The Abridged Psychrometric Chart - Honeywell AUTOMATIC CONTROL Engineering Manual

PSYCHROMETRIC CHART FUNDAMENTALS

THE ABRIDGED PSYCHROMETRIC CHART

Figure 2 is an abridged form of Chart No. 1. Some of the
scale lines have been removed to simplify illustrations of the
psychrometric processes. Smaller charts are used in most of
the subsequent examples. Data in the examples is taken from
full-scale charts
The major lines and scales on the abridged psychrometric
chart identified in bold letters are:
— Dry-bulb temperature lines
— Wet-bulb temperature lines
— Enthalpy or total heat lines
— Relative humidity lines
— Humidity ratio or moisture content lines
— Saturation temperature or dew point scale
— Volume lines in cubic feet per pound of dry air
1.0
0.8
ENGINEERING MANUAL OF AUTOMATIC CONTROL
1.0
Fig. 2. Abridged Chart No. 1.
40
The chart also contains a protractor nomograph with the
following scales:
— Enthalpy/humidity ratio scale
— Sensible heat/total heat ratio scale
When lines are drawn on the chart indicating changes in
psychrometric conditions, they are called process lines.
With the exception of relative humidity, all lines are straight.
Wet-bulb lines and enthalpy (total heat) lines are not exactly
the same so care must be taken to follow the correct line. The
dry-bulb lines are not necessarily parallel to each other and
incline slightly from the vertical position. The purpose of the
two enthalpy scales (one on the protractor and one on the chart)
is to provide reference points when drawing an enthalpy (total
.030
.028
60
.026
.024
55
.022
.020
50
.018
.016
.014
45
.012
.010
40
.008
.006
35
.004
.002
30
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