Development and Evaluation of Carbon Dioxide Sensors for Building Applications

Current global efforts in building information research include the development of low-cost, high reliability sensing systems capable of quantifying metrics such as human occupancy, indoor environmental quality, and building system dynamics. Such information is of high value for model development, building energy management, and improving occupant comfort. Further, indoor air quality (IAQ) has been a growing concern in recent years, only to be exacerbated by the COVID-19 pandemic. A common provisional measure for IAQ is carbon dioxide (CO2), which is regularly used to inform the ventilation control of buildings. However, few commercially available sensors exist that can reliably measure CO2 while being low cost, exhibiting low power consumption, and being easily deployable for use in applications such as occupancy monitoring. 

This work presents research related to the initial development and evaluation of low-cost, stable, and easily deployable sensors for monitoring indoor CO2 levels in buildings. Two different types of sensors are presented that have the potential to perform as well as current commercially available CO2 sensing technologies, at significantly lower costs. The first is a chemiresistive sensor that is fabricated using a carbon nanotube thin film in conjunction with a blend of branched poly(ethylenimine) (PEI) and poly(ethylene glycol) (PEG), which serve as a CO2 absorbing layer. The second is a resonant mass sensor, functionalized with similar polymer-based materials including a blend of PEI and poly(ethylene oxide) (PEO). Prototype sensors were assessed in a bench-top environmental test chamber which varied temperatures, relative humidity levels, CO2 concentrations, as well as other gas constituents to simulate typical and extreme indoor conditions. The results indicate that the proposed system could ultimately serve as an attractive alternative to commercial CO2 sensors that are currently available.