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Reinhard Radermacher - One of the best experts on this subject based on the ideXlab platform.

  • dynamic modeling and characteristic analysis of a two stage vapor injection heat pump system under frosting conditions
    International Journal of Refrigeration-revue Internationale Du Froid, 2017
    Co-Authors: Hongtao Qiao, Vikrant Aute, Reinhard Radermacher
    Abstract:

    Abstract This paper presents a distributed-parameter dynamic heat exchanger model integrated with a detailed frost growth model to account for non-uniform frost formation on a fan-supplied finned-tube coil. A novel, iteration-free approach is proposed to solve the air flow redistribution by linearizing a system of non-linear air pressure drop equalization equations, resulting in a significant improvement in the computational efficiency. As a continuation and extension of our previous work, the developed models along with the component models described in Qiao et al. (2015a) are applied for the first time to explore the frosting dynamics of a two-stage Flash Tank vapor injection heat pump system. It is found that frost formation degrades the heating performance of the system substantially. Meanwhile, the simulation indicates that air and refrigerant flow maldistribution, resulting from non-uniform frost growth on the outdoor heat exchanger, can lead to unstable system hunting behavior. Comparisons between the simulation results and experimental data indicate that the proposed models can reasonably predict the time-dependent heat transfer and fluid flow phenomena of the system.

  • Transient modeling of a Flash Tank vapor injection heat pump system - Part I: Model development
    International Journal of Refrigeration, 2015
    Co-Authors: Hongtao Qiao, Vikrant Aute, Reinhard Radermacher
    Abstract:

    This two-part article explores the dynamic behavior of a Flash Tank vapor injection heat pump system from a numerical simulation perspective. Part I provides a first-principles model describing the transient heat transfer and flow phenomena of the system with detailed modeling techniques for each component. The vapor injection scroll compressor is analyzed with the internal heat transfer between the refrigerant and metallic parts taken into account. Lumped-parameter models are developed for the Flash Tank and expansion devices. Heat exchangers are modeled using a finite volume approach and accounting for the complex tube circuitry. The separated flow model without interfacial exchange is utilized for two-phase flows in order to incorporate an appropriate void fraction model so that a more accurate prediction for refrigerant mass distribution can be achieved. The modular nature of the component models allows flexibility in the system configuration. Transient simulations are carried out for start-up and shut-down operations. A detailed comparison of model predictions against experimental data is presented in the companion paper.

  • Transient and steady-state experimental investigation of Flash Tank vapor injection heat pump cycle control strategy
    International Journal of Refrigeration-revue Internationale Du Froid, 2011
    Co-Authors: Xing Xu, Yunho Hwang, Reinhard Radermacher
    Abstract:

    Abstract Recent research on vapor injection technique has been mostly focused on performance improvement using different system configurations. The Flash Tank cycle typically shows better performance than the internal heat exchanger cycle. However, the Flash Tank cycle control strategy is not yet clearly defined. In this study, a novel cycle control strategy is proposed for an R-410A vapor injection Flash Tank heat pump system and its feasibility was experimentally investigated. The proposed novel cycle control strategy utilized an electronic expansion valve (EEV) for the upper-stage expansion and a thermostatic expansion valve for the lower-stage expansion, and applied an electric heater in the vapor injection line to introduce superheat to the injected vapor by providing a control signal to the upper-stage EEV. Both transient and steady-state system behaviors were studied. The proposed cycle control strategy was found to be able to provide reliable control to the system.

  • Simulation and Validation of a Two-Stage Flash Tank Cycle using R410A as a Refrigerant
    2011
    Co-Authors: Jonathan Winkler, Vikrant Aute, Xudong Wang, Reinhard Radermacher
    Abstract:

    Investigating alternative system configurations is a means to improving vapor compression system COP by increasing system capacity and reducing compressor power consumption. The characterization and optimization of alternative system configurations can be conducted through the use of simulation. This paper presents a vapor compression system simulation tool capable of modeling a two-stage Flash Tank cycle. The key component model in the simulation of a two-stage Flash Tank cycle is the compressor. The component-based nature of the simulation tool allows for the use of any type of two-stage compressor model, including a vapor-injection compressor. The simulation assumptions and approach are presented in this paper. The experimental validation for both the baseline cycle and Flash Tank cycle are presented for an R410A system operating in both heating and cooling modes. A total of 52 test points were included in the validation for the two operating modes. The calculated capacity for 48 of the 52 test points was predicted to within 5% of experimental values.

  • two stage heat pump system with vapor injected scroll compressor using r410a as a refrigerant
    International Journal of Refrigeration-revue Internationale Du Froid, 2009
    Co-Authors: Xudong Wang, Yunho Hwang, Reinhard Radermacher
    Abstract:

    Abstract Refrigerant vapor-injection technique has been well justified to improve the performance of systems in refrigeration applications. However, it has not received much attention for air conditioning applications, particularly for air conditioning in hot climates and for heat pumping in cold climates. In this study, the performance of an 11 kW R410A heat pump system with a two-stage vapor-injected scroll compressor was experimentally investigated. The vapor-injected scroll compressor was tested with the cycle options of both Flash Tank and internal heat exchanger configurations. A cooling capacity gain of around 14% with 4% COP improvement at the ambient temperature of 46.1 °C and about 30% heating capacity improvement with 20% COP gain at the ambient temperature of −17.8 °C were found for the vapor-injected R410A heat pump system as compared to the conventional system which has the same compressor displacement volume.

Hongtao Qiao - One of the best experts on this subject based on the ideXlab platform.

  • dynamic modeling and characteristic analysis of a two stage vapor injection heat pump system under frosting conditions
    International Journal of Refrigeration-revue Internationale Du Froid, 2017
    Co-Authors: Hongtao Qiao, Vikrant Aute, Reinhard Radermacher
    Abstract:

    Abstract This paper presents a distributed-parameter dynamic heat exchanger model integrated with a detailed frost growth model to account for non-uniform frost formation on a fan-supplied finned-tube coil. A novel, iteration-free approach is proposed to solve the air flow redistribution by linearizing a system of non-linear air pressure drop equalization equations, resulting in a significant improvement in the computational efficiency. As a continuation and extension of our previous work, the developed models along with the component models described in Qiao et al. (2015a) are applied for the first time to explore the frosting dynamics of a two-stage Flash Tank vapor injection heat pump system. It is found that frost formation degrades the heating performance of the system substantially. Meanwhile, the simulation indicates that air and refrigerant flow maldistribution, resulting from non-uniform frost growth on the outdoor heat exchanger, can lead to unstable system hunting behavior. Comparisons between the simulation results and experimental data indicate that the proposed models can reasonably predict the time-dependent heat transfer and fluid flow phenomena of the system.

  • Transient modeling of a Flash Tank vapor injection heat pump system - Part I: Model development
    International Journal of Refrigeration, 2015
    Co-Authors: Hongtao Qiao, Vikrant Aute, Reinhard Radermacher
    Abstract:

    This two-part article explores the dynamic behavior of a Flash Tank vapor injection heat pump system from a numerical simulation perspective. Part I provides a first-principles model describing the transient heat transfer and flow phenomena of the system with detailed modeling techniques for each component. The vapor injection scroll compressor is analyzed with the internal heat transfer between the refrigerant and metallic parts taken into account. Lumped-parameter models are developed for the Flash Tank and expansion devices. Heat exchangers are modeled using a finite volume approach and accounting for the complex tube circuitry. The separated flow model without interfacial exchange is utilized for two-phase flows in order to incorporate an appropriate void fraction model so that a more accurate prediction for refrigerant mass distribution can be achieved. The modular nature of the component models allows flexibility in the system configuration. Transient simulations are carried out for start-up and shut-down operations. A detailed comparison of model predictions against experimental data is presented in the companion paper.

  • transient modeling of a Flash Tank vapor injection heat pump system part ii simulation results and experimental validation
    International Journal of Refrigeration-revue Internationale Du Froid, 2015
    Co-Authors: Hongtao Qiao, Vikrant Aute, Reinhard Radermache
    Abstract:

    Abstract This two-part article investigates the transient characteristics of a Flash Tank vapor injection system through modeling and experimental validation. The first part describes the detailed modeling techniques for each component, and the second part describes the transient simulations that are carried out for the overall system under start-up and shut-down operations and presents the results. After comparing the predictions of the proposed model with the experimental data, it was concluded that the proposed model can adequately capture the transient heat transfer and flow phenomena of the system. The dynamic system response when subjected to a step change in the opening of the upper-stage EEV (electronic expansion valve) was also investigated. It was found that EEV opening has a significant impact on the system performance and the liquid level in the Flash Tank, but exhibits little effect on the suction pressure. These findings were corroborated through experiments.

Vikrant Aute - One of the best experts on this subject based on the ideXlab platform.

  • dynamic modeling and characteristic analysis of a two stage vapor injection heat pump system under frosting conditions
    International Journal of Refrigeration-revue Internationale Du Froid, 2017
    Co-Authors: Hongtao Qiao, Vikrant Aute, Reinhard Radermacher
    Abstract:

    Abstract This paper presents a distributed-parameter dynamic heat exchanger model integrated with a detailed frost growth model to account for non-uniform frost formation on a fan-supplied finned-tube coil. A novel, iteration-free approach is proposed to solve the air flow redistribution by linearizing a system of non-linear air pressure drop equalization equations, resulting in a significant improvement in the computational efficiency. As a continuation and extension of our previous work, the developed models along with the component models described in Qiao et al. (2015a) are applied for the first time to explore the frosting dynamics of a two-stage Flash Tank vapor injection heat pump system. It is found that frost formation degrades the heating performance of the system substantially. Meanwhile, the simulation indicates that air and refrigerant flow maldistribution, resulting from non-uniform frost growth on the outdoor heat exchanger, can lead to unstable system hunting behavior. Comparisons between the simulation results and experimental data indicate that the proposed models can reasonably predict the time-dependent heat transfer and fluid flow phenomena of the system.

  • Transient modeling of a Flash Tank vapor injection heat pump system - Part I: Model development
    International Journal of Refrigeration, 2015
    Co-Authors: Hongtao Qiao, Vikrant Aute, Reinhard Radermacher
    Abstract:

    This two-part article explores the dynamic behavior of a Flash Tank vapor injection heat pump system from a numerical simulation perspective. Part I provides a first-principles model describing the transient heat transfer and flow phenomena of the system with detailed modeling techniques for each component. The vapor injection scroll compressor is analyzed with the internal heat transfer between the refrigerant and metallic parts taken into account. Lumped-parameter models are developed for the Flash Tank and expansion devices. Heat exchangers are modeled using a finite volume approach and accounting for the complex tube circuitry. The separated flow model without interfacial exchange is utilized for two-phase flows in order to incorporate an appropriate void fraction model so that a more accurate prediction for refrigerant mass distribution can be achieved. The modular nature of the component models allows flexibility in the system configuration. Transient simulations are carried out for start-up and shut-down operations. A detailed comparison of model predictions against experimental data is presented in the companion paper.

  • transient modeling of a Flash Tank vapor injection heat pump system part ii simulation results and experimental validation
    International Journal of Refrigeration-revue Internationale Du Froid, 2015
    Co-Authors: Hongtao Qiao, Vikrant Aute, Reinhard Radermache
    Abstract:

    Abstract This two-part article investigates the transient characteristics of a Flash Tank vapor injection system through modeling and experimental validation. The first part describes the detailed modeling techniques for each component, and the second part describes the transient simulations that are carried out for the overall system under start-up and shut-down operations and presents the results. After comparing the predictions of the proposed model with the experimental data, it was concluded that the proposed model can adequately capture the transient heat transfer and flow phenomena of the system. The dynamic system response when subjected to a step change in the opening of the upper-stage EEV (electronic expansion valve) was also investigated. It was found that EEV opening has a significant impact on the system performance and the liquid level in the Flash Tank, but exhibits little effect on the suction pressure. These findings were corroborated through experiments.

  • modelica based transient modeling of a Flash Tank vapor injection system and experimental validation
    2012 Purdue Conferences. 14th International Refrigeration and Air-Conditioning Conference at Purdue., 2012
    Co-Authors: Vire Hano, Vikrant Aute, Jiazhe Ling, Reinhard Radermache
    Abstract:

    The Flash Tank vapor injection cycle is widely used and has been proven effective for improving system performance compared with the conventional systems. A good control design for this type of cycle to make the syste m work properly under various operation conditions is a ch allenge and one often has to resort to experimental studies, which are time-consuming and costly. In this paper, a tra nsient mathematical model for a Flash Tank vapor in jection heat pump system with an economized scroll compressor is presented. The compressor model is a map-based model. The heat exchangers are modeled using the finite volume method. The valves are modeled using empirical cor relations. The resulting equations are solved using a commerci ally available differential algebraic equation solv er. The simulation results are compared against experimenta l data and the comparison indicates that the model can predict system transient behavior during startup reasonably well. Using this validated model, the impact of th e upper-stage EEV opening is investigated.

  • Simulation and Validation of a Two-Stage Flash Tank Cycle using R410A as a Refrigerant
    2011
    Co-Authors: Jonathan Winkler, Vikrant Aute, Xudong Wang, Reinhard Radermacher
    Abstract:

    Investigating alternative system configurations is a means to improving vapor compression system COP by increasing system capacity and reducing compressor power consumption. The characterization and optimization of alternative system configurations can be conducted through the use of simulation. This paper presents a vapor compression system simulation tool capable of modeling a two-stage Flash Tank cycle. The key component model in the simulation of a two-stage Flash Tank cycle is the compressor. The component-based nature of the simulation tool allows for the use of any type of two-stage compressor model, including a vapor-injection compressor. The simulation assumptions and approach are presented in this paper. The experimental validation for both the baseline cycle and Flash Tank cycle are presented for an R410A system operating in both heating and cooling modes. A total of 52 test points were included in the validation for the two operating modes. The calculated capacity for 48 of the 52 test points was predicted to within 5% of experimental values.

Yunho Hwang - One of the best experts on this subject based on the ideXlab platform.

  • life cycle climate performance evaluation lccp on cooling and heating systems in south korea
    Applied Thermal Engineering, 2017
    Co-Authors: Seyoung Choi, Jinwoo Oh, Yunho Hwang
    Abstract:

    Abstract In this study, a life cycle climate performance (LCCP) of cooling and heating systems is developed and evaluated for South Korean weather conditions. While a heat pump is widely used for both space cooling and heating in United States, the heat pump is only used for space cooling and a gas boiler is used instead for space heating in South Korea. Therefore, LCCP evaluation method is extended with the gas boiler. The evaluation results show that the use of the heat pump for space heating can reduce CO2 emissions by 11–17%. Moreover, various low global warming potential (GWP) refrigerants, cycle options and weather conditions are applied and evaluated. Low GWP refrigerants reduce the direct emissions by decreasing the charging amount compared to R410A. In case of using R290, total CO2 emissions are reduced by 19–22%. The vapor injection cycle with a Flash Tank with R410A improves energy efficiency and it reduces CO2 emissions by 7–10%. Applying the VI cycle with R32 or R290, the total emissions are reduced by 27–35%.

  • Transient and steady-state experimental investigation of Flash Tank vapor injection heat pump cycle control strategy
    International Journal of Refrigeration-revue Internationale Du Froid, 2011
    Co-Authors: Xing Xu, Yunho Hwang, Reinhard Radermacher
    Abstract:

    Abstract Recent research on vapor injection technique has been mostly focused on performance improvement using different system configurations. The Flash Tank cycle typically shows better performance than the internal heat exchanger cycle. However, the Flash Tank cycle control strategy is not yet clearly defined. In this study, a novel cycle control strategy is proposed for an R-410A vapor injection Flash Tank heat pump system and its feasibility was experimentally investigated. The proposed novel cycle control strategy utilized an electronic expansion valve (EEV) for the upper-stage expansion and a thermostatic expansion valve for the lower-stage expansion, and applied an electric heater in the vapor injection line to introduce superheat to the injected vapor by providing a control signal to the upper-stage EEV. Both transient and steady-state system behaviors were studied. The proposed cycle control strategy was found to be able to provide reliable control to the system.

  • two stage heat pump system with vapor injected scroll compressor using r410a as a refrigerant
    International Journal of Refrigeration-revue Internationale Du Froid, 2009
    Co-Authors: Xudong Wang, Yunho Hwang, Reinhard Radermacher
    Abstract:

    Abstract Refrigerant vapor-injection technique has been well justified to improve the performance of systems in refrigeration applications. However, it has not received much attention for air conditioning applications, particularly for air conditioning in hot climates and for heat pumping in cold climates. In this study, the performance of an 11 kW R410A heat pump system with a two-stage vapor-injected scroll compressor was experimentally investigated. The vapor-injected scroll compressor was tested with the cycle options of both Flash Tank and internal heat exchanger configurations. A cooling capacity gain of around 14% with 4% COP improvement at the ambient temperature of 46.1 °C and about 30% heating capacity improvement with 20% COP gain at the ambient temperature of −17.8 °C were found for the vapor-injected R410A heat pump system as compared to the conventional system which has the same compressor displacement volume.

Radermache Reinhard - One of the best experts on this subject based on the ideXlab platform.

  • Simulink Based Transient Modeling of a Flash Tank vapor Injection System and Experimental Validation
    Purdue University, 2016
    Co-Authors: Hano Vire, Ling Jiazhe, Aute Vikra, Radermache Reinhard
    Abstract:

    Dynamic simulations of vapor compression system are an important field of research since they allow investigation into the behavior of a system under time-varying conditions, which is essential for development of an effective control strategy for the system. It is particularly important for advanced cycles such as a Flash Tank vapor injection (FTVI) cycle since additional control parameters, such as injection vapor temperature or Flash Tank liquid level, are involved in such systems. In this study, a mathematical model for an R410A-based FTVI cycle is developed in Simulink. The model is based on an actual system that consists of two sets of heat exchangers, a high-side EEV, a low-side TXV, a Flash Tank and a scroll compressor with a vapor injection port The injection port can be turned off or on. The model has been used to simulate the operation of the system at ASHRAE High Temperature Cyclic test conditions with both the injection port on and off. The simulation results with the injection port open are compared to with measured data, The test methodology involved a startup cycle lasting for 1000 seconds, followed by several step changes in the EEV opening area lasting for 1500 seconds, and concluding with a shutdown of the system. The suction, injection and discharge pressures and temperatures have been compared, along with the indoor unit capacity and compressor power consumption. The TXV opening and Flash Tank liquid level have also been recorded. The results compare well with the experimental results, as well as with the simulation results from models developed on the Modelica platform. The model shows good potential for application to simulation of advanced cycles

  • Performance Analysis of a Vapor Injection Cycle with Flash Tank Using a Low-GWP Inorganic Blend Refrigerant
    Purdue University, 2016
    Co-Authors: Dangelo, Jose Vicente Hallak, Ling Jiazhe, Aute Vikra, Hugo Valenca De ,araujo, Radermache Reinhard
    Abstract:

    Large scale refrigeration systems are used in many chemical processes to provide cold utilities which are essential in different stages of these processes. These refrigeration systems are great energy consumers and the costs of the compression and condensation processes have a significant impact on the cost of the final products. Therefore, it is very important that these refrigeration cycles operate in an optimized way, in order to reduce production costs. This work presents a study that combines an alternative cycle with a mixture refrigerant of low GWP, presenting a parametric analysis of some operating variables in a vapor injection refrigeration cycle with a Flash Tank (FTVI) using mixture refrigerant NH3/CO2, analyzing the influence of refrigerant mixture composition over the thermodynamic performance of this cycle, evaluating COP and also the refrigerant mass flow rate necessary to provide a cooling rate of 1 kW at the evaporator of the cycle. In this parametric analysis, the following operating variables were analyzed as a function of mixed refrigerant composition (wt%) and expansion ratio in the upper-stage valve: COP; compressor power; refrigerant mass flow rate; refrigerant temperature glide; mass flow ratio between vapor and feed streams in the Flash Tank; mass composition of liquid and vapor outlet streams from the Flash Tank and compression ratio. A basic vapor compression (VC) cycle was analyzed as well, by means of comparison. A mixture refrigerant NH3/CO2 gives a maximum COP at 30 wt% of NH3. Considering the expansion ratio in the upper-stage valve, it was verified that in the range of maximum COP the expansion ratio of 50% presents a slightly better COP. FTVI cycles present COPs that are 10 to 45% greater than the ones of the VC cycle, depending on the composition of mixture refrigerant and expansion ratio used.

  • Steady State Modeling of Advanced Vapor Compression Systems
    Purdue University, 2016
    Co-Authors: Esh Mohamed, Aute Vikra, Radermache Reinhard
    Abstract:

    The use of heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems is always increasing. This is because the HVACR systems are necessary for food production and ability to inhabit buildings that otherwise would be inhabitable. Thus, there is continued research focused on improving the efficiency and reducing the negative environmental impact of these systems. The basic vapor compression cycle (i.e., evaporator, condenser, expansion device and compressor), which is still the main underlying HVAC&R technology worldwide, has already reached its limits and researchers are investigating more creative and complex cycles to improve capacity and efficiency. This motivates the development of an enhanced general vapor compression system steady state solver. Steady state simulations require less time than transient simulations, and are used in system design optimization and cost minimization for given performance. This paper presents a comprehensive vapor compression system steady state solver which has several novel features compared to the existing solvers. Firstly, this proposed solver is capable of simulating large number of different designs of vapor compression systems. This includes arbitrary system configurations, multiple air and refrigerant paths, and user defined refrigerants. The solver uses a component-based solution scheme in which the component models are treated as black box objects. This allows a system engineer to quickly assemble and simulate a system where in the component models and performance data comes from disparate sources. This allows different vapor compression systems design engineers, and manufacturers to use the solver without the need to expose any possible confidential component data. The solver is validated using a vapor injection heat pump system with a Flash Tank and the preliminary modeling results match the experimental results within 10% accuracy. This heat pump system model is also tuned in order to improve the validation accuracy. A parametric case study for a variable refrigerant flow (VRF) system is presented as well to demonstrate the applicability to larger systems

  • A New Dynamic Heat Exchanger Model with Frosting and Defrosting
    Purdue University, 2014
    Co-Authors: Qiao Hongtao, Aute Vikra, Radermache Reinhard
    Abstract:

    In this paper, a dynamic heat exchanger model that unifies the frosting and defrosting analyses is presented. A novel scheme is proposed to solve the air flow redistribution due to non-uniform frost blockage. Unlike the existing defrost models which separate analysis for tubes and fins, the proposed defrost model unifies the analysis to maintain model consistency. The first-principles based frost and defrost models developed in this research allow for a more realistic assessment of the heat pump systems and greatly facilitate the design of controls. Utilizing the developed models, the transient behavior of a Flash Tank vapor injection heat pump under frosting and defrosting conditions is investigated and validated against experimental data

  • An Improved Moving Boundary Heat Exchanger Model with Pressure Drop
    Purdue University, 2014
    Co-Authors: Qiao Hongtao, Aute Vikra, Radermache Reinhard
    Abstract:

    A literature review indicates that almost all moving boundary heat exchanger models used in dynamic simulations of heat pumps rely on the common hypothesis that the refrigerant pressure drop is negligible. In fact, it is important to include the momentum balance in some applications, such as electronics cooling where microchannels are commonly used and significant pressure drop is observed and large-scale heat exchangers in solar thermal plants where tube length can be longer than several hundred meters. In addition, a comprehensive and robust switching approach is needed to handle transitions between different model states due to phase change. It is found that the current switching methods in the literature exhibit several shortcomings which may cause serious errors and stability issues when simulating cycling transients of vapor compression systems. The objective of this paper is to propose an improved moving boundary formulation that aims to fill in the above research gaps. Specifically, two different approaches are presented to account for the refrigerant pressure drop across the heat exchanger. A novel and comprehensive switching scheme is introduced to ensure smooth transition between different model representations under large disturbances. The proposed model is validated using measured data. The validation shows that the proposed heat exchanger model along with other supporting component models can reasonably capture the start-up transients of a Flash Tank vapor injection heat pump system