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 66F effective temperature to 75F effective temperature for 98 percent of all personnel. The winter comfort zone extends from 63F effective temperature to 71F effective temperature for 97 percent of all personnel.

Dew-Point Temperature

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.