Explain stack ventilation and how it improves indoor cooling in tropical climates.

• A. It relies on external wind pressure on openings to push air through.
• B. Stack ventilation uses buoyancy from heated indoor air rising and drawing in cooler air from lower openings, creating vertical air movement that cools spaces.
• C. It blocks airflow to keep spaces sealed.
• D. It uses mechanical fans to exhaust air at high speed.

Answer: (B)

Stack ventilation uses buoyancy to move air: when indoor air is heated by sun, people, and equipment, it becomes lighter and rises to exit through high openings. As the warm air climbs, cooler outdoor air is drawn in through lower openings to replace it, creating a continuous vertical flow that sweeps through the space. That upward movement carries heat and moisture out of the building, reducing the indoor thermal load and improving comfort in tropical climates where outdoor air is often hot and humid. The effect is strongest when there are openings at different vertical levels and a sufficient height difference to sustain the draft; it can be boosted by features like solar chimneys or atria that increase buoyancy. This is a passive strategy, unlike ventilation driven by wind pressure, airtight sealing, or mechanical exhaust fans.