All:

I've come across some poorly documented simplified methods for accounting
for latent portion of annual ventilation/infiltration loads. The fundamental
equations used in the method include a term defined as a "Humidity Factor".

It appears that, at one time, by someone, a 'Humidity Factor' was calculated
for each TMY2 site. From what I can gather (I have a table by TMY2 city) the
'Humidity Factor' for the TMY2 data set ranged from a maximum of 3.83 (Guam)
to a minimum of 1 (Pheonix, AZ, Fairbanks, AK and several other sites with
low humidity climates). As an intermediate point - Louisville, KY's
Humidity Factor is 2.27.

I'd like to understand how a 'Humidity Factor' is determined for a given
TMY2 dataset (again, poor documentation). My web-searches have returned
examples where others have used this factor in various energy estimating
methods - but I have found no one who has sourced the derivations.

Does anyone out there recall the fundamental method(s) used to derive the
'Humidity Factor'?

Deep thanks in advance for ANY assistance,

Chris Balbach, CEM, PE, LEED AP