A longitudinal study of ventilation rates in California office buildings and self-reported occupant outcomes including respiratory illness absence

Background

Limited evidence has associated lower ventilation rates (VRs) in offices with higher illness-related absence rates.

Methods

We studied spaces in office buildings, selected without knowledge of their VRs, in three California climate zones. In each study space, real-time logging sensors measured carbon dioxide and thermal parameters for one year. Web-based surveys every three months collected data on occupants’ health outcomes. Using multivariate models, relationships were assessed between CO₂ concentrations, or VRs estimated from CO₂, and adverse occupant outcomes including respiratory infections and illness absences. For all outcomes, positive associations were hypothesized with higher CO₂ levels (and negative associations with higher VRs).

Results

Low survey response limited sample size and study power. In the 16 study spaces, CO₂ concentrations were uniformly low over the year, and most estimated VRs ranged from twice to nine times the California office minimum VR standard (7 L/s or 15 cfm per person). Primary CO₂ and VR metrics had no statistically significant relationships with occupant outcomes.

Conclusions

Within the observed range of uniformly low CO₂ and high VRs (mostly 16–42 L/s per person), little variation in contaminant concentrations would be expected, which would explain lack of relationships with occupant outcomes. These high VRs resulted partly from frequently used energy-saving “economizer” cycles in moderate California climates, but VRs at other times also substantially exceeded required VRs. These findings suggest, consistent with theory, that within a higher VR range, increased VRs do not reduce respiratory illness. Further studies are needed to better characterize such relationships.