The Experts below are selected from a list of 24561 Experts worldwide ranked by ideXlab platform
K.t. Chan - One of the best experts on this subject based on the ideXlab platform.
-
Comprehensive Environmental Assessment for Cooling Towers with Various Controls
Indoor and Built Environment, 2009Co-Authors: F W Yu, K.t. ChanAbstract:Cooling towers are generally used in water-cooled Chiller systems, which provide cooling energy for commercial buildings. This article assesses how the various control systems of cooling towers influence plume emissions and the electricity and water consumption of a chilled water system. Integrated with real control of cooling tower fans, Chiller and cooling tower models were developed to analyze how the energy performance of a Chiller and the water loss rate varied under different operating conditions. The status of air flows through the cooling tower was investigated to judge plume formation under various cooling tower controls. A simulation analysis on a chilled water system serving an office building showed that optimizing the fan speed control of cooling towers enables the annual electricity and water consumption costs to save 4.6% while also reducing the plume generation. The optimum control means adjusting the temperature of cooling water leaving the cooling tower in response to the Chiller load an...
-
Improved energy performance of air cooled centrifugal Chillers with variable chilled water flow
Energy Conversion and Management, 2008Co-Authors: F W Yu, K.t. ChanAbstract:Abstract This paper considers how to apply optimum condensing temperature control and variable chilled water flow to increase the coefficient of performance (COP) of air cooled centrifugal Chillers. A thermodynamic model for the Chillers was developed and validated using a wide range of operating data and specifications. The model considers real process phenomena, including capacity control by the inlet guide vanes of the compressor and an algorithm to determine the number and speed of condenser fans staged based on a set point of condensing temperature. Based on the validated model, it was found that optimizing the control of condensing temperature and varying the evaporator’s chilled water flow rate enable the COP to increase by 0.8–191.7%, depending on the load and ambient conditions. A cooling load profile of an office building in a subtropical climate was considered to assess the potential electricity savings resulting from the increased Chiller COP and optimum staging of Chillers and pumps. There is 16.3–21.0% reduction in the annual electricity consumption of the building’s Chiller plant. The results of this paper provide useful information on how to implement a low energy Chiller plant.
-
Part load performance of air-cooled centrifugal Chillers with variable speed condenser fan control
Building and Environment, 2007Co-Authors: F W Yu, K.t. ChanAbstract:Abstract Air-cooled centrifugal Chillers are commonly used in commercial buildings but their performance analysis is lacking. This paper investigates the part load performance of the Chillers via a thermodynamic model. The model was validated using a wide range of operating data from an existing Chiller with specific settings of outdoor temperature and condensing pressure in controlling the condensing temperature. The validated model was developed specifically to ascertain the maximum coefficient of performance of Chiller (COP) together with the strategy for optimizing the condensing temperature under various operating conditions. It is found that the highest COP occurs at a part load ratio (PLR) of 0.71–0.84, depending on the outdoor temperature and the control of condensing temperature, rather than at full load. Yet the Chillers operating at such part load conditions will cause extra energy used for the early staging of chilled water pumps. To minimize the overall Chiller plant energy consumption, it is still preferable to implement Chiller sequencing based on the full load condition than on the aforementioned PLRs. The results of this paper present criteria for implementing low-energy strategies for operating air-cooled Chillers satisfying a given building cooling load profile.
-
Parameterization study on the operating efficiency of air-cooled Chillers
Advances in Building Technology, 2007Co-Authors: K.t. ChanAbstract:Publisher Summary This chapter presents a parameterization study aimed at exploring the behaviors of the operating parameters of the aircooled reciprocating Chillers by the hybrid use of the operating data of an existing Chiller and predicted data by a Chiller system model. A Chiller system model taking into account the thermodynamic properties of the vapor compression cycle and the operating balances with the Chiller components is developed and validated to predict other parameters influencing the Chiller efficiency. Increasing the chilled water flow and the evaporating temperature to enhance the evaporator performance is likely to be offset by the additional pump power and a trade off study between the two should be carried out. The constraints of the chilled water temperature reset control for improved efficiency lie on the limited enhancement on the evaporator performance and the additional pump power from the increased chilled water flow. The realistic compressor power performance can be predicted using an empirical expression of compressor efficiency relating to the part load ratio. The chapter finally identifies the fluctuating compressor power and Chiller efficiency by the multiple number of capacity control steps.
-
Constraints of using thermostatic expansion valves to operate air-cooled Chillers at lower condensing temperatures
Applied Thermal Engineering, 2006Co-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.
F W Yu - One of the best experts on this subject based on the ideXlab platform.
-
Analysis of Chiller system performance with different component combinations
Applied Thermal Engineering, 2019Co-Authors: F W Yu, W.t. HoAbstract:Abstract A large-scale Chiller system operates with many components and their different combinations influence the system coefficient of performance (COP)—cooling capacity output divided by the total electric power input of components. This study aims to analyse how different component combinations and their transitions influenced the system COP. A total of 12,541 sets of operating conditions were collected at 15-min intervals from an existing system with five Chillers of two different capacities. A total of 51 types of combinations of operating system components were identified. The development of general linear models ascertained that the two highest significant variables were the system part load ratio and component combination. The pair-up combinations with the same number of operating Chillers, pumps and cooling towers accounted for 58.23% of the total time with a higher average system COP of 3.34. Results of network analysis indicated that the system COP tended to be higher when the transition was outside clusters with pair-up combinations. Survival analysis identified specific ranges for the temperature of return chilled water and the temperature of water leaving the condensers to prolong the pair-up combination in order to increase the system COP.
-
Comprehensive Environmental Assessment for Cooling Towers with Various Controls
Indoor and Built Environment, 2009Co-Authors: F W Yu, K.t. ChanAbstract:Cooling towers are generally used in water-cooled Chiller systems, which provide cooling energy for commercial buildings. This article assesses how the various control systems of cooling towers influence plume emissions and the electricity and water consumption of a chilled water system. Integrated with real control of cooling tower fans, Chiller and cooling tower models were developed to analyze how the energy performance of a Chiller and the water loss rate varied under different operating conditions. The status of air flows through the cooling tower was investigated to judge plume formation under various cooling tower controls. A simulation analysis on a chilled water system serving an office building showed that optimizing the fan speed control of cooling towers enables the annual electricity and water consumption costs to save 4.6% while also reducing the plume generation. The optimum control means adjusting the temperature of cooling water leaving the cooling tower in response to the Chiller load an...
-
Improved energy performance of air cooled centrifugal Chillers with variable chilled water flow
Energy Conversion and Management, 2008Co-Authors: F W Yu, K.t. ChanAbstract:Abstract This paper considers how to apply optimum condensing temperature control and variable chilled water flow to increase the coefficient of performance (COP) of air cooled centrifugal Chillers. A thermodynamic model for the Chillers was developed and validated using a wide range of operating data and specifications. The model considers real process phenomena, including capacity control by the inlet guide vanes of the compressor and an algorithm to determine the number and speed of condenser fans staged based on a set point of condensing temperature. Based on the validated model, it was found that optimizing the control of condensing temperature and varying the evaporator’s chilled water flow rate enable the COP to increase by 0.8–191.7%, depending on the load and ambient conditions. A cooling load profile of an office building in a subtropical climate was considered to assess the potential electricity savings resulting from the increased Chiller COP and optimum staging of Chillers and pumps. There is 16.3–21.0% reduction in the annual electricity consumption of the building’s Chiller plant. The results of this paper provide useful information on how to implement a low energy Chiller plant.
-
Part load performance of air-cooled centrifugal Chillers with variable speed condenser fan control
Building and Environment, 2007Co-Authors: F W Yu, K.t. ChanAbstract:Abstract Air-cooled centrifugal Chillers are commonly used in commercial buildings but their performance analysis is lacking. This paper investigates the part load performance of the Chillers via a thermodynamic model. The model was validated using a wide range of operating data from an existing Chiller with specific settings of outdoor temperature and condensing pressure in controlling the condensing temperature. The validated model was developed specifically to ascertain the maximum coefficient of performance of Chiller (COP) together with the strategy for optimizing the condensing temperature under various operating conditions. It is found that the highest COP occurs at a part load ratio (PLR) of 0.71–0.84, depending on the outdoor temperature and the control of condensing temperature, rather than at full load. Yet the Chillers operating at such part load conditions will cause extra energy used for the early staging of chilled water pumps. To minimize the overall Chiller plant energy consumption, it is still preferable to implement Chiller sequencing based on the full load condition than on the aforementioned PLRs. The results of this paper present criteria for implementing low-energy strategies for operating air-cooled Chillers satisfying a given building cooling load profile.
-
Constraints of using thermostatic expansion valves to operate air-cooled Chillers at lower condensing temperatures
Applied Thermal Engineering, 2006Co-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.
Atsushi Akisawa - One of the best experts on this subject based on the ideXlab platform.
-
Experimental Investigation of the Effect of Generator Temperature on the Performance of Solution Transportation Absorption Chiller
International Journal of Air-Conditioning and Refrigeration, 2017Co-Authors: Koji Enoki, Fumi Watanabe, Atsushi Akisawa, Toshitaka TakeiAbstract:It is effective to recover waste heat to reduce primary energy consumption. From this point of view, we proposed and examined a new idea of heat transportation using ammonia–water as the working fluid in the system named the Solution Transportation Absorption Chiller (STA). As waste heat sources are not necessarily located close to areas of heat demand, conventionally, absorption Chillers are located on heat source side and produce chilled water that is transported to heat demand side through pipelines with an insulation. In contrast, the proposed system STA divides an absorption Chiller into two parts. The generator and the condenser are located on heat source side while the evaporator and the absorber are on heat demand side. Both the conventional system and STA system satisfy the same boundary condition of heat recovery and heat supply to the demand side, STA can work for transferring thermal energy as the conventional system does even though the temperature of the media is ambient without an insulation. Our previous studies of the STA were based on the experimental investigation with the STA facility where the cooling power was 90[Formula: see text]kW (25.6 refrigeration ton) at the generator temperature 120[Formula: see text]C from 0[Formula: see text]m (normal absorption Chiller) to 1000[Formula: see text]m. Thus, the Coefficient of Performance (COP) of STA was found to have almost the same value of 0.65 with conventional absorption Chillers without depending on the transportation distances. The objective of this study is to examine the effect of generator temperature from 100[Formula: see text]C to 120[Formula: see text]C on the performance of solution transportation of ammonia–water solution, because the generator temperature is directly linked to the waste heat temperature, so its effect needs to be investigated. The experimental facility tested the performance with 0[Formula: see text]m (normal absorption Chiller), 200[Formula: see text]m and 500[Formula: see text]m distance. The results indicate that the effect of the generator temperature and solution transportation distances showed no significant on the COP.
-
Experimental Investigation of the Effect of Generator Temperature on the Performance of Solution Transportation Absorption Chiller
International Journal of Air-conditioning and Refrigeration, 2017Co-Authors: Koji Enoki, Fumi Watanabe, Atsushi Akisawa, Toshitaka TakeiAbstract:It is effective to recover waste heat to reduce primary energy consumption. From this point of view, we proposed and examined a new idea of heat transportation using ammonia–water as the working fluid in the system named the Solution Transportation Absorption Chiller (STA). As waste heat sources are not necessarily located close to areas of heat demand, conventionally, absorption Chillers are located on heat source side and produce chilled water that is transported to heat demand side through pipelines with an insulation. In contrast, the proposed system STA divides an absorption Chiller into two parts. The generator and the condenser are located on heat source side while the evaporator and the absorber are on heat demand side. Both the conventional system and STA system satisfy the same boundary condition of heat recovery and heat supply to the demand side, STA can work for transferring thermal energy as the conventional system does even though the temperature of the media is ambient without an insulatio...
-
A new cycle time allocation for enhancing the performance of two-bed adsorption Chillers
International Journal of Refrigeration-revue Internationale Du Froid, 2009Co-Authors: Takahiko Miyazaki, Bidyut Baran Saha, Ibrahim I. El-sharkawy, Atsushi Akisawa, Anutosh ChakrabortyAbstract:Abstract The present study proposed a new cycle time allocation in silica gel-water based adsorption Chillers to enhance their performances. The new cycle time allocation not only improves the cooling capacity and coefficient of performance (COP), but also contributes in the reduction of delivered chilled water fluctuations. In a conventional adsorption Chiller operation, the appropriate pre-heating/pre-cooling process enhances the cooling capacity, whereas the excess pre-heating/pre-cooling time abates the average cooling capacity. The proposed new cycle time allocation allows the continuous cooling effect over the cycle without sacrificing the effect of pre-heating/pre-cooling. Simulation results showed that the new cycle time was effective for both RD type silica gel-water and CaCl2-in-silica gel-water pairs, and the cooling capacity was increased as much as by 6%.
-
study on a dual mode multi stage multi bed regenerative adsorption Chiller
Renewable Energy, 2006Co-Authors: Bidyut Baran Saha, Yoshinori Hamamoto, Kim Choon Ng, Shigeru Koyama, Atsushi Akisawa, Takao KashiwagiAbstract:In this paper, a detailed parametric study on a dual-mode silica gel–water adsorption Chiller is performed. This advanced adsorption Chiller utilizes effectively low-temperature solar or waste heat sources of temperature between 40 and 95°C. Two operation modes are possible for the advanced Chiller. The first operation mode will be to work as a highly efficient conventional Chiller where the driving source temperature is between 60 and 95°C. The second operation mode will be to work as an advanced three-stage adsorption Chiller where the available driving source temperature is very low (between 40 and 60°C). With this very low driving source temperature in combination with a coolant at 30°C, no other cycle except an advanced adsorption cycle with staged regeneration will be operational. In this paper, the effect of chilled-water inlet temperature, heat transfer fluid flow rates and adsorption–desorption cycle time effect on cooling capacity and COP of the dual-mode Chiller is performed. Simulation results show that both cooling capacity and COP values increase with the increase of chilled water inlet temperature with driving source temperature at 50 and 80°C in three-stage mode, and single-stage multi-bed mode, respectively. However, the delivered chilled-water temperature increases with chilled-water inlet temperature in both modes.
-
multi bed regenerative adsorption Chiller improving the utilization of waste heat and reducing the chilled water outlet temperature fluctuation
International Journal of Refrigeration-revue Internationale Du Froid, 2001Co-Authors: Hui Tong Chua, Takao Kashiwagi, Kim Choon Ng, Atsushi Akisawa, A Malek, Bidyut Baran SahaAbstract:A multi-bed regenerative adsorption Chiller design is proposed. The concept aims to extract the most enthalpy from the low-grade waste heat before it is purged into the drain. It is also able to minimise the chilled water temperature fluctuation so that downstream temperature smoothing device may be downsized or even eliminated in applications where tighter temperature control may be required. The design also avoids a master-and-slave configuration so that materials invested are not under-utilised. Because of the nature of low-grade waste heat utilization, the performance of adsorption Chillers is measured in terms of the recovery efficiency, η instead of the conventional COP. For the same waste heat source flowrate and inlet temperature, a four-bed Chiller generates 70% more cooling capacity than a typical two-bed Chiller. A six-bed Chiller in turn generates 40% more than that of a four-bed Chiller. Since the beds can be triggered into operation sequentially during start-up, the risk of ice formation in the evaporator during start-up is greatly reduced compared with that of a two-bed Chiller.
Jincui Zhang - One of the best experts on this subject based on the ideXlab platform.
-
experimental study on improved two bed silica gel water adsorption Chiller
Energy Conversion and Management, 2008Co-Authors: D.c. Wang, Jincui ZhangAbstract:Abstract A novel silica gel–water adsorption Chiller with two chambers has been built in Shanghai Jiao Tong University (SJTU). This Chiller combines two single bed systems (basic system) without any vacuum valves. One adsorber, one condenser and one evaporator are housed in the same chamber to constitute one adsorption/desorption unit. In this work, the Chiller is developed and improved. The improved Chiller is composed of three vacuum chambers: two adsorption/desorption vacuum chambers (the same structure as the former Chiller) and one heat pipe working vacuum chamber. The evaporators of these two adsorption/desorption units are combined by a heat pipe. So, no valves are installed in the chilled water sub system and one vacuum valve connects the two adsorption/desorption chambers together to improve its performance. The performance of the Chiller is tested. As the results, the refrigerating capacity and the COP of the Chiller are, respectively, 8.69 kW and 0.388 for the heat source temperature of 82.5 °C, the cooling water temperature of 30.4 °C and the chilled water outlet temperature of 11.9 °C. For a chilled water outlet temperature of 16.5 °C, the COP reaches 0.432, while the refrigerating capacity is near 11 kW. There is an improvement of at least 12% for the COP compared with the former Chillers.
-
Experimental study on improved two-bed silica gel–water adsorption Chiller
Energy Conversion and Management, 2008Co-Authors: Zaizhong Xia, D.c. Wang, Jincui ZhangAbstract:Abstract A novel silica gel–water adsorption Chiller with two chambers has been built in Shanghai Jiao Tong University (SJTU). This Chiller combines two single bed systems (basic system) without any vacuum valves. One adsorber, one condenser and one evaporator are housed in the same chamber to constitute one adsorption/desorption unit. In this work, the Chiller is developed and improved. The improved Chiller is composed of three vacuum chambers: two adsorption/desorption vacuum chambers (the same structure as the former Chiller) and one heat pipe working vacuum chamber. The evaporators of these two adsorption/desorption units are combined by a heat pipe. So, no valves are installed in the chilled water sub system and one vacuum valve connects the two adsorption/desorption chambers together to improve its performance. The performance of the Chiller is tested. As the results, the refrigerating capacity and the COP of the Chiller are, respectively, 8.69 kW and 0.388 for the heat source temperature of 82.5 °C, the cooling water temperature of 30.4 °C and the chilled water outlet temperature of 11.9 °C. For a chilled water outlet temperature of 16.5 °C, the COP reaches 0.432, while the refrigerating capacity is near 11 kW. There is an improvement of at least 12% for the COP compared with the former Chillers.
Bidyut Baran Saha - One of the best experts on this subject based on the ideXlab platform.
-
A new cycle time allocation for enhancing the performance of two-bed adsorption Chillers
International Journal of Refrigeration-revue Internationale Du Froid, 2009Co-Authors: Takahiko Miyazaki, Bidyut Baran Saha, Ibrahim I. El-sharkawy, Atsushi Akisawa, Anutosh ChakrabortyAbstract:Abstract The present study proposed a new cycle time allocation in silica gel-water based adsorption Chillers to enhance their performances. The new cycle time allocation not only improves the cooling capacity and coefficient of performance (COP), but also contributes in the reduction of delivered chilled water fluctuations. In a conventional adsorption Chiller operation, the appropriate pre-heating/pre-cooling process enhances the cooling capacity, whereas the excess pre-heating/pre-cooling time abates the average cooling capacity. The proposed new cycle time allocation allows the continuous cooling effect over the cycle without sacrificing the effect of pre-heating/pre-cooling. Simulation results showed that the new cycle time was effective for both RD type silica gel-water and CaCl2-in-silica gel-water pairs, and the cooling capacity was increased as much as by 6%.
-
study on a dual mode multi stage multi bed regenerative adsorption Chiller
Renewable Energy, 2006Co-Authors: Bidyut Baran Saha, Yoshinori Hamamoto, Kim Choon Ng, Shigeru Koyama, Atsushi Akisawa, Takao KashiwagiAbstract:In this paper, a detailed parametric study on a dual-mode silica gel–water adsorption Chiller is performed. This advanced adsorption Chiller utilizes effectively low-temperature solar or waste heat sources of temperature between 40 and 95°C. Two operation modes are possible for the advanced Chiller. The first operation mode will be to work as a highly efficient conventional Chiller where the driving source temperature is between 60 and 95°C. The second operation mode will be to work as an advanced three-stage adsorption Chiller where the available driving source temperature is very low (between 40 and 60°C). With this very low driving source temperature in combination with a coolant at 30°C, no other cycle except an advanced adsorption cycle with staged regeneration will be operational. In this paper, the effect of chilled-water inlet temperature, heat transfer fluid flow rates and adsorption–desorption cycle time effect on cooling capacity and COP of the dual-mode Chiller is performed. Simulation results show that both cooling capacity and COP values increase with the increase of chilled water inlet temperature with driving source temperature at 50 and 80°C in three-stage mode, and single-stage multi-bed mode, respectively. However, the delivered chilled-water temperature increases with chilled-water inlet temperature in both modes.
-
multi bed regenerative adsorption Chiller improving the utilization of waste heat and reducing the chilled water outlet temperature fluctuation
International Journal of Refrigeration-revue Internationale Du Froid, 2001Co-Authors: Hui Tong Chua, Takao Kashiwagi, Kim Choon Ng, Atsushi Akisawa, A Malek, Bidyut Baran SahaAbstract:A multi-bed regenerative adsorption Chiller design is proposed. The concept aims to extract the most enthalpy from the low-grade waste heat before it is purged into the drain. It is also able to minimise the chilled water temperature fluctuation so that downstream temperature smoothing device may be downsized or even eliminated in applications where tighter temperature control may be required. The design also avoids a master-and-slave configuration so that materials invested are not under-utilised. Because of the nature of low-grade waste heat utilization, the performance of adsorption Chillers is measured in terms of the recovery efficiency, η instead of the conventional COP. For the same waste heat source flowrate and inlet temperature, a four-bed Chiller generates 70% more cooling capacity than a typical two-bed Chiller. A six-bed Chiller in turn generates 40% more than that of a four-bed Chiller. Since the beds can be triggered into operation sequentially during start-up, the risk of ice formation in the evaporator during start-up is greatly reduced compared with that of a two-bed Chiller.
-
Thermodynamic analysis of absorption Chillers: Internal dissipation and process average temperature
Applied Thermal Engineering, 1998Co-Authors: Kim Choon Ng, Atsushi Akisawa, Hui Tong Chua, Jeffrey M. Gordon, K. Tu, T. Kashiwagi, Bidyut Baran SahaAbstract:Abstract Absorption Chillers operate well below their reversible or endoreversible limits because their thermodynamic behavior is dominated by internal dissipation, a significant part of which occurs in the Chiller’s heat exchangers. This fact has summarily been omitted from earlier analyses. It translates into incorrect values for the refrigerant process-average temperature (PAT), and leads to noticeable errors in Chiller diagnostics and optimization. Using experimental measurements from an absorption Chiller, in concert with a computer simulation code and an analytic thermodynamic model, we fortify these claims with quantitative examples. The correct PAT is derived and its significance in Chiller analysis is highlighted. Aspects of Chiller optimization that are unique to absorption technology, as opposed to conventional vapor-cycle reciprocating Chillers, are also illustrated. We also substantiate that commercial absorption Chiller technology has empirically evolved to close to optimal operating conditions.