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API RP 500, Ventilation

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Free Area of Inlet Openings formula

\(\large{ A =  \frac{ V }{ 1200 \; \sqrt{    \frac{ h \; \left( T_i \;-\; T_o  \right) }{ T_i  }    }  }   }\)   

Where:

\(\large{ A }\) = free area of inlet (or outlet) opening (s)

\(\large{ V }\) = volume of building to be ventilated

\(\large{ h }\) = height from the center of the louver opening to the Neutral Pressure Level (NPL)

\(\large{ T_i }\) = temperature of indoor air

\(\large{ T_o }\) = temperature of outdoor air

 

Height from the center of the louver opening to the Neutral Pressure Level formula

\(\large{ h =  \frac{ H }{  1 \;+\; \left[  \left( \frac{ A_1 }{ A_2 } \right)^2  \;  \left( \frac{ T_i }{ T_o } \right)   \right]   }     }\)   

Where:

\(\large{ h }\) = height from the center of the louver opening to the Neutral Pressure Level (NPL).  The NPL is the point on the vertical surface of a building where the interior and exterior pressures are equal.

\(\large{ H }\) = vertical distance (center to center) between A_1 and A_2

\(\large{ A_1 }\) = free area of lower opening

\(\large{ A_2 }\) = free area of upper opening

\(\large{ T_i }\) = temperature of indoor air

\(\large{ T_o }\) = temperature of outdoor air

 

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