Handbook of air conditioning and refrigeration / Shan K

20.24 CHAPTER TWENTY
compensates for inlet and outlet system effect losses must operate on a performance curve that intersects
with point Ps, which has a volume flow rate of V˙ d and a total pressure rise of �pss including
system effect losses, in in. WC (Pa). That is,
(20.24)
System effect directly affects the performance of the air system as well as the function of the air
conditioning system. Because the air velocity at the fan inlet and outlet is usually between 1500 and
3000 fpm (7.5 and 15 m/s), system effect losses may amount to 5 to 20 percent of the system pressure
loss of the air system.
Inlet and outlet system effect losses must be calculated correctly. Moreover, air systems must be
designed to reduce system effect losses to save energy.
20.7 COMBINATION OF FAN-DUCT SYSTEMS
�p ss ��p sy ��p s,i ��p s,o
The purposes of combining fan-duct systems are as follows:
● To increase the volume flow rate of the combined fan-duct system
● To provide the required pressure characteristics for the combined fan-duct system
● To balance the volume flow of the combined fan-duct system
● To maintain a required space pressure characteristic
FIGURE 20.9 Two-fan fan-duct system connected in series.