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Calculation of the Flow Through a Horizontal Ceiling/Floor Vent.



Leonard Y. Cooper


Calculation of the flow through a horizontal vent located in a ceiling or floor of a multi-room compartment is considered. It is assumed that the environments of the two, vent-connected spaces near the elevation of the vent are of arbitrary relative buoyancy and cross-vent pressure difference. An anomaly of the standard vent flow model is discussed. The problem occurs in practical vent configurations of unstable hydrostatic equilibrium, where, for example, one gas overlays a relatively less-dense gas. In such configurations the cross-vent flow is not uni-directional. Previously published experimental data on a variety of related flow configurations are used to develop a general flow model which does not suffer from the standard model anomaly. The model developed leads to a uniformly valid algorithm, called VENTCL, for horizontal vent flow calcualtions suitable for general use in zone-type compartment fire models. Based on an assumption of total consumption of net oxygen flow rate, the algorithm is used in an example application where steady-state rate-of-burning in a ceiling-vented room is estimated as a function of room temperature, vent area, and oxygen concentration.
NIST Interagency/Internal Report (NISTIR) - 89-4052
Report Number


vents, algorithms, building fires, compartment fires, computer models, computer programs, fire models, pressure differential, pressure effects, zone models, ceiling vents, oxygen concentration


Cooper, L. (1989), Calculation of the Flow Through a Horizontal Ceiling/Floor Vent., NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed May 27, 2024)


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Created February 1, 1989, Updated November 10, 2018