Calibrating Temperature Relative Humidity Sensors

There are three sensors on the BEVO Beacon that measure Temperature (T) and Relative Humidity (RH) which help us understand the thermal comfort conditions in a space and indicate when the AC is operating.

Incubator

We calibrated the Temperature (T) and Relative Humidity (RH) sensors by comparing there readings to a reference monitor -- we use a Michell Instruments S8000 Chilled Mirror Hygrometer -- in an incubator that was retrofitted with a cooling unit which provided a wider span of T/RH to calibrate over.

Due to the size of the incubator, we could only calibrate 4 sensors at a time. The process for each batch is as follows:

1. Start data collection on the Beacons and reference monitor
2. Turn on the heat to increase the temperature to approximately 30C and hold -- this process should last 12 minutes in total
3. Introduce a desiccant and hold for another 12 minutes
4. Open the door to the incubator to allow the temperature to drop to room temperature and keep the door open for another 12 minutes
5. Remove the desiccant, close the door, and begin cooling to approximately 18C -- this process should last 12 minutes in total
6. Introduce a desiccant and hold for another 12 minutes

This process ensures that we calibrate the sensors under 5 different conditions: hot/humid, hot/dry, "typical" indoor conditions, cold/humid, cold/dry. However, researchers might want to use a different process and limit their calibration under tighter conditions that would be more realistic.

Univariate, linear least-squares regression models are created for each sensor on each BEVO Beacon from the single 1-hour experiment. We do not perform additional experiments such as with carbon dioxide, TVOCs, or PM. However, we validate the models by monitoring T/RH conditions during other calibration procedures and comparing those measurements to the BEVO Beacons.