Calculate outdoor air and return air fractions from CFM values, or find required OA CFM from a target OA%. Includes economizer analysis.
| System Type | Typical OA% | Notes |
|---|---|---|
| Minimum ventilation (VAV cooling) | 10–20% | ASHRAE 62.1 minimum; summer operation |
| Partial economizer | 20–70% | OA cooler than return; free cooling assist |
| Full economizer | 70–100% | Compressor relief; dry/cool OA conditions |
| 100% OA (DOAS, Labs, OR) | 100% | No recirculation; critical / hazardous spaces |
| Heating mode | 10–15% | Minimize cold OA; increase RA for heat retention |
| Dedicated OA unit | 100% | Supplies only ventilation air; separate recirculation |
This calculator handles one step. AIM Works runs the complete MEP design workflow — thermal load calculations, duct & pipe networks, equipment selection, code compliance, and an AI design assistant — in one tool.