Strojniski Vestnik-journal of Mechanical Engineering, 2020
In this article is presented thermodynamic analysis of a cascade heat pump system designed for us... more In this article is presented thermodynamic analysis of a cascade heat pump system designed for using in high-temperature heating systems. The own thermodynamic model was built by using properties of working fluids from the CoolProp base. The cascade heat pump was designed to use ambient air as heat source with temperature tamb= –20 °C and for heating water in the high-temperature heating system up to 70 °C. The projected heating capacity of the cascade heat pump was 100 kW. The coefficient of performance (COP) of the cascade heat pump system due to use of different working mediums combinations in cycles of the cascade heat pump was investigated. For the best combination of working fluids (mediums) sub-cooling, super-heating, pressure loss in compressor’s suction line, as well as exergy efficiency of the heat pump were analysed as a function of the mean temperature of the cascade heat exchanger.
Precise understanding of heat transfer processes inside the latent thermal energy storage exposed... more Precise understanding of heat transfer processes inside the latent thermal energy storage exposed to different initial and boundary conditions is crucial for development of optimized design and operating features of similar devices. The paper presents 3D numerical study of phase change material heat storage in the shape of vertical cylinder reservoir with axially placed heat source/sink equipped with variable number of conductance enhancing longitudinal rectangular fins. As the principally important observed is the case of vertically variable heat flux supplied to the phase change material during the melting process. The numerical modeling is based on the physical model of the process and is being carried out by Fluent software that uses finite volume method for solving continuity, momentum and energy equations. The coupling between pressure and velocity is based on the Semi-Implicit Pressure-Linked Equation (SIMPLE) algorithm. The results of numerical simulations are verified throu...
Energy saving estimation model (ESEM) use normal distribution (Gaussian) probability theory to pr... more Energy saving estimation model (ESEM) use normal distribution (Gaussian) probability theory to predict potential savings for previously determined system improvements. Those improvements are low/high cost investments based on data gathered during one year monitoring of typical hypermarket facility HVAC system. The consumption of electrical energy and natural gas has been monitored and system segments with largest amount of energy consumption have been marked. Gathered data pointed out to fan units as the biggest energy consumers and suggested that system energy-saving improvement must be focused on fans energy consumption control. This paper deals with ESEM inputs and outputs in order to provide correct financial estimation of specific investment.
Strojniški vestnik - Journal of Mechanical Engineering, 2020
In this article is presented thermodynamic analysis of a cascade heat pump system designed for us... more In this article is presented thermodynamic analysis of a cascade heat pump system designed for using in high-temperature heating systems. The own thermodynamic model was built by using properties of working fluids from the CoolProp base. The cascade heat pump was designed to use ambient air as heat source with temperature t amb =-20 °C and for heating water in the high-temperature heating system up to 70 °C. The projected heating capacity of the cascade heat pump was 100 kW. The coefficient of performance (COP) of the cascade heat pump system due to use of different working mediums combinations in cycles of the cascade heat pump was investigated. For the best combination of working fluids (mediums) sub-cooling, super-heating, pressure loss in compressor's suction line, as well as exergy efficiency of the heat pump were analysed as a function of the mean temperature of the cascade heat exchanger. Keywords: cascade heat pumps, working mediums, coefficient of performance, exergy ef...
Retrofitting of fossil fuel powered hot water radiator heating systems of the existing buildings ... more Retrofitting of fossil fuel powered hot water radiator heating systems of the existing buildings by groundwater heat pumps can provide significant energy savings followed by economic and environmental benefits. The paper describes the procedure for selection of optimal low-temperature groundwater heat pump vapor compression cycle based on thermodynamic analysis of applied high temperature heat pump heating system. In comparative energy and exergy analysis observed are six different heating cycles, five of which utilize two-stage refrigerant compression, and one operate as basic one-stage heat pump system with an auxiliary heater. The systems validation is performed accounting strongly for the boundary conditions of the selected location.
In this article are presented experimental and numerical determinations of thermal transmittance ... more In this article are presented experimental and numerical determinations of thermal transmittance performed on three different types of window frames (vinyl, aluminium and wooden) within the same insulated glass unit. Good agreement between experimental and numerical results was attained. Using the numerical models, thermal improvement techniques of the frames and their influence on thermal transmittance of frames were studied. The first thermal improvement technique was using the insulation materials inserted inside large air cavities. By filling the cavity of vinyl frame with the polyurethane foam, thermal transmittance of vinyl frame was lowered by 10%. The second technique was based on repeating the procedure with materials installed inside frames with the materials that have lower thermal conductivity. This technique can be applied on thermal breaks and on steel profiles inside cavities. The result of this thermal improvement (attained by replacing thermal break material with material that has lower thermal conductivity) was certain reduction of the thermal transmittance of frames, by 9%. Using stainless steel instead of the oxidized steel was reduction of the thermal transmittance of vinyl frame by 3%. For the case of wooden frames was analysed the influence of shifting glazing unit deeper into profile upon the thermal transmittance of the frame. Installing the glass unit by 5 mm deeper into the wooden frame reduced glass thermal transmittance by 5%.
Strojniski Vestnik-journal of Mechanical Engineering, 2020
In this article is presented thermodynamic analysis of a cascade heat pump system designed for us... more In this article is presented thermodynamic analysis of a cascade heat pump system designed for using in high-temperature heating systems. The own thermodynamic model was built by using properties of working fluids from the CoolProp base. The cascade heat pump was designed to use ambient air as heat source with temperature tamb= –20 °C and for heating water in the high-temperature heating system up to 70 °C. The projected heating capacity of the cascade heat pump was 100 kW. The coefficient of performance (COP) of the cascade heat pump system due to use of different working mediums combinations in cycles of the cascade heat pump was investigated. For the best combination of working fluids (mediums) sub-cooling, super-heating, pressure loss in compressor’s suction line, as well as exergy efficiency of the heat pump were analysed as a function of the mean temperature of the cascade heat exchanger.
Precise understanding of heat transfer processes inside the latent thermal energy storage exposed... more Precise understanding of heat transfer processes inside the latent thermal energy storage exposed to different initial and boundary conditions is crucial for development of optimized design and operating features of similar devices. The paper presents 3D numerical study of phase change material heat storage in the shape of vertical cylinder reservoir with axially placed heat source/sink equipped with variable number of conductance enhancing longitudinal rectangular fins. As the principally important observed is the case of vertically variable heat flux supplied to the phase change material during the melting process. The numerical modeling is based on the physical model of the process and is being carried out by Fluent software that uses finite volume method for solving continuity, momentum and energy equations. The coupling between pressure and velocity is based on the Semi-Implicit Pressure-Linked Equation (SIMPLE) algorithm. The results of numerical simulations are verified throu...
Energy saving estimation model (ESEM) use normal distribution (Gaussian) probability theory to pr... more Energy saving estimation model (ESEM) use normal distribution (Gaussian) probability theory to predict potential savings for previously determined system improvements. Those improvements are low/high cost investments based on data gathered during one year monitoring of typical hypermarket facility HVAC system. The consumption of electrical energy and natural gas has been monitored and system segments with largest amount of energy consumption have been marked. Gathered data pointed out to fan units as the biggest energy consumers and suggested that system energy-saving improvement must be focused on fans energy consumption control. This paper deals with ESEM inputs and outputs in order to provide correct financial estimation of specific investment.
Strojniški vestnik - Journal of Mechanical Engineering, 2020
In this article is presented thermodynamic analysis of a cascade heat pump system designed for us... more In this article is presented thermodynamic analysis of a cascade heat pump system designed for using in high-temperature heating systems. The own thermodynamic model was built by using properties of working fluids from the CoolProp base. The cascade heat pump was designed to use ambient air as heat source with temperature t amb =-20 °C and for heating water in the high-temperature heating system up to 70 °C. The projected heating capacity of the cascade heat pump was 100 kW. The coefficient of performance (COP) of the cascade heat pump system due to use of different working mediums combinations in cycles of the cascade heat pump was investigated. For the best combination of working fluids (mediums) sub-cooling, super-heating, pressure loss in compressor's suction line, as well as exergy efficiency of the heat pump were analysed as a function of the mean temperature of the cascade heat exchanger. Keywords: cascade heat pumps, working mediums, coefficient of performance, exergy ef...
Retrofitting of fossil fuel powered hot water radiator heating systems of the existing buildings ... more Retrofitting of fossil fuel powered hot water radiator heating systems of the existing buildings by groundwater heat pumps can provide significant energy savings followed by economic and environmental benefits. The paper describes the procedure for selection of optimal low-temperature groundwater heat pump vapor compression cycle based on thermodynamic analysis of applied high temperature heat pump heating system. In comparative energy and exergy analysis observed are six different heating cycles, five of which utilize two-stage refrigerant compression, and one operate as basic one-stage heat pump system with an auxiliary heater. The systems validation is performed accounting strongly for the boundary conditions of the selected location.
In this article are presented experimental and numerical determinations of thermal transmittance ... more In this article are presented experimental and numerical determinations of thermal transmittance performed on three different types of window frames (vinyl, aluminium and wooden) within the same insulated glass unit. Good agreement between experimental and numerical results was attained. Using the numerical models, thermal improvement techniques of the frames and their influence on thermal transmittance of frames were studied. The first thermal improvement technique was using the insulation materials inserted inside large air cavities. By filling the cavity of vinyl frame with the polyurethane foam, thermal transmittance of vinyl frame was lowered by 10%. The second technique was based on repeating the procedure with materials installed inside frames with the materials that have lower thermal conductivity. This technique can be applied on thermal breaks and on steel profiles inside cavities. The result of this thermal improvement (attained by replacing thermal break material with material that has lower thermal conductivity) was certain reduction of the thermal transmittance of frames, by 9%. Using stainless steel instead of the oxidized steel was reduction of the thermal transmittance of vinyl frame by 3%. For the case of wooden frames was analysed the influence of shifting glazing unit deeper into profile upon the thermal transmittance of the frame. Installing the glass unit by 5 mm deeper into the wooden frame reduced glass thermal transmittance by 5%.
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