For my research, I want to examine green building techniques, and more specifically, I want to focus on strategies for retrofitting existing buildings to connect with district energy systems. There is a national trend of cities revitalizing their downtowns, bringing new development and density. In some downtowns one will find skyscrapers connected by underground pipes that deliver heating and cooling to the building, of which was produced by thermal energy created during non-peak hours. This is district energy, where multiple buildings within a geographic area participate in a more sustainable approach to meeting the energy needs of their buildings. For the most part, it seems new development projects are the ones being connected to these types of systems. If this is true, then something must be preventing the others from not connecting. What are the obstacles, and how can downtowns retrofit and connect their larger buildings to district energy? For downtowns that do not have district energy, what are the thresholds that make it feasible? Is there a history of developers choosing not to connect to existing systems, and if so what were the reasons? With those questions in mind, my research will analyze current trends and allow me to present strategies for increasing the participation within existing district systems. The biggest buildings in our cities consume a great deal of energy at very high costs. By making it the trend to use district energy, less energy is consumed, less energy is wasted, and less money is spent.