Math/Unit/Parameter Errors

[mjdanowski]

First, I seem to have found a bug with plumbing flow parameters. When you try to add a unit of flow (lets say 1GPM) to a formula on a plumbing flow parameter formula, it automatically converts it to CFM.

Second, for some reason, Revit sees (<PARAM in °F> / 1°F) different as (<PARAM in °F> * 1 1/°F) which is odd to me, since they are the same thing. Multiplying by the inverse of a unit should equal the same as dividing by it outright. This is even more alarming to me because it drastically changes the value of the computation, rather then just give me an "inconsistent units" error.

Third, if you look at the attached screenshot, the parameter "Flow|Global" has a valid syntax formula, that is just throwing out random numbers. The answer to that formula posted SHOULD be around 0.8, however it is showing 5? What scares me more, if I change "Water System Delta" to 7 instead of 14, the value of flow parameter only changes by .2.


Am I going insane, have I messed up my syntax? If I had to guess this has to do with some hidden (like THAT would ever happen..) unit conversion that is fouling the entire thing up.

Thanks!

[mjdanowski]

I am pretty sure it has to do with some CRAZY conversion with temperature...

[mjdanowski]

there are some massive problems with the parameterized handling of units within Revit

[Paul.Hellawell]

Indeed. Its the same with electrics too, probably airflow also (out on a limb here).

My workaround was to make all my own shared parameters for the elecrical side of it. Kinda sucks, but is a workaround.

[mjdanowski]

I actually sent in a support request for this and found out:

A) Is a defect, it has been noted.

C) This is a confusion of how Revit calculates units. The "base" unit for temperature is apparently in Kelvin, so when you have something like that in Fahrenheit you get a funky number.

For example, 1 degree F is around 256K, however 2F is ~257L So if you have 30F / 1F you essentially have 272K / 256K = 1.0625, not 30 with no units.

So I wouldn't say this is so much a bug with the software, rather an unexpected functionality in regards to how things are calculated.