Indoor thermal comfort and Carbon Dioxide concentration : a comparative study of air conditioned and naturally ventilated houses in Sri Lanka

Carbon Dioxide (CO2) is considered as a useful and easily measurable indicator for the ventilation and air quality of the indoor environment. Although this pollutant itself is not causing serious health issues with lower concentration and short durations, the higher concentration can indicate the lower ventilation level and possible air contamination with other pollutants. The study compared the naturally ventilated and air conditioned bedrooms in terms of thermal comfort and CO2 concentration. For naturally ventilated bedrooms, the temperature and the humidity level was higher than the air conditioned bedrooms. All the air-conditioned houses, including the houses with larger floor area and volume, build up higher CO2 levels which are more than the recommended concentration level. The CO2 level of the air conditioned houses significantly vary with the room size, number of occupants and the ventilation. For the studied air conditioned houses, no fresh air intake was provided mechanically. However, this air tightness has drastically increased the CO2 concentration, especially with smaller floor area. The air-conditioned houses have to compromise in order to achieve the higher energy efficiency with an acceptable level of indoor air quality. Maintaining the air change rate at 0.5 ach level would minimise the health risk due to CO2 emission