But technology from Azevap, LLC, Phoenix, Ariz., that cools despite increased wet-bulb temperature and relative humidity could put evaporative coolers on the fast track. A new suite of coolers with Opto 22 control hardware addresses scaling and reliability issues of other water-level control systems.

The AZFlow water-distribution and metering system applies just enough water to the media to offset evaporation. Recirculating coolers, on the other hand, bathe the media at an average rate more than 2.5 times the evaporation rate. This results in water entrainment and greater salinity, which, in turn, lead to more scaling.

Performance of most coolers using 12-in. media degrades relatively quickly over the first few months of operation, from a high of about 80% to less than 70%. But AZFlow coolers are said to be scale-free and maintain efficiencies of 85 to 90% after several years of service.

The system measures ambient air temperature, humidity, and airflow using sensors that connect to the processor via analog I/O modules residing on a Snap rack. An algorithm executed by a Linux-based controller correlates instantaneous water-evaporation and water-application rates to deliver the proper amount.

The controller, programmed by Opto-Solutions (opto-solutions.com), communicates with Opto 22 I/O modules to implement cooling strategies.

Besides reading I/Os, aggregating data, and controlling the valve that wets the media, the controls also connect to other components. For instance, an RS-485 serial interface reads the amps and horsepower of the variable frequency drives regulating the fans. Interfaces to I/O modules let the controller turn fans on and off. Also, I/O modules connect the controller to float switches and valves to warn of clogged drains. All control processes and data are shown on a Webbased display.

The Bank of America office building in downtown Phoenix installed an early version of the cooler in 2003. Less than six months later, the system had already paid for itself, the manufacturer claims.