In buildings
Since buildings are not totally sealed (at the very minimum, there is always a ground level entrance), the stack effect will cause air infiltration. During the heating season, the 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 theUsefulness in passive cooling
Some buildings are designed with strategically placed openings at different heights to induce the stack effect where cool air enters through low-level windows or vents, and warm air escapes through higher-level openings like skylights, roof vents, or clerestory windows. This vertical movement of air creates a natural ventilation system that can significantly reduce indoor temperatures. Combining the stack effect with cross ventilation, where airflow moves across the building from one side to the other, can enhance the overall cooling effect. The stack effect is used both in traditional buildings and modern green architecture. Examples of traditional usage include the wind towers common in Middle Eastern architecture, which capture and direct cooler breezes into the building while expelling hot air to maintain comfortable indoor temperatures. Contemporary sustainable buildings often make use of the stack effect along with related non-electric techniques like ground coupling, earth sheltering, and evaporative cooling to enhance the passive cooling profile of a building. By carefully designing the building's structure, orientation and ventilation paths, architects can leverage the stack effect to reduce reliance on mechanical cooling systems and improve overall energy efficiency.Normal and reverse stack effect
Two regimes of stack effect can exist in buildings: normal and reverse. Normal stack effect occurs in buildings which are maintained at a higher temperature than the outdoor environment. Warm air within the building has a low density (or high specific volume) and exhibits a greater buoyancy force. Consequently, it rises from lower levels to upper levels through penetrations between floors. This presents a situation where floors underneath the neutral axis of the building have a net negative pressure, whereas floors above the neutral axis have a net positive pressure. The net negative pressure on lower floors can induce outdoor air to infiltrate the building through doors, windows, or ductwork without backdraft dampers. Warm air will attempt to exfiltrate the building envelope through floors above the neutral axis. Mechanical refrigeration equipment provides sensible and latent cooling during summer months. This reduces the dry-bulb temperature of the air within the building relative to the outdoor ambient air. It also decreases the specific volume of the air contained within the building, thereby reducing the buoyancy force. Consequently, cool air will travel vertically down the building through elevator shafts, stairwells, and unsealed utility penetrations (i.e.,In flue gas stacks and chimneys
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 allowed air into the mine. At the foot of the upcast shaft a furnace was kept continuously burning. The shaft (commonly several hundred yards deep) behaved like a chimney and air rose through it drawing fresh air down the downcast stack and around the mine.Cause
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. That pressure difference ( ''ΔP'' ) is the driving force for the stack effect and it can be calculated with the equations presented below. The equations apply only to buildings where air is both inside and outside the buildings. 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) of 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 inside, the equations will only provide an approximation and ''h'' is the height of the flue gas stack or chimney. : : SI units: : : U.S. customary units: :Induced flow
The draft (draught inSee also
* HVAC (heating, ventilation and air conditioning) * Ventilation shaft * Solar chimney * Solar updraft tower * Draft (boiler) * Inco Superstack * Ekibastuz GRES-2 Power Station * Windcatcher * Cross ventilationReferences
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