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3.3 CO2 Concentration Limit

California's Building Energy Efficiency Title 24 Standards specifies that:

Demand ventilation controls shall maintain CO2 concentrations less than or equal to 600 ppm plus the outdoor air CO2 concentration in all rooms with CO2 sensors” and specifies that the outdoor CO2 concentration, if not measured, should be assumed to equal 400 ppm. Thus, the maximum CO2 set point must be 1000 ppm or less, when the outdoor air CO2 concentration is not measured. 

This figure provides estimates of the steady state relationship of indoor CO2 concentrations with ventilation rates per persons in three different building types. To develop the figure, estimates of CO2 generation rates per occupant for office and elementary schools were from Persily and de Jonge [12], and from Chan et al. [13] for retail stores. The relationship varies among space types because CO2 generation rates per person vary as a function of occupant features (e.g., weight) and activity levels: 0.0048 L/s-person (office), 0.003 L/s-person (classroom, K-3 grade), 0.01 L/s-person (retail store). This figure can be used to select CO2 set point concentrations for DCV applications when a default set point is not utilized.