Calculator
Example data table
| Scenario | Volume (m³) | Outdoor (ppm) | Current (ppm) | Target (ppm) | Net source (g/h) | Leak (ACH) | Mode | Time (min) |
|---|---|---|---|---|---|---|---|---|
| Seedling house | 72 | 420 | 1100 | 800 | 0 | 0.2 | Purge | 30 |
| Enrichment test | 120 | 420 | 900 | 1000 | 45 | 0.5 | Steady | — |
| Hot day venting | 200 | 450 | 1600 | 900 | 0 | 1.0 | Purge | 15 |
Formula used
This calculator uses a simple mass-balance model for a well-mixed greenhouse:
- Volume V = Area × Height
- Leak airflow Q_leak = ACH_leak × V
- Net CO2 source G = Injection − Uptake (converted to mg/h)
- Steady state: C_target = C_out + G / (η·Q_total)
- Purge mode: C(t)=C_out + G/(ηQ) + (C0−C_out−G/(ηQ))·e^{−(ηQ/V)t}
Here η is mixing efficiency. Concentrations are computed in mg/m³ internally, using temperature-adjusted ppm conversion for CO2.
How to use this calculator
- Enter floor area, average height, and temperature.
- Enter outdoor, current indoor, and target CO2 readings.
- Optionally add injection and plant uptake rates.
- Set leakage ACH and mixing efficiency for realism.
- Pick “purge” for fast corrections, or “steady” to hold a setpoint.
- Click Calculate, then export CSV or PDF for records.
Tip: If your result seems too high, check sensor placement and mixing. CO2 stratifies quickly in calm air.