READING PSYCHROMETRIC CHART

To the novice, a psychrometric chart seems a dizzying maze of lines and curves going every which way, but once a few fundamental things are understood about the psych chart, it is not really that difficult to understand. If we dissect the components piece by piece, the usefulness of the chart will be clearer.

Temperature: Dry Bulb

Dry Bulb Temperature (DBT) is the temperature that we measure with a standard thermometer that has no water on its surface. When people refer to the temperature of the air, they are commonly referring to its dry bulb temperature. Several temperature scales commonly are used in measuring the temperature. In the inch-pound (I-P) system of units, at standard atmosphere, the Fahrenheit scale has a water freezing point of 32°F and a boiling point of 212°F. In the International System (SI) of units, the Celsius scale has a water freezing point of 0°C and a boiling point of 100°C. On the Kelvin scale, 0ºK equals -273°C.

Dry-bulb temperature is located on the X-axis, of the psychrometric chart and lines of constant temperature are represented by vertical chart lines.