MIL-HDBK-1011/2

APPENDIX C (continued)

Similarly for the large-scale model:

delta Pnl = (1/2 p Unl2)Cpn

EQUATION:

(23)

The total pressure coefficient measured on the large- scale model is assumed

to equal that on the small-scale model, and that on the full-scale building.

The interior wind velocities on the large-scale model Unl have been measured,

as well as the pressure differentials, WPns and WPnl. Dividing one equation

by the other leads to:

Uns = (delta Pns / delta Pnl) 1/2 Unl

EQUATION:

(24)

Interior air velocity ratios (the final answers) are then obtained as:

EQUATION:

Cvn = Uns /Uref

(25)

where

Uns

is the interior air velocity of the small-scale model for

the direction n, and

Cvn

is the ratio of interior air velocity to a reference mean

free-stream velocity.

1.3.4.3

Procedure for High-Rise Buildings. The second procedure is

particularly appropriate for the determination of interior airflow rates in

highrise buildings composed of typical floors, or typical living units. This

method may become cumbersome when many different interior space models are

required for a single building. An alternative method has been suggested by

Vickery (1981) to streamline the determination of airflow rates in highrise

buildingw with many different interior spaces.

Starting with mean pressure distributions obtained from a

small-scale model, interior airflow rates are computed analytically. Each

interior space is in essence a closed conduit. Basic laws of closed-conduit

flow can be used to determine airflow rates through each space, given the

pressure differential across the conduit, and the pressure loss coefficients

through halls, through openings, and around corners. A number of such computer

models have been developed. Refer to paras. 2.3 to 2.3.3 of this Appendix.

Use of Wind Tunnel Air Flow Rates. The airflow rates obtained from

1.3.5

wind tunnel tests alone do not determine whether or not a building can be

naturally ventilated. Interior airflow rates must be combined with other

information, particularly probability distributions of directional reference

velocities, temperature, humidity, and solar radiation, in order to determine

the appropriateness of naturally ventilating a space. See Appendices B and C,

para 1.1 for the minimum climatic considerations.

1.4

Field Modeling. Researchers at the Florida Solar Energy Center

(FSEC) have proposed testing small scale models outdoors in the natural wind

to observe airflow through naturally ventilated buildings. Their limited

testing (Chandra et al., 1983) shows excellent correlation between a one-story

building and a model tested in this manner on the actual building site.

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