Hi @edpmay ,
Good question and you are right that the only difference between u_value and u_factor is the resistance of the interior and exterior air films. You’ll see that the same convention is followed with r_value and r_factor if you read through the SDK docs like those here for WindowConstruction:
Admittedly, there’s no strict definition of a “factor” vs. a “value” that I’m able to point to in order to justify my vocabulary decision here. But hopefully you would agree with me that the currently informal way that the practice in North America uses these terms results in a lot of unhelpful ambiguity. Especially when air films are often not included for R but they are for U but there’s no easy way to tell whether the air film resistance is included or not.
So, for the sake of trying to be clear, honeybee_energy calls all numbers that have the air film resistance a “factor” and all numbers that lack the air films a “value”.
FYI, in case you are interested, you’ll see that the LBT SDK also has methods for computing R-factors and U-factors under different indoor/outdoor temperatures and orientations of the construction:
You can use this to get the “summer” vs. “winter” numbers if that’s important to you. As you would see in the source code there, all of the R and U values/factors are for NFRC winter conditions assuming a 1mx1m vertically-oriented window construction.