TOWARD A SOLUTION OF ALLOCATION IN LIFE CYCLE INVENTORIES: THE USE OF LEAST SQUARES TECHNIQUES

Purpose: The matrix method for the solution of the so-called inventory problem in LCA generally determines the inventory vector related to a specific system of processes by solving a system of linear equations. The paper proposes a new approach to deal with systems characterized by a rectangular (and thus non-invertible) coefficients matrix. The approach, based on the application of regression techniques, allows solving the system without using computational expedients such as the allocation procedure. Methods: The regression techniques used in the paper are (besides the ordinary least squares, OLS) total least squares (TLS) and data least squares (DLS). In this paper, the authors present the application of TLS and DLS to a case study related to the production of bricks, showing the differences between the results accomplished by the traditional matrix approach and those obtained with these techniques. The system boundaries were chosen such that the resulting technology matrix was not too big and thus easy to display, but at the same time complex enough to provide a valid demonstrative example for analyzing the results of the application of the above-described techniques. Results and discussion: The results obtained for the case study taken into consideration showed an obvious but not overwhelming difference between the inventory vectors obtained by using the least-squares techniques and those obtained with the solutions based upon allocation. The inventory vectors obtained with the DLS and TLS techniques are closer to those obtained with the physical rather than with the economic allocation. However, this finding most probably cannot be generalized to every inventory problem. Conclusions: Since the solution of the inventory problem in life cycle inventory (LCI) is not a standard forecasting problem because the real solution (the real inventory vector related to the investigated functional unit) is unknown, we are not able to compute a proper performance indicator for the implemented algorithms. However, considering that the obtained least squares solutions are unique and their differences from the traditional solutions are not overwhelming, this methodology is worthy of further investigation. Recommendations: In order to make TLS and DLS techniques a valuable alternative to the traditional allocation procedures, there is a need to optimize them for the very particular systems that commonly occur in LCI, i.e., systems with sparse coefficients matrices and a vector of constants whose entries are almost always all null but one. This optimization is crucial for their applicability in the LCI contex

UN MODELLO ALLE DIFFERENZE FINITE DI UN PANNELLO FOTOVOLTAICO ACCOPPIATO A MATERIALE A CAMBIAMENTO DI FASE

La diffusione commerciale dei dispositivi fotovoltaici presenta negli ultimi anni un trend di crescita significativa a livello internazionale. Numerose ricerche sono state svolte al fine di incrementare l\u2019efficienza di conversione elettrica dei pannelli fotovoltaici e tra le soluzioni indagate \ue8 stato sperimentato l\u2019impiego di materiali a cambiamento di fase (MCF) per ridurre i picchi di temperatura di funzionamento. Nel lavoro \ue8 stato sviluppato un algoritmo di calcolo in grado di fornire l\u2019andamento temporale della temperatura di un pannello fotovoltaico accoppiato a materiale a cambiamento di fase (Sistema PV-MCF). La determinazione della distribuzione di temperature che interessano un sistema PV-MCF \ue8 stata affrontata con il metodo delle differenze finite in geometria monodimensionale. Sono state definite le equazioni di conservazione dell\u2019energia per ogni punto nodale in cui \ue8 stato discretizzato il sistema fisico, differenziandole per i nodi \u201cinterni\u201d e per i nodi \u201csuperficiali\u201d. Le equazioni alle differenze finite sono state formulate esplicitamente rispetto alla variabile temporale e sono state codificate in un apposito software. Il confronto con alcune soluzioni analitiche largamente impiegate nella bibliografia di settore ha permesso di verificare la correttezza e la validit\ue0 dell\u2019approccio sviluppato

Life cycle energy and environmental assessment of the thermal insulation improvement in residential buildings

The refurbishment of the building stock is a key strategy towards the achievement of the climate and energy goals of the European Union. This study aims at evaluating the energy and environmental impacts associated with retrofitting a residential apartment to improve its vertical envelope thermal insulation. Two insulation materials, stone wool and cellulose fibers, are compared. The life cycle assessment methodology is applied assuming 1 m2 of retrofitted vertical envelope as functional unit. Moreover, to estimate the net energy and environmental benefits achievable in the retrofitted scenario compared with the non‐retrofitted one, a second analysis is performed in which the system boundaries are expanded to include the building operational phase, and 1 m2 of walkable floor per year is assumed as reference. The results show that the use of cellulose fibers involve lower impacts in most of the assessed categories compared to stone wool, except for abiotic resource depletion. In detail, the use of cellulose fibers allows to reduce the impact on climate change up to 20% and the consumption of primary energy up to 10%. The evaluation of the net energy and environmental benefits shows the effectiveness of the retrofit energy policies

Life Cycle Assessment of Wood Chips from Residual Biomass: A Case Study

The paper describes the results of a Life Cycle Assessment study of wood chips obtained from a residual forest biomass, to be used for energy purpose. The analysis is referred to 1 kg of wood chips as functional unit. The system boundaries include the collection of the residual biomass, the chipping process of biomass, the collection and transport of wood chips to the energy plant. The results show that the supply chain examined, with reference to the functional unit, causes an impact of 0.027 kg CO2eq and a consumption of 0.406 MJ of primary energy. A dominance analysis was developed to identify the most impactful stages of the production chain: the steps that contribute most to the impacts within the supply chain are the indirect drag and the chipping process, responsible for the 42% of the overall greenhouse gas emissions and primary energy consumption. Lastly, a sensitivity analysis was carried out, to assess the variation of the impacts related to the distance between the wood chips production site and the place of use. The sensitivity analysis shows that is important to have short supply chains within the proposed domain in order to lower the energy and environmental impacts

Life Cycle Environmental Impacts and Health Effects of Protein-Rich Food as Meat Alternatives: A Review

The food sector is responsible for a considerable impact on the environment in most environmental contexts: the food supply chain causes greenhouse gas emissions, water consumption, reduction in cultivable land, and other environmental impacts. Thus, a change in food supply is required to reduce the environmental impacts caused by the food supply chain and to meet the increasing demand for sufficient and qualitative nutrition. Large herds of livestock are inappropriate to achieve these goals due to the relevant impact of meat supply chain on the environment, e.g., the land used to grow feed for animals is eight times more than that for human nutrition. The search for meat alternatives, especially for the intake of critical nutrients such as protein, is a consequent step. In the above context, this paper summarizes the health aspects of protein-rich food alternatives to meat and carries out a literature review on the life-cycle environmental impacts of this alternative food

Development of an early design tool for the sustainability assessment of positive energy districts: methodology, implementation and case-studies

The concept of Positive Energy District is one of the research ideas that embody the ambitions of decarbonization, renovation (both literal and in a wider perspective) and inclusivity for the urban environment portrayed in the EU activities. In this framework, the paper presents a modeling and simulation tool which allows for an early-design depth to be applied in the field of Positive Energy Districts renovation design and integrated performance assessment. The work aims at creating a tool for stakeholders and designers that would allow them to: a) Calculate carbon impacts along the life cycle for different technical systems and materials used for retrofitting; b) Compute use stage carbon emissions, including import-export of electricity; c) Computations of PED carbon emission balances, along the expected useful life of the district computing both embodied and the use stage carbon emissions. The tool has been created as a spreadsheet including typical profiles of energy use per building archetype, with the inclusion of available and free Life Cycle Assessment data within the life cycle carbon assessment and aims at jointly developing use stage and life cycle considerations. It was tested on a district case studies in the EU

Pandemia e mondo del lavoro: cosa è successo e cosa abbiamo imparato?

Il ricorso massiccio al telelavoro durante la pandemia da Covid-19, ha fatto emergere la consapevolezza che questo strumento potrebbe comportare anche importanti conseguenze da un punto di vista energetico-ambientale. Un nuovo studio ha analizzato i potenziali pro e contro del lavoro a distanz

Experimental and Computational Fluid Dynamic study of an active ventilated façade integrating battery and distributed MPPT

Ventilated Façades integrating photovoltaic panels are a promising way to improve efficiency and the thermal-physical performances of buildings. Due the inherent intermittence of the non-programmable renewable energy sources, their increasing usage implies the use of energy storage systems to mitigate the mismatch between power generation and the buildings’ load demand. The main purpose of this paper is to investigate the thermo-fluid dynamic performances of a prototype integrating a photovoltaic cell and a battery as a module of an active ventilated façade. Based on an experimental setup, a numerical study in steady state conditions of flow through the air cavity of the module has been carried out and implemented in a fluid-dynamics Finite Volume code. In order to assess the viability of the prototype, the calibrated model was lastly used to predict thermal performance of the prototype on different climate conditions supporting its further improvement