Evaluation of the neutral criterion of indoor air quality for air-conditioned offices in subtropical climates

Occupant-generated carbon dioxide (CO2) is used as the tracer gas to determine ventilation rate. Although CO2 concentration may not provide a comprehensive indication of indoor air quality (IAQ), it can be a good indicator of the concentration of other human bioeffluents perceived as a nuisance and be used to identify the acceptability of IAQ in a space by its occupants. In this study, the acceptability of IAQ in air-conditioned offices was evaluated by the subjective responses of the office occupants with respect to indoor CO2 concentration. CO2 concentrations at 396 sample locations were measured and subjective responses at those locations were recorded by an electronic questionnaire. Specifically, an occupant’s indirect acceptability of the perceived IAQ indicated on a semantic differential evaluation scale was correlated to the occupant’s direct acceptability described by a dichotomous scale. The overall acceptability of IAQ from all occupants was then described by a logistic regression model and shown to correlate with indoor CO2 concentration.