Optimal Load Shift Control Strategy for CHPWH system Based on Load Separation Method

¹ Department of Architecture, Graduate school, Konkuk University, Seoul, 05029, South Korea
² School of Architecture, College of Architecture, Konkuk University, Seoul, 05029, South Korea

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Abstract. As global electrification accelerates, the central heat pump water heater (CHPWH) system has gained increasing attention as an efficient and sustainable alternative for domestic hot water supply. However, the conventional CHPWH system experiences performance degradation because the introduction of return water increases the heat pump inlet temperature, thereby reducing its operational efficiency. To address this issue, a swing-tank-based Load separation method has been proposed for the CHPWH system, in which the primary water heating Load for cold water heating is separated from the temperature maintenance Load associated with return water. By introducing this Load separation method, the system enables Load shift based on time-of-use (TOU) electricity pricing. This control strategy reduces heat pump operation during high electricity price periods and increases operation during low price periods, thereby achieving energy Load leveling and improving overall system efficiency. Nevertheless, detailed modeling studies and systematic validation of the effects of TOU-based Load shift in such systems remain limited. Therefore, in this study, a TOU-responsive Load shift control strategy is proposed and optimized for a multi-family residential building in Seattle, and a swing tank-based Load separation CHPWH system is modeled using TRNSYS. The analysis results demonstrate that the developed model reliably reproduces the on-off operation pattern of the heat pump, with quantitative validation showing Willmott's d index and cosine similarity values exceeding 0.80. Furthermore, the proposed TOU-based Load shift strategy reduces electric energy consumption by an average of approximately 46% compared to a conventional single-sensor-based system operated without considering TOU pricing. These results confirm that electricity price-driven Load shift control can significantly enhance the energy efficiency of the CHPWH system. In addition, the developed TRNSYS-based model provides a foundation for future research on advanced control strategies, such as machine learning-based Load forecasting and tank size optimization, thereby supporting the development of a more stable CHPWH system and further improving its performance and operational flexibility.