ACADEMY SERIES · EPISODE 8Psychrometrics & Sizing

How to Read a Psychrometric Chart

Heating, humidification, mixing and cooling each become an arrow on the psychrometric chart. From a single point at 22 °C and 50% relative humidity, you can read the humidity ratio, the dew point and the enthalpy. This episode covers the chart's axes and curves, how steam and adiabatic humidification differ on it, mixing and the summer cycle, and how capacity is calculated straight from the chart.

Published: 8 October 2026Narration: Turkish and English6:43

In this video

  • On the psychrometric chart, the horizontal axis is dry-bulb temperature and the vertical axis is the humidity ratio (grams of vapour per kilogram of dry air); the 100% RH curve marks the most vapour the air can hold.
  • From a single point at 22 °C and 50% RH you can read a humidity ratio of about 8.2 g/kg, a dew point of about 11 °C and an enthalpy of about 43 kJ/kg.
  • Resistive steam humidification draws an almost vertical arrow; in adiabatic humidification the point slides up and to the left along constant enthalpy, and each gram of water added cools the air by about 2.5 °C.
  • Capacity comes from the humidity-ratio difference, not the RH difference: raising 10,000 m³/h from 30% to 50% at 22 °C takes about 40 kg of steam per hour, and a 20% service margin leads to a unit in the 50 kg/h class.
  • Duct air is kept clear of saturation; a high-limit humidistat caps supply humidity at 85–90% RH.

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