An approach of the sizing of a data center that reuses the waste heat is the aim of this document, focusing in the modular design of its different parts, the perform of the cooling systems using CO2 as main coolant and an analysis of the energetic consequences extracted from it, all together with a previous literature review of every technology used. This literature review was actually the starting point of the design as it allowed to gather information about data center, its cooling machinery... for later develop an own idea of the arquitecture and the thermal energy operation of the designing. Due to this idea of building a low energy consumption data center, the results were analyzed around parameters like the PUE (Power Usage Effectivenes), which is a measure of the electricity consumed by a data center, and the energy savings derivated of the waste heat management cooling systems. The main conclusions that are extracted from this way of designing that centers, is that there are benefits in every aspect studied. A modular pre-engineerized structuring reduces cost for the company and leads to efficiency gains, as all energy flow is better utilized. Furthermore, the environmental impact of the waste heat usage and its positive economical consequences gives to this type of projects very good future perspective.