## modeling and control of energy systemsN. Deliiski, L. Dzurenda, D. Angelski, P. Vitchev, K. Atanasova1Computation of Energy Consumption and Efficiency of Concrete Pits during Boiling of Logs for Veneer Production

Кey Words: Concrete pits; non-frozen logs; boiling; energy consumption; energy efficiency; veneer production.

Abstract. An approach for computing the energy consumption and energy efficiency of pits during boiling of non-frozen logs intended for veneer production has been presented. The approach is based on the use of two personal mathematical models: 1D non-linear model of the unsteady distribution of the temperature along the radius in the central cross section of non-frozen logs subjected to boiling at conductive boundary conditions, and model of the thermal balance of concrete pits during boiling of wood materials in them. For numerical solving of the models and practical application of the suggested approach, a software packages were prepared in the calculation environment of Visual FORTRAN Professional and in Excel respectively. With the help of the first model, the boiling times of beech logs with a diameter of 0.4 m, initial temperature of 0, 10, and 20 °C and moisture content of 0.6 kg∙kg-1 were determined at water temperatures in the pit equal to 70, 80, and 90 °C. Using the determined logs’ boiling durations, with the help of the second model the change in energy required for the entire boiling process and that for each of the components of the thermal balance was calculated. Computer simulations were performed for a well-insulated concrete pit with working volume of 20 m3 and degree of filling it with logs 45%, 60%, and 75%. It was found that the energy consumption of the pit decreases from 159.7 to 145.3 kWh·m-3 when the initial temperature of the logs increases from 0 °C to 20 °C at temperature of the boiling water of 80 °C and maximum possible degree of feeling of 75%. In this case, the thermal efficiency of the pit decreases from 32.2% to 26.1%. It was found also that at the same degree of feeling of the pit the increase in the boiling water temperature from 70 °C to 90 °C causes an increase in the energy consumption of the pit from 135.3 to 170.9 kWh·m-3 when the initial temperature of the logs is equal to 10 °C. Under these conditions the thermal efficiency of the pit decreases from 29.9% to 28.8%. The approach can be applied to compute the energy consumption and thermal balances of concrete pits during boiling of non-frozen logs to any desired final average mass temperature required for the mechanical processing of the plasticized wood. It could be easily modified and used to calculate the energy consumption and efficiency of concrete pits of any design and construction parameters.

## modeling and control of energy systemsT. Radeva, Use of Photovoltaic Energy for Own Needs for an Educational Center for Out-Of-Class Activities and Culture

Key Words: Photovoltaic systems; solar power generation; educational institutions; design engineering; energy management.

Abstract. The solar modules that are produced have a rather fragile structure and must therefore be mechanically protected on both sides. For this purpose, a so-called sandwich structure is used, in which the photovoltaics are placed on a solid base and covered with a transparent upper protective layer. The coefficient of thermal expansion of the materials of the upper and lower protective layers must be the same and, moreover, comparable to that of the photovoltaic cell and the bonding resin used. Currently, the most widely used materials are glass and plastic. Photocells sealed under glass have the advantage that they do not change their optical, mechanical and electrical properties during prolonged outdoor operation. Polymers cannot prevent the penetration of moisture, so they are only suitable when the photovoltaics and metal contacts are protected by an anti-corrosion coating. Plastics are lighter than glass, but they have the effect of aging with prolonged exposure to atmospheric conditions, which strongly affects their qualities. The upper transparent protective layer allows easy cleaning of the solar cells, but during their installation, they must be placed in such a way as to avoid their heavy contamination and the retention of snow on them. This is practically achieved by the southern orientation of the panels and their placement at an angle corresponding to the latitude of the site, as well as taking into account the season of operation. Some panels are oriented to the southwest so that they can produce the necessary energy for the afternoon maximum. For most locations, a slope angle close to horizontal will provide the most energy year-round. The cells used today have an efficiency of 3-20% in converting solar energy into electricity. A photovoltaic generator is a set of modules that convert solar energy into direct current (DC) electricity. It consists of a module formed by several photovoltaic cells, connecting several such modules form a panel, and several panels connected together form an array. Connecting several arrays electrically in parallel forms a photovoltaic generator or photovoltaic park. By connecting a certain number of photovoltaic cells in parallel and in series, any desired power can be obtained. The main element of the photovoltaic generator is the photovoltaic cell, where the conversion of solar radiation into flowing electric current takes place. The present work presents a practical task of a photovoltaic energy system for a public educational building. The purpose of the case study is to provide technical measures to improve the energy efficiency of the building, according to the technical specification and the current regulations. Public school buildings are mainly used during the daylight hours, where solar energy will be used for self-consumption.

## education and qualificationM. Hadjiski, R. Kaltenborn, Personalized Learning Based on Artificial Intelligence as a Challenge for Modern Education Systems

Key Words: Personalized learning in education; evolution of modern personalized education; potential possibilities of personalized learning systems; possible ways to implement effective personalized training; artificial intelligence.

Abstract. The article provides a critical analysis of the achievements and insufficiently convincing results of the multi-year attempts to introduce personalized education in educational structures of different types. The evolution of personalized learning systems with varying degrees of student involvement in the functioning of the system is discussed. The great potential possibilities of personalized learning systems emphasizing the active role of students are discussed. Two variants of metastructures have been developed for the implementation of personalized training – component and functional. The main dimensions within which personalized learning systems can be treated with a view to determining their weights in multifactor optimization are derived. Possible ways to implement effective personalized training are analyzed. The notion that personalized learning can meet the challenges of the time is substantiated if it is treated as a holistic problem with a large dimension, with student-centered functioning, with finding an optimal combination of algorithms, applications and procedures in technological implementation, with a new level of competence of teachers and students in the field of artificial intelligence, with direct corporate interest for a long time horizon.