Detailed Simulation Tool Research Articles

Optimizing Hybrid Electric Microcar Design: A Simulation-Based Approach to Fuel-Cell Powertrains Analysis

Abstract The pressing need to reduce emissions and pollutants requires a significant diversification of mobility solutions and energy sources used to this aim. Light quadricycles with electric powertrains are increasingly recognized in research and industrial sectors as viable alternatives for achieving urban sustainable mobility solutions. Their lightweight design, compact dimensions, simplified prototyping and manufacturing processes, high efficiency, and lower emissions across the entire life cycle contribute to their growing importance. In line with this trend, integrating a hydrogen fuel cells stack with a battery pack is a promising powertrain solution, leveraging both technologies’ strengths. However, the design and development of such hybrid systems necessitate advanced methodologies that can address the problem of significant prototyping costs and time commitments while still ensuring optimal configurations. The availability of detailed simulation tools integrated with hardware components (vehicle simulation platforms) plays a crucial role in this endeavor, enabling insights on local phenomena which otherwise would be neglected, as such the purge phase, strongly impacting on the global consumption. These test platforms encompass all the main subsystems to account for all the vehicle demands while ensuring very good reliability for the predictions of performance and allowing the validation of the components. This enables the possibility of testing the vehicle under a wide set of operating conditions (e.g., weather conditions and driving cycles) within a simulated environment, thus reducing the costs related to the component sizing issues. In this context, the work presented in this paper, develops the fuel cell stack sizing analysis of a hybrid electric microcar, proposing a methodological approach for the powertrain design process. A detailed simulation platform is introduced for a hybrid electric microcar. The two energy sources, namely the Li-ion battery pack and the fuel cell stack, have been experimentally characterized and implemented into the model, also considering the experimental performances of the balance of plant elements as of the DC-DC converter. A linear scale-up method is implemented on the fuel cell stack to consider different configurations, and a deep analysis of the hydrogen consumption, comprising the scale-up of the purge phase, is presented, proposing two different approaches to the problem. From a technological standpoint, different results regarding the choice of fuel cell size have been found. As an example, the role of purging and its relationship with the size of the fuel cell stack may lead to a 14 % increase in the vehicle’s estimated range with respect to the baseline. Cost analyses are then needed to reach a trade-off between the costs and the technological standpoints.

Modeling of axion and electromagnetic fields interaction in particle-in-cell simulations

The axion, a theoretically well-motivated particle, has been searched for extensively via its hypothetical interactions with ordinary matter and fields. Recently, a new axion detection approach has been considered utilizing the ultra-intense electromagnetic fields produced by laser–plasma interactions. However, a detailed simulation tool has not hitherto been available to help understand the axion-coupled laser–plasma interactions in such a complex environment. In this paper, we report a custom-developed particle-in-cell (PIC) simulation method that incorporates the axion field, the electromagnetic fields, and their interactions. The axion field equation and modified Maxwell’s equations are numerically solved, with the axion-induced modulation of the electromagnetic field being treated as a first-order perturbation to handle the huge orders of magnitude difference between the two types of field. The simulation is benchmarked with well-studied effects such as axion–photon conversion and the propagation of an extremely weak laser pulse in a magnetized plasma. Such an extended PIC simulation provides a powerful tool to study axions under ultra-intense electromagnetic fields in the laboratory or in astrophysical processes.

A Review on the Zone Refining Process Technology toward Ultra‐Purification of Gallium for GaAs/GaN‐based Optoelectronic Device Applications

AbstractUltrapure gallium up to 99.9999%/ 99.99999% (6N/7N) purity level is a highly demanding material needed for the growth of gallium‐based group III–V semiconductor compounds and optoelectronic devices. However, general extraction of gallium from Bayer liquor contains high impurity content and ultra‐purification of the same cannot be accomplished by a single step. Thus, the purpose of this review is to assess various purification processes for the production of ultra‐pure gallium and to critically examine its applications in the optoelectronics industry. Through this research survey, it is found that zone refining of the zone melting process stands tall over other methods in purifying materials even up to 13N. Hence, scientists are adopting detailed mathematical models and simulation tools for designing unique zone refining systems for material purification. Current‐day technology even adopts intelligence methods such as machine learning, which sheds light on the importance of different zone refining parameters that influence the purification process. Here, the practical aspects of zone refining and how the feedback from the theoretical models or performance prediction through intelligence methods can be effectively incorporated into practice have also been emphasized

Analysis of the Physical Phenomena and Modelling Procedures of Building Heating and Cooling Emission System Energy Losses

An important research issue in assessing the energy performance of buildings concerns the modelling of the interaction between the built environment and the heating/cooling emission systems. Several methods can be used to evaluate the effect of the heating emitter characteristics, including the possible embedment in the building structure, non-uniform space temperature distribution, and the accuracy of the indoor temperature control. Generally, technical standards specify simplified, yet insufficiently validated methods, based on tabulated values. This paper outlines the main simplified procedures for assessing the efficiency of the emission subsystem, with a particular focus on the hydronic systems. It describes the essential datasets required for the analysis and highlights the interaction with phenomena related to the emitter heat loss. The simplified calculation procedures are then methodologically compared with detailed simulation tools, such as EnergyPlus, to identify differences and limitations in the models. The main discrepancies in the procedures and the required input data are highlighted, and possible strategies for improving the simplified methods are presented. A building representative of the European residential building stock is then analysed in the Italian climate using different calculation procedures. The results, in terms of thermal output of the emitter, are then analysed and compared.

Automated energy performance certificate based urban building energy modelling approach for predicting heat load profiles of districts

Urban building energy modelling (UBEM) for analysing buildings in their spatial and functional context is an arising method. Only a few UBEM procedures use detailed building simulation tools, which are essential for high temporal and spatial resolution. This paper aims at developing a detailed automated physical bottom-up UBEM framework based on archetypes using Energy Performance Certificate data for predicting hourly heat load profiles of residential buildings. Simulation results are compared to and validated with measurements of two district heating networks and values from the TABULA typology. A comparison of the simulated hourly heat load profile for space heating and domestic hot water with measurement data results in a CV(RMSE) of 0.3, NMBE of 0.085, R2 of 0.85 and r of 0.94 for a sample size of 66 residential buildings, solely based on an estimation of the 3 classification criteria of the archetypes (building period, building condition and building type) and an estimation of the conditioned gross floor area for each measured building. Hence, the model can be declared as calibrated according to acceptance criteria in literature.

A review of microwave-assisted process intensified multiphase reactors

Microwaves provide alternative heating and allow process intensification due to their rapid, volumetric, and selective nature. Recognizing the central role of multiphase reactors in chemical industry, a recent surge in employing microwaves is observed. Here, we review the recent experimental and modeling investigations of microwave heating of multiphase reactors with emphasis on chemical engineering applications. We demonstrate that there is accumulated evidence for improved performance via microwave heating and a clear opportunity for further process intensification. In most of the cases, this improved performance stems from a temperature gradient between two phases. We discuss the ongoing debate on the mechanism by which microwaves affect chemical processes exacerbated by the inability of measuring the temperature distribution in a microwave cavity. We outline recent progress in this direction in monolith reactors and needs for future work. We underscore the lack of detailed modeling and simulation tools even for single-phase systems and emphasize the imperative for multiscale predictive modeling to bridge the experimental-modeling gap. Promising results are shown by a few recently published modeling studies that can predict the experimental measurements in complex multiphase reactors. A combination of experimental and modeling tools can provide a comprehensive picture of the microwave multiphase reactors as well as a means toward scale-up and optimization.

Modelling of heat generators: technical standards vs detailed dynamic simulation tools

In the last years, international technical standards have introduced several procedures for modelling the heat generation sub-system, both providing new calculation methods and updating the old ones. A still open issue concerns the modelling of these sub-systems, by adapting the standard procedure – usually founded on simplified assumptions – to the structure of a detailed dynamic simulation tool. In this paper, the main procedures introduced by the international technical standards issued under the Mandate M/480 EN of 2010 on the heat generation sub-systems are presented, with a focus on combustion systems, chillers, and heat pumps. Simplifications and assumptions are analysed, by pointing out the limits related to the simplified modelling based on empirical correlations and tabulated values. The heat generation standardised models are compared with the ones used in detailed simulation tools, such as EnergyPlus. The main differences in the input data and in the model options are presented, and advices for the completion of the information commonly found in technical data sheets are provided. The paper is aimed both at promoting an effective application of the standards in the building design field and at contributing to the standardisation activity for the achievement of more accurate calculation models.

Review of Methods to Accelerate Electromagnetic Transient Simulation of Power Systems

Converter-based generators are increasingly replacing classical synchronous generation, resulting in significant challenges to the operation and planning of modern power systems. Power electronics (PE)-based equipment, along with non-linear PE-driven loads, introduce time-varying characteristics and fast switching behavior that increases the complexity of the power system model. Faster control actions are needed to overcome the fast switching dynamics to ensure the reliability and stability of future power systems. Thus, this requires advanced and detailed simulation methods and tools with highly accurate equivalent models to embody the relatively slower electromechanical to faster electromagnetic transient (EMT) phenomena. Conventional transient stability analysis using positive-sequence simulators has become inadequate for representing converter-dominated power systems, while EMT simulators suffer from the high computational burden. This review paper presents accelerated EMT simulation methods and tools that are categorized and discussed in three topics: system equivalents, simulation methods, and accelerating tools. Dynamic system equivalent techniques are discussed to model small to large interconnected external systems of the grid network. Moreover, a systematic review is made for existing EMT simulation methods, along with advanced co-simulation methods, for addressing simulation speed and accuracy issues in large power system networks. Emerging hardware-based simulation tools are reviewed that reduce the computational burden and increase the simulation efficiency of the power system model. Challenges and trends in EMT simulation are also presented and concluded by providing perspectives on this research topic.

Assessment of three solar-assisted heat pump typologies in Canada: parallel, series, and ice storage

This paper discusses the energy savings, operating costs, and net present values of three typologies of solar assisted heat pump in Canada: parallel systems, series systems, and ice storage systems. Typologies are evaluated for three detached house archetypes of varying energy performances, and across a variety of Canadian climates. Hourly energy modelling is accomplished with a custom spreadsheet tool. The models developed are approximate and meant for high level analysis. This work is meant as a first step in a process of verifying the potential for each of the typologies. In most cases, the parallel system performs best in terms of annual energy savings. The paper goes over the models, assumptions, and some results. Recommendations are discussed for future research focusing on system payback times. The next step will consist of using a detailed sub-hourly simulation tool for the typology that has been found to be the most promising.

Parametric Performance Analysis and Energy Model Calibration Workflow Integration—A Scalable Approach for Buildings

High efficiency paradigms and rigorous normative standards for new and existing buildings are fundamental components of sustainability and energy transitions strategies today. However, optimistic assumptions and simplifications are often considered in the design phase and, even when detailed simulation tools are used, the validation of simulation results remains an issue. Further, empirical evidences indicate that the gap between predicted and measured performance can be quite large owing to different types of errors made in the building life cycle phases. Consequently, the discrepancy between a priori performance assessment and a posteriori measured performance can hinder the development and diffusion of energy efficiency practices, especially considering the investment risk. The approach proposed in the research is rooted on the integration of parametric simulation techniques, adopted in the design phase, and inverse modelling techniques applied in Measurement and Verification (M&V) practice, i.e., model calibration, in the operation phase. The research focuses on the analysis of these technical aspects for a Passive House case study, showing an efficient and transparent way to link design and operation performance analysis, reducing effort in modelling and monitoring. The approach can be used to detect and highlight the impact of critical assumptions in the design phase as well as to guarantee the robustness of energy performance management in the operational phase, providing parametric performance boundaries to ease monitoring process and identification of insights in a simple, robust and scalable way.

Residential building stock model for evaluating energy retrofit programs in Saudi Arabia

This paper describes the development of a residential building stock model for the Kingdom of Saudi Arabia using an engineering bottom-up approach. The model is suitable for evaluating the impact of any energy efficiency or demand-side management program targeted for the residential building sector. The model accounts for the make-up and the characteristics of the existing Saudi housing stock using 54 prototypes representing KSA residential buildings including their type, vintage, and location. The model relies on a detailed building simulation tool to predict hourly energy consumption. The model predictions have been verified against actual reported data for energy consumption levels associated to main four Saudi regions. As an application of the building stock model, the benefits of a series of energy retrofit measures and programs are evaluated for both households and Saudi government. The analysis results clearly indicate that large-scale implementation of retrofit programs for existing KSA housing stock is cost-effective and has a wide range of economic, environmental, and social benefits. In particular, a full and targeted implementation of optimal retrofit programs can reduce the annual electricity consumption of the KSA residential sector by 50% in addition to similar decreases in carbon emissions and electricity generation capacities. The analysis results clearly indicate that for the retrofit program to be effective, the energy efficiency measures need to be tailored to the housing type, vintage, and location. Optimal sets of retrofit measures have been identified for the various categories of KSA housing stock as part of the based analysis carried out in this study.

Potential Application of HRTSim for Comprehensive Simulation of Large-Scale Power Systems with Distributed Generation

AbstractCurrently, the number of distributed generation (DG) objects in the world is growing mainly due to renewable energy sources (RES). However, the integration of a large volume of DG based on RES into existing electric power systems (EPS) is associated with a number of significant problems. For a comprehensive study and solution of these problems, it is necessary to carry out detailed simulation of real EPS, which is not always feasible with the help of existing tools. Therefore, the article proposes the use of an alternative solution – the Hybrid Real-Time Power System Simulator (HRTSim). To confirm the properties and capabilities of the HRTSim, the simulation results of a test scheme obtained using the HRTSim and the widely used digital hardware-software complex RTDS were compared. The results of a comprehensive comparison in both complexes confirmed the adequacy of information about the processes in equipment and EPS as a whole, obtained by the HRTSim. Thus, it is proved that further use the HRTSim as a tool for detailed and adequate simulation of real EPS with DG will provide complete and reliable information about normal and abnormal quasi-steady-state and transient processes, which is necessary for reliable and efficient design, research and subsequent operation of EPS with DG.

Multi-objective optimization model predictive dispatch precooling and ceiling fans in office buildings under different summer weather conditions

In summer, a ceiling fan has a tremendous potential to cool rooms, resulting in energy saving and a peak load reduction. During the critical peak pricing (CPP) period of the electricity, one method to attain substantial energy cost saving is to turn off the heating, ventilating and air conditioning (HVAC) system, but this may result in overheating. Fortunately, precooling and ceiling fans can be used to reduce the feeling of hot sensation. Therefore, the best control strategy for an HVAC system and ceiling fans is to maximize energy cost saving without much thermal comfort sacrifice. This paper presents a multi-objective optimization model predictive control (MO-MPC) of precooling temperature setpoint and ceiling fan speed. The proposed MO-MPC integrates an optimization engine, Dakota, and a detailed energy simulation tool, EnergyPlus, to determine the optimal control strategies considering the energy cost and thermal comfort simultaneously. A sub-program of substituting EnergyPlus with decision tree regression models for building climate prediction is deployed. If the calculation time is too long to achieve real-time control, this sub-program can be adopted to accelerate the calculation. In this study, the proposed MO-MPC framework is applied to a small and large building in four different cities with different CPPs. For a summer day, compared with the baseline cases of no precooling and no ceiling fan, the optimal strategies for the small building achieve energy cost savings between 10.3% and 33.3% and a peak power load decrease from 44.0% to 51.9%. Without precooling but with a ceiling fan control, on a particular summer day, for the large building case in Shanghai, 7.4% energy saving is achieved. The optimal control of the precooling temperature and ceiling fans result in a 14.4% energy cost saving. By using the decision tree regression models instead of EnergyPlus, the calculation time of the big office reduces from about 10 hours 40 minutes to 24.4 minutes.

Energy Efficiency and Integration of Urban Electrical Transport Systems: EVs and Metro-Trains of Two Real European Lines

Transport is a main source of pollutants in cities, where air quality is a major concern. New transport technologies, such as electric vehicles, and public transport modalities, such as urban railways, have arisen as solutions to this important problem. One of the main difficulties for the adoption of electric vehicles by consumers is the scarcity of a suitable charging infrastructure. The use of the railway power supplies to charge electric vehicle batteries could facilitate the deployment of charging infrastructure in cities. It would reduce the cost because of the use of an existing installation. Furthermore, electric vehicles can use braking energy from trains that was previously wasted in rheostats. This paper presents the results of a collaboration between research teams from University of Rome Sapienza and Comillas Pontifical University. In this work, two real European cases are studied: an Italian metro line and a Spanish metro line. The energy performance of these metro lines and their capacity to charge electric vehicles have been studied by means of detailed simulation tools. Their results have shown that the use of regenerated energy is 98% for short interval of trains in both cases. However, the use of regenerated energy decreases as the train intervals grow. In a daily operation, an important amount of regenerated energy is wasted in the Italian and Spanish case. Using this energy, a significant number of electric vehicles could be charged every day.

Assessing the reliability of Turkish building energy performance tool (BEP-TR2) by case tests

This paper aims to draw a general picture of the simplified software for calculation building energy performance based on Turkish Regulations called BEP-tr.v2, which was released at the end of 2017. Even the tool has a simplified calculation methodology, the discussion in this paper is going to be focused on assessing the accuracy of the tool by test cases. The assessing procedure for the tool has two steps. In the first step, box type cases are analyzed, and the results are compared with the results of a detailed energy simulation tool (BES) to perceive the percentage of deviations. In the second step, a current building is selected to use as a test case. The model results are compared with the real consumptions of the building to see the convergence rate of the tool (Bep-TR2). The results showed that the net energy calculation procedure of the methodology needs to be improved.

The effect of glazing on nZEB performance

In the last decades, European countries have provided for stringent energy requirements for new buildings. In improving the energy performance of buildings, windows play a significant role as they largely influence the energy need. The windows design should base on the balanced trade-off between the solar heat gains and the heat transfer by transmission.In the paper, for some Italian climatic zones, the relation between the optimal window-to-wall ratio (WWR) and the energy need in residential nearly zero-energy buildings (nZEBs) is investigated. In the case studies, the envelope thermo-physical properties are consistent with the nZEB requirements established at national level. The energy performance assessment is carried out by means of a detailed dynamic simulation tool (EnergyPlus). The influence of different orientations and sizes of windows on the energy performance and the peak power are studied. The paper analyses the effect of WWR in the design of nZEBs.

Virtual Solar Field - Validation of a detailed transient simulation tool for line focus STE fields with single phase heat transfer fluid

Simulation models enable designers and operators to test different settings of the real systems while avoiding the large costs associated with experimental or practical systems. However, creating models that resemble the real physical system with acceptable accuracy and computational time remains a challenge for developers of such tools. With this motivation, a new simulation tool, the Virtual Solar Field (VSF), has been developed for line-focus power plants with single-phase heat transfer fluid (HTF) to assist in plant control during transient processes. VSF is a whole-field model based on an efficient coupling of hydraulic and thermal solvers that take into account the flow distribution in the parallel loops, as well as the transient conditions in the field.In this paper, some validation cases for VSF using data from Andasol-3 power plant are shown. Five test cases are examined, which include normal operation, start-up and evening operation during clear-sky and strong transients. The results show very good agreement with the real plant and some discrepancies are discussed and studied. The main sources of discrepancies are associated with difficulties in modelling all fine details of reality using the current technologies in some commercial power plants. For example, small cloud passage are not detected by the few weather stations in the power plant, as well as knowing the exact loop valve settings is not possible in Andasol-3. In addition, an overview of the potential applications of VSF are mentioned and briefly discussed. VSF offers a suitable platform for testing novel control strategies and assessing the performance of the solar fields.

Evaluation of Passive Cooling Systems for Residential Buildings in the Kingdom of Saudi Arabia

In this paper, passive cooling strategies have been investigated to evaluate their effectiveness in reducing cooling thermal loads and air conditioning energy consumption for residential buildings in Kingdom of Saudi Arabia (KSA). Specifically, three passive cooling techniques have been evaluated including natural ventilation, downdraft evaporative cooling, and earth tube cooling. These passive cooling systems are applied to a prototypical KSA residential villa model with an improved building envelope. The analysis has been carried using detailed simulation tool for several cities representing different climate conditions throughout KSA. The impact of the passive cooling systems is evaluated on both energy consumption and electrical peak demand for residential villas with and without improved building envelope for five cities, representatives of various climate conditions in KSA. It is found that both natural ventilation and evaporative cooling provide a significant reduction in cooling energy use and electrical peak demand for the prototypical villa located in dry KSA climates such as that of Riyadh and Tabuk. Natural ventilation alone has reduced the cooling energy end-use by 22%, while the evaporative cooling system has resulted in 64% savings in cooling energy end-use. Moreover, the natural ventilation is found to have a high potential in all KSA climates, while evaporative cooling can be suitable only in hot and dry climates such as Riyadh and Tabuk. Finally, the analysis showed that natural ventilation provided the lowest electrical peak demand when applied into the improved envelope residential buildings in all five cities in KSA.

Optimal operation of large district heating networks through fast fluid-dynamic simulation

Optimization of the operating conditions of district heating networks is usually performed limiting the analysis to the primary energy related with heat production. An additional aspect that should be considered is the role played by the pumping system. Pumping may contribute to about 10% of the total primary energy consumption, especially in large networks or when small temperature levels are applied. Furthermore, the increasing share of waste heat or renewable energy sources from distributed producers requires a flexible and efficient pumping system. A further aspect which pumping strategy should face is system operation when malfunctions in the plants, pumps or pipes occur.Optimization of the pumping system requires the use of detailed simulation tools, which may need significant computational resources, especially in the case of large networks. A reduced model, based on Proper Orthogonal Decomposition combined with Radial basis functions (POD-RBF model) is proposed in this paper. This approach allows maintaining high level of accuracy despite reductions of more than 80% in the computational time. This make the approach effective tool for control strategy operations. An application to a large district heating network shows that reductions of about 20% in the pumping request and effective management of failures are possible.

Analysis of Vertical Ground Heat Exchangers: The New CaRM Tool

The ground source heat pump systems are worldwide used for space heating and cooling of buildings. The energy efficiency of the heat pump depends on the temperature of the heat carrier fluid on the ground side, which is affected by the annual ground load profile and the arrangement of the boreholes.This paper conducts long-term analysis of two office buildings with unbalanced load profiles in Italy. Work focuses the effects of the heat imbalance on the heat pump entering fluid temperature over ten simulated years. A detailed numerical simulation tool was used to conduct the analysis.