MULTIPLICATION OF MICROORGANISMS IN AN EVAPORATIVE AIR COOLER AND POSSIBLE INDOOR AIR CONTAMINATION

Evaporative air coolers (EACs) cool and humidify hot, dry, outdoor air by pulling it through pads that are wetted continuously by recirculated water. An EAC in a single-family house was examined for three summer months, during which the amount of dissolved solids in the sump water rose to ten times the level in the chlorinated tap water supply. Although the concentration of bacteria in the tap water was always <10 colony-forming units per milliliter (cfu.mL), the concentration in the cooler water reached 1 × 105cfu/mL in the ninth week. Indoors and outdoors, the concentrations of airborne microorganisms were similar on individual days, but throughout the study they varied from 102 to 104 cfu/m3 for bacteria, and from 102 to ≥103 cfu/m3 for fungi. When the EAC was not operating, the concentration of airbone microorganisms tended to be higher indoors than outdoors. When operating, the cooler introduced large volumes of outdoor air into the house and there was less difference between the indoor and the outdoor microbiological air quality. Although the pads of the EAC appeared to filter microoganisms from the outdoor air, the types of bacteria that predominated in the sump water were more abundant in the indoor air, and several types of bacteria and fungi were found only in the sump water and in the indoor air. © 1990.