AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Occupancy Sensing with Chair-Embedded Thermocouples: Applications for Evaluating Human-Associated Bioaerosol and VOC Emission Factors
DANIELLE WAGNER, Aayush Mathur, Brandon E. Boor, Purdue University
Abstract Number: 820 Working Group: Indoor Aerosols
Abstract Human occupants in office environments are an important indoor source of bioaerosols and volatile organic compounds (VOCs). Concentrations of human-associated bioaerosols and VOCs are strongly linked to occupancy patterns. Reliable methods for counting occupants in an indoor space must be implemented in order to determine per-person bioaerosol and VOC emission factors (no. or μg h-1 person-1), thereby improving our understanding of how occupants shape the composition of indoor air. Occupancy sensing inferred from carbon dioxide measurement or bi-directional door sensors are subject to uncertainties. The objective of this study is to evaluate a new sensing technique to precisely determine spatiotemporal occupancy patterns in an office through use of chair-embedded thermocouples.
Occupancy was tracked for six months in the Herrick Living Laboratories at Purdue University, which are four modern open-plan offices with precisely controlled HVAC systems. One office with a twenty desk capacity was evaluated. A K-type thermocouple was securely mounted to each chair cushion surface and connected to a portable USB data logger. The seat temperature was detected every 15 seconds. An algorithm was developed to identify rapid surface temperature shifts corresponding to changes in chair occupancy. A seated individual counts toward occupancy, whereas an empty seat counts as zero; thus an error is introduced for those standing in the room for short periods. The count was summed for all twenty chairs to calculate the number of people in the room with 15-second time-resolution.
The chair-embedded thermocouples were integrated with real-time measurements of bioaerosol and VOC concentrations to estimate per-person emission factors over time. Daily and weekly trends in occupancy were determined for the office. Spatial occupancy maps were created to visualize the location of emission sources. The mapping allows for insight into whether pollutant origins are from multiple additive or single human sources. This method of occupancy detection is most effective in spaces where people are usually seated, such as offices and classrooms. Being able to more accurately denote the relationships between occupants and resulting concentrations of bioeffluents can inform exposure studies and ventilation control strategies.