The Psychrometric Chart Explained

Green Building

The Psychrometric Chart Explained

Figure 1: The psychrometric chart. Illustration by Daniel Overbey.

Originally published on June 13, 2018 by BNP Media through the Building Enclosure Blog.

It is one of the intimidating charts for any building design professional: the psychrometric chart.

At first blush, the “psych chart” looks very complicated. There are layers of axes and curved reference lines. However, a closer examination will reveal that – at its essence – the chart is visually conveying the answers to two related questions:

  1. How much sensible (dry-bulb) heat is in the air? (See the green lines on chart above.)
  2. How much latent (moisture-related) heat is in the air? (See the cyan lines on chart above.)

Let’s unpack the psych chart one piece at a time and make sense of it all.

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