A New Approach to Estimating Carbon Dioxide Generation Rates from Building Occupants

Indoor carbon dioxide (CO2) concentrations have been used in the fields of building ventilation and indoor air quality (IAQ) for decades. Specific applications include the estimation of ventilation rates, control of outdoor air ventilation rates based on indoor CO2 as an indicator of occupancy, and use of CO2 as an IAQ performance metric. All of these applications require values for the CO2 generation rates of the occupants of the space or building being considered. Human CO2 generation rates depend on their level of physical activity as well as their sex, age, and body size. Historically and currently, these rates have been based on formula and data from the literature that are many decades old. In many cases, a single value for an adult on the order of 0.3 L/min is used independent of individual characteristics that are known to impact CO2 generation rates. While the fields of human metabolism and exercise physiology have been studying human energy use, oxygen consumption and CO2 generation for many decades, that knowledge has not been incorporated by the ventilation and IAQ communities. This paper describes the known dependencies of CO2 generation rates on occupant characteristics and presents a calculation method for estimating these generation rates based on these concepts. This method is more robust and up-to-date than previously-established calculation procedures and will support more accurate values of CO2 generation rates for use in ventilation and IAQ applications. The paper also compares the CO2 generation rates using the new approach to those from the approach commonly used today as well as the resulting steady-state concentrations for different space types.