Impact of Independently Controlling Ventilation Rate per Person and Ventilation Rate per Floor Area on Perceived Air Quality, Sick Building Symptoms and Decision Making

Ventilation standards for commercial buildings set a minimum required outdoor air ventilation rate per occupant to control indoor levels of pollutants including bioeffluents from occupants and their activities and/or a minimum ventilation rate per unit floor area to control indoor levels of pollutants from the building and products used in the building. However, few data are available to indicate the relative importance of controlling occupant-related or building-generated pollutants with ventilation. An experimental facility was designed that allows the independent control of ventilation per occupant and ventilation per floor area in a simulated office environment. Two studies were conducted to measure the impact of either occupant or floor-area based ventilation separately. Thirty-two subjects were assigned to groups of four and each group experienced two different blinded ventilation scenarios in different sequences, with four groups participating in each study. Each test condition lasted four hours and each group experienced two conditions per day in a self-paired study design. The order of presentation of test conditions, day of testing and gender were balanced. Temperature, relative humidity and airflow rates were controlled and logged continuously. Particle number concentrations, size resolved particle mass concentrations, CO₂ and ozone were logged continuously. Short-term integrated measurements of volatile organic compounds were collected during each session. The subjects were surveyed using on-line instruments to assess perceived air quality (PAQ), sick building syndrome (SBS) symptoms and decision-making performance. The resulting data were analyzed using statistical models. Neither changing the ventilation rate per person nor changing the ventilation rate per floor area, in the range and for the duration tested here, had consistent statistically significant effects on PAQ or SBS symptoms. However, moderate reductions in either occupant-based ventilation rate or floor-area based ventilation rate had a significant and independent negative impact on a range of decision-making measures. These results provide compelling evidence that changes in outdoor air ventilation rate influences human performance even when PAQ and SBS symptoms are unaffected. The results for occupant-based ventilation agree with previous work that measured the relationship between CO₂concentration and decision-making performance in an office setting, with CO₂ levels modified by injection of pure CO₂. The results for area-based ventilation represent the first controlled human study showing a statistically significant reduction in decision-making performance as a function of decreased ventilation rate per unit floor area of office space. Further study should focus on quantifying the influence of outdoor air on cognitive function across a wider range of ventilation settings to identify the optimal ventilation rate for occupancy and for floor area