This study addresses the challenge that the eCO2 output of MOX-type CO2 sensors, estimated from TVOC, is strongly affected by environmental factors such as atmospheric pressure, temperature, and humidity, making it difficult to use directly for occupancy estimation. We propose a calibration method based on regression models that explicitly incorporate atmospheric pressure as an explanatory variable. A MOX sensor and an NDIR sensor, used as a reference, were colocated in the same environment, and continuous multi-day data of CO2, TVOC, temperature, humidity, and pressure were collected to construct the calibration models. Incorporating pressure improved accuracy, and comparison of linear regression, multiple linear regression, second-order polynomial regression, and random forest (RF) showed that RF performed best, with RMSE reduced by approximately 42% compared with the uncalibrated values. For occupancy estimation, we examined a regression model using RF with explanatory variables including CO2, illuminance, temperature, humidity, and temporal features. Although the NDIR-only approach achieved the highest accuracy, for eCO2, calibration improved performance, and combining it with illuminance and temporal features enabled accuracy close to that of the NDIR sensor.
View full abstract