How does the spreadsheet calculate the static pressure?
The spreadsheet uses the straight friction loss method. It does NOT use static regain. This will induce a small error, but it is a much simpler method and is commonly used in the industry. Specifically, the sheet calculates velocity pressure using the formula (V/4005) squared, which assumes standard temperature air. All loss factors are published as a function of the velocity pressure. For example, the loss factor for a 90 elbow, in smooth stamped steel R/D >2.0, is 0.13. So the losses for the 90 elbows are a formula Q*VP*LF, where Q is quantity, VP is velocity pressure, and LF is loss factor. The entire formula looks like this: (Q1*VP1*LF1)+(Q2*VP2*LF2)+(Q3*VP3*LF3)+… where 1, 2, and 3 represent different loss factors. In this case there are four loss factors in each size pipe; one for a hood entry, one for an elbow, one for a wye, and one for straight pipe. • The introduction notes say that flex hose losses can vary greatly. What does that mean in terms of the margin of error in the
