Correlation of thermal environments with the bacterial concentration in bedrooms with intermittent and continuous heating modes

Bacteria in built environments are profoundly affected by indoor thermal conditions. In China, continuous and intermittent heating modes give rise to distinct thermal environments in winter. However, the quantitative relationships between bacterial concentration and thermal conditions in the context of heating modes remain unclear. To this end, we recorded the temperature and relative humidity (RH) in 15 intermittently and 15 continuously heated residences in 27 cities across China and obtained the bacterial concentrations via the quantitative polymerase chain reaction technology. For the intermittently heated residences whose temperatures were lower than 18°C, the bacterial concentration negatively correlated with RH while the correlation was positive for those with T > 18°C. For the continuously heated residences, a quadratic correlation was found between temperature and the bacterial concentration which was highest at 23°C. For lower bacterial risk, we suggest that (1) RH in the intermittent heating region should be in the range of 40%–60% and (2) temperature in the continuous heating region should not exceed 22°C. The bacteria-adjusted thermal zones for intermittent and continuous heating are 66% and 77% of the original thermal comfort zone, respectively. Our study provides insights into the set-points of indoor thermal environments based on the microbial perspective.