Analytical/computational studies of the ground thermal characteristics for underground battery vault applications

Analytical and computational studies were carried out to ascertain the ground thermal characteristics for underground vault configurations to house batteries for telecommunication (voice and data) equipment. The goal of the work was to identify the parameters related to the ground that affect vault thermal behavior to ensure constant battery temperatures and hence enhance their performance. An analytical approach was supplemented with computational solutions obtained via a commercial package. The project overall goal is for Reliance Comm/Tec to be able to devise an improved design methodology regarding the development of underground vault systems. Work here reported suggests that the degree of ground water saturation affects the thermal characteristics of the ground, especially the thermal diffusivity. The ground can be characterized as a porous substance, and that the amount of water in the porous matrix strongly influences the transient characteristics of the ground. That is, as the amount of water increases in the ground, the value of the thermal diffusivity sharply decreases for low to medium porosities, or slightly increases for high porosities. Finally, as the amount of water increases in the ground, the effects of surface thermal disturbances (heat flux and temperature) are concentrated near the surface. Thus shallow battery vaults are particularly affected