Investigating the relationship between indoor environment and workplace productivity in naturally and mechanically ventilated office environments

Abstract

This paper uses a case study-based approach to empirically investigate the relationship between indoor environment and workplace productivity in two contrasting office environments: one naturally ventilated, the other mechanically ventilated. Environmental parameters were continuously monitored over 19 months. Transverse and longitudinal surveys recorded occupants’ perception of their working environment and self-reported productivity, while performance tasks (numerical and proofreading) measured cognitive capability as proxy for measured productivity. Indoor temperatures and CO2 concentrations were found to be higher and more variable in the naturally ventilated office. However, the correlation between occupant perception of their indoor environment and perceived productivity was stronger in the mechanically ventilated office. Occupants of the naturally ventilated office were found to be more tolerant of their environment than their counterparts in the mechanically ventilated office. Task performance was affected by indoor environmental conditions such as indoor temperature and CO2 concentration. Interestingly in the naturally ventilated office, the median scores were up to 12% higher for tests conducted at CO2 concentrations <1400 ppm, compared to those conducted above 1400 ppm, whereas in the mechanically ventilated office, this threshold was only 1000 ppm. The study showed that higher concentrations of CO2 were associated with lower task scores and longer task durations, reinforcing the need for good levels of ventilation in workspaces. It was found that occupants in NV workspaces were able to adapt to a broader range of environmental conditions. Therefore, controlling the indoor environment within narrow ranges (expending significant amounts of energy in the process) may not always be necessary to improve comfort and productivity. On the other hand, controlling indoor environment within a narrow range – as is common in MV workspaces – may be counterproductive, creating occupants who are less tolerant of small changes in their environmental conditions. The study also demonstrates occupant surveys can provide useful feedback on perceived comfort and productivity at relatively low cost. Insights from such surveys can be used to improve indoor environment in workspaces.