Handbook of air conditioning and refrigeration / Shan K

High-Temperature Fans
AIR SYSTEMS: COMPONENTS—FANS, COILS, FILTERS, AND HUMIDIFIERS 15.27
FIGURE 15.22 Single- and double-width centrifugal fans: (a) single-width single-inlet (SWSI); (b) doublewidth
double-inlet (DWDI).
Drive arrangements include the location of bearing and sometimes the position of the motor. For
centrifugal fans, there are eight standard drive arrangements, as shown in Fig. 15.23. There are only
two drive arrangements, 4 and 9, for axial fans. Arrangements 1, 2, 3, 7, and 8 can include either
belt drive or direct drive. Arrangements 4 is for direct drive only. Arrangements 9 and 10 are for
belt drive only. However, in arrangement 9 for centrifugal fans, the motor is located outside the
base, whereas in arrangement 10, the motor is located inside the base. This arrangement is often
used with a weatherproof hood for outdoor installation.
Motor location is always specified as W, X, Y, or Z position, facing the fan drive side. The
direction of rotation and discharge position of centrifugal fans are specified from the drive side of
the fan, as shown in Fig. 15.24. In single-inlet fans, the drive side is always opposite the fan inlet,
regardless of the actual position of the fan drive.
When fans are operated in high-temperature airstreams, the yield strength of the fan structure may
decrease. Operating temperatures are usually classified as �20 to 200°F (�29 to 93°C) normal or
standard fan construction, 201 to 300°F (94 to 150°C), 301 to 400°F (151 to 204°C), 401 to 750°F
(205 to 400°C).
The rpm limits on classes I and II must be multiplied by a speed factor 0.9 when the operating
temperature is 401 to 500°F (201 to 260°C). A lower speed factor should be used at higher
temperatures. Cooling of the fan bearings is a significant problem. Generally, bearings should
be kept out of the airstream except when operating at room temperature. In many antifriction
bearings, grease can be used up to 200°F (93°C). Oil bearings or high-temperature grease is required
for temperatures higher than 300°F (150°C). Special coolant should be applied to the
shaft and bearings at higher temperatures. High-temperature aluminum paint can protect surface
finishes.