Evaluation of Solar Heat Gain

To evaluate the heat load on an enclosure, you must take into account:
• Total surface area of the enclosure
• Color of the enclosure
• Internal heat load
• Maximum allowable internal temperature
• Maximum ambient temperature
• Solar load
Examples:
1. What amount of heat energy must be removed from a 24 x 20 x 12 (surface area = 14 ft.²) ANSI 61 gray enclosure located outdoors and without any heat dissipated internally, to maintain the enclosure temperature equal to the ambient (temperature rise = 0 degrees)? From the chart below, at 0 F temperature rise we find the solar load is approximately 14 W/ft.² (14 ft.² x 14 W/ft.² = 196 W). This is the heat energy that must be removed to maintain the enclosure temperature at ambient.

2. If the same enclosure has internal equipment dissipating 200 W of heat, what is the amount of heat energy that must be removed to maintain the enclosure at a temperature rise of 20 F above the ambient temperature? From the chart below, at 20 F temperature rise we find the solar load is approximately 6 W/ft.² (14 ft.² x 6 W/ft.² = 84 W). All of the internally dissipated heat of 200 W must also be removed. 84 W + 200 W = 284 W. This is the total amount of heat energy that must be removed to maintain the enclosure at 20 F above the ambient temperature.

3. What is the expected temperature rise above the ambient temperature due to solar heat gain for an enclosure with ANSI 61 gray finish? From the chart below, the temperature rise due to solar heat load can be found by locating the intersection of the data curve for the given finish and the 0 Solar Generated Heat Load axis. For ANSI 61 gray, the temperature rise due to solar heat is about 40 F.