Stack effect: Difference between revisions

Revision as of 11:57, 10 January 2017

Revision as of 12:05, 10 January 2017

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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.<ref name="Lecture2">[http://www.ides-edu.eu/wp-content/uploads/2013/04/Ventilation_lecture-2_PH-Alleen-lezen.pdf Natural Ventilation Lecture 2]</ref><ref name="Lecture3">[http://www.ides-edu.eu/wp-content/uploads/2013/04/Ventilation_lecture-3_PH-Alleen-lezen.pdf Natural Ventilation Lecture 3]</ref> 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<ref name="Lecture2"/> 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 fuelflue gas stack or chimney.

:<math>\Delta P = C a h \bigg(\frac {1}{T_o} - \frac {1}{T_i}\bigg)</math>

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The draft (draught in [[British English]]) flow rate induced by the stack effect can be calculated with the equation presented below.<ref name=Lecture2/><ref name=Lecture3/><ref>[http://www.wbdg.org/resources/naturalventilation.php ''Natural Ventilation'', Andy Walker, National Renewable Energy Laboratory] (US Department of Energy)</ref> The equation applies 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 and '''''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. Reference<ref name=Lecture2/> explains how the NPL affects the stack effect in high-rise buildings.

For fuelflue gas stacks or chimneys, where air is on the outside and combustion fuelflue 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.

:<math>Q = C A \sqrt {2gh\frac{T_i - T_o}{T_i}}</math>