I have always used .1 static (friction per 100ft) pressure when designing a duct system and determining duct size. But what effect does External Static Pressure total have on blower performance if say the total ESP turns out to be .45 or so counting filter, grills, elbows etc.? Is this ESP number different than what my air duct calculator "friction" number shows?
If I have designed a four ton system that the book says at .1 ESP produces 1645CFM yet after installation ESP total is .45 or greater I will have lost a couple of hundred CFM's right? So velocity will be reduced because I have to much pipe now which in one situation I am seeing is leading to duct sweating.
How should I design a duct system to anticipate the CFM loss with real ESP totals?