Design and Application of CO2 Sensor Systems for Enhanced Indoor Air Quality Management

This paper discusses the design and application of
$\text{CO}_{2}$
sensor systems for indoor air quality management. It is important to install CO
2
sensors and monitor indoor environments because exposure to high concentrations of
$\text{CO}_{2}$
can cause various health problems. The choice of measurement intervals can delay the assessment of potential risks, so this study investigates the appropriate measurement intervals. Additionally, while it is necessary to use optical
$\text{CO}_{2}$
sensors to accurately measure
$\text{CO}_{2}$
concentrations, this paper also reports the findings on the usefulness of combining optical
$\text{CO}_{2}$
sensors with VOC sensors, which are considered to have relatively low accuracy in measuring
$\text{CO}_{2}$
. To conduct this study, we developed a
$\text{CO}_{2}$
measurement device and a smartphone app for viewing the measurement data, and conducted measurements. Regarding differences due to measurement intervals, it was found that with a 10-minute interval, many increases in
$\text{CO}_{2}$
concentration went undetected, whereas with a 5-minute interval, almost all increases were detected, and with a 2-minute interval, the fluctuations in CO
2
concentration were detected almost accurately. Therefore, in indoor environments with minimal human traffic, a 5-minute measurement interval is sufficient, while in environments with high human traffic, a measurement interval of up to 2 minutes is necessary. In the investigation combining optical
$\text{CO}_{2}$
sensors and VOC sensors, both sensors indicated high
$\text{CO}_{2}$
concentrations when the
$\text{CO}_{2}$
levels increased due to human respiration. However, during
$\text{CO}_{2}$
elevation caused by gas stove usage, only the optical
$\text{CO}_{2}$
sensor showed high
$\text{CO}_{2}$
concentrations, while the VOC sensor remained constant. This suggests that in certain indoor situations, such as determining the number of people in a room where a gas stove is used, the combination of optical
$\text{CO}_{2}$
sensors and VOC sensors can be useful.