Balancing of a Water and Air System (PDF
Balancing of a Water and Air System (PDF
Balancing of a Water and Air System (PDF
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Wet bulb temperature_____________°F<br />
Dry bulb temperature _____________°F<br />
(3) On Table 8 A&B find, the Foot³ <strong>of</strong> the leaving air <strong>of</strong> the evaporate.<br />
(4) Divide the Foot³ by one pound <strong>of</strong> air; this is the air density <strong>of</strong> the air. <strong>Air</strong><br />
density_____________________ or use Table 9B or 9C for air density<br />
(5) Find the CFM <strong>of</strong> the system<br />
CFM_______________________<br />
(6) Using the Wet bulb find the enthalpy <strong>of</strong> the air that is going in <strong>and</strong> out <strong>of</strong> the<br />
evaporator Tables 11<br />
Enthalpy air in ____________ EP<br />
Enthalpy air out ____________ EP<br />
Difference in EP _____________∆EP<br />
(7) Run the formula; <strong>Air</strong> Density X 60 X CFM X ∆EP = BTUH<br />
Example 6: Find the total heat that <strong>of</strong> a evaporator fan coil is absorbing from air with 4050<br />
cfm <strong>and</strong> entering air <strong>of</strong> 76º dry bulb <strong>and</strong> 64ºwet bulb, leaving air <strong>of</strong> 58ºdry bulb <strong>and</strong> 54ºwet<br />
bulb.<br />
Solution<br />
76º dry bulb <strong>and</strong> 66ºwet bulb has a enthalpy <strong>of</strong> 30.75<br />
58ºdry bulb <strong>and</strong> 54ºwet bulb has a enthalpy <strong>of</strong> 22.60 <strong>and</strong> a air density <strong>of</strong> 0.0757<br />
<strong>Air</strong> density X 60 X cfm X ∆ enthalpy = Btuh<br />
0.0757 X 60 X 4050 X 8.15 = 149,920 Btuh<br />
Example 7: Find the airflow <strong>and</strong> velocity fpm <strong>of</strong> a fan coil with a duct <strong>of</strong> 48 X 36 <strong>and</strong> a 75<br />
gpm with an entering water <strong>of</strong> 45º <strong>and</strong> a leaving water 56º. On the airside, the entering air<br />
temperature is 78º dry bulb <strong>and</strong> 65º wet bulb with a leaving air temperature <strong>of</strong> 60º dry<br />
bulb <strong>and</strong> 56º wet bulb.<br />
Solution<br />
Btuh = gpm X 60 X 8.337 X ∆ Temperature water<br />
Cfm = Btuh / (air density X 60 X ∆ enthalpy (h1-h2)<br />
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