Most underground mines require heating or cooling systems to meet health and safety standards in the working areas. In regions where daily or seasonal fluctuations of environmental conditions exist, these systems tend to be over-sized and operate at low average load factors, which increase both investment and operating costs. One possible approach to stabilize the temperature of the fresh air supplied to the mine, and so reducing the investment in large heating or cooling systems, is to use fragmented rock as a thermal regenerator or thermal storage system. These packed rock beds act as thermal inertial units, damping the atmospheric temperature oscillations to provide a more constant fresh air temperature. However, although regenerators exist in some mines, and they have been studied in detail, there is a lack of tools to design new and sufficiently large packed rock beds. This work fills the existing gap by presenting a methodology to design and evaluate the impact on the ventilation systems of these regenerators. The method is validated using existing rock bed systems found in the literature, and illustrates possible designs for small (daily attemperation) and large size (seasonal attemperation) regenerators in both hot and cold climates.