The Experts below are selected from a list of 3060 Experts worldwide ranked by ideXlab platform
K T Chan - One of the best experts on this subject based on the ideXlab platform.
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Optimum condenser fan staging for air-cooled chillers
Applied Thermal Engineering, 2020Co-Authors: F W Yu, K T ChanAbstract:This paper considers how the staging of condenser fans can be optimized to improve the efficiency of air-cooled chillers at part load. An experiment on an air-cooled reciprocating chiller confirmed that when all condenser fans are staged to enhance heat rejection airflow, the heat transfer coefficient of the condenser can be optimized, enabling the Condensing Temperature and chiller power to decrease considerably with less fluctuation. Chiller efficiency, in turn, can be improved by 4.4-40.1%, depending on the load conditions and outdoor Temperatures. An algorithm is introduced to compute the number of staged condenser fans based on a set point of Condensing Temperature for any given head rejection. With this algorithm, the strategy for optimizing the staging of condenser fans is discussed.Department of Building Services Engineerin
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Tune up of the set point of Condensing Temperature for more energy efficient air cooled chillers
Energy Conversion and Management, 2020Co-Authors: F W Yu, K T ChanAbstract:This paper presents how to tune up the set point of the Condensing Temperature for improving the coefficient of performance (COP) of air cooled chillers under various operating conditions. The thermodynamic model of an air cooled screw chiller was developed using the simulation program TRNSYS and validated using the operating data and specifications of the chiller. A new configuration of variable speed condenser fans was proposed for the chiller. An algorithm was introduced to make use of a set point of Condensing Temperature to determine the number and speed of condenser fans staged at any given cooling capacity. A model was used to investigate how the COP changes with various set points of Condensing Temperature. It was found that the optimum set point for maximum COP is a function of outdoor Temperature and chiller load. Depending on the operating conditions, the COP could increase by 12.1-110.4% when the variable speed condenser fans and the optimum set point of Condensing Temperature were applied to the existing air cooled screw chillers. This provides important insights into the development of more energy efficient air cooled chillers.Department of Building Services Engineerin
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Constraints of using thermostatic expansion valves to operate air-cooled chillers at lower Condensing Temperatures
Applied Thermal Engineering, 2020Co-Authors: F W Yu, K T ChanAbstract:Thermostatic expansion valves (TXVs) have long been used in air-cooled chillers to implement head pressure control under which the Condensing Temperature is kept high at around 50 °C by staging condenser fans as few as possible. This paper considers how TXVs prevent the chillers from operating with an increased COP at lower Condensing Temperatures when the chiller load or outdoor Temperature drops. An analysis on an existing air-cooled reciprocating chiller showed that the range of differential pressures across TXVs restricts the maximum heat rejection airflow required to increase the chiller COP, though the set point of Condensing Temperature is reduced to 22 °C from a high level of 45 °C. It is possible to use electronic expansion valves to meet the differential pressure requirements for maximum chiller COP. There is a maximum of 28.7% increase in the chiller COP when the heat rejection airflow is able to be maximized in various operating conditions. The results of this paper emphasize criteria for lowering the Condensing Temperature to enhance the performance of air-cooled chillers.Department of Building Services Engineerin
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Applying Condensing-Temperature control in air-cooled reciprocating water chillers for energy efficiency
Applied Energy, 2020Co-Authors: K T Chan, F W YuAbstract:This paper reports on the modelling and findings of the energy performance of an air-cooled reciprocating multiple-chiller plant under the conventional head pressure control and the new Condensing-Temperature control in a subtropical climate. The simulation model was validated using the operating data of an existing chiller plant. As noted from this existing air-cooled reciprocating chiller plant, there was a substantial efficiency drop at part-load resulting from the head pressure control. If operating at variable lower Condensing-Temperatures based on the established operating mode of the condenser fans and compressors, it is shown that the chiller consumption can be maintained below 2 kW/refrigeration ton throughout the entire range of outdoor Temperature and part-load conditions, giving an average efficiency of 1.08 kW/refrigeration ton. The energy imposition due to cycling on more condenser fans can be compensated by the reduced compressor consumption. Potential energy savings of 18.2 and 29% in the annual chiller consumption are achievable by applying the Condensing-Temperature control to two existing chiller plants studied. This supports the need to develop the Condensing-Temperature control as an improvement to the conventional head pressure control.Department of Building Services Engineerin
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Logistic regression-based optimal control for air-cooled chiller
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: F W Yu, W.t. Ho, K T ChanAbstract:Abstract Air-cooled chillers normally operate under head pressure control without minimizing the electric power at part load operation. This study considers logistic regression to implement optimal control for an air-cooled chiller. Random forest models were developed for the chiller operating under two modes: the normal mode – switching on and off condenser fans at constant speed based on a fixed Condensing Temperature set point; the VSD mode – controlling all condenser fans at variable speed based on an adjustable set point instead. Genetic algorithm was then applied to simulate the maximum coefficient of performance (COP) with optimal operating variables. The COP at a low chiller load could increase by up to 110% and 67% in the normal and VSD modes, respectively. Logistic regression ascertained that the optimal control depended highly on the Condensing Temperature and the condenser airflow rate. The regression models served to adjust the Condensing Temperature set point to achieve maximum COP.
F W Yu - One of the best experts on this subject based on the ideXlab platform.
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Optimum condenser fan staging for air-cooled chillers
Applied Thermal Engineering, 2020Co-Authors: F W Yu, K T ChanAbstract:This paper considers how the staging of condenser fans can be optimized to improve the efficiency of air-cooled chillers at part load. An experiment on an air-cooled reciprocating chiller confirmed that when all condenser fans are staged to enhance heat rejection airflow, the heat transfer coefficient of the condenser can be optimized, enabling the Condensing Temperature and chiller power to decrease considerably with less fluctuation. Chiller efficiency, in turn, can be improved by 4.4-40.1%, depending on the load conditions and outdoor Temperatures. An algorithm is introduced to compute the number of staged condenser fans based on a set point of Condensing Temperature for any given head rejection. With this algorithm, the strategy for optimizing the staging of condenser fans is discussed.Department of Building Services Engineerin
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Tune up of the set point of Condensing Temperature for more energy efficient air cooled chillers
Energy Conversion and Management, 2020Co-Authors: F W Yu, K T ChanAbstract:This paper presents how to tune up the set point of the Condensing Temperature for improving the coefficient of performance (COP) of air cooled chillers under various operating conditions. The thermodynamic model of an air cooled screw chiller was developed using the simulation program TRNSYS and validated using the operating data and specifications of the chiller. A new configuration of variable speed condenser fans was proposed for the chiller. An algorithm was introduced to make use of a set point of Condensing Temperature to determine the number and speed of condenser fans staged at any given cooling capacity. A model was used to investigate how the COP changes with various set points of Condensing Temperature. It was found that the optimum set point for maximum COP is a function of outdoor Temperature and chiller load. Depending on the operating conditions, the COP could increase by 12.1-110.4% when the variable speed condenser fans and the optimum set point of Condensing Temperature were applied to the existing air cooled screw chillers. This provides important insights into the development of more energy efficient air cooled chillers.Department of Building Services Engineerin
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Constraints of using thermostatic expansion valves to operate air-cooled chillers at lower Condensing Temperatures
Applied Thermal Engineering, 2020Co-Authors: F W Yu, K T ChanAbstract:Thermostatic expansion valves (TXVs) have long been used in air-cooled chillers to implement head pressure control under which the Condensing Temperature is kept high at around 50 °C by staging condenser fans as few as possible. This paper considers how TXVs prevent the chillers from operating with an increased COP at lower Condensing Temperatures when the chiller load or outdoor Temperature drops. An analysis on an existing air-cooled reciprocating chiller showed that the range of differential pressures across TXVs restricts the maximum heat rejection airflow required to increase the chiller COP, though the set point of Condensing Temperature is reduced to 22 °C from a high level of 45 °C. It is possible to use electronic expansion valves to meet the differential pressure requirements for maximum chiller COP. There is a maximum of 28.7% increase in the chiller COP when the heat rejection airflow is able to be maximized in various operating conditions. The results of this paper emphasize criteria for lowering the Condensing Temperature to enhance the performance of air-cooled chillers.Department of Building Services Engineerin
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Applying Condensing-Temperature control in air-cooled reciprocating water chillers for energy efficiency
Applied Energy, 2020Co-Authors: K T Chan, F W YuAbstract:This paper reports on the modelling and findings of the energy performance of an air-cooled reciprocating multiple-chiller plant under the conventional head pressure control and the new Condensing-Temperature control in a subtropical climate. The simulation model was validated using the operating data of an existing chiller plant. As noted from this existing air-cooled reciprocating chiller plant, there was a substantial efficiency drop at part-load resulting from the head pressure control. If operating at variable lower Condensing-Temperatures based on the established operating mode of the condenser fans and compressors, it is shown that the chiller consumption can be maintained below 2 kW/refrigeration ton throughout the entire range of outdoor Temperature and part-load conditions, giving an average efficiency of 1.08 kW/refrigeration ton. The energy imposition due to cycling on more condenser fans can be compensated by the reduced compressor consumption. Potential energy savings of 18.2 and 29% in the annual chiller consumption are achievable by applying the Condensing-Temperature control to two existing chiller plants studied. This supports the need to develop the Condensing-Temperature control as an improvement to the conventional head pressure control.Department of Building Services Engineerin
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Logistic regression-based optimal control for air-cooled chiller
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: F W Yu, W.t. Ho, K T ChanAbstract:Abstract Air-cooled chillers normally operate under head pressure control without minimizing the electric power at part load operation. This study considers logistic regression to implement optimal control for an air-cooled chiller. Random forest models were developed for the chiller operating under two modes: the normal mode – switching on and off condenser fans at constant speed based on a fixed Condensing Temperature set point; the VSD mode – controlling all condenser fans at variable speed based on an adjustable set point instead. Genetic algorithm was then applied to simulate the maximum coefficient of performance (COP) with optimal operating variables. The COP at a low chiller load could increase by up to 110% and 67% in the normal and VSD modes, respectively. Logistic regression ascertained that the optimal control depended highly on the Condensing Temperature and the condenser airflow rate. The regression models served to adjust the Condensing Temperature set point to achieve maximum COP.
Haruki Sato - One of the best experts on this subject based on the ideXlab platform.
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Performance of supercritical cycles for geothermal binary design
Energy Conversion and Management, 2002Co-Authors: Zhaolin Gu, Haruki SatoAbstract:Supercritical cycles for geothermal power generation systems are studied to raise the power output and thermal efficiency by selecting natural fluids and new organic working fluids as the working fluids and optimizing the cyclic parameters, especially the Condensing Temperature or pressure. For a given liquid dominated geothermal resource, thermodynamic parameters, using propane, R-125 and R-134a as the working fluids, respectively, are calculated to show the features of supercritical power cycles and compare to other design results shown in references. Greater power output shows that propane and R-134a are appropriate working fluids of supercritical cycles for geothermal binary design.
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Performance of supercritical cycles for geothermal binary design
Energy Conversion and Management, 2002Co-Authors: Zhaolin Gu, Haruki SatoAbstract:Supercritical cycles for geothermal power generation systems are studied to raise the power output and thermal efficiency by selecting natural fluids and new organic working fluids as the working fluids and optimizing the cyclic parameters, especially the Condensing Temperature or pressure. For a given liquid dominated geothermal resource, thermodynamic parameters, using propane, R-125 and R-134a as the working fluids, respectively, are calculated to show the features of supercritical power cycles and compare to other design results shown in references. Greater power output shows that propane and R-134a are appropriate working fluids of supercritical cycles for geothermal binary design. © 2002 Elsevier Science Ltd. All rights reserved.
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Optimization of cyclic parameters of a supercritical cycle for geothermal power generation
Energy Conversion and Management, 2001Co-Authors: Zhaolin Gu, Haruki SatoAbstract:A supercritical power cycle with a regenerative process is studied to reach the maximum thermal efficiency by the choice of an appropriate working fluid and optimization of the cyclic state parameters, especially the Condensing Temperature or pressure. For given geothermal resources, the thermodynamic state parameters are calculated to show the features of the supercritical power cycle compared to other design results. The criteria for the choice of working fluids are also set up.
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Optimization of cyclic parameters of a supercritical cycle for geothermal power generation
Energy Conversion and Management, 2001Co-Authors: Zhaolin Gu, Haruki SatoAbstract:A supercritical power cycle with a regenerative process is studied to reach the maximum thermal efficiency by the choice of an appropriate working fluid and optimization of the cyclic state parameters, especially the Condensing Temperature or pressure. For given geothermal resources, the thermodynamic state parameters are calculated to show the features of the supercritical power cycle compared to other design results. The criteria for the choice of working fluids are also set up. © 2001 Elsevier Science Ltd.
Ziwen Xing - One of the best experts on this subject based on the ideXlab platform.
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Investigation of characteristics of discharge pressure pulsation in a twin-screw refrigeration compressor
Archive: Journal of Mechanical Engineering Science 1959-1982 (vols 1-23), 2018Co-Authors: Wenqing Chen, Ziwen Xing, Xiaokun Wu, Xiaolin WangAbstract:In this paper, characteristics of discharge pressure pulsation in a twin-screw refrigeration compressor are investigated. A thermodynamic model is developed and validated using data from a comprehensive experimental study. This validated model is then applied to investigate effects of key parameters including Condensing Temperature, compressor rotational speed, super-feed pressure, part-load operation, and design parameters on the discharge pressure pulsation. The results showed that the discharge pressure pulsation was mainly due to periodic variations of mass and energy flow from the working volumes to the discharge chamber. As the Condensing Temperature increased or decreased from the design condition, the compressor was in either over- or undercompression leading to an increase in the amplitude of the pressure pulsation. The gas super-feed pressure could increase the pressure pulsation at Condensing Temperatures below the design value and reduce the pressure pulsation at Condensing Temperatures above the design value. The analysis also demonstrated that the pressure pulsation was lower at part-load conditions. However, the compressor rotational speed increased both the amplitude and frequency of the pressure pulsation. Theoretical analysis of design parameters indicated that a large discharge volume with a high number of lobes could lower the pressure pulsation. These analyses provide useful information for the compressor design and optimization.
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Performance analysis of a refrigerant extracting twin screw compressor employed in multi-Temperature heat pump systems
International Journal of Refrigeration, 2016Co-Authors: Zhaorui Zhao, Yafen Tian, Feng Hou, Ziwen XingAbstract:Heat pump systems are widely used in heat recovery applications where high Temperature waste heat is abundantly available. High Temperature heat pumps are capable of recovering heat from the condenser of a refrigeration system to supply heat for processing or heating. However, conventional systems are unable to supply heat at more than one Temperature level, while significant efficiency loss is caused by the large Condensing Temperature difference between high and mid Temperature condensers. In this paper, a novel type of refrigerant extracting screw compressor and a modified system is designed. Mathematical models are formulated for the working process and performance prediction. Therefore, the pressure of refrigerant within the compressing chamber and the COP of the heat recovery multi-Temperature heat pump system are calculated. Furthermore, the influence of the internal volumetric ratio, operating condition, properties of refrigerant extraction and mid-stage Condensing Temperature on the performance are discussed.
Zhaolin Gu - One of the best experts on this subject based on the ideXlab platform.
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Performance of supercritical cycles for geothermal binary design
Energy Conversion and Management, 2002Co-Authors: Zhaolin Gu, Haruki SatoAbstract:Supercritical cycles for geothermal power generation systems are studied to raise the power output and thermal efficiency by selecting natural fluids and new organic working fluids as the working fluids and optimizing the cyclic parameters, especially the Condensing Temperature or pressure. For a given liquid dominated geothermal resource, thermodynamic parameters, using propane, R-125 and R-134a as the working fluids, respectively, are calculated to show the features of supercritical power cycles and compare to other design results shown in references. Greater power output shows that propane and R-134a are appropriate working fluids of supercritical cycles for geothermal binary design.
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Performance of supercritical cycles for geothermal binary design
Energy Conversion and Management, 2002Co-Authors: Zhaolin Gu, Haruki SatoAbstract:Supercritical cycles for geothermal power generation systems are studied to raise the power output and thermal efficiency by selecting natural fluids and new organic working fluids as the working fluids and optimizing the cyclic parameters, especially the Condensing Temperature or pressure. For a given liquid dominated geothermal resource, thermodynamic parameters, using propane, R-125 and R-134a as the working fluids, respectively, are calculated to show the features of supercritical power cycles and compare to other design results shown in references. Greater power output shows that propane and R-134a are appropriate working fluids of supercritical cycles for geothermal binary design. © 2002 Elsevier Science Ltd. All rights reserved.
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Optimization of cyclic parameters of a supercritical cycle for geothermal power generation
Energy Conversion and Management, 2001Co-Authors: Zhaolin Gu, Haruki SatoAbstract:A supercritical power cycle with a regenerative process is studied to reach the maximum thermal efficiency by the choice of an appropriate working fluid and optimization of the cyclic state parameters, especially the Condensing Temperature or pressure. For given geothermal resources, the thermodynamic state parameters are calculated to show the features of the supercritical power cycle compared to other design results. The criteria for the choice of working fluids are also set up.
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Optimization of cyclic parameters of a supercritical cycle for geothermal power generation
Energy Conversion and Management, 2001Co-Authors: Zhaolin Gu, Haruki SatoAbstract:A supercritical power cycle with a regenerative process is studied to reach the maximum thermal efficiency by the choice of an appropriate working fluid and optimization of the cyclic state parameters, especially the Condensing Temperature or pressure. For given geothermal resources, the thermodynamic state parameters are calculated to show the features of the supercritical power cycle compared to other design results. The criteria for the choice of working fluids are also set up. © 2001 Elsevier Science Ltd.