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The Psychrometric Chart

(courtesy of Hong Kong University)
The psychrometric chart is an aid for studying:
  • the temperature level,
  • the humidity level, and
  • the thermodynamics of air
The chart shows that the moisture holding capacity of air is temperature dependent. When the moisture level in the atmosphere exceeds the saturation point, it starts to condense and precipitate out of the atmosphere. This continues until the saturation temperature is reached. The curves in the chart indicate the saturation temperatures of water in the atmosphere. The points along these curves are called dew points.

In the management of IAQ, it is important to recognize that:
  • air dynamics directly affect the consumption of energy in an air conditioning system;
  • relative humidity and dew point of our indoor environment directly affect our health and comfort;
  • growth of insects and micro-organisms in an indoor environment can best be controlled through temperature and relative humidity.


Psychrometric Charts, Wikipedia
Psychrometric Chart Tutorial, University of Wisconsin