Niagara’s evaporative heat exchangers, aftercoolers and condensers are generally termed “Wet Surface Air Coolers” (WSAC).

Unlike conventional open-circuit cooling towers where the water is exposed to airborne contaminants (dust, dirt, algae/biological organisms) that can cause fouling on downstream equipment,  in a WSAC, warm process fluids or vapors are cooled in a closed-loop tube bundle (that is, the process never comes into contact with the outside air). Open-loop water is sprayed over the tube bundle while air flow is induced over this same bundle resulting in the cooling effect.   

The evaporation load for a WSAC is about the same as for a conventional open-circuit  cooling tower. However, one of the significant advantages of the WSAC over a conventional tower is a single approach to the wet bulb for the process being cooled. With a cooling tower and heat exchanger system there are two approaches; one approach in the tower and the second approach in the heat exchanger. The single approach makes the WSAC a more efficient cooler.

A WSAC can operate at higher cycles of concentration leading to lower make-up and blow-down rates. This represents best use of water for maintaining a tight water balance. WSAC’s are often used as “wastewater concentrators”, since they can use blowdown from existing towers as makeup water, thus reducing total system blowdown while increasing the heat load handling capability of the plant.

Open-loop spray water on the WSAC is virtually freeze-proof. Only when the unit is not operating and there is standing water in the basin can there be any freezing. This is easily protected against by using small immersion heaters to maintain a demand-ready system.

Closed-loop evaporative coolers consume less parasitic energy than CT for same heat rejection. Typical fan horsepower reduced by 10-25%. Typical pumping horsepower reduction of 10-40%.

The circulating (spray) rate of a WSAC is much less than an open cooling tower and the corresponding drift amount is much less. Drift eliminators (DEs) can be added to a WSAC to further reduce the quantity of drift emitted during operation. Typical guaranteed drift rate in a WSAC with DEs is 0.005% of the circulating
water flow rate; without DEs is 0.02%.

While plumes are a fact of life for any evaporative cooling device, particularly open-circuit cooling towers, there are several techniques used to reduce or abate the plume in a WSAC.