Natural Ventilation Planning
Natural ventilation uses outdoor air to dilute heat, odors, and indoor pollutants. It works best when openings, room volume, wind direction, and temperature difference are reviewed together. This calculator turns those linked items into a practical airflow estimate. It does not replace a detailed code review, but it helps early design choices.
Why Airflow Matters
A room may feel stuffy even when windows are present. The issue is often weak pressure difference, limited opening area, or poor cross flow. Air changes per hour show how many room volumes are replaced each hour. Higher values can support cooling and freshness, yet too much flow may create drafts or energy loss.
Wind Driven Flow
Wind can push air through an inlet and pull it from an outlet. The effective opening area depends on the smaller path, screens, louvers, and sash position. A discharge coefficient accounts for losses at edges and fittings. A pressure coefficient difference describes how strongly wind acts across the building faces.
Stack Driven Flow
Stack flow comes from warm air rising. When indoor air is warmer than outdoor air, upper openings can exhaust buoyant air. Lower openings admit replacement air. Taller vertical separation increases the stack effect. Larger temperature difference also increases it. The calculator estimates this effect with absolute temperature and opening height.
Using Results Carefully
The combined airflow shown here uses a square root combination of wind and stack flows. This avoids simply adding two drivers that may not act together. Results should be checked against local codes, climate, noise, security, and rain protection. Designers should also review occupant control and maintenance.
Design Tips
Place openings on more than one side when possible. Keep interior paths clear. Use high and low openings for stack assistance. Consider insect screens and louvers in the effective area. Test several wind speeds and temperature cases. A small change in opening area can strongly change air change rate.
Example Workflow
Start with measured room dimensions. Enter the free area of the limiting opening. Choose a discharge coefficient that matches the hardware. Then compare a calm case with a windy case. If the air change rate is low, increase clear opening area, improve outlet placement, or add height separation safely.