Demand-Controlled Ventilation Rate from a CO2 Setpoint
The outdoor air per person that holds a CO2 setpoint: the steady-state single-zone mass balance C_in = C_oa + N/Q, solved as Q = N / (C_set - C_oa) with a sedentary generation of about 0.0106 cfm per person. A 1,100 ppm setpoint against 400 ppm outdoor air works out to the classic 15.1 cfm/person office rate; tighten to 800 ppm and the DCV control must drive 1.75x the air. Equilibrium airflow in one fully mixed zone - CO2 is an occupancy indicator, and the ASHRAE 62.1 Ventilation Rate Procedure governs the minimum. A controls and commissioning aid.
Formula and source
dC_frac = (co2_set_ppm - co2_oa_ppm) / 1e6; Q_person_cfm = gen_cfm / dC_frac; Q_total_cfm = Q_person_cfm x n; co2_check_ppm = co2_oa_ppm + (gen_cfm / Q_person_cfm) x 1e6.
The steady-state single-zone CO2 mass balance (C_in = C_oa + N / Q, solved for the per-person outdoor airflow Q = N / (C_set - C_oa)) with the ASHRAE 62.1 note that CO2 indicates occupant-generated bioeffluents and a common sedentary generation rate of about 0.0106 cfm per person, by name.
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