Comparison of Natural and Mechanical Ventilation In Bedrooms – Importance of CO₂ Sensor Positioning

People spend over 20 years of their life in bedrooms, and it is observed that adequate bedroom ventilation and outdoor air supply improves sleep quality and next-day performance. Most of the published literature focused on the ventilation rate in the entire bedrooms rather than in the breathing zone of the sleeping persons. For the purpose of avoiding higher exposure to carbon dioxide (CO₂) at nighttime, it is crucial to focus on the actual ventilation rate through CO₂ measurements in the breathing zone during sleep. The main objective of this study was to examine the spatial distribution of the CO₂ concentration close to the breathing zone of a sleeping person in bedrooms with natural ventilation (NV) and bedrooms with mechanical ventilation (MV). In this study, a bedroom equipped with trickle ventilation on the window and a bedroom equipped with mechanical ventilation are adopted for representative conditions. The field measurements were performed in the residential buildings during the heating season in a cold climate. CO₂ sensors were placed vertically and horizontally at 0.5 m distance from the sleeping person’s head and near the door. The ventilation rate was estimated based on the measured CO₂ decay in the morning after the person left the bedroom. The results showed that when the trickle vent on the window was kept open and the bedroom door closed, there was a continuous CO₂ build-up throughout the night, and it reached up to 3200 ppm. By contrast, in the bedroom with mechanical air supply, the CO₂ build-up raised to 1500 ppm within 1 hour and then reached steady state at around 1000 ppm. It was observed that there was only a slight difference in the CO₂ levels measured at different points around the head