Personal CO2 bubble: Context-dependent variations and wearable sensors usability

Abstract

High CO2 concentration in inhaled air has been shown to negatively impact work performance and increase acute health symptoms. As respiratory CO2 is constantly exhaled, it may not dissipate in surrounding air in absence of adequate air movement and is instead re-inhaled into the airways (breathing in a CO2-rich bubble). In this study, we explored the impacts of context-dependent factors such as office activities, desk settings, and personal differences on the inhalation zone CO2 concentration and on concentrations at a below-neck wearable sensor. While all factors were found to significantly impact measurements at both measuring points, desk settings (empty desk, desk with a fan, desk with laptop, desk with monitor) was found to be the most dominant factor. Presence of a small portable desk fan was found to significantly reduce the CO2 concentration. On average, we observed a 177 ppm reduction in CO2 concentration when using a fan, which is 25 ppm higher than the background CO2 measurement (650 ppm). Among 41 test subjects, we found distinct relationships between the inhalation zone CO2 concentration and the wearable sensor measurements and, by applying a hierarchical clustering algorithm, we found 4 clusters of relationships. While below-neck wearable sensors could be used as an exact measure of inhalation of CO2 concentration for 29% of the subjects, we identified a boundary point (917 ppm) separating high and low inhalation zone CO2 concentration measurements.

Validity of CO2 based ventilation design

“…The manikin was exposed to higher CO2 concentration than the concentration at the exhaust. These results concurred with the recently reported results [18]. In [18] the elevated CO2 concentration in the inhaled air is attributed to the personal CO2 bubble generated in the breathing zone due to the exhaled air, i.e.…”

Ceiling-fan-integrated air conditioning: Airflow and temperature characteristics of a sidewall-supply jet interacting with a ceiling fan

“…The air movement offsets the need for air cooling by increasing the convective cooling of the occupants' bodies. It has also been found that a modest air speed significantly reduces a CO2 bubble that accumulates in a person's breathing zone under still air conditions in workstations [16]. Finally, higher air temperatures and air speeds have also recently been shown to be far more effective (compared to cooler temperatures and still-air) at restoring comfort to occupants who have just entered a space with elevated metabolic rate and stored body heat from walking [17,18].…”

Smart Desks to Promote Comfort, Health, and Productivity in Offices: A Vision for Future Workplaces

“…CO 2 concentrations exceeding 950 ppm were found to cause significant declines in cognitive scores, even though the level of exposure is considered acceptable by ASHRAE 62.1, which provides ventilation guidelines for acceptable indoor air quality (Allen et al, 2016). Past studies have shown that the exhaled CO 2 does not immediately dissipate with the surrounding air when occupants are sedentary and results in a buildup of a personal CO 2 bubble around the occupant's head (Ozkaynak et al, 1996;Ghahramani et al, 2019). A recent study has shown that using a desk fan can dissipate the CO 2 bubble and reduce the CO 2 concentration by 177 ppm on average (Ghahramani et al, 2019).…”

“…Past studies have shown that the exhaled CO 2 does not immediately dissipate with the surrounding air when occupants are sedentary and results in a buildup of a personal CO 2 bubble around the occupant's head (Ozkaynak et al, 1996;Ghahramani et al, 2019). A recent study has shown that using a desk fan can dissipate the CO 2 bubble and reduce the CO 2 concentration by 177 ppm on average (Ghahramani et al, 2019). The use of personal fans can maintain comfortable thermal conditions while also reducing CO 2 concentration and improving perceived air quality even when the air movement is from recirculated room air (Zhang et al, 2010;Ghahramani et al, 2019).…”

“…A recent study has shown that using a desk fan can dissipate the CO 2 bubble and reduce the CO 2 concentration by 177 ppm on average (Ghahramani et al, 2019). The use of personal fans can maintain comfortable thermal conditions while also reducing CO 2 concentration and improving perceived air quality even when the air movement is from recirculated room air (Zhang et al, 2010;Ghahramani et al, 2019). Control algorithms that consider both thermal comfort and improvement in air quality need to be developed for control of PCS devices, such as fans or local air terminals.…”