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The railway sector's energy impact is increasing, and this trend is expected to persist over the next decade. Particularly, the energy consumption of Heating Ventilation, and Air Conditioning (HVAC) systems is significant among various services provided on board (30 % of total energy requirements) due to the rising attention to passengers' thermal comfort. In this framework, this research proposes an innovative method for enhancing indoor thermal comfort while also studying the associated energy consequences. It consists of an advanced passenger-centric-control framework for HVAC systems that prioritizes comfort, utilising optimized indoor air setpoints, which surpasses the rule-based control logic proposed by the existing standards. To analyse the proposed control framework, a novel mathematical model for the energy, economic, and environmental performance analyses of train HVAC systems, which can incorporate weather data associated with actual railway paths, is developed and validated. To prove the potential of the proposed method, a proof-of-concept analysis is conducted. In particular, for an existing railway coach operating in Italy, the standard and the innovative control logic are tested and compared. The results show an interesting thermal comfort hours increase (≃+1000 h) and energy savings (−27 % yearly), proving the benefits potentially achievable by adopting the proposed method.

Abstract This paper presents and discusses the performance improvement and operational flexibility of a Single-Stage Combined Absorption Power and Refrigeration Cycle (SSAPRC) with an integrated compression booster. The compression booster is placed between the absorber and the evaporator. A mechanical compressor and later a thermal compressor (vapor-ejector) are used as a compression booster. This added feature is very interesting for this type of cycle, because they generate power that could be used in the cycle itself to produce the compression needed to enhance the cycle’s performance. The energetic and exergetic performance of these new modified combined absorption cycles have been analyzed for typical thermal boundary conditions and design parameters. The integration of a mechanical compressor or a vapor ejector reduces the required driving temperature of the cycle, and when a certain split ratio is exceeded the system can work in dual-output mode producing power and cooling. The use of a vapor ejector further improved the net power output of the system. The proposed cycle configurations have an outstanding adaptability and flexibility to respond to the variation of heat source and heat rejection temperatures by adjusting the compression ratio. These cycles are therefore excellent candidates to provide simultaneous power and refrigeration, using renewable energy sources such as solar thermal energy, biomass or waste-derived fuels in polygeneration systems for remote locations or those with difficult access to the electrical grid.

Abstract Nowadays, due also to high hygrothermal comfort requirements, the energy consumption for heating/cooling of modern trains can reach 30% of the related overall electricity demand. Energy-saving of train Heating, Ventilation and Air Conditioning systems can be suitably assessed through dynamic simulation approaches. Specifically, the weather solicitation has to be dynamically accounted for by considering the actual moving train location and orientation. Through such methodology different innovative actions for energy efficiency, environmental impact reduction and comfort enhancement can be analysed by also assessing their economic feasibility. In this paper, a novel simulation tool for the complete performance analysis of trains was developed in TRNSYS environment. To show the capabilities of the considered approach, a novel case study referred to an existing medium-distance train operating in South Italy is presented. Heating/cooling loads and demands, and the related electricity requirements, are dynamically assessed for the standard and revamped train. Several energy saving actions are considered for the coupling between the envelope and the Heating, Ventilation and Air Conditioning systems enhancement. The obtained results return significant benefits in terms of energy saving, avoided CO2 emissions and comfort. Paybacks depend on operating conditions. Useful design and operating criteria for trains manufacturers and users are provided.

Abstract In this work the thermoacoustic performance of a stack realized with open-cell foam is analysed. Starting from the elementary cell and its strut parameters the pore structure has been investigated to improve the power conversion inside a standing-wave thermoacoustic engine. The so called “Johnson-Champoux-Allard” model is used for this scope. Results are compared with those provided by ordinary stack realized with straight pores whose cross-sections have regular shapes (i.e. circular, parallel plate). Since thermoacoustic performance is strongly affected by stack properties (such as its length, its porosity, the geometry, the shape of its pores, the operating frequency as well as the type of material), an optimization procedure has been used to optimize the thermoacoustic engine performance for the same working conditions (thermal power provided by the heat exchangers and the related temperatures). This study reveals that, for the investigated working conditions, partially reticulated open-cell foams have the best performance with respect to fully reticulated open-cell foams and the traditional stacks.

Abstract The effects of five commercially available hydrolytic enzyme additives on methane yields from dehydrated paper pulp sludge (DPPS) were determined in 5L pilot-scale reactors operated in semi-continuous mode for 60 days. Methane production was 40% and 43% higher in reactors receiving Novozymes and Novalin additives, respectively, compared to controls. Effects of time of DPPS inclusion on bacterial and archaeal microbial communities were many times larger than effects of enzyme type as enzyme addition did not produce rearrangements larger than random fluctuations observed in reactors receiving only DPPS. The ratio between volatile organic acids and alkalinity signified progressive decrease in process stability until day 45 irrespective of enzyme supplementation. Complementation with clarified pig slurry (1.5% vol.) for subsequent 15 days effectively stabilized process parameters and was sufficient for microbial communities to maintain DPPS hydrolytic capacity and process additional carbon flow derived from hydrolytic activity of enzyme additives. Consequently, initially unadapted full-scale biogas plant inoculum was capable of significantly increased methane yields from DPPS. Based on annual DPPS availability in EU the potential for additional energy recovery was estimated to be in the range of nearly 1 TJ.

An application of the theory of exergetic cost and the exergoeconomic evaluation of a conventional vapour-compression heat pump are described. Included are effects of malfunctioning by plant components. Evaluation of the achievable exergy saving by restoring the original efficiency of a single device is included. A vapour-compression heat pump is used in a numerical example.

The present study investigates the use and implementation of energy efficient measures and strategies for building applications, toward the Nearly Zero Energy Buildings target. Specifically, objective of the study is to implement building integrated photovoltaic thermal devices coupled with a phase change materials heat exchanger acting as an active thermal storage building component, with the aim to add flexibility to the building while still maintaining indoor comfort conditions. To show the potentials of the novel configuration proposed in this paper, a multi-zone grey-box model is developed and validated to capture the thermal dynamics of a building, and a control strategy applied to the whole system is developed for energy management purpose. The whole simulation model, including thermophysical properties of the building-system and the control features, is implemented in a MATLAB environment. To assess the model and application potentials toward the optimal design and operation of the proposed system for energy efficiency and flexibility goals, a suitable case study analysis is conducted. Thus, a sensitivity analysis, using an evolutionary algorithm, is performed by considering economic and energy objective functions which focuses on the reduction of the building energy demand, load variability and economic aspects. In this regard, the optimal design configuration is underlined in a way that the operation of the components can be maximized to provide flexibility to the building: in average working conditions one single layer of PCM can provide around 186.3 Wh/K per unit of temperature and width. A rule-based management strategy is proposed to prove the possibility to shift and shave the energy peaks during high energy request periods, demand response events. Finally, by considering an approximate economic calculation, the simple payback, taking into account only the positive effects on the winter management, is around 13.5 years.

This paper presents a detailed finite-volume model of a concentrating photovoltaic/thermal (PVT) solar collector. The PVT solar collector consists in a parabolic trough concentrator and a linear triangular receiver. The bottom surfaces of the triangular receiver are equipped with triple-junction cells whereas the top surface is covered by an absorbing surface. The cooling fluid (water) flows inside a channel along the longitudinal direction of the PVT collector. The system was discretized along its axis and, for each slice of the discretized computational domain, mass and energy balances were considered. The model allows one to evaluate both thermodynamic and electrical parameters along the axis of the PVT collector. Then, for each slice of the computational domain, exergy balances were also considered in order to evaluate the corresponding exergy destruction rate and exergetic efficiency. Therefore, the model also calculates the magnitude of the irreversibilities inside the collector and it allows one to detect where these irreversibilities occur. A sensitivity analysis is also performed with the scope to evaluate the effect of the variation of the main design/environmental parameters on the energetic and exergetic performance of the PVT collector.