01
Use four labels with one time base
Outdoor describes entering ventilation air; return describes the zone return; mixed is downstream of their junction; supply is downstream of conditioning and fans at the defined point. Record locations precisely and take readings close enough in time for the system to be comparable.
Use a common pressure, consistent input pair and instrument method. Plot labels make the operational sequence visible without changing the numeric evidence.
02
Verified comparison set
At 101.325 kPa, outdoor 32 °C/55% RH gives 16.493 g/kg and 74.423 kJ/kg. Return 24 °C/50% gives 9.300 g/kg and 47.819 kJ/kg. Supply 13 °C/90% gives 8.387 g/kg and 34.258 kJ/kg.
The supply RH is high because the air is cold and near saturation; its humidity ratio is lower than both return and outdoor air. Reading RH alone would obscure the actual dehumidification.
03
Check the mixed state
A valid ideal mixed state lies between outdoor and return states under dry-air mass and energy weighting. Predict it from flows, then compare measured dry bulb, humidity ratio and enthalpy. Use the difference as a diagnostic prompt, not automatic proof of a damper fault.
Stratification is common near mixing boxes. Traverse or use multiple points when the decision justifies it.
04
Check the conditioning path
From mixed to supply, delta temperature shows sensible direction and delta humidity ratio shows moisture direction. Cooling with W reduction supports condensation or another moisture-removal mechanism. Reheat downstream should raise dry bulb at nearly constant W.
Fan heat, duct gain, leakage and sensor placement can bend the observed path away from the ideal chart line.
05
Decision and next action
Flag a result only when the difference exceeds combined measurement and operating uncertainty. Repeat after control stabilization, inspect independent airflow evidence and retain both measured and predicted states.
Next action: plot the three verified states, calculate a predicted mixed state from actual dry-air flows, and export the comparison for the commissioning record.