Stack Effect – Defined
The “stack effect” is when warm air moves upward in a building. This happens in summer and winter, but is most pronounced in the winter because indoor-outdoor temperature differences are the greatest. Dec 23, · Stack effect, also called chimney effect, drives airflow through buildings. Controlling air movement into and through a building can increase energy efficiency and save money. What Is Stack Effect? Stack effect is air movement caused by thermal differences. Higher-temperature air is less dense than cooler air.
Stack effect or chimney effect is the movement of air into and out of buildings, chimneysflue-gas stacksor other containers, resulting from air buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force.
The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect helps drive natural ventilationair infiltrationand fires e. Since buildings are not totally sealed at the very minimum, there is always a ground level entrancethe stack effect will cause air infiltration. During the heating season, how to start an online literary magazine warmer indoor air rises up through the building and escapes at the top either through open windows, ventilation openings, or unintentional holes in ceilings, like ceiling fans and recessed lights.
The rising warm air reduces the pressure in the base of the building, drawing cold air in through either open doors, windows, or other openings and leakage. During the cooling season, the stack effect is effech, but is typically weaker due to lower temperature differences.
In a modern high-rise building with a well-sealed envelopewyat stack effect can create significant pressure differences that must be given design consideration and may need to be addressed with mechanical ventilation.
Stairwells, shafts, elevators, and the like, tend to contribute fefect the stack effect, while interior partitions, floors, and fire separations can mitigate it. Especially in case of fire, the stack effect needs to be controlled to prevent the spread of smoke and fire, and to maintain tenable conditions for occupants and firefighters.
Smoke extraction is a key consideration in new constructions and must be evaluated in design stages. The Grenfell Tower fireas a result of which 71 people died,  was in part exacerbated by the stack effect.
A cavity between the outer aluminium cladding and the inner insulation formed a chimney and drew the fire upwards. The stack effect in industrial flue gas stacks is similar to that in buildings, except that it involves hot flue gases having large temperature differences with the ambient outside air. Furthermore, an industrial flue gas stack typically provides little obstruction for the flue gas along its length and is, in fact, normally optimized to enhance the stack effect to reduce fan energy requirements.
Large temperature differences between the outside air and the flue gases can create a strong stack effect in chimneys for buildings using a fireplace for heating.
Before the development of large volume fans, mines were ventilated using the stack effect. A downcast shaft effwct air into the mine. At the foot of the upcast shaft a furnace was kept continuously burning.
The shaft commonly several hundred wffect deep behaved like a chimney and air rose through it drawing fresh air down the downcast stack and around the mine. There is a pressure difference between the outside air and the air inside the building caused by the difference in temperature between the outside air and the inside air.
For buildings with one or two floors, h is the height of the building. For multi-floor, high-rise buildings, h is the distance from the openings at the neutral pressure level NPL xtack the building to either the topmost openings or the lowest openings. Reference  explains how the NPL affects the stack effect in high-rise buildings. For flue gas stacks and chimneys, where air is on the outside and combustion flue gases are on the what is a simulation program, the equations will only provide an approximation and h is the height of the flue gas stack or chimney.
The draft draught in British English flow rate induced by the stack effect can be calculated with the equation presented below. For buildings with one or two floors, h is the height of the building efrect A is the flow area of the openings. For multi-floor, high-rise buildings, A is the flow area of the openings and h is the distance from the openings at the neutral pressure level NPL of the building to either the topmost openings or the lowest openings.
For flue gas stacks or chimneys, where air is on the outside and combustion flue gases are on the inside, the equation will only provide an approximation. Also, A is the cross-sectional flow area and h is the height of the flue gas stack or chimney. This equation assumes that the resistance to the draft flow is similar to the resistance of flow through an orifice characterized by a discharge coefficient C.
From Wikipedia, the free encyclopedia. This article needs attention from an expert in Engineering. The specific problem is: See Talk page, section "missing explanation, where the constant C stems from". WikiProject Engineering may be able to help recruit an expert. July Concept in physics. Retrieved The Guardian. Retrieved 16 November Update: Grenfell What is the stack effect fire investigation".
Retrieved 6 July The Independent. Archived from the original on 14 June Retrieved how to check ups battery health June Archived from the original PDF on 12 February Retrieved 12 February Retrieved 4 October National Institute of Building Sciences.
Retrieved 1 April AM10 Natural ventilation in non-domestic buildings. ISBN Heating, ventilation, and air conditioning. Architectural acoustics Architectural engineering Architectural technologist Building services engineering Building information modeling BIM Deep energy retrofit Duct leakage testing Environmental engineering Hydronic balancing Kitchen exhaust cleaning Mechanical engineering Mechanical, electrical, and plumbing Mold growth, assessment, and remediation How to build faith in yourself reclamation Testing, adjusting, what is the stack effect. Categories : Building engineering Chemical engineering Heating, ventilation, and air conditioning Thermodynamics Buoyancy.
Hidden categories: Articles needing expert attention sstack July All articles needing expert attention Engineering articles needing expert attention Articles with short description Short description is different from Wikidata All accuracy disputes Articles with disputed statements stafk June Namespaces Article Talk. Views Read Edit View history. Help Learn to edit Community portal Recent staci Upload file. Download as PDF Printable version.
What is the Stack Effect?
Sometimes called the chimney effect, the stack effect is a naturally-induced vertical flow of air through a structure. In low-rise structures, the effect is often small enough as to be negligible, but in high-rise towers, the stack effect can be a powerful driver of airflow. Stack effect is a phenomenon that occurs whenever the temperature inside a building and outside it are different. Sometimes stack effect can be useful: It contributes to natural ventilation. However, it often has adverse effects that reduce the quality of the occupant experience in a building. When poorly managed, stack effect can exertFile Size: 1MB. Mar 23, · One of our basement repair experts, Aaron, explains the stack effect and how it can draw soil gases and moisture into your basement or crawlspace. Aaron also.
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. 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. 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.
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. 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.
The most important factor in determining the effectiveness of this type of natural ventilation is dependent upon the size of the building. 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.
Other factors, such as the shape of the building itself, and its orientation i. 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. What is the Stack Effect? CONS Cannot completely control temperatures.