Figure 7-1.Comfort zones and lines.
Relative humidity is determined by using a sling
psychrometer. It consists of a wet-bulb thermometer
and a dry-bulb thermometer, as shown in figure 7-2.
The wet-bulb thermometer is an ordinary thermometer
similar to the dry-bulb thermometer, except that the
bulb is enclosed in a wick that is wet with distilled
water. The wet bulb is cooled as the moisture
evaporates from it while it is being spun through the
air. This action causes the wet-bulb thermometer to
register a lower temperature than the dry-bulb
thermometer. Tables and charts have been designed
that use these two temperatures to arrive at a relative
humidity for certain conditions.
A comfort zone chart is shown in figure 7-3. The
comfort zone is the range of effective temperatures
within which the majority of adults feel comfortable.
In looking over the chart, note that the comfort zone
represents a considerable area. The charts show the
wet- and dry-bulb temperature combinations that are
comfortable to the majority of adults. The summer
comfort zone extends from 66°F effective temperature
to 75°F effective temperature for 98 percent of all
personnel. The winter comfort zone extends from 63°F
effective temperature to 71°F effective temperature for
97 percent of all personnel.
The dew point depends on the amount of water
vapor in the air. If the air at a certain temperature is not
Figure 7-2.A standard sling psychrometer.