This document represents the memory derived from a project carried out as a Traineeship period at NTNU/SINTEF and reflects the tasks accomplished during its course. Such tasks are divided in two paths: the design and manufacture of a CTES unit for further work at SINTEF’s lab, and an academic research about the benefits derived from the use of R744 as a working fluid in the refrigeration systems of supermarkets, including the derived technologies with the objective to spread them among the scientific community. The study of R744 as a working fluid concludes that it is a valuable asset for a sustainable future, since with current technologies it performs even better than most of the Hydro-Fluorocarbon refrigerants that nowadays possess the market, while having Global Warming Potential and Ozone Depletion Potential both 0. With the technologies available nowadays, CO2 can be used as a working fluid anywhere in the world and has no unavoidable drawbacks. Regarding the design of the CTES tank, it is designed to be used in a modular arrangement in supermarkets, including several units in parallel if necessary. The unit/s aim to be placed on top of the cabinets (so each cabinet would have its own) which is a space that is generally unused. To take advantage of such placement, the thermosiphon principle can be used when discharging the tank/s so no energy is consumed by the compressors of the refrigeration system. The core of the tank is based on three tube coils through which the refrigerant flows The coils change their diameter following a certain sequence in order to cover all the volume of the tank, so that the heat exchange is enhanced while having the same length in every coil, which is necessary to sustain the thermosiphon principle. The design is carried out through an iterative process to stablish the dimension of the different components of the tank. A gathering of the operation and control strategies that can be done in a refrigeration system that includes the designed CTES unit is also included in this document, as well as an energetic study of the implementation of such CTES unit in a generic refrigeration system. The result shows that the energy consumption can be reduced as much as 38,9% with respect to the base case. Also, the process and materials used during the manufacture of the coils of the tank are depicted. These coils are built at the end of the Traineeship period and delivered to the co-director of this project for further work. Finally, an environmental and economic analysis is included, which shows that the CTES pays off both economically and environmentally before a lifespan of 20 years.