Faculty of Mechanical Engineering

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Author: search.filters.author.Gjerasimovska, NatashaHas files: No

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    Item type:Publication,
    Thermal characteristics of combined compressor - ejector refrigeration/heat pump systems for HVAC&R
    (National Library of Serbia, 2024)
    Gjerasimovski, Aleksandar
    ;
    Sharevska, Maja
    ;
    Gjerasimovska, Natasha
    ;
    Sharevska, Monika
    ;
    <jats:p>Thermal characteristics of combined compressor ? ejector refrigeration/heat pump systems applied in heating, ventilation, air conditioning and refrigeration (HVAC&R) of buildings are investigated. An original model for estimation of the thermal characteristics of the combined cycles is developed, to determine the influence of the evaporation, interstage, condensation, and generating temperature conditions on mechanical and thermal COP of the combined system, and to optimize the thermal parameters of the cycle. Results are presented for different temperature conditions, with R134a as a suitable refrigerant. A comparison between the thermal characteristics of the simple mechanical vapor compression cycle, the simple ejector thermocompression cycle, and the combined compressor ? ejector refrigeration/heat pump cycle is given. The benefits of implementation of combined compressor ? ejector refrigeration/heat pump cycles in HVAC&R systems are discussed. The temperature lift or temperature difference between condensing temperature and interstage temperature significantly influences the thermal (ejector) COP. If temperature lift is between 10 K and 20 K, high values of thermal COP can be achieved (0.5-1.0, for generating temperature equal to 80?C; 1.0-1.8, for generating temperature equal to 120?C). If temperature lift is between 30 K and 40 K, very low values of COPth can be obtained</jats:p>
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    Item type:Publication,
    Thermal characteristics of combined compressor - ejector refrigeration/heat pump systems for HVAC&R
    (National Library of Serbia, 2023)
    Gjerasimovski, Aleksandar
    ;
    Sharevska, Maja
    ;
    Gjerasimovska, Natasha
    ;
    Sharevska, Monika
    ;
    Thermal characteristics of combined compressor - ejector refrigeration/heat pump systems applied in heating, ventilation, air conditioning and refrigeration (HVAC&R) of buildings are investigated. An original model for estimation of the thermal characteristics of the combined cycles is developed, to determine the influence of the evaporation, interstage, condensation, and generating temperature conditions on mechanical and thermal COPs of the combined system, and to optimize the thermal parameters of the cycle. Results are presented for different temperature conditions, with R134a as a suitable refrigerant. A comparison between the thermal characteristics of the simple mechanical vapor compression cycle, the simple ejector thermocompression cycle, and the combined compressor - ejector refrigeration / heat pump cycle is given. The benefits of implementation of combined compressor - ejector refrigeration/heat pump cycles in HVAC&R systems are discussed. The temperature lift or temperature difference between condensing temperature and interstage temperature significantly influences the thermal (ejector) coefficient of performance. If temperature lift is between 10 K and 20 K, high values of thermal COPs can be achieved (0.5÷1.0, for generating temperature equal to 80ºC; 1.0÷1.8, for generating temperature equal to 120ºC); If temperature lift is between 30 K and 40 K, very low values of COPth can be obtained (0.05÷0.3). High values of mechanical COPs can be achieved (24.8÷6.9), for compressor stage temperature lift 10÷30 K.
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    Item type:Publication,
    Energy efficient buildings and combined thermal systems for electricity production, heating, refrigeration and air conditioning
    (SMEITS, 2020-12-23)
    Gjerasimovski, Aleksandar
    ;
    Sharevska, Maja
    ;
    Gjerasimovska, Natasha
    ;
    Sharevska, Monika
    ;
    Šarevski, Vasko
    <jats:p>Thermal characteristics of energy efficient buildings are analyzed and energy demands are estimated. A concept of combined compressor – ejector thermal system for simultaneous production of electricity, heating, refrigeration and air conditioning is exposed. The performance characteristics of the natural gas prime motor – electric generator are assessed and optimum construction of the combined compressor – ejector refrigeration / heat pump unit is proposed to satisfy the energy demands for electricity, heating, cooling and air conditioning. Basic thermal calculations, material and energy balances of the complete thermal system are carried out and optimizing procedures for the thermal system components are given. A comparison of the proposed thermal systems and energy (natural gas) consumption with the conventional thermal systems and energy consumption for electricity, heating (natural gas - boiler), cooling (electricity – compressor refrigeration system) and air conditioning is made.</jats:p>