Ancient secrets of heat mitigation
One of the oldest means of cooling buildings is certainly evaporative cooling. In the 19th-century American Southwest, for example, small structures were cooled by means of wood towers as high as 20 feet tall with dripping water that benefited from prevailing breezes. One problem was that the open systems led to microbial growth and scale build-up, breeding both disease and inefficiency.
Still, the same mechanical effect undergirds some of today's innovative buildings, especially where they include evaporative condensers, a basic but energy-efficient technology. And many operational problems of water-based equipment are, well, history.
Of course, today's packaged evaporative units are smaller and better, and can save up to 20 percent of condenser energy in a typical building. For example, the FirstMass Bank Building in Springfield, Mass., employs five twin evaporative condensers (for information on the devices, circle 310 on the card found on page 65). Energy savings and perceived maintenance advantages led to the selection.
The design called for three unit sizes from 50 to 100 tons. To minimize structural loading, the selected product features a molded plastic housing, an aluminum frame and copper coils. While the build-up of scale on heat-transfer coils-which can diminish efficiency-is often a concern with evaporative systems, but the installed units have coils that expand and contract with heating and cooling cycles, causing the scale to fall off into the sump.
The retrofit was hoped to save the facility as much as 50 percent in compressor horsepower as compared with existing air-cooled equipment. A post-occupancy evaluation showed that the new system saved about 190 kW at design conditions, amounting to $36,100 in annual savings.
Also, the systems requires no chemicals or cleaning to prevent scale, adds Richard Sisk, president of mechanical contractor Technicool, Agawam, Mass., which installed the system.