The calculation of heat flow in the ground, in particular the time-dependent heat loss through the foundation, poses particular problems due to three-dimensional flow and very long time scales. In this paper a new tool of analysis called “dynamic thermal networks” is presented briefly and used to analyze the time scales for the time-dependent heat loss for different types of foundations: a slab-on-ground, a cellar, and a split-level foundation.

The heat loss may be divided into a transmittive and an absorptive component. The transmittive and absorptive step-response fluxes and the corresponding weighting functions provide a precise description of the time scales of the heat flow to the ground. It is shown that the transmittive component has time scales of a decade and even more, while the absorptive component has a time scale of days only.