138
Table 34 —
Fan Type and Application
1/2”
MINIMUM
P + 1/2”
1
ENSURE ADEQUATE
HEIGHT/CLEARANCE
FOR DRAIN TO FLOOR
Fig. 114 —
Condensate Drain, Blow-Thru Trapping
(All Sizes)
a39-4178
MIXING
BOX
H
E
A
T
C
O
O
L
FAN
Fig. 115 —
Draw-Thru Example
Return
Duct
0.5 in. wg
MXB
0.4 in. wg
Clean
Filter
0.2 in. wg
Heating
Coil
0.2
in. wg
Cooling
Coil
1.2 in. wg
MIXING
BOX
C
O
O
L
FAN
PLENUM
Fig. 116 —
Blow-Thru Example
Static Pressure Between the Fan
and Drain
(Coil and Plenum Section)
1.2 in. wg
Static Pressure Between the Fan
and Drain
(Coil and Plenum Section)
1.2 in. wg
External Static Pressure
Downstream of Fan
2.3 in. wg
Trap Against Static Pressure Downstream of Fan - Static Pressure
Between Fan and Drain =
2.3 in. wg - 1.2 in. wg = 1.1 in. wg
TYPE
CHARACTERISTICS
APPLICATION
FORWARD-CURVED (FC)
SIDE VIEW
• Double-width, double-inlet (DWDI) construction.
• Best at low or medium pressure (approximately 0 to 5 in. wg).
• Horsepower increases continuously with increase in air quantity (overloads) as
static pressure decreases.
• Less expensive than AF fans.
• Runs at relatively low speed, typically 400 to 1200 rpm.
• Blades curve toward direction of rotation.
For low to medium pressure
air-handling applications.
AIRFOIL (AF)
SIDE VIEW
• Double-width, double-inlet (DWDI) construction.
• Best in high capacity and high-pressure applications (4 to 8 in. wg).
• Horsepower peaks at high capacities.
• Most expensive of centrifugal fans.
• Operates at high speeds, typically 1200 to 2800 rpm. About double the speed of
FC fan for similar air quantity.
• Blades have aerodynamic shape similar to airplane wing and are curved away
from direction of rotation.
For medium to high air capacity
and pressure applications.
PLENUM (PAF)
END VIEW
• Single-width, single-inlet (SWSI) construction.
• Characteristics similar to DWDI airfoil fan.
• Blades have aerodynamic shape similar to airplane wing and are curved away
from direction of rotation. Fewer blades and wider blade spacing than AF fans.
Best in applications with limited
space or multiple ducts.
