Arkansas HVACR NewsMagazine September 2023

HVACR NewsMagazine September 2023

Tech News

• C Exit = Pressure Loss Coefficient For a Wall Cap Fitting VP = Velocity Pressure = 1 x 0.18 = 0.18” W.C. pressure loss for the wall cap exit Step 7: Let’s add up all of our losses. The total pressure loss is: PL Total = ∑PL SD + ∑PL C’s = PL 10’ + 4PL C Elbow + PL C-Exit •

If we look at the system design point of 600 CFM @ 0.60” W.C., we can see that the total pressure loss of our 8” exhaust duct system is above the range hood blower curve, meaning our exhaust duct system resistance is too high. We want to size our exhaust duct such that our total pressure loss result is below, or exactly on, the hood blower curve such that we can meet or exceed the rated hood exhaust CFM. This is an iterative process that will sometimes take several tries to confirm the correct size duct. What duct size should be used to exhaust 600 CFM @ 0.1 ″ W.C. for the “CP55IQ” exhaust hood?

= 0.055 + 0.36 + 0.18 = 0.595” W.C. total hood exhaust duct pressure loss

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