? p

= vapor pressure differential, in. Hg (kPa)

? T

= temperature difference, F ( C)

?

= efficiency, %

v

= specific volume, ft ³/lb (m ³/kg)

?

= density, lb/ft ³ (kg/m ³)

A

= area, in. ² or ft ² (mm ² or m ²)

bhp

= fan brake horsepower, hp (kW)

C _s

= separation coefficient

D

= diameter, in. (mm)

db

= dry-bulb temperature, F( C)

F

= outdoor air fraction required by critical zone.

H

= height, in. (mm)

k

= insulation thermal conductivity, Btu in/h ft ² F (W/m K)

K

= velocity decay coefficient

L

= length, ft (m)

M

= permeance, gr/h ft ² in. Hg (ng/[s m ² Pa])

M _v

= mass of water vapor, gr/h (g/s)

NC

= noise criteria

p

= pressure, in. wg (Pa)

P

= perimeter, in. (mm)

P

= power, W

q

= heat gain, Btu/h (W)

Q

= airflow rate, cfm (L/s)

R

= required ventilation rate, cfm (L/s)

R

= thermal resistance, F ft ² h/Btu (m ² K/W)

RH

= relative humidity, %

t

= thickness, in. (mm)

T

= throw distance

T

= temperature, F( C)

U

= overall heat transfer coefficient, Btu/h ft ² F (W/m ² K)

V

= linear average velocity, fpm (m/s)

vp

= vapor pressure, in. Hg (kPa)

W

= width of duct, in. (mm)

W

= humidity ratio, lb _w/lb _a (kg _w/kg _a)

wb

= wet-bulb temperature, F( C)