01
Best input and use case
Dry bulb plus humidity ratio directly establishes the sensible and vapor contributions. Dry bulb plus RH is convenient for measured states. Enthalpy differences help compare airside energy changes and close ideal mixing balances when every value uses the same reference and dry-air basis.
Absolute enthalpy depends on a declared reference convention; process differences are usually the useful quantity. Do not combine a value from a different basis or equation convention without reconciliation.
02
Verified worked examples
At 25 °C, 50% RH and 101.325 kPa, enthalpy is 50.326 kJ/kg dry air. At 30 °C, 50% RH it is 64.217 kJ/kg dry air; sensible heating that state to 40 °C at constant humidity ratio raises it to 74.525 kJ/kg, a change of 10.308 kJ/kg.
Cooling the 30 °C state to saturated 12 °C produces 34.105 kJ/kg, removes 4.581 g water/kg dry air and removes 30.112 kJ/kg dry air in the idealized process model.
03
Interpret energy with moisture
Two states at the same temperature can have different enthalpy because vapor carries energy. Two states with similar enthalpy can have different temperature and humidity ratio. Inspect the complete state before interpreting comfort or condensation.
To estimate an airside rate, multiply enthalpy difference by dry-air mass flow, not uncorrected volume flow. Document sign convention and whether fan or duct gains are included.
04
Common mistakes
Do not label kJ/kg dry air as kJ/kg moist air. Do not infer equipment capacity from two uncertain spot readings without synchronized airflow and sensor data. Do not mix SI and IP reference conventions based only on unit conversion.
Enthalpy is not temperature and is not a direct comfort index. Apparent imbalance can come from condensate, leakage, heat transfer, fan work or measurement uncertainty.
05
Limits and next workflow
The relation is the documented ASHRAE-style perfect-gas expression retained in the source register. The process calculator models ideal state changes, not coil selection or performance certification.
Use the process-interpretation reference to classify the direction of heat and moisture change, then retain start, end, pressure, mass basis and calculated difference together.