Numerical Investigations of the Thermal State of Overhead Lines and Underground Cables in Distribution Networks

As part of extensive activities on the reduction of CO2 emissions, a rapid expansion of power generation using new more fuel efficient technologies (large, medium and embedded scale with combined heat and power (CHP) projects) and renewable energy (wind, biomass, solar PV) is currently taking place in numerous European countries, including the UK. The research presented in this thesis is a part of a UK government funded project, which aims to find answers to how to accommodate increased renewable energy into the distribution network. Current ratings, which are limited by the temperature of the conductors used in the distribution network, are based on worst case scenario conditions and are conservative. The temperature limits can be lifted if one takes into consideration the dynamic changes in the surrounding environmental conditions of the conductors. Implementation of real-time thermal rating of existing power systems could result in greater installed capacities of distributed generation (DG). This research aims to provide new insights into the thermal state of overhead line conductors (OHL) and underground cables (UGC) by using Computational Fluid Dynamic methods. An algorithm consists of building the geometry of the calculation domain, meshing, choosing a model, inputting initial conditions, initiation of the calculation, and analysing results. A part of the UK power system was chosen by Scottish Power Energy Networks for monitoring essential data of OHL conductors in order to validate results of the temperatures of the conductors

Real-time thermal state and component loading estimation in active distribution networks

Highly stochastic loading and distributed generation in the emerging active distribution networks means that electric utilities need to deploy intelligent network management tools in order to use their assets to the fullest. Real-Time Thermal Rating (RTTR) provides the possibility for short term and even real-time active distribution network management, enabling the network to run closer to an overload state without damage. In this dissertation, pertinent developments and proposals are presented in three stages on the path towards the development of a real-time monitoring and operation system for active distribution networks. The first stage is the development of distribution network component thermal models for real time implementation. In this dissertation, a numerical model of the air-gap convective heat transfer for underground cable installations inside unfilled conduit is developed. In addition, a dynamic thermal model is developed for prefabricated secondary substation cabins. The most dominant but difficult to solve heat transfer mechanism, natural convection, is modelled by introducing the stack effect principle into the problem. Measurements from a scaled model of prefabricated substations, measurements from actual cabins and 3D Finite Element Method (FEM) simulations are used to validate the numerical model. In the second stage, this dissertation explores the usability of customer level automatic meter reading (AMR) measurements for distribution network state estimation and for load forecasting applications. A method to forecast substation level loads with their respective confidence intervals using hourly AMR metered customer level consumptions is presented. The forecasting and monitoring of a distribution network in real-time can be met with the modeling of classified type load classes. However, it requires careful incorporation of the necessary factors, such as within-group and between-group correlations of customer classes. Binding the aforementioned findings, in the third stage, a framework for day-ahead hour-by-hour thermal state forecasting and thermal ratings of distribution network components is proposed and studied. This work has demonstrated that up to three hours ahead thermal state forecasting of an active distribution network can be achieved with an acceptable level of accuracy. In this dissertation, the benefits and practical implications of the real-time thermal rating are investigated. The introduction of real-time thermal rating in an active distribution network management system enhances the loading capacity significantly compared to static rating. This has been revealed through an increased utilization of installed DGs and through better integration potential of additional DGs

IEA ECES Annex 31 Final Report - Energy Storage with Energy Efficient Buildings and Districts: Optimization and Automation

At present, the energy requirements in buildings are majorly met from non-renewable sources where the contribution of renewable sources is still in its initial stage. Meeting the peak energy demand by non-renewable energy sources is highly expensive for the utility companies and it critically influences the environment through GHG emissions. In addition, renewable energy sources are inherently intermittent in nature. Therefore, to make both renewable and nonrenewable energy sources more efficient in building/district applications, they should be integrated with energy storage systems. Nevertheless, determination of the optimal operation and integration of energy storage with buildings/districts are not straightforward. The real strength of integrating energy storage technologies with buildings/districts is stalled by the high computational demand (or even lack of) tools and optimization techniques. Annex 31 aims to resolve this gap by critically addressing the challenges in integrating energy storage systems in buildings/districts from the perspective of design, development of simplified modeling tools and optimization techniques

Magnetohydrodynamics (MHD) Engineering Test Facility (ETF) 200 MWe power plant Conceptual Design Engineering Report (CDER)

The reference conceptual design of the magnetohydrodynamic (MHD) Engineering Test Facility (ETF), a prototype 200 MWe coal-fired electric generating plant designed to demonstrate the commercial feasibility of open cycle MHD, is summarized. Main elements of the design, systems, and plant facilities are illustrated. System design descriptions are included for closed cycle cooling water, industrial gas systems, fuel oil, boiler flue gas, coal management, seed management, slag management, plant industrial waste, fire service water, oxidant supply, MHD power ventilatin

Geothermal system optimization in mining environments

Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2010-2011Les ressources particulières à l’environnement minier, tel que l’eau inondant des galeries et des stériles exothermiques, permettent de diminuer les coûts d’installation des systèmes de pompes à chaleur géothermique. Les particularités de l’environnement minier posent toutefois un défi de taille lors de la conception d’un système puisque l’approche utilisée doit considérer, par exemple, la conductivité hydraulique accrue par les excavations ou la génération de chaleur provenant de l’oxydation de minéraux. L’objectif de ce projet de recherche est de simuler l’opération de systèmes géothermiques issus de sites miniers dans le but de démontrer les économies d’énergie potentielles et faciliter l’installation des systèmes. Des approches numériques sont développées avec le programme HydroGeoSphere pour application à des études de cas réalisées aux Mines Gaspé à Murdochville et à la Halde Sud de la Mine Doyon en Abitibi. Un système de pompes à chaleur d’aquifère aux Mines Gaspé est optimisé avec un modèle numérique où sont superposés des éléments 1D et 3D pour représenter les excavations. Les simulations démontrent que le système peut être opéré à partir d’anciens puits de ventilation afin d’éviter d’effectuer des forages. Les stériles de la Halde Sud sont d’abord caractérisés avec un test de réponse thermique conventionnel, analysé avec l’équation de la ligne-source et le principe de superposition considérant les variations du taux d’injection de chaleur. Une méthode numérique est aussi développée pour analyser l’essai influencé par l’hétérogénéité des matériaux et le gradient géothermique prononcé. Le mort terrain et le roc sous la halde sont caractérisés à l’aide d’un nouveau test de réponse thermique effectué avec des câbles chauffants. Des simulations numériques reproduisent ensuite la distribution de température lors d’essais types, laquelle devient rapidement homogène durant la période de restitution thermique ce qui permet d’analyser la température dans le forage sans connaître la position du capteur. L’opération d’un système de pompes à chaleur couplées au sol aménagé sous la Halde Sud est finalement simulée. L’optimisation des charges de chauffage indique que l’échangeur de chaleur situé sous les stériles peut fournir plus d’énergie thermique qu’un échangeur situé dans un environnent conventionnel, réduisant la longueur de forage à l’installation.Resources associated to mining environments, such as mine water and exothermic waste rock, allow a reduction of installation costs of ground source heat pump systems. Compared to other environments, caution is required when designing systems in mining environments because of enhanced hydraulic conductivity created by mine voids or heat generation due to oxidation of minerals. The objective of this study is to simulate the operation of geothermal systems on mine sites to demonstrate energy savings and promote installation. Numerical modeling approaches are developed with the program HydroGeoSphere applied for case studies conducted at the Gaspé Mines in Murdochville and at the South Dump of the Doyon Mine in Abitibi. A groundwater heat pump system at the Gaspé Mines is optimized with a numerical model, where 1D and 3D elements are superposed to adequately represent the mine voids. The simulations show that the system can be operated using former mining shafts to avoid drilling boreholes. Waste rock of the South Dump is initially characterized with a conventional thermal response test analyzed with the lines-source equation and the superposition principle accounting for variations of heat injection rates. A numerical method is also developed to analyze the test that was affected by the heterogeneity of materials and the strong geothermal gradient. The overburden and the host rock below the dump are characterized with a novel thermal response test using heating cables. Numerical simulations then reproduce the temperature distribution during typical tests, which homogenizes rapidly during the recovery period allowing the analysis of temperature inside the borehole without knowing the position of the sensor. The operation of a ground-coupled heat pump system installed under the South Dump is finally simulated. The optimization of heating loads indicates that the heat exchanger located beneath the waste pile can provide more thermal energy than an exchanger located in a conventional environment, reducing bore length required for a given system

Life Cycle & Technoeconomic Modeling

This book aims to perform an impartial analysis to evaluate the implications of the environmental costs and impacts of a wide range of technologies and energy strategies. This information is intended to be used to support decision-making by groups, including researchers, industry, regulators, and policy-makers. Life cycle assessment (LCA) and technoeconomic analysis can be applied to a wide variety of technologies and energy strategies, both established and emerging. LCA is a method used to evaluate the possible environmental impacts of a product, material, process, or activity. It assesses the environmental impact throughout the life cycle of a system, from the acquisition of materials to the manufacture, use, and final disposal of a product. Technoeconomic analysis refers to cost evaluations, including production cost and life cycle cost. Often, in order to carry out technoeconomic analysis, researchers are required to obtain data on the performance of new technologies that operate on a very small scale in order to subsequently design configurations on a commercial scale and estimate the costs of such expansions. The results of the developed models help identify possible market applications and provide an estimate of long-term impacts. These methods, together with other forms of decision analysis, are very useful in the development and improvement of energy objectives, since they will serve to compare different decisions, evaluating their political and economic feasibility and providing guidance on potential financial and technological risks

Radon reduction, improvement of indoor air quality, and energy savings through an original solar ventilation system

This study evaluated the improvement of indoor air quality and energy savings achieved, by an original solar ventilation system installed at test sites exhibiting elevated radon levels. Conventional residential energy conservation measures that limit air exchange rates between the indoors and outdoors have been shown to increase concentrations of radioactive radon decay products as well as other indoor air contaminants. Growing concern about radon lung cancer risks, carbon monoxide poisoning, and the sick building syndrome have increased demand for improved indoor air quality. Due to added heating and cooling loads, ventilation generally incurs substantial installation and operational costs. All commercially available radon mitigation systems, even those equipped with heat recovery devices, operate with net energy loss, and few alleviate other indoor air pollutants. The ventilation system investigated combines energy conservation with low-cost radon reduction and indoor air quality management. Drawing on established mitigation techniques of ventilation, air supply and pressurization, the Solar Radon Reduction System (SRRS) provides energy efficient make-up air for combustion appliances and stack effect losses. Indoor air quality is improved through dilution, slight pressurization, and reduced radon infiltration with induced-draft ventilation. Solar heating of intake air enables the SRRS to operate with energy gain during cold weather, and the blower provides low-energy summertime cooling when outdoor temperatures drop below indoor levels. The system was installed at six homes in Waterloo and Cedar Falls, Iowa, and a detailed assessment was conducted of the extent that the SRRS reduced radon levels and provided energy savings as well as how the system could be improved. Blower door tests were initially conducted to characterize the airtightness of each house. Electronic control units to trigger system operation based on radon levels and intake temperatures were devised, and PC data acquisition systems were installed at each site. The research methodology included synchronized hourly radon concentrations collected at the test homes and a control house maintained with closed conditions over five 10-day test periods. Operational modes tested included radon-trigger, temperature-trigger, and combined trigger system performance. Outlet temperatures and fan status were continuously recorded at five test homes, and dataloggers were additionally placed at two of the sites to measure inlet, outlet and basement temperature and humidity, solar radiation, and outdoor-basement pressure differentials. Fan rates were added to infiltration estimates for each house to determine system effects on house air time constants. The SRRS was found to improve overall indoor air quality with energy benefits and to significantly reduce radon, up to 73% from closed house levels as high as 21 pCi/L. SRRS effectiveness was found to be related to the duration of system operation and dwelling leakiness; increased weatherization and fan capacity appear to enhance pressurization and dilution gains. An inverse correlation of winter temperatures and solar availability was found to be beneficial for solar heat collection. The control house exhibited fluctuating radon levels apparently due to weather-related factors, which correlated closely with radon trends particularly at the more leaky test sites. Thus a separate closed house was found to serve as an appropriate reference for simultaneous multi-home remediation comparisons. This study shows the SRRS is a promising energy-efficient indoor air improvement technique that can attain radon concentrations below the EPA guideline in existing dwellings with elevated levels

Fire performance of residential shipping containers designed with a shaft wall system

seven story building made of shipping containers is planned to be built in Barcelona, Spain. This study mainly aimed to evaluate the fire performance of one of these residential shipping containers whose walls and ceiling will have a shaft wall system installed. The default assembly consisted of three fire resistant gypsum boards for vertical panels and a mineral wool layer within the framing system. This work aimed to assess if system variants (e.g. less gypsum boards, no mineral wool layer) could still be adequate considering fire resistance purposes. To determine if steel temperatures would attain a predetermined temperature of 300-350ºC (a temperature value above which mechanical properties of steel start to change significantly) the temperature evolution within the shaft wall system and the corrugated steel profile of the container was analysed under different fire conditions. Diamonds simulator (v. 2020; Buildsoft) was used to perform the heat transfer analysis from the inside surface of the container (where the fire source was present) and within the shaft wall and the corrugated profile. To do so gas temperatures near the walls and the ceiling were required, so these temperatures were obtained from two sources: (1) The standard fire curve ISO834; (2) CFD simulations performed using the Fire Dynamics Simulator (FDS). Post-flashover fire scenarios were modelled in FDS taking into account the type of fuel present in residential buildings according to international standards. The results obtained indicate that temperatures lower than 350ºC were attained on the ribbed steel sheet under all the tested heat exposure conditions. When changing the assembly by removing the mineral wool layer, fire resistance was found to still be adequate. Therefore, under the tested conditions, the structural response of the containers would comply with fire protection standards, even in the case where insulation was reduced.Postprint (published version