Many buildings across the country were unable to maintain comfortable temperatures this winter due to the extreme cold. While thermostats were set to maintain comfortable temperatures, many residents found it nearly impossible to keep warm, even if the buildings were tall. A possible reaction for this could be the stack effect.

The stack effect is a common but not well-understood problem. The stack effect can cause huge problems after construction is completed, once a building is occupied; that is why Mechartes does its best to recognize it before it occurs, helping our clients to deal with it at the conceptual stage.

Check out this article for a diagnosis and tips for prevention if you think you could be affected. So, what is the stack effect in buildings? Here’s all you need to know.

An Overview of the Stack Effect

The stack effect can be explained as indoor air being blown through a building envelope by large volumes of outside air. All types of buildings use this phenomenon to circulate air, cool, and heat. Understanding the stack effect is a matter of knowing two basic concepts. The first is that heat follows cold. To achieve a uniform temperature through its flow, air seeks equilibrium at all times.

Secondly, cold air sinks and hot air rises. Because of this, the upper levels of a tall building are generally warmer. Lower pressure at the bottom is caused by this law of physics, causing the convection of air. At the bottom, cracks and air gaps are created by the pressure difference and the flow of air. This is also known as the Chimney Effect.

Tall buildings experience this phenomenon when outdoor temperatures are significantly lower than inside temperatures. The warmer, indoor air rises, so it pushes upwards through various openings in the upper floors to exit the building. Due to this movement, the lower levels experience negative air pressure, which draws cold air from the outdoors. Lower floors are subject to negative pressure when the building is tall and the temperature outdoors is cold.

If not addressed properly, the air in a high-rise building on the street level is likely to be replaced in under a minute. It may take up to 30 minutes for this same area to get warm again, with closed doors, which then creates unmanageable heating requirements in extremely cold temperatures. So how does the stack effect work? Scroll down to learn.

Here’s How the Stack Effect Works

Picture a ground-floor business in a 70 storey tower. Their location has prompted them to have street and lobby entrances. During the morning and lunch hours, both entrances see high levels of traffic. If the outdoor temperatures fall below 20 to 30 degrees Fahrenheit, the building will be under extreme negative pressure.

Let’s assume some pressure readings that confirm the above scenario. Similar to the morning rush hour, if both sets of doors were opened simultaneously, air would exit the store and enter the lobby while the opposite would happen outside. Considering the current volume of the room, if it remained as is, the warm air would replace it within 60 seconds with 20-degree air. It was necessary to disrupt the airflow out of the space to help minimize the stack effect in this room. To reduce cold air infiltration during rush hour, a revolving door will be the right option, as it prevents two entrances from opening simultaneously. So, if a stack effect does happen, can that be managed?

How to Manage Stack Effect?

The stack effect can be minimized in several straightforward ways, but we will be focusing on each space at the ground level or sub-grad level. In most cases (retailers, supermarkets, restaurants, etc.) these spaces share common walls with the core of the building.

Whenever there is a connection between the building core and the outside, the buoyant air leaking through these openings can create negative pressure on lower floors and pull air in. Separating the lower-level spaces from the building core is the key to solving subsequent stack effects.

The walls, floors, floor slabs above and below must be sealed to prevent leakage into the building area. The spaces can be regulated by their environment if you achieve this since they will no longer be affected by the building pressure. It has been our experience that the plans before construction meetings are often not followed to seal the openings.

Once a space is occupied, it’s very difficult to detect and correct the stack effect. So, how does Mechartes handle the stack effect in buildings?

How Mechartes Can Help with the Stack Effect in Buildings

We believe that sealing the space in three stages is the most effective way to do it:

• If all surfaces are exposed after demolition, it is recommended you seal the surfaces before applying pressure to make sure there are no openings.

• As soon as construction has begun, the space should undergo another pressure test before the ceiling is closed, so there are no further leaks.

• Early in the building process, check that no openings have been accidentally created.

• A final pressure test should be performed to inspect for leaks after substantial completion.

• The previous tests should have identified any openings at this point.

Building owners and managers can save up to 30 percent by utilizing natural ventilation. The stack effect within a building should be controlled by controlling how air is mixed in with the current air. The flow of air can be directed through occupied spaces by interior walls and window transoms. Indirect pathways ensure that fresher air mixes with and removes stale air. A stack effect should sweep stale air upwards and out of interior exhaust openings. For natural ventilation, new buildings should be constructed so that they catch the summer breeze and block the winter cold.

It usually takes an average of one day or evening to complete a pressure test. Compared to the effects of stacking, this process has a minimal financial impact. As we assist clients with high-rise projects where the stack effect could occur, we inform them of the risks that could result and how to prevent them. Mechartes also offers pressure testing and commissioning to assist clients with troubleshooting pressurization issues. Feel free to contact us if your building has experienced extreme temperature fluctuations. Rest assured as we can provide a resolution to your problem.