Thermal device for a refrigerant fluid or a heat transfer fluid, the device comprising: - a circuit for circulating said fluid, in which the fluid circulates over time at different temperatures, - a thermal store and heat exchanger arranged on said circuit and enclosing an interior volume: -- in which the fluid circulates, between an inlet and an outlet, and -- in which is arranged phase change material, in contact with the fluid which circulates, to thermally exchange between each other, characterised in that: - the phase change material is arranged, within said interior volume, in a plurality of store and release thermal energy elements, - having a modular construction, the thermal store and heat exchanger comprises several adjacent modules, structurally separate and of which at least some individually comprise a base separating two adjacent modules, each base: -- splitting the volume into a succession of sub-volumes (7, 7b, etc.), in which are arranged said store and release thermal energy elements, around which and/or wherein the fluid circulates, in heat exchanges with each other, -- and having at least one passage for allowing the sub-volumes to communicate therebetween, - and, for creating baffles in the thermal store and heat exchanger on the fluid path: -- said passages for allowing the sub-volumes to communicate therebetween are offset from one of said passage to the following one, and/or -- inside the corresponding module, and for creating therein other sub-volumes (7a, 7c), partitions stand which keep communications between said other sub-volumes, for the circulation of the fluid. - a circuit for circulating said fluid, in which the fluid circulates over time at different temperatures, - a thermal store and heat exchanger arranged on said circuit and enclosing an interior volume: -- in which the fluid circulates, between an inlet and an outlet, and -- in which is arranged phase change material, in contact with the fluid which circulates, to thermally exchange between each other, -- in which the fluid circulates, between an inlet and an outlet, and -- in which is arranged phase change material, in contact with the fluid which circulates, to thermally exchange between each other, - the phase change material is arranged, within said interior volume, in a plurality of store and release thermal energy elements, - having a modular construction, the thermal store and heat exchanger comprises several adjacent modules, structurally separate and of which at least some individually comprise a base separating two adjacent modules, each base: -- splitting the volume into a succession of sub-volumes (7, 7b, etc.), in which are arranged said store and release thermal energy elements, around which and/or wherein the fluid circulates, in heat exchanges with each other, -- and having at least one passage for allowing the sub-volumes to communicate therebetween, -- splitting the volume into a succession of sub-volumes (7, 7b, etc.), in which are arranged said store and release thermal energy elements, around which and/or wherein the fluid circulates, in heat exchanges with each other, -- and having at least one passage for allowing the sub-volumes to communicate therebetween, - and, for creating baffles in the thermal store and heat exchanger on the fluid path: -- said passages for allowing the sub-volumes to communicate therebetween are offset from one of said passage to the following one, and/or -- inside the corresponding module, and for creating therein other sub-volumes (7a, 7c), partitions stand which keep communications between said other sub-volumes, for the circulation of the fluid. -- said passages for allowing the sub-volumes to communicate therebetween are offset from one of said passage to the following one, and/or -- inside the corresponding module, and for creating therein other sub-volumes (7a, 7c), partitions stand which keep communications between said other sub-volumes, for the circulation of the fluid.