Hybrid packed-bed latent and sensible thermal storage routing strategies for PV/T-assisted heat-pump domestic hot water systems

Domestic hot water (DHW) remains a challenging end-use for residential decarbonisation since it imposes a persistent year-round thermal load and often accentuates the mismatch between solar availability and user demand. This study evaluates PV/T-driven heat pump DHW systems based on a hybrid thermal energy storage (TES) concept, in which a packed-bed latent heat TES (PB-LHTES) complements a sensible TES (STES) buffer to capture surplus PV/T heat and shift it to demand peaks while limiting auxiliary electricity use. The work specifically quantifies how temperature-based routing at the storage-heat pump interface governs usable heat quality, heat-pump duty, and seasonal performance. A computationally efficient PB-LHTES model is developed for minute-resolution dynamic simulations and validated against experimental data, enabling its integration into building-scale DHW analyses. The validated PB-LHTES component and the DHW profile generator are coupled within a TRNSYS-based framework to perform annual minute-resolution simulations for a five-storey apartment case study. Four configurations with identical component sizing are compared, including a reference PV/T + air-to-water heat pump + STES system and enhanced solutions integrating PB-LHTES with alternative routing strategies and water-to-water heat pump layouts. The results show that PB-LHTES integration improves both solar-energy utilisation and heat-pump operation, increasing the solar contribution factor and the electrical renewable factor by up to 141% and 155%, respectively. The most effective performance is obtained for the configuration combining PB-LHTES with a water-to-water heat pump and temperature-dependent routing strategy. This solution reduces annual DHW-system electricity consumption from 5.78 to 3.27 MWh, increases the annual mean COP from 2.50 to 4.31, and lowers CO 2 emissions by 55.58% relative to the reference case. It also reduces overheating and narrows the STES outlet temperature fluctuations, maintaining the most stable year-round delivery band before mixing. The findings demonstrate that temperature-based routing at the storage-heat pump interface is a key lever for improving PV/T-assisted DHW systems with hybrid latent-sensible TES by enhancing heat quality, heat-pump operation, and year-round DHW delivery stability.