Experimental Study Of Human Carbon Dioxide Generaton Rate At Different Activity Levels

Nowadays,people spend 80-90%of their time indoors,working in buildings,sleeping,resting,and exercising.As a result,people have high demands not only on their comfort but also on their health.Indoor carbon dioxide concentrations have long been used as an important indicator of indoor air quality,but also as a tracer gas for indoor environmental quality and ventilation efficiency.For residential buildings,the main source of indoor CO₂ is human metabolism,so indoor CO₂ generation is widely used in ventilation design and control.However,current CO₂ generation data are based on methods and data from several decades ago,and most of the data in the domestic ventilation standards are borrowed from foreign standards,the applicability to the Chinese population needs to be further studied.The current study found that there is a strong correlation between CO₂ generation and activity levels.In the past,CO₂ generation was calculated indirectly from the metabolic rate data of human activity,and systematic experimental measurements of CO₂ generation at different activity levels were rare.In the present study,the carbon dioxide generation at different activity levels was experimentally measured by collecting exhaled carbon dioxide gas directly using a high-precision indirect calorimeter（COSMED K5）.99 subjects aged between 20 and 70 years participated in the experimental test,with 10 years as an age group,10 males and 10 females in each age group（except for the following）.（9 males in the 40-49 age group）.The experiments were carried out in an artificial climate chamber at the Xi’an University of Architecture and Technology and the experiments were carried out during the transition season in order to exclude climatic influences.During the experiment,the air temperature was controlled at 26°C±0.5°C,the relative humidity was controlled at 50%and the wind speed was 0.01 m/s.A total of 18 activity states were tested for carbon dioxide production,including sedentary,standing office activities,household activities and walking.The results showed that CO₂ production increased significantly with increasing activity levels.Age has a small effect on the amount of carbon dioxide generated,with the maximum absolute difference being 0.05 L/min.This result makes it easier to design ventilation in public buildings without the need to differentiate between different age groups.The effect of gender on the amount of CO₂ generated.For the same level of activity,women produce less CO₂ than men,which is probably mainly due to differences in body composition between men and women.In order to better apply this to practical design,a regression equation for CO₂ generation was established using lasso regression with gender and age as the main influencing factors.A comparison with the CO₂ generationrates models in mainstream ventilation standards at home and abroad shows that there are significant differences between the proposed regression equation and the CO₂ generation predicted by the models in ASHRAE 62.1 and ASTM D6245-18.The CO₂ generation for males in this study is close to the ASHRAE 62.1 data,while the data for females is below the ASHRAE 62.1 standard.Compared to ASTM D6245-18,the model predicts higher CO₂ generation for both males and females than the model prediction in ASTM D6245-18.Applying the regression model of CO₂ generation ratesto the calculation of the fresh air requirement for ventilation design,it was found that the fresh air requirement for different activity levels in this study was on average 8.0%-30.1%lower than the standard,therefore,according to previous design standards,the high fresh air requirement resulted in an unnecessary increase in fresh air energy consumption.These findings provide basic data for designers and researchers in the field of ventilation and indoor air quality,as well as for future revisions of ventilation standards.