Investigating the effect of CO2 concentration on reported thermal comfort

Abstract

The need to predict occupants’ perception of thermal discomfort has become one of the priorities in the quest to reduce energy demand in buildings. Drawn from physical and physiological principles, the current thermal comfort models have long been associated with environmental and personal variables. Research has shown that there is often gap between modelled and perceived thermal comfort sensation. One of the reasons may be additional parameters playing a role which are not currently accounted for in the models. One plausible candidate and causal pathway is elevated CO2 levels stimulating the human respiratory system resulting in increased metabolic rate and heat exchange with the environment. The hypothesis is that people may feel warmer when indoor CO2 concentration increases. To investigate this hypothesis, two empirical studies were carried out in London; the first one was undertaken in a climate chamber over the summer of 2014, and the second one in an office setting over the winter of 2015. Findings from the first experiment showed that participants felt on average warmer as CO2 concentration increased but ambient temperature remained constant. However the relationship between reported comfort and CO2 concentration was not significant. One may suggest that heating setpoint may be adjusted at lower temperature in winter while keeping CO2 concentration low enough not to affect cognitive performance. This conjecture initiated the study design of the second experiment. As ambient temperature decreased by 3.1±0.5°C, CO2 concentration increased by 297±45ppm. In this instance, participants felt slightly colder at the end of the sessions; however a modest relationship between CO2 was found. Thus future studies may chose to increase the variation in CO2 concentration, and decrease the variation in operative temperature. To conclude the picture that is emerging from this research shows that there is no significant relationship between reported thermal comfort and CO2 concentration; although this may be due to the relatively small sample size in the first study, and the relatively small variation in CO2 concentration in the second study. This finding may support building operation strategies that optimise fresh-air level independently of the provision of thermal comfort

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ORCID for S. Gauthier: orcid.org/0000-0002-1720-1736

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