Handbook of air conditioning and refrigeration / Shan K

3.22 CHAPTER THREE
3.7 SOLAR ANGLES
Basic Solar Angles
TABLE 3.4 R Values of Enclosed Airspace R a,h�ft 2 �°F/Btu
Mean Temperature Type of Direction Width of
Emissivity E †
temperature, °F difference, °F surface of heat flow airspace, in. 0.05 0.2 0.82
Summer, 90 10 Horizontal Upward 0.5 2.03 1.51 0.73
3.5 2.66 1.83 0.80
Vertical Horizontal 0.5 2.34 1.67 0.77
3.5 3.40 2.15 0.85
Horizontal Downward 0.5 2.34 1.67 0.77
3.5 8.19 3.41 1.00
Winter, 50 10 Horizontal Upward 0.5 2.05 1.60 0.84
3.5 2.66 1.95 0.93
Vertical Horizontal 0.5 2.54 1.88 0.91
3.5 3.40 2.32 1.01
Horizontal Downward 0.5 2.55 1.89 0.92
3.5 9.27 4.09 1.24
† Emissity E � 1/(1/e1 � 1/e 2 � 1), where e 1, e 2 indicate the emittances on two sides of the airspace.
Source: Abridged with permission from ASHRAE Handbook 1989, Fundamentals.
and the direction of airflow. The R values of the enclosed airspaces R a,h�ft 2 �°F/Btu (m 2 �°C/W),
abridged from data published in ASHRAE Handbook 1989, Fundamentals, are presented in Table 3.4.
The basic solar angles between the sun’s rays and a specific surface under consideration are shown
in Figs. 3.6 and 3.7.
FIGURE 3.6 Basic solar angles and position of sun’s rays at summer solstice.