Façade-Level Monitoring of CO₂ Variability under Urban Heat Island Conditions using Low-Cost Sensor Data Loggers

The research examines how urban microclimate impacts outdoor/indoor CO2 interplay, and also takes a look at how realtime ventilation gets impacted in an operational building. The main challenge is lack of adequate data, correlating urban heat island effect and microclimate, especially while designing a building for energy performance and health. To begin, assemble the s.

ensor module using a non-dispersive infrared carbon dioxide sensor and a combined temperature and humidity probe. Secure both sensors together as a single functional module. Configure the microcontroller based data logger by connecting a realtime clock module and installing the secure digital card shield.

Ensure that all components are firmly seated on the microcontroller. Set the logging frequency to one reading every 10 minutes using the data logger configuration interface. Confirm that the selected interval is correctly saved in the system settings.

To test sensor function and perform calibration, place all carbon dioxide and temperature humidity sensors in a well-ventilated outdoor area. Arrange the sensors so that they're equally exposed to ambient air. Now, connect the sensor modules to a stable power source, such as a 230-volt alternating current to direct current adapter.

Allow the sensors to stabilize for 10 minutes. Then, record the baseline carbon dioxide concentration of approximately 410 parts per million to verify consistency across devices. Now, place the assembled sensor module and data logger inside a weather-resistant housing made of polypropylene.

Ensure that all wiring is fully insulated and that all connectors are firmly secured. Identify contrasting thermal zones within the locality around the building or zone of interest. Install sensor modules on multiple facades where applicable to capture thermal and pollutant variation.

After mounting the sensor module, confirm that it is securely attached to the facade. Maintain a mounting height between one and two meters above the local floor level for each facade. Adjust the exact height is needed based on accessibility, available supporting infrastructure, and facade geometry.

Now, record the directional orientation of each sensor location, such as an east facing facade adjacent to a road, and document nearby obstructions including heating, ventilation, and air conditioning units or walls. Verify sensor output by observing live readings on the display or logger interface. Confirm that the connection is stable and that active data recording is underway.

Allow the data logger to operate continuously for 24 hours with a data logging interval of 10 minutes to capture full-day variations in carbon dioxide concentration, temperature, and humidity. Verify that timestamps remain synchronized across all sensors before deployment and again after deployment. Now, record the start time and stop time manually in a field logbook to provide redundant backup documentation.

For wireless fidelity-enabled loggers, connect to the local service set identifier and download the log files through the internet protocol-based dashboard. Process the retrieved data using a spreadsheet or data analysis software to prepare it for visualization. Next, generate a multi-variable line plot showing carbon dioxide concentration and temperature on the primary vertical axis and relative humidity on the secondary vertical axis to allow direct trend comparison.

Label the horizontal axis as time. Add a legend to distinguish variables and annotate peak values, typically between 11 and 15 hours for intersite comparison. Perform data validation by reviewing the collected dataset for anomalies.

Identify and remove outliers or data points flagged due to timestamp irregularities or device communication errors. Finally, recalibrate sensors if post-experiment analysis indicates sensor drift exceeding 3%or a variation of more than 10 parts per million. Repeat the baseline calibration procedure in open air conditions and reacquire data under identical environmental conditions.

External carbon dioxide concentrations were significantly higher at concrete-dominant facades compared to adjacent green facades across all monitored cities. In Chennai, elevated carbon dioxide levels at the east facade coincided with higher local temperatures near the sensor compared to the shaded facade. In Pune, the difference in carbon dioxide concentration between facades occurred despite only a one degree Celsius increase in temperature at the concrete facade.

Green zones consistently exhibited lower temperatures, higher humidity, and faster carbon dioxide dispersion rates compared to concretized facades across all sites. Our studies highlight that urban heat island effect has a direct impact on the outdoor CO2 and air quality, and this translates into an increased CO2 buildup indoors. And this is true for naturally ventilated buildings as well.

Our protocol is low-cost, scalable, field-ready, and visually reproducible across building typologies and climatic conditions. Our future studies will focus on community level air quality index, energy efficiency in buildings, climate adaptive ventilation strategies, and cognitive performance of the building occupants.