Handbook of air conditioning and refrigeration / Shan K

22.36 CHAPTER TWENTY-TWO
The pressure difference across the closed stairwell door is 0.1 in. WC (25 Pa). The pressure differences
between the stairwell and the outdoors on floors other than the fire floor whose stairwell
doors remain open are also 0.1 in. WC (25 Pa), because the pressure drop of the open stairwell door
is ignored. Determine the volume flow rates of the zone smoke control and stairwell pressurization
systems.
Solution
1. The volume flow rate of the zone smoke exhaust system from the fire floor V˙ ex at a rate of 6
ach is
The volume flow rate of air supplied to the floors immediately above and below the fire floor is
12,000 cfm (5663 L/s).
2. The volume flow rate of air that is discharged through the open stairwell door to the fire floor
, in cfm (L/s), and is exhausted through the zone smoke control system is
V˙ fire
3. The volume flow rate discharged from the first-floor exit door is assumed to be the same as
that from the open stairwell door on the fire floor (6300 cfm, or 2973 L/s).
4. From the given data, the leakage area on the stairwell wall, including cracks around the stairwell
door, is
A leak � 0.25 � 0.00011 � 600 � 0.32 ft 2
If the pressure difference across the closed stairwell door is 0.1 in. WC, from Eq. (22.10), the air
leakage rate V˙ leak through the cracks of the stairwell wall on each floor whose stairwell door is
closed can be calculated:
5. It is possible that the fire floor and the pressurized floors immediately above and below are all
in the lower 10 floors. Because of the stack effect in this 20-story building, air mixed with hot gas
from the burning fire is discharged from the upper 10 stories.
In a 20-story building, assume that there are four open stairwell doors. One is on the fire floor,
and another is the first-floor exit door. Then the remaining two opened stairwell doors should each
discharge a combined air path that may be a combination of six parallel paths, as shown in
Fig. 22.9.
a-b-o
a-c-d-o
a-c-e-f-o
a-g-h-o
a-g-i-j-o
a-k-l-o
V˙ ex � 6 � 10,000 � 10
60
V˙ fire � v crit A door � 300 � 3 � 7 � 6300 cfm (2973 L/s)
V˙ leak � 2610 A(�p) 1/2 � 2610 � 0.32(0.1) 1 / 2 � 264 cfm (125 L / s)
6. The leakage area for the external wall for each floor is
� 10,000 cfm (4719 L / s)
A leak � 4800 � 0.00021 � 1.0 ft 2
The leakage area for a floor area of 10,000 ft2 is
Aleak � 10,000 � 0.000052 � 0.52 ft2