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Handbook of air conditioning and refrigeration / Shan K

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22.24 CHAPTER TWENTY-TWO<br />

FIGURE 22.5 Pressure characteristics <strong>of</strong> a VAV cooling system using supply-relief fan combination.<br />

During the <strong>air</strong> economizer cycle, when the outdoor damper is fully open <strong>and</strong> the recirculating<br />

damper was closed, the pressure difference between the ceiling plenum <strong>and</strong> outdoors �p pl,o was<br />

� 0.038 in. WC (9.5 Pa) when only two relief fans were operating, <strong>and</strong> �p pl,o was � 0.04 in. WC<br />

(10 Pa) when only one relief fan was operating.<br />

The pressure difference between the conditioned space <strong>and</strong> the <strong>air</strong> in the ceiling plenum �p r,pl<br />

was so small because <strong>of</strong> gaps between the ceiling tiles. During recirculation mode, the space pressure<br />

is about � 0.064 in. WG (16 Pag). Space pressure was lower when more relief fans were operating<br />

during the <strong>air</strong> economizer cycle.<br />

22.9 SMOKE CONTROL AND FIRE SAFETY<br />

Fire Safety in Buildings<br />

Recirculating mode Air economizer<br />

Outdoor damper 10% open 100% open<br />

Outdoor <strong>air</strong>, cfm 3330<br />

Recirculating damper 100% open 100% closed<br />

Relief fans operated 1 fan All 3 fans<br />

Relief damper 15% open 100% open<br />

�p pl,o in. WC (Pa) � 0.06 (15) � 0.018 (4.5)<br />

�p pl,m in. WC (Pa) � 0.20 (50)<br />

�p o,m in. WC (Pa) � 0.14 (35)<br />

�p r,pl in. WC (Pa) � 0.004 (1) � 0.004 (1)<br />

Fire safety is a critical design factor in high-rise buildings. On November 21, 1980, in Las Vegas,<br />

the MGM Gr<strong>and</strong> Hotel fire took 85 lives. Smoke inhalation is the primary killer in building fires.<br />

According to the annual survey taken by the National Fire Protection Association (NFPA), there<br />

was a slight increase in civilian fire deaths to a total <strong>of</strong> 4585 people who lost their lives in 1995,

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