Abstract
Many of the district heat supply systems in Japan (133 districts, as of end of March 2017) were installed in the 1990s and have been in use for over 20 years. Therefore, improving system efficiency is a goal as the time for renovation approaches. Further, in the context of the Great East Japan Earthquake, in addition to energy conservation during normal times in cities, business continuity performance in the regional units during emergencies has become necessary. From the above two points, it is expected that the plan for renovation and new installation of Cogeneration Systems (CGSs) in the district heat supply system will increase. Hence, understanding the form of the district heat supply system that utilizes the existing CGSs and the details and effects of its renovation, are considered important.
Therefore, in this study, First of all CGS installation utilization patterns in the district heat supply system are categorized. Nextly, the form of 24 existing district heat supply systems utilizing CGS in the metropolitan area were investigated, and the CGS installation utilization patterns for 17 systems were identified. Subsequently, among the 17 systems, the details of renovation and new additions in 9 systems, in which CGSs were renovated or recently added, were examined. Further, to examine the effects of renovation, the energy consumption of the heat supply system before and after renovation was investigated. Finally, the effect of CGS renovation was evaluated by setting up index. The efficiency of the heat supply system was utilized as the evaluation index. From the above survey analyses, the following three findings are presented.
By combining the 3 types of heat supply system plants and the 7 types of destination facilities of the generated power supply, 10 types of CGS installation utilization patterns emerge. Further, from the actual survey results, there were 12 districts that consumed generated power in the CGS installation buildings, and there were 3 districts that supplied generated power to the outside of the CGS installation building.
Based on the results of the survey on the renovation details of 9 districts, there were a total of 6 cases of CGS renovation, namely, new installation for the plant, new installation for the consumers, transition from individual reception to collective power reception, change in the installation site, change in the supply destination of generated power, and addition of emergency response.
Among the 9 districts surveyed for cases of renovation, there were 5 districts where the energy consumption of the heat supply system could be investigated. The heat supply system efficiency and the emergency power supply rate of these districts were calculated. The power generation efficiency tended to improve, and the overall efficiency showed a trend of slight decrease or an increase of 4 to 6 points. Further, the heat supply system efficiency tended to improve by 1.1 to 1.4 times in all the surveyed districts before and after renovation.
