Vancouver-based pharmaceutical specialty and medical-device manufacturer Angiotech (angiotech.com) maintains a plant in Reading, Pa., that assembles and packages products such as surgical needles and sterile, disposable scalpels. Unfortunately, the plant was having difficulty controlling the humidity in its Class 8 cleanroom. Facility support manager John Garbini tried everything from balanced air dampers, to reduced air pressure — even a large industrial desiccant unit. But nothing worked.

“Extremes in cleanroom temperature and humidity were all too common,” says Garbini. “So our employees were either too hot or cold. The air-handling compressors constantly slammed on and off, but humidity would not stay within company specs, which are more stringent than Federal cleanroom standards.”

Humidity that is too high encourages bacterial growth and tends to degrade products such as moisture-activated sutures. These are intended to slowly dissolve in human tissue after a surgical incision heals. Humidity that is too low, on the other hand, promotes static electricity, which gives employees small shocks and interferes with computerized packaging and labeling equipment.

To address these problems, Angiotech turned to Woburn, Mass.-based Rawal Devices Inc. (rawal.com), which recommended the APR Control device along with a new air handler. The control smoothly modulates a direct expansion, air-conditioning system so it dehumidifies a space without overcooling it. The device varies refrigerant flow according to suction pressure, which changes with the temperature of the air that crosses the evaporator coil.

What's more, when a system filter clogs or belt breaks, the control never lets coil temperature fall below freezing. This spares cleanrooms from water damage caused by melting coil ice. The control also continuously monitors the heat content of return air, so the air conditioner humidifies more efficiently than systems with thermostats and humidistats, and without the risk of coil icing, liquid slugging, or excessive compressor cycling.

“The APR Control worked so well that we purchased another for our second cleanroom,” says Garbini. “Today the temperature is holding steady and so is the relative humidity, at about 50%, in both cleanrooms.”