Inter- and intra-individual variability in CO2 production and metabolic rate

Carbon dioxide generated by the human body and exhaled (VCO2) is commonly used for ventilation controls, while the metabolic rate (i.e., energy expenditure EE) is an important parameter defining human thermal comfort in buildings. These two parameters are interlinked, as VCO2 is dependent on human metabolism, and metabolic rate is a function of food oxidation and exhaled CO2. With the advancement of a human-centered approach to the built environment, understanding the variation of these parameters across individuals and even within the same individuals becomes important. Therefore, this study reports the variability of 6 individuals’ exhaled CO2 rates and metabolic rates during different low-level activities and thermal exposures in the range of 22-28oC. In addition, the measured values were compared to the standard ones to understand the discrepancies between them. VCO2 and EE increase with the increase in the activity level, and the overall magnitude of values is greater in males compared to females. Intra-individual variability in VCO2 and metabolic rate was about 19-52%, while inter-individual reached 44%. The variability could be attributed to differences in respiration rate, breathing depth, body composition, and thermal history of individuals that would require further investigation. When compared to standardized approaches, VCO2 values were overpredicted by 11-15%, and metabolic rate values were overestimated in some almost twice.