According to Eurostat data cited by the European Commission, approximately 50 % of all energy consumed in the European Union (EU) is used for heating and cooling [1]. Alarmingly, over 70 % of this energy is still sourced from fossil fuels, with only about one-quarter derived from renewable sources [2]. These figures underscore the urgent necessity to decarbonise this sector, which remains one of the most carbon-intensive components of the EU's energy landscape. Aligned with the European Green Deal and the Fit for 55 packages [3], the EU has committed to reducing Greenhouse Gas (GHG) emissions by at least 55 % by 2030 compared to 1990 levels. Additionally, the revised Renewable Energy Directive (RED III) sets a binding target of at least 42 % share of renewable energy in final energy consumption, with the potential to rise to 45 %, while energy efficiency improvements must reach about 10 % relative to projected primary and final energy consumption levels.

In this policy context, modernising heating and cooling systems is crucial. The transition to energy-efficient, low-carbon, renewable-based heating technologies, such as heat pumps, district heating powered by Renewable Energy Sources (RES) and solar thermal systems, can contribute significantly to the achievement of climate and energy targets. This shift aids emissions reduction, enhances energy security, reduces dependency on fossil fuel imports and supports the creation of green jobs across EU member states.

Introduction to the RESHeat System

The RESHeat (Renewable Energy System for Residential Building Heating and Electricity Production) is a pioneering renewable-integrated solution precisely designed to meet residential heating, cooling, and domestic hot water (DHW) requirements [24]. Developed under the EU Horizon 2020 initiative, RESHeat strategically combines PV/T modules, solar energy collectors, advanced heat pump technology, underground thermal energy storage, and intelligent control systems [25]. Its design aims to achieve maximum renewable energy utilization, reduce environmental impacts, and optimize economic viability for residential settings.

The RESHeat system realizes its holistic integration of renewable energy sources with advanced thermal energy management and storage technologies. Aligning to its operation are sun-tracked and stationary PV/T modules, which simultaneously generate electricity and thermal energy [19]. Due to the reuse of waste heat from PV/T combined with underground energy storage, the high COP of the heat pump with a yearly average of over five is achieved [26]. A highly efficient ground regeneration technique is developed due to the thermal energy recovery underground. Another notable innovation is the employment of a glycol-water heat pump integrated with thermal energy storage solutions. The underground thermal storage exploits stable ground temperatures to support consistent heat pump performance throughout seasonal changes, thus ensuring high system efficiency [27]. The system employs these modules to improve overall efficiency, significantly outperforming conventional photovoltaic or thermal collectors operated separately [28].

The RESHeat project has established demonstration sites in both Poland and Italy, enabling comparative analysis of system performance under distinct European conditions. The Polish demonstration represents a cold temperate continental climate with long heating seasons and relatively stable ground temperatures, whereas the Italian demonstration is situated in a Mediterranean climate characterised by hot summers, mild winters, and higher solar availability. In addition to these climatic contrasts, the two sites differ in terms of system configuration, component sizing, and operational strategies, which significantly affect energy demand patterns and environmental outcomes. While a Life Cycle Assessment (LCA) of the Polish demonstration has been reported in our previous work [19], the present study provides the first in-depth environmental assessment of the Italian demonstration. This offers novel insights into the regional dependence of RESHeat’s sustainability performance and complements the earlier findings from Poland, thereby contributing to a more comprehensive understanding of the system’s applicability across diverse contexts.

Italian demonstration sites at the ATER building, located in Palombara Sabina near Rome, exemplify the practical application of RESHeat technology. The building, constructed in 1980 - 1985, comprises 13 apartments and was initially equipped with a conventional natural gas boiler [27]. The original system had a maximum heat input of 69 kW, delivering a heating output ranging from 51.8 kW to 65 kW, with an efficiency of 96 %. The annual heating demand for the building is approximately 54.92 MWh, while its annual cooling demand reaches 37.70 MWh [29].

The RESHeat installation at the ATER demo site comprises (shown in Figure 1):

• 75 stationary PV/T modules, each module rated at 300 W, collectively delivering a peak electrical output of 22.5 kW.

• Water-to-water RE56 heat pump, providing a maximum heating capacity of 85 kW and cooling capacity of 74 kW.

• 4 1000-liter buffer tanks without heat exchangers and 2 800-liter buffer tanks with integrated heat exchangers.

• 1 dry cooler with a maximum capacity of 146.7 kW for thermal regulation.

• 26 fan coil units distributed throughout the apartments for precise heating and cooling delivery.

The RESHeat system operation is specifically tailored to seasonal variations, effectively managing energy production and utilization throughout the year.

Figure 1.

The schematic of RESHeat in Italy [29]

Winter Mode: During the heating season, the PV/T modules primarily provide electricity to power the heat pump. Simultaneously, thermal energy captured by the PV/T modules is utilized directly at the heat pump's source side, enhancing the COP of the heat pump. Excess thermal energy is stored in buffer tanks, maintaining optimal temperature levels for efficient heat pump operation. The heat pump supplies heat to the apartments through fan coils, achieving precise and comfortable indoor temperatures.

Summer Mode: In the non-heating season, the system continues to utilize PV/T modules for electrical and thermal energy production. The heat pump operates in cooling mode, providing cooling to the apartments via fan coils. Excess thermal energy generated by the PV/T modules and the operational heat from the heat pump are dissipated using the dry cooler, ensuring efficient thermal management and maintaining optimal system performance.

The RESHeat system is still in the demonstration phase, making early-stage environmental evaluation essential for guiding future development and deployment. Conducting a comprehensive LCA is necessary to accurately capture the system’s environmental footprint across all life cycle stages, including production, operation, and end-of-life. Such an evaluation enables the identification of environmental hotspots, quantifies potential trade-offs, and provides a scientific basis for decision-making in system optimization. Moreover, early environmental assessment ensures that the RESHeat system aligns with sustainability goals and regulatory frameworks, particularly those related to climate neutrality, resource efficiency, and the circular economy.

This paper evaluates the environmental impacts of the RESHeat system implemented at the Italian demonstration site, focusing on its overall sustainability within the context of residential heating, cooling, and domestic hot water supply. The ReCiPe 2016 Midpoint (H) method was applied to ensure a robust and multidimensional environmental evaluation. This method enables detailed quantification of environmental impacts across several key categories, such as global warming potential, fossil resource scarcity, water consumption, human toxicity, ecotoxicity, terrestrial acidification, and particulate matter formation. The assessment includes not only the direct emissions from system operation but also the embedded environmental impacts of the materials and processes involved in the system’s construction and decommissioning. Particular attention was paid to the impact of material reuse and recycling strategies. These strategies can significantly reduce environmental impacts, particularly greenhouse gas emissions and the consumption of non-renewable natural resources. A comprehensive environmental analysis of the RESHeat system installed in Italy was conducted by integrating real operational data with a detailed breakdown of the system’s components into their constituent parts and applying the advanced life cycle assessment (LCA) methodology.

The novelty of this study lies in its comprehensive scope and in the fact that it is the first in-depth environmental assessment of a fully operational RESHeat system implemented in Italy. The analysis covers all stages of the system’s life cycle: from raw material extraction and component manufacturing, through the operational phase, to end-of-life scenarios. The potential environmental benefits of material reuse and recycling were also assessed.

The findings offer valuable insights into the environmental impact of individual components, such as PV/T modules, heat pumps, and storage tanks, on the overall footprint of the system. These results serve as a foundation for future system optimization and support the advancement of sustainable heating and cooling technologies in the residential sector, aligning with the principles of the circular economy.

Life Cycle Assessment was employed to assess the environmental impacts of the RESHeat system across its lifecycle stages: construction, operational and end-of-life stages. The ReCiPe 2016 (Midpoint H) method was used to evaluate environmental categories, including global warming potential, resource scarcity, water consumption, and human health impacts. The functional unit is the environmental impact associated with electricity and heat generation by the RESHeat system over one year. No allocation procedure was applied to the PV/T system since both energy outputs are included within the same functional unit, allocation between thermal and electrical outputs was avoided. The system boundaries of the study are defined on a cradle-to-grave basis (Figure 2), covering from material acquisition and system construction, operation and end-of-life stages. The methods follow the International Organization for Standardization (ISO) 14040 guidelines. Solar irradiation used for electricity and heat generation was considered carbon-free. Given the relatively minor contribution of transportation processes, their impact is considered negligible and thus excluded from the analysis. The impact assessment includes ecological damage, resource depletion and health damage. For waste management in the end-of-life stage, it is assumed that 61.7% of steel, 90% of aluminium, and 41% of copper are recycled and reused. The remaining parts are treated by landfilling [30]. Their reported figures are based on Ecoinvent data and European waste management statistics available at that time. These values are adopted to ensure methodological consistency and comparability with previous LCA studies. Furthermore, the recycled materials are assumed to be directly reused in the system without additional processing [19].

Figure 2.

The system boundary defined and the four steps of LCA methodology

The energy flows of Italy’s demonstration are shown in Table 1. In the RESHeat system demonstration in Italy, the total heating demand reaches 103.42 MWh/y, which is primarily met through central heating and domestic hot water needs, at 54.92 MWh/y and 48.5 MWh/y respectively. Additionally, the system encounters a cooling demand of 37.7 MWh/y. The energy supply side features a significant contribution from PV/T systems, which generate 54.65 MWh/y of thermal energy. Heat pumps supplement this by providing another 16 MWh/y of thermal energy. On the electricity front, the PV/T systems produce 30 MWh/y, comfortably exceeding the total electricity demand of the system, which is 28 MWh/y.

The inventory may encompass materials such as steel, copper, and plastics, among others, and the production and disposal of these materials entail varying degrees of environmental impacts. The inventory list of the heat pump and gas boiler systems draws on data from Greening and Azapagic [30]. Additionally, data for the PV/T panels are sourced from Fthenakis and Kim [31], while sun-tracking solar system data are obtained from Chow and Ji [32] and Menzies and Roderick [33]. The underground storage tank inventory is sourced from Suer et al. [34]. The inventory of system infrastructure is from the site survey. The inventories of the facilities installed in the Italy demonstration are provided in Tables 2 to 7. This comprehensive coverage includes components such as heat pumps, PV/T panels, heat exchangers, hybrid systems, storage tanks, and fan coils.

The combination of OpenLCA software and the Ecoinvent database, along with the ReCipe 2016 midpoint (H) impact assessment method, forms a robust framework for conducting a comprehensive and reliable environmental evaluation of the heating systems as shown in Figure 3. This approach ensures the study’s credibility and enables informed decision-making for promoting sustainable heating solutions with reduced environmental impacts. The core part of LCA is the life cycle impact assessment, where the life cycle inventory data is weighted to derive the system’s potential impacts on the environment. During this process, the significance of different environmental impact impacts is considered, such as global warming potential, acidification potential, resource depletion, etc. Ultimately, through the interpretation of results, we gain a comprehensive understanding of the system’s environmental performance and guide system improvement and optimization to minimize its environmental impacts.

Figure 3 illustrates the methodological framework adopted to quantify environmental impacts at both the component and system levels. The procedure begins with defining product and energy flows, establishing corresponding processes, and constructing product systems, followed by calculation of properties using the ReCiPe 2016 Midpoint (H) method. This stepwise approach ensures consistency in assessing material inputs, energy categories, and allocation strategies, thereby enabling a comprehensive life cycle evaluation of the RESHeat system.

Figure 3.

A block diagram of the calculation process

The environmental impact results for the RESHeat system demonstration are shown in Table 8. The total greenhouse gas emissions associated with the construction of the RESHeat system amount to 7,227.62 kg CO₂ eq after accounting for material recycling and reuse. Without reuse, the material-related emissions would reach 36,982.26 kg CO₂ eq. However, the application of reuse strategies is expected to reduce this by up to 29,796.25 kg CO₂ eq, representing 80.57 % of the total material-related impact. Fossil resource scarcity shows a considerable initial demand of 24,284.70 kg oil eq due to material use. However, through reuse, this figure is dramatically reduced by over 20,902.10 kg oil eq, leading to a much lower net impact of 3,394.73 kg oil eq. This significant decrease highlights the potential of reuse strategies in conserving non-renewable fossil resources, which is crucial for sustainable development. Water consumption initially stands at 456.25 m³, but is effectively reduced to 158.43 m³ through the reuse of materials, showcasing efficient water management and conservation within the system. The impact on terrestrial and marine ecotoxicity also sees substantial reductions through reuse, with terrestrial ecotoxicity decreasing from 104,089.66 kg 1,4-DCB to 38,434.03 kg 1,4-DCB, and marine ecotoxicity from 1,676.66 kg 1,4-DCB to 742.69 kg 1,4-DCB.

The end-of-life stage analysis highlights the vital role of recycling and reuse in mitigating these impacts. Recycling plays a modest yet important role in reducing reliance on virgin materials, contributing marginally to fossil resource and ecotoxicity reductions. In contrast, reuse has a much more pronounced effect, significantly lowering total environmental burdens. Reuse proves significantly more effective, cutting fossil resource scarcity by 86 % and global warming potential by 80 %. Reuse also leads to major reductions in water use, terrestrial and marine ecotoxicity, and particulate matter formation. These findings demonstrate that integrating reuse strategies in system design is crucial for improving sustainability performance. Overall, the RESHeat system can significantly reduce its environmental footprint through effective material reuse and recycling, aligning better with circular economy principles and long-term climate and resource conservation goals.

From a component-level perspective, the environmental impacts of the RESHeat system in Italy are primarily driven by the construction phase and the PV/T panels. Construction dominates in categories such as fossil resource scarcity (88 %), terrestrial ecotoxicity (65 %), and fine particulate matter formation (91 %), indicating a heavy reliance on non-renewable, mineral-intensive materials and emission-intensive processes. PV/T panels also contribute substantially across multiple impact categories, including water consumption (75 %), global warming (50 %), freshwater eutrophication (77 %), and ionising radiation (79 %), due to their material composition and manufacturing complexity (Figure 4).

Figure 4.

The environmental impacts of the RESHeat system in Italy

Heat pumps and other auxiliary components show relatively minor environmental burdens across most categories. However, their cumulative impact still warrants consideration, especially as system deployment scales up. Overall, construction and PV/T panels are the most environmentally intensive parts of the RESHeat system. Prioritising reuse, material innovation, and cleaner manufacturing processes for these components is key to reducing the system’s life cycle footprint and supporting long-term sustainability goals.

From the sensitivity analysis in previous study [19], results showed that shorter lifetimes increase environmental impacts, for example CO₂ emissions were 19.8 % higher at 20 years compared to the 25-year baseline. While longer lifetimes reduce them, with a 13.2 % decrease at 30 years. Resource use and ecotoxicity categories were identified as the most sensitive.

While comparing with other heating systems, the RESHeat systems exhibit significant environmental advantages over the conventional gas boiler, with reductions of 62 % - 95 % in global warming potential [19]. Compared with other CCHP systems, RESHeat shows intermediate performance: while CCHP-2 [35] has the highest impacts (125 kg CO₂ eq/m²y ) due to high energy demand and grid dependency, the compact CCHP-1 system [35] demonstrates the lowest burdens (1.3 kg CO₂ eq/m²y). Overall, RESHeat provides a balanced solution with substantial environmental benefits over fossil-based heating, while being more scalable than the highly compact CCHP-1 design.

This article presents a comprehensive LCA of the RESHeat system implemented at the Italian demonstration site, using the ReCiPe 2016 (Midpoint H) methodology. The primary objective is to evaluate the system’s environmental performance over one year of electricity and heat production, covering all life cycle stages - from raw material extraction, through operation, to end-of-life.

The analysis provides a detailed breakdown of individual components including the construction phase, fan coils, buffer tanks, heat exchangers, PV/T modules, and the heat pump, and quantifies their contributions across a wide range of environmental impact categories. These include global warming potential, fossil resource scarcity, water consumption, ionizing radiation, eutrophication, ecotoxicity, human toxicity, particulate matter formation, ozone formation, land use, and mineral resource depletion.

A particular focus is placed on the role of reuse and recycling strategies, which demonstrate substantial potential for environmental impact mitigation - achieving up to 80.6 % reduction in CO₂ emissions, 86 % in fossil resource use, and 65 % in water consumption. The results identify the construction phase and PV/T modules as the most environmentally burdensome components, suggesting that improved material selection and cleaner manufacturing processes are key to further reducing the system’s environmental footprint.

The main assumptions and innovations presented in the article are as follows:

• A comprehensive LCA of the RESHeat system demonstration in Italy, covering the entire life cycle - from raw material extraction, through operation, to end-of-life-which is rarely addressed in full in existing literature. The calculations are based on empirical data from a fully operational RESHeat installation, ensuring high practical relevance and bridging the gap between theoretical modelling and real-world performance.

• The use of a robust, multi-indicator ReCiPe 2016 Midpoint (H) methodology to evaluate a broad spectrum of environmental impact categories, including global warming potential, fossil resource depletion, water consumption, and toxicity.

• A component-level assessment, in which each major element of the system (e.g., PV/T panels, heat pump, heat exchangers) is individually analysed to determine its specific environmental contribution. The construction phase and PV/T modules are identified as the most environmentally impactful, providing a clear direction for targeted optimization in future system iterations.

• The evaluation of multiple end-of-life strategies, demonstrating that reuse and recycling of materials can reduce the environmental impact of the system by up to 80 % in key impact categories, significantly supporting circular economy objectives.

The research presented in this article also identifies promising directions for future work. These include the further optimization of material selection and component design, as well as the integration of economic and social impact assessments to enable a complete Life Cycle Sustainability Assessment (LCSA). The results not only deliver site-specific environmental insights but also underline the potential relevance of RESHeat for policy frameworks promoting low-carbon building energy solutions and its replicability in other climatic and operational contexts. Nevertheless, this study primarily addressed environmental dimensions, and future research will incorporate a more detailed techno-economic assessment to complement the present findings. In addition, the application of dynamic LCA modelling under variable operating conditions is recommended to more accurately reflect the system’s real-world performance over time. These measures will contribute to the development of a heating system that is not only environmentally sustainable but also economically viable and socially responsible. Ultimately, they will enhance the overall sustainability of the RESHeat system and support its broader implementation in residential energy applications. The proposed research directions are fully aligned with current EU strategies on resource efficiency and the principles of the circular economy.