01
Select the process boundary
Sensible change holds humidity ratio constant. Cooling with condensation moves horizontally to dew point, then follows saturation while removing moisture. Isothermal moisture change isolates a humidity-ratio change at fixed dry bulb. Select the mode that matches the intended balance, not the equipment name.
A real coil, humidifier or dryer can combine several effects. Break the observation into measured start and end states before deciding whether the ideal path is a useful explanation.
02
Verified heating example
Start at 30 °C, 50% RH and 101.325 kPa, then select sensible change to 40 °C. Humidity ratio remains 13.312 g/kg, RH falls to 28.754%, end enthalpy is 74.525 kJ/kg and enthalpy change is +10.308 kJ/kg dry air.
The horizontal chart path shows why lower RH does not prove dehumidification: water content stayed constant. Use this distinction when reviewing winter heating complaints.
03
Verified cooling and moisture examples
Cooling the same start state to 12 °C reaches saturation, leaving 8.732 g/kg and 34.105 kJ/kg. The ideal model reports 4.581 g/kg condensate and 30.112 kJ/kg dry-air heat removal.
An isothermal change at 30 °C to 8.000 g/kg produces 30.301% RH and 50.634 kJ/kg. This isolated path removes 5.312 g/kg moisture; real desiccant or spray equipment may also change temperature.
04
Interpretation and mistakes
Read delta dry bulb and delta humidity ratio first: they classify sensible and moisture direction. Then inspect enthalpy change. A path is a balance result, not a claim about coil leaving-air uniformity or device efficiency.
Do not force a target below saturation in sensible-only mode, assume all cooling removes water, or equate condensate per kg dry air with a flow rate. Convert with verified dry-air mass flow and operating time.
05
Limits, evidence and next action
The modes are deterministic idealizations tested for state conservation, saturation handling and failure behavior. They omit bypass factor, apparatus dew point, fan heat, casing loss, spray-water energy and control dynamics.
Use the process reference to diagnose an observed path. For two incoming streams, switch to the mixing calculator rather than approximating a mixture with a temperature average.