THE EFFECT OF THERMAL CAPACITANCE AND PHASE-CHANGE ON OUTSIDE PLANT ELECTRONIC ENCLOSURES

This paper examines the effect of heat storage on temperatures inside telecommunications outside plant electronic enclosures. A simple thermal analog model is developed to represent the heat flow in an enclosure that contains a thin envelope of phase change material (PCM). From this model, two sets of equations are obtained for the internal and the PCM temperatures: one for temperatures when the PCM is in a sensible heat storage mode and the second for temperatures when the PCM is in its latent heat storage mode. Exact solutions are obtained for both modes when the daily outside temperature and solar load are modeled by sinusoidal functions. For the sensible mode, the solution yields simple expressions for enclosure damping and delay factors, which may be useful in steady-state estimations of enclosure temperature. For the latent mode, the internal temperature is shown to be a simple exponential function of time, with maximum value determined by the phase change temperature and internal heat generation. The analytical results are compared with initial data from several small capacitive outside plant enclosures. From the comparison, it appears that the analytical expressions may provide a good method for estimating temperatures in these enclosures.