In this paper, the thermal performance of the heat storage unit made of repeatable modules was carried out. The heat accumulator that is used in solar installations may be a separate unit, or it may be a building wall insulated on the inner and outer surfaces. It is a heat storage unit with dynamic discharge using forced air flow through the channels. The transient temperature field in the walls of the channels was modeled using three different methods: finite volume method (FVM), control volume based finite element method (CVFEM), and finite element method (FEM). The CVFEM was chosen for the construction of a full model of the heat storage unit due to the ease of modeling a solid filling of a heat storage unit with a complex shape. The numerical model of the heat storage unit with the air flow through channels was developed. The CFD simulation was also carried out. In the mathematical model of the heat accumulator, it was taken into account that air flow can be laminar, transitional or turbulent. The finite volume method with integral averaging of air temperature over the finite volume length was developed so that accurate air temperature distribution can be determined even with a small number of finite volumes. (C) 2019 Elsevier Ltd. All rights reserved.