Seasonality and Trends in Indoor Air Quality Based on Continuous Monitoring

摘要

Maintaining adequate indoor air quality (LAQ) in occupied spaces is important for human health and wellbeing, and it is strongly related to energy consumption. In terms of LAQ, it is usually recommended that concentrations of carbon dioxide (CO_2) should not exceed 1000 ppm, total volatile organic compounds (TVOCs) not exceed 300-400 /μg/ m~3, and PM_(2.5) not exceed 10 - 25 μg/m~3. In practice, relatively little is known about how LAQ varies over a long timeperiod (several months to years); and economic as well as climatic challenges may limit possibilities to always maintain optimal, steady indoor conditions. Nevertheless, understanding the temporal variations that each individual building exhibit due to its location, design, condition, or use, could lead to more effective operation strategies. This study utilizes continuous time series data on CO_2, TVOCs, and PM_(2.5) collected using IoT sensors located in the breathing zone of over 2400 spaces in about 260 buildings. About 90% of the buildings are located in Finland, and the majority of them are mechanically ventilated offices. About 45% of the spaces have been monitored for over a year, and 15% over three years. In this study, we analyzed the time series data in order to detect seasonal patterns and trends. Our results indicate these time series were stationary for 75%, 85% and 90% of the spaces regarding daily maximum CO_2, TVOCs and PM2.5, respectively. We will present results from both stationary and non-stationary cases and discuss about observed differences; further analyses leading to forecasting concentrations of the LAQ parameters monitored.