LAUSR

Abstract Adequate supply of fresh outdoor air is important to create healthy and comfortable indoor building environments. Currently, most of the residential buildings in mild climate European countries, such as Portugal or Spain, remain naturally ventilated. Distinct concerns have emerged in the building community regarding the indoor air quality (IAQ) in these buildings since several studies have shown that they are often poorly ventilated. The main cause has been identified as occupants' different window opening behavior, which can vary notably from one apartment to the next. This work presents a comparative method for evaluating occupants' exposure to CO 2 concentration levels in existing buildings based on the comparison of cumulative frequency distribution curves. Indoor CO 2 concentration levels recorded over 17 months in the bedrooms and living rooms of eight apartments of a naturally ventilated residential building located in Porto (Portugal) were used as experimental input data for developing the method and to calibrate the IAQ performance of an EnergyPlus building model. The calibrated building model exhibited a good agreement with the recorded data on the apartments, reporting maximum Root Mean Square Errors (RMSE) for the majority of the apartments below 5% and 10% for the living rooms and bedrooms, respectively.