Publications
16 results found
Acha Izquierdo S, Le Brun N, Shah N, et al., 2019, Assessing the modelling approach and datasets required for fault detection in photovoltaic systems, IEEE Industry Applications Society Annual Meeting, Publisher: IEEE
Reliable monitoring for photovoltaic assets (PVs) is essential to ensuring uptake, long term performance, and maximum return on investment of renewable systems. To this end this paper investigates the input data and machine learning techniques required for day-behind predictions of PV generation, within the scope of conducting informed maintenance of these systems. Five years of PV generation data at hourly intervals were retrieved from four commercial building-mounted PV installations in the UK, as well as weather data retrieved from MIDAS. A support vector machine, random forest and artificial neural network were trained to predict PV power generation. Random forest performed best, achieving an average mean relative error of 2.7%. Irradiance, previous generation and solar position were found to be the most important variables. Overall, this work shows how low-cost data driven analysis of PV systems can be used to support the effective management of such assets.
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
Escriva EJS, Acha S, LeBrun N, et al., 2019, Modelling of a real CO2 booster installation and evaluation of control strategies for heat recovery applications in supermarkets, International Journal of Refrigeration, Vol: 107, Pages: 288-300, ISSN: 0140-7007
This paper compares and quantifies the energy, environmental and economic benefits of various control strategies recovering heat from a CO2 booster system in a supermarket for space heating with the purpose of understanding its potential for displacing natural gas fuelled boilers. A theoretical steady-state model that simulates the behaviour of the CO2 system is developed and validated against field measurements obtained from an existing refrigeration system in a food-retail building located in the United Kingdom. Five heat recovery strategies are analysed by modifying the mass flows and pressure levels in the condenser. The model shows that a reduction of 48% in natural-gas consumption is feasible by the installation of a de-superheater and without any advanced operating strategy. However, the CO2 system can fully supply the entire space-heating requirement by adopting alternative control strategies, albeit by penalising the coefficient of performance (COP) of the compressor. Results show that the best energy strategy can reduce total consumption by 32%, while the best economic strategy can reduce costs by 6%. Findings from this work suggest that heat recovery systems can bring substantial benefits to improve the overall efficiency of energy-intensive buildings; although trade-offs need to be carefully considered and further analysed before embarking on such initiatives.
Voulgaropoulos V, Zadrazil I, Le Brun N, et al., 2019, On the link between experimentally‐measured turbulence quantities and polymer‐induced drag reduction in pipe flows, AIChE Journal, Vol: 65, Pages: 1-13, ISSN: 0001-1541
In this study, we investigate the hydrodynamics of polymer‐induced drag reduction in horizontal turbulent pipe flows. We provide spatiotemporally resolved information of velocity and its gradients obtained with particle image velocimetry (PIV) measurements in solutions of water with dissolved polyethylene oxide (PEO) of three different molecular weights, at various dilute concentrations and with flow Reynolds numbers from 35, 000 to 210, 000. We find that the local magnitudes of important turbulent flow variables correlate with the measured levels of drag reduction irrespective of the flow Reynolds number, polymer weight and concentration. Contour maps illustrate the spatial characteristics of this correlation. A relationship between the drag reduction and the turbulent flow variables is found. The effects of the polymer molecular weight, its concentration and the Reynolds number on the flow are further examined through joint probability distributions of the fluctuations of the streamwise and spanwise velocity components.
Le Brun N, Markides CN, 2019, A Galinstan-Filled Capillary Probe for Thermal Conductivity Measurements and Its Application to Molten Eutectic KNO3-NaNO3-NaNO2 (HTS) up to 700K (vol 36, 3222, 2015), INTERNATIONAL JOURNAL OF THERMOPHYSICS, Vol: 40, ISSN: 0195-928X
The successful measurement of the thermal conductivity of molten salts is a challenging undertaking due to the electrically conducting and possibly also aggressive nature of the materials, as well as the elevated temperatures at which these data are required. For accurate and reproducible measurements, it is important to develop a suitable experimental apparatus and methodology. In this study, we explore a modified version of the transient hot-wire method, which employs a molten-metal-filled capillary in order to circumvent some of the issues encountered in previous studies. Specifically, by using a novel flexible U-shaped quartz-capillary, filled with a eutectic mixture of gallium, indium and tin, commercially known as Galinstan, we proceed to measure the thermal conductivity of molten eutectic KNO3–NaNO3–NaNO2–NaNO2. The new probe is demonstrated as being able to measure the thermal conductivity of this molten salt, which is found to range from 0.48 W⋅m−1⋅K−1 at 500 K to 0.47 W⋅m−1⋅K−1 at close to 700 K, with an overall expanded uncertainty (95 % confidence) of 3.1 %. The quartz is found to retain its electrically insulating properties and no current leakage is detected in the sample over the investigated temperature range. The thermal conductivity data reported in the present study are also used to elucidate a partial disagreement found in the literature for this material.
Olympios A, Le Brun N, Acha Izquierdo S, et al., 2019, Installation of a dynamic controller for the optimal operation of a CHP engine in a supermarket under uncertainty, ECOS2019: 32nd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems
This work is concerned with the integration and coordination of decentralized combined heat and power (CHP) systems in commercial buildings. Although extensive research has been performed on theoretically optimizing the design, sizing and operation of CHP systems, less effort has been devoted to an understanding of the practical challenges and the effects of uncertainty in implementing advanced algorithms to real-world applications. This paper provides details of an undergoing field trial involving the installation of a dynamic controller for the optimal operation of an existing CHP engine, which provides electricity and heat to a supermarket. The challenges in developing and applying an optimization framework and the software architecture required to implement it are discussed. Deterministic approaches that involve no measure of uncertainty provide limited useful insight to decision makers. For this reason, the methodology here develops a stochastic programming technique, which performs Monte Carlo simulations that can consider the uncertainty related to the exporting electricity price. The method involves the formation of a bi-objective function that represents a compromise between maximizing the expected savings and minimizing the associated risk. The results reveal a risk-return trade-off, demonstrating that conservative operation choices emerging from the stochastic approach can reduce risk by about 15% at the expense of a noticeably smaller reduction of about 10% in expected savings.
Ayoub AN, Gaigneux A, Le Brun N, et al., 2019, The development of a carbon roadmap investment strategy for carbon intensive food retail industries, International Conference on Sustainable Energy and Resource Use in Food Chains including Workshop on Energy Recovery Conversion and Management, Publisher: Elsevier, Pages: 333-342, ISSN: 1876-6102
This work presents an approach to develop an innovative decarbonisation investment strategy framework for carbon intensive UK industries by using statistical analysis and optimisation modelling. The case study focuses on taking a representative sample of retail buildings and assesses the financial viability of installing low-carbon Combined Heat and Power units (CHPs) and Photovoltaic Solar Panels (PVs) across a portfolio of buildings. Simulation of each building are initially conducted, and the results generate a set of regression coefficients, via a multivariate adaptive regression splines (MARS), which are inputted into a Mixed Integer Linear Programming (MILP) problem. Solving the MILP yields the optimal decarbonisation investment strategy for the case study up to 2050, considering market trends such as electricity prices, gas prices and policy incentives. Results indicate the level of investment required per year, the operational and carbon savings associated, and a program for such investments. This method is reiterated for several scenarios where different parameters such as utility prices, capital costs and grid carbon factors are forecasted up to 2050 (following the Future Energy Scenarios from National Grid). This work shows how a clear mathematical framework can assist decision-makers in commercial organisations to reduce their carbon footprint cost-effectively and thus reach science-based targets.
Sorrentino A, Pantaleo AM, Markides C, et al., 2018, Energy performance and profitability of biomass boilers in commercial sector: the case study of Sainsbury’s stores in the UK, 73rd Conference of the Italian Thermal Machines Engineering Association (ATI 2018), Publisher: Elsevier, Pages: 539-646, ISSN: 1876-6102
Commercial buildings or shopping malls are characterized by large thermal and electrical energy consumptions with high variability of energy demand. Therefore, there is a large interest to explore novel renewable energy generation systems for these applications. A novel flexible configuration of biomass-fired CHP system with organic Rankine cycle(ORC) is here proposedand applied to the case study of Sainsbury’s supermarkets in the UK.The proposed configuration adoptsa molten salt (MS) circuitto transfer heat from the biomass furnace to the ORC plant. A thermal Energy Storage (TES) is proposedtoimprove the flexible operation of the plantand reduce the size of the biomass boiler. Molten salts have been preferredto thermal oil as they have no fire risks and low environmental impactand can be used as medium for a Two Tank TES with a “direct heating” scheme. The planthas beenanalysedusing real input data of biomass boiler installed, conversion efficiency and heat demand from the store. The model is informed by hourly energy costs and electricity feed in tariff in order to define optimal size and operation of the bottoming ORC for the specific case study of large commercial energy end userin the UK.The results show that the use of thermal storage in a biomass-fired ORC plant can improve the boiler efficiency and reduce the biomass consumption in thermal-load following operating mode and increase the investment profitability.
Le Brun N, Charogiannis A, Hewitt GF, et al., 2017, Tackling coolant freezing in generation-IV molten salt reactors, 25th International Conference on Nuclear Engineering, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1-7
In this study we describe an experimental system designed to simulate the conditions of transient freezing which can occur in abnormal behaviour of molten salt reactors (MSRs). Freezing of coolant is indeed one of the main technical challenges preventing the deployment of MSR. First a novel experimental technique is presented by which it is possible to accurately track the growth of the solidified layer of fluid near a cold surface in an internal flow of liquid. This scenario simulates the possible solidification of a molten salt coolant over a cold wall inside the piping system of the MSR. Specifically, we conducted measurements using water as a simulant for the molten salt, and liquid nitrogen to achieve high heat removal rate at the wall. Particle image velocimetry and planar induced fluorescence were used as diagnostic techniques to track the growth of the solid layer. In addition this study describes a thermo-hydraulic model which has been used to characterise transient freezing in internal flow and compares the said model with the experiments. The numerical simulations were shown to be able to capture qualitatively and quantitatively all the essential processes involved in internal flow transient freezing. Accurate numerical predictive tools such the one presented in this work are essential in simulating the behaviour of MSR under accident conditions.
Le Brun N, Hewitt GF, Markides CN, 2016, Transient freezing of molten salts in pipe-flow systems: application to the direct reactor auxiliary cooling system (DRACS), Applied Energy, Vol: 186, Pages: 56-67, ISSN: 0306-2619
The possibility of molten-salt freezing in pipe-flow systems is a key concern for the solar-energy industry and a safety issue in the new generation of molten-salt reactors, worthy of careful consideration. This paper tackles the problem of coolant solidification in complex pipe networks by developing a transient thermohydraulic model and applying it to the ‘Direct Reactor Auxiliary Cooling System’ (DRACS), the passive-safety system proposed for the Generation-IV molten-salt reactors. The results indicate that DRACS, as currently envisioned, is prone to failure due to freezing in the air/molten-salt heat exchanger, which can occur after approximately 20 minutes, leading to reactor temperatures above 900 °C within 4 hours. The occurrence of this scenario is related to an unstable behaviour mode of DRACS in which newly formed solid-salt deposit on the pipe walls acts to decrease the flow-rate in the secondary loop, facilitating additional solid-salt deposition. Conservative criteria are suggested to facilitate preliminary assessments of early-stage DRACS designs. The present study is, to the knowledge of the authors, the first of its kind in serving to illustrate possible safety concerns in molten-salt reactors, which are otherwise considered very safe in the literature. Furthermore, and from a broader prospective, the analytical tools developed in this study can also be applied to examine the freezing propensity of molten-salt flows in other complex piping systems where standard, finite element approaches are computationally too expensive.
Le Brun N, Markides C, 2016, A transient model for simulating the freezing process of molten-salt coolants, ICIEA 2016, Publisher: EDP Sciences
Even though molten salts have many useful characteristic, especially as coolants for nuclear reactors, they are prone to freezing due to their high melting point. The solidification of the salt inside the piping system could cause structural damage and stop the flow of coolant with possible serious problems. Modelling the freezing process is therefore of primary importance for nuclear safety. In this study a quasi-steady thermo-hydraulic model has been derived and implemented to describe the transient freezing of molten salts. The partial differential equations describing the solidification/melting of the salt are solved numerically using a combination of standard explicit and implicit methods. Validation of the model is presented based on previous experimental studies for two separate cases.
Le Brun N, Markides C, 2016, Framework for the energetic assessment of South and South-East Asia fixed chimney bull’s trench kiln, ICIEA 2016, Publisher: EDP Sciences
One of the major sources of fuel consumption and greenhouse gas emission in South and South-East Asia is brick manufacturing. One of the most commonly implemented technologies for brick manufacturing in this region is the fixed chimney Bull’s trench kiln (FCBTK). This type of technology largely depends on manual labour and is very inefficient when compared to more modern technologies. Because the adoption of more advanced technologies is hindered by the socio-economical background, the much needed innovations in the brick sector are necessarily related to improving/modifying the FCBTK already operational. However, few scientific studies have been conducted on FCBTK probably due to the basic level of technological development. Such studies are however important to systematically and methodologically assess the challenges and solutions in FCBTK. In this study we develop a thermo-energetic model to evaluate the importance of the parameters pertained to FCBTK construction and operation. The prospective of this study is to build an initial thermo-energetic framework that will serve as a basis to investigate possible energetic improvements.
Freeman J, Guarracino I, Unamba CK, et al., 2016, Developing a test bed for small-scale ORC expanders in waste-heat recovery applications, 3rd Annual Engine ORC Consortium Workshop
Le Brun N, Markides, Bismarck, et al., 2016, On the drag reduction effect and shear stability of improved acrylamide copolymers for enhanced hydraulic fracturing, Chemical Engineering Science, Vol: 146, Pages: 135-143, ISSN: 0009-2509
Polymeric drag reducers, such as partially hydrolysed polyacrylamide (PHPAAm), are important chemical additives in hydraulic fracturing fluids as they can significantly decrease the frictional pressure drop in the casing (by up to 80%),resulting in an increase of the injection rate that can be delivered to the fracturing point. The incorporation of sodium 2-acrylamido-2-methylpropane sulfonic acid (NaAMPS) moieties in to polyacrylamide (PAAm) can further improve the performance of fracturing fluids by addressing some compatibility issues related to the use of PHPA Am, e.g., the sensitivity to water salinity . In this study, three types of poly(acrylamide-co-NaAMPS) and pure PHPAAm were investigated with respect to polymer induced drag reduction and mechanical polymer degradationin turbulent pipe flow in a pressure-driven pipe flow facility. The test section comprised a horizontal 1” bore circular cross-section pipe. The facility was modified in order to allow, long time/length experiments by automatically recirculating the polymer solution in a closed-loop through the test section.The presence of NaAMPS groups in the copolymer backbone is found to increase the ability of PHPAAm to reduce frictional drag while the vulnerability to mechanical degradation remains unaffected. The drag reduction of NaAMPS copolymer solutions can be described by a modified version of Virk’s correlation (1967), extended to include the effect of Reynolds number. Polymer mechanical degradation is found to proceed until the friction reducer is almost ineffective in reducing drag. This phenomenon is in contrast with the most common correlationfor polymer degradation, which predicts the existence of a n asymptotic(but finite) limit to the reduced drag reduction.
Acha S, Le Brun N, Lambert R, et al., 2016, UK half-hourly regional electricity cost modelling for commercial end users
The rising prices of electricity in the UK risks rendering businesses uncompetitive if these costs are not controlled. This issue has created the need to properly comprehend the tariffs and costing framework that influence the total cost of electricity for non-domestic customers. This paper details an open source method to model UK electricity regional costs (MUKERC) for commercial end-users; allowing users to visualise and calculate the cost of the electricity they consume. The methodology consists in a bottom-up model that defines individually all the tariff components and then aggregates them to quantify the cost of a kWh across each half-hour of the day. The disaggregated structure of MUKERC allows users to conduct specific analysis of tariff components and to understand their rich temporal and spatial features. This granularity facilitates understanding which tariffs influence costs more during different time periods. Emphasis is given to showcasing commodity prices and network charges; known as Transmission Use of System and Distribution Use of System tariffs. ‘Representative day’ electricity price curves for different day types, voltage level connections, and across different UK regions for 2016-17 are presented. Outputs from MUKERC can better inform companies on their energy costs and therefore allows them to perform comprehensive and bespoke energy management and energy efficiency strategies as it is possible to understand when and where the cost of electricity is more expensive. Results show that commercial buildings connected at Low Voltage in North Wales and Merseyside and the South West face the highest average electricity prices, whereas consumers connected to High Voltage in London and the North West have the cheapest electricity in the UK. Other significant findings indicate sites connected at low-voltage pay 7.5% more than high-voltage sites, winter weekday costs are 18% higher than summer weekday costs, and overall weekdays are 35% more
Le Brun N, Markides CNM, 2015, A Galinstan-Filled Capillary Probe for Thermal Conductivity Measurements and its Application to Molten Eutectic KNO3-NaNO3-NO2 (HTS) up to 700 K, International Journal of Thermophysics, Vol: 36, Pages: 3222-3238, ISSN: 1572-9567
The successful measurement of the thermal conductivity of molten salts isa challenging undertaking due to the electrically conducting and possibly alsoaggressive nature of the materials, as well as the elevated temperatures atwhich these data are required. For accurate and reproducible measurementsit is important to develop a suitable experimental apparatus and methodology.In this study we explore a modified version of the transient hot-wiremethod, which employs a molten-metal-filled capillary in order to circumventsome of the issues encountered in previous studies. Specifically, by using anovel flexible U-shaped quartz-capillary, filled with a eutectic mixture of gallium,indium and tin, commercially known as Galinstan, we proceed to measurethe thermal conductivity of molten eutectic KNO3−NaNO3−NaNO2.The new probe is demonstrated as being able to measure the thermal conductivityof this molten salt, which is found to range from 0.48 W/m K at500 K to 0.47 W/m K at close to 700 K, with an overall expanded uncertainty(95% confidence) of 3.1%. The quartz is found to retain its electricallyinsulating properties and no current leakage is detected in the sample overthe investigated temperature range. The thermal conductivity data reportedin the present study are also used to elucidate a partial disagreement foundin the literature for this material.
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