0 is 0, but -1 is -920

[sven.129574]

OK, I've actually gotten kind of used to the funky Kelvin math in Revit that makes 61 °F minus 60 °F come out to -458.67 °F. There are ways to compensate for that (usually by adding 0 °F). But can anyone explain this next one to me? It looks to me like Revit can't handle Fahrenheit-to-Kelvin conversions in formulas for Fahrenheit temperatures below 0. Try this experiment:

1. Go into the family editor.
2. Create an HVAC parameter of type "Temperature".
3. Go to the "Formula" cell for the parameter, and type or paste in a value of "-1 °F".
4. Revit calculates the value to be -255.93 K, or -920.34 °F.

If you put a value of 0 °F in the Formula column, there is no problem. Revit calculates the value to be 0 °F, or 255.37 K.

If you put "-1 °F" in the"Value" column, again there is no problem. Revit keeps the value at -1 °F or correctly converts it to 254.82 K if you have your units set to Kelvin.

Even with funky Kelvin math, I can't figure out any way this makes sense.

[Steve_Stafford]

I believe it is a bug sir, I'll let you know if I hear differently...supports seems to think that it has been fixed in builds of a future version.

[sven.129574]

Thanks, Steve. I had to seriously suspect a bug, due to negative Kelvins not existing and the 920-degree discontinuity in what I would have expected to be a continuous range of results. But then again, people are always eager to declare unexpected behavior to be a bug, even when it is just a result of misuse, or a "Why would anyone ever want that" feature. It's nice to have confirmation, and assurances that it will get corrected.

[tkunsman]

I believe it is a bug sir, I'll let you know if I hear differently...supports seems to think that it has been fixed in builds of a future version.

It has not been fixed in 2016 or at least the student edition.