Psych Chart Question

[vesterholt]

Looking at cold weather psychrometric charts, it appears that air at around -23F or so has enthalpy of less than zero. How is this possible?

http://www.homepower.com/sites/default/files/uploads/Psychrometric_Chart.jpg

 

[P-E]

Possible it is. Zero enthalpy is based on a set condition. It can go negative. Entropy on the other hand can not.

 

[sislam012]

guys how would you solve this non-standard psychrometric problem " Air at 80F db, 75F wb compressed to 100 psia, then cooled to 45F, 14 psia. What is the dewpoint?"

 

[Audi Driver P.E.]

Find the RH at the first point (approx 82%, it looks like), then determine where the 45F crosses that RH line and find the DP temperature at that intersection. At least, that is how I would do it. Not sure if that is correct.