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The nZEB objectives have raised the standard of building performance and changed the way in which buildings are designed and used. Although energy dynamic simulation tools are potentially the most suitable way for accurately evaluating and forecasting the thermal performance, they need several data inputs and user's knowledge that can affect the reliability of the results. It is precisely these two aspects that proved to be particularly critical, since the reliability of the ICT calculation tools has been widely proven in recent time.However, in order to foster credibility in sustainable architecture, bridging the gap between predicted and measured performance is pivotal to boost the building market towards energy efficiency and provide reliable data to inhabitant, investors and policy maker.The present research aims to identify and quantify the main factors that affect the energy performance gap through a detailed energy analysis carried out on a case study, which can be considered one of the first nearly zero energy residential complex built in Italy. Based on the analysis, the study identifies the main causes of the deviation between the calculated and measured data and demonstrates how it is possible to achieve very reliable models and, therefore, real buildings.Although the procedure traces a classic model calibration scheme, actually it consists of a verification of possible downstream errors mainly due to human factors, such as the provision of incorrect technical data or inappropriate operation.Some observations on the technical, management and regulatory gaps that may generate these errors are reported at the end of the study, together with practical suggestions that can provide effective solutions.

The nZEB objectives have raised the standard of building performance and changed the way in which buildings are designed and used. Although energy dynamic simulation tools are potentially the most suitable way for accurately evaluating and forecasting the thermal performance, they need several data inputs and user's knowledge that can affect the reliability of the results. It is precisely these two aspects that proved to be particularly critical, since the reliability of the ICT calculation tools has been widely proven in recent time.However, in order to foster credibility in sustainable architecture, bridging the gap between predicted and measured performance is pivotal to boost the building market towards energy efficiency and provide reliable data to inhabitant, investors and policy maker.The present research aims to identify and quantify the main factors that affect the energy performance gap through a detailed energy analysis carried out on a case study, which can be considered one of the first nearly zero energy residential complex built in Italy. Based on the analysis, the study identifies the main causes of the deviation between the calculated and measured data and demonstrates how it is possible to achieve very reliable models and, therefore, real buildings.Although the procedure traces a classic model calibration scheme, actually it consists of a verification of possible downstream errors mainly due to human factors, such as the provision of incorrect technical data or inappropriate operation.Some observations on the technical, management and regulatory gaps that may generate these errors are reported at the end of the study, together with practical suggestions that can provide effective solutions.

Abstract The photovoltaic-thermal collector is one of the most interesting technology for solar energy conversion, combining electric and thermal energy production in a single device. Vapour-compression heat pump is already considered the most suitable clean technology for buildings thermal energy needs. The combination of these two technologies in an integrated ”photovoltaic-thermal solar-assisted heat pump” (PVT-SAHP) system allows reaching a high fraction of the building thermal needs covered by renewable energy sources and to improve the performances of both the photovoltaic-thermal collector and the heat pump. The first is cooled down increasing its energy conversion efficiency, while providing low-temperature thermal energy to the second, which benefits from a higher evaporation temperature. The review study presents the state-of-art of photovoltaic-thermal solar-assisted heat pump systems intended to cover thermal energy needs in buildings, with a particular focus on the integration methodologies, the possible configurations, the use of different sources and the design of sub-system components. These issues are addressed by much scientific research, to improve the reliability and applicability of this technology, as an option for the building decarbonization. This study aims to present PVT-SAHP systems in an organic and critical way to propose a useful tool for future research developments. More in detail, the work highlights the fact that the integration of photovoltaic-thermal collectors as evaporator of the heat pump in direct-expansion systems allows the highest heat recovery and performances. However, the distinction of the two circuits lead to more reliable, flexible and robust systems, especially when combined with a second heat source, being able to cover both heating and cooling needs. The implementation of real-time control strategy, as well as the continuous development of the compressor and refrigerant industries is positively influencing this technology, which is receiving more and more attention from scientific research as a suitable solution for nearly zero energy buildings.

Abstract The photovoltaic-thermal collector is one of the most interesting technology for solar energy conversion, combining electric and thermal energy production in a single device. Vapour-compression heat pump is already considered the most suitable clean technology for buildings thermal energy needs. The combination of these two technologies in an integrated ”photovoltaic-thermal solar-assisted heat pump” (PVT-SAHP) system allows reaching a high fraction of the building thermal needs covered by renewable energy sources and to improve the performances of both the photovoltaic-thermal collector and the heat pump. The first is cooled down increasing its energy conversion efficiency, while providing low-temperature thermal energy to the second, which benefits from a higher evaporation temperature. The review study presents the state-of-art of photovoltaic-thermal solar-assisted heat pump systems intended to cover thermal energy needs in buildings, with a particular focus on the integration methodologies, the possible configurations, the use of different sources and the design of sub-system components. These issues are addressed by much scientific research, to improve the reliability and applicability of this technology, as an option for the building decarbonization. This study aims to present PVT-SAHP systems in an organic and critical way to propose a useful tool for future research developments. More in detail, the work highlights the fact that the integration of photovoltaic-thermal collectors as evaporator of the heat pump in direct-expansion systems allows the highest heat recovery and performances. However, the distinction of the two circuits lead to more reliable, flexible and robust systems, especially when combined with a second heat source, being able to cover both heating and cooling needs. The implementation of real-time control strategy, as well as the continuous development of the compressor and refrigerant industries is positively influencing this technology, which is receiving more and more attention from scientific research as a suitable solution for nearly zero energy buildings.

According to the recent policies regarding energy use in buildings and the need of retrofit strategies, the aim of this work is to support policies concerning the installation of ground source heat exchangers in urban and historical areas, raising the awareness on the potential energy saving achievable with optimal sizing and limited impact on the urban environment. Archetypes have been developed distinguishing among existing and historic buildings, focusing on single-family terrace houses, which are the typical residential buildings in European historic centres.A methodology for the optimal sizing of ground source heat pumps, eventually considering dual-source system or air system has been developed combining simulations of a photovoltaic system to estimate the self-sufficiency and the self-consumption for five orientations of the building. Extreme results have been obtained for warm climates, with negligible heating energy demand and possibly free cooling systems rather than traditional cooling systems needed in wintertime. Penalty temperature was acceptable despite unbalanced energy demands. With proper inclination, photovoltaic systems could provide up to 40% of self-sufficiency share also in northern climates. An energy - economic analysis was carried out obtaining a variety of cases representing a general overview of the European building stock and the potential benefits achievable in terms of renewable energy share, energy savings and economic investments needed to be extended to simulations at urban scale.

According to the recent policies regarding energy use in buildings and the need of retrofit strategies, the aim of this work is to support policies concerning the installation of ground source heat exchangers in urban and historical areas, raising the awareness on the potential energy saving achievable with optimal sizing and limited impact on the urban environment. Archetypes have been developed distinguishing among existing and historic buildings, focusing on single-family terrace houses, which are the typical residential buildings in European historic centres.A methodology for the optimal sizing of ground source heat pumps, eventually considering dual-source system or air system has been developed combining simulations of a photovoltaic system to estimate the self-sufficiency and the self-consumption for five orientations of the building. Extreme results have been obtained for warm climates, with negligible heating energy demand and possibly free cooling systems rather than traditional cooling systems needed in wintertime. Penalty temperature was acceptable despite unbalanced energy demands. With proper inclination, photovoltaic systems could provide up to 40% of self-sufficiency share also in northern climates. An energy - economic analysis was carried out obtaining a variety of cases representing a general overview of the European building stock and the potential benefits achievable in terms of renewable energy share, energy savings and economic investments needed to be extended to simulations at urban scale.