heating systems, Second Law analysis, boiler room, electric heating, heat pump, exergy efficiency.


The main features of energy and exergy methods of analysis the energy transformations efficiency in typical heating systems (boilers, electric heating, heat pumps with electric drive) are presented. The equations of energy and exergy balances of systems and their elements are made. Based on them, expressions for calculating efficiency indicators are obtained. The results of calculations and comparison of energy conversion coefficients (COP - Coefficient of Performance) and exergy efficiencies (Exergy Efficiency or Second Low Efficiency) are presented. It is shown that heating systems based on fuel boilers and electric heaters are characterized by high COP values, which does not focus on taking measures to improve them. At the same time, such systems have rather low values of exergetic efficiency. It is shown that exergy efficiency of a typical electric heating system reaches about 3%, and heating based on fuel boilers - about 6,5 %. The analysis of the main reasons of thermodynamic irreversibility in the specified systems is executed. The diagram of changes exergetic efficiency in consecutive elements of a typical heating system on the example of a fuel boiler room is given. It is shown that in a fuel boiler the main irreversibilities occur at the stages of combustion and heat transfer at a large temperature difference. In electric heating systems, the main exergy losses occur during the production of electricity at thermal power plants and during the conversion of electricity into heat in electric heaters. Possibilities and main ways to reduce the thermodynamic irreversibility of the heating system from the steam boiler house during its conversion into a mini - CHP are considered. The analysis of thermodynamic losses in heat pump heating systems is performed. The conditions under which such systems become more energy efficient than systems based on fuel boilers are defined. The reasons for the wide practical application of boilers and electric heating are revealed, despite their low thermodynamic perfection.


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