There is growing interest in the utilization of unused, but possible, energy sources to reduce carbon-dioxide emissions and fossil-energy consumption, and especially to comply with the Kyoto Protocol which came into effect in 2005. Detailed considerations of plant location, land use and life cycle analysis, however, have not yet been fully estimated with a view to confirming the advantages of the new energy-source usage. A model for heat energy from river water and treated sewage water, and waste-heat energy from municipal solid-waste incineration plants was built and applied to the Tokyo urban area in Japan, considering the spatial and time-related distribution of demands and supplies, the shapes of buildings in the demand area, and life-cycle analysis. The model selected areas were those which should use these energies without prejudice, and sometimes the areas were far from the energy-source point. The reduction of carbon-dioxide emissions resulting from new energy-sources was about 8% of the reduction target for Tokyo in 1990. The model was able to precisely evaluate the new energy-usage, using data from both supply and demand sides. (c) 2007 Elsevier Ltd. All rights reserved.