PropSI vs HAPropSI ref state excel

[Clifford Bradford]

I'm comparing results using HAPropsSI and PropsSI in Excel. When I run dry air cases the c_p and c_v are acceptably close to one another but the specific enthalpies are quite different.  =HAPropsSI("Hha","Tdb",CONVERT($A7,"C","K"),"P",CONVERT($B7,"atm","Pa"),"HumRat",$D7 is 15.08713 kJ/kg

while:

=PropsSI("HMASS","T",CONVERT($A7,"C","K"),"P",CONVERT($B7,"atm","Pa"),"HEOS::Air")

is 414.3746 kJ/kg

inputs are:

A7 = 15

B7 = 1

D7 = 0

I assume the difference is due to the reference state but I'm not sure what the difference is. HAPropsSI calculates an approximately 0 enthalpy at 0°C and 1 atm while for PropsSI it is at ~195°C. Is there anyway to set the referene state consistently in Excel?

[Ian Bell]

Not in Excel (because the order of cell evaluation is non-deterministic), but in other environments like Python, yes you can set the reference state to whatever you like.

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[Paco Calvino - UPC]

I've been facing a similar issue for a long time.

What I do is to compute enthalpies difference for an arbitrary T and p using PropsSI and HAPropSI. Then I add/subtract that value to PropsSI or HAPropsSI results when needed. 

I hope this would help. 

Regards,

[Clifford Bradford]

Maybe this is something the user could set based on an event like opening the workbook? I notice in the CoolProp.xlam that there is a "Private Sub Workbook_Open()" that gets the Refprop path and I assume it runs whenever Excel starts up/the add-in is enabled. 

In any case could there me more [unified] documentation of the reference states?

[Clifford Bradford]

Francisco, great tip. Yes that was how I was validating the enthalpies by calculating a Dh from a given dry air reference case.