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Handbook of air conditioning and refrigeration / Shan K

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where volume flow rate <strong>of</strong> supply <strong>air</strong>, cfm [m3 V˙ s �<br />

/(60 s)]<br />

Ts,Tr � temperature <strong>of</strong> supply <strong>and</strong> space <strong>air</strong>, °F (°C)<br />

HEATING SYSTEMS, FURNACES, AND BOILERS 8.19<br />

FIGURE 8.5 Typical low-pressure ducted warm <strong>air</strong> heating system. (a) Supply <strong>and</strong> return duct; (b) supply<br />

duct <strong>and</strong> return plenum.<br />

In Eq. (8.9), � s represents the density <strong>of</strong> supply <strong>air</strong>. For a supply <strong>air</strong> temperature <strong>of</strong> 100°F (38°C)<br />

<strong>and</strong> a relative humidity around 20 percent, � s can be taken as 0.07 lb/ft 3 (1.12 kg/m 3 ). The term c pa<br />

indicates the specific heat <strong>of</strong> moist <strong>air</strong>. For simplicity, its value can still be taken as 0.243 Btu/lb�°F<br />

(1017 J/kg�°C).

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