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Refrigeration systems are crucial in retail food stores to ensure appropriate merchandising of food products. This paper compares four different CO 2 refrigeration system configurations in terms of cooling performance, environmental impact, power consumption and annual running costs. The systems studied were the conventional booster refrigeration system with gas bypass (reference system), the all CO 2 cascade system with gas bypass, a booster system with a gas bypass compressor, and integrated cascade all CO 2 system with gas bypass compressor. The weather conditions of London, UK, and Athens, Greece, were used for the modelling of energy consumption and environmental impacts to represent moderate and warm climatic conditions respectively. The control strategies for the refrigeration systems were derived from experimental tests in the laboratory on a conventional booster refrigeration system. The results from the analysis showed that the CO 2 booster system with gas bypass compressor can provide best performance with 5.0% energy savings for the warm climate and 3.65% for the moderate climate, followed by the integrated cascade all CO 2 system with gas bypass compressor, with 3.6% and 2.1% savings over the reference system for the warm and moderate climates respectively. [ABSTRACT FROM AUTHOR]

Carbon dioxide heat pump is considered a potential low-carbon combined cooling and heating solution. However, there is a strong need for simple methods to improve the energy efficiency of the carbon dioxide heat pump due to the larger throttling losses that result in poor performance. Given this, a compact water-cooled subcooler-assisted carbon dioxide heat pump for combined cooling and heating is designed in this paper. An experimental test platform is built, where experimental investigations are performed to reveal the working performance. Furthermore, a matching control strategy is developed and verified as well. The experiments demonstrated that the adoption of the water-cooled subcooler has significantly improved the cooling performance. The cooling capacity (Q ̇ c) and cooling coefficient of performance (COP c) are increased by up to 20.2% and 31.5%, respectively. Moreover, the optimal discharge pressure is lowered by 0.5 MPa. However, the heating performance is somewhat degraded, for which the control strategy with the synergistic variation of subcooling degree and compressor rotation speed is developed. The deteriorated heating performance is thus mitigated. The developed control strategy has been verified in practice, and the carbon dioxide heat pump performance could be maintained at the highest possible level. Q ̇ c and COP c are further improved by a maximum of 40.7% and 37.7%, respectively. The heating and overall coefficient of performance could reach 2.55 and 5.10 at the return water and outlet water temperatures of 40 °C and 75 °C, respectively. • A compact water-cooled subcooler-assisted CO 2 heat pump is designed. • The cooling capacity and cooling coefficient of performance are greatly increased. • A synergistic control strategy for subcooling degree and rotation speed is developed. • The developed control strategy has been verified in practice. • The CO 2 heat pump performance can be maintained at the highest possible level. [ABSTRACT FROM AUTHOR]

• A novel energy storage-based supercritical CO 2 power system with ejector is proposed. • Thermodynamic analysis and parametric optimization are carried out. • Power regulation capacities in energy storage and release conditions are examined. • Correspondence between storage tank pressure and system performance is conducted. The application of supercritical CO 2 (S-CO 2) in power generation systems shows huge advantages of compactness and high efficiency for nuclear energy utilization. However, it is difficult to achieve a quick response for reactor power regulation system in isolated power gird, and amounts of nuclear heat is wasted by bypass regulation to track the power load. In this paper, a novel energy storage-based supercritical CO 2 power system with ejector is proposed to realize the rapid energy storage and energy release in system operation to guarantee high conversion efficiency of nuclear energy. Thermodynamic mathematical models are established to examine the performance of the proposed system. The parametric analysis and optimization are performed to acquire the optimum system performance. Furthermore, the performance evaluation in energy storage conditions and energy release conditions are presented to show the power regulation capacity of the proposed system. Results show that the appropriate split ratios of recompression supercritical CO 2 power system for different main compressor outlet pressures are both about 0.3. The optimum thermal efficiency of the proposed system is 44.58% and the corresponding exergy efficiency is 66.94% under the given system conditions. In addition, 10% of mass flow rate storage for the S-CO 2 results in a decrease in power load of 41.2%, and 10% of mass flow rate release for the S-CO 2 can achieve an increase in power load of 45.59%. Furthermore, the maximum regulation capacity for the power load increases with the pressure of the high-pressure energy storage tank. Meanwhile, the energy release conditions with a low pressure of high-pressure energy storage tank and a high entrainment ratio of the ejector result in the decrease in net power output. [ABSTRACT FROM AUTHOR]

Abstract: Coal fired power generation will continue to provide energy to the world for the foreseeable future. However, this energy use is a significant contributor to increased atmospheric CO2 concentration and, hence, global warming. Capture and disposal of CO2 has received increased R&D attention in the last decade as the technology promises to be the most cost effective for large scale reductions in CO2 emissions. This paper addresses CO2 transport via pipeline from capture site to disposal site, in terms of system optimization, energy efficiency and overall economics. Technically, CO2 can be transported through pipelines in the form of a gas, a supercritical fluid or in the subcooled liquid state. Operationally, most CO2 pipelines used for enhanced oil recovery transport CO2 as a supercritical fluid. In this paper, supercritical fluid and subcooled liquid transport are examined and compared, including their impacts on energy efficiency and cost. Using a commercially available process simulator, ASPEN PLUS 10.1, the results show that subcooled liquid transport maximizes the energy efficiency and minimizes the cost of CO2 transport over long distances under both isothermal and adiabatic conditions. Pipeline transport of subcooled liquid CO2 can be ideally used in areas of cold climate or by burying and insulating the pipeline. In very warm climates, periodic refrigeration to cool the CO2 below its critical point of 31.1°C, may prove economical. Simulations have been used to determine the maximum safe pipeline distances to subsequent booster stations as a function of inlet pressure, environmental temperature and ground level heat flux conditions. [Copyright &y& Elsevier]

• A novel CCHP system based on Compressed Carbon dioxide Energy Storage is proposed. • Wind turbine waste heat is utilized to optimize the system performance. • Under the designed conditions, the system power efficiency can reach 0.48. • The impact of wind turbine waste heat on the system performance is confirmed. Due to climate change and the increase in energy demand caused by population growth, considerable attention is being given to wind energy and combined cooling, heating, and power (CCHP) systems, which are known for their high energy utilization. With the rapid growth of wind power generation, the waste heat generated by wind turbines and the intermittency of wind power have emerged as problems to be addressed. Therefore, this paper proposes a low-temperature CCHP system based on transcritical compressed CO 2 energy storage which utilizes wind power and wind turbine waste heat. A mathematical model of this system is developed and applied, and system characteristics are evaluated from the perspective of thermodynamics. The performance indices (system power efficiency (SPE), system energy efficiency (SENE), and exergy density (E D)) are defined, and sensitivity analysis of the key factors affecting system performance is conducted. Based on the parameters under the design condition, the SPE of the system is 0.48, the SENE is 1.19, and the E D is 11.51 kWh/m3. Storage pressure and waste heat temperature have a great influence on the thermodynamic performance of the system, while ambient temperature only affects cooling energy, heating energy, and E D. The variation of the pressure difference at the main throttle valve mainly affects SPE and E D of the system. [ABSTRACT FROM AUTHOR]

Olefins are important platform chemicals widely used in industry. In terms of the short supply of oil resources, natural gas and coal are two significant alternative feedstocks. In this paper, energy consumption and GHG emissions of olefins production are analysed with life cycle assessment methods. Results showed the energy consumption and GHG emissions of natural gas-to-olefins are roughly equivalent to those of oil-to-olefins, while coal-to-olefins suffers from higher energy consumption and serious GHG emissions, including 5793 kg eq. CO 2 /t olefins of direct emissions and 5714 kg eq. CO 2 /t olefins of indirect emissions. To address the problem, the effect of carbon capture on coal-to-olefins is investigated. In comprehensive consideration of energy utilization, environmental impact, and economic benefit, the coal-to-olefins with 80% CO 2 capture of the direct emissions is found to be an appropriate choice. With this carbon capture configuration, the direct emissions of the coal-to-olefins are reduced to 1161 kg eq. CO 2 /t olefins. However, the indirect emissions are still not captured, which should be strictly monitored and significantly reduced. Finally, a scenario analysis is conducted to estimate resource utilization and GHG emissions of olefins production of China in 2020. Several suggestions are also proposed for policy making on the sustainable development of olefins industry. [ABSTRACT FROM AUTHOR]

Abstract: The present paper reports the results obtained on a carbon dioxide transcritical power cycle using an energy and exergy analysis. The procedure consisted of modifying the inlet pressure to the turbine from 66bar, by means of the software HYSYS®, maintaining constant each evaluated turbine inlet temperature (60, 90, 120 and 150°C) until the net work was approximately zero. As a result, an increase up to 25% for the exergy efficiency, and up to 300% for the energy efficiency are obtained when the inlet temperature to the turbine is risen from 60 to 150°C. Consequently, the analysis shows the viability of implementing this process as alternative energy, because of the possibility to recovery energy from waste heat from industrial processes. [Copyright &y& Elsevier]

Abstract: Combined Heat and Power (CHP) plants are increasingly used, when feasible, as a mean to reduce fuel consumption and CO2 emissions. The thermal and electrical production must be adapted to load requirements and must lead to the fulfilment of all the constraints imposed by energy saving regulations. As one of such requirements [a minimum “fuel energy savings ratio” (FESR)] is an integral constraint that can be evaluated only at the end of each year of production, during the design phase of the plant it is of the utmost importance to have a fast algorithm able to simulate and optimize the operating conditions of all the candidate CHPs configurations, as the non-compliance with FESR regulations may lead to loose significant tax discounts, and therefore make the investment less profitable. The paper describes a suitable algorithm and its application to the optimization of a real CHP site located in Italy; besides, this work has led, as a further step toward the optimized control of larger systems, to the introduction of an additional degree of freedom (“on–off” state of some machines) extending in principle the optimization procedure to multinode CHP plants. [Copyright &y& Elsevier]

Plug-in hybrid vehicles (PHEVs) are gaining attention over the world due to their ability to reduce gasoline/diesel consumption by using electricity from the grid. Despite the efforts of Society of Automotive Engineers Recommended Practice SAE J1711, it has not yet been established a worldwide methodology for calculation of fuel consumption and emission factors when regarding emission standards, with distinct driving cycles. This paper intends to contribute to the creation of this broader methodology, based on SAE J1711, aiming a fair comparison among vehicle technologies, and giving insight on electric grid impact and on CO2 life-cycle emissions. The methodology was applied to two simulated PHEVs exploring two different powertrain configurations: series and parallel; different driving cycles: CAFE, FTP75, NEDC and JC08; different driving distances (specially analyzing the average commuting daily distance of 20km) and different user behaviours regarding battery recharging. CO2 emissions were calculated for fuel consumption, electricity generation and cradle-to-grave. Electric grid power demand was estimated. Maintenance, manufacturer and use costs were discussed. [Copyright &y& Elsevier]

Abstract: This paper presents the exergy analysis of variable air volume (VAV) systems used in office buildings for air-conditioning. The mathematical models are developed using the engineering equations solver (EES) environment. The following indicators are presented: energy efficiency, exergy efficiency, and equivalent-CO2 emissions due to the generation of electricity used by the VAV system. [Copyright &y& Elsevier]

• iG-CLC coupled with supercritical steam cycle efficiently captures CO 2. • iG-CLC is most efficient when operated at 0.5 MPa. • Biomass-CLC is less efficient than coal-CLC due to high sulphur and chlorine. • Advanced ultrasupercritical steam cycle is not suitable for CLC. • Long oxygen carrier lifetime means lower energy efficiency penalty. Chemical looping combustion is a cost-competitive solution for producing low carbon electricity. In this paper, we investigate by means of a process modelling study, the coupling of chemical looping combustion of solid fuels with advanced steam-based power cycles, viz. supercritical, ultra-supercritical and advanced ultra-supercritical Rankine cycles. The energy and exergy efficiencies of the various chemical looping combustion power plant configurations are compared against the reference plants without carbon capture. Our models incorporate practical considerations for reactor design. With an upper operating temperature limit of 950 °C, the maximum efficiencies achievable by integrated gasification combined cycle chemical looping combustion (IGCC–CLC) and in situ gasification chemical looping combustion power plants (iG-CLC) are 41.3% and 41.5%, respectively. Overall, iG-CLC emerges as the most efficient CLC configuration. Comparing to an integrated gasification combined cycle without carbon capture, the energy efficiency penalties for capturing CO 2 from iG-CLC coupled with subcritical, supercritical, ultra-supercritical or advanced ultra-supercritical steam cycles are 5.1%, 5.0%, 5.2% or 13.0%, respectively. The biomass-fired chemical looping combustion power plants also show low energy efficiency penalties (<2.5%) compared to the reference biomass power plants without CO 2 capture. Our modelling results suggest that chemical looping combustion will remain an attractive carbon capture technology for solid fuel power plants, in a future when supercritical steam turbines become the norm. [ABSTRACT FROM AUTHOR]

The role of energy management has greatly expanded in industries. Major industries are contracting with energy service providers to implement energy management practices to improve efficiency. The effort to introduce energy management in small and medium scale enterprises (SME) is very limited due to the lack of initiation, expertise and financial limitations. In manufacturing, energy cost is usually a small portion of the total production cost, and therefore, energy cost receives relatively little attention. Another problem is lack of knowledge about the underlying principles involved in energy management. There is a well-recognized need to target SME with information on energy management concepts and practises. This paper aims to provide a guideline for entrepreneurs in implementing energy management. It reviews the methodology of energy management that was introduced in a German bakery with a clear and consistent path toward introducing energy management. The methodology, tools used, results and difficulties encountered during the study are discussed. [Copyright &y& Elsevier]

• Comprehensive analyses of six CO 2 booster refrigeration solutions are conducted. • The energy efficiency level of the solutions is revealed, and application feasibility in China is evaluated. • The CO 2 refrigeration system combined with flooded evaporation and parallel compression is optimal. • These CO 2 solutions are recommended for use in northern China, while it is not suitable for hot climate regions. The cold chain industry related to people's livelihood in China is developing rapidly today. The energy efficiency level and environmentally-friendly characteristics of cold chain equipment need to be enhanced and improved urgently. The CO 2 booster refrigeration systems (BRS) are widely used and developed in European supermarkets due to outstanding environmental benefits. The two objectives of this paper are to reveal the energy efficiency level of six CO 2 BRS solutions under five typical Chinese climate conditions, as well as to objectively evaluate the application feasibility in Chinese supermarkets to inform manufacturers. Comprehensive analyses consist of energy efficiency, economy, and environment are conducted. The results show that the CO 2 BRS assisted with flooded evaporation and parallel compression has the best performance. For most cities, its annual energy efficiency ratio improved by 3.9 ~ 23.2%, the payback period is averaging less than 5.5 years, and the total equivalent warming impact reduced by 11.9 ~ 52.9% compared to the reference systems. The CO 2 BRS solutions are proved to be good alternatives and recommended for use in northern China, while it is not suitable for hot climate cities, such as Guangzhou, and further modifications are required. For the reference systems, the R134a/CO 2 cascade refrigeration system can be considered a short-term transition solution in southern China, considering its relatively decent performance. [ABSTRACT FROM AUTHOR]