The method
Before using the result
- Supported range: −50 to 80 °C, relative humidity above 0% and at most 100%, and absolute pressure above the saturation vapour pressure.
- Air is a well-mixed equilibrium mixture at the entered absolute pressure. RH must be above zero to report a finite dew point.
- Chart curves use the entered pressure and stop where the saturated air state is outside the method range.
Worked examples
These original training examples illustrate the method for North American Technician Excellence Certification (NATE). Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.
1. Worked example
Read a service air state before deciding whether a comfort complaint concerns temperature, moisture or both. Compare the dry-bulb reading with humidity ratio rather than treating relative humidity as a fixed water content.
- Dry-bulb temperature
- 25 °C
- Relative humidity
- 60 %
- Absolute atmospheric pressure
- 101.325 kPa
- Vapour pressure = 0.6 × saturation pressure at 25 °C.
- Humidity ratio = 0.011895048534430516 kg water/kg dry air.
- Enthalpy = 55.45263614146174 kJ/kg dry air.
- Dew point: 16.70113 °C
- Wet bulb: 19.47105 °C
- Humidity ratio: 11.89505 g/kg dry air
- Enthalpy: 55.45264 kJ/kg dry air
2. Comparison example
Compare a different supplied condition using the same method. For Technical Conquer, the important check is that the input meaning, units and method assumptions still match the problem.
- Dry-bulb temperature
- 30 °C
- Relative humidity
- 50 %
- Absolute atmospheric pressure
- 101.325 kPa
- Vapour pressure = 0.5 × saturation pressure at 30 °C.
- Humidity ratio = 0.01331020383863019 kg water/kg dry air.
- Enthalpy = 64.21152917460967 kJ/kg dry air.
- Dew point: 18.44664 °C
- Wet bulb: 22.00524 °C
- Humidity ratio: 13.3102 g/kg dry air
- Enthalpy: 64.21153 kJ/kg dry air
Check your understanding
1. Which relationship is used?
Water vapour pressure = RH × saturation pressure; W = 0.621945 pv/(p−pv). Wet bulb and dew point use standard psychrometric relationships.
2. Which assumption should you check first?
Supported range: −50 to 80 °C, relative humidity above 0% and at most 100%, and absolute pressure above the saturation vapour pressure.
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 North American Technician Excellence Certification (NATE) 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.