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No 4 (2024)
Articles
Analysis of Problems in the State of Heat Supply to Residential Buildings Using Heat Pump Circuits
Abstract
Currently, the energy-efficient use of heat exchangers such as heat pumps is difficult in most regions of the Russian Federation. Most of the modern heat supply problems of built-in heat pump systems can be solved by organizational and technical means. First of all, it is necessary to streamline and compare foreign and domestic experience in the processes of design, production and installation work in the construction industry. The regulatory documentation also needs to take into account the climatic specifics of the regions and, accordingly, the modern building materials used in Russia. All the indicated points will directly affect the composition of the project documentation and will affect such sections as PPR and PIC. The purpose of the article is to analyze the main problems that hinder the formation of efficient production of thermal energy by heat pumps. The article uses general theoretical methods of cognition (analysis, synthesis, analogy, generalization, comparison), etc. As a result of the study, the problems of using heat pump devices on the territory of the Russian Federation are identified and formulated. These include gaps in regulatory documentation, the lack of incentive government programs, the lack of service support from most device manufacturers and the lack of a real physical and mathematical model of the software of the internal circuit of a heat pump system, on the basis of which it would be possible to predict the performance of the device within the life cycle of a construction project. The main organizational and technological solutions for the effective use of heat pump devices within the life cycle of low-rise buildings and structures are formulated.
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Analytical Confirmation of the Calculated Dependencies for Heat Exchange in a Plate Recuperator when Humidifying the Auxiliary Flow
Abstract
The relevance of the study is related to the need to ensure maximum reduction of energy consumption while ensuring the calculated parameters of the indoor climate in buildings under the Law of the Russian Federation “On Energy Saving...” and the updated version of SP 131. The purpose of the study is to obtain an approximate analytical expression of this dependence, which makes it possible to additionally confirm the results of field and numerical experiments previously performed by the authors for this flow treatment scheme. The objective of the study is to build a simplified mathematical model of the processes of changing the heat and humidity state of the air in the recuperator, identify the main factors affecting the increasing multiplier to the coefficient of temperature efficiency of the device and obtain the necessary numerical coefficients in formulas linking the desired and initial parameters. The general equation of thermal balance and heat transfer for the heat exchanger as a whole is used, including the integral characteristics of the apparatus in a dimensionless form, as well as standard techniques of algebraic transformations. An approximate analytical expression is obtained for an increasing multiplier to the coefficient of thermal efficiency of the recuperator taking into account the additional cooling of the inflow due to the heat consumption for evaporation. It is shown that the general structure of this ratio coincides with the one found by the authors earlier by processing the results of numerical modeling of a two-dimensional temperature field in a heat exchanger, taking into account experimental data on the amount of moisture carried away, which confirms their correctness and reliability.
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Physical and Mechanical Properties of Butt Welded Joints of Aluminum Alloys
Abstract
Along with the improvement of joining technologies with argon arc, plasma and laser welding for aluminum alloy elements, high efficiency of joints made with the use of friction stir welding (FSW), which has low energy consumption and is almost equally strong as base metal, has been achieved. However, the processes of friction stir welding have not been sufficiently studied and can lead to softening of aluminum alloy welds up to 0.65 of base metal strength. When studying the effect of friction stir welding and mechanized electric arc welding in argon medium, welded joints of aluminum alloys of Al-Si-Mg (AD35T1, 6082-T6) and Al-Zn-Mg alloying systems (1915T) were subjected to tensile and impact tests. The values of strength, elastic and plastic characteristics of argon arc welded specimens of 1915T, AD35T1 and 6082-T6 alloys were obtained. For alloy 6082-T6, the same characteristics are presented for FSW welded specimens. Decrease in strength and ductility in the zones of welded joints for both welding methods is observed. At the same time, the highest relative values of strength and offset yield strength of the welded joint are fixed for friction stir welding. Slight decrease in modulus of elasticity obtained for argon-arc welded specimens was recorded. The impact strength is constant for each welded joint zones in the temperature range of +20 – -60оC and increased in weld metal of FSW butt joints of alloy 6082-T6.
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Numerical Simulation of Compensation Injection Problems Near Deep Excavations
Abstract
The stress-strain state (SSS) of the “ground foundation – foundation pit under the protection of a fence – compensation injection zone” system is complex, multifactorial and transforming in space. Taking into account a wide range of phenomena when changing the SSS of the soil base is associated with significant difficulties, especially without the use of numerical modeling using software and computer systems. Numerical modeling in the implementation of the finite element method (FEM) for the problems of complex interaction of a soil basis with underground structures during compensatory grouting makes it possible to assign injection zones in any position in space (horizontally, vertically, at an angle), determine the necessary injection parameters to achieve the building lifting of the soil basis when solving the inverse problem. In this study, using examples of numerical modeling of compensation grouting problems near the pit fence with different locations of existing buildings, the authors identified the determining factors affecting the distribution of internal forces in the enclosing structures of the excavation, as well as on the existing structures of the underground structure. The results of comparison of calculations in two-dimensional and three-dimensional formulations are presented, an increase in the bending moment of the retaining wall when carrying out work on compensatory injection by 187-279% is shown for different parameters of the distance to the grouting horizon. The results of the conducted studies confirm the need to take into account the increase in internal efforts during the work on compensatory injection in the structures of the pit fences when assigning reinforcement. In addition, in some cases it is necessary to provide additional protective measures to prevent a negative impact on the constructed underground structures to reduce emergency situations.
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Transformable Fire Barriers for Filling Openings (Overview)
Abstract
The review of scientific and technical literature on the problem of ensuring fire safety of public and industrial buildings by dividing rooms into fire compartments using transformable fire barriers (TFB), as well as by protecting openings with transformable fire fillings is presented. The general classification of TFB is presented, the requirements for TFB are described, the use cases of various types of TFB and their design features are considered. Engineering solutions for transformable fire shelters, as well as mobile fire barriers, are presented. It has been established that the fire resistance limit of TFB is higher when used in combination with water irrigation, but the disadvantage of the system is the high consumption of coolant (from 0.12 liters/s of water per 1 linear meter of opening width), which, in addition to material costs, also has a destructive effect on finishing materials and building structures. A possible way to solve these problems is to use various fillers in the working cloth that emit inert or extinguishing gases, but this method needs additional verification in the form of modeling and physical experiments.
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Design of Earthquake-Resistant Buildings. New Generation Standards
Abstract
In modern practice of designing buildings in seismic areas, there is a constant increase in the level of detail of models, however, calculations often ignore the fact that seismic impact is a random process with large variability of parameters, and the interaction of the structure with a nonlinearly deformable foundation is not always taken into account correctly. In addition, when calculating seismic impacts, it is necessary to use modern material models that take into account the nonlinear nature of deformation under cyclic loads. All the factors described above indicate the need to develop complex methods for calculating seismic impacts. The article describes an integrated approach to the calculations of buildings and structures being built in seismic areas, and also provides the main theses for the STO “Construction in seismic areas. Basic provisions”. The section “materials used and research methods” presents the key components of the proposed methodology (nonlinear calculation method, material models and foundation model). The section “research results” presents the main provisions of the proposed two-level calculation. In conclusion, it was concluded that it is necessary to update modern standards and methods of calculation for seismic impacts.
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Analysis of the Cost of Fuel and Energy Resources During the Overhaul of an Apartment Building
Abstract
The study presents tools for calculating the consumption of fuel and energy resources when carrying out major repairs of a multi-apartment residential building. The purpose of the study is to reduce energy consumption during the work phase and increase the efficiency of the capital construction project. The methodological approaches of the study are based on calculation, analysis and comparison of the obtained values of consumption of fuel and energy resources when carrying out major repairs of an apartment building. Based on the results of the study, it was established that the structure of energy costs during major repairs is determined to a greater extent by the «machinery and mechanisms» consumer group, which may include a different number of subgroups. Analysis of the calculated values of consumption of fuel and energy resources showed that significant energy consumption during repair work is due to the mechanization of labor using construction machines (truck crane, truck) and equipment (roof burner, combined sprayer, etc.).
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