One of the main global goals is the reduction of the energy consumption and the most appropriate way for achieving this aim is to target one of most critical sectors, the residential. The selected technology for this work is the district energy network, which spreads heat to the buildings glad to a driven fluid going through pipes. The evolution of this technology relies on two aspects, reducing the temperature of the working fluid and lately moving from water to refrigerants, for reaching a more efficient system also by balancing the demand of an whole district. This work presents a methodology, a tool meant for decision makers whether implementing a district heating network based on $CO_2$ in a neighborhood and in what terms, in this way the best design alternatives are evaluated before making a decision. The process is characterized by the definition of a superstructure made of energy technologies, which has to satisfy the demand of the buildings and taking advantage of natural resources available, and in parallel the study of the network considering the available streets of a district. On this work has been first defined a method to drive the designer along the evaluation of a general project and then studied a real district. For this case study the district of Ronquoz in Sion (Switzerland) is select, since it is going to face an important requalification in the following years.