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Finding the Optimal Balance between Building Energy Conservation and Occupant Health Protection: A New Mobile Indoor Air Sensor Array for Building Ventilation Automation

Figure 1: New mobile sensor nodes (red circles)
monitoring pollutant levels in the vicinity (green circles)
of living persons, versus the traditional stationary
sensor (black circle) placed near the return vent
for demand-controlled ventilation.




Lynn Hildemann and Ram Rajagopal, Civil and Environmental Engineering



Current demand-controlled ventilation (DCV) systems adjust outdoor air-supply rates based on indoor occupancies, which are measured by carbon dioxide (CO2) sensors to conserve energy. However, these sensors do not directly measure/adjust for changes in levels of indoor air toxics, such as carcinogenic volatile organic compounds and virus-containing aerosols. More importantly, the current sensors of DCV are stationary air monitors (mounted on a wall/ceiling) – they do not reflect actual exposures of occupants who can move around in a building. A goal of this project is to install and test the new “exposure-based” DCV system in a real office building with an existing CO2-based DCV system. 

Figure 2(a): A commercially available real-time air sensor with
wireless connection to a smart phone; and 2(b): Indoor air sensor
nodes (red circles) carried by occupants and economizers (blue squares)
installed in different indoor compartments in a public building.


Professors Lynn Hildemann and Ram Rajagopal aim to design a new “mobile” indoor air-sensor array to regulate the operation of demand-control ventilation (DCV). Instead of placing an air-quality sensor at a fixed location, they will have occupants carry air sensors. By tracking the time-varying positions of occupants, this new “living” sensor array can instantaneously detect occupants entering or exiting a room. By monitoring the real-time air toxics concentrations within the breathing zones of moving occupants, this air-sensor array can accurately measure the levels of exposures when in close proximity to indoor emissions, such as particle resuspension due to walking and VOC emissions from furniture and electronics.       



In addition to the automation of building ventilation, the array will be able track the presence and transmission of infectious diseases inside public buildings. This mobile array of sensors will provide information that will allow systems to simultaneously achieve energy conservation and human health protection for existing built urban environments, and contribute towards making modern work environments more sustainable and healthy.  


Using Indoor Positioning and Mobile Sensing for Spatial Exposure and Environmental Characterizations: Pilot Demonstration of PM2.5 Mapping, Environmental Science & Technology Letters, Publication Date (Web): January 4, 2019
Awarded 2016