What You Need to Know About The Stack Effect

Stack Effect and Natural Ventilation

If you’ve ever noticed that the attic in your house is warmer than the floors below? If so, then you’ve seen the stack ventilation in action. Stack effect ventilation uses this same principle to ventilate a building naturally. By taking advantage of the differences in air density inside, outside, and throughout the building a space can be made cooler.

mv stack effect

Many large commercial and industrial buildings utilize natural ventilation. By designing their building to vent the warm, stagnant air through the rooftop, and replace it with cool, fresh air the building is made cooler and more comfortable. This process is also known as the “Chimney Effect”, as it works the same way.

What is the Stack Effect?

When the air at the floor level of a building is warmer than the air at the ceiling, it is naturally compelled to flow to upward. Cold air is denser so it falls to the floor and/or will move into a building where the air is warmer.

This is a result of the density of the air particles at a molecular level. Warm air is less dense and as such rises upward. Different temperatures of air rise or fall accordingly. They tend to rest at different levels and “stack” one on top of the other.
Creating two openings in the building, one low and one high, to achieve a natural flow of air. If the temperature inside the building is higher than the temperature outside, the warmer air will naturally flow up and out through the higher opening. The resulting vacuum this movement creates will cause cooler air to be drawn in through the lower opening. Installing natural ventilators on a building’s roof, and wall louvers near the floor, allow for this air to easily travel through the building.

How Well does Stack Effect Ventilation Work?

The most important factor in determining the effectiveness of this type of natural ventilation is dependent upon the size of the building. If the building’s ceiling isn’t very high than the warm air is not actually moving away from the inhabitants. In these situations ventilating with the chimney effect has little impact. Stack effect ventilation requires a high ceiling to work properly.

The amount of heat in the building also plays a part. A building with a high-temperature process (say a glass furnace or a steel caster) will heat the air up to a higher temperature, causing it to rise faster. This increased rate means that the air moves through the building faster, turning over the air in the building more times per hour. Buildings with less heat, like a distribution center, may see less benefit. That isn’t to say that lower heat buildings can’t utilize natural ventilation, it would just require a different configuration or possibly powered intake air.

Other factors, such as the shape of the building itself, and its orientation (i.e. whether or not the intake side faces the wind) will impact how much of an impact the chimney effect ultimately has on the building.

In short, stack effect ventilation can make a huge difference in any facility. Directing warm air away from the building personnel, and letting it escape through the roof, will have a huge impact on interior conditions. Furthermore, technological advancements, such as CFD air-flow computer modeling, can make predicting the impact of natural ventilation easier to see

The Pros and Cons of Stack Effect Ventilation

PROS

  • Does not require the wind to be blowing. Works even when the air is completel
  • Relis on teh natural elements (Temperature and Gravity)
  • No Operating Costs.
  • No Emissions / No Energy Consumption.

CONS

  • Cannot completely control temperatures. The impact depends on exterior temperatures.
  • Can bring dust or polluted air into buildings

In conclusion, it’s important to weigh the Pros and Cons of stack-effect ventilation and see if your building can benefit from environmentally friendly ventilation. Our design team is confident that we’ll find the right system design for your facility.

Moffitt is now the exclusive U.S. partner for Colt Smoke Control & Daylighting Products.Learn More
+