Handbook of air conditioning and refrigeration / Shan K

AIR SYSTEMS: FAN COMBINATION AND SMOKE CONTROL 22.35
FIGURE 22.8 Bottom injection, and bottom and top injection: (a) bottom injection; (b) bottom and top
injection.
Here, for simplicity, �p c � o again can be taken as 0.4 in. WC (100 Pa). Then
�p b � c ��p f,sN fl
(22.17)
where N fl � number of floors. Actually, part of the velocity pressure discharged from the bottom inlet
may be converted to static pressure, so that �p b � c is smaller. However, more data are needed
before it can be calculated accurately.
In a stairwell pressurization system with top and bottom injection, as shown in Fig. 22.8b, the
system pressure loss can be calculated as it is in bottom injection, but �p b � c may be smaller.
Computer-aided design software for zone smoke control systems are available to assist designers.
Example 22.1. In a smoke control system serving a 20-story high-rise building, each floor has the
following construction characteristics:
Floor area 10,000 ft 2 (929 m 2 )
Area of the external wall 4800 ft 2 (446 m 2 )
Vertical distance between floor and floor 10 ft (3m)
Area of the stairwell wall 600 ft 2 (56 m 2 )
Elevator shaft (three elevators) wall area 1000 ft 2 (93 m 2 )
Area of stairwell door 3 � 7 � 21 ft 2 (2 m 2 )
Volume flow rate of supply air to conditioned
space through AHU on each floor 12,000 cfm (5663 L/s)