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Indoor air quality (IAQ) is crucial for the health, well-being, and productivity of office occupants. IAQ is strongly influenced by occupancy and the operational mode of the heating, ventilation, and air conditioning (HVAC) system. This study investigates the spatiotemporal variations in ozone (O3) and carbon dioxide (CO2) concentrations throughout the HVAC system of a LEED-certified office building. A four-month field measurement campaign was conducted at the Ray W. Herrick Laboratories, employing an automated multi-point sampling system to monitor O3 and CO2 at eight locations throughout the HVAC system. The objectives of this study are to characterize the spatiotemporal distribution of these gases under different ventilation modes and occupancy levels, and to identify O3 loss mechanisms in the office and its HVAC system. Spatiotemporal variations in O3 and CO2 concentrations were observed throughout the HVAC system. Results indicate that outdoor air exchange rates (AERs) significantly impact indoor O3 levels, with higher AERs resulting in increased indoor O3 but reduced CO2 concentrations. Measurements reveal that HVAC filters and ducts contribute to O3 loss, with up to 18% O3 removal observed in the longest HVAC duct segment. Additionally, occupancy influences O3 deposition onto human skin and clothing surfaces. This research underscores the limitations of ventilation standards that focus only on CO2, highlighting the need for ventilation strategies that consider the effects of occupancy and outdoor AERs on different gases. By integrating multi-point gas sampling into building automation systems, more effective control strategies can be developed to enhance IAQ and occupant health while reducing energy consumption. 

Good indoor air quality in office environments is essential for occupant health and productivity. In open-plan offices, displacement ventilation has been recognized for its higher efficiency compared to mixing ventilation. This study evaluates the performance of displacement ventilation in an open-plan office under cooling and heating conditions, considering various supply ventilation rates, supply air temperatures, and occupancy levels. Field measurements were conducted over three months in a living laboratory office in a high-performance building. The indoor environment was controlled by an independent variable air volume (VAV) air conditioning system. The supply ventilation rate ranged from 6 to 12 h^−1. Real-time measurements of carbon dioxide (CO2) concentrations in the supply air, return air, and breathing zone of the office were conducted to assess occupants’ exposure to CO2 and ventilation efficiency. The results show that the supply ventilation rate plays an important role in shaping the air distribution and overall effectiveness of the mechanical ventilation system. Higher supply ventilation rates can enhance air distribution robustness, improving ventilation efficiency and reducing CO2 exposure under both cooling and heating conditions. These findings also suggest the need for an optimized control logic that differs from the conventional control logic used in VAV systems. Specifically, during the heating condition of displacement ventilation, it is recommended to maintain the supply ventilation rate at a higher level to effectively mitigate the impact of occupant behavior on air quality, minimize CO2 exposure risks, and ensure a more robust and reliable indoor air distribution.