Understand a moist-air state
Use this psychrometric calculator and chart to describe an air condition from dry-bulb temperature and a second known property. It helps with cooling-coil discussions, indoor humidity checks and comparisons between outdoor and conditioned air. Calculate without an account, then inspect the chart and numerical properties together. A single plotted state describes air properties; it is not by itself a cooling load, ventilation design or equipment performance prediction.
ASHRAE equations and required inputs
The existing psychrometric-math module implements ASHRAE Fundamentals saturation-pressure equations and moist-air relationships. Enter dry-bulb temperature, barometric pressure and a supported second property such as relative humidity, wet-bulb temperature, dew point or humidity ratio. For relative humidity, vapour pressure is RH × saturation pressure and W = 0.621945 pv / (p − pv). Enthalpy is h = 1.006T + W(2501 + 1.86T), in kJ/kg dry air.
Worked example at indoor conditions
Assume dry-bulb temperature 24°C, relative humidity 55% and barometric pressure 101,325 Pa, equivalent to 101.325 kPa. Select the relative-humidity input mode and enter those values. The result is humidity ratio 0.010244 kg/kg dry air, or about 10.244 g/kg, and enthalpy 50.22 kJ/kg dry air. The computed wet-bulb temperature is approximately 17.85°C and dew point is approximately 14.41°C.
Interpret the outputs carefully
For this assumed state the specific volume is approximately 0.85566 m³/kg dry air. Dew point provides a useful first warning about condensation: a surface colder than the dew point may collect moisture if exposed to that air. It does not specify insulation thickness or guarantee a dry installation. Keep dry-air mass basis consistent when using enthalpy or humidity ratio in a coil energy or moisture balance calculation.
Pressure, units and model limits
Use a suitable actual barometric pressure when altitude or site conditions differ from the example. The calculator validates dry-bulb temperature between −20°C and 60°C and pressure between 60 and 110 kPa. Relative humidity must remain within physically valid bounds. I-P enthalpy has a different reference datum, so it is not obtained by a simple SI multiplier. The chart is a visual aid, not a substitute for reading validated values.
Singapore project review
Treat this output as a draft for review, not a stamped design or an approval. For a Singapore submission, check the applicable SS553 requirements and the project specification with the responsible designer. Verify the input schedule, record the assumptions, and reconcile the calculation with drawings and manufacturer data. This tool does not identify every applicable requirement, certify compliance, or replace professional judgement about installation, operation, safety, and maintenance. Retain the calculation date and revision so later changes can be traced to their original assumptions.