Single-zone steady-state CO₂

Estimate steady indoor CO₂ from a specified total generation rate and outdoor airflow.

How this calculation works

Enter total carbon dioxide generation, outdoor-air supply flow and the outdoor concentration. Generation and airflow must use the same temperature and pressure basis. Dividing generation by outdoor flow gives a volume fraction, which is multiplied by one million to express the concentration rise in parts per million by volume. Adding the outdoor background gives the predicted indoor steady-state value. The flow input is fresh outdoor air, not the total supply including recirculated air. This model assumes one perfectly mixed zone, constant generation and enough time to reach equilibrium. It excludes removal processes and transfer from neighboring zones. The numerical concentration limit belongs to the dilute-model scope and is not a health threshold. Neither the result nor the example determines acceptable air quality, occupancy or ventilation-code compliance.

Inputs and units

Total CO₂ generation (L/s)
Outdoor-air supply (L/s)
Outdoor CO₂ concentration (ppmv)

Method and formula

Csteady = Coutdoor + 10⁶ G/Qoutdoor, with G and Q at the same temperature/pressure basis in L/s and concentrations in ppm by volume.

Worked example

Example inputs

Total CO₂ generation: 0.05 L/s
Outdoor-air supply: 100 L/s
Outdoor CO₂ concentration: 420 ppmv

Calculation steps

CO₂ excess above outdoors = 1000000 × 0.05 / 100 = 500 ppmv.
Predicted steady-state concentration = 420 + 500 = 920 ppmv.

Example results

Predicted steady-state CO₂: 920 ppmv
CO₂ above outdoors: 500 ppmv

Example notes

A CO₂ estimate is not an overall indoor-air-quality or health assessment.

Assumptions

One perfectly mixed zone; constant generation and outdoor flow; steady state reached.
No CO₂ removal, recirculation treatment or transfer from neighboring zones.

Limitations

Supply input is outdoor air, not total recirculating supply.
No health threshold, occupancy recommendation or ventilation-code determination.
Numerical scope capped at 10000 ppmv to retain a dilute-tracer approximation.
Preliminary educational check; verify inputs and equipment data before design or operation.

Sources

NIST: Carbon dioxide ventilation metric: Single-zone mass balance, equations 1–3; constant generation, outdoor concentration and outdoor airflow