The NEBB Professional 2024 - Quarter 2

able to provide shelter.” A canopy is distinct from an awning, which is a cantilevered cover attached to the building, because the canopy can be suspended or free standing. Figure 3 illustrates a canopy connection as envisioned by the Industrial Ventilation Handbook. 1

With this nomenclature, Equation 2 gives the total perimeter, P, and Equation 3 yields the cross-sectional bypass area, A B . X and Y are the nominal dimensions of the exhaust HEPA filter.

Equation 2:

P = 2 * x + 2 * y

Equation 3:

Figure 3: Canopy Connection

A B = P * D Equation 4 gives the bypass CFM (Q B ) as a function of area and velocity, V B , where K V is an empirical, dimen sionless correction factor. Q B = A B * V B * K V Our internal laboratory research at VTG, LLC. charac terizes the variation (loss of constancy) of work access opening inflow, Q I , at various canopy suction pres Equation 4:

Figure 4

1 Adapted from Fig. 4-4 of Industrial Ventilation Handbook – A Manual of Recommended Practice , American Conference of Governmental Industrial Hygienists (ACGIH)- 19th edition 1986.

The NEBB Professional | Quarter 2 | 2024

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