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Jincan Chen - One of the best experts on this subject based on the ideXlab platform.

  • The maximum Coefficient of Performance of a two-stage combined heat pump system affected by multi-irreversibilities
    International journal of ambient energy, 2001
    Co-Authors: Jincan Chen, C. Wu
    Abstract:

    A general cycle model which includes the multi-irreversibilities often existing in real heat pump systems is established and used to analyse the influence of the irreversibility of finite-rate heat transfer across finite temperature differences, the heat leak between the external heat reservoirs, and the internal dissipation of the working fluid on the Performance of a two-stage combined heat pump system. The Coefficient of Performance is taken as an objective function for optimisation. The maximum Coefficient of Performance with non-zero specific heating load is determined and other corresponding Performance parameters, such as the specific heating load, temperatures of the working fluid in the isothermal processes, the optimal distribution of the heat transfer areas of heat exchangers, and the power input of the heat pump system, are calculated. The results obtained here are more general than those obtained from a two-stage endoreversible combined heat pump system and can guide the optimal design and operation of real combined heat pump systems.

  • Performance characteristics of a two-stage irreversible combined refrigeration system at maximum Coefficient of Performance
    Energy Conversion and Management, 1999
    Co-Authors: Jincan Chen
    Abstract:

    A general cycle model of a two-stage combined refrigeration system is established and used for analizing the influence of multi-irreversibilities, such as finite rate heat transfer, heat leak between the heat reservoirs and internal dissipation of the working fluid, on the Performance of the refrigeration system. The Coefficient of Performance is taken as an objective function for optimization. The maximum Coefficient of Performance is calculated, and other corresponding Performance parameters, such as the temperatures of the working fluid in the isothermal processes, the optimal distribution of the heat transfer areas and the power input of the refrigeration system, are determined. The results obtained here are more general than those obtained from a two-stage endoreversible combined refrigeration system and can guide the optimal design and operation of real combined refrigerator systems.

  • The Coefficient of Performance of a multi-temperature-level absorption heat transformer at maximum specific heating load
    Journal of Physics D, 1998
    Co-Authors: Jincan Chen
    Abstract:

    An endoreversible cycle model of a multi-temperature-level absorption heat transformer is set up and used to analyse the Performance of the heat transformer affected by the irreversibility of finite-rate heat transfer. The key Performance parameters, such as the Coefficient of Performance, specific heating load, temperatures of the working fluid in the heat exchangers, heat-transfer areas of the heat exchangers and so on, are optimized. Some new results which are conducive to the optimal design and operation of real heat transformer systems are obtained and several special cases are discussed in detail. Moreover, the endoreversible cycle model is generalized to become an irreversible cycle model. The important results describing the optimal Performance of a multi-temperature-level absorption heat transformer affected simultaneously by the internal and external irreversibilities can be obtained simply and conveniently from the corresponding formulae of the endoreversible cycle model because of the introduction both of the equivalent temperatures and of the equivalent overall heat-transfer Coefficients.

  • Thermodynamic analysis of the Performance of a solar absorption heat transformer at maximum Coefficient of Performance
    International Journal of Energy Research, 1997
    Co-Authors: Jincan Chen
    Abstract:

    It is proven that a solar absorption heat transformer affected by the irreversibility of finite-rate heat transfer may be modelled as an equivalent combined system consisting of a solar collector and an endoreversible absorption heat transformer, the latter being further treated as a combined cycle having an endoreversible heat pump driven by an endoreversible heat engine. The maximum Coefficient of Performance of the system is determined, based on the linear heat loss model for solar collectors and the general optimum relation for endoreversible absorption heat transformers. The optimality problems concerning the primary Performance parameters of the system are discussed. The results obtained here may serve as a good guide for the evaluation of existing real solar absorption heat transformers or provide some theoretical bases for the optimal design of future solar absorption heat transformers. © 1997 by John Wiley & Sons, Ltd.

  • The maximum Coefficient of Performance of thermoelectric heat pumps
    International journal of ambient energy, 1996
    Co-Authors: Jincan Chen, Bjarne Andresen
    Abstract:

    SYNOPSIS The effect of three main irreversibilities existing in thermoelectric devices on the Performance of a thermoelectric heat pump is investigated. The Coefficient of Performance and the heating load of the heat pump are derived. The optimal Performance of the heat pump at maximum Coefficient of Performance is discussed, and the rational working region of the heat pump is determined. The optimal structure of the device is also described. The results obtained here are more realistic than those derived from nonequilibrium thermodynamics.

Maciej Szumski - One of the best experts on this subject based on the ideXlab platform.

  • MMAR - Design and implementation of the air/water heat pump controller with increased Coefficient of Performance
    2016 21st International Conference on Methods and Models in Automation and Robotics (MMAR), 2016
    Co-Authors: Piotr Tatjewski, Piotr Marusak, Marian Rubik, Piotr Ziętek, Maciej Szumski, Maciej Lawrynczuk
    Abstract:

    A control algorithm designed to increase the economic Performance of the air/water heat pump is described. The heat pump itself has very fast dynamics when compared with the heated object; therefore the controller uses static pump modeling to derive the control action. The algorithm controls the compressor in order to stabilize the temperature of water flowing out of the condenser and the expansion valve in order to minimize superheat and fulfill the superheat constraints. The algorithm provides stable operation of the heat pump and ensures increase of the Coefficient of Performance (COP) for different conditions in which the controlled device operates (in a wide range of air temperature). An average 10% improvement of COP when compared to the catalogue data of the tested pump with standard controller was achieved. The control algorithm was successfully implemented in the ecoTRONIC200 microprocessor controller.

  • Design and implementation of the air/water heat pump controller with increased Coefficient of Performance
    2016 21st International Conference on Methods and Models in Automation and Robotics (MMAR), 2016
    Co-Authors: Piotr Tatjewski, Maciej Ławryńczuk, Piotr Marusak, Marian Rubik, Piotr Ziętek, Maciej Szumski
    Abstract:

    A control algorithm designed to increase the economic Performance of the air/water heat pump is described. The heat pump itself has very fast dynamics when compared with the heated object; therefore the controller uses static pump modeling to derive the control action. The algorithm controls the compressor in order to stabilize the temperature of water flowing out of the condenser and the expansion valve in order to minimize superheat and fulfill the superheat constraints. The algorithm provides stable operation of the heat pump and ensures increase of the Coefficient of Performance (COP) for different conditions in which the controlled device operates (in a wide range of air temperature). An average 10% improvement of COP when compared to the catalogue data of the tested pump with standard controller was achieved. The control algorithm was successfully implemented in the ecoTRONIC200 microprocessor controller.

K T Chan - One of the best experts on this subject based on the ideXlab platform.

  • modelling of the Coefficient of Performance of an air cooled screw chiller with variable speed condenser fans
    Building and Environment, 2006
    Co-Authors: F W Yu, K T Chan
    Abstract:

    Air-cooled chillers are generally recognized as energy intensive equipment in air-conditioned buildings in the subtropical climate. This paper considers how the use of variable speed condenser fans enables these chillers to operate more efficiently. The thermodynamic model of an air-cooled screw chiller was developed using the simulation program TRNSYS and validated using the field data and specifications of the chiller. The staging of condenser fans and the control of their speed in various operating conditions were described. A comparison was made on the Coefficient of Performance of the chiller in the steady state with various control strategies: head pressure control with constant or variable speed condenser fans; condensing temperature control (CTC) with constant or variable speed condenser fans. Potential improvements in the chiller COP due to the use of CTC with variable speed condenser fans were discussed. The findings of this paper are useful in developing more energy efficient air-cooled chillers.

  • advanced control of heat rejection airflow for improving the Coefficient of Performance of air cooled chillers
    Applied Thermal Engineering, 2006
    Co-Authors: F W Yu, K T Chan
    Abstract:

    Abstract Air-cooled chillers are generally the major electricity consumers in air-conditioned buildings in the subtropical climate. This paper presents how the Coefficient of Performance (COP) of these chillers can be improved by modulating heat rejection airflow via variable speed condenser fans. 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. The set point of condensing temperature was used to determine the number and speed of condenser fans staged in various operating conditions. It is found that adjusting the set point in response to the outdoor temperature alone cannot achieve maximum COP when using variable speed condenser fans. Advanced control is proposed for these fans to minimize the chiller electric demand. Compared to the traditional head pressure control with constant speed condenser fans, the use of variable speed condenser fans with the advanced control enables the chiller COP to increase by 4.0–127.5%, which corresponds to a decrease of 1.8–154.6 kW in the chiller electric demand. This provides important insights into how air-cooled chillers can operate more efficiently.

J. M. M. Roco - One of the best experts on this subject based on the ideXlab platform.

  • Coefficient of Performance for a low dissipation carnot like refrigerator with nonadiabatic dissipation
    Physical Review E, 2013
    Co-Authors: Yong Hu, Calvo A Hernandez, Jizhou He, Jianhui Wang, Feifei Wu, J. M. M. Roco
    Abstract:

    : We study the Coefficient of Performance (COP) and its bounds for a Carnot-like refrigerator working between two heat reservoirs at constant temperatures T(h) and T(c), under two optimization criteria χ and Ω. In view of the fact that an "adiabatic" process usually takes finite time and is nonisentropic, the nonadiabatic dissipation and the finite time required for the adiabatic processes are taken into account by assuming low dissipation. For given optimization criteria, we find that the lower and upper bounds of the COP are the same as the corresponding ones obtained from the previous idealized models where any adiabatic process is undergone instantaneously with constant entropy. To describe some particular models with very fast adiabatic transitions, we also consider the influence of the nonadiabatic dissipation on the bounds of the COP, under the assumption that the irreversible entropy production in the adiabatic process is constant and independent of time. Our theoretical predictions match the observed COPs of real refrigerators more closely than the ones derived in the previous models, providing a strong argument in favor of our approach.

  • Coefficient of Performance under optimized figure of merit in minimally nonlinear irreversible refrigerator
    EPL, 2013
    Co-Authors: Yuki Izumida, Calvo A Hernandez, Koji Okuda, J. M. M. Roco
    Abstract:

    We apply the model of minimally nonlinear irreversible heat engines developed by Izumida and Okuda (EPL, 97 (2012) 10004) to refrigerators. The model assumes extended Onsager relations including a new nonlinear term accounting for dissipation effects. The bounds for the optimized regime under an appropriate figure of merit and the tight-coupling condition are analyzed and successfully compared with those obtained previously for low-dissipation Carnot refrigerators in the finite-time thermodynamics framework. Besides, we study the bounds for the nontight-coupling case numerically. We also introduce a leaky low-dissipation Carnot refrigerator and show that it serves as an example of the minimally nonlinear irreversible refrigerator, by calculating its Onsager Coefficients explicitly.

  • Coefficient of Performance at maximum figure of merit and its bounds for low dissipation carnot like refrigerators
    Physical Review E, 2012
    Co-Authors: Yang Wang, Mingxing Li, Z C Tu, Calvo A Hernandez, J. M. M. Roco
    Abstract:

    : The figure of merit for refrigerators performing finite-time Carnot-like cycles between two reservoirs at temperature T(h) and T(c) (Coefficient of Performance at maximum figure of merit is bounded between 0 and (sqrt[9+8e(c)] - 3)/2 for the low-dissipation refrigerators, where e(c) = T(c)/(T(h) - T(c)) is the Carnot Coefficient of Performance for reversible refrigerators. These bounds can be reached for extremely asymmetric low-dissipation cases when the ratio between the dissipation constants of the processes in contact with the cold and hot reservoirs approaches to zero or infinity, respectively. The observed Coefficients of Performance for real refrigerators are located in the region between the lower and upper bounds, which is in good agreement with our theoretical estimation.

  • Irreversible refrigerators under per-unit-time Coefficient of Performance optimization
    Applied Physics Letters, 1997
    Co-Authors: Santiago Velasco, J. M. M. Roco, Alejandro Medina, A Calvo Hernández
    Abstract:

    A finite-time thermodynamics analysis is used to investigate the optimal Coefficient of Performance (COP) of an irreversible Carnot refrigerator using the per-unit-time COP as an objective function for optimization. The model includes finite-rate heat transfers between the refrigerant and the external heat reservoirs, heat leak between heat reservoirs, and internal dissipations of the refrigerant. Heat conductances associated with heat transfers are optimized by maximizing the cooling power per unit of capital invested in the refrigerator. The obtained results are consistent with Performance data for real low-temperature refrigerators.

F W Yu - One of the best experts on this subject based on the ideXlab platform.

  • modelling of the Coefficient of Performance of an air cooled screw chiller with variable speed condenser fans
    Building and Environment, 2006
    Co-Authors: F W Yu, K T Chan
    Abstract:

    Air-cooled chillers are generally recognized as energy intensive equipment in air-conditioned buildings in the subtropical climate. This paper considers how the use of variable speed condenser fans enables these chillers to operate more efficiently. The thermodynamic model of an air-cooled screw chiller was developed using the simulation program TRNSYS and validated using the field data and specifications of the chiller. The staging of condenser fans and the control of their speed in various operating conditions were described. A comparison was made on the Coefficient of Performance of the chiller in the steady state with various control strategies: head pressure control with constant or variable speed condenser fans; condensing temperature control (CTC) with constant or variable speed condenser fans. Potential improvements in the chiller COP due to the use of CTC with variable speed condenser fans were discussed. The findings of this paper are useful in developing more energy efficient air-cooled chillers.

  • advanced control of heat rejection airflow for improving the Coefficient of Performance of air cooled chillers
    Applied Thermal Engineering, 2006
    Co-Authors: F W Yu, K T Chan
    Abstract:

    Abstract Air-cooled chillers are generally the major electricity consumers in air-conditioned buildings in the subtropical climate. This paper presents how the Coefficient of Performance (COP) of these chillers can be improved by modulating heat rejection airflow via variable speed condenser fans. 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. The set point of condensing temperature was used to determine the number and speed of condenser fans staged in various operating conditions. It is found that adjusting the set point in response to the outdoor temperature alone cannot achieve maximum COP when using variable speed condenser fans. Advanced control is proposed for these fans to minimize the chiller electric demand. Compared to the traditional head pressure control with constant speed condenser fans, the use of variable speed condenser fans with the advanced control enables the chiller COP to increase by 4.0–127.5%, which corresponds to a decrease of 1.8–154.6 kW in the chiller electric demand. This provides important insights into how air-cooled chillers can operate more efficiently.