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Multistage centrifugal pumps are widely used, and improving their efficiency is an indispensable part of energy conservation. A multi-objective optimization method combining experimental design, surrogate model, and optimization algorithm is proposed to re-design impellers and diffusers for improving pump performance. In the paper, nine variables were selected by the Plackett–Burman design with the head and minimum efficiency index (MEI) as the optimization objectives. The Gaussian process regression (GPR) was used to establish the surrogate model, and multi-objective optimization of the impeller and diffuser was carried out by non-dominated sorting genetic algorithm II (NSGA-II). The optimization results show that head and efficiency at the designed point 1.0 Q d increased by 8.8% and 2.8% respectively, and C MEI decreased by 1.34%. Meanwhile, the energy loss and flow characteristics of the original and optimization models were analyzed with the entropy production theory. Compared with the original model, the energy loss was reduced, and the flow in the interaction area between the impeller and diffuser becomes more stable for the optimized model. Moreover, the influencing mechanism of the pump geometrical parameters on the hydraulic performance and flow characteristics were discussed and analyzed. • A PB-GRP-GA multi-objective optimization method is proposed. • Internal energy losses were identified by Entropy Production Rate. • Influence mechanism of geometry on performance was revealed. • Higher MEI of pump model was achieved and verified by experiments. [ABSTRACT FROM AUTHOR]

Environmental degradation has become one of the major challenges facing the global community. This paper aims to explore the more effective options to combat environmental degradation by investigating the linearity and nonlinearity (trade openness set as a threshold variable) of energy efficiency, natural gas, renewable energy and ecological footprint. To this end, linear and non-linear panel models were constructed using panel data from 60 countries. The results of the linear analysis show that improving energy efficiency, and increasing the consumption of natural gas and renewable energy are conducive to inhibiting environmental degradation. Energy efficiency has the most significant negative correlation with ecological footprint, followed by renewable energy, and then natural gas, implying that improving energy efficiency and developing renewable energy is a more effective strategy to combat environmental degradation. The results of the nonlinear analysis show that there are threshold effects of trade openness between energy efficiency and ecological footprint, and between renewable energy and ecological footprint. The negative impact of both renewable energy and energy efficiency on the ecological footprint increases when trade openness exceeds the threshold. This suggests that, in terms of curbing environmental degradation, enhancing trade openness may further increase the negative impacts of energy efficiency and renewable energy on ecological footprint. At the same time, this confirms the positive role of trade openness in environmental protection. [Display omitted] • Exploring more effective option to combat environmental degradation. • Energy efficiency, renewable energy, natural gas can reduce ecological footprint. • Trade openness help energy efficiency, renewables lower ecological footprint. • The most effective strategy is energy efficiency, followed by renewables and natural gas. [ABSTRACT FROM AUTHOR]

In this paper, two generic photovoltaic (PV) panels (poly-Si and mono-Si) were experimentally tested in typical Mediterranean climatic conditions. The focus of the applied experimental approach was to examine the effect of backside convective thermal profile and its impact on temperature distribution, i.e. on panel electrical efficiency. Therefore, a series of measurements was made in 2015, from April to July, as well as CFD modeling in order to obtain a detailed analysis of the possible working regimes. According to the obtained experimental and CFD results, the present design of typical PV panels have an unfavorable impact on PV panel electrical efficiency. Namely, typical contemporary panel designs lead to two typical backside convective air temperature profiles which have a direct impact on the effectiveness of natural cooling. As shown in the obtained measurements, the specific convective profiles at the backside of PV panels have a significant influence on the degradation rate of panel electrical efficiency in the estimated amount of 2.5% up to 4.5%. The results of the research discussed in this paper signal the need to provide a possible redesign of the backside surface in conventional PV panels, in order to increase their average efficiency (more efficient backside thermal dissipation). [ABSTRACT FROM AUTHOR]

High-powered, medium-speed diesel engines are widely used in merchant ships. Improving energy efficiency by using energy rationally is critical to reducing both environmental pollution and transport charges. In this paper, the energy efficiency of marine high-powered, medium-speed diesel engine is investigated. A new thermal cycle model of the marine engine is developed using AVL-Boost software. The thermodynamic data of the engine thermal cycle are obtained from the AVL-Boost software. The energy efficiency of the marine diesel engine is evaluated using both energy balance and exergy analysis. From the energy balance analysis, about 25% of the total energy is lost through exhaust heat. This forms the largest energy loss. However, using exergy analysis the largest energy loss originates from the irreversible exergy loss produced during the combustion process. This represents about 36% of the total energy loss. To explore ways to reduce energy loss and improve the energy efficiency, the effects of critical combustion parameters in the thermal cycle (combustion quality index, combustion starting angle and combustion duration angle) on energy distributions are discussed. The decrease in the combustion quality index, combustion starting angle and combustion duration angle (within a reasonable range) all contribute to reduce the total energy loss, increasing the indicated work and improving energy efficiency. • Evaluation of energy efficiency of high-powered medium-speed marine diesel engine by both energy balance and exergy analysis. • Model of diesel engine thermodynamic cycle is developed. • Effects of combustion parameters on energy loss are investigated to improve the energy efficiency. [ABSTRACT FROM AUTHOR]

This paper conducts a systematic study to address the problems of high flow loss and low energy efficiency of centrifugal pumps caused by the development of secondary flow within the impeller. Based on the forces balance in the direction perpendicular to the streamline, theoretical calculations are drawn to redesign blade thickness for a 5-blade centrifugal impeller to suppress the secondary flow. The correlations between the development of internal secondary flow within the impeller and energy efficiency of centrifugal pump under full flow rate conditions are illustrated by numerical simulations validated by experimental tests. Secondary flow coefficient and entropy production rate (EPR) are introduced and extracted to quantitative analysis the secondary flow level and energy loss inside the impeller. Results indicate that the blade redesign methods proposed here can efficiently inhibit the development of secondary flow and improve the energy efficiency. Moreover, the secondary flow coefficient introduced in this paper can quantitatively reflect the intensity of secondary flow under various flow rates of different impellers. Combining with the entropy production analysis of impeller, the consistent change trend of total secondary flow coefficient and entropy production reveals that the improvement of pump energy efficiency benefits from the reduction of turbulence EPR which results from the suppression of internal secondary flow. • Theoretical calculations of blade thickness for low specific speed centrifugal pump. • Blade redesign based on secondary flow suppression to improve energy efficiency. • Quantitative analysis of secondary flow and energy losses in the impeller. • Improvement of energy efficiency attributes to the reduction of turbulence EPR. [ABSTRACT FROM AUTHOR]

Battery equalization is a critical technology in energy storage systems, so that each storage cell has equal state. In the application of electric vehicle, equalization circuits and algorithms have been widely studied for the purpose of prolonging driving time, but optimization of equalization efficiency is a difficult task in the battery equalization of electric vehicle. In this paper, an optimization model with a linear form is proposed to incorporate both energy loss and equalization time for an energy-bus equalizer. In the consideration of different working status of electric vehicle, i.e., charging, discharging, and driving, dynamic equalization has been investigated, and a model predictive control approach is proposed to cope with frequent change of working status. According to simulation and experimental results, it can be concluded that energy and time efficiency can be significantly improved during dynamic battery equalization, and that the proposed equalization system is easily implemented with competitive simplicity due to the linearized system model. [ABSTRACT FROM AUTHOR]

Low-temperature combustion in homogeneous charge compression ignition (HCCI) engine is one of the most promising technologies allowing to meet future emission targets for internal combustion engines. Whereas majority of research is centred on combustion itself, this paper for the first time points out the piston's energy losses induced by friction and blow-by in HCCI engine with negative valve overlap. The energy losses for HCCI and spark ignition (SI) operating modes were compared and thoroughly analysed with the use of the ring pack model. The input data for the simulations came from measurements made on a single-cylinder research engine capable of dual-mode combustion. The energy losses associated with friction of the rings against the cylinder varied from 8.2% of the indicated energy at the lowest load to 2.2% at the highest load tested, and were higher than in the SI mode by approximately 7%. The losses due to the gas leakage through the ring pack in the HCCI mode varied from 8% to 3.3%, respectively, and these losses were about twice as high as in the SI engine. The results demonstrated that energy losses due to blow-by are comparable with the friction losses of the rings, which are usually regarded as the prime source of inefficiency. • HCCI cycle effect on the ring pack energy losses is demonstrated. • Negative valve overlap in HCCI engine highly affects the ring pack performance. • The energy losses due to blow-by in an HCCI mode are 100% higher than in an SI mode. • The energy losses due to friction of the rings are higher by 7% in an HCCI engine. • The energy losses related to blow-by and rings' friction are comparable. [ABSTRACT FROM AUTHOR]

Abstract: We can get an (energy efficiency) EE improvement if we produce a flatter daily load curve, leading to a higher efficiency of the power system, making better use of the generation and transport electricity chain, thus avoiding over-investment in equipment used just few hours a year. Tariff flexibility of the (Time of Use) TOU type is one of these measures. Generally, TOU systems are designed to minimize total system cost, which may cause losses in distribution companies (DISCOs), generating opposition. On the contrary, the present paper proposes a TOU system for electricity consumption in Chile where optimal prices are obtained in order to maximize total income of DISCOs. In this manner, the proposed TOU system is, by definition, beneficial for DISCOs and it may lead to a win–win situation among DISCOs and consumers. In particular, we show that such a system, implemented in a country like Chile, would allow for DISCOs a total potential benefit of 811.7 millions of dollars for the 3-year study period (2005–2007), considering initiatives that promote a 5% savings in real consumption during on-peak hours, obtained by the spread or difference between the proposed and the current systems. [Copyright &y& Elsevier]

Abstract: The recently developed entransy theory is introduced in this paper to tackle the heat transfer processes in building central chilled water systems so as to improve their energy efficiency. We first divide the irreversible heat transfer processes into four categories: (1) air mixing processes; (2) heat transfer processes between chilled water and air; (3) chilled water mixing processes; and (4) heat transfer processes between chilled water and refrigerant. The formulas of entransy dissipation rates for each irreversible process are derived, and then the total entransy dissipation rate in the whole chilled water systems is obtained, which connects the geometrical structures of each heat exchanger and the operating parameters of each fluid directly to the demands of users and the supply of refrigerating unit. Based on the formula of entransy dissipation rate together with the conditional extremum method in mathematics, two optimization equation groups are deduced theoretically. Simultaneously solving such equation groups will easily find the optimal central chilled water system with the highest energy efficiency. Finally, a simple building central chilled water system with two users is taken as an example to illustrate the applications of the newly proposed optimization principle. [Copyright &y& Elsevier]

This paper examines the asymmetric long-run and short-run impacts of energy efficiency on carbon emissions for 28 developed and 34 developing economies, covering the period 1990–2017. The asymmetries are investigated by employing a nonlinear panel autoregressive distributed lag modelling framework. The analysis accounts for nonlinear complexities in energy relations and heterogeneity between developed and developing economies. The asymmetric long-run impacts of energy efficiency on carbon emissions are evident for developed and developing economies, but the effects are heterogeneous. In the long-run, a 1% increase in positive shocks (in energy efficiency) leads to a fall in carbon emissions by 1.24% and 1.19% for developed and developing economies, respectively. A similar rise in negative shocks (in energy efficiency) leads to an increase in carbon emissions by 0.37% and 1.06% for developed and developing economies, respectively. The short-run impacts are observed to be symmetric for both developed and developing economies. These results imply that the broader benefits of energy efficiency, like employment and energy productivity, should be considered in energy efficiency policy assessment. The developing economies should create a strong substitution effect between energy and other inputs to compensate for energy efficiency losses. [Display omitted] • Asymmetric impacts of energy efficiency on carbon emissions are examined. • Data covers 28 developed economies and 34 developing economies over the period 1990–2017. • A nonlinear panel autoregressive distributed lag model is employed. • Asymmetric long-run impacts are evident for developed and developing economies. • Symmetric short-run impacts exist for developed and developing economies. [ABSTRACT FROM AUTHOR]

Integrating energy efficiency as a key criterion in production management is critical to increasing energy efficiency while maintaining productivity in manufacturing systems. However, this integration still poses a huge challenge for decision-makers due to a lack of knowledge about the linkage between energy efficiency and productivity. Consequently, related energy-saving potential remains unexploited. In this context, this paper presents an innovative Energy Value Mapping (EVM) method to promote the systematic integration of energy efficiency into production management. The method includes three consecutive phases: (i) energy loss modeling to reveal the coupling relation between energy losses and productivity variables; (ii) lean energy analysis using production-oriented energy performance indicators to highlight energy inefficiencies and indicate improvement directions; (iii) improvement strategies determination to improve energy efficiency simultaneously considering traditional production management decisions. Furthermore, an industrial case study of a die-casting plant has demonstrated the effeteness and practicality of the method, showing its great potential in identifying, visualizing, quantifying, analyzing, and decreasing the energy losses related to production and operations management. The results showed that the overall energy demand of the process chain could be reduced by 6.17% with the energy utilization and time utilization being increased by 5.0%, 4.8%, respectively. • A method for integrating energy efficiency into production management is proposed. • The coupling relation between energy losses and productivity variables is studied. • A set of energy performance indicators is developed to expose energy losses. • The method permits to increase energy efficiency while maintaining productivity. • Overall energy demand was reduced by 6.17% by implementing the proposed method. [ABSTRACT FROM AUTHOR]