due to its good corrosion resistance and heat transfer characteristics. However, 300 series SS has become a viable alternative over the past five years, thanks to the lower metal costs due to improved control over alloy composition and other manufacturing cost reductions. Even though evaporative cooling devices have been widely used for decades, the changing back-drop of complexity and variation of water chemistry, metallurgy, and the multiple environmental restraints encountered, has resulted in neither a good understanding nor a guideline on when it makes sense to upgrade to SS versus when it is better to stay with galvanized steel.
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