System Boundary Selection Research Articles

Characterizing spatiotemporal dynamics of carbon emissions in peri-urban residential communities: A life cycle perspective

Building stock provides favorable material and welfare support to the urbanization process, but also triggers significant resource extraction and carbon emissions. Spatial explicit stock studies have focused mainly on developed areas and mature cities, with less attention paid to peri-urban areas. In terms of carbon emission, inconsistent system boundary selection and lack of building life cycle analysis limit the accuracy and comparability of results. Moreover, the absence of spatial distribution of emissions undermines support to regional carbon reduction initiatives. In this study, the Yangtze River Delta Integration Demonstration Area (YRDA), which is considered as a typical peri-urban area in China, was selected to study the spatiotemporal pattern of material flows and stocks at the residential community scale since the reform of the housing system in 1998, and to analyze spatiotemporal dynamics of carbon emissions over the life cycle of buildings. The results show that material inputs in peri-urban areas have experienced a fluctuating increase, with a gradual decline after 2016 as housing policies were tightened, and have a lower residential stock intensity than city centers. Residential carbon emissions also fluctuate while trending upwards, with operation accounting for the highest share of emissions, followed by building material production, with demolition now causing a rapid growth in emissions. Material stocks and residential carbon emissions display significant spatial heterogeneity, and a new concentration area has formed at the intersection of the three administrative districts that of YRDA. The study underscores the influence of economic growth and housing policy on the spatiotemporal pattern of building stocks, flows and carbon emissions, offering insights for cross-boundary ecosystem governance and regional circular economy development.

Comparing apples and oranges: Some confusion about using and interpreting physical trade matrices versus multi-regional input–output analysis

The questions of how to account for upstream land requirements is highly relevant for assigning responsibility for global land use. Two approaches, physical trade flow analysis and multi-regional input–output analysis have been frequently used for land accounting of international trade leading to diametrically opposed results for countries such as China. In this study, we investigate and explain the differences by comparing the estimates of cropland embodied in international trade for China from studies using physical trade flows (PTF) and multi-regional input–output (MRIO) analysis and provide a step-wise calculation to explain the gap between estimates from these different approaches and their interpretation. Our results show that the gap between PTF and MRIO is largely due to the system boundary selection and truncation errors from the boundary cut-off. These two approaches should be used for different research purposes. If focusing on the flows of a particular product, in particular primary products such as rice, wheat or other grains, among countries the higher level of detail of physical flow model is more suited. Whereas when accounting for the total embodied land in trade and consumption-based land use by recipient countries to analyze drivers of land use, MRIO is more suitable for tracking entire global supply chains.

Carbon footprinting of electronic products

In order to mitigate the effects of global warming, companies are being compelled by governments, investors, and customers to control their greenhouse gas (GHG) emissions. Similar to the European Union’s legislation on the airline industry, legislation is expected to require the electronics industry to assess their product’s carbon footprint before sale or use, as the electronics industry’s contribution to global GHG emissions is comparable to the airline industry’s contribution. Thus, it is necessary for members of the electronics industry to assess their current GHG emission rates and identify methods to reduce environmental impacts. Organizations use Carbon Footprint (CF) analysis methods to identify and quantify the GHG emissions associated with the life cycle stages of their product or services. This paper discusses the prevailing methods used by organizations to estimate the CF of their electronics products and identifies the challenges faced by the electronics industry when adopting these methods in an environment of decreasing product development cycles with complex and diffuse supply chains. We find that, as a result of the inconsistencies arising from the system boundary selection methods and databases, the use of outdated LCA approaches, and the lack of supplier’s emissions-related data, the CFs of electronic products are typically underestimated. To address these challenges, we present a comprehensive approach to the carbon footprinting of electronic products that involves the use of product-group-oriented standards, hybrid life cycle assessment techniques, and the integration of CF into products’ supply chains. A case study on commercial- and military-grade DC–DC buck converters demonstrating the recommended approach is presented.

Life Cycle Assessment of electricity production in Italy from anaerobic co-digestion of pig slurry and energy crops

This study aims to evaluate the environmental consequences and energy requirements of a biogas production system and its further conversion into bioenergy by means of the Life Cycle Assessment (LCA) methodology. To do so, an Italian biogas plant operating with pig slurry and two energy crops (maize and triticale silages) as feedstock was assessed in detail in order to identify the environmental hotspots. The environmental profile was estimated through six impact categories: abiotic depletion potential (ADP), acidification potential (AP), eutrophication potential (EP), global warming potential (GWP), ozone layer depletion potential (ODP) and photochemical oxidation potential (POFP). An energy analysis related to the cumulative non-renewable fossil and nuclear energy demand (CED) was also performed, considering this indicator as an additional impact category.According to the results, the biomass production subsystem was identified as the main environmental key issue in terms of ADP, AP, EP, ODP and CED, with contributions ranging from 26% to 61% of the total impact. Regarding ADP, ODP and CED, these results are mainly related with diesel requirements in agricultural machinery, derived combustion emissions and mineral fertilizers production. Concerning AP and EP the production field emissions derived from fertilizers application was observed as the main contributor. Concerning GWP, this step presents an environmental credit due to the uptake of CO2 during crop growth, which contributes to offset the GHG emissions. The bioenergy production plant significantly contributes to the environmental impact in categories such as GWP (43%) and POFP (59%), mostly related with emissions produced in the gas engine and biogas losses. Emissions derived from digestate storage contribute to AP (52%) and EP (41%). The use of the digestate as an organic fertilizer has a beneficial role because this action avoids the production and use of mineral fertilizers.A sensitivity analysis was also conducted to assess the influence of variations in important parameters of biogas systems. The environmental profile of the biogas system turned out to be highly dependent on the selection of system boundaries and the allocation method.To sum up, this study aims to assess the environmental performance of a biogas technology available not only in Italy but also in other European countries. The environmental analysis of the process under study highlights the environmental benefits of the co-digestion processes, which not only produces biofuel but also reduces the disposal of solid wastes and produces digestate, with special value in the fertilization of agricultural soil.

Sustainability assessment of novel chemical processes at early stage: application to biobased processes

Chemical conversions have been a cornerstone of industrial revolution and societal progress. Continuing this progress in a resource constrained world poses a critical challenge which demands the development of innovative chemical processes to meet our energy and material needs in a sustainable way. This challenge forms the basis for this article. We report a method for quick preliminary assessment of chemical processes at the laboratory stage. The proposed method enables a review of chemical processes within a broader sustainability context. It is inspired by green chemistry principles, techno-economic analysis and some elements of environmental life-cycle assessment (LCA). This method evaluates a proposed chemical process against comparable existing processes using a multi-criteria approach that integrates various economic and environmental indicators. An effort has been made to incorporate quantitative and qualitative information about the processes while making the method transparent and easy to implement based on information available at an early stage in process development. The idea is to provide a data-based assessment tool for chemists and engineers to develop sustainable chemistry. This paper describes the method in detail and examines plausibility of the results. A biobased process for the production of but-1,3-diene has been analyzed using this method. This biobased process is compared with a conventional process for the production of but-1,3-diene from petroleum sources. The effects of uncertainty in the underlying model parameters and assumptions are also analyzed, along with the effect of system boundary selection on the assessment outcome. Analysis and testing of the method shows that it can be used as a valuable tool for sustainable process development.

Life-Cycle Perspective on Residential Water Conservation Strategies

Motivated by the desire to understand the impact of water supply systems on the environment, a life cycle-based hybrid methodology is used to assess the performance of two conservation scenarios, water efficiency, and rainwater harvesting, relative to the base case. The analysis carried out for the City of Toronto's residential sector estimates the operational energy use and GHG emissions, and the embodied burdens associated with water-efficient devices and rainwater tanks. Hydraulic simulations, performed on a hypothetical network to expose the impact of demand peak factor on pressure distribution at nodes, revealed some of the rainwater scenario strengths such as hydraulic stress curtailment and capital investment postponement. While both strategies led to significant water savings, the associated energy expenditures and emissions varied with the selection of system boundaries. Nevertheless, both conservation strategies are worthwhile pursuing for rendering the existing water systems more sustainable. DOI: 10.1061/ASCE1076-0342201016:140 CE Database subject headings: Water distribution systems; Energy consumption; Emissions; Life cycles; Conservation; Residential location. Author keywords: Water supply systems; Demand management; Rainwater harvesting; Energy use; GHG emissions; Life-cycle approach.

System boundary selection in life-cycle inventories using hybrid approaches.

Life-cycle assessment (LCA) is a method for evaluating the environmental impacts of products holistically, including direct and supply chain impacts. The current LCA methodologies and the standards by the International Organization for Standardization (ISO) impose practical difficulties for drawing system boundaries; decisions on inclusion or exclusion of processes in an analysis (the cutoff criteria) are typically not made on a scientific basis. In particular, the requirement of deciding which processes could be excluded from the inventory can be rather difficult to meet because many excluded processes have often never been assessed by the practitioner, and therefore, their negligibility cannot be guaranteed. LCA studies utilizing economic input-output analysis have shown that, in practice, excluded processes can contribute as much to the product system under study as included processes; thus, the subjective determination of the system boundary may lead to invalid results. System boundaries in LCA are discussed herein with particular attention to outlining hybrid approaches as methods for resolving the boundary selection problem in LCA. An input-output model can be used to describe at least a part of a product system, and an ISO-compatible system boundary selection procedure can be designed by applying hybrid input-output-assisted approaches. There are several hybrid input-output analysis-based LCA methods that can be implemented in practice for broadening system boundary and also for ISO compliance.

Compact Simulation Model of Non-air Conditioned Room and Estimation of Its Thermal Characteristics under Winter Conditions.

This study investigates thermal behavior of an occupied room exposed to winter weather conditions by means of quasi-steady-state model of the room. The space is not air-conditioned during the winter season, i.e. there is no humidity control and thermal performance of heaters maintains desired indoor air temperature. To obtain pure thermodynamic characteristics of the space, the model was set up and a series of tests was carried out in order to validate the mathematical model and find the thermal characteristics of the enclosure, which could be used directly for direct control techniques (DDC) if applied. The build -up model's method imposes boundary conditions onto room-faced surroundings walls and couples Fourier equations' thermal network employing modified Biot number. It also enables us to simulate an hourly energy use as well as heat flux calculus based on sub-hourly time steps. The model features a water equivalent content of the room, time-varying heat transfer coefficients, and boundary conditions onto surrounding walls, respectively. As a full dynamic method it accounts for thermal influence of outdoor climate conditions, occupancy use and other internal sources of thermal energy. The paper emphasizes selection of system boundaries and practical calculus of radiation heat exchanges without claiming shape factor algebra. The numerical results of temperature transient time responses obtained from mathematical model are well in accordance with those obtained from measurement in the actual room.

The Relative Mass-Energy-Economic (RMEE) Method for System Boundary Selection

Life-Cycle Assessment (LCA) is a decision analysis tool used to compare alternatives to providing a given product or service. To ensure a fair comparison, LCA must select system boundaries in a consistent manner. The Relative Mass-Energy-Economic (RMEE) (pronounced ‘army’) of system boundary selection is a practical and quantitative method of defining system boundaries. RMEE compares each input to a system with the system’s functional unit on a mass, energy and economic basis. If this ratio of input to functional unit is less than a selected “cut-off” (defined as ‘ZRMEE’) then the input is excluded from the analysis and all unit processes upstream of that input are outside the system boundary. Ignoring unit processes outside the system boundary limits the size of the LCA analysis but adds a source of uncertainty for the overall results. The lower the value of the Z cut-off ratio the larger the system boundary is, resulting in a greater number of unit processes. The relationship between the ZRMEE cut-off and the uncertainty introduced to the results of an LCA are explored. The relationship between ZRMEE and uncertainty has been derived by analyzing 800 random systems of four different types, with the RMEE method of system boundary selection applied at different ZRMEE values. The uncertainty introduced to the overall results increases as the selected ZRMEE becomes larger.

The relative mass-energy-economic (RMEE) method for system boundary selection Part 1: A means to systematically and quantitatively select LCA boundaries

Life-cycle assessment (LCA) is being used more and more as a decision making tool to compare alternative systems of providing a given product or service. Each system is theoretically made up of a near infinite number of elements or unit processes to produce the product or service. In practice, time and resources to complete an LCA are limited, hence the need to draw practical boundaries on the systems being analyzed. However, how does the LCA practitioner draw fair boundaries on two or more different systems being compared? In other words, how does one decide which unit processes to include in each system? A consistent quantitative method of selecting boundaries is essential for comparative LCA studies.