The interest in the underground seasonal thermal energy storage system as a renewable energy option for residential applications increases in the recent decades. The system, basically, uses the shallow ground as an energy reservoir that absorbs and release the heat in the hot and cold seasons, respectively. This paper presents, by means of a mathematical model, a novel open-loop ground thermal storage configuration using a network of bayonet tube heat exchangers. A validated two-dimensional multiphase model describing mass, momentum and conjugate heat transfer between a bayonet tube and surrounding ground have been used to study the influence of air inlet velocity and pipe length on the performance of the storage system. The results indicate that the air inlet velocity and the pipe length have proportional and inversely proportional relations with the amplitude of the air outlet temperature, respectively. These parameters, therefore, have a significant impact on the extracted or stored energy in the ground. The benefit of the open-loop storage system conducted here is to predict, prior numerical computation, the important characteristics such as heat transfer, pressure drop, and energy saving, correctly.