Optimum Operation Control Strategies for a PV-Assisted Centralized Thermal System with Multiple Storage Devices

In the framework of the EU-funded H2020 innovation project “e-SAFE”, a centralized thermal system for Domestic Hot Water (DHW) production has been developed and implemented in a residential pilot building in Southern Italy. The system integrates a PV-assisted air-to-water heat pump, a central storage tank, and innovative slim decentralized 140-liter tanks (called e-TANK), one per dwelling. The system is designed to exploit the interaction between on-site PV generation and thermal storage, thus maximizing self-consumption and operational efficiency while reducing energy waste. The central tank stores technical water, which is circulated only when required to recharge the decentralized units, avoiding continuous recirculation and minimizing Legionella risk. This configuration allows lower operating temperatures, improving heat pump performance and enabling smart control strategies. To assess system performance, dynamic simulations were carried out in TRNSYS and compared to a traditional centralized DHW solution under the same boundary conditions. Eight scenarios were analysed, four for each system configuration, by varying setpoint temperatures and recirculation operation modes. Key performance indicators such as heat losses, electricity consumption, heat pump runtime, seasonal coefficient of performance (SCOP), and number of on/off cycles were used to evaluate efficiency and system durability. The results highlight that the e-SAFE configuration, despite the slightly higher thermal losses due to the presence of decentralized storage devices, significantly reduces the number of on/off cycles and enables higher SCOP values: indeed, the best e-SAFE configurations achieve SCOP = 3.47 against SCOP ranging between 2.63 and 2.86 for the traditional centralised system. Moreover, it can lower electricity consumption and improves the potential service life of the heat pump. The ability to shift heat pump operation to times of PV availability, and the decoupling of generation and demand, play a crucial role in enhancing renewable energy utilization. These findings confirm the suitability of integrating decentralized thermal storage and smart control strategies in energy-efficient retrofits to optimize DHW systems in multifamily residential buildings.