Bayesian assessments for acceptable airborne bacteria levels in air-conditioned spaces

The level of indoor airborne bacteria is usually selected as a reference to identify the cleanliness of a Heating, Ventilating and Air-Conditioning system. This study proposes an epistemic approach for assessing acceptance of air-conditioned spaces against certain acceptable airborne bacteria levels. From the thermal environmental conditions and a sample test of the airborne bacteria level, the assessment model can give a rapid estimation of the probability of an unsatisfactory indoor environment. An office having a higher risk of unsatisfactory Indoor Air Quality (IAQ) would require a lower sample test value to fulfill the IAQ acceptance at certain confidence level. The model parameters were determined from databases of 529 air-conditioned spaces in Hong Kong, with airborne bacteria levels ranging from 41 to 2304 CFU·m-3, air temperatures from 13.4 to 27.8°C and relative humidities from 29 to 88%. This model would be useful to policymakers for making a fast response to the microbiological pollutant problem while avoiding an inappropriate level of reliance on the results.