An Approximate Thermal Model for Outdoor Electronics Cabinets

Electronic systems are typically installed in outdoor loop plant 1 in metal cabinets which are essentially unventilated. The cabinets are subject to ambient temperature excursions from - 4 0 to 120°F and subject to solar heating which can raise the cabinet interior temperatures 30°F above ambient. With a thermal design limit of 185°F at circuit boards, the allowable temperature rise because of circuit dissipation is, thus, limited to about 35°F. The current trend toward greater circuit miniaturization and higher power density further aggravates an already difficult thermal design problem and points up the need for a comprehensive thermal analysis of the outdoor electronic cabinet. This paper is a step in that direction. The circuit boards are typically arranged in outdoor cabinets (see Fig. 1) in much the same way as in conventional central office equipment bays and, to thus extent, the heat transfer mechanisms are similar. In both cases, heat is removed from the circuit boards by 227 WIDTH C O M