Predicting indoor particle concentration in mechanically ventilated classrooms using neural networks: Model development and generalization ability analysis

This study presents a comprehensive analysis of the model development (structure, parameter settings, and prediction accuracy) and generalization ability of neural networks in the classroom setting. A normalized database for model prediction and verification including indoor parameters from 27 high school classrooms over the course of four semesters was set up (a total of 14,112 sets of data for each variable). Three different models were compared: a back propagation artificial neural network (BP-ANN), a nonlinear autoregressive exogenous neural network (NARX), and a long-term and short-term memory neural network (LSTM). For the prediction of PM1 and PM2.5, which are impacted by outdoor PM concentrations, the best performance was achieved by the NARX model: the mean absolute percentage error (MAPE), root mean squared error (RMSE), and coefficient of determination (R2) were 41–55%, 0.45–1.27 μg/m3, and 0.81–0.87, respectively. The R2 of this model was 22% higher than that of the BP-ANN model and much higher than that of the LSTM model. For the prediction of indoor PM10, which are mostly emitted by indoor sources, relatively good performance was achieved by the LSTM model. The trained NARX model was used successfully to predict indoor time-series PM2.5 concentration and source strength in classrooms in five Chinese cities and five American cities. The calculated indoor source strength was 95.5–119.1 μg/h/P, within the range of the measured indoor source strength. The indoor PM2.5 concentrations calculated by a theoretical equation without the consideration of indoor source were 20.8–60.0% smaller than those calculated by the trained model.