## 1 Introduction
The integration of a hybrid system with active thermal storage proves to be an effective solution for demand-side management. [PERSON] et al. [23] conducted an exergy and exergy cost analysis of a solar-assisted heat pump with seasonal storage to provide electricity, heat, and domestic hot water (DHW) for social housing. They found that the monthly exergy efficiency of the photovoltaic-thermal (PVT) field varied between 13% in July and 17% in April for weather conditions in Spain. The highest thermal exergy production occurred in May due to cooler ambient temperatures compared to the highest solar fuel months from June to August. [PERSON] et al. [24] proposed a hybrid PV/T solar field combined with a seasonal storage tank and a water-to-water heat pump. Simulation results demonstrated that this setup could meet 80% of the building's hot water demand. [PERSON] et al. [25] conducted a detailed exergy analysis of a hybrid system with a supplementary boiler operating in both heating and cooling modes. Their study reveals significant differences in the components that contribute the most to the overall exergy consumption in each mode. The comparison of exergy consumption shows that the distribution of exergy losses varies between heating and cooling operations, with distinct components contributing to the overall exergy inefficiencies in each mode. [PERSON] et al. [26] investigated a hybrid system combining a hydrothermal heat pump and a pellet boiler, and their findings indicated that this system can be effectively applied to smart farm heating. The study demonstrated that the hybrid system not only performs efficiently in terms of heating but also offers significant energy cost savings, making it a viable solution for smart farm applications. Moreover, various types of heat pump-biomass hybrid systems are already available on the European market [27; 28], showing great potential to accelerate the decarbonization of the building sector. These systems offer an efficient and sustainable way to reduce reliance on fossil fuels, thereby improving the overall energy efficiency of residential and commercial buildings. From the state-of-the-art study conducted, it can be observed that hybridization with a biomass boiler is rarely considered, highlighting a significant research gap. Additionally, there is a lack of studies analyzing the configuration of hybrid systems--whether in series or parallel integration--while also accounting for the necessary auxiliary bypass systems when the heat pump is stopped for technical reasons, from energy, economic, and environmental perspectives. Furthermore, optimization of the operating point based on the heat pump cut-off temperature, across all configurations, is also absent in the current literature. Therefore, this article presents a guide for selecting the most appropriate configuration based on the criteria adopted for such selection. A dynamic model of the seasonal energy performance of a HHP system composed by an air-to-water heat pump coupled to a backup device (a biomass boiler) is presented. Different configurations of the HHP have been developed to account for some key performance indicators (KPI), including efficiency, CO2 emissions, operational costs, and more. The dynamic model of the hybrid system has been developed by means of TRNSYS 18 [29]. The main goal of this investigation is to analyze the role played by the backup biomass boiler, the system control logic, and the heat pump defrosting cycle with respect to the building's design heating load on the seasonal performance factor of the HHP system.