Summary
Evaluating the sustainability of the urban water cycle is not straightforward, although a variety of methods have been proposed. Given the lack of integrated data about sewers, we applied the ...eco‐efficiency approach to two case studies located in Spain with contrasting climate, population, and urban and sewer configurations. Our goal was to determine critical variables and life cycle stages and provide results for decision making. We used life cycle assessment and life cycle costing to evaluate their environmental and economic impacts. Results showed that both cities have a similar profile, albeit their contrasting features, that is, operation and maintenance, was the main environmental issue (50% to 70% of the impacts) and pipe installation registered the greatest economic capital expenditure (70% to 75%) due to labor. The location of the wastewater treatment plant (WWTP) is an essential factor in our analysis mainly due to the topography effects (e.g., the annual pump energy was 13 times greater in Calafell). Using the eco‐efficiency portfolio, we observed that sewers might be less eco‐efficient than WWTPs and that we need to envision their design in the context of an integrated WWTP‐sewer management to improve sewer performance. In terms of methodological approach, the bidimensional nature of eco‐efficiency enables the benchmarking of product systems and might be more easily interpreted by the general public. However, there are still some constraints that should be addressed to improve communication, such as the selection of indicators discussed in the article.
Many industrial processes and conventional fossil fuel energy production systems used in small-medium industries, such as internal combustion engines and gas turbines, provide low or medium ...temperature (i.e., 200–500
°C) heat fluxes as a by-product, which are typically wasted in the environment. The possibility of exploiting this wasted heat, converting it into electric energy by means of different energy systems, is investigated in this article, by extending the usual range of operation of existing technologies or introducing novel concepts. In particular, among the small size bottoming cycle technologies, the identified solutions which could allow to improve the energy saving performance of an existing plant by generating a certain amount of electric energy are: the Organic Rankine Cycle, the Stirling engine and the Inverted Brayton Cycle; this last is an original thermodynamic concept included in the performed comparative analysis.
Moreover, this paper provides a parametric investigation of the thermodynamic performance of the different systems; in particular, for the Inverted Brayton Cycle, the effects of the heat source characteristics and of the cycle design parameters on the achievable efficiency and specific power are shown. Furthermore, a comparison with other existing energy recovery solutions is performed, in order to assess the market potential. The analysis shows that the highest electric efficiency values, more than 20% with reference to the input heat content, are obtained with the Organic Rankine Cycle, while not negligible values of efficiency (up to 10%) are achievable with the Inverted Brayton Cycle, if the available temperature is higher than 400
°C.
This paper presents a review of the organic Rankine cycle and supercritical Rankine cycle for the conversion of low-grade heat into electrical power, as well as selection criteria of potential ...working fluids, screening of 35 working fluids for the two cycles and analyses of the influence of fluid properties on cycle performance. The thermodynamic and physical properties, stability, environmental impacts, safety and compatibility, and availability and cost are among the important considerations when selecting a working fluid. The paper discusses the types of working fluids, influence of latent heat, density and specific heat, and the effectiveness of superheating. A discussion of the 35 screened working fluids is also presented.
Mammalian tissues are fuelled by circulating nutrients, including glucose, amino acids, and various intermediary metabolites. Under aerobic conditions, glucose is generally assumed to be burned fully ...by tissues via the tricarboxylic acid cycle (TCA cycle) to carbon dioxide. Alternatively, glucose can be catabolized anaerobically via glycolysis to lactate, which is itself also a potential nutrient for tissues and tumours. The quantitative relevance of circulating lactate or other metabolic intermediates as fuels remains unclear. Here we systematically examine the fluxes of circulating metabolites in mice, and find that lactate can be a primary source of carbon for the TCA cycle and thus of energy. Intravenous infusions of
C-labelled nutrients reveal that, on a molar basis, the circulatory turnover flux of lactate is the highest of all metabolites and exceeds that of glucose by 1.1-fold in fed mice and 2.5-fold in fasting mice; lactate is made primarily from glucose but also from other sources. In both fed and fasted mice,
C-lactate extensively labels TCA cycle intermediates in all tissues. Quantitative analysis reveals that during the fasted state, the contribution of glucose to tissue TCA metabolism is primarily indirect (via circulating lactate) in all tissues except the brain. In genetically engineered lung and pancreatic cancer tumours in fasted mice, the contribution of circulating lactate to TCA cycle intermediates exceeds that of glucose, with glutamine making a larger contribution than lactate in pancreatic cancer. Thus, glycolysis and the TCA cycle are uncoupled at the level of lactate, which is a primary circulating TCA substrate in most tissues and tumours.
•The main differences are the extent of the refurbishment and the system boundaries.•The reference of the expected service life needs to be established to facilitate comparison.•Process Analysis is ...the most used LCI method, instead of Input–Output or Hybrid.•Most refurbishment LCAs focus on building energy retrofits: increasing insulation.•The environmental impacts of structure or finishing reparations were not studied.
This review organises and summarises the recent contributions related to the environmental evaluation of building refurbishment and renovation using the lifecycle assessment (LCA) methodology. This paper classifies the recent contributions in this field and selects the primary methodology options. The review shows that most LCAs focus on energy refurbishment, comparing the environmental impacts before and after refurbishment. In contrast, almost none of the LCAs study the environmental impact of building system reparations, such as structure or finishing. The more frequently studied life cycle stages are those related to the manufacturing and use phases. Similarly, the most considered impact categories are the global warming potential and embodied energy. The main barriers found for disseminations are discussed: system boundaries interpretation of EN 15978, functional unit, LCI methods, operational stage and the end-of-life stage definition.
•The best performing system among pure ammonia, steam Rankine and Kalina cycles were decided at same working condition.•Performance optimisation results were compared for pure ammonia, steam Rankine ...and Kalina cycles.•To show a wide vision for all real working cases, steam content at turbine outlet were considered.•Economic parameters for the case of using the best performing sub-cycle was calculated.•Impact of using best performing sub-cycle on CO2 emission reduction was investigated.•The best cycle configurations in terms of performance and emission were decided.
There are many studies on the Kalina cycle and steam Rankine cycles. However, there are not enough comparative and descriptive studies on why the Kalina cycle or steam Rankine cycle should be selected. In addition to that, almost there are no papers on why Kalina cycle and steam Rankine cycle are commonly used systems rather than the pure ammonia cycle. For these reasons, the present paper was designed, analysed and compared comprehensively the Kalina, steam Rankine and pure ammonia cycles as a subsystem for use in a cogeneration cycle. Moreover, the pure ammonia cycle system was analysed for both simple and regenerative designs to comprehensively present all cases. After deciding the best cogeneration system configuration for the present system, the economic and environmental analyses of the best performing system were performed. In addition to all these, during the study, the condensing temperature remained constant to be able to analyse systems in line with real working conditions. As a result of the comprehensive analyses, the Kalina cycle showed the best performance. The maximum net power, thermal and exergy efficiencies of the Kalina cycle were calculated at ammonia-water concertation of X = 25% and a turbine inlet temperature of t = 340 °C as 365.92 kW, 25.52%, 57.96% respectively. Thanks to the power generated by integrating the Kalina cycle into the system, 244.53 kg-CO2/h carbon dioxide was reduced and the total cost of the Kalina cycle and the payback period was found as 343,975.26$ and 2.2 years. The maximum thermal and exergy efficiencies of the Kalina cycle-based cogeneration system were calculated as 72.13% and 78.60%.
This study aims to assess the comprehensive energy, environmental and economic performance of a retrofit zero energy building (ZEB). Three life cycle assessments were conducted: life cycle energy ...(LCE), life cycle carbon emissions (LCCE) and life cycle cost (LCC). Actual building construction cost data and energy use data were used in the assessments. The analysis results indicated that during the whole building life span, the operational life stage (B6) was a major contributor to LCE (82%) and LCCE (77%), but not to LCC (18%). Within the life cycle embodied carbon (LCEC), A3 was the life stage with the highest contribution (56%), which is mainly related to the manufacturing of building assemblies. This case study provides new empirical evidence of ZEB performance in the United States. The findings suggest that to achieve the carbon neutrality goal, current ZEB certifications or designations are not adequate to measure actual building performance. A further reduction of operational energy, in addition to reducing the embodied carbon released during manufacturing, should be the focus.
•An approach is proposed for structures under progressive and sudden deterioration.•The proposed approach is based on the renewal theory of renewal-reward processes.•The lifetime resilience losses ...are proposed to consider resilience to lifetime hazards.•Multi-objective optimization is used for life-cycle management.•The optimization considers intervention costs, failure risks and resilience losses.
Civil infrastructure during its service life is subject to progressive deterioration due to aggressive environments and sudden deterioration due to natural and/or manmade hazards. This paper presents a general approach to perform life-cycle management considering both types of deterioration. As an important aspect of life-cycle asset management under hazards, the present study introduces a novel concept, referred to as lifetime resilience. The lifetime resilience of a deteriorating structure is characterized by its cumulative losses to lifetime hazards. By modeling lifetime hazards and life-cycle performance as renewal-reward processes, the proposed approach resorts to the renewal theory to formulate analytical expressions of expected values of lifetime intervention costs, lifetime failure risks, and lifetime resilience losses. Owing to the efficiency in evaluating these expressions, a generic life-cycle management framework is proposed using multi-objective optimization. This proposed framework is applicable to a wide range of civil infrastructure systems under various types of hazards. The proposed approach is illustrated by using a numerical example.
The environmental performance of existing buildings can have a major role in achieving significant reductions in CO2 emissions: In the UK, around 75% 2050's housing stock has already been built. ...While building performance improvement efforts mostly focus on operational performance, buildings environmental impact is the result of processes that occur throughout their life cycle.
To achieve significant emission reductions in an economically viable way, this study uses Life Cycle Performance approaches to carry a cross-comparison between the refurbishment and replacement of two housing archetypes in London: mid-terrace-house and a bungalow. Specifically, the study integrates Life Cycle Carbon Footprint (LCCF) and Life Cycle Cost (LCC) protocols (EN 15978:2011 and BS ISO 15686–5), thermal simulations (EnergyPlus), building generative design framework (PLOOTO - Parametric Lay-Out Organisation generator) and mathematical optimisation algorithms (NSGA-II).
Results show that the optimal refurbishment archetypes generally performed better than replacements (Refurbishments LCCF ranges between 1,100 and 1,500 kgCO2e/m2 and LCC 440-680 £/m2, compared to that of the replacements scenarios, ranging 1,220-1,850 kgCO2e/m2 and 550-890 £/m2). The study also highlights benefit of incentivising re-use to achieve quicker emissions reductions. The study lastly discusses a range of embodied and operational performance issues.
•Carbon footprint and cost of refurbished and new houses in London were compared.•A breakdown of embodied and operational carbon and cost is presented (60 years).•Refurbishments perform better than replacements, in terms of life cycle performance.•Evidence shows that refurbishment is preferable on short time scale (20 years) too.
Purpose
Life cycle sustainability analysis (LCSA) is being developed as a holistic tool to evaluate environmental, economic and social impacts of products or services throughout their life cycle. ...This study responds to the need expressed by the scientific community to develop and test LCSA methodology, by assessing the sustainability of a concentrated solar power (CSP) plant based on HYSOL technology (an innovative configuration delivering improved efficiency and power dispatchability).
Methods
The methodology proposed consists of three stages: goal and scope definition, modelling and application of tools, and interpretation of results. The goal of the case study was to investigate to what extent may the HYSOL technology improve the sustainability of power generation in the Spanish electricity sector. To this purpose, several sustainability sub-questions were framed and different analysis tools were applied as follows: attributional and consequential life cycle assessment, life cycle cost (LCC) analysis and multiregional input-output analysis (MRIO), and social life cycle assessment (S-LCA) in combination with social risk assessment (with the Social Hotspots Database). Visual diagrams representing the sustainability of the analysed scenarios were also produced to facilitate the interpretation of results and decision making.
Results and discussion
The results obtained in the three sustainability dimensions were integrated using a “questions and answers” layout, each answer describing a specific element of sustainability. The HYSOL technology was investigated considering two different operation modes: HYSOL BIO with biomethane as hybridization fuel and HYSOL NG with natural gas. The results indicated that the deployment of HYSOL technology would produce a reduction in the climate change impact of the electricity sector for both operation modes. The LCC analysis indicated economic benefits per MWh for a HYSOL NG power plant, but losses for a HYSOL BIO power plant. The MRIO analysis indicated an increase in goods and services generation, and value added for the HYSOL technology affecting primarily Spain and to a lower extent other foreign economies. The social analysis indicated that both alternatives would provide a slight increase of social welfare Spain.
Conclusions
The methodological approach described in this investigation provided flexibility in the selection of objectives and analysis tools, which helped to quantify the sustainability effect of the system at a micro and meso level in the three sustainability dimensions. The results indicated that the innovation of HYSOL power plants is well aimed to improve the sustainability of CSP technology and the Spanish electricity sector.
PDF
