A Status-transition Model for CO2 Heat Pump Water Heater Based on Modified Lorentz cycle

Year 2019, , 26 - 33, 02.03.2019

Yasuaki Bando , Hironori Hattori Yoshiharu Amano

https://doi.org/10.5541/ijot.499185

Abstract

Energy management is a systematic activity for improving energy performances of a target system, and an energy management system is expected to solve operational planning problems and report or suggest opportunities for performance improvement. An equipment model is required to reflect the characteristics of the actual equipment’s performance and to have a simple structure to apply to operational planning problems. The model should be able to diagnose changes with performance degradation over time. In this study, we proposed a thermodynamically-sound model of a CO2 heat pump water heater, suitable for solving operational planning problems and diagnosing degradation of equipment. The proposed model consists of a heat pump unit (HP) and a hot water storage tank (ST). The HP model is a status-transition model, constructed based on the Lorentz efficiency, which is identified by experimental values and a theoretical maximum coefficient of performance (COP) for a trans-critical heat pump cycle. The ST model is simplified and can describe temperature distribution in the ST because the unit COP of the HP influences the thermal stratification of the ST. The proposed model is preferable in its simplicity and robust performance for a wide temperature range by comparison with a conventional statistical regression model.

Keywords

energy management system, heat pump water heater, Lorentz cycle, operational planning

References

• Energy Management Standardization Technical Committee, “International Standard Energy Management Method ~EnPI Implementation Guide~ Practice [ISO Compliant Version],” Japan Electronics and Information Technology Industries Association, 6-11, 2016 (in Japanese).
• The Energy Data and Modeling Center, “Japanese Version of Handbook of Japan's & World Energy & Economic Statistics,” The Institute of Energy Economics, Japan, 92-93, 2017 (in Japanese).
• Agency for Natural Resources and Energy, “Long-term Energy Supply and Demand Outlook”, 2015 (in Japanese).
• Nagai, T., Yoshida, A., Amano, Y., “Impact of Utilizing PV Surplus Power on CO2 Emission of Residential Energy System,” Proceedings of the 35th Japan Society of Energy and Resources Conference, 33-38, 2016 (in Japanese).
• Céline, W., François M., Daniel, F., Steven, K., “Optimization of an SOFC-based decentralized polygeneration system for providing energy services in an office-building in Tōkyō,” Applied Thermal Engineering 26, 1409-1419, 2006.
• Iwafune, Y., Kanamori, J., Sakakibara, H., “A comparison of the effects of energy management using heat pump water heaters and batteries in photovoltaic -installed houses,” Energy Conversion and Management 148, 146-160, 2017.
• Stene, J., “Residential CO2 heat pump system for combined space heating and hot water heating,” International Journal of Refrigeration, 28, 1259-1265, 2005.
• Poul, A. Ø., Anders, N. A., “Booster heat pumps and central heat pumps in district heating,” Applied Energy 184, 1374-1388, 2016.
• Bando Y., Amano Y., “Modeling of CO2 heat pump water heater for energy management,” Transactions of the JSME, Vol. 84, No .859, 1-14, 2018 (in Japanese).
• Yokoyama R., Shimizu T., Takemura K., Ito K., “Performance Analysis of a Hot Water Supply System with a CO2 Heat Pump by Numerical Simulation (2nd Report, Modeling of Hot Water Storage Tank and Analysis of System)," JSME International Journal Series B, Vol. 71, No. 712, 151-158, 2006.
• Andou T., Machida K., Imagawa T, Yamamoto T., “Development of Energy-Saving Technology for CO2 Heat Pump Water Heater,” Panasonic Technical Journal, Vol. 56 No. 2, 27-32, 2010 (in Japanese).
• Wakamatsu Y., Hashimoto K, “Development of a Simulation Model to Predict Temperature Distribution in Hot Water Storage Tanks for Improving Efficiency of CO2 heat Pump Water Heaters –A Model for Heat Pump Water Heaters with Basic Functions–,” Energy Engineering Research Laboratory Rep. No. M12003, 1-20, 2013 (in Japanese).
• Building Research Institute, “Description and method of calculation and judgment based on energy saving standard in 2013,” Institute for Building Environment and Energy Conservation, 457-458, 937-942, 2013 (in Japanese).