# Psych Chart Question



## vesterholt (Feb 9, 2015)

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


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## P-E (Feb 10, 2015)

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


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## sislam012 (Jul 9, 2015)

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?"


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## Audi Driver P.E. (Oct 12, 2015)

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.


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