On the Impact of CO2 Concentration in the Inhaled Air on the CO2 Emission Rate by People

Current paper presents information, obtained by a human subjects experiment, about the impact of CO2 concentration in the inhaled air on the CO2 emission rate by people. Thirty subjects, 15 females and 15 males, participated in the experiment. All subjects, feeling thermally neutral at 26oC, were exposed in a small chamber under perfect mixing conditions to a low (800 ppm) and to a high (1700 ppm) concentration of CO2. During the exposure period of 60 minutes volume flow rate of both supply air and exhaust air as well as air temperature, relative humidity and CO2 volume fraction in both streams was measured continuously. The exposure period was divided into two phases with respect to CO2 volume fraction time variation: build-up phase with duration of 11 to 15 minutes, followed by a steady state phase. Based on the records of the measured parameters the CO2 emission rate for each participant was calculated for the steady-state phase. At the lower CO2 concentration in the inhaled air (812±72 ppm), the group average CO2 emission rate was 7.1% higher than that at the higher CO2 concentration (1699±67 ppm). The result was statistically significant (p=0.0015) and was registered after 15 minutes of exposure. This result suggests that CO2 emission rate by people in occupied spaces depends on both personal parameters (Metabolic rate, W) and environmental parameters (inhaled air composition). It may be concluded that all calculations based on the assumption that metabolic CO2 generation rate in occupied spaces by people depends only on the metabolic rate is with unknown uncertainty.