In Japan, approximately 60 percent of the primary energy supply is lost as waste heat due to low thermal energy conversion efficiency. (Fig. 1)A lot of effect has been made for energy conservation in industry which uses various energy sources since 1973 when the oil crisis happened. (Fig.2) However, waste heat is not recovered sufficiently at low temperature. Since most of energy in residential and commercial areas is used for air-conditioning and hot water supply, the temperature of heat for residential and commercial use is almost equal to that of waste heat discharged from industrial sources.Therefore, Broad Area Energy Utilization Network System (Eco-Energy City) project, which started in 1993 and will continue over a period of 8 years, is a large-scale national energy conservation project of the Agency of Industrial Science and technology (AIST) of the Ministry of International Trade and Industry (MITI). The aim of this project is to accelerate the full scale utilization of industrial waste heat for residential and commercial use by technological breakthroughs. The concept of the project is as follows:1) Waste and unutilized heat discharged from industrial sources at relatively high temperature is recovered very efficiently, in multiple stages and in various ways.2) Recovered heat is transported with a small heat loss over a long distance to residential and commercial areas that have various patterns of consuming relatively low-temperature heat.3) Transported heat is supplied at consumer sites in different ways depending on the individual consumption pattern.4) Thermal energy is utilized in the following forms: Cascaded use, combined use and recyclingThe key to success is to develop innovative technologies of heat recovery, heat transport, heat supply and systematization of energy supply and demand.
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