Publications
49 results found
Maghrabi A, Song J, Sapin P, et al., 2023, Electricity demand reduction through waste heat recovery in olefins plants based on a technology-agnostic approach, Energy Conversion and Management: X, Vol: 20, Pages: 1-18, ISSN: 2590-1745
Developing systematic approaches for the identification of optimal WHR options in industrial applications is key to reducing plant-scale energy demands. In particular, electricity consumption accounts for more than half of industrial energy use, and its share is expected to grow with progressive electrification. In this paper, industrial WHR technologies including organic Rankine cycle (ORC) and absorption systems are investigated, and tools are developed to understand the sustainability and techno-economic impact of integrating these technologies within industrial processes and facilities. We specifically propose a data-driven technology-agnostic approach to evaluate the use of heat engines, which can in practice be ORC systems, and thermally-driven (i.e., absorption) heat pumps in the context of industrial WHR for plant-scale electricity demand reduction. The aim of this work is to explore three pathways for achieving efficiency improvements in bulk chemicals plants, represented here by olefins production facilities: (i) direct onsite power generation; (ii) enhancement of existing power generation processes; and (iii) reduction in power consumption by compressor efficiency improvements through waste-heat-driven cooling. The techno-economic performance of these technologies is assessed for five different countries representing a diverse portfolio of climates, technical and economic parameters (including utility prices), using fine-tuned thermodynamic and market-based costing models. The results reveal that the proposed approach has the potential to reduce emissions by between 5,000 tCO2(eq.)/year and 101,500 tCO2(eq.)/year depending on the scenario. The marginal abatement cost of the proposed solutions ranges from -1,200 $/tCO2(eq.) to -35 $/tCO2(eq.), with a payback time between 1.5 and 8 years depending on the scenario considered.
Mersch M, Sapin P, Olympios AV, et al., 2023, A unified framework for the thermo-economic optimisation of compressed-air energy storage systems with solid and liquid thermal stores, Energy Conversion and Management, Vol: 287, Pages: 1-15, ISSN: 0196-8904
Compressed-air energy storage is an attractive option for satisfying the increasing storage demands of electricity grids with high shares of renewable generation. It is a proven technology that can store multiple gigawatt hours of electricity for hours, days and even weeks at a competitive cost and efficiency. However, compressed–air energy storage plants need to be designed carefully to deliver these benefits. In this work, a consistent thermo-economic optimisation framework is applied to assess the performance and costs of different compressed–air energy storage configurations across different scales. Special attention is paid to the thermal energy stores, with both solid packed-bed stores and liquid stores examined as viable options for advanced compressed–air energy storage plants and different storage materials proposed for both options. The comprehensive thermo-economic optimisation, considering different system layouts, thermal energy storage technologies and storage materials, and system scales is a key novelty of the presented work. A configuration with two packed–bed thermal energy stores using Basalt as the storage material is found to perform best, achieving an energy capital cost of 140 $/kWh, a power capital cost of 970 $/kW and a roundtrip efficiency of 76% at a nominal discharge power of 50 MW and a charging / discharging duration of 6 h. The best-performing liquid storage material is solar salt, which is associated with an energy capital cost of 170 $/kWh and a power capital cost of 1,230 $/kW. Systems with liquid thermal energy stores however are found generally to perform worse than systems with packed–bed thermal energy stores both in terms of cost and efficiency across all scales.
Sapin P, Olympios AV, Mersch M, et al., 2023, Paper No 715 - Design and operational optimisation of an integrated thermal energy storage ground-source heat pump with time-varying electricity prices, 14th IEA Heat Pump Conference 2023
A detailed methodology is proposed to design and optimise the operation of a ground-source heat pump(GSHP) coupled to a phase-change material (PCM) thermal battery. The objective is to minimise the cost ofsupplying space heating and hot water to a medium-demand house in the UK during a typical winter day withfluctuating electricity prices. A bespoke 8-kW GSHP is designed and used to optimise the charging scheduleof the thermal battery to minimise daily operational costs while meeting the heat demand. If no limit is imposedon the size of the thermal battery, in the best scenario, a 41-kWh thermal battery is required to achieve costsas low as 1.85 £/day. However, large PCM batteries mean high upfront costs and little space restrictions.Therefore, a constraint is imposed on the thermal store capacity to identify the optimal trade-off that can beachieved between PCM battery size and daily power consumption costs. Operational costs strongly depend onthe battery size, increasing from 1.85 £/day for a 41-kWh thermal battery to 3.50 £/day for a 6.3-kWh store.
Handagama NB, White MT, Sapin P, et al., 2023, Renewable and waste-heat utilisation technologies, Publisher: Cambridge University Press, ISBN: 9781108691093
Understand the science and engineering behind renewable and waste-heat utilisation techniques with this thorough reference. Provides you with the knowledge and tools necessary to assess the technical and economic potential of heat-upgrading, heat-to-power and thermally-driven heating and cooling technologies, as well as a variety of thermal energy storage solutions. In particular, design-agnostic thermodynamic performance indicators and technology-specific design and costing methods are provided, which can be used to select the most suitable technologies for a wide range of applications, typically waste-heat recovery opportunities that exist within various industries, or domestic heating and cooling supply using renewable heat sources. Essential reading for professionals across the energy sector, chemical, manufacturing and mechanical engineering who have an interest in energy generation, conversion, storage and efficient heat utilisation.
Olympios AV, Sapin P, Freeman J, et al., 2022, Operational optimisation of an air-source heat pump system with thermal energy storage for domestic applications, Energy Conversion and Management, Vol: 273, Pages: 1-23, ISSN: 0196-8904
Electricity-driven air-source heat pumps are a promising element of the transition to lower-carbon energy systems. In this work, operational optimisation is performed of an air-source heat pump system aimed at providing space heating and domestic hot water to a single-family dwelling. The novelty of this work lies in the development of comprehensive thermal network models of two different system configurations: (i) a standard configuration of a heat pump system coupled to a hot-water cylinder; and (ii) an advanced configuration of a heat pump system coupled to two phase-change material thermal stores. Three different objective functions (operational cost, coefficient of performance, and self-sufficiency from a locally installed solar-PV system) are investigated and the proposed mixed-integer, non-linear optimisation problems are solved by employing a genetic algorithm. Simulations are conducted at two carefully selected European locations with different climate characteristics (Oban in Scotland, UK, and Munich in Southern Germany) over four seasons represented by typical weather weeks. Comparison of key results against a conventional operating strategy reveals that the use of smart operational strategies for the operation of the heat pump and thermal stores can lead to considerable economic savings for consumers and significant performance improvements over the system lifetime. Optimising the operation of the standard configuration leads to average annual cost savings of up to 22% and 20% at the UK and German locations, respectively. The optimisation of the advanced configuration with the two PCM stores shows even higher potential for economic savings – up to 39% and 29% per year at the respective locations – as this configuration allows for greater operational flexibility, and high-electricity-price periods can be almost completely avoided. Depending on the objective function, configuration and location, the system seasonal coefficient of performance va
Al Kindi A, Sapin PAUL, Pantaleo A, et al., 2022, Thermo-economic analysis of steam accumulation and solid thermal energy storage in direct steam generation concentrated solar power plants, Energy Conversion and Management, Vol: 274, Pages: 1-27, ISSN: 0196-8904
In direct steam generation (DSG) concentrated solar power (CSP) plants, a common thermal energy storage (TES) option relies on steam accumulation. This conventional option is constrained by temperature and pressure limits, and delivers saturated or slightly superheated steam at reduced pressure during discharge, which is undesirable for part-load turbine operation. However, steam accumulation can be integrated with sensible-heat storage in concrete to provide higher-temperature superheated steam at higher pressure. In this paper, this conventional steam accumulation option (existing) and an integrated concrete-steam TES option (extended) are described and analysed, and their thermo-economic performance are compared taking the 50-MW Khi Solar One DSG CSP plant in South Africa as a case study. The results show that the extended option with five 10-m long, square cross-section concrete blocks, each with 3600 equally spaced tubes, provides an additional TES capacity of 177 MWh compared to the existing configuration as a result of utilising most of the available thermal power in the solar receivers. Moreover, the extended option delivers 58 % more electricity with a 13 % enhancement in thermalefficiency during TES discharging mode. With an estimated additional investment of $4.2M, the levelised costs of storage and electricity for Khi Solar One with the extended TES option are, respectively, 29 % and 6 % lower than those obtained with the existing TES option. With the extended TES option, the projected net present value of Khi Solar One increases by 73 %, from $41M to $71M, at an average electricity price of 280 $/MWh.
Maghrabi A, Song J, Sapin P, et al., 2022, Data-driven approaches for techno-economic assessment of waste heat recovery and utilisation in the industrial sector, 17th Conference on Sustainable Development of Energy, Water and Environment Systems (SDEWES 2022)
The industrial sector is a critical element in the sustainability transition as it is currently the largestconsumer of fossil fuels, and the consumption is forecasted to continue to increase. Approximatelyone-fifth of the total industrial primary energy consumption is wasted due to the lack of provenattractive schemes for effective recovery. When addressing the opportunities of industrial wasteheat recovery (WHR), it is found that the feasibility depends on multiple factors, including the formsand capacities of the heat sources, the potential heat sinks, and the effectiveness, technologicalmaturity, and economic impact of available technologies. Developing systematic approaches toidentify optimal WHR options for different applications is key to effectively reduce plant-scaleenergy consumption. In particular, power consumption accounts for more than half of the industrialenergy use, and its share is expected to grow with the expansion of electrification aspirations. Inthis paper, industrial WHR technologies are investigated, and tools are developed to understand thesustainability and techno-economic impact of integrating these technologies within industrialprocesses. We specifically propose a data-driven technology-agnostic approach to evaluate the useof heat engines, which can in practice be organic Rankine cycle (ORC) systems, and of thermally-driven (i.e., absorption) heat pumps in the context of industrial WHR for plant-scale power demandreduction. The scope of this work explores three pathways to achieving efficiency improvementsin bulk chemicals plants, represented by olefins production facilities, which are: (i) direct onsitepower generation; (ii) enhancement of existing power generation processes; and (iii) reduction inpower consumption by compressor efficiency improvements through waste-heat-driven cooling.The techno-economic performance of these technologies is assessed, with particular attention toindustrial facilities that reside in hot climates, using fi
Specklin M, Deligant M, Sapin P, et al., 2022, Numerical study of a liquid-piston compressor system for hydrogen applications, APPLIED THERMAL ENGINEERING, Vol: 216, ISSN: 1359-4311
The use of a liquid-piston system for hydrogen compression is investigated in this paper by means of a computational fluid dynamics (CFD) analysis. In the specific context of hydrogen-driven vehicles, high-pressure storage tanks are key to provide substantial range. The present study focuses on the intermediary compression stage of a compression-storage-dispensing (CSD) station, bringing hydrogen gas from 15 bar to 450 bar, i.e., for a pressure ratio of 30. Until now the liquid-piston technology has not been investigated for hydrogen gas compression at very high pressure, which is the purpose of this study. Simulations of the compressible two-phase flow problem are performed with a volume-of-fluid (VOF) framework using a real gas model for the gaseous phase to account for compressibility effects at large pressure ratios. A particular attention is paid to the numerical model formulation and to the treatment of the thermal boundary conditions. Results are reported using both time-resolved instantaneous bulk thermodynamic variables and global integrated quantities. Different compression scenarios are investigated, which highlights the compromise between compression efficiency and power density. To achieve the targeted pressure ratio at a power density of approximately 540 kW/m, the compression energy cost reaches 1.67 kWh/kg. Finally the paper proposes an innovative solution to minimise cost and achieve quasi-isothermal compression, based on internal forced convection. For a similar power density, a high-speed fan in the top part of the compression chamber (modelled as a volumetric momentum source of 2500 N/m) increases heat transfer and leads to a 25-% reduction in compression consumption.
Taleb AI, Barfuß C, Sapin P, et al., 2022, Simulation of thermally induced thermodynamic losses in reciprocating compressors and expanders: Influence of real-gas effects, Applied Thermal Engineering, Vol: 217, Pages: 118738-118738, ISSN: 1359-4311
The efficiency of positive-displacement components is of prime importance in determining the overall performance of a variety of thermodynamic systems. Losses due to the unsteady thermal-energy exchange between the working fluid and the solid walls of the device are an important loss mechanism. In this work, heat transfer in gas-spring devices is investigated numerically in order to focus explicitly on these thermodynamic losses. The specific aim of the study is to investigate the behaviour of real gases in gas springs and compare this to that of ideal gases in order to understand the impact of real-gas effects on the thermally induced losses in reciprocating expanders and compressors. This work relates these losses to the fluid properties and quantifies the influence of the thermophysical models applied. A CFD-model of a gas spring is developed in OpenFOAM. Four different fluid models are compared: (i) a perfect-gas model (i.e., an ideal-gas model with constant thermodynamic and transport properties); (ii) an ideal-gas model with temperature-dependent properties; (iii) a real-gas model using the Peng-Robinson equation-of-state with temperature and density-dependent properties; and (iv) a real-gas model using gas-property tables to interpolate values of thermodynamic and transport properties as functions of temperature and pressure. Results indicate that for simple, mono- and diatomic gases, like helium or nitrogen, there is a negligible difference in the pressure and temperature oscillations over a cycle between the ideal and real-gas models. However, when considering heavier (organic) molecules, such as propane, the ideal-gas model tends to overestimate the temperature and pressure (by as much as 20%) compared to the real-gas model. A real-gas model that uses the Peng-Robinson equation of state underestimates the pressure relative to the more accurate model based on look-up tables by as much as 10%. Furthermore, both ideal-gas and Peng-Robinson models underestimat
Olympios AV, Aunedi M, Mersch M, et al., 2022, Delivering net-zero carbon heat: technoeconomic and whole-system comparisons of domestic electricity- and hydrogen-driven technologies in the UK, Energy Conversion and Management, Vol: 262, ISSN: 0196-8904
Proposed sustainable transition pathways for moving away from natural gas in domestic heating focus on two main energy vectors: electricity and hydrogen. Electrification would be implemented by using vapour-compression heat pumps, which are currently experiencing market growth in many countries. On the other hand, hydrogen could substitute natural gas in boilers or be used in thermally–driven absorption heat pumps. In this paper, a consistent thermodynamic and economic methodology is developed to assess the competitiveness of these options. The three technologies, along with the option of district heating, are for the first time compared for different weather/ambient conditions and fuel-price scenarios, first from a homeowner’s and then from a whole-energy system perspective. For the former, two-dimensional decision maps are generated to identify the most cost-effective technologies for different combinations of fuel prices. It is shown that, in the UK, hydrogen technologies are economically favourable if hydrogen is supplied to domestic end-users at a price below half of the electricity price. Otherwise, electrification and the use of conventional electric heat pumps will be preferred. From a whole-energy system perspective, the total system cost per household (which accounts for upstream generation and storage, as well as technology investment, installation and maintenance) associated with electric heat pumps varies between 790 and 880 £/year for different scenarios, making it the least-cost decarbonisation pathway. If hydrogen is produced by electrolysis, the total system cost associated with hydrogen technologies is notably higher, varying between 1410 and 1880 £/year. However, this total system cost drops to 1150 £/year with hydrogen produced cost-effectively by methane reforming and carbon capture and storage, thus reducing the gap between electricity- and hydrogen-driven technologies.
Zhao Y, Song J, Liu M, et al., 2022, Thermo-economic assessments of pumped-thermal electricity storage systems employing sensible heat storage materials, Renewable Energy, Vol: 186, Pages: 431-456, ISSN: 0960-1481
Three distinct pumped-thermal electricity storage (PTES) system variants based on currently available sensible heat storage materials are presented: (i) Joule-Brayton PTES systems with solid thermal reservoirs; (ii) Joule-Brayton PTES systems with liquid thermal stores; and (iii) transcritical Rankine PTES systems with liquid thermal stores. Parametric design optimisation is performed for each PTES system variant considering various system configurations, working fluids and storage media from a thermodynamic perspective. The results show that amongst the investigated systems, the recuperative transcritical Rankine PTES system with CO2 as the working fluid and Therminol VP-1 as the storage material achieves the highest roundtrip efficiency of 68%. Further to the optimal thermodynamic performance of these system, their corresponding capital costs are also evaluated. The economic performance comparisons of selected optimal PTES designs reveal that the recuperative transcritical Rankine PTES system with CO2 and Therminol VP-1 exhibits the lowest capital cost of 209 M$ for the given power capacity (50 MW) and discharge duration (6 h). The influences of the power capacity and discharge duration are also investigated, with results showing that the lowest power and energy capital costs are 3790 $/kW (discharge duration of 2 h) and 396 $/kWh (discharge duration of 12 h), respectively.
Gkaniatsou E, Chen C, Cui FS, et al., 2022, Producing cold from heat with aluminum carboxylate-based metal-organic frameworks, Cell Reports Physical Science, Vol: 3, Pages: 1-18, ISSN: 2666-3864
Worldwide cooling energy demands will increase by four times by 2050. Thermally driven cooling technology is an alternative solution to electric heat pumps in removing hazardous refrigerants and harnessing renewables and waste heat. We highlight the advantages of water-stable microporous aluminum-carboxylate-based metal-organic frameworks, or Al-MOFs, as sorbents in the application of producing cold from heat. Here, we synthesize the Al-MOFs with green and scalable processes, which are prerequisites for exploring various industrial and civil applications. A proof-of-concept full-scale adsorption chiller with different Al-MOFs is built up with optimized configurations derived from various characterization techniques. The tested Al-MOFs achieve thermal efficiency above 0.6 and specific cooling power over 1 kW/kg in typical cooling scenarios. Notably, when solar thermal energy is used as the heat source in an outdoor validation, Al-MOFs are weather-resilient solutions that exhibit a stable energy conversion efficiency under fluctuating operating conditions (ambient temperature and solar irradiation).
Khaljani M, Harrison J, Surplus D, et al., 2021, A combined experimental and modelling investigation of an overground compressed-air energy storage system with a reversible liquid-piston gas compressor/expander, Energy Conversion and Management, Vol: 245, Pages: 1-19, ISSN: 0196-8904
We consider a small-scale overground compressed-air energy storage (CAES) system intended for use in micro-grid power networks. This work goes beyond previous efforts in the literature by developing and showing results from a first-of-a-kind small-scale (20 kWh) near-isothermal CAES system employing a novel, reversible liquid-piston gas compressor and expander (LPGC/E). Additionally, we extend our study to assessments, for the first time, of the economic and environmental characteristics of these small-scale overground CAES systems through a combination of experimental, thermodynamic, technoeconomic and environmental analyses. Five system configurations are considered: (1) CAESbase, which is the base-case system; (2) CAESplate, in which parallel plates are inserted into the LPGC/E as a heat exchanger for achieving near-isothermal compression and expansion; (3) CAESPCM, in which a phase change material (PCM) is employed to store thermal energy from the compressed air during charging that is later recovered during discharge; (4) CAESPCM&plate, which is a combination of the CAESplate and CAESPCM arrangements; and (5) CAESheater, in which a heater is utilised instead of the PCM to preheat the compressed air during discharge. Data for the validation of a computational design tool based on which the assessments were performed were obtained from a prototype of the CAESbase system. Results show that the CAESPCM&plate system exhibits the highest roundtrip efficiency of 63% and the shortest payback period of 7 years; the latter with the inclusion of governmental incentives and an electricity smart export guarantee (SEG) support rate of 5.5 p/kWh (6.8 ¢/kWh). The CAESPCM&plate system is found to be cost-effective even without incentives, with a payback period of 10 years. This system is also associated with 71 tonnes of fuel consumption savings and reduced CO2 emissions amounting to 51 tonnes over a lifetime of 20 years.
Olympios AV, McTigue JD, Sapin P, et al., 2021, Pumped-thermal electricity storage based on Brayton cycles, Reference Module in Earth Systems and Environmental Sciences, ISBN: 9780124095489
Pumped-thermal electricity storage (PTES) based on a reversible (Joule-)Brayton cycle is a promising grid-scale energy storage technology, whose working principle is to store electricity in the form of high-grade thermal energy. This chapter provides an overview of the inner workings, operating principle and current development status of the many PTES variants, as proposed to date in the scientific literature or by manufacturers. The potential and competitiveness of the various candidate designs is quantified by – and discussed thanks to the definition of – specific techno-economic indicators. Investment cost and thermodynamic performance estimates are reported and used to assess the value of this technology as a potential large-scale, long-duration and long-lifetime energy storage option with unique sector-coupling features and low geographical constraints.
Song J, Olympios A, Mersch M, et al., 2021, Integrated organic Rankine cycle (ORC) and heat pump (HP) systems for domestic heating, ECOS 2021 - The 34rth International Conference On Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, Publisher: ECOS
Space and water heating represent a significant share of the overall energy consumption in the domestic sector. Decarbonising heat, though challenging, is acknowledged as having a key role to play(as exemplifiedby the Domestic Renewable Heat Incentive launched in 2014 in the UK, amongst other)in achievingemissionsreduction targets andalleviatingproblems related to energy shortage and environmental deterioration. Novel, highly efficientheating technologies have attracted increasing interest in this context, in particular in regions with colderclimatesand higherheating demands. Specifically, thermally-driven heat-pumping technologies are a promising solution to meetingenergy-efficiency targets by increasing the effectiveheat-to-fuelratio(HFR)of heatingsystems. In this paper,thermally-driven integrated organic Rankine cycle (ORC) and heat pump (HP) systems are proposed for domestic heating applications, in which the ORC system is driven by heat from fuel (e.g., gas) combustion and generates power to drive an air-source vapour-compression HP system. A heat-transfer fluid is heatedin the condensers of the two sub-systems to the required temperature for heat provision. Two system configurations with reversed heat-transfer fluidflow directions are presented and compared. Suitable, lowglobal-warming-potential (GWP) working fluids for both the ORC and HP systems are considered and parametric optimisation is performed to determine optimal thermodynamic performanceand system layouts. In aconfiguration in whichthe heat-transfer fluidflows firstthroughthe HP condenser andthen through the ORC condenser in series,the HFRreaches values of 1.26-2.04 forair-source temperaturesranging from -15 to 15 °C and for heat provision temperaturesfrom 35 °C to 60 °C.Aperformance enhancement up to 8-19% relative to theconfiguration withthe heat-transfer fluidflowingin thereversedirection, i.e., through the ORC condenser and then theHP condenser in serie
Mersch M, Olympios A, Sapin P, et al., 2021, Solar-thermal heating potential in the UK: A techno-economic whole-energy system analysis, ECOS 2021 - The 34rth International Conference On Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, Publisher: ECOS
We investigate the potential of solar-thermal collectorsas a sustainable heat-generation technology in the UK. The costs and performance of commercially-available collectors are surveyed and four representative collectors are investigated using a techno-economic model of solar heating for households. A parametric study of different collectorsand storage tank sizes is conducted to assess the potential and economics of different system layouts. It is shown that moderately-sized systems with a collector area of 4m2 and a tank size of 150L can provide up to 70% of the domestic hot water demand of a typical household in the UK. Based on the data from the solar-thermal heating model at household scale, performance maps are developed to estimate the heat output from different systems under varying operating conditions. These are then used to assess solar-thermal systems in a heating-sector decarbonisation model.The model is a mixed-integer linear programming model that optimises the capacity expansion of the UK domestic heating sector until 2050 as well as the annual operating schedules of the different technologies. It is found that solar-thermal heating requires incentives in order to be competitive with hydrogen boilers or electric heat pumps. However, if solar thermal collectors are deployed, they provide significant system value by reducing the demand for carbon-neutral hydrogen or electricity. An investment incentive of £3,000per solar-thermal system leads to a deployment of over150GW of solar-thermal capacity by 2050, which reduces the annual hydrogen demand by 240 TWh compared to the baseline without solar-thermal heating, while the electricity demand increases by 90 TWh due to heat pumps and electric resistive heatersbeing used as backup heatingtechnologies.
Enayatollahi H, Sapin P, Unamba CK, et al., 2021, A control-oriented ANFIS model of evaporator in a 1-kWe organic Rankine cycle prototype, Electronics, Vol: 10, Pages: 1-18, ISSN: 1450-5843
This paper presents a control-oriented neuro-fuzzy model of brazed-plate evaporators for use in organic Rankine cycle (ORC) engines for waste heat recovery from exhaust-gas streams of diesel engines, amongst other applications. Careful modelling of the evaporator is both crucial to assess the dynamic performance of the ORC system and challenging due to the high nonlinearity of its governing equations. The proposed adaptive neuro-fuzzy inference system (ANFIS) model consists of two separate neuro-fuzzy sub-models for predicting the evaporator output temperature and evaporating pressure. Experimental data are collected from a 1-kWe ORC prototype to train, and verify the accuracy of the ANFIS model, which benefits from the feed-forward output calculation and backpropagation capability of the neural network, while keeping the interpretability of fuzzy systems. The effect of training the models using gradient-descent least-square estimate (GD-LSE) and particle swarm optimisation (PSO) techniques is investigated, and the performance of both techniques are compared in terms of RMSEs and correlation coefficients. The simulation results indicate strong learning ability and high generalisation performance for both. Training the ANFIS models using the PSO algorithm improved the obtained test data RMSE values by 29% for the evaporator outlet temperature and by 18% for the evaporator outlet pressure. The accuracy and speed of the model illustrate its potential for real-time control purposes.
Olympios A, Krishnaswamy A, Stollery C, et al., 2021, Techno-economic comparison of hydrogen- and electricity-driven technologies for the decarbonisation of domestic heating, 16th Conference on Sustainable Development of Energy, Water and Environment Systems (SDEWES 2021)
Sustainable transition pathways currently being proposed for moving away from the use of natural gas and oil in domestic heating focus on two main energy vectors: electricity and hydrogen. The former transition would most likely be implemented using electric vapour-compression heat pumps, which are currently experiencing market growth in many industrialised countries. Electric heat pumps have proven to be an efficient alternative to gas boilers under certain conditions, but their techno-economic potential is highly dependent on the local climate conditions. Hydrogen-based heating systems, which could potentially utilise existing natural gas infrastructure, are being proposed as providing an attractive opportunity to maximise the use of existing assets to facilitate the energy-system transition. In this case, hydrogen can substitute natural gas in boilers or in thermally driven absorption heat pumps. Both heating system transition pathways may involve either installing new technologies at the household level or producing heat in centralised hubs and distributing it via district-heating systems. Although the potential of hydrogen in the context of heating decarbonisation has been explored in the past, a comprehensive comparison of electricity- and hydrogen-driven domestic heating options is lacking in literature. In this paper, a thermodynamic and economic methodology is developed to assess the competitiveness of a domestic-scale ammonia-water absorption heat pump driven by heat from a hydrogen boiler compared to a standalone hydrogen boiler, a classic vapour-compression heat pump and district heating, all from a homeowner’s perspective. Using a previously developed electric heat pump model, the different systems are compared for various climate conditions and fuel-price scenarios under a unified framework. The coefficient of performance of the absorption heat pump system under design conditions and the total system cost are found to be 1.4 and £5400, resp
Liu Z, Romagnoli A, Sapin P, et al., 2021, Dynamic control strategies for a solar-ORC system using first-law dynamic and data-driven machine learning models, 6th International Seminar on ORC Power Systems, Pages: 1-14, ISSN: 2709-7609
In this study, we developed and assessed the potential of dynamic control strategies for a domestic scale 1-kW solar thermal power system based on a non-recuperated organic Rankine cycle (ORC) engine coupled to a solar energy system. Such solar-driven systems suffer from part-load performance deterioration due to diurnal and inter-seasonal fluctuations in solar irradiance and ambient temperature. Real-time control strategies for adjusting the operating parameters of these systems have shown great potential to optimise their transient response to time-varying conditions, thus allowing significant gains in the power output delivered by the system. Dynamic model predictive control strategies rely on the development of computationally efficient, fast-solving models. In contrast, traditional physics-based dynamic process models are often too complex to be used for real-time controls. Machine learning techniques (MLTs), especially deep learning artificial neural networks (ANN), have been applied successfully for controlling and optimising nonlinear dynamic systems. In this study, the solar system was controlled using a fuzzy logic controller with optimised decision parameters for maximum solar energy absorption. For the sake of obtaining the optimal ORC thermal efficiency at any instantaneous time, particularly during part-load operation, the first-law ORC model was first replaced by a fast-solving feedforward network model, which was then integrated with a multi-objective genetic algorithm, such that the optimal ORC operating parameters can be obtained. Despite the fact that the feedforward network model was trained using steady-state ORC performance data, it showed comparable results compared with the first-principle model in the dynamic context, with a mean absolute error of 3.3 percent for power prediction and 0.186 percentage points for efficiency prediction.
Olympios AV, Pantaleo AM, Sapin P, et al., 2020, On the value of combined heat and power (CHP) systems and heat pumps in centralised and distributed heating systems: Lessons from multi-fidelity modelling approaches, Applied Energy, Vol: 274, Pages: 1-19, ISSN: 0306-2619
This paper presents a multi-scale framework for the design and comparison of centralised and distributed heat generation solutions. An extensive analysis of commercially available products on the UK market is conducted to gather information on the performance and cost of a range of gas-fired combined heat and power (CHP) systems, air-source heat pumps (ASHPs) and ground-source heat pumps (GSHPs). Data-driven models with associated uncertainty bounds are derived from the collected data, which capture cost and performance variations with scale (i.e., size and rating) and operating conditions. In addition, a comprehensive thermoeconomic (thermodynamic and component-costing) heat pump model, validated against manufacturer data, is developed to capture design-related performance and cost variations, thus reducing technology-related model uncertainties. The novelty of this paper lies in the use of multi-fidelity approaches for the comparison of the economic and environmental potential of important heat-generation solutions: (i) centralised gas-fired CHP systems associated with district heating network; (ii) gas-fired CHP systems or GSHPs providing heat to differentiated energy communities; and (iii) small-scale micro-CHP systems, ASHPs or GSHPs, installed at the household level. The pathways are evaluated for the case of the Isle of Dogs district in London, UK. A centralised CHP system appears as the most profitable option, achieving annual savings of £13 M compared to the use of decentralised boilers and a levelised cost of heat equal to 31 £/MWhth. However, if the carbon intensity of the electrical grid continues to reduce at current rates, CHP systems will only provide minimal carbon savings compared to boilers (<6%), with heat pumps achieving significant heat decarbonisation (55–62%). Differentiating between high- and low-performance and cost heat pump designs shows that the former, although 25% more expensive, have significantly lower annualised
Olympios A, Hoisenpoori P, Mersch M, et al., 2020, Optimal design of low-temperature heat-pumping technologies and implications to the whole energy system, The 33rd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems.
This paper presents a methodology for identifying optimal designs for air-source heat pumps suitable for domestic heating applications from the whole-energy system perspective, accounting explicitly for a trade-off between cost and efficiency, as well as for the influence of the outside air temperature during off-design operation. The work combines dedicated brazed-plate and plate-fin heat-exchanger models with compressor efficiency maps, as well as equipment costing techniques, in order to develop a comprehensive technoeconomic model of a low-temperature air-source heat pump with a single-stage-compressor, based on the vapour-compression cycle. The cost and performance predictions are validated against manufacturer data and a non-linear thermodynamic optimisation model is developed to obtain optimal component sizes for a set of competing working fluids and design conditions. The cost and off-design performance of different configurations are integrated into a whole-energy system capacity-expansion and unit-dispatch model of the UK power and heat system. The aim is to assess the system value of proposed designs, as well as the implications of their deployment on the power generation mix and total transition cost of electrifying domestic heat in the UK as a pathway towards meeting a national net-zero emission target by 2050. Refrigerant R152a appears to have the best design and off-design performance, especially compared to the commonly used R410a. The size of the heat exchangers has a major effect on heat pump performance and cost. From a wholesystem perspective, high-performance heat pumps enable a ~20 GW (~10%) reduction in the required installed power generation capacity compared to smaller-heat-exchanger, low-performance heat pumps, which in turn requires lower and more realistic power-grid expansion rates. However, it is shown that the improved performance as a result of larger heat exchangers does not compensate overall for the increased technology cost, with
Sapin P, Simpson M, Olympios A, et al., 2020, Cost-benefit analysis of reversible reciprocating-piston engines with adjustable volume ratio in pumped thermal electricity storage, 33rd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems (ECOS 2020), Publisher: Curran Associates, Inc.
Decarbonisation of heating, cooling and/or power services through the utilisation of renewable en-ergy sources relies on the development of efficient and economically-viable energy storage technolo-gies, ideally without geographical constraints. Pumped thermal electricity storage (PTES) is a strongcandidate technology – along with reversible Rankine cycle, (advanced adiabatic) compressed airenergy storage (CAES), and liquid air energy storage (LAES). One of the leading PTES variants isthe reversible Joule-Brayton cycle engine, where energy is stored as sensible heat in hot and coldthermal stores, while the temperature difference is achieved through gas compression and expansionprocesses. For cost reasons, and to achieve high round-trip efficiencies, it is advantageous for thecompression and expansion machines used in PTES plants to be reversible. Positive-displacementdevices offer this possibility. In particular, recent developments in pneumatically or electromagneti-cally actuated intake and exhaust valves could pave the way for high-efficiency reversible reciprocat-ing compression-expansion devices based on variable-valve control in real time. Advanced variablevalve timing (VVT) is a promising feature that allows piston machines not only to be operated bothas reversible compression and expansion devices, but also to maintain high efficiencies over a widerange of operating conditions, thanks to the possibility of adjusting the built-in volume ratio of a par-ticular machine. With enhanced part-load performance, such disruptive piston machines offer greatpotential for round-trip efficiency enhancement and cost minimisation of PTES storage plants. In thiswork, a cost-benefit analysis of innovative VVT-fitted reciprocating-piston technology is performedusing: (i) comprehensive dynamic reduced-order models to predict the compressor-expander perfor-mance for design optimisation, and (ii) Schumann-style one-dimensional models for simulating heatand mass transf
Nemati H, Moghimi MA, Sapin P, et al., 2020, Shape optimisation of air-cooled finned-tube heat exchangers, International Journal of Thermal Sciences, Vol: 150, Pages: 1-14, ISSN: 1290-0729
The use of annular fins in air-cooled heat exchangers is a well-known solution, commonly used in air-conditioning and heat-recovery systems, for enhancing the air-side heat transfer. Although associated with additional material and manufacturing costs, custom-designed finned-tube heat exchangers can be cost-effective. In this article, the shape of the annular fins in a multi-row air heat exchanger is optimised in order to enhance performance without incurring a manufacturing cost penalty. The air-side heat transfer, pressure drop and entropy generation in a regular, four-row heat exchanger are predicted using a steady-state turbulent CFD model and validated against experimental data. The validated simulation tool is then used to perform model-based optimisation of the fin shapes. The originality of the proposed approach lies in optimising the shape of each fin row individually, resulting in a non-homogenous custom bundle of tubes. Evidence of this local-optimisation potential is first provided by a short preliminary study, followed by four distinct optimisation studies (with four distinct objective functions), aimed at addressing the major problems faced by designers. Response-surface methods – namely, NLPQL for single-objective and MOGA for multi-objective optimisations – are used to determine the optimum configuration for each optimisation strategy. It is shown that elliptical annular-shaped fins minimise the pressure drop and entropy generation, while circular-shaped fins at the entrance region (i.e., first row) can be employed to maximise heat transfer. The results also show that, for the scenario in which the total heat transfer rate is maximised and the pressure drop minimised, the pressure drop is reduced by up to 31%, the fin weight is reduced up to 23%, with as little as a 14% decrease in the total air-side heat transfer, relative to the case in which all the fins across the tube bundle are circular. Moreover, in all optimised cases, the entropy
Kadivar MR, Moghimi MA, Sapin P, et al., 2019, Annulus eccentricity optimisation of a phase-change material (PCM) horizontal double-pipe thermal energy store, Journal of Energy Storage, Vol: 26, ISSN: 2352-152X
The application of phase-change materials (PCMs) has received significant interest for use in thermal energy storage (TES) systems that can adjust the mismatch between the energy availability and demand. In the building sector, for example, PCMs can be used to reduce air-conditioning energy consumption by increasing the thermal capacity of the walls. However, as promising this technology may be, the poor thermal conductivity of PCMs has acted as a barrier to its commercialization, with many heat-transfer enhancement solutions proposed in the literature, such as microencapsulation or metal foam inserts, being either too costly and/or complex. The present study focuses on a low-cost and highly practical solution, in which natural-convective heat transfer is enhanced by placing the PCM in an eccentric annulus within a horizontal double-pipe TES heat exchanger. This paper presents an annulus-eccentricity optimisation study, whereby the optimal radial and tangential eccentricities are determined to minimize the charging time of a PCM thermal energy store. The storage performance of several geometrical configurations is predicted using a computational fluid dynamics (CFD) model based on the enthalpy-porosity formulation. The optimal geometrical configuration is then determined with response surface methods. The horizontal double-pipe heat exchanger studied considered here is an annulus filled with N-eicosane as the PCM for initial studies. In presence of N-eicosane, for the concentric configuration (which is the baseline case), the charging is completed at Fo = 0.64, while the charging of optimum eccentric geometries with the quickest and slowest charging is completed at Fo = 0.09 and Fo = 2.31, respectively. In addition, an investigation on the discharging performance of the studied configurations with N-eicosane shows the quickest discharge occurs with the concentric annulus case at Fo = 0.99, while the discharge time of the proposed optimum annuli is about three times
Pantaleo A, Simpson M, Rotolo G, et al., 2019, Thermoeconomic optimisation of small-scale organic Rankine cycle systems based on screw vs. piston expander maps in waste heat recovery applications, Energy Conversion and Management, Vol: 200, ISSN: 0196-8904
The high cost of organic Rankine cycle (ORC) systems is a key barrier to their implementation in waste heat recovery (WHR) applications. In particular, the choice ofexpansion device has a significant influence on this cost, strongly affecting the economic viabilityof an installation. In this work, numerical simulations and optimisation strategies are used to compare the performance and profitability of small-scale ORC systems using reciprocating-piston orsingle/two-stage screw expanders whenre covering heat from the exhaust gases of a 185-kWinternal combustion engine operating in baseload mode. The study goes beyond previous work by directly comparingthese small-scaleexpanders fora broad range of working fluids, and by exploring the sensitivity of project viability to key parameters such as electricity price and onsite heat demand.For the piston expander, a lumped-massmodel and optimisation based on artificial neural networks are used to generate performance maps, while performance and cost correlations from the literature are used for the screw expanders. The thermodynamic analysisshows that two-stage screw expanders typically deliver more power than either single-stage screw or piston expanders due to their higher conversion efficiencyat the required pressure ratios. The best fluids areacetone and ethanol, as these provide a compromise between the exergy losses in the condenser and in the evaporatorin this application. The maximum net power output isfound to be 17.7kW, from an ORC engine operating withacetone anda two-stage screw expander. On the other hand, the thermoeconomic optimisation shows that reciprocating-piston expandersshow a potential for lowerspecific costs, and sincesuchan expander technology is not mature, especially at these scales, this finding motivates further consideration of this component. A minimum specific investment cost of 1630€/kW is observed for an ORC engine with a pisto
Simpson M, Chatzopoulou M, Oyewunmi O, et al., 2019, Technoeconomic analysis of internal combustion engine - organic Rankine cycle systems for combined heat and power in energy-intensive buildings, Applied Energy, Vol: 253, Pages: 1-13, ISSN: 0306-2619
For buildings with low heat-to-power demand ratios, installation of internal combustion engines (ICEs) for combined heat and power (CHP) results in large amounts of unused heat. In the UK, such installations risk being ineligible for the CHP Quality Assurance (CHPQA) programme and incurring additional levies. A technoeconomic optimisation of small-scale organic Rankine cycle (ORC) engines is performed, in which the ORC engines recover heat from the ICE exhaust gases to increase the total efficiency and meet CHPQA requirements. Two competing system configurations are assessed. In the first, the ORC engine also recovers heat from the CHP-ICE jacket water to generate additional power. In the second, the ORC engine operates at a higher condensing temperature, which prohibits jacket-water heat recovery but allows heat from the condenser to be delivered to the building. When optimised for minimum specific investment cost, the first configuration is initially found to deliver 20% more power (25.8 kW) at design conditions, and a minimum specific investment cost (1600 £/kW) that is 8% lower than the second configuration. However, the first configuration leads to less heat from the CHP-ICE being supplied to the building, increasing the cost of meeting the heat demand. By establishing part-load performance curves for both the CHP-ICE and ORC engines, the economic benefits from realistic operation can be evaluated. The present study goes beyond previous work by testing the configurations against a comprehensive database of real historical electricity and heating demand for thirty energy-intensive buildings at half-hour resolution. The discounted payback period for the second configuration is found to lie between 3.5 and 7.5 years for all of the buildings considered, while the first configuration is seen to recoup its costs for only 23% of the buildings. The broad applicability of the second configuration offers attractive opportunities to increase manufacturing volumes an
Unamba CK, Sapin P, Li X, et al., 2019, Operational optimisation of a non-recuperative 1-kWe organic Rankine cycle engine prototype, Applied Sciences, Vol: 9, Pages: 3024-3024, ISSN: 2076-3417
Several heat-to-power conversion technologies are being proposed as suitable for waste-heat recovery (WHR) applications, including thermoelectric generators, hot-air (e.g., Ericsson or Stirling) engines and vapour-cycle engines such as steam or organic Rankine cycle (ORC) power systems. The latter technology has demonstrated the highest efficiencies at small and intermediate scales and low to medium heat-source temperatures and is considered a suitable option for WHR in relevant applications. However, ORC systems experience variations in performance at part-load or off-design conditions, which need to be predicted accurately by empirical or physics-based models if one is to assess accurately the techno-economic potential of such ORC-WHR solutions. This paper presents results from an experimental investigation of the part-load performance of a 1-kWe ORC engine, operated with R245fa as a working fluid, with the aim of producing high-fidelity steady-state and transient data relating to the operational performance of this system. The experimental apparatus is composed of a rotary-vane pump, brazed-plate evaporator and condenser units and a scroll expander magnetically coupled to a generator with an adjustable resistive load. An electric heater is used to provide a hot oil-stream to the evaporator, supplied at three different temperatures in the current study: 100, 120 and 140 ∘ C. The optimal operating conditions, that is, pump speed and expander load, are determined at various heat-source conditions, thus resulting in a total of 124 steady-state data points used to analyse the part-load performance of the engine. A maximum thermal efficiency of 4.2 ± 0.1% is reported for a heat-source temperature of 120 ∘ C, while a maximum net power output of 508 ± 2 W is obtained for a heat-source temperature at 140 ∘ C. For a 100- ∘ C heat source, a maximum exergy efficiency of 18.7 ± 0.3% is achieved. A detailed exergy analysis all
Li X, Song J, Simpson M, et al., 2019, THERMO-ECONOMIC COMPARISON OF ORGANIC RANKINE AND CO2 CYCLE SYSTEMS FOR LOW-TO-MEDIUM TEMPERATURE APPLICATIONS, 5th International Seminar on ORC Power Systems
Olympios A, Pantaleo AM, Sapin P, et al., 2019, Centralised vs distributed energy systems options: District heating for the Isle of Dogs in London, ICAE2019: The 11th International Conference on Applied Energy
This work focuses on a multi-scale framework for the design and comparison of low-carbon heat generation solutions to serve the residential and commercial thermal energy demand of high energy density urban areas. The adopted methodology assesses the cost and performance of four configurations integrated in a district heating network: (i) centralised cogeneration with gas turbine and bottoming steam turbine with flexible heat-to-electricity ratio; (ii) centralised cogeneration with gas-fired internal combustion engine; (iii) distributed building-integrated ground-source heat pumps for domestic hot water only; and (iv) distributed building-integrated ground-source heat pumps for both domestic hot water and space heating. Cost and performance data were obtained by conducting relevant market research and developing a simplified heat pump thermodynamic model. The different configurations are evaluated utilizing whole-year space heating and hot water demand profiles for the Isle of Dogs area in East London, UK. Scale effects are included by considering various technology size scenarios and the results indicate that a 50 MW centralised internal combustion cogeneration system appears to be the most profitable option, while the competitiveness of building-integrated heat pumps is dependent on their size.
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