Ground coupled heat pumps are a notoriously efficient system for heating and cooling buildings. Sometimes the characteristics of the building and the user’s needs are such that the amount of heat extracted from the ground during the winter season can be considerably different from the amount injected in summer. This situation can cause a progressive cooling or heating of the ground with a negative effect on the energy efficiency and correct operation of the system. In these cases, an accurate sizing has to be done. In systems already built, it could be necessary to intervene a posteriori to remedy an excessive ground thermal drift due to the energy unbalance. In this work, such a situation relating to a real office building in Italy is investigated and several solutions are examined, one of which has been then implemented. In particular, a hybrid heat pump using as heat sink both the ground and external air is compared with common solutions through computer simulations using a dedicate... [more]

Photovoltaic system is utilized to generate energy that relies upon the ecological conditions, for example, temperature, irradiance, and the load associated with it. Considering the non-linear component of photovoltaic (PV) array and the issue of low effectiveness because of the variable natural conditions, the Maximum Power Point Tracking (MPPT) method is required to extract the maximum power from the PV system. The adopted control is executed utilizing an Adaptive Sliding Mode Controller (ASMC) and the enhancement is actualized utilizing an Improved Pattern Search Method (IPSM). This work employs IPSM based optimization approach in order to command the underlying ASMC controller. The upper level decision determines the sliding surface for the adaptive controller. As a non-linear strategy, the stability of the adaptive controller is guaranteed by conducting a Liapunov analysis. On the practical side, MATLAB/Simulink is used as simulator for the controller implementation and coupling w... [more]

In order to reduce the cost of wellheads, the production rate of the gas wells in the Hechuan Gas Field are mostly measured in groups, which raises a stringent barrier for industries to determine the production rate of each single well. The technique for determining the production of a single well from the production of the well-group can be called the production splitting method (PSM). In this work, we proposed a novel PSM for the multi-well-monitor system (MWMS) on the basis of the Beggs and Brill (BB) correlation. This proposed method can account for the multi-phase flow together with the features of the pipelines. Specifically, we discretize the pipeline into small segments and recognize the flow pattern in each segment. The pressure drop along the pipeline is calculated with the Beggs and Brill correlation, and the production of each well is subsequently determined with a trial method. We also applied this proposed method to a field case, and the calculated results show that the r... [more]

In the present numerical study, implicit large eddy simulations (LES) of non-reacting multi-components mixing processes of cryogenic nitrogen and n-dodecane fuel injections under transcritical and supercritical conditions are carried out, using a modified reacting flow solver, originally available in the open source software OpenFOAM®. To this end, the Peng-Robinson (PR) cubic equation of state (EOS) is considered and the solver is modified to account for the real-fluid thermodynamics. At high pressure conditions, the variable transport properties such as dynamic viscosity and thermal conductivity are accurately computed using the Chung transport model. To deal with the multicomponent species mixing, molar averaged homogeneous classical mixing rules are used. For the velocity-pressure coupling, a PIMPLE based compressible algorithm is employed. For both cryogenic and non-cryogenic fuel injections, qualitative and quantitative analyses are performed, and the results show significant eff... [more]

The increased penetration of renewable energy sources in the electrical grid raises the need for more power system flexibility. One of the high potential groups to provide such flexibility is the industry. Incentives to do so are provided by variable pricing and remuneration of supplied ancillary services. The operational flexibility of a chlor-alkali electrolysis process shows opportunities in the current energy and ancillary services markets. A co-optimisation of operating the chlor-alkali process under an hourly variable priced electricity sourcing strategy and the delivery of Frequency Containment Reserve (FCR) is the core of this work. A short term price prediction for the Day-Ahead Market (DAM) and FCR market as input for a deterministic optimisation shows good results under standard DAM price patterns, but leaves room for improvement in case of price fluctuations, e.g., as caused by Renewable Energy Sources (RES). A two-stage stochastic optimisation is considered to cope with th... [more]

Utility companies have a great interest in identifying energy losses. Here, we focus on Non-Technical Losses (NTL), which refer to losses caused by utility theft or meter errors. Typically, utility companies resort to machine learning solutions to automate and optimise the identification of such losses. This paper extends an existing NTL-detection framework: by including knowledge-based NTL segmentation, we have detected some opportunities for improving the accuracy and the explanations provided to the utility company. Our improved models focus on specific types of NTL and therefore, the explanations provided are easier to interpret, allowing stakeholders to make more informed decisions. The improvements and results presented in the article may benefit other industrial frameworks.

Liquefied natural gas (LNG) is one of the most influential fuels of the 21st century, especially in terms of the global economy. The demand for LNG is forecasted to reach 400 million tonnes by 2020, increasing up to 500 million tonnes in 2030. Due to its high mass and volumetric energy density, LNG is the perfect fuel for long-distance transport, as well as for use in mobile applications. It is also characterized by low levels of emissions, which is why it has been officially approved for use as a marine fuel in Emission Control Areas (ECAs) where stricter controls have been established to minimize the airborne emissions produced by ships. LNG is also an emerging fuel in heavy road and rail transport. As a cryogenic fuel that is characterized by a boiling temperature of about 120 K (−153 °C), LNG requires the special construction of cryogenic mobile installations to fulfill conflicting requirements, such as a robust mechanical construction and a low number of heat leaks to colder parts... [more]

In concentrating solar systems, it is essential to study the optical losses of the collectors. A fundamental parameter is the intercept factor, namely, the fraction of sunrays reflected by the concentrator that reaches the receiver. Optical profilometry studies the relationship between the collector profile and the intercept factor, which influences the collection efficiency. Profilometric analyses were performed on a micro-parabolic trough collector (m-PTC), with reduced sizes and greater mirror curvature than a usual PTC. The proposed technique projects a luminous pattern (structured light) both on the collector with an opaque covering and on a flat reference plane. Measurement set-up and calibration technique were developed for m-PTC. A program coded in Python analyzed the images and reconstructs the mirror profile. The tilted reference plane was reconstructed using an original geometric model and a calibration procedure. The focal length of each parabolic section was calculated, pr... [more]

In the five-phase permanent magnet synchronous motor (PMSM) control system, the torque ripple caused by coil inter-turn short-circuit (ITSC)fault will make the motor performance worse. Due to the existence of the short-circuit current in the faulty phase and the third harmonic component in the permanent magnet flux linkage, the electromagnetic torque will contain even-order ripple components when the faulty phase is removed. Torque ripple also cause speed ripple. In this paper, the repetitive controller (RC) is used to perform proportional gain compensation for speed ripple. By designing the RC and connecting RC and proportional integral (PI) controller in parallel for the speed loop, the torque ripple amplitude can be reduced. It can be seen from the simulation and experimental results that the torque ripple suppression strategy based on RC can effectively suppress the torque ripple under ITSC fault.

Output-only methods are widely used to characterize the dynamic behavior of very diverse structures. However, their application to floating structures may be limited due to their strong nonlinear behavior. Therefore, since there is very little experience on the application of these experimental tools to these very peculiar structures, it is very important to develop studies, either based on numerical simulations or on real experimental data, to better understand their potential and limitations. In an initial phase, the use of numerical simulations permits a better control of all the involved variables. In this work, the Covariance-driven Stochastic Subspace Identification (SSI-COV) algorithm is applied to numerically simulated data of two different solutions to Floating Offshore Wind Turbines (FOWT) and for its capability of tracking the rigid body motion modal properties and susceptibility to different modeling restrictions and environmental conditions tested. The feasibility of apply... [more]

Biomass gasification is the most reliable thermochemical conversion technology for the conversion of biomass into gaseous fuels such as H2, CO, and CH4. The performance of a gasification process can be estimated using thermodynamic equilibrium models. This type of model generally assumes the system reaches equilibrium, while in reality the system may only approach equilibrium leading to some errors between experimental and model results. In this study non-stoichiometric equilibrium models are modified and improved with correction factors inserted into the design equations so that when the Gibbs free energy is minimized model predictions will more closely match experimental values. The equilibrium models are implemented in MatLab and optimized based on experimental values from the literature using the optimization toolbox. The modified non-stoichiometric models are shown to be more accurate than unmodified models based on the calculated root mean square error values. These models can be... [more]

With the continuous development of new energy, there is more and more research on step-up inverters in photovoltaic and wind power generation systems. The Z-source inverter has become a research hotspot because of its small output THD (Total Harmonic Distortion) and high reliability. However, the traditional Z-source inverters cannot meet the higher boost requirements of new energy power generation. The quasi-z-source inverter with stronger boosting ability came into being. The high step-up Z-source inverters presented in existing literature is only focused on one or several topologies and lacks a comparative analysis on different topologies. Based on the quasi-Z-source inverter, this paper proposes a family of quasi-z-source inverters with a coupled inductor. The required voltage gain can be obtained by changing the turns ratio of the coupled inductor, which provides a new control variable for the system and makes the design of the system becomes more flexible. Through the analysis an... [more]

Heat pumps (HPs) are being developed with a new emphasis on cold climates. To lower the environmental impact of greenhouse gas (GHG) emissions, alternate low global warming potential (GWP) refrigerants must also replace the exclusive use of the refrigerant R410A, preferably without re-engineering the mechanical hardware. In this paper, we analyze the performance of four low-GWP alternative refrigerants (R32, R452B, R454B, and R466A) relative to the conventional R410A and draw conclusions on the relative performances for providing heating in cold climates based on the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) 210/240 standard for two-speed heat pumps. The simulations are carried using the Department of Energy, Oak Ridge National Laboratory (DOE/ORNL) Heat Pump Design Model (HPDM), a well-known heating, ventilation, and air conditioning (HVAC) modeling and design tool in the public domain and the HVAC research and development community. The results of the simulation a... [more]

Water hydraulic fracturing involves pumping low viscosity fluid and proppant mixture into the artificial fracture under a high pumping rate. In that high Reynolds number conditions (HRNCs, Re > 2000), the turbulence effect is one of the key factors affecting proppant transportation and placement. In this paper, a Eulerian multiphase model was used to simulate the proppant particle transport in a parallel slot under HRNCs. Turbulence effects in high pumping rates and frictional stress among the proppant particles were taken into consideration, and the Johnson-Jackson wall boundary conditions were used to describe the particle-wall interaction. The numerical simulation result was validated with laboratory-scale slot experiment results. The simulation results demonstrate that the pattern of the proppant bank is significantly affected by the vortex near the wellbore, and the whole proppant transport process can be divided into four stages under HRNCs. Furthermore, the proppant placement st... [more]

The primary energy consumption and greenhouse gas emissions from nickel smelting products have been assessed through case studies using a process model based on mass and energy balance. The required primary energy for producing nickel metal, nickel oxide, ferronickel, and nickel pig iron is 174 GJ/t alloy (174 GJ/t contained Ni), 369 GJ/t alloy (485 GJ/t contained Ni), 110 GJ/t alloy (309 GJ/t contained Ni), and 60 GJ/t alloy (598 GJ/t contained Ni), respectively. Furthermore, the associated GHG emissions are 14 tCO2-eq/t alloy (14 tCO2-eq/t contained Ni), 30 t CO2-eq/t alloy (40 t CO2-eq/t contained Ni), 6 t CO2-eq/t alloy (18 t CO2-eq/t contained Ni), and 7 t CO2-eq/t alloy (69 t CO2-eq/t contained Ni). A possible carbon emission reduction can be observed by comparing ore type, ore grade, and electricity source, as well as allocation strategy. The suggested process model overcomes the limitation of a conventional life cycle assessment study which considers the process as a ‘black box... [more]

Our paper focuses on eliciting the factors that constitute threats and dangers for urban energy networks, information networks, and energy grids in the cities. Moreover, we attempt to determine how these threats are perceived by the inhabitants of those cities. Urban energy networks tend to play an increasing role in achieving energy efficiency and environmental sustainability in large urban centers. Even though they do not necessarily correspond to reality, public opinions can substantially influence the adoption of relevant technologies in populous urban locations. We use the public opinion representative survey data from the Czech Republic (a sample of 1023 respondents) in order to show how people perceive the dangers and threats for urban energy networks from such events as: (i) Extensive and long-term power outage; (ii) service disruption of the Internet, mobile networks or telephone landlines; (iii) cyber-attacks, and (iv) the technological dependence of the state on multinationa... [more]

The present work is mapped to scrutinize the consequence of biodiesel and gaseous fuel properties, and their impact on compression-ignition (CI) engine combustion and emission characteristics in single and dual fuel operation. Biodiesel prepared from non-edible oil source derived from Thevetia peruviana belonging to the plant family of Apocynaceaeis. The fuel has been referred as methyl ester of Thevetia peruviana (METP) and adopted as pilot fuel for the effective combustion of compressed gaseous fuel of hydrogen. This investigation is an effort to augment the engine performance of a biodiesel-gaseous fueled diesel engine operated under varied engine parameters. Subsequently, consequences of gas flow rate, injection timing, gas entry type, and manifold gas injection on the modified dual-fuel engine using conventional mechanical fuel injections (CMFIS) for optimum engine performance were investigated. Fuel consumption, CO, UHC, and smoke formations are spotted to be less besides higher... [more]

This paper presents a new concept and research results of DC-DC high-voltage-gain, high-frequency step-up resonant converters. The proposed topologies are optimized towards minimizing the number of switches and improvements in efficiency. Another relevant advantage of such type of converters is that they have a common input and output negative point. The proposed converters are based on the resonant switched-capacitor voltage multiplier circuit, and that is why they are compared with a classic converter from this family. The included results show the operating principle, possible switching methods with the consideration of their impact on the voltage gain level, as well as the voltage and current ripples. The operating concepts and analytical calculations are confirmed by simulation and experimental results.

Granite is one of those materials that due to its thermal parameters is used as a filling for storage beds, including high-temperature ones. The article analyzes local material that was extracted in Strzegom, Poland. The purpose of the paper is the assessment of storage material with regard to its cooperation with a heat source that is available for a short time, e.g., a solar installation. Three different shapes of granite material were tested: rock, cube and sphere. Each shape has its advantages and disadvantages, which are associated with economic and strength aspects. The article presents experimental tests of the material, which were conducted in order to determine the efficiency of the charging process. The results show that rock-shaped granite filling elements are characterized with the best parameters during the charging process, and that they obtained the highest first- and second-law efficiency in the entire tested range of inlet air temperature and flow rate. The efficiency... [more]

Geological sequestration of CO2-rich gas as a CO2 capture and storage technique has a lower technical and cost barrier compared to industrial scale-up. In this study, we have proposed CO2 capture and storage via hydrate in geological formation within the hydrate stability zone as a novel technique to contribute to global warming mitigation strategies, including carbon capture, utilization, and storage (CCUS) and to prevent vast methane release into the atmosphere caused by hydrate melting. We have attempted to enhance total gas uptake and CO2 capture efficiency in hydrate in the presence of kinetic promoters while using diluted CO2 gas (CO2-N2 mixture). Experiments are performed using unfrozen sands within hydrate stability zone condition and in the presence of low dosage surfactant and amino acids. Hydrate formation parameters, including sub-cooling temperature, induction time, total gas uptake, and split fraction, are calculated during the single-step formation and dissociation proce... [more]

 Borehole heat exchangers (BHEs) generally employ water-antifreeze solutions to allow working fluid temperatures to fall below 0 °C. However, some local regulations have forbidden antifreeze additives (even non-toxic ones) to avoid groundwater pollution in case of pipe leakage. This paper presents a techno-economic and environmental analysis of four different fluids: propylene glycol at 25% and 33% weight concentrations, calcium chloride at 20% weight concentration (CaCl2 20%), and pure water. Thermal loads from 36 case studies in six different climate zones are used to perform BHE sizing and compare the abovementioned fluids from the economic, operational, and environmental points of view. The economic analysis and the carbon footprint assessment are performed on a life cycle of 25 years considering the installation (BHE drilling, fluid) and operation (heat pump and ground-side circulation pump energy demand, fluid replacement) of the simulated GSHPs. Results highlight that using... [more]

Increasing the share of renewable energies in electricity and heat generation is the cornerstone of a climate-friendly energy transition. However, as renewable technologies rely on diverse natural resources, the design of decarbonized energy systems inevitably leads to environmental trade-offs. This paper presents the case study of a comprehensive impact assessment for different future development scenarios of a decentralized renewable energy system in Germany. It applies an adapted ecological scarcity method (ESM) that improves decision-support by ranking the investigated scenarios and revealing their main environmental shortcomings: increased mineral resource use and pollutant emissions due to required technical infrastructure and a substantial increase in land use due to biomass combustion. Concerning the case study, the paper suggests extending the set of considered options, e.g., towards including imported wind energy. More generally, the findings underline the need for a comprehe... [more]

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With the increasing shares of intermittent renewable sources in the grid, it becomes increasingly essential to quantify the requirements of the power systems flexibility. In this article, an adjusted weight flexibility metric (AWFM) is developed to quantify the available flexibility within individual generators as well as within the overall system. The developed metric is useful for power system operators who require a fast, simple, and offline metric. This provides a more realistic and accurate quantification of the available technical flexibility without performing time-consuming multi-temporal simulations. Another interesting feature is that it can be used to facilitate scenario comparisons. This is achieved by developing a new framework to assure the consistency of the metric and by proposing a new adjusted weighting mechanism based on correlation analysis and analytic hierarchy process (AHP). A new ranking approach based on flexibility was also proposed to increase the share of th... [more]

The application of advanced technologies for engine efficiency improvement and emissions reduction also increase the occurrence possibility of abnormal combustions such as incomplete combustion, misfire, knock or pre-ignition. Novel promising combustion modes, which are basically dominated by chemical reaction kinetics show a major difficulty in combustion control. The challenge in precise combustion control is hard to overcome by the traditional engine map-based control method because it cannot monitor the combustion state of each cycle, hence, real-time cycle-resolved in-cylinder combustion diagnosis and control are required. In the past, cylinder pressure and ion current sensors, as the two most commonly used sensors for in-cylinder combustion diagnosis and control, have enjoyed a seemingly competitive relationship, so all related researches only use one of the sensors. However, these two sensors have their own unique features. In this study, the idea is to combine the information o... [more]