Which condition contributes to stack effect in a building?

Which condition contributes to stack effect in a building?

• A. Mechanical ventilation
• B. Outdoor temperature only
• C. Indoor/outdoor temperature difference
• D. Solar radiation

Answer: (C)

Stack effect happens when there’s a buoyancy-driven air flow due to a temperature difference between inside and outside. Warmer indoor air is less dense and tends to rise, exiting through the building’s upper openings. Cooler outdoor air then gets drawn in at lower levels to replace it, creating a vertical air movement that changes everywhere from bottom to top. The strength of this effect rises with a larger indoor-outdoor temperature difference and with greater building height, since more buoyancy and a longer column of air amplify the flow. Mechanical ventilation can influence how this flow manifests, but it’s not what creates stack effect. Outdoor temperature alone isn’t enough to cause it—the key factor is the temperature difference across the building. Solar radiation can change temperatures, but the direct cause of stack effect is the indoor-outdoor temperature difference.

Stack effect happens when there’s a buoyancy-driven air flow due to a temperature difference between inside and outside. Warmer indoor air is less dense and tends to rise, exiting through the building’s upper openings. Cooler outdoor air then gets drawn in at lower levels to replace it, creating a vertical air movement that changes everywhere from bottom to top. The strength of this effect rises with a larger indoor-outdoor temperature difference and with greater building height, since more buoyancy and a longer column of air amplify the flow. Mechanical ventilation can influence how this flow manifests, but it’s not what creates stack effect. Outdoor temperature alone isn’t enough to cause it—the key factor is the temperature difference across the building. Solar radiation can change temperatures, but the direct cause of stack effect is the indoor-outdoor temperature difference.