The set of conditions specified for cooling-load estimates is more complex and includes dry-bulb temperature, humidity, and solar intensity. Peak-load conditions during the cooling season usually correspond to the maximum solar conditions rather than to the peak outdoor-air temperature. Thus, it is often necessary to make several calculations at different times of the day or times of the year to fix the appropriate maximum-cooling-capacity requirements. When the cooling-load calculation is made will depend on the geographic location and-on the orientation of the space being considered. For example, peak solar loading on an east-facing room may occur at 8 A.M., while for a west room the maximum load may occur at 4 P.M. Peak solar loads for south-facing rooms will occur during the winter rather than the summer. Of course, when a cooling system serves several spaces with different orientations, the peak sys; tem load may occur at a time other than the peak for any of the several spaces. Fortunately, after making a number of such calculations one begins to recognize likely choices for times when the peak load may occur.

Table 4-3 provides outdoor design temperature data for a number of locations. The table provides the 97.5 percent dry-bulb temperature for winter and the 2.5 percent dry-bulb and coincident wet-bulb temperature for summer. The 2.5 percent drybulb temperature is the temperature exceeded by 2.5 percent of the hours during June to September. The mean coincident wet-bulb temperature is the mean wet-bulb temperature occurring at that 25 percent dry-bullftemperature. Tables 4-10 to 4-12, which provide additional data relative to the solar load, will be discussed when the solar load for windows and the thermal transmission for walls and roof are studied.