MULTIVARIATE-ANALYSIS COMPARING MICROBIAL AIR CONTENT OF AN AIR-CONDITIONED BUILDING AND A NATURALLY VENTILATED BUILDING OVER ONE-YEAR

Heating, ventilation and air-conditioning (HVAC) may be responsible fo r the production and spread of airborne microorganisms in office build ings. In order to compare airborne microbiological flora in an air-con ditioned building with that in a naturally ventilated building, eight sets of measurements were made over a 1-year period. Concurrently with other environmental measurements, air samples were collected in each building, from three offices and from the outdoor air, using the Ander sen single-stage sampler. Three different media were used to culture f ungi, staphylococci and mesophilic bacteria. Multivariate analysis rev ealed a group of offices more contaminated than others, and a, marked seasonal variation in fungal concentrations. A comparison of mean leve ls of microorganisms measured in the two buildings showed that the air microbial content was significantly higher and more variable in the n aturally ventilated building than in the air-conditioned building. Mor eover, in the naturally ventilated building, the interior fungal conte nt was strongly dependent on the outdoor content, while in the air-con ditioned building fungal concentrations remained constant despite sign ificant variations measured outside. This was confirmed by a statistic al comparison of the correlation coefficients between indoor and outdo or concentrations. No difference was observed regarding gaseous pollut ants and temperature, but relative humidity was significantly higher i n the air-conditioned building. The effect of HVAC was to prevent the intake of outdoor particles and to dilute the indoor concentrations. T hese results are consistent with the presence of high-efficiency filte rs and a steam humidifier in the HVAC system under study. Copyright (C ) 1996 Elsevier Science Ltd