• Energy Research

Abstract Starting from the results of a Life Cycle Assessment of small solar assisted heat driven chillers, the application of such methodology has been extended to systems with a conventional compression chiller assisted by a photovoltaic plant (PV). This study aims to provide a comprehensive compared investigation of these two families of solar assisted cooling systems (with solar thermal or PV). Results indicate that, in many cases, the systems with the PV grid connected plant performed best. In addition, two more configurations were investigated to further define the PV assisted systems, which minimise their interaction with the grid through the use of electricity storages. These systems performed worse than the PV grid connected systems and the solar thermal assisted systems in nearly all the analysed cases.

Abstract Starting from the results of a Life Cycle Assessment of small solar assisted heat driven chillers, the application of such methodology has been extended to systems with a conventional compression chiller assisted by a photovoltaic plant (PV). This study aims to provide a comprehensive compared investigation of these two families of solar assisted cooling systems (with solar thermal or PV). Results indicate that, in many cases, the systems with the PV grid connected plant performed best. In addition, two more configurations were investigated to further define the PV assisted systems, which minimise their interaction with the grid through the use of electricity storages. These systems performed worse than the PV grid connected systems and the solar thermal assisted systems in nearly all the analysed cases.

Abstract This paper presents a combined experimental and numerical procedure, developed to test the thermophysical behaviour of a real scale PCM wallboard, aiming at providing reliable data for the validation of building energy performance simulation tools. Data obtained from two experimental tests, conducted on real building elements integrating PCM undergoing complete and incomplete phase change, are considered for assessing the impact of thermal properties and hysteresis. A comprehensive comparative numerical analysis, performed by means of an in-house developed simulation tool, called DETECt, is carried out to investigate the reliability of several modelling and simulation approaches available in literature. Monitored data are used to compare the reliability of several modelling and simulation approaches (three different specific heat curves and four modelling approaches for hysteresis) to find out the appropriate temperature dependent heat capacity curves which realistically describe the PCM performance. Results The use of cp – temperature curves characterized through thermophysical analysis (e.g. DSC) under conditions much different than those that the PCM can undergo during the operation of a building can lead to significant discrepancies in performances with the actual data. Moreover, in case of incomplete phase transitions, the lower the accuracy of the cp – temperature curves, the higher the influence of the hysteresis modelling approach on the reliability of simulation results; a better agreement between monitored data and simulation results is observed when hysteresis is modelled by considering the transition between heating and cooling (and vice versa), by switching from the melting to the solidification curves according to the liquid and solid mass fraction. The study shows that the more refined modelling of the phase change allows results to be consistent with the thermo-physics phenomena of composite PCM under real conditions and achieve more reliable results.

Abstract This paper presents a combined experimental and numerical procedure, developed to test the thermophysical behaviour of a real scale PCM wallboard, aiming at providing reliable data for the validation of building energy performance simulation tools. Data obtained from two experimental tests, conducted on real building elements integrating PCM undergoing complete and incomplete phase change, are considered for assessing the impact of thermal properties and hysteresis. A comprehensive comparative numerical analysis, performed by means of an in-house developed simulation tool, called DETECt, is carried out to investigate the reliability of several modelling and simulation approaches available in literature. Monitored data are used to compare the reliability of several modelling and simulation approaches (three different specific heat curves and four modelling approaches for hysteresis) to find out the appropriate temperature dependent heat capacity curves which realistically describe the PCM performance. Results The use of cp – temperature curves characterized through thermophysical analysis (e.g. DSC) under conditions much different than those that the PCM can undergo during the operation of a building can lead to significant discrepancies in performances with the actual data. Moreover, in case of incomplete phase transitions, the lower the accuracy of the cp – temperature curves, the higher the influence of the hysteresis modelling approach on the reliability of simulation results; a better agreement between monitored data and simulation results is observed when hysteresis is modelled by considering the transition between heating and cooling (and vice versa), by switching from the melting to the solidification curves according to the liquid and solid mass fraction. The study shows that the more refined modelling of the phase change allows results to be consistent with the thermo-physics phenomena of composite PCM under real conditions and achieve more reliable results.

Anaerobic digestion (AD) uses biomass to produce biogas to generate heat and/or electricity. Several studies have reported that the adoption of AD may not necessarily lead to sustainable practices. For example, energy crops may cause significant impact due to the requirement of intensive agricultural practices. Then, residual biomasses are starting to be considered as alternative biomass for energy valorisation trough AD. In this context, this study assesses the potential environmental impacts related to the energy valorisation of agro-food industry waste though the Life Cycle Assessment methodology (ISO 14040). The system examined consists of a real anaerobic digester coupled with a combined heat and power plant (AD-CHP) operating in Sicily. The analysis accountsfor all the impacts occurring from the delivery of the biomass to the AD-CHP plant up to the electricity generation in the CHP. The main outcomes of the study include the eco-profile of the energy system providing electricity and the assessment of the contribution of each life cycle phase aimed at identifying the potential improvement area. Specifically, it highlights that direct emissions are responsible for the highest impact in global warming potential (66%) and feedstock transport contributes for the highest impact (64%) in mineral, fossil fuels and renewable depletion. The contribution of the electricity consumption to the different impact categories is in general relevant ranging from a minimum of about 22% for global warming potential up to 82% for freshwater ecotoxicity. The obtained results can provide useful information to improve the sustainability AD-CHP systems.

Anaerobic digestion (AD) uses biomass to produce biogas to generate heat and/or electricity. Several studies have reported that the adoption of AD may not necessarily lead to sustainable practices. For example, energy crops may cause significant impact due to the requirement of intensive agricultural practices. Then, residual biomasses are starting to be considered as alternative biomass for energy valorisation trough AD. In this context, this study assesses the potential environmental impacts related to the energy valorisation of agro-food industry waste though the Life Cycle Assessment methodology (ISO 14040). The system examined consists of a real anaerobic digester coupled with a combined heat and power plant (AD-CHP) operating in Sicily. The analysis accountsfor all the impacts occurring from the delivery of the biomass to the AD-CHP plant up to the electricity generation in the CHP. The main outcomes of the study include the eco-profile of the energy system providing electricity and the assessment of the contribution of each life cycle phase aimed at identifying the potential improvement area. Specifically, it highlights that direct emissions are responsible for the highest impact in global warming potential (66%) and feedstock transport contributes for the highest impact (64%) in mineral, fossil fuels and renewable depletion. The contribution of the electricity consumption to the different impact categories is in general relevant ranging from a minimum of about 22% for global warming potential up to 82% for freshwater ecotoxicity. The obtained results can provide useful information to improve the sustainability AD-CHP systems.

Abstract The paper starts from the results of one of the six case-studies of the SubTask B in the International Energy Agency joint Solar Heating and Cooling Task40 and Energy Conservation in Buildings and Community Systems Annex 52, whose purpose is to document state of the art and needs for current thermo-physical simulation tools in application to Net Zero Energy Buildings. The authors extend the Net Zero Energy Buildings (Net ZEB) methodological framework, introducing the life-cycle perspective in the energy balance and thus including the embodied energy of building and its components. The case study is an Italian building, tailored to be a Net ZEB, in which the magnitude of the deficit from the net zero energy target is assessed according to a life-cycle approach. The annual final energy balance, assessed with regard to electricity, shows a deficit which makes the case study a nearly Net ZEB, when the encountered energy flows are measured at the final level. Shifting from final to primary energy balance the case-study moves to a non-Net ZEB condition, because of the large difference between the conversion factors of photovoltaics generated electricity and imported electricity. The adoption of a life cycle perspective and the addition of embodied energy to the balance causes an even largest shift from the nearly ZEB target: the primary energy demand is nearly doubled in comparison to the primary energy case.

Abstract The paper starts from the results of one of the six case-studies of the SubTask B in the International Energy Agency joint Solar Heating and Cooling Task40 and Energy Conservation in Buildings and Community Systems Annex 52, whose purpose is to document state of the art and needs for current thermo-physical simulation tools in application to Net Zero Energy Buildings. The authors extend the Net Zero Energy Buildings (Net ZEB) methodological framework, introducing the life-cycle perspective in the energy balance and thus including the embodied energy of building and its components. The case study is an Italian building, tailored to be a Net ZEB, in which the magnitude of the deficit from the net zero energy target is assessed according to a life-cycle approach. The annual final energy balance, assessed with regard to electricity, shows a deficit which makes the case study a nearly Net ZEB, when the encountered energy flows are measured at the final level. Shifting from final to primary energy balance the case-study moves to a non-Net ZEB condition, because of the large difference between the conversion factors of photovoltaics generated electricity and imported electricity. The adoption of a life cycle perspective and the addition of embodied energy to the balance causes an even largest shift from the nearly ZEB target: the primary energy demand is nearly doubled in comparison to the primary energy case.