18-20: What is the Best Metallurgy for My Package Evaporative Cooling Device

Evaporative condensers are used almost exclusively in industrial refrigeration systems, especially with ammonia applications in the U.S. Their unparalleled heat rejection efficiency, associated with the lowest first costs, comes from evaporative cooling, which means the inside of the condenser is being constantly exposed to aerated water for the majority of its operation 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 evaporative condensers are hot dipped galvanized carbon steel (HDG) and 300 series stainless steel (SS). HDG 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. Even though evaporative condensers have been widely used for decades, the 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 HDG.