During what condition does the stack effect become more pronounced in a building?

The stack effect, also known as the chimney effect, is a natural phenomenon that occurs when warm air rises and creates an upward movement of air within a building. This effect becomes more pronounced when there is a significant temperature difference between the inside and outside of the building.

When the inside air is warmer than the outside air, it becomes less dense and rises toward the upper parts of the building. This upward movement creates a negative pressure at the lower levels, drawing in cooler air from outside to replace the rising warm air. A substantial temperature difference enhances this effect, allowing for greater air movement and ventilation within the building.

This phenomenon can be particularly relevant in taller buildings where the vertical height allows for a more significant difference in air pressure created by the temperature variance. Consequently, the stack effect can lead to increased energy use for heating and cooling and may impact indoor air quality.

In contrast, when the temperature difference is minimal, the driving force behind the stack effect is reduced. Similarly, a low building height can diminish the effect since there is less distance for the warm air to rise and create noticeable pressure differences. Calm wind conditions may also affect the overall airflow but do not impact the stack effect as fundamentally as temperature differences do.