Investigate sky temperature algorithm

[nealkruis]

Standard 140 revealed noticeable differences in sky temperature between CSE and other programs on cloudy days.

I noticed a significant difference between the ACM documentation and the source code.

In calculating sky emissivity, the ACM (equation 76) shows:

eSky = e0 + 0.784*(1 - e0)*cldCvr/10

While the source code shows:

eSky = e0 + 0.467*(1 - e0)*cldCvr/10

As a point of comparison, TRNSYS uses:

eSky = e0 + 0.9*(1 - e0)*cldCvr/10

The "test program" reference results in Standard 140 use the same methodology as described in the ACM for equation 73 (which, to my knowledge is not actually used in CSE):

[nealkruis]

Found an old ACM with more details:

I think we're using equation 75 when we should be using equation 76.