Enthalpy difference

[jwasir]

Hi All,

Can someone explain why there is enthalpy difference between 2 attached PH charts?

[seanf]

Normally when your using enthalpy values, your using them to calculate the difference between two points on the same chart. So different people making different charts are able to pick any point along the enthalpy axis, and use it as a reference point giving it the zero enthalpy value. The values on the charts are not absolute values.

[sterl]

Somewhere in the early stages of ASRE it was decided to use Minus 40-Deg F and Saturation of Liquid Phase as 0-point for a given refrigerant's enthalpy because that largely kept them out of the negative numbers end of things. see https://www.baltimoreaircoil.com%2Fenglish%2Fresource-library%2Ffile%2F1485&usg=AOvVaw0JA5StHQYtHIQtGSs034fI

Utilizing the same starting point supported better analysis for such things as refrigerant to refrigerant heat exchange and comparisons of refrigerant performance for a specific design. Though frankly the concept of liquid water enthalpy at minus 40 confronts common sense...


ASHRAE has honored that ever since but others did not: so the Danfoss chart is using the much maligned Euro standard established NOT by Users but by the chemical manufacturers. So a typical circuit plotted on the Danfoss chart occupies maybe 8 per cent of the page area....Visually a bust.

And for entertainment, considering you are in Canada:

https://www.academia.edu/6887719/ammonia_r717_pressure_enthalpy_chart?auto=download

i got no answer for the obvious question about that one....