Being metric, the Dry Bulb & Wet Bulb Inside temperature parameters I had setup were in degrees Celsius. The Capacity parameters are in kW's so in order to use the temperature parameters in the formula I would need to remove the units.
Easy, I thought. I'll just divide by 1°C and that will give me a unitless value.
Unfortunately Revit decided to throw a curve ball at me. Internally all its calculations are done in Kelvin. For example, if I use my DB in a formula and its value is set to 20, Revit actually uses 293.15. So then I thought I'd divide by 1 K... No luck!
After trying for 3 hours I eventually gave up and went to bed.
With a fresh head I did some playing around in Excel to try and figure out how Revit was getting the results it was and eventually I came to this:
|Unitless Temperature Parameter|
So essentially what Revit is doing here is:
(293.15-272.15) / (546.3/546.3) or 20/1 = 20
Now hopefully someone else doesn't have to go insane trying to figure this out!