01
Start with delta temperature and delta moisture
Compare dry bulb and humidity ratio from start to end. Temperature change classifies the sensible direction; humidity-ratio change shows moisture addition or removal. Relative humidity alone can move in the opposite direction because its denominator changes with temperature.
Then inspect enthalpy difference on the same basis. This three-part check prevents a familiar mistake: calling lower RH dehumidification after sensible heating.
02
Sensible heating example
At 30 °C, 50% RH and 101.325 kPa, humidity ratio is 13.312 g/kg. Heating to 40 °C without moisture transfer keeps that value fixed, lowers RH to 28.754% and raises enthalpy by 10.308 kJ/kg dry air.
The chart path is horizontal. The result describes an ideal state transition, not heater efficiency or delivered capacity.
03
Cooling through dew point
Cooling first moves left at constant humidity ratio. Once saturation is reached, further ideal cooling requires water removal. From the same 30 °C start to saturated 12 °C, the model leaves 8.732 g/kg and reports 4.581 g condensate/kg dry air.
Real coil leaving air may be a mixture of bypassed and surface-conditioned air. Apparatus dew point, bypass factor and drainage require equipment-specific analysis.
04
Moisture change and mixing
At fixed 30 °C, reducing humidity ratio to 8.000 g/kg produces 30.301% RH. A real desiccant process often releases heat, so an exactly vertical chart path is a controlled model rather than a universal device path.
For mixing, conserve dry-air mass, water vapor and enthalpy. A 2:1 mix of 30 °C/50% RH and 15 °C/80% RH produces 25.029 °C and 58.947% RH at 101.325 kPa.
05
Decision steps and limits
Label measured and modeled states separately; synchronize readings; verify pressure; compare delta T, delta W and delta h; then look for saturation crossing. Only after those checks should you infer a likely heat, moisture or mixing mechanism.
Next action: reproduce one example in the process workbench and export the start, end, assumptions and balance. Do not use the ideal path alone for equipment selection or compliance.