Installing a self-cleaning filter in an HVAC cooling water system can protect heat exchangers, pumps, valves and nozzles while continuously removing entrained solids and providing continuous flow, even when the system is backwashed. If properly selected and configured, such a system can actually operate for years or even decades with little to no maintenance.
A great example of the effectiveness of this technology is the filter system that supplies water to the HVAC cooling towers at the International Airport. The airport has over 30 miles of runways and covers 4,930 acres. With 35,000 employees, it serves over 90 airlines and 60 million passengers each year, making this international airport one of the busiest in the world.
All of these passengers and employees are served by a heating, ventilation, and air conditioning plant that features a cooling tower in the central terminal area. It operates 24 hours a day, 7 days a week in all weather conditions. At full capacity, the tower circulates 25,000 gallons per minute (gpm) of water.
Since space is limited, filters that protect the tower and associated equipment are also the primary source of dirt and other impurities removed from the entire system.
Open cooling towers collect a variety of contaminants, from road dust and pipe scale to seasonal leaves and even the occasional branch collected during stormy weather. Anything larger than 0.062 inches (1.6 mm) is removed by the filters, producing a clean discharge water of 200 parts per million (ppm). This means that with a system flow of 25,000 gpm, an average of 1.9 pounds of contaminants are removed for every 1,000 gallons, removing approximately 9.5 tons of waste from the cooling water stream each day.
Advantage:
The automatic control system continuously monitors the filter and initiates a backwash cycle when flow restriction reaches a predetermined level. A high-efficiency rotating backwash arm extends the entire length of the filter screen, isolating the section it contacts. When the backwash arm is vented to atmospheric pressure through the backwash valve, flow through the screen is reversed and debris collected in the area below the backwash arm flows out of the filter.
