By Chad Edmondson
What cooling construction materials are best suited for HVAC applications? It’s a question you will have to address if you are designing a cooling tower system or selecting one for a replacement. The answer will vary of course, depending on the client’s budget, application, location, and access to service. Just remember that it is selection of material for the cold-water basin that is the most critical. So let’s start there.
The cold-water basin is located at the bottom of the tower and collects the water after it has flowed through the fill. Since the tower literally rests atop the basin, if it corrodes or deteriorates, there is a good chance the whole tower will have to be replaced. So material selection (along with service and water treatment) are very important.
Cold-water basins, which can be located above or below grade, can be made of galvanized steel, fiberglass, stainless steel, or concrete. If it is an on grade tower installation, we have found that concrete basins perform the best in terms of corrosion resistance and lifecycle. However, depending on the budget and location, concrete may not be an option. If that’s the case, the chart below summarizes all the options.
If you select a metal cold-water basin, keep in mind that filtration (e.g. a sweeping system) is a must to keep the basin clean. Otherwise, sediment may interfere with your chemical treatment and the metal (galvanized or stainless steel) will corrode.
Hot Water Basins
Crossflow towers, but not counterflow towers, also have “hot water” or “distribution” basins. This is basically a shallow pan that sits above the tower fill. Hot water from the condenser loop flows into the hot water basin and then drains by gravity into the fill below via a multitude of small nozzles in the bottom of the pan. Counterflow towers do not have hot-water basins since they are designed with pressurized hot water nozzles to distribute the water to the fill. Hot water basins are typically made either of galvanized steel, stainless steel, or FRP. Budget will determine which material you choose.
Cooling Tower Structure
The structural frame of a cooling tower is typically made of galvanized steel, but stainless steel is also an option. Fiberglass reinforced polyester casing panels, steel, or stainless casing panels for extra corrosion resistance are all options. Louvers are typically fiberglass but are available in G-235 hot-dip galvanized steel, thermosetting hybrid polymer, and stainless steel.
Typically, we have found that for overall cooling tower lifecycle cost a stainless-steel factory assembled tower (no basin) installed on top of a field-constructed concrete sump/basin offers the longest life. If initial cost is a concern then a polyurethane coated cold water basin provides excellent corrosion resistance at a more affordable price.