Balancing of a Water and Air System (PDF

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Pressure Total pressure Velocity pressure
Example 8: Find the GPM of a 6” pipe SCH 40 with a pressure of 42.45 and a total
pressure of 42.47. Use fig. 11.3 for Gallons per foot
Solution
• Total pressure – pressure = velocity pressure
• 1040 X √ velocity pressure = FPM
• FPM X Gallons per foot = GPM
• 42.47 total pressure – 42.45 pressure = 0.02 velocity pressure
• 1040 X √ 0.02 = 147.08 FPM
• 147.08 FPM X 1.5 Gallons per foot = 220.62 GPM
Example 9: Find the ton of a chiller of example 8 with an entering water of 55.8 ºF and a leaving
water of 45.2 ºF.
Solution 1
• Tons = GPM X 60 X 8.337 X ∆ Temperature of the water / 12,000 btuh per ton
• 220.62 gallons X 60 minutes X 8.337 X 10.6 ∆T = 1,169,800.4 btuh
• 1,169,800.4 btuh / 12,000 btuh per ton = 97.48 tons
Solution 2
• Tons = GPM X ∆ Temperature of the water X specific heat X specific gravity / 24
• 220.62 gallons X 10.6 ∆T X 1 SH X 1 SG = 2338.57
• 2338.57 / 24 = 97.44 tons
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