Demand-Controlled Ventilation Rate from 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.

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.

The single-zone mass balance is a public closed-form relation; ASHRAE 62.1 is readable free at ashrae.org.

Estimate. AHJ and licensed professional govern.

Field names used by the API: n, co2_set_ppm, co2_oa_ppm, gen_cfm, Q_person_cfm, Q_total_cfm, co2_check_ppm

• Mass balance C_in = C_oa + N / Q at steady state in one fully mixed zone; Q = N / (C_set - C_oa)single-zone mass balance
• Generation rate about 0.0106 cfm CO2 per sedentary person (editable for activity level)ASHRAE 62.1 guidance
• Indicator only CO2 indicates occupancy; the Ventilation Rate Procedure governs the minimum outdoor airASHRAE 62.1