The aim of this article is to deal with the cooler for microclimate controls, the thermo-electric cooler and its optimum design. The semi-conductor thermo-elements are optimizingly arranged to procure the optimum electric current and obtain a maximum refrigeration output. According to the optimum design method, the authors have made a set of coolers with 384 W (refrigeration output), 1 000 W(power consumption), 24 V (DC) (input voltage) and 40 A (DC)(current). The testing results are fully in agreement with the design requirements.