Revit uses the Excess Head (K) method to compute the head loss through a fitting.
Revit computes the head loss through a fitting using the formula below.
where:
g: acceleration of gravity, 32.17 ft/sec2
h: head loss
K: Resistance Coefficient, a unitless factor
L: length as indicated
v: velocity in ft/second
Note that Revit does not report the loss in head (units of length). The loss is reported in units of pressure (e.g., PSI). To convert head loss to pressure drop, you need to multiply by the density of the fluid and convert square feet to square inches.
where:
ρ: density of fluid (lb/ft2)
ΔP: Pressure drop in PSI
When using manufacturer's valve families for pressure loss analysis, be sure to check that the K Coefficient parameters have been set correctly.