Evaluation of the microbiological indoor air quality at a commercial building in Muscat, Oman, utilizing an all-air multi-zone HVAC system
by Muthuraman Subbiah, Sivaraj Murugan, Kumar Ayyappan
Building Engineering, Vol.3, No.3, 2025;
This study evaluates the microbiological indoor air quality (IAQ) of a commercial office building in Muscat, Oman, equipped with an all-air multi-zone heating, ventilation, and air-conditioning (HVAC) system operating under hot-arid climatic conditions. Active air sampling was conducted at multiple locations, including open-plan offices, outdoor air intake, supply air diffusers, fan coil units, and the humidification water tank of the air handling unit (AHU), across different seasons. Airborne bacteria were analyzed using incubation at 22 ℃ and 37 ℃ to distinguish environmental and human-associated microbial populations, while fungal concentrations were assessed at 25 ℃, with results expressed as colony-forming units per cubic meter (CFU/m3). For analytical consistency, data from the three office spaces investigated were aggregated and evaluated as seasonal averages. Bacterial concentrations in indoor air generally ranged from 32 to 496 CFU/m3 at 37 ℃ and 4 to 500 CFU/m3 at 22 ℃, indicating low to moderate contamination levels under normal operating conditions. In contrast, a pronounced increase in fungal concentrations was observed during the initial winter sampling, exceeding 2000 CFU/m3, which was attributed to an exceptional flooding event. Comparative analysis of outdoor air, AHU-treated air, and indoor air demonstrated that the HVAC system effectively reduced microbial loads during standard climatic conditions. The findings provide region-specific baseline data on microbiological IAQ and highlight the influence of HVAC operation, seasonal variation, and extreme environmental events on indoor bioaerosol levels in commercial buildings located in hot-arid climates.
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