7/27/2019 For Flue Gas Stacks and Chimneys

1/2

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:

where:

P= available pressure difference, in Pa

C= 0.0342

a = atmospheric pressure, in Pa

h = height or distance, in m

To = absolute outside temperature, inK

Ti = absolute inside temperature, in K

U.S. customary units:

where:

P= available pressure difference, inpsi

C= 0.0188

a = atmospheric pressure, inpsi

h = height or distance, in ft

To = absolute outside temperature, inR

Ti = absolute inside temperature, in R

The flow induced by the stack effect

The draft (draught in British English) flow rate induced by the stack effect can be calculated

with the equation presented below.[2][3][4] 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[2] explains how the NPL affects the stack effect in high-rise buildings.

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.

SI units:

where:

Q = stack effect draft (draught in British English) flow rate, m/s

http://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/Kelvinhttp://en.wikipedia.org/wiki/Kelvinhttp://en.wikipedia.org/wiki/U.S._customary_unitshttp://en.wikipedia.org/wiki/Pound-force_per_square_inchhttp://en.wikipedia.org/wiki/Pound-force_per_square_inchhttp://en.wikipedia.org/wiki/Rankine_scalehttp://en.wikipedia.org/wiki/Rankine_scalehttp://en.wikipedia.org/wiki/British_Englishhttp://en.wikipedia.org/wiki/Stack_effect#cite_note-Lecture2-2http://en.wikipedia.org/wiki/Stack_effect#cite_note-Lecture2-2http://en.wikipedia.org/wiki/Stack_effect#cite_note-Lecture3-3http://en.wikipedia.org/wiki/Stack_effect#cite_note-4http://en.wikipedia.org/wiki/Stack_effect#cite_note-Lecture2-2http://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/Kelvinhttp://en.wikipedia.org/wiki/U.S._customary_unitshttp://en.wikipedia.org/wiki/Pound-force_per_square_inchhttp://en.wikipedia.org/wiki/Pound-force_per_square_inchhttp://en.wikipedia.org/wiki/Rankine_scalehttp://en.wikipedia.org/wiki/British_Englishhttp://en.wikipedia.org/wiki/Stack_effect#cite_note-Lecture2-2http://en.wikipedia.org/wiki/Stack_effect#cite_note-Lecture3-3http://en.wikipedia.org/wiki/Stack_effect#cite_note-4http://en.wikipedia.org/wiki/Stack_effect#cite_note-Lecture2-2http://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/SI

7/27/2019 For Flue Gas Stacks and Chimneys

2/2

A = flow area, m

C= discharge coefficient (usually taken to be from 0.65 to 0.70)

g= gravitational acceleration, 9.81 m/s

h = height or distance, m

Ti = average inside temperature, KTo = outside air temperature, K

U.S. customary units:

where:

Q = stack effect draft flow rate, ft/s

A = area, ft

C= discharge coefficient (usually taken to be from 0.65 to 0.70)

g= gravitational acceleration, 32.17 ft/s

h = height or distance, ft

Ti = average inside temperature,R

To = outside air temperature, R

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.

The stack effect in chimneys: the gauges represent

absolute air pressure and the airflow is indicated with light grey arrows. The

gauge dials move clockwise with increasing pressure

http://en.wikipedia.org/wiki/Standard_gravityhttp://en.wikipedia.org/wiki/U.S._customary_unitshttp://en.wikipedia.org/wiki/Rankine_scalehttp://en.wikipedia.org/wiki/Rankine_scalehttp://en.wikipedia.org/wiki/Standard_gravityhttp://en.wikipedia.org/wiki/U.S._customary_unitshttp://en.wikipedia.org/wiki/Rankine_scale