The demand for resource circulation of heat exchangers in air conditioners is expected to grow rapidly; however, the market stocking time is relatively long. Therefore, this scenario was used as a case study for sustainable products design. A material flow analysis was conducted to estimate the balance between global relative resource consumption for shipment, waste, and installed stock from publicly available information up to 2050. Based on the projected demand through 2050, the shipment volume for each year was calculated on a cooling capacity basis. From this analysis, the waste volume was calculated. Using the shipment volume on the basis of yearly cooling capacity, the shipment volume on a resource basis was calculated considering the heat transfer coefficient. The balance between the waste volume and the installed stock was estimated. The resource circulation was simulated by defining variables such as the ratio of units that can be converted from waste to shipment and the ratio of heat exchangers using circulated resources in the total number of shipments. The results indicate that the shipment, waste, and installed stock of resources projected for 2050 were greater than those at the 2021 levels by factors of 2.2, 2.8, and 2.9, respectively. In addition, they were greater than those of the 2021 levels in the scenarios by factors of 1.8, 2.2, and 2.8 accounting for the increase of heat transfer coefficient into account, indicating the importance of improvement of heat transfer. The simulation of circulation showed that a fully closed loop in 2050 would be difficult to achieve owing to the shortage of heat exchangers for waste-to-shipment. Sensitivity analysis also indicated that even under conditions where there is no predicted shortage of circulated resources for 2050, achieving the target in a short period of time may cause a rapid increase in demand for circulating resources. This would subsequently, lead to a shortage of supply compared to demand. Thus, it is important to account for these dynamics relating resource circulation and strategy planning during analysis.

1. [1] European Commission, “The European Green Deal,” 2019.
2. [2] Ellen MacArthur Foundation, “Towards the circular economy Vol.1: an economic and business rationale for and accelerated transition,” 2013.
3. [3] European Commission, “A new Circular Economy Action Plan For a cleaner and more competitive Europe,” 2020.
4. [4] European Commission, “Regulation of the European Parliament and of the Council Concerning Batteries and Waste Batteries, Repealing Directive 2006/66/EC and Amending Regulation (EU) No 2019/1020,” 2020.
5. [5] Y. Umeda, K. Kitagawa, Y. Hirose, K. Akaho, Y. Sakai, and M. Ohta, “Potential impacts of the European Union’s circular economy policy on Japanese manufacturers,” Int. J. Automation Technol., Vol.14, No.6, pp. 857-866, doi: 10.20965/ijat.2020.p0857, 2020.
6. [6] K. Halada, “Activities of circular economy in Japan – towards global multi-value circulation –,” Int. J. Automation Technol., Vol.14, No.6, pp. 867-872, doi: 10.20965/ijat.2020.p0867, 2020.
7. [7] International Energy Agency (IEA), “The role of gas in Today’s Energy Transitions,” 2019.
8. [8] International Energy Agency (IEA), “Energy Technology Perspectives 2020 - Special Report on Carbon Capture Utilisation and Storage,” 2020.
9. [9] International Renewable Energy Agency (IRENA), “World Energy Transitions Outlook 2022,” 2022.
10. [10] N. Sako, M. Koyama, T. Okubo, and Y. Kikuchi, “Techno-economic and life cycle analyses of battery-assisted hydrogen production systems from photovoltaic power,” J. Clean Prod., Vol.298, 126809, doi: 10.1016/j.jclepro.2021.126809, 2021.
11. [11] Y. Kishita, E. Kunii, S. Fukushige, Y. Umeda, and J. Fujimoto, “Scenario analysis of global resource circulation with traceability index targeting sustainable manufacturing,” Int. J. Automation Technol., Vol.3, No.1, pp. 3-10, doi: 10.20965/ijat.2009.p0003, 2009.
12. [12] S. Hasegawa, Y. Kinoshita, T. Yamada, M. Inoue, and S. Bracke, “Disassembly reuse part selection for recovery rate and cost with lifetime analysis,” Int. J. Automation Technol., Vol.12, No.6, pp. 822-832, doi: 10.20965/ijat.2018.p0822, 2018.
13. [13] K. Yoda, H. Irie, Y. Kinoshita, T. Yamada, S. Yamada, and M. Inoue, “Remanufacturing option selection with disassembly for recovery rate and profit,” Int. J. Automation Technol., Vo.14, No.6, pp. 930-942, doi: 10.20965/ijat.2020.p0930, 2020.
14. [14] M. Saidani, B. Yannou, Y. Leroy, F. Cluzel, and A. Kendall, “A taxonomy of circular economy indicators,” J. Clean Prod., Vol.207, pp. 542-559, doi: 10.1016/j.jclepro.2018.10.014, 2019.
15. [15] Ellen MacArthur Foundation, “Circularity Indicators an Approach to Measuring Circularity Non-Technical Case Studies,” 2015.
16. [16] Y. Geng, J. Fu, J. Sarkis, and B. Xue, “Towards a national circular economy indicator system in China: An evaluation and critical analysis,” J. Clean Prod., Vol.23, pp. 216-224, doi: 10.1016/j.jclepro.2011.07.005, 2012.
17. [17] R. H. Li and C. H. Su, “Evaluation of the circular economy development level of Chinese chemical enterprises,” Procedia Environ. Sci., Vol.13, pp. 1595-1601, doi: 10.1016/j.proenv.2012.01.151, 2012.
18. [18] H. Murata, N. Yokono, S. Fukushige, and H. Kobayashi, “A lifecycle simulation method for global reuse,” Int. J. Automation Technol., Vol.12, No.6, pp. 814-821, doi: 10.20965/ijat.2018.p0814, 2018.
19. [19] Y. Kikuchi, A. Heiho, Y. Dou, I. Suwa, I. C. Chen, Y. Fukushima, and C. Tokoro, “Defining requirements on technology systems assessment from life cycle perspectives: Cases on recycling of photovoltaic and secondary batteries,” Int. J. Automation Technol., Vol.14, No.6, pp. 890-908, doi: 10.20965/ijat.2020.p0890, 2020.
20. [20] A. Ishigaki, T. Yamada, and S. M. Gupta, “Design of a closed-loop supply chain with stochastic product returns,” Int. J. Automation Technol., Vol.11, No.4, pp. 563-571, doi: 10.20965/ijat.2017.p0563, 2017.
21. [21] L. T. Biardeau, L. W. Davis, P. Gertler, and C. Wolfram, “Heat exposure and global air conditioning,” Nat. Sustain., Vol.3, pp. 25-28, doi: 10.1038/s41893-019-0441-9, 2020.
22. [22] D. Nishijima, “Product lifetime, energy efficiency and climate change: A case study of air conditioners in Japan,” J. Environ. Manage., Vol.181, pp. 582-589, doi: 10.1016/j.jenvman.2016.07.010, 2016.
23. [23] N. Shah, P. Waide, and A. Phadke, “Cooling the Planet: Opportunities for Deployment of Superefficient Room Air Conditioners Cooling the Planet: Opportunities for Deployment of Superefficient Room Air Conditioners,” Lawrence Berkeley National Laboratory, 2013.
24. [24] I. Ibnu Hakim, R. Sukarno, and N. Putra, “Utilization of U-shaped finned heat pipe heat exchanger in energy-efficient HVAC systems,” Therm. Sci. Eng. Prog., Vol.25, 100984, doi: 10.1016/j.tsep.2021.100984, 2021.
25. [25] A. Miyara, “Recent Directions in Heat Exchanger and Heat Transfer Enhancement,” J. Heat Transf. Soc. Japan, Vol.54, pp. 12-18, 2015 (in Japanese).
26. [26] Y. Shibata, “Research and Development on Improvement in Performance of Heat Exchangers for Air-conditioners,” Proc. of Thermal Engineering Conf. 2007, A13, 2007 (in Japanese).
27. [27] T. Nishizawa, Y. Handa, S. Yoneda, Q. Fang, S. Ohara, Y. Oshita, S. Fujii, and Y. Kikuchi, “Hotspot analysis of environmental load at the manufacturing stage of commercial air conditioners,” Proc. of the 17th Meeting of the Institute of Life Cycle Assessment, Japan, 2022 (in Japanese).
28. [28] T. Jin, G. Li, Y. Cao, R. Xu, S. Shao, and B. Yang, “Experimental research on applying the copper-clad aluminum tube as connecting tubes of air conditioners,” Energy Build, Vol.97, pp. 1-5, doi: 10.1016/j.enbuild.2015.03.023, 2015.
29. [29] International Energy Agency (IEA), “The Future of Cooling Opportunities for energy-efficient air conditioning,” 2018.
30. [30] National Institute for Environmental Studies, “Lifespan database for Vehicles, Equipment, and Structures: LiVES,” 2010
31. [31] K. Nomura, “Duration of assets: examination of directly observed discard data in Japan,” KEIO Discuss, 2005.
32. [32] Cabinet Office Government of Japan, “Consumer Confidence Survey 2021,” 2021 (in Japanese).
33. [33] S. Huysman, J. De Schaepmeester, K. Ragaert, J. Dewulf, and S. De Meester, “Performance indicators for a circular economy: A case study on post-industrial plastic waste,” Resour. Conserv. Recycl., Vol.120, pp. 46-54, doi: 10.1016/j.resconrec.2017.01.013, 2017.
34. [34] Y. Kikuchi, I. Suwa, A. Heiho, Y. Dou, S. Lim, T. Namihira, K. Mochidzuki, T. Koita, and C. Tokoro, “Separation of cathode particles and aluminum current foil in lithium-ion battery by high-voltage pulsed discharge Part II: Prospective life cycle assessment based on experimental data,” Waste Manag., Vol.132, pp. 86-95, doi: 10.1016/j.wasman.2021.07.016, 2021.
35. [35] S. Fujii, Y. Oshita, Y. Kikuchi, and S. Ohara, “Material Flow Analysis on Resource Circulation Attributable to Air Conditioners,” Proc. of the SCEJ 87th Annual Meeting, 2022 (in Japanese).