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Approximately 35 % high-temperature waste heat in the steel industry is carried by blast furnace slag and steelmaking slag, and thermal radiation is a primary pathway for this waste heat to dissipate into the ambient environment. Thermophotovoltaic (TPV) systems can convert short-wavelength thermal radiation into electrical energy, but the long-wavelength radiation is still wasted. Here, this work introduces a concept of spectral-splitting (SS) for full-spectrum thermal radiation utilization, allowing simultaneous waste heat recovery by TPV and heat-to-power methods such as Stirling engine (SE). To further demonstrate this concept, an SS TPV-SE system is designed. An optical transmission window of 0–1.7 μm is applied for TPV, and an over 5 μm absorption window is applied for SE. Results show that, with a 0.1 × 1 m molten slag chute, the SS TPV-SE system yields an output power of over 1300 W and achieves an overall efficiency of around 19 %, resulting in an about 58 % improvement compared to the standalone TPV system, and leads to a CO 2 emission reduction of 7516 kg/year. Provided the improved energy efficiency and environmental sustainability, the spectral-splitting concept presented in this work provides a promising approach to enhancing waste heat recovery in the steel industry. • A novel concept of spectral-splitting and cascade utilization of thermal radiation is introduced. • A SS TPV-SE structure for waste heat recovery in steel industry is developed and evaluated. • Numerical simulations are performed to optimize the operating parameters of the SS TPV-SE system. • A comparison is conducted between the SS TPV-SE system and existed WHR methods in terms of efficiency and output power. [ABSTRACT FROM AUTHOR]

The high thermal management energy consumption is a crucial reason for the severe driving range degradation of electric vehicles (EVs) at low temperatures. Currently, heat pumps and waste heat recovery technology have been widely used to improve the energy efficiency of thermal management systems and alleviate the driving range degradation of EVs in low-temperature environments. However, the conventional waste heat recovery heat pump, with the ambient air and waste heat as heat sources, operates at a single evaporation temperature, resulting in poor performance of the heat pump at low temperatures because the low-energy-grade ambient air source limits the recovery efficiency of the high-energy-grade waste heat. To address the issues, in this study, a thermal management system with dual-evaporation temperature for EVs, which can switch between the single-evaporation temperature and the dual-evaporation temperature modes to match the energy grade of the ambient air and waste heat sources, is proposed. A simulation model of the proposed system is established and validated. The appropriate compressor volume ratio, the heating performance under different operation modes, the energy-saving operation strategy adapted to different operating conditions, and the energy-saving and range extension effect of the proposed system are investigated. The results indicate that the heating energy consumption in dual-evaporation temperature mode can be reduced by 25.2 % and 9.5 % compared to that in single-air source mode and single-evaporation temperature mode, respectively, at −10 °C with waste heat of 1500 W. In Beijing, the proposed system and operation strategy can achieve an average heating energy saving of 14.2 % and an average driving range extension of 12.4 % under HWFET, compared with the conventional thermal management system without waste heat recovery. • A thermal management system with dual-evaporation temperature is proposed for electric vehicles. • Energy-saving operation strategy adapted to different operating conditions is presented. • Heating energy can be saved by 33.3 % at −10 °C with waste heat of 2000 W. • More than 10 % driving range extension can be achieved in January in Beijing. [ABSTRACT FROM AUTHOR]

Thermophotovoltaic (TPV) technology converts thermal radiation into electricity directly based on the photovoltaic effect of TPV cells, and have enormous potential applications in waste heat recovery, grid-scale energy storage, concentrating solar-thermal power generation, etc. Currently, the lack of a standardized method for measuring energy conversion efficiency of TPV cell hinders the objective assessment and comparison of TPV cells as well as the selection of cells for diverse applications. This work theoretically and experimentally demonstrates a towards-standardization TPV cell efficiency measuring system with near-perfect blackbody incident radiation spectra in the temperature range of 600–1600 °C, which is described by Planck's law and exhibits stability, reproducibility, and color temperatures close to those in practical TPV applications. By conducting a systematic characterization of thermal radiation and TPV cell, we show a good agreement between the calculated and the measured incident spectra, and the prediction error of the TPV cell model is less than 1.7%. In addition, we propose to use the relative error due to the deviation from the perfect blackbody spectrum to quantify the quality of a realistic incident spectrum. Compared to the conventional experiment arrangement where cells are placed directly towards the opening of high-temperature blackbody radiation source, our system, featuring an optical path configuration with an off-axis parabolic reflector, significantly reduces the relative error by three to four orders of magnitude, and those in our system is less than 0.68% for the GaSb and InAs cells. Our thorough study and the developed measurement system will shed light on the urgently needed standard evaluation method of TPV cell efficiency, which can substantially facilitate the objective appraisal of the cell's performance and accelerate the application of efficient TPV energy conversion system. • A TPV cell efficiency measuring system is experimentally demonstrated. • Near-perfect blackbody incident radiation spectra at 600–1600 °C are provided in the system. • The spectrum-related efficiency measuring error is less than 0.68% for GaSb and InAs cells. • A TPV cell model is established whose prediction error is less than 1.7%. [ABSTRACT FROM AUTHOR]

In this study, to investigate the dynamic characteristics of automotive thermoelectric generators (ATEGs), a detailed transient energy, exergy, and economics analysis is conducted for a novel ATEG with heat pipes and a traditional ATEG for the first time. Moreover, this study provides a comprehensive analysis of the discrepancies between the results derived from the steady-state model and the transient model. To achieve this objective, a transient CFD and thermal-electric hybrid numerical model is established to accurately predict the transient characteristics of the ATEG. Results indicate that the novel ATEG achieves average improvements of 60.99 % in output voltage and 32.98 % in output power over the traditional ATEG during a complete driving cycle. Additionally, the steady-state model overestimates the performance of the ATEG. The exergy efficiency is minimally impacted by the use of heat pipes and fluctuations in transient exhaust heat, consistently remaining around 19 % for both ATEGs. In a single driving cycle, the novel and traditional ATEGs generate 0.0442 kWh and 0.0307 kWh of electricity, respectively. The cost payback periods are 2.86 years for the novel ATEG and 1.83 years for the traditional ATEG, and it is found that using steady-state models for economic analysis may underestimate the cost payback period. This study successfully bridges the research gap in energy, exergy, and economic analyses under transient conditions, offering valuable insights into the dynamic properties of ATEGs. • A transient energy, exergy and economic analysis of ATEGs is performed. • Dynamic performance differences between two ATEGs under driving cycles are compared in detail. • A comparison is made between the calculations of steady-state and transient models. • The exergy efficiency is largely unaffected by the transient fluctuating heat source. • Steady-state model overestimates ATEG's performance, underestimating the cost recovery period. [ABSTRACT FROM AUTHOR]

The production of hydrogen by proton exchange membrane water electrolyzers (PEMWEs) integrated with renewable energy sources is receiving significant interest for its environmental benefits. While, powered by intermittent renewable electricity, the frequent start-up/shut-down events put forward an urgent need for PEMWEs to have rapid start-up capabilities and will significantly accelerate the degradation of electrolyzer, increasing the failure risk and cutting down the cost-effectiveness. In this paper, a novel hydrogen production and hot standby dual-mode system aiming at fast start-up ability as well as slow degradation is proposed. Thermal energy storage based on phase change material (PCM) is used to manage the heat of the electrolyzer by recovering the heat produced during hydrogen production mode and utilizing it to maintain the electrolyzer temperature during hot standby mode. The operating strategy has been given and the dynamic performance has been analyzed. Results indicated that an electrolyzer with a capacity of 397.2 Nm3/h can cut start-up time by up to 785 s (from 1067 to 282 s). In the extreme situation, from 0 A to the rated current of 320 A, the start-up time of PEMWE is reduced from 118 s to 88 s, and the voltage overshoot is reduced by 23.91 % when compared to that of a cold start. Moreover, through waste heat recovery and utilization, the system efficiency can be improved. The system employing PCM with a higher melting point (64 °C) achieves an efficiency of 58.86 %, which is 1 % and 2.2 % greater than the systems using PCM melting at 45 °C and without heat storage, respectively. • Hydrogen production and hot standby dual-mode system via heat storage and PEMWE. • Recover heat to keep hot standby temperature, for high efficiency, fast startup and low degradation. • Dynamic response analysis, multi-criteria evaluation by analytical hierarchy process. • Reduce startup time by 785 s, rise efficiency by 2.2 %, reduce cost due to lower degradation. [ABSTRACT FROM AUTHOR]

A prototype of a multistage cooling system with a cooling capacity of 20 kW is assembled and studied. The traditional single-stage system is split into two sub-systems according to the temperature level, which reduces the temperature difference and irreversible heat transfer loss, and further improves the system's energy efficiency. The system mainly features three modes including free-air cooling, refrigeration-based cooling and waste heat recovery, which can achieve efficient cooling while capable of recovering the waste heat to the surrounding heat users. The efficiency of the proposed cooling and heat recovery system was assessed by measuring its energy reuse effectiveness (ERE). The energy savings and environmental benefits of the system were analyzed across five cities in China, each representing different climates. Results indicate that the system achieved an ERE of 0.91 in Beijing, 38.9 % lower than the national average of the city. Additionally, an economic analysis showed a payback period of less than two years for the proposed system across all climates considered, which is 30 % shorter than that of a single-stage cooling system. • A multi-stage data center cooling system with waste heat recovery is proposed. • Temperature gradation reduces heat transfer temperature difference and irreversible loss. • Heat transfer performance of a 20 kW scale system is experimented and analyzed. • Energy Reuse Effectiveness in Beijing is 0.91, and payback period is within 2 years. [ABSTRACT FROM AUTHOR]

The power consumption of data centers (DCs) has increased dramatically due to the rising demand for computing power. However, a huge amount of low-grade electronic waste heat generated by these DCs is dissipated directly into the environment with the assistance of the energy-driven cooling system, thereby doubling the production of energy waste. Thus, innovative cooling and low-grade waste heat recovery technologies in DCs are urgently needed. In this study, we proposed a loop heat pipe battery (LHPB) with dual gradient wicks relay. According to the gradient wick relay strategy, the heat leakage at the evaporator inlet was alleviated, allowing the vapor inside to remove heat more rapidly and impact the micro-generator installed at the condenser inlet. Furthermore, two kinds of high-efficiency microgenerators were designed. The experimental results showed that under forced convection cooling of a 12 V fan, the cooling capacity of the LHPB with wicks relay was 288 W with a junction temperature maintained below 85 °C. The minimum total thermal resistance and nominal power usage effectiveness were 0.20 °C/W and 1.0015, respectively. The maximum rotor speed was 10,716 r/min and the maximum output power of the two generators was 195 and 280 mW. The LHPB with wicks relay demonstrated an innovative solution to promote low-grade waste heat harvesting during efficient electronics cooling and the potential to be a promising energy-saving device in future DCs. The proposed optimization strategy provides guidance for the evolution of the LHPB with wicks relay. • A dual-wick heat pipe battery for promoting cooling and waste heat harvesting was proposed. • Two adaptable high-efficiency microgenerators were developed and compared. • A remarkable electrical power of 280 mW was obtained when cooling a 200 W electronic chip. • The LHPB with wicks relay successfully drove various electronic devices during cooling. [ABSTRACT FROM AUTHOR]

This study focuses on harnessing excess heat from Power-to-X technologies in future energy hubs. By coupling thermodynamics with an optimization model, a novel analysis is performed using the Greenlab Skive energy hub, which includes hydrogen and methanol synthesizers, as a case study. Pinch analysis techniques are employed to design a heat exchanger network that can thermally integrate processes within the energy hub. Through the EnerHub2X modelling framework, three scenarios are optimized to explore and compare the potential of excess heat recovery. Excess heat is utilized through an optimally designed heat exchanger network, which achieves up to 3.49 MW of heat recovery. This leads to increased profits due to reduced natural gas costs and higher methanol sales. Upgrading excess heat and distributing it to the district heating network yields the highest profit, driven by increased compressed hydrogen and methanol production and the sale of heat to district heating. Thermal integration reduces waste heat by 14.5%, while utilizing excess heat in the district heating network results in 60% further reduction. An economic assessment confirms the feasibility and profitability of the project. Sensitivity analyses are undertaken to analyse the impact of critical parameters on the model, such as electricity and heat prices, along with the selling prices of methanol and hydrogen. The results highlight that excess heat utilization enhances profitability, energy efficiency, and sustainability. By implementing waste heat recovery techniques and exploring alternative options, future energy hubs can strengthen their business models and play a crucial role in Europe's green transition and clean fuel production. • Pinch analysis is combined with a multi-carrier energy system model. • Excess heat utilization value from Power-to-X production in energy hubs is assessed. • Effective use of excess heat significantly reduces waste heat and gas consumption. • Connection of large-scale electrolysis to district heating provides additional value. [ABSTRACT FROM AUTHOR]

Abundant and stable industrial low-grade waste heat (LGWH) creates opportunities for adsorption refrigeration (AR) using natural refrigerants to realize near-zero-carbon cooling applications. In this study, to achieve the simultaneous optimization design of working pairs, processes and networks, a superstructure of the integrated waste heat recovery network and adsorption refrigeration (WHRN-AR) system is extracted, and a multi-scale mixed integer non-linear programming (MINLP) optimization framework is formulated. At the microscopic scale, a general adsorption capacity prediction model based on the exponential decayed adsorption phase density distribution, shape selection adsorption concentration and zeolite's accessible volume is developed. At the mesoscale level, a comprehensive LGWH-driven AR thermodynamic process is constructed to effectively couple LGWH recovery and cold energy production. At the macroscale level, the energy network, including waste heat recovery, medium streams, pipes and pumps, is modelled to optimize the entire system. The WHRN-AR system and optimization framework are successfully applied to three practical industrial designs with different cooling specifications, in which the total annual cost (TAC) is minimized, 11 zeolite/NH 3 working pairs, processes and networks are simultaneously optimized, and energy efficiencies are observed. In case 3, 4 working pairs can achieve a maximum cooling capacity (Q ev) of 1800 kW at a desorption temperature of 343 K, and the integrated system reduces CO 2 emissions by 76.6 %, lowing them to 42.2 kg/h compared to the electric refrigeration. Last, to represent the practical energy requirement for LGWH recovery, a power-based coefficient of performance for cooling (COP C P) is further introduced to analyze and compare the solution results. [Display omitted] • A new multi-scale MINLP framework is formulated for the WHRN-AR system. • A prediction model for adsorption capacity is developed to screen working pairs. • 11 zeolite/NH 3 working pairs, processes and networks are simultaneously optimized. • A power-based coefficient of performance for cooling (COP C P) is presented. • The integrated system can reduce 76.6 % of CO 2 emissions for the Q ev of 1800 kW. [ABSTRACT FROM AUTHOR]

Increasing renewables' portion in energy matrix around the world has made the scientists to propose innovative techniques for recovering the available waste heat of energy systems to produce excess energies in the Waste-to-X framework. This study proposes a green sustainable multi-generation energy system (MES), producing power, heat, cold, and potable water, driven by a hydrogen-fueled gas engine. The engine's heating potential is recovered to run some bottoming systems comprising proton exchange membrane electrolyzer (PEME), absorption/electrical chiller cycles (ACC/ECC), organic Rankine cycle (ORC), dryer unit, heat pump cycle (HPC), and reverse osmosis desalination unit. The combination of ACC with dryer and HPC is an innovative idea which utilized to produce heating load in this study. A detailed sustainability evaluation framework (technical and eco-environment) is derived to approve performance of the MES. The construction feasibility of the MES in different climatic conditions is sought by considering 5 case study cities around the world. Afterwards, best working fluid of the ECC/HPC and ORC is selected and then the sensitivity of the MES performance to design variables is investigated trough a comprehensive parametric study. Results illustrated that the MES shows the best performance in the city of Willington in which the emission of 84.8 tons of CO 2 is prevented annually which is equivalent to saving of 16,291.6 m3 natural gas. The working fluid selection outputs proved that considering R22 and R123 for ECC/HPC and ORC leads the best techno-economic performance. The sensitivity study demonstrated that the highest and lowest influence of the MES's techno-economic performance is related to the ECC evaporator and ORC turbine temperatures, respectively. So that, increasing ECC evaporator temperature led to a relative variation of 8.2%, 4.5%, and 7.5% in energy recovery factor, exergy efficiency, and levelized cost of productions, respectively. [Display omitted] • Renewable-based combined system is designed to produce power, heat, cold and potable water. • Parametric investigation is conducted to study impact of some decision variables. • The feasibility of system implementation is sought in five cities around the world. • CO 2 emission reduction and natural gas saving of 84.8 tons and 16,291.6 m3 is achieved. [ABSTRACT FROM AUTHOR]

Global reliance on traditional cooling systems is a pressing concern, especially given their substantial energy demands and refrigerant-related greenhouse gas emissions. The need for sustainable cooling solutions is especially urgent in hot and humid regions. This study presents an innovative solution by introducing a compact, solar-driven cooling system that integrates a Desiccant Wheel (DW) and a Thermoelectric Cooler (TEC). This novel combination leverages solar energy to enhance cooling efficiency while reducing environmental impact. The system's performance was tested through experimental methods and non-dimensional analysis, which served to validate the TRNSYS simulation. The simulation included custom components representing the DW and TEC's physical characteristics. Results demonstrated that the system effectively reduces air temperature and humidity to maintain thermal comfort, achieving Coefficients of Performance (COP) of 0.94 and 1.13in Toronto and Vancouver, respectively. A key feature of the system is the heat recovery design, which uses waste heat from the TEC to regenerate the desiccant material, enhancing COP by 68%. Further analysis through TRNSYS simulation explored the system's adaptability to various climate conditions by testing a range of temperatures (26–43°C) and relative humidity levels (30–100%). This analysis identified three operational regions, optimizing the system's application based on environmental conditions. A life cycle assessment determined a Global Warming Potential (GWP) of 0.0172 kg CO 2 per kW of cooling capacity and an Energy Payback Time (EPBT) of 3.34 years. The economic analysis indicated a total system cost of $2719, predominantly due to the DW and TEC components. In conclusion, this research offers a sustainable and efficient cooling system that provides thermal comfort in hot and humid climates, marking a significant advancement in climate control technology. • Evaluation of innovative hybrid cooling for improved indoor climate control. • The validated system boosts COP from 0.56 to 0.94, ensuring thermal comfort. • Heat recovery strategy boosts system efficiency by 68% in diverse climates. • Life cycle assessment shows 0.0172 kg CO 2 per kW of cooling capacity. • The system demonstrates a 3.34-year energy payback, highlighting cost savings. [ABSTRACT FROM AUTHOR]

Ammonia has attracted significant research attention due to its high hydrogen content and lack of elemental carbon. Unfortunately, the thermal efficiency of ammonia gas turbines is relatively low. To address this problem, this paper proposes a cyclic system that combines an ammonia gas turbine with the T-CO 2 power cycle. The cycle, based on comprehensive energy distribution and utilization, makes full use of the cooling capacity of liquid ammonia fuel to cool CO 2 below the critical point and uses the waste heat of the ammonia gas turbine in stages. The paper begins by establishing and validating a thermodynamic model of the combined cycle. Numerical simulations show that, under the basic operating conditions, the energy efficiency of the combined cycle is 53.44%. Next, an analysis of the regenerator of the bottom cycle shows that it introduces a low heat source, which avoids a pinch point in the regenerator. Finally, the study investigates how different key parameters affect the performance of the combined cycle. A calculation indicates that changing the temperature and pressure of the ammonia turbine inlet increases the efficiency of the combined cycle by up to 32.75%. The maximum efficiency of the combined thermal cycle is 62.42%. For a gas turbine inlet pressure not exceeding 5 bar, a small pressure ratio improves the cycle efficiency. • A combined ammonia gas turbine and T-CO 2 cycle system is proposed and evaluated. • The cold energy of liquid ammonia is used to condense the CO 2. • Adding a T-CO 2 bottom cycle increases the efficiency by 32.75%. [ABSTRACT FROM AUTHOR]

The fully open absorption heat pump (FOAHP) is a novel approach for recovering and reusing waste heat and water from flue gas. By employing open-type towers in the absorption, regeneration, and condensation processes, the recovery efficiency is substantially enhanced while concurrently lowering system costs. However, as a complex system with multiparameter, nonlinear, and strongly coupled characteristics, research on system design is lacking, which hinders the widespread application of FOAHPs. To address this issue, this study proposes a model-based optimization framework to determine the design parameters of FOAHPs. A physical model of the system was established and utilized to obtain a matrix of system performance parameters for 6700 sets under a wide range of design parameter inputs. The dataset was then adopted to train and verify the data-driven model of the system, which reduced the computational time to 0.085126 s and provided a foundation for global optimization with multiple design parameters. Subsequently, a sensitivity analysis of the design parameters was conducted to elucidate their influence on the system characteristics. Based on data-driven model, the system's design parameters were globally optimized by combining genetic algorithm with the optimization objectives of the coefficient of performance (COP), flue gas recovery efficiency (η), and life cycle benefit (LCB). Results show that the optimized design parameters improved the COP and η of the system from 0.835 and 0.543 to 1.089 and 0.722, respectively, and the LCB from 71,309 USD to 149,843 USD, at which time the system heating capacity increases from 470,102 kWh to 840,182 kWh in one heating season. This study provides a foundational framework and data support for the global multi-objective optimization of the design parameters of FOAHPs. • Proposed a novel FOAHP system to recovery waste heat and water from flue gas. • Framework for global optimization of design parameters for FOAHP is established. • Design optimizations of system under the objectives of COP , η , and LCB are obtained. • The optimized COP , η , and LCB increased by 0.25, 0.18 and 78,534 USD, respectively. • Explained from the perspectives of thermodynamics and heat and mass transfer. [ABSTRACT FROM AUTHOR]

Water scarcity and energy crisis have recently become two severe global problems. Low-grade waste heat, a substantial byproduct of energy consumption, promises to provide safe water by driving sorption-based atmospheric water harvesting (SAWH) device. Herein, a low-grade waste heat-driven atmospheric water generator (LWG) is constructed with rapid kinetics at the system level. Solely in 3 h, the device obtains 1.766 g g−1 of water productivity and up to 98 % of water recovery ratio driven by 120 °C of waste heat. Further, an optimized multi-cycle operation strategy is proposed to guide LWG's daily water harvesting, enabling it to predictably obtain over 15 kg m−2 day−1 water productivity by maximizing systemic sorption and desorption-condensation rates. The strategy not only is widely suitable for all SAWH devices, but also provides a universal optimization guideline for sorption-based dehumidification, thermal storage, and electric thermal management. • Low-grade waste heat-driven water generator (LWG) is developed to extract water. • Advanced structural design endows LWG with ideal heat and mass transfer properties. • 1.3 kWh kg water −2 of energy consumption is far superior to most active SAWH devices. • Solely in 3 h, 98 % of water recovery ratio is realized at 120 °C waste heat. • An optimized multi-cycle strategy is proposed to maximum kinetics and water yield. [ABSTRACT FROM AUTHOR]

Waste-heat recovery (WHR) holds significant potential for decarbonising district heating (DH) systems. Yet, its valorisation remains a challenge for a broader adoption. Contracts often establish schemes dictating pricing schedules and calculation methodology. However, DH utilities might leverage their informational advantage about internal operations to determine prices that maximise their own benefits. Such strategic pricing, along with the choice of particular schemes, substantially influences the extent and distribution of WHR benefits. This study explores the effects of various waste-heat pricing schemes and their temporal granularity on two data centre (DC) cases under DH utility's strategic pricing. We propose a bilevel optimisation problem representing the DH-DC interaction, where the DH utility determines its optimal waste-heat price level considering the DC's response. Scenarios include the schemes: operational cost, free (hourly), electricity-cost indexed (daily), and uniform (annual) pricing. Our findings reveal that pricing schemes affect waste-heat utilisation, displacement of specific DH generators, and economic benefits allocation. Granular schemes are the most cost-effective, whereas infrequent schemes boost summer WHR, benefiting DC operators. Notably, the electricity-cost indexed scheme demonstrates divergent outcomes for smaller and larger DCs, offering prices that maximise WHR for smaller facilities and restricting it for the larger ones to periods of low electricity prices. [Display omitted] • Explores 4 strategic pricing cases for waste heat recovery in district heating (DH) • Interaction between DH and waste-heat source is modelled as a Stackelberg game • Pricing scheme granularity results in trade-offs between CO 2 and cost savings • Flatter prices redistribute economic gains more equally, at the expense of CO 2 cuts • Split-incentive on CO 2 reduction: benefiting DH at the expense waste-heat provider [ABSTRACT FROM AUTHOR]

Installing carbon capture and storage (BECCS) capability at existing biomass-fired combined heat and power (bio-CHP) plants with substantial emissions of biogenic CO 2 could achieve significant quantities of the negative CO 2 emissions required to meet climate targets. However, it is unclear which CO 2 capture technology is optimal for extensive BECCS deployment in bio-CHP plants operating in district heating (DH) systems. This is in part due to inconsistent views regarding the perceived value of high-exergy energy carriers at the plant level and the extended energy system to which it belongs. This work evaluates how a bio-CHP plant in a DH system performs when equipped with CO 2 capture systems with inherently different exergy requirements per unit of CO 2 captured from the flue gases. The analysis is based upon steady-state process models of the steam cycle of an existing biomass-fired CHP plant as well as two chemical absorption-based CO 2 capture technologies that use hot potassium carbonate (HPC) and amine-based (monoethanolamine or MEA) solvents. The models were developed to quantify the plant energy and exergy performances, both at the plant and system levels. In addition, heat recovery from the CO 2 capture and conditioning units was considered, as well as the possibility of integrating large-scale heat pumps into the plant or using domestic heat pumps within the local DH system. The results show that the HPC process has more recoverable excess heat (∼3.58 MJ/kgCO 2,captured) than the MEA process (2.09 MJ/kgCO 2,captured) at temperature levels suitable for district heating, which is consistent with values reported in previous similar comparative studies. However, using energy performance within the plant boundary as a figure of merit is biased in favor of the HPC process. Considering heat and power, the energy efficiency of the bio-CHP plant fitted with HPC and MEA are estimated to be 90 % and 76 %, respectively. Whereas considering exergy performance within the plant boundary, the analysis emphasizes the significant advantage the amine-based capture process has over the HPC process. Higher exergy efficiency for the CHP plant with the MEA capture process (∼35 %) compared to the plant with the HPC process (∼26 %) implies a relatively superior ability of the plant to adapt its product output, i.e., heat and power production, and negative-CO 2 emissions. Furthermore, advanced amine solvents allow the BECCS plant to capture well beyond 90 % of its total CO 2 emissions with relatively low increased specific heat demand. [ABSTRACT FROM AUTHOR]

Achieving cost-effective hydrogen production is key to facilitating the use of hydrogen as an alternative to fossil fuels. This study adopts a mixed integer linear programming approach to simultaneously derive the optimal sizing and operation of hydrogen generation sites. Waste heat recovery solutions to serve a district heating network were considered, resulting in an 18.9% reduction in hydrogen production costs compared to conventional designs, with up to 5.3% of the reduction attributable to waste heat utilization. A global sensitivity analysis indicated that renewable availability, imported electricity costs, and electrolyzer conversion efficiency are the most influential parameters in reducing total costs. Additionally, the study explores the impact of modeling fidelity on optimization results, revealing that nominal efficiency assumptions commonly used in the literature can lead to sizing errors and cost inefficiencies. Implementing piecewise linear approximations for electrolyzer performance significantly enhances the accuracy of these predictions. Overall, the findings underscore the crucial interconnection between the optimal sizing and operation of hydrogen generation sites, emphasizing that these should not be treated as separate steps in the design process. This work provides a robust foundation for advancing the optimal design of hydrogen generation sites and offers practical recommendations to reduce hydrogen costs. • Concurrent optimization of sizing and operation of a hydrogen generation site. • Waste heat recovery is considered to reduce total cost of the site. • Levelized cost of hydrogen reduced by 18.9% compared to conventional design solution. • Global Sensitivity Analysis identifies most influential parameters. • Neglecting partial load operation impacts the optimal sizing. [ABSTRACT FROM AUTHOR]

A highly efficient and clean biomass energy-based calcium carbide-acetylene production system, including low-carbon energy supply, solid waste recycling and cascade utilization of waste heat, has been developed for the conventional energy-intensive and highly polluting fossil fuel-dependent calcium carbide industry. This system supplies the carbide-acetylene production plant with energy from the gasification of biomass and converts the plant's solid waste carbide slag into the calcium feedstock required by the plant. The waste heat from the plant's high-temperature exhaust gases is recycled and used via the multi-stage heat exchange, so that the energy cascade conversion and utilization is achieved. A simulation model of the plant is created in Aspen Plus, and a mathematical model for the biomass gasification process and cycle compensation of the calcium source through the Fortran language is written and embedded. When calculating the carbon consumption and CO 2 e emissions of the system, it was found that the carbon consumption and CO 2 e emissions of the conventional process were 5.43 t Coal·t−1C 2 H 2 and 2.25 t CO 2 e·t−1C 2 H 2 , respectively. However, the carbon consumption of the new process was reduced by 65.19%, and carbon emissions by 27.24% in comparison. The energy analysis shows that the energy efficiency of the system is 36.21% for the conventional process and 44.82% for the new processes. The exergy analysis of the effective energy shows that the exergy efficiency of the new process is 73.20%, which is 52.98% better than that of the conventional process. Introduction of an index, the levelized income of acetylene product (LIOA), to characterize the product income of the system. When the price of acetylene is between 2.23 $/kg and 4.19 $/kg, the LIOA for the conventional and the new processes are 1.41 $/kg to 3.38 $/kg and − 1.28 $/kg to 0.68 $/kg, respectively. It is worth noting that the critical price (PC C 2 H 2 ) for products generating net revenue from the new process is 3.17 $/kg. This study is of great importance for the development of a low-carbon biomass-coupled calcium carbide-acetylene process. On the basis of the conventional calcium carbide acetylene production process, a multi-level low-carbon calcium carbide production model coupling with biomass energy drive, high-energy furnace gas waste heat recovery and utilization, and calcium based solid waste recycling is constructed to efficiently promote the transformation of the calcium carbide industry system from the dilemma of high energy consumption, high material consumption, and heavy pollution to green development with low energy consumption, low material consumption, and low pollution. [Display omitted] • An integrated multi-level low carbon strategy is constructed for the carbide industry. • The synergistic effect of multiple objectives on the comprehensive performance is investigated. • The innovative process shows superior environmental and energy conversion capabilities. • A levelized product income analysis enables accurate revenue predictions for the system. [ABSTRACT FROM AUTHOR]

Global issues such as the energy crisis and carbon emissions impulse the development of waste heat recovery and energy storage technologies. In most practical industrial scenarios, the electricity supply and consumption cannot be perfectly matched and effective utilization of waste heat is in urgent need. In the present study, we develop a mathematical model to evaluate the thermally integrated pumped thermal electricity storage (TI-PTES) system to achieve off-peak electricity storage along with low-grade waste heat recovery. A double-layer optimization for screening working fluid pairs with high round-trip efficiency is carried out from 24 fluids of the heat pump and 21 fluids of the Organic Rankine cycle (ORC). In the first-layer multi-objective optimization, 3 types of working fluid pair combination strategies are compared and the great improvement of round-trip efficiency by using zeotropic fluids is proved. Among 7 energy storage temperatures covering from 393.15 K to 423.15 K with an increment interval of 5 K, the highest round-trip efficiency of 101.29% is achieved by adopting the zeotropic fluid pair [90Diethyl ether_10Pentane - 80Butane_20Pentane] at 398.15 K. Furthermore, in the second-layer single-objective optimization, the thermo-economic performance indicators of TI-PTES is evaluated and compared under different designing weighting factor groups, which effectively contributes to the screening of working fluids according to designer's trade-off. Finally, through varying energy storage temperatures and designing weighting factors, optimal working fluid pair recommendations including pure fluids and zeotropic ones were proposed to the fluid selection of TI-PTES. • The double-layer optimization procedure is proposed for working fluid pair screening. • 3 fluid pair combination strategies are compared under 7 energy storage temperatures. • The highest round-trip efficiency of 101.29% is obtained by the zeotropic fluid pair. • Thermo-economic indicators are effectively adjusted by 3 weighting factor groups. • Working fluid pair recommendations including pure and zeotropic fluids are offered. [ABSTRACT FROM AUTHOR]

To realize rapid cooling of the battery at high temperatures and effective latent heat recovery from phase change materials (PCMs), a thermoelectric-based battery thermal management system (BTMS) is proposed. Additionally, a transient multiphysics numerical model is developed to predict the system's thermal performance, and the concept of the latent heat recovery rate of PCMs is introduced. Results show that the introduction of thermoelectric coolers (TECs) significantly enhances the system's efficiency in cooling the battery at high temperatures (Stage 1) and recovering PCM latent heat (Stage 2). The overall thermal performance can be further improved by utilizing PCMs with a higher mass fraction of expanded graphite (EG) or increasing the TEC input current. Moreover, after the end of Stage 2, the power supply for TECs is interrupted, and the system enters Stage 3, which only relies on PCMs to control the battery temperature. The duration of Stage 3 increases with the EG mass fraction, achieving a peak of 3830 s at an EG mass fraction of 12%. Considering the thermal performance and power consumption of the system, the optimal solution is determined as an EG mass fraction of 12% and a TEC input current of 4 A. In this situation, the required time for Stage 1 and Stage 2 is 170 s and 620 s, with the latent heat recovery rate of PCMs up to 361.94 J/kg/s. The findings will provide new insights for the development of the thermoelectric-based BTMS. • TEC helps to recover the latent heat of PCMs. • A thermal-electric-fluid multi-physical field numerical model for the BTMS is developed. • The integration of TEC significantly improves the cooling efficiency of the BTMS. • The 12%EG-based PCM and 4 A TEC input current are selected as the optimal configuration. [ABSTRACT FROM AUTHOR]

The accelerating urbanization, rapid industrial development, and excessive consumption of fossil fuels pose survival challenges such as energy depletion and environmental degradation for humanity. In the context of industrial park development, constructing a low-carbon energy system, increasing the proportion of renewable energy, enhancing energy-level matching, and utilizing heat pumps for deep waste heat recovery are effective approaches to reduce fossil energy consumption and alleviate environmental pressures. Addressing issues such as diverse thermal flows in industrial sites, complex electricity-heat-cooling energy demands, and unclear industrial-building energy coupling mechanisms, this paper proposes a two-stage planning framework, comprising the following five steps: (1) constructing a waste heat utilization system centered around heat pumps, (2) establishing a mechanism for matching heat sources, equipment, and thermal sinks, (3) establishing an energy conversion model and energy quality quantification system, (4) optimizing waste heat utilization path allocation, and (5) conducting a system energy flow analysis. Case studies demonstrate that the proposed system achieves optimized matching of multiple heat sources and sinks in industrial and building scenarios through thermal integration, meeting diverse energy demands in the park, including electricity, cooling, and multi-grade heat. After coupling with traditional steam pipeline networks, the annual total cost and annual steam power consumption decrease by 33% and 39% respectively, with a waste heat contribution rate of up to 26% and a renewable energy penetration rate of up to 25%, and a waste heat recovery system payback period of 6 years. By establishing an energy quality quantification system and conducting multi-objective optimization considering losses and economic costs, this paper provides Pareto frontier solutions, offering references for engineering proposals. The proposed networked waste heat recovery system is characterized by low energy consumption and high economic efficiency, effectively integrating the energy characteristics of industrial parks and demonstrating engineering applicability. [Display omitted] • Focusing on industrial-building energy conjugation issues • Proposing a low-carbon energy system planning framework for industrial parks • Establishing a networked matching mechanism for cold and hot flow streams • Short system recovery cycle, good economic performance • High contribution rates of waste heat and renewable energy, evident low-carbon effect [ABSTRACT FROM AUTHOR]

In the face of climate change, energy efficiency has become an urgent global concern. Exchanging energy between industrial sectors and urban buildings offers a promising avenue to enhance efficiency, mainly through energy exchange. This study establishes a generic method to facilitate designing optimal energy usage for districts with residential and industrial/commercial stakeholders in close proximity. Specifically, it focuses on harnessing industrial excess heat to meet the space heating needs of neighboring buildings. Given pervasive uncertainty in numerous parameters, a thorough global sensitivity analysis demonstrates the significant influence of specific factors, enabling the selection of more robust solutions by considering uncertainty in the most impactful parameters. This work validates the approach using a real case study in Montréal, Canada and underscores the advantages of district energy systems. Notably, this approach demonstrates the potential for a remarkable 96% reduction in emissions compared to current emission levels. The results clearly illustrate that disrupting traditional energy supply arrangements can play an essential role in reducing emissions within urban environments, thus taking critical steps toward achieving net-zero cities and society. • Introducing a generic optimization model for urban heating system retrofitting. • Decarbonizing building heat demand through industrial excess heat recovery. • Performing global sensitivity analysis to prioritize model parameters. • Optimizing decisions in uncertain conditions. • Demonstrating the potential for 96% annual emissions reduction in a real case study. [ABSTRACT FROM AUTHOR]

This paper investigates waste heat (WH) valorisation on maritime vessels from a systemic perspective. It aims to demonstrate how a set of innovative waste heat recovery (WHR) technologies can synergistically work together to valorise waste heat in multiple ways. It proposes and develops a dedicated techno-economic analysis framework and model, surpassing previous literature that focused on individual technologies or specific combinations. Employing a Mixed Integer Linear Programming (MILP) approach, this study evaluates the dynamic and flexible operation of the WHR system throughout the round-trip journey of a vessel. Identifying the most profitable WHR system layout, determining the capacity of technologies, optimising the interconnections between technologies, and establishing strategic WH dispatching are all among the key objectives of the study. An average-scale vessel with a 36 MW diesel engine, is selected for this study which involves a 17-day journey with multiple stops in Northern Europe. The vessel adequately represents the complexity of onboard energy systems in terms of types and variability of demands, as well as WH availability. The proposed WHR system, which is tailored for the selected vessel, integrates three active technologies: an isobaric expansion engine (IEE) to contribute to mechanical power demand, a sorption system for providing cooling, and an advanced Organic Rankine Cycle (ORC) for trigeneration of power, heating, and cooling. All technologies are supported by the passive WHR technology of Thermal Energy Storage (TES). The results show that deployment of the optimised WHR system onboard the selected vessel enhances energy efficiency by 5 to 7.5 percentage points and reduces fuel consumption by 13%. The study also explores economic key performance indicators (KPIs), such as the Internal Rate of Return (IRR) which is found at about 15%, clearly evidencing a compelling solution to ship owners. Additionally, the discussion includes a detailed analysis of the contribution of individual technologies in covering onboard demands, as well as their synergistic interactions. This work clarifies the role, value, and benefit of WHR technologies onboard, advancing the understanding from individual WH recovery interventions to a system-level approach. This is especially valuable in practice, considering its adaptability across various vessel types within the global fleet. • Comprehensive techno-economic analysis of waste heat recovery on maritime vessels • Unified techno-economic framework for integrated optimization of multiple technologies • Emerging technologies considered such as ORC, thermal energy storage, Sorption • Promising technical and economic potential, up to 14% energy savings • Identified technology and system-level advancements needed to increase competitiveness [ABSTRACT FROM AUTHOR]

Thermoelectric technology plays a crucial role in harnessing waste heat from automobile exhaust, and developing low-resistance and high-efficiency thermoelectric generator is currently a focal point of research. The intermediate fluid thermoelectric generator (IFTEG) introduces a structural modification to conventional designs by utilizing boiling-condensation heat transfer of the intermediate fluid to enhance power generation performance. In this study, we constructed an experimental system to investigate the thermoelectric characteristics of IFTEG. The results demonstrate that the IFTEG outperforms traditional thermoelectric generators, exhibiting a remarkable increase in total output power ranging from 171% to 283%, a reduction in pressure drop ranging from 23% to 42%, and a significant improvement in voltage distribution uniformity across the modules. Increasing the exhaust temperature and flow rate significantly enhances the net output power while minimally affecting the voltage distribution uniformity. The net output power of 10.17 W and the net thermoelectric conversion efficiency of 1.39% are achieved at 200 °C and 30 m3/h. Overall, this novel generator offers advantages such as low pressure loss, high efficiency, and high reliability. The findings of this study provide valuable guidance for the development of exhaust thermoelectric generators. • The thermoelectric performance of IFTEG is experimentally investigated. • The power output of IFTEG can be enhanced by 171%–283%. • The pressure drop of IFTEG be reduced by 23%–42%. • The distribution of module voltage becomes more uniform. [ABSTRACT FROM AUTHOR]

Wastewater heat, a promising alternative to traditional district heating and cooling sources, can be recovered using heat pumps and transmitted to surrounding buildings for winter heating and summer cooling. Despite its potential benefits, the policies to support wastewater heat recovery remain limited. This study provides support policies for local governments to encourage energy recovery in urban wastewater treatment plants, incorporating subsidies and renewable energy certificates. The local government aims to maximize the recovered energy, minimize the subsidy expenditure, and minimize the certificate price. Urban wastewater treatment plants seek to optimize producer profits under realistic planning constraints. This model was applied in Chengdu, China, which indicates that plants with a daily treatment scale exceeding 30,000 m 3 can invest in heat recovery without support policies, achieving recovery ratios of only 27%–29%. As the calculated electricity charge accounts for about 90% of operating cost, the electricity price subsidy proves the most significant in improving the installed capacities, followed by renewable energy certificates, capital refunds, and tax reductions. Electricity prices and renewable energy certificates have combination and substitution effects. Further analysis shows that heat pump efficiencies have low sensitivity in project feasibility. Fluctuations in infrastructure costs have a minimal impact, while charges for heating and cooling services significantly influence feasibility. Lowering the available thermal energy ratio also affects project returns. The government can reduce risks in sensitive parameters by electricity price subsidies or renewable energy certificates. [Display omitted] • Support policies are proposed to encourage investment in wastewater heat recovery. • A bi-level model of local government and urban wastewater treatment plant was developed. • Electricity price subsidy, energy certificate outperform capital refund, tax breaks. • Electricity price and energy certificates have combination and substitution effects. • Lower sensitivities are found in heat pump efficiency and infrastructure cost. [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) devices can convert heat into electricity and have gained great interest as energy harvesters in many applications, such as self-powered sensors, solar TE generators and industrial waste heat recovery. Not many techniques are usually available for their characterization under operating conditions. Consequently, only current-voltage (power output) curves are typically reported to account for their performance, which provide limited information. Impedance spectroscopy, which has been mainly applied to the study of TE modules suspended in air or vacuum, has the advantage to be used under operating conditions. Here, we exploit this advantage and provide an in-depth analysis of the impedance response of standard TE devices when they operate under a small temperature difference. First, we derive the physical models (equivalent circuits) for the two most common operating conditions: (i) constant temperature difference and (ii) constant heat power input. Then, we use the obtained equivalent circuit to successfully fit experimental impedance measurements in both operating modes, which show significant differences. From the fittings, it is possible to obtain the thermal contact resistance between the TE device and the heat exchangers (heat source and heat sink) among other key parameters. In addition, we analyze the variations found in the impedance spectra for different current output levels. Moreover, we show how different electrical resistances, extracted from the impedance results, directly relate to the slope of the I - V curve (power output), and can provide very valuable information about the different processes that determine its value. All these results establish impedance spectroscopy as a very powerful tool to characterize TE devices under operating conditions and as a method that can provide highly valuable insights into their performance. • Equivalent circuits to use impedance spectroscopy under operating conditions. • Constant temperature difference and constant heat power input modes analyzed. • Main parameters can be obtained (module properties and thermal contact resistances). • The origin of the processes that govern the I-V curve (power) can be identified. • Powerful tool for in-situ characterization of devices and systems in applications. [ABSTRACT FROM AUTHOR]

In recent years, considerable effort has been dedicated to the development of highly efficient thermoelectric generators for waste heat recovery and thermoelectric power generation. In this study, we present employing twisted tapes with variable twist ratio to enhance thermal energy extraction efficiency, coupled with two-stage thermoelectric modules for heat-to-electricity conversion, resulting in a substantial increase in the power output of the thermoelectric generator. We established an experimental system that validated the superior power generation and heat recovery characteristics of the two-stage thermoelectric generator. Building upon these findings, we propose further optimizing the variable twist ratio twisted tapes to enhance the power output. We investigated the impact of tape pitch ratio, twist ratio, and twist ratio variation range on thermoelectric performance. Experimental results indicate that the influence of flow instability is more pronounced than that of swirl intensity, and twist tapes with the maximum twist ratio variation rate yield the highest net output power. Compared to an unmodified thermoelectric generator, the two-stage thermoelectric generator employing twist tapes with a twist ratio increase from π to 3π achieves a maximum net output power gain of up to 100%. These findings provide a practical framework for integrating innovative power generation modules and optimized heat exchanger designs into the application of waste heat recovery thermoelectric generators, marking a significant advancement in the field of thermoelectric generators. • Two-stage thermoelectric modules boosts power output. • Variable twist ratio twisted tapes to boost thermal energy extraction efficiency. • Impact of tape pitch ratio and variable twist ratio on thermoelectric performance. • Optimized thermoelectric generator net output power doubled. [ABSTRACT FROM AUTHOR]

A new peaking system utilizing a molten salt furnace energy storage system coupled with a blast furnace gas thermal power unit in a steel mill is proposed, which stores excess blast furnace gas thermal energy in molten salt and releases the thermal energy for power generation during peak power demand. The heating efficiency of 74.57% is experimentally verified by building a molten salt furnace, and a 135 MW blast furnace gas thermal power unit is simulated using modeling to explore the energy storage and peak shifting performance and economic feasibility of the system. The results show that during the charging phase, the system can recover up to 9.361 t/h of standard coal, increasing the low valley regulation ratio to 20.31% with the increase of extraction rate. During the discharging phase, the system can provide an additional 17.42 MW of generating power, with a peak modulation ratio of 12.90%. The exergy losses from the combustion process dominates the overall system exergy losses with a maximum of 21.00 MW, followed by the exergy from the turbine, which occupies 18.42% of the input energy. The cycle efficiency of the system is up to 63.54%, and the molten salt temperature has a more significant impact on the system performance than the molten salt flow rate. The economic feasibility analysis yields a peaking capacity cost of $74.28/kWh for the modified system. The system will complete 100% recovery of the investment cost in 4.90 years, and thereafter, the annual profit is more than $3.71 Million. The peaking hours and regional electricity price are the main factors affecting the system. The effect of critical factors on the payback years of the system was further explored, and the payback years remains within 8 years only when the molten salt temperature is above 500 °C and the molten salt flow rate exceeds 400 t/h. [Display omitted] • Validating the proposed gas utilization system in steel plants by experiment and simulation. • Experiments on a 1.05 MW molten salt furnace yielded an efficiency of 75.75%. • Combustion and turbine are critical to system exergy losses. • The modified unit achieves 152.42 MW generating power and 63.54% cycle efficiency. • System payback costs are within 4.90 years, with peak tariffs dominating profit and loss. [ABSTRACT FROM AUTHOR]

Maximizing energy efficiency through waste heat recovery (WHR) processes is crucial for sustainable and eco-friendly operations across multiple industries, notably in wastewater treatment plants (WWTPs). This work proposes a comprehensive approach for assessing the WHR feasibility in WWTPs, structured in two main objectives. Firstly, an Artificial Neural Network (ANN) model is developed to accurately predict WHR based on operational data, including biogas temperature, biogas pressure, daily production in kWh, and WHR values in kWh th. The second objective focuses on economically evaluating the WHR feasibility based on the estimated WHR values obtained by the ANN model, and then realistically assessing the economic feasibility of integrating the Organic Rankine Cycle (ORC) and Seasonal Thermal Energy Storage (STES) systems. With an application to the As-Samra WWTP located in Jordan, the developed ANN model demonstrates promising results in the validation phase, with a root mean square error (RMSE) of 2206 kWh/day, a mean absolute error (MAE) of 1674 kWh/day, and an R-squared (R 2 ) value of 68%. On the other hand, the economic analysis reveals that an optimal ORC system of 412.14 kW e capacity yields a Net Present Value (NPV) of 2.09 million US dollars, a Levelized Cost of Energy (LCOE) of 0.0749 USD/kWh, a Payback Period (PBP) of 4.8 years, and annual revenues of 428 kUSD. This work also investigates the techno-economic feasibility of integrating ORC-STES. Results indicate that the LCOE and PBP are highly affected by the ORC's capital cost, and integrating STES increases the LCOE to 0.0824 USD/kWh, rendering its integration with ORC infeasible. This study aims to advance the understanding and application of WHR in WWTPs, paving the way for more efficient and sustainable practices in the field. • Analyzing the waste heat recovery (WHR) feasibility in wastewater treatment plants. • Developing data-driven approach-based artificial neural network for WHR estimation. • Economic analysis: Organic Rankine Cycle (ORC) and Seasonal Thermal Energy Storage. • Electricity via WHR using ORC costs 0.0749 $/kWh, yielding 428 k$ yearly revenue. • Integrating seasonal thermal storage increases the levelized cost to 0.0824 $/kWh. [ABSTRACT FROM AUTHOR]

To enable the exploitation of the industry sectors' huge waste heat potential this study investigates the utilization of packed bed thermal energy storage systems for the waste heat recovery in the iron and steel industry. The main goal is to assess the partial cycle operation of a packed bed thermal energy storage with industrial exhaust gas that is contaminated with high amounts of metal powder. A continuously rising accumulation of powder particles inside the packed bed requires the storage to be charged from the bottom in order to facilitate the removal of powder hold-up. Therefore, investigations focus on the dependency of the thermal performance of the storage on the flow direction of heat transfer fluid during charging/discharging. Exergy efficiency and thermocline degradation are evaluated as key performance indicators for different flow directions of the heat transfer fluid using a lab-scale test rig. Results show that, compared to charging from the top, a slightly faster thermocline degradation occurs for a storage that is charged from the bottom. Still, energy and exergy efficiencies in partial cycle operation are well above 85% and 80% respectively regardless of the heat transfer fluid flow direction. The thermal power rate during discharging is stable between 74% and 93% with respect to the maximum input rate for both charging the storage from the top and from the bottom. All in all, packed bed thermal energy storage systems are found to be suitable for waste heat recovery in industrial processes. Only a marginal deterioration of the thermal performance of the storage has to be expected if the storage is required to be charged from the bottom. • Impact of air flow direction during charging on thermocline degradation is minimal. • Steady state energy and exergy efficiency in forward operation are 90% and 86%. • Steady state energy and exergy efficiency in reverse operation are 85% and 80%. • Deterioration of partial cycle energy efficiency of max. 5% is measured. • Deterioration of partial cycle exergy efficiency of max. 7% is measured. [ABSTRACT FROM AUTHOR]

Renewable evaporative energy from atmospheric air is a recently emerged research field that demonstrates the great potential for significant energy savings in the air conditioning of buildings, data/big-data/integrated-big-data centers, agricultural storage facilities, and greenhouses. Here, we develop a method for an essential increase in the harvesting efficiency of renewable air evaporative energy by enhancing the water evaporation rate through the shaping of the air-water interface (AWI) by the menisci formed in superhydrophilic hierarchical surface nano/microstructures. Using this method, we achieve a 10-fold rise in the evaporation rate for the microscale AWI shaping. For the first time, we discover the superevaporation effect that provides an unprecedented 130-fold rise in the evaporation rate at the hierarchical nano/microscale AWI shaping. Furthermore, based on these findings, for the first time, we elaborate a novel material with an engineered AWI for a significant increase in the harvesting of renewable air evaporative energy in the dew point (Maisotsenko cycle) indirect evaporative air conditioning systems whose operation is fundamentally based on utilizing renewable air evaporative energy. The dew point cooling device fabricated using this novel material shows significantly superior cooling performance, validating the substantially enhanced harvesting of the air's evaporative energy. Our findings can essentially advance the emerging field of renewable air evaporative energy and, besides the air conditioning technology, can provide significant efficiency enhancements in water purification/desalination, thermal management, gas turbine power generation, and waste heat recovery technologies. • A method for efficient harvesting renewable air evaporative energy is proposed. • The proposed method is based on the shaping of the air-water interface to enhance evaporation. • A 10-fold rise in the evaporation rate for microscale AWI shaping is achieved. • Superevaporation from nano/microshaped air-water interface was found. • A proof-of-concept dew-point evaporative cooler validates the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

Hydrogen-enriched natural gas (HENG) is a low-carbon fuel and its utilization in combustion devices has been under extensive discussion recently as it is a promising way to reduce the CO 2 emission during combustion. The applicability of HENG in the existing natural gas-fired combustion equipment in terms of its efficiency and emissions attracts increasing attention, especially for industrial and domestic small-scale boilers. In this study, the thermal efficiency and pollutant emissions of a 4.2 MW th HENG-fired boiler integrated with external flue gas recirculation (FGR) were respectively evaluated based on the thermodynamic and heat transfer models and the Chemical Reaction Network model. Results suggested that NOx emission rose by ∼19% as the hydrogen volumetric fraction in the fuel increased from 0 to 0.4 at a constant excess air ratio and FGR rate. To suppress the NOx rise, the FGR rate was tuned higher while the system thermal efficiency decreased subsequently. To further improve the overall system thermal efficiency, a cascade flue gas waste heat recovery strategy including sensible heat recovery using an external economizer and latent heat recovery using dual-spray heat exchangers was proposed. The thermodynamic analysis demonstrated that the external economizer improved the overall system thermal efficiency by 0.4% - 0.7% and the dual-spray heat exchangers promoted the overall system thermal efficiency by over 5%. Thus, a comprehensive performance optimization strategy was developed for HENG-fired boilers in terms of their overall system thermal efficiency promotion, NOx emission control, and CO 2 emission reduction. • The effects of hydrogen addition on the gas-fired boiler performance were assessed. • Thermodynamic and heat transfer models were established to study the boiler efficiency. • The Chemical Reaction Network model was used to study pollutant emissions. • Flue gas recirculation technology was applied to suppress the NOx emission. • A cascade flue gas waste heat recovery strategy was proposed and confirmed. [ABSTRACT FROM AUTHOR]

The generation capability of the waste heat recovery system cannot be fully utilized by relying solely on the exhaust gas, as the mass flow rate and temperature of exhaust fluctuate in real time. The volatility of ship engine conditions and the instability of power demand can pose a challenge to real-time power allocation. Developing integrated prediction and control methods for power allocation becomes necessary. An integrated system is devised to fully utilize waste energy from marine diesel engines by combining a regenerative organic Rankine cycle with a controllable packed bed. The trends of thermodynamic properties and dynamic charging and discharging processes of the system are analyzed. To provide a plausible management strategy for allocating power in real time, a bidirectional long-short-term memory network power prediction method based on improved complete ensemble empirical mode decomposition with adaptive noise and improved marine predator algorithm is proposed. It is found that 315.6 kW of power can be obtained from the system, and its payback period is 6.84 years. In addition, by using the proposed model, the system can reduce diesel engine power generation. The findings suggest the proposed solution is a viable and meaningful strategy. [Display omitted] • The RORC-PB integrated system to fully use marine engine waste heat is proposed. • The dynamic charging and discharging of the RORC-PB system are studied. • A plausible management strategy for allocating power in real time is provided. [ABSTRACT FROM AUTHOR]

The reversible solid oxide cell (rSOC) is a promising technology for advancing energy decarbonization by enabling bidirectional conversion between electricity and hydrogen in a single device. However, previous studies have not fully explored the operational flexibility of rSOCs due to inadequate consideration of heat recovery potentials and dynamics of operating mode transitions. To address this research gap, this paper presents a model-based optimal operation method for managing multi-energy transactions in rSOC-based microgrids, aiming to minimize operation costs. The method incorporates detailed operational models of the rSOC, including a lumped thermal model to account for heat recovery capability and modeling of various operating modes and their transitions. Additionally, a linearization process is introduced to address nonlinear and implicit operational constraints, resulting in a computationally efficient mixed-integer linear programming (MILP) formulation for the operation model. Comparative case studies are conducted using modified energy portfolios of a Danish energy island. The results demonstrate that the proposed method effectively captures operating mode transitions within the rSOC and enhances its profitability via waste heat recovery. Notably, the rSOC model contributes to enhanced operational flexibility through heat recovery behaviors and a wider temperature range, resulting in substantial economic savings for the microgrid. • Dynamic transition modeling of operating modes in rSOCs. • Waste heat recovery analysis from rSOCs for district heating systems. • Computationally efficient economic operation model for rSOC-integrated microgrids. • Unleashing rSOC flexibility through heat recovery and extended temperature range. • Enhanced cost-effectiveness of microgrids through heat recovery benefits of rSOCs. [ABSTRACT FROM AUTHOR]

The data usage surge drives greater data center demand, amplifying global CO 2 emissions. Mitigating climate change necessitates reducing data center CO 2 emissions. Reusing waste heat from data centers offers a potential energy efficiency boost and environmental impact reduction. This study utilizes liquid cooling technology to raise waste heat temperature for building space heating and introduces the concept of 'data furnaces,' where data centers directly supply waste heat to heat buildings on-site, reducing district heating consumption and lowering CO 2 emissions. Efficiently designing a heat recovery heat exchanger system that accounts for both heat rejection and cooling sides of a liquid cooling system is crucial for achieving complete heat recovery without using heat pump, a commonly overlooked aspect in existing literature. To address this issue, we propose two heat exchanger schemes: connecting the building space heating network to the secondary side (Scheme 1) and the primary side (Scheme 2) of the cooling distribution unit. Implementing these innovations leads to the elimination of dependence on a heat pump, substantially cutting energy and CO 2 emissions. Using TRNSYS software, we develop, model, and compare waste heat recovery schemes to curb district heating consumption and CO 2 emissions. To demonstrate broad implications of the proposed approaches for energy efficiency and sustainability in the data centers and building space heating networks, a showcase study examines constant 25 kW waste heat from a direct-to-chip liquid-cooled rack in an office building with 285.7 MWh annual space heating demand. A novel waste heat recovery rate relationship graph is created to assist system design, uncovering an unexpected result in Scheme 2: waste heat recovery decreases as outdoor temperature falls. In contrast, Scheme 1 maintains a stable waste heat recovery rate around 25 kW, regardless of outdoor temperature fluctuations. As a result, Scheme 1 reuses 155.2 MWh of waste heat annually compared to 138 MWh for Scheme 2. Schemes 1 and 2 yield annual electricity savings of 2290.5 kWh and 905.2 kWh, respectively, for the cooling system. Both schemes achieve profitability within a year through a 25-year life cycle analysis (LCC) and substantially reduce CO 2 emissions, with Scheme 1 saving 291,996 kgCO 2 and Scheme 2 saving 258,192 kgCO 2. The study addresses critical gaps in existing literature by emphasizes LCC. The proposed heat exchanger designs represent pioneering solutions for optimizing waste heat recovery, particularly in challenging climates. New findings offer substantial benefits to both liquid-cooled and air-cooled facilities, making significant contributions to achieve carbon neutrality in data center operations. • Non-heat pump data center waste heat recovery for space heating is studied. • Two schemes, recovering from both sides of cooling distribution unit, are compared. • The two schemes achieve payback in under a year due to the elimination of heat pump. • Waste heat recovery on the secondary side outperforms that on the primary side. • Novel relationship graphs facilitate data center waste heat recovery system design. [ABSTRACT FROM AUTHOR]

Research effort in analyzing the energy consumption of buildings in districts or cities is increasing as new paradigms of distributed energy production and sharing are spreading. In this work, the Urban Building Energy Model of the Quad, an area of the University of California Davis campus, is presented, validated, and analyzed for possible actions to reduce the district cooling energy consumption. Energy conservation measures involve buildings' air handling units and district chilled water generation. To investigate this system, a district cooling networks module has been developed in EUReCA, the Urban Building Energy Modeling tool used for the analyses. The model has been validated with energy demand and temperature data from 2018 to 2020, resulting in a district cooling demand deviation lower than 7% for 2018 and 2019. Normalized Root Mean Square Error is lower than 35% for each building, proving the reliability at the hourly time scale. Systems energy reduction actions like heat recovery units' installation and heuristic control of the air supply cooling temperature are beneficial in reducing the cooling demand, and they allow a more efficient discharging of the chilled water storage, reducing the average electricity price by load shifting during peak demand. • The Urban Building Energy Model of UC Davis quad was created with the EUReCA tool. • The chilled water network was simulated with the new developed module. • Results were validated using hourly energy consumption and temperature data. • Energy conservation scenarios were evaluated both at building and generation side. • Chilled water network's flexibility benefits from buildings' cooling demand reduction. [ABSTRACT FROM AUTHOR]

The Organic Rankine Cycle (ORC) is widely used in industrial waste heat recovery due to its simple structure and easy maintenance. However, in the context of smart manufacturing in the process industry, traditional model-based optimization control methods are unable to adapt to the varying operating conditions of the ORC system or sudden changes in operating modes. Deep reinforcement learning (DRL) has significant advantages in situations with uncertainty as it directly achieves control objectives by interacting with the environment without requiring an explicit model of the controlled plant. Nevertheless, direct application of DRL to physical ORC systems presents unacceptable safety risks, and its generalization performance under model-plant mismatch is insufficient to support ORC control requirements. Therefore, this paper proposes a Sim2Real transfer learning-based DRL control method for ORC superheat control, which aims to provide a new simple, feasible, and user-friendly solution for energy system optimization control. Experimental results show that the proposed method greatly improves the training speed of DRL in ORC control problems and solves the generalization performance issue of the agent under multiple operating conditions through Sim2Real transfer. • A practical and user friendly method, DRL Sim2Real transfer learning, is proposed. • The surrogate based virtual prototype for pre training is used to ensure safety. • Limitations of traditional model based optimization control methods are addressed. • Closed loop data is used for VP modeling to enhance computational efficiency. • The significance of level of exploration during Sim2Real transfer is emphasized. [ABSTRACT FROM AUTHOR]

Radioisotope thermophotovoltaic (RTPV) generators face a fundamental challenge, which is the significant output loss and energy wastage caused by the substantial thermal deposition resulting from the arrival of infrared radiation from the heat source at the energy conversion unit. This contradiction has gradually become a key limiting factor for its further development in recent years. In this work, a novel hybrid system based on the thermophotovoltaic-thermoelectric (TPV-TE) effect is proposed, in which the Bi 2 Te 3 -based I/W-type thermoelectric leg plays both heat dissipation and heat recovery for power supply. The heat recovery thermoelectric legs were prepared using a cold pressing mould and sintering method, and their Seebeck effect was used to convert the unwanted heat recover from InGaAs thermophotovoltaic cells into electrical power. The design preparation scheme of the heat recovery hybrid module and its potential application performance at 700–1000 K heat source temperature were investigated through experimental tests and simulations. The W-type TPV-TE heat recovery hybrid system exhibits good gain of 12.9% at 1000 K, and the output power can be increased by additional 21.6% in series mode. Simulations for environmental applications show better heat recovery in deep space than on Earth, with an output gain of 63.7% and an energy conversion efficiency of 11.23%. The heat recovery design enhances the competitiveness of the RTPV and provides new ideas for optimizing other heat recovery applications for thermal energy conversion systems. • The novel I/W TPV-TE-HRL heat recovery hybrid system was proposed. • The W-type TPV-TE heat recovery hybrid system with gain of 12.9% at 1000 K. • The output power of TPV cell and W-type TE-HRL can be increased by 21.6% in series mode. • W-type TE-TPV series can reach 11.23% energy conversion efficiency when used in deep space. [ABSTRACT FROM AUTHOR]

Carbon capture and utilization (CCU) by methanation combines CO 2 capture and Power-to-Gas (PtG) routes, and could simultaneously realize excess clean energy storage and industrial flue gas carbon mitigation. However, a problem of large energy consumption is associated with the long-chain CCU-methanation process. In contrast, integrated carbon capture and utilization (ICCU) could largely reduce energy consumption by integrating CO 2 capture and methanation in just one reaction device. Although progressive work has been done on the development of ICCU-methanation, it still lacks of quantitative evaluation on the energy consumption and production cost. Herein, techno-economic analysis is conducted on calcium looping-based ICCU-methanation and the reference CCU-methanation. Results show that ICCU-methanation only requires 1/3 coal consumed by CCU-methanation to complete carbon capture of a 1000 MWe coal-fired power plant. When waste heat recovery is considered, the plant equipped with ICCU releases 83.6 kg CO 2 per 1 MWe h−1 of electricity comparing to 148.93 kg of CCU. Meanwhile, CH 4 cost by ICCU scheme is 837.1 € t−1, much lower than the 962.86 € t−1 of CCU. After taking the recovery of waste heat and carbon tax into account, the cost of CH 4 produced by ICCU becomes to be 443.26 € t−1, approaching the market price of natural gas (429 € t−1), showing a promising application perspective. • ICCU-methanation process based on calcium looping is simulated and evaluated. • ICCU-methanation only requires 1/3 coal consumed by CCU-methanation. • Cost of CH 4 produced by ICCU approaching the market price of natural gas. [ABSTRACT FROM AUTHOR]

Energy, exergy, and exergoeconomic analyses were performed for two plastic-integrated gasification combined cycle (plastic-IGCC) systems to evaluate the performance of the plastic waste-to-energy cycles. Plastic waste-to-energy is a promising plastic treatment method that can resolve both plastic waste and environmental issues. Thus, improving the efficiency and economy of plastic-IGCC has become crucial because energy is generated during plastic waste-to-energy treatment while treating waste. The difference between the two modeled cycles is the location of heat recovery from the high-temperature syngas. In Cases 1 and 2, heat from the syngas was recovered with a heat recovery steam generator and a gas heater, respectively, to increase the temperature of the air entering the gasifier. The maximum net efficiency for Case 2 increased by 8.2% (from 35.41% to 43.57%), unlike that of Case 1, without changing exergy destruction. To assess the economic value and market potential, the unit electricity cost was examined for the condition in which the highest efficiency was obtained. The unit exergoeconomic costs for Cases 1 and 2 were 0.141 and 0.108 $/kWh, respectively, which were within the range of those in other energy recovery combined cycles; in addition, using air heaters for heat recovery reduced costs. The use of the air heater for heat recovery benefited energy and economic aspects without significantly changing exergy destruction. These findings have important implications for understanding the impact of gasifier agent conditions and energy recovery methods on the optimum conditions for plastic-IGCC. This study aimed to provide insights into the optimal design and operation of plastic-IGCC systems, considering both energy and economic aspects. • Modeling integrated plastic gasification combined cycles with heat recovery. • Identifying appropriate operating conditions for waste-to-energy recovery cycles. • Evaluating power cycles with exergoeconomic analysis. • Significant increase in the cycle efficiency with heat recovery at a gasifier. [ABSTRACT FROM AUTHOR]

Direct air capture (DAC) technology plays a crucial role in mitigating the effects of global warming by capturing carbon dioxide (CO 2) directly from the atmosphere. A significant technical challenge for DAC is its high thermal energy consumption, which results in an unacceptable overall cost (600 $ t CO 2 – 1). The combination of a high-temperature heat pump (HTHP) and DAC system offers a substantial reduction in thermal energy consumption, decreased reliance on renewable energy sources, and enhanced DAC system flexibility. This study presents three distinct thermal integration strategies that combine an HTHP with solid adsorbent-based DAC and verifies their effectiveness in reducing energy consumption and CO 2 emissions compared to a traditional DAC system. Among them, the deeply integrated DAC-HTHP system (I-DAC) exploits low-grade adsorption heat and waste heat, providing direct heating and cooling energy to the DAC system via refrigerant condensation and evaporation processes. Simulation results indicate that the I-DAC system achieves an extremely low operating energy consumption of 2.77 GJ t CO 2 – 1 , representing a 69.5% reduction than traditional DAC under the same conditions. Consequently, the I-DAC offers a cost-effective (32.0–46.2 $ t CO 2 – 1) negative emission solution. We also demonstrate that the I-DAC is promising for wide application in cities to recycle waste heat and remove CO 2 from the air. The comprehensive implementation of the I-DAC in 105 cities could yield a net annual productivity of 980 MtCO 2. • Proposed a deeply thermal integrated DAC system (I-DAC) with waste heat recovery heat pump. • I-DAC achieved a 69.5% reduction in specific energy consumption compared to base-DAC. • I-DAC offers a cost-effective and scalable negative emission solution for climate change mitigation. • Successful implementation of I-DAC in 105 cities could yield a net annual capture capacity of 980 MtCO 2 by 2050. • Highlights the potential of I-DAC to recycle waste heat and remove CO 2 from the air, with policy implications [ABSTRACT FROM AUTHOR]

• A composition adjustment organic Rankine cycle was proposed. • Optimum working fluids used in trunk and branch processes were selected. • Optimized operation conditions and optimal performance were obtained. The efficiency improvement of organic Rankine cycle, which is an efficient way to recover the waste heat of internal combustion engines, is an eternal topic. The 3D construction method of thermodynamic cycle provides a possible way to construct efficient thermodynamic cycles based on zeotropic working fluid, whose core is to improve the thermodynamic performance by using different working fluids in different thermodynamic processes. Based on the 3D construction method of thermodynamic cycle, a composition adjustment organic Rankine cycle was proposed in this paper to recover the waste heat of internal combustion engines. The optimum working fluid used in trunk and branch processes were selected according to the requirements of different thermodynamic processes. The effects of key parameters were analyzed, and the optimized operation conditions and optimal performance were obtained. The results shown that the composition adjustment organic Rankine cycle performs best when using R123/toluene (0.9/0.1) in trunk process and R123/toluene (0.96/0.04), R123/toluene (0.66/0.34) in low-pressure and high-pressure branch processes, respectively. Under the optimal condition, the net output power, thermal efficiency and exergy efficiency are 50.07 kW, 10.96% and 45.79%, respectively. The irreversible losses in evaporator I and evaporator II account for 35.01% and 30.54% of the total irreversible losses in composition adjustment organic Rankine cycle respectively. This work provided an advanced power cycle for the waste heat recovery of internal combustion engines. What's more, composition adjustment organic Rankine cycle proves the feasibility of the 3D construction method and opens up a novel way to construct efficient thermodynamic cycles. [ABSTRACT FROM AUTHOR]

• Integrated model of ICE and CTPC in GT-SUITE calibrated against experimental data. • Performance prediction of four CTPC system layouts under a cruise driving cycle. • Control structure of mode switch module and PID controllers are proposed. • CTPC systems show strong robustness against highly transient heat sources. • Enhancing pump and turbine performance facilitates CTPC integration with ICE. Carbon dioxide transcritical power cycle (CTPC) systems are considered a new and particularly interesting technology for waste-heat recovery. In heavy-duty truck engine applications, challenges arise from the highly transient nature of the available heat sources. This paper presents an integrated model of CTPC systems recovering heat from a truck diesel engine, developed in GT-SUITE software and calibrated against experimental data, considers the likely fuel consumption improvements and identifies directions for further improvement. The transient performance of four different CTPC systems is predicted over a heavy-heavy duty driving cycle with a control structure comprising a mode switch module and two PID controllers implemented to realize stable, safe and optimal operation. Three operating modes are defined: startup mode, power mode, and stop mode. The results demonstrate that CTPC systems are robust and able to operate safely even when the heat sources are highly transient, indicating a promising potential for the deployment of this technology in such applications. Furthermore, a system layout with both a preheater and a recuperator appears as the most promising, allowing a 2.3% improvement in brake thermal efficiency over the whole driving cycle by utilizing 48.9% of the exhaust and 72.8% of the coolant energy, even when the pump and turbine efficiencies are as low as 50%. Finally, factor analysis suggests that important directions aimed at improving the performance and facilitating CTPC system integration with vehicle engines are: (1) ensuring long-duration operation in power mode, e.g., by employment in long-haul trucks; and (2) enhancing pump and turbine performance. [ABSTRACT FROM AUTHOR]

• A heat pump using a Knudsen compressor is designed and demonstrated. • This heat pump is driven by thermal energy, and it is free from moving parts. • Experiments confirm heat transport with an output power of 3.09 W. • The output power tends to increase linearly as the temperature difference decreases. • The thermal efficiency of the proposed heat pump is analyzed. A heat pump with low power consumption and a simple mechanical configuration is required to save energy and reduce carbon dioxide emissions. We show the design and demonstration of a novel heat pump using a Knudsen compressor, referring this device as a Knudsen heat pump. Water is employed as a refrigerant. The motionless nature of the Knudsen heat pump is accomplished by using a Knudsen compressor to transport the refrigerant vapor from the evaporator to the condenser, and thermal energy alone supplies the needed power. We employ a simple single-stage Knudsen compressor powered by light from a halogen lamp as an energy source. Experiments confirmed heat transport from the evaporator to the condenser with an output power of 3.09 W. The output power tended to increase linearly as the temperature difference between the evaporator and condenser decreased. The pressure-enthalpy diagram of the proposed Knudsen heat pump cycle was shown, and the thermal efficiency of this heat pump was analyzed. The application of a multi-stage Knudsen compressor to improve the heat pump performance was also discussed. This heat pump is free from noise, vibration, and maintenance, and it can utilize low-quality energy, such as a solar energy, and it does not require any electrical input. These properties make the Knudsen heat pump a particularly significant technology in harsh environments such as space and desert. [ABSTRACT FROM AUTHOR]

• Data centre sector is fast expanding and energy efficiency can be improved. • A systematic approach to waste heat recovery within data centres is proposed. • The applicability of the four stages framework is demonstrated through a case study. • The decision support system delivers a streamlined and optimised heat recovery strategy. Data centre sector is emerging as one of the largest and fastest growing industrial sectors, accounting for 3% of the global electricity supply and contributing to 4% of total greenhouse gas emissions. A framework for waste heat energy recovery and its accompanying decision support system is presented with the ability to evaluate the waste heat (source) and potential demand (sink) compatibility, perform exergy and temporal availability analysis, and undertake cost-benefits and environmental impact analysis of available heat recovery technologies. This four stages framework is implemented through the case study of a medium-sized commercial data centre to provide evidence of its applicability. The results demonstrated that the framework and decision support system can deliver a streamlined and optimised heat recovery strategy for reducing overall energy requirement in the data centre. About 68% of the inevitable waste heat from IT equipment can be recovered by the recommended solution, allowing the recovered waste heat in the form of warm water to be fed back into the facility for applications such as space heating, achieving about 10% improvement in data centre power usage effectiveness. The solutions given by the decision support system are generally accessible for most data centres as the technologies are readily available and often lead to short payback time and substantial energy savings. [ABSTRACT FROM AUTHOR]

• Increased value of straw under carbon- and resource-constrained energy scenarios. • Attractiveness of gasification with Fischer-Tropsch synthesis to produce biofuels. • Integrated energy system planning optimizes excess heat recovery from biorefineries. • Current domestic biomass resources would not attain energy self-sufficiency targets. The long-lived dependence on fossil fuels has led to a slow pace in the transition to renewable energy sources in the heavy-duty sectors of the energy system. While bioenergy might represent a possible alternative, biomass is a limited resource, whose use is restricted by potential technical, environmental and social impliations. Because residual biomass inherently minimises these negative impacts, when its sustainable use is ensured, it could lend itself to multiple options, including production of back-up power, heating and alternative transport fuels. This study investigates different pathways for the optimal use of the most abundant residual biomass in Denmark, i.e. straw, from a technical, economic and environmental perspective. We harness the strengths of two bottom-up model typologies by means of soft-linkage to reveal insights from both perspectives: the multi-sectoral model, TIMES-DK, provides a system assessment of the whole energy sector, while the geographically detailed optimization model, Balmorel-OptiFlow, supports the analysis of biorefinery plant size, location and area-specific recovery of excess heat. Modelling results of carbon- and resource-constrained energy scenarios reveal the increased value of straw in a future decarbonised energy system and the attractiveness of the gasification route with Fischer-Tropsch synthesis for the production of biofuels to supply the heavy segments of the transport sector. Moreover, relying on current domestic biomass resources would not attain the energy self-sufficiency targets in a carbon-constrained case. [ABSTRACT FROM AUTHOR]

• A numerical model of exhaust-based segmented thermoelectric generator is built. • The optimal CoSb 3 ratio reduces with shorter segmented thermoelectric elements. • Heat transfer enhancement increases the optimal segmented ratio of CoSb 3. • Different ratios of p-n type further improve the performance of segmented models. • Application of optimal segmented ratio at system level shows better performance. Thermoelectric generators have been regarded as a prospective technique used for recovering engine exhaust heat. Segmented structure is more appropriate for large temperature gradient between the heat and cold source. This work establishes a numerical model of segmented thermoelectric generator for engine waste heat recovery based on the component level and system level simultaneously. Two patterns of p-n ratios are conducted to compare the properties between segmented and traditional models as well as optimize the segmented ratios under various conditions to get better performance. In the pattern of same p-n segmented ratios, the effects of structural parameters and thermodynamic boundary conditions on the output performance are analyzed. The optimal proportion of medium temperature material (CoSb 3) increases with longer thermoelectric elements and higher heat transfer coefficient, whereas the cross section area shows hardly any influence on it. And then the power improvement capacity in view of the property difference between p-type and n-type material is investigated in the second pattern. The maximum output power is improved by approximately 13.8% compared with that of original segmented model. Finally, the application of optimal segmented ratio design in a thermoelectric generator system demonstrates better performance and further increases the output power by 6.8%. [ABSTRACT FROM AUTHOR]

• A novel vehicle energy supply system with waste heat recovery is integrated. • Influence from the season changes on overall thermal-economic performance has been studied. • The optimal working condition and parameter selection in the bottom cycle are achieved. • The suitable working fluid for the proposed system is recommended. A novel vehicle energy supply system is proposed through integrating a waste heat recovery organic Rankine cycle subsystem to the conventional vehicle air conditioning subsystem. Based on an actual vehicle engine operation data at different engine load, the overall thermal and economic performances of the proposed vehicle energy supply system are investigated through comparing with the conventional and the vehicle energy supply system with a standalone waste heat recovery organic Rankine cycle subsystem, considering the influences from the ambient temperature, the working fluid selection, the turbine inlet temperature under different seasons. The analysing results indicated that the proposed vehicle energy supply system hold prominent thermal and economic performance advantages compared to that of the conventional vehicle energy supply system with a standalone waste heat recovery organic Rankine cycle subsystem. With the change of season, the proposed system showed the best overall performance in winter, the spring/autumn is the next, the summer was the worst under the rated vehicle engine load. Both the maximal gasoline oil saving rate and the minimal static payback period are obtained at a certain organic Rankine cycle evaporating pressure. The maximal gasoline oil saving rate at 9.73 kg/h, and the minimal payback period at 769 h are achieved. Moreover, Cyclo-pentane is the best working fluid of the waste heat recovery subsystem for the integrated vehicle energy supply system scheme under the operating conditions in this research. [ABSTRACT FROM AUTHOR]

• First benchmark of on-going Hot Sedimentary Aquifer exploitation. • Scope for heat recovery optimisation from geothermal resources. • Application of hydrocarbon exploitation concepts in geothermal context. The Netherlands experienced the fastest European expansion of geothermal energy exploitation in the past decade. The first Dutch geothermal sites proved that Hot Sedimentary Aquifers exploitation can play an important role in a future low-carbon energy mix. In this study, we estimate that with the expansion rate of the past four years, geothermal heat production from Lower Cretaceous Hot Sedimentary Aquifers could cover up to 20% of the heat demand in the province of Zuid-Holland by 2050. Although this is a significant amount, we show in this study that only 1% of the potentially recoverable heat will be recovered by 2050. This is because of inefficient doublet deployment on a 'first-come, first served' basis with operational parameters that focus on objectives of small decentralised heat grid demands. Instead, similar to the common-practise approach in the hydrocarbon industry, a regional coordinated 'masterplan' approach could be used to increase heat recovery. Utilising numerical simulations for flow and heat transfer in the subsurface, we showed that the heat recovery efficiency could be increased by tens of percentages with such coordinated doublet deployment. Based on calculations of the Levelized Costs Of Heat for both deployment strategies, we also show that current financial support schemes do not favour heat recovery optimisation. This study emphasises that although Hot Sedimentary Aquifer resources have the potential to cover a significant part of our energy demand, a radical change in financial support schemes and legislation are required to unlock their true potential. [ABSTRACT FROM AUTHOR]

• Modelling and experimental results of reciprocating expander were presented. • Variable valve timing was employed to control the expansion ratio of the expander. • The expander provide 2.5 kW power output and 70% isentropic efficiency. • Dynamic model predicts torque and pressure traces with reasonable accuracy. • Model predicts power and isentropic efficiency within ±10% and ±30% accuracy. This paper presents a reciprocating expander concept for organic Rankine cycle applications using a novel rotating variable timing admission valve system, enabling the adjustment of the expansion ratio in real time while the expander is running. An organic Rankine cycle experimental test rig with n-pentane as the working fluid and a single-cylinder reciprocating piston expander was developed. Experiments were conducted for evaporation temperatures ranging from 125 °C to 150 °C and condensation temperatures ranging from 20 °C to 40 °C. The performance of the reciprocating piston expander was investigated in terms of the torque of the expander, pressure inside the cylinder, isentropic efficiency of the expander, and net power produced by the expander. Based on the experimental data, a dynamic model of the system was formulated in the object-oriented language, Modelica. The model was validated using the experimental results and then used to predict the performance of the expander. Special attention was paid to the robust modelling of the valve actuation to avoid computational inefficiencies caused by singularities of state variables or their derivatives. The results indicate that the expander produces up to 2.5 kW of electricity from a low-temperature heat source while operating at pressure ratios ranging from 10 to 16.5 with an isentropic efficiency of approximately 70%. The relative differences between the model and the measurements of the isentropic efficiency and power output of the expander per revolution were ±10% and ±30%, respectively. [ABSTRACT FROM AUTHOR]