Heat exchange system of an industrial truck

The truck (2) has an electrical-drive unit comprising a driver seat and/or a driver cabin. A modular, replaceable energy converter unit (1) has a cooling unit with a cooling medium and/or cooling elements for cooling the energy converter unit. The cooling unit has a heat-contact surface for heat dissipation. The electric drive unit has another heat-contact surface for heat absorption. Heat of the cooling medium and the cooling elements is transferred to a heating medium and/or a heating element of a heating unit of the electric-drive unit in a heat transfer-phase. The energy converter unit is formed as a fuel cell unit or a diesel motor-generator unit.