I cannot figure out why some specific duct fittings do not show a “Pressure Drop” calculated from ASHRAE Tables.
I mean, the corresponding ASHRAE Table does really exist inside Revit, and I can select it, but it gives no value as a “Pressure Drop”, just a “0”.
Trying to find out if the fault is in ASHRAE Table itself OR in the Revit implementation, I have made a test and I wanted to show it to the forum. I designed a very simple duct network as follows:
One rectangular duct 275 mmX275 mm supplies air to 2 air terminals:
Diffuser.1 is 120 lt/sec, and Diffuser.2 (on a branch flexible duct) is 135 lt/sec. Total flow is 255 lt/sec.
I have put 2 rectangular elbows, 1 rectangular-to-round tap, 1 rectangular-to-round transition, etc.
You can see all those network fittings in the image below.
The network does not have disconnects, and the System Inspector shows all the flows normally.
I select the tap to the branch duct, I select Loss Method “Coefficient from ASHRAE Table”, “Edit…” and then I select the ASHRAE Standard Fixture: SR5-11. After OK… nothing happens. We have no Pressure Drop calculated. Why ?
After that, I go to the Original ASHRAE Duct Fitting Database Software to see if actually there is some kind of problem with the specific values (for example out of range).
I select the same ASHRAE Standard Fixture: SR5-11 , I put in the data (dimensions and flows), and immediately I have the right Pressure Drop for: a) the Main flow and b) for the Branch flow.
From this simple test I have concluded that something is obviously wrong in the ASHRAE Table Method implementation in Revit, and not in the ASHRAE Tables themselves.
This abnormal behavior does not happen for all duct fittings. It just happens for some specific types of fittings.
For example, the 2 rectangular elbows are having pressures drops calculated normally from ASHRAE Tables, as they should.
