Simulation of a solar domestic water heating system, with different collector efficiences and different volumen storage tanks

This paper shows the modeling and dynamic simulation, of a domestic solar water heating installation. The results of simulations performed on an annual basis for a solar system, operated in Santander (Spain), which provides hot water for a family (four persons) are presented. The installation consists in a solar flat collector, a water storage tank, a source of auxiliary energy, and a device for blending water. The mathematical model is used to evaluate the annual variation of the solar fraction respect to the volume of the storage tank, demand hot water temperature required, difference of this temperature and preset storage tank water temperature, and consumption profile of the domestic hot water demand. The results for a number of designs with different storage tank volumes, show that the systems with greater volume yield higher solar fraction values. However, when a larger storage tank volume is used, the solar fraction is less sensitive to a variation of these operation parameters. The results of this simulation may be used to design a solar collector system

Cogeneration in district heating systems

The District Heating systems (DH) are distribution systems of thermal energy, normally in the way of hot water that is supplied to great areas of population, so the users of these systems use them in the heating of their buildings and in the preparation of the hot tap water that is consumed in the buildings. The kinds of power stations that supply the thermal energy to the DH systems are as wide and varied as could be imagined: big boilers rooms, geothermal stations, solar stations,?, but mainly and due to the high energetic efficiency, the power stations which have been widely spread in the last years are Combined Heat and Power plants (CHP). In this article, it is presented a brief description of the DH systems in the first place and then, it is shown the main advantages that the centralized thermal production has, compared with the individual systems, and the kinds of CHP Plants more extensively used in the DH systems are described. Furthermore, this article focus on the different aspects that contribute to optimize the electric and thermal production in the CHP plants, as the operation way, thermal storage or the requirements that the DH systems have to achieve

The use of humidifiers as an energetic alternative to air conditioning: case of a teaching building in Santiago de Compostela

RESUMEN. El presente artículo es una propuesta para reducir la temperatura en un espacio denominado Claustro en el edificio Escuela Técnica Superior de Ingeniería, de la Universidad de Santiago (U.S.C.). Este espacio dispone de un lucernario abierto con alta radiación solar y que en verano llega a alcanzar los 37ºC. El espacio tiene un volumen de unos 7.000 m3 y una instalación convencional de aire acondicionado es demasiado cara. Nuestra propuesta para reducir la temperatura es aumentar la humedad en el ambiente y una renovación simultánea del aire, con un coste más reducido y menos energía consumida.ABSTRACT. The next paper is a proposal to reduce the temperature in a space named Cloister in the building Escuela Técnica Superior de Ingeniería, of the University of Santiago (U.S.C.). This space has a transparent roof with high solar radiation, and the temperature has reached 37ºC in summer. The atrium has a volume of approximately 7.000 m3 and a complete installation of air conditioning is too expensive. Our solution to diminish the temperature is to increase the dampness of the air and to renew it at the same time, with a minor cost and energy consumption

Dynamic model for energy predicting in WECS

This paper presents a dynamic simulation model of a wind generator, that allow to predict the quantity of removable energy in a specific place, using as initial condition wind measurements register in that place. The model is composed of four modules.The frist one is used to model de wind behaviour. The second is orientend to the aerodynamics model. The third is focused on the mechanical connection between the hub and the electrical machine. Finally, the fourth is dedicated to the electrical machine. The first model dedicated to the wind behaviour, includes an stochastic model. The aerodynamics conversion is base on the Strip Theory. The connection between the hub and the electrical machine used the mechanical differential equations. Finally, the electrical machine is modelled using the Power System Blockset including in Matlab Simulink

Numerical model of a three-phase Busbar Trunking System

The thermal behavior of an industrial Low Voltage non-segregated three-phase busduct is analyzed by means of the comparison of a 3D numerical model with experimental results. This model has been carried out using COMSOL Multiphysics, software based on finite element method. The numerical model replicates the short-circuit test, using the same geometry configuration and the boundary conditions of the laboratory in which this assay is carried out. The standard IEC 61439 is applied, both in test and model, in order to obtain the steady state temperatures in several parts of the busbar system. As a result of the data comparison can be concluded that the experimental test is replicated with sufficient accuracy by the numerical model. In fact, the average error of all the temperatures is smaller than 5%. As a general conclusion, the numerical model developed can be considered accurate enough to use it in the first steps of the busbar design.The authors of this research wish to acknowledge to the Spanish Ministry of Science for the financial support to the National Research Project: Performance of the insulating systems in transformers: alternative dielectrics, thermal-fluid modelling and post-mortem analysis (DPI2013-43897-P)

Understanding the ageing performance of alternative dielectric fluids

Mineral oil has traditionally been used as a cooling fluid in power transformers, but its low biodegradability and low fire point have motivated the search of alternatives. In this work, six different dielectric fluids have been studied, including four vegetable liquids, from sunflower, rapeseed, soybean, and palm, one synthetic ester and a mineral oil used for comparison. These oils were subjected to an accelerated thermal ageing in glass vessels at 150°C for four weeks (672 hours) in presence of Kraft insulating paper. Different oils parameters were measured during the ageing, i.e. breakdown voltage, dielectric dissipation factor, permittivity, DC resistivity, density, kinematic viscosity, flash and fire points, interfacial tension, acidity, and dissolved gases; additionally, the degree of polymerisation (DP) of the paper was measured. Results showed that the changes of the natural esters properties, except for the palm oil, were similar along the ageing time. Palm oil results were similar to those of the mineral oil, whereas synthetic ester showed a behaviour similar to natural esters. The kraft paper degradation was higher in the mineral oil, followed by the synthetic ester and the palm oil. No significant differences were found in the ageing with the natural esters.This work was supported in part by the European Union’s Horizon 2020 Research and Innovation Program, through the Marie Sklodowska-Curie, under Grant 823969, and in part by the Ministry of Economy, through the National Research Project: Gestión del Ciclo de Vida de Transformadores Aislados con Fluidos Biodegradables, under Grant PID 2019-107126RBC22

Effect of TiO2 and ZnO nanoparticles on the performance of dielectric nanofluids based on vegetable esters during their aging

Over the last few decades the insulating performance of transformer oils has been broadly studied under the point of view of nanotechnology, which tries to improve the insulating and heat dissipation performance of transformer oils by suspending nanoparticles. Many authors have analyzed the thermal and dielectric behavior of vegetable oil based-nanofluids, however, very few works have studied the evolution of these liquids during thermal aging and their stability. In this paper has been evaluated the performance of aged vegetable oil based-nanofluids, which have been subjected to accelerated thermal aging at 150 °C. Nanoparticles of TiO2 and ZnO have been dispersed in a commercial natural ester. Breakdown voltage, resistivity, dissipation factor and acidity of nanofluid samples have been measured according to standard methods, as well as stability. Moreover, it has been analyzed the degradation of Kraft paper through the degree of polymerization (DP). The results have showed that although nanoparticles improve breakdown voltage, they increase the ageing of insulation liquids and dielectric paper.This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 823969.The authors of this research wish to thank the Ministry of Economy for its financial support for the National Research Project: Improvement of Insulation Systems of Transformers through Dielectric Nanofluids (DPI2015-71219-C2 1-R)

Evaluation of the optimal connection of power transformers in the substations of a hospital

Transformers are installed in power distribution systems to perform changes in supply voltage. Large consumers often have several transformers installed in parallel to ensure continuity of supply in the event of failure. These machines can achieve very high efficiency, but their efficiency is not constant since it depends on the power demanded at each time. Therefore, the level of efficiency that correspond to the operation of a specific transformer depends on two factors: machine technical characteristics and electrical load. In this work, the authors have proposed a methodology which shows the optimal number of transformers to be connected at each period in the substations of a large Spanish hospital, in order to achieve the maximum seasonal efficiency of these machines. The results of the energy saving are determined with respect to the current situation, in which all the transformers are permanently connected. On the other hand, the European Union has established a new regulation that sets the minimum energy efficiency requirements for new power transformers. This efficiency improvement is proposed to be applied gradually in two stages, a first limit came into force in 2015, while a more restrictive approach will appear in the year 2021. This work has also studied the potential energy savings that would occur when the substations of the hospital have more efficient transformers complying with the new European Regulation 548/2014

Energy meter behaviour under non-sinusoidal conditions

Currently, there are two energy meters types installed: electromechanicals and electronics. The first ones are still the most frequent. However, new facilities tend to use electronics energy meters based on solid-state technology. Electromechanicals devices present characteristics already well known that allows us to measure only energy consumption. However, now the rules that manage the energy supply are totally new, there is a competitive electricity market. This way, detailed information on the energy consumption of each client is needed. In this point, electronic meters seem to be the best option to face the new challenges. This study will review the operating principles of solid-state energy meters. The behavior of some three phases models under nonsinusoidal conditions is studied. Experimental setup and test methodology are discussed as well

Ageing of crepe paper in mineral oil and natural ester

Several billion liters of transformer oil are used in oil filled transformers worldwide. These machines are voltage transformation devices in which during their operation the heat of windings and iron core firstly is transferred to the insulation oil and then to the cooling medium. Currently, this type of transformers mainly utilizes mineral oils due to their proven good service performance. However, mineral oil has certain limitations such as their low flashpoint and biodegradability which conditions its use in indoor environments, and it may cause a high environmental impact during its use. The development of biodegradable liquids (synthetic and natural esters) has provided an alternative. Nevertheless, a question arises when natural esters are used in power transformers, are they compatible with the rest of materials used in their design. Nowadays, although several studies of accelerated thermal ageing have been undertaken there are few works that study the impact of insulation liquid and temperature on the degradation rate of other cellulosic materials such as crepe paper. This paper can take different shapes of the surface being insulated and has greater surface area which allows to retain more oil reducing the working temperature of the transformer. For this reason, this work has compared the impact of the type of insulation oil (a mineral oil and a natural ester) and the temperature (150o C, 130oC and 110oC) on lifetime of this insulation paper. Degree of polymerization has been measured to quantify the effects. Additionally, the degradation suffered by insulation oils has been evaluated through the measurement of acidity, dissipation factor and DC resistivity. It has been found that the degradation suffered by natural ester is higher than mineral oil, however, the biodegradable liquid extends the life of crepe paper.This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 823969