Define and use thermodynamic constants

[dmey]

This is something to keep in mind for future releases -- I think it would make sense to use proper names for thermodynamic constants which are currently used and reported in PsychroLib as numbers. For example, in some functions, we use the number 2501.0 instead of using a global thermodynamic constant named latent heat of vaporisation of water or similar. There are not many we use so this would not be a lot of work.

[didierthevenard]

ASHRAE writes the SI psychrometrics chapter with identifiable thermodynamic constants but for some reason the IP chapter does not show them explicitly, so there is a bit more work than it would appear at first glance. I remember looking into it and there were issues with the need to add additional conversions because some of the constants involve square inches and others feet (version 1 of PsychroLib was actually using some thermodynamic constants in SI but not IP for that reason).

[dmey]

I see -- OK this can be a work in progress. How about we make a list of all the constants we use in psychrolib in let's say SI and add them to a table. Then we can more easily see if we can/should calculate them for a set of more fundamental constants or at least give them a proper variable name? I have created a 'Future' milestone and added this to them so that we can keep an eye on it. This milestone is a "placeholder for issues not yet scheduled in another specific milestone. This is for features that go beyond the scope of our initial goal. We are unlikely to work any time soon on issues in this milestone."