Enthalpy of air from air tables differ from enthalpy from psychrometric chart
Enthalpy of air from air tables differ from enthalpy from psychrometric chart
(OP)
Hi,
I have uploaded two images. One is a table of Low Pressure Air Properties. The other is a typical psychrometric chart.
If you look up the enthalpy of air at 60F (520 R) in the low pressure air table, you get an enthalpy of 127.27 btu/lbm.
If you look up the enthalpy of air with zero humidity (dry air) in the psychrometric chart at 60F, you get an enthalpy of roughly 13 btu/lbm.
I know I am making some basic mistake here. Can anyone spot why these values do not match or what mistake I am making?
Thanks

I have uploaded two images. One is a table of Low Pressure Air Properties. The other is a typical psychrometric chart.
If you look up the enthalpy of air at 60F (520 R) in the low pressure air table, you get an enthalpy of 127.27 btu/lbm.
If you look up the enthalpy of air with zero humidity (dry air) in the psychrometric chart at 60F, you get an enthalpy of roughly 13 btu/lbm.
I know I am making some basic mistake here. Can anyone spot why these values do not match or what mistake I am making?
Thanks






RE: Enthalpy of air from air tables differ from enthalpy from psychrometric chart
your table may have zero at actual zero °Rankin or Kelvin. the HVAC chart may have it at 0°F or so.
RE: Enthalpy of air from air tables differ from enthalpy from psychrometric chart
On the tables I looked up the following
520 R (60F) ==> h =124.37 btu/lbm
545 R (85F) ==> h approx 130 btu/lbm
delta h (low pressure air tables) approx 5.73 btu/lbm
On the phychrometric chart
60 F ==> h approx 14.5
85F ==> h approx 20.5
delta h (psychrometric chart) approx 6 btu/lbm
The two enthalpies are likely the same and have a different zero point. Thank you very much, that really helped me out.
RE: Enthalpy of air from air tables differ from enthalpy from psychrometric chart