Comparison of the indoor air quality in an office operating with natural or mechanical ventilation using short-term intensive pollutant monitoring

Building ventilation systems are used to mitigate occupant exposure to airborne pollutants such as particulate matter (PM), carbon dioxide and total volatile organic compounds. Building rating systems such as Leadership in Energy and Environmental Design promote the use of natural ventilation to reduce building energy consumption while improving occupant satisfaction. A number of investigations have attempted to compare indoor air quality (IAQ) between spaces with natural or mechanical ventilation without reaching a consensus regarding quantitative impacts. This work provides direct quantitative comparison of the IAQ of a single office space designed for operation with either mechanical or natural ventilation. Natural ventilation has been shown to maintain pollutant accumulation below current standards governing IAQ but is subject to significant airflow variability. In contrast, the mechanical ventilation was shown to result in lower levels of indoor pollution and provide tight control of pollutant levels. The correlation between natural ventilation air exchange rate and concentration of total volatile organic compounds was -0.66 compared to no significant correlation for mechanical ventilation. Average indoor to outdoor PM2.5 ratios were found to be 0.87 and 0.5 for natural and mechanical ventilation, respectively. These results show difficulty in controlling indoor pollutants using prescriptive standard ventilation strategies and that performance-based hybrid ventilation systems provide the most flexibility in meeting IAQ needs.