The method
Before using the result
- Use simultaneous representative measurements at a common pressure. Lower outlet RH alone does not prove water removal.
Worked examples
These original training examples illustrate the method for IICRC Applied Structural Drying Technician (ASD). Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.
1. Worked example
Compare simultaneous inlet and outlet humidity states around a dehumidifier. Explain grain depression independently of the rise in outlet temperature.
- Inlet temperature
- 25 °C
- Inlet RH
- 70 %
- Outlet temperature
- 30 °C
- Outlet RH
- 30 %
- Absolute atmospheric pressure
- 101.325 kPa
- Inlet W = 0.013921934095722953; outlet W = 0.007918338368745807 kg/kg.
- Grain depression = (0.013921934095722953 − 0.007918338368745807) × 7000.
- Inlet GPP: 97.45354 grains/lb dry air
- Outlet GPP: 55.42837 grains/lb dry air
- Grain depression: 42.02517 grains/lb dry air
- Humidity-ratio difference: 6.003596 g/kg dry air
2. Comparison example
Compare a different supplied condition using the same method. For Restoration Cert Lab, the important check is that the input meaning, units and method assumptions still match the problem.
- Inlet temperature
- 25 °C
- Inlet RH
- 70 %
- Outlet temperature
- 30 °C
- Outlet RH
- 35 %
- Absolute atmospheric pressure
- 101.325 kPa
- Inlet W = 0.013921934095722953; outlet W = 0.009257705623190136 kg/kg.
- Grain depression = (0.013921934095722953 − 0.009257705623190136) × 7000.
- Inlet GPP: 97.45354 grains/lb dry air
- Outlet GPP: 64.80394 grains/lb dry air
- Grain depression: 32.6496 grains/lb dry air
- Humidity-ratio difference: 4.664228 g/kg dry air
Check your understanding
1. Which relationship is used?
GPP = humidity ratio × 7000; grain depression = inlet GPP − outlet GPP.
2. Which assumption should you check first?
Use simultaneous representative measurements at a common pressure. Lower outlet RH alone does not prove water removal.
3. How should you verify a different unit system?
Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.
Continue with the matching exam topic
This tool connects to IICRC Applied Structural Drying Technician (ASD) free practice. Work through a question independently, then use the calculation steps to identify where your method differs. The tool stays free whether or not you choose paid preparation.