The largest cost driver of factory assembled cooling towers is the primary material that forms the casing of the cooling tower. This material not only contains the water being re-circulated through the cooling tower but also must structurally support a mechanical fan system, internal components, and water weight including a sump full of water. There has generally been a trade-off between the long-term durability achieved through the choice of materials of construction of the casing and overall cooling tower cost.
The less expensive galvanized metal cooling towers are the most susceptible to corrosion and, therefore can have a shorter life than stainless steel towers. The Galvanizing of steel will delay the corrosion of the underlying steel because it corrodes preferentially to the steel. However, once a section or sliver of the zinc galvanizing has become compromised the thin sheet metal underneath can corrode quickly.
Some manufacturers have been promoting a Hybrid cooling tower, which consists of a stainless steel sump or basin and galvanized metal on the upper walls. This provides better durability than the all galvanized construction and is not nearly as costly as an all stainless steel cooling tower.
FRP (Fiber Reinforced Polyester) has been used as a cooling tower casing material for some time. Pultruded FRP when made heavy enough can handle cooling tower loads and provide very good corrosion protection. Good quality FRP towers, however can be near as expensive as stainless steel towers. Low quality FRP cooling tower panels have been imported from the 3rd World manufacturing locations which can be priced as low as any cooling towers but are not of a quality to be considered herein which are manufactured in the United States.
A paradigm shift has occurred with the development by Delta Cooling Towers of a full product line of unitarily molded corrosion proof engineered plastic (HDPE) cooling towers. The significance of this advancement is a break off the traditional trade-off between durability as measured by corrosion resistance and cost. Excellent corrosion protection is achieved at costs comparable with lesser corrosion protected cooling towers. Unlike other cooling tower manufacturers that use a range of materials of construction at various price points depending on the materials of construction, Delta Cooling Towers only offers one material of construction for the casing.
Delta Cooling Towers are molded in an engineered plastic (HDPE) that forms a casing that is a unitary structure without joints or seams. All other manufacturers put panels together, generally of metal (galvanized or stainless steel) or FRP, to create the cooling tower casing. The Delta unitarily molded towers can be up to 23 feet long and 10 feet tall. These developments were achieved by substantial investment in proprietary molding capability allowing the product to be competitive on unit cost with the less durable galvanized steel towers while providing the long-term durability equal to or exceeding the stainless cooling towers.
Download Properties of Construction here.