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Author: Ahmed Ali Okasha
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 162
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Book Description
The US EPA listed R134a as unacceptable refrigerant for newly light-duty vehicles manufactured or sold in the United States as of model year 2021. Carbon dioxide CO2 (R744) has been revived as a natural environmentally friendly refrigerant and is considered a strong alternative to R134a as it has a global warming potential (GWP) of 1 compared to 1300 for R134a. In an air-conditioning system and due to the different thermodynamic properties of CO2, the heat rejection process at the high-pressure side will take place above the critical point for high ambient/sink temperatures. Therefore, for a given ambient temperature, the GC pressure (high-side pressure) can be optimized and controlled independently. Either through simulations or experiments, researchers have been focusing on developing control correlations for the GC pressure to maximize the COP using offline control correlations or online methods. Maximizing COP does not mean that the system is working at its highest cooling/heating capacity that might be desired for example in a transient start-up operation to cool down or heat up the car cabin in the shortest possible time. In addition, offline control correlations suffer deviation from the true optimum as they rely on the system model. Online methods, on the other hand, can be more accurate but often lack the fast convergence to the optimum solution. The aim of this thesis was to develop a new strategy to optimize and control the CO2 transcritical air conditioning system for not only optimum COP, but also optimum cooling/heating capacity or a tradeoff solution based on the system state i.e. transient, steady state, or capacity demand. To find the Pareto Front or the best non-dominated solutions between the COP and the cooling capacity for any set of operating conditions, the existing Non-Dominated Sorting Genetic Algorithm II (NSGA-II) is used, and the results are generated based on a transcritical CO2 thermodynamic model. The best solutions of both objectives COP and cooling capacity are presented by a Pareto Front for a given operating conditions. Each solution of the Pareto Front has a unique GC pressure and superheat. An optimization parameter k that ranges from 0 to 1 is introduced to easily select maximum COP, maximum cooling capacity, or any of trade-off solutions. Based on the system operating conditions, the high-level optimizer signals the system actuators, the GC pressure, and superheat reference values. The proposed optimization and control approach can be employed as a hybrid offline and online strategy. Based on the current operating conditions, the high-level optimizer will provide an initial estimate of the optimum solution to the online optimizer, which will start searching for the true optimum online from this close initial guess. An optional online optimizer can be integrated in the loop e.g. before the controller, resulting in conjunction with the offline optimizer in a hybrid solution. Such hybrid solution can reduce the time to approach the desired operating point compared to online only methods. Compared to offline only methods, this can additionally enhance COP and Qc based on the actual system characteristics, while it is also able to adapt to changing system characteristics. While the results in this thesis are presented in terms of the cooling capacity, the same findings can be applied for the heating capacity. For further experimental investigations of the transcritical cycle, a modular transcritical CO2 heat pump system and its coolant system have been constructed at the MSU Turbomachinery Lab that support cooling, heating, and dehumidification modes. Several parameters' effects on the system performance have been analyzed and the experimental results are reported.
Author: Ahmed Ali Okasha
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 162
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Book Description
The US EPA listed R134a as unacceptable refrigerant for newly light-duty vehicles manufactured or sold in the United States as of model year 2021. Carbon dioxide CO2 (R744) has been revived as a natural environmentally friendly refrigerant and is considered a strong alternative to R134a as it has a global warming potential (GWP) of 1 compared to 1300 for R134a. In an air-conditioning system and due to the different thermodynamic properties of CO2, the heat rejection process at the high-pressure side will take place above the critical point for high ambient/sink temperatures. Therefore, for a given ambient temperature, the GC pressure (high-side pressure) can be optimized and controlled independently. Either through simulations or experiments, researchers have been focusing on developing control correlations for the GC pressure to maximize the COP using offline control correlations or online methods. Maximizing COP does not mean that the system is working at its highest cooling/heating capacity that might be desired for example in a transient start-up operation to cool down or heat up the car cabin in the shortest possible time. In addition, offline control correlations suffer deviation from the true optimum as they rely on the system model. Online methods, on the other hand, can be more accurate but often lack the fast convergence to the optimum solution. The aim of this thesis was to develop a new strategy to optimize and control the CO2 transcritical air conditioning system for not only optimum COP, but also optimum cooling/heating capacity or a tradeoff solution based on the system state i.e. transient, steady state, or capacity demand. To find the Pareto Front or the best non-dominated solutions between the COP and the cooling capacity for any set of operating conditions, the existing Non-Dominated Sorting Genetic Algorithm II (NSGA-II) is used, and the results are generated based on a transcritical CO2 thermodynamic model. The best solutions of both objectives COP and cooling capacity are presented by a Pareto Front for a given operating conditions. Each solution of the Pareto Front has a unique GC pressure and superheat. An optimization parameter k that ranges from 0 to 1 is introduced to easily select maximum COP, maximum cooling capacity, or any of trade-off solutions. Based on the system operating conditions, the high-level optimizer signals the system actuators, the GC pressure, and superheat reference values. The proposed optimization and control approach can be employed as a hybrid offline and online strategy. Based on the current operating conditions, the high-level optimizer will provide an initial estimate of the optimum solution to the online optimizer, which will start searching for the true optimum online from this close initial guess. An optional online optimizer can be integrated in the loop e.g. before the controller, resulting in conjunction with the offline optimizer in a hybrid solution. Such hybrid solution can reduce the time to approach the desired operating point compared to online only methods. Compared to offline only methods, this can additionally enhance COP and Qc based on the actual system characteristics, while it is also able to adapt to changing system characteristics. While the results in this thesis are presented in terms of the cooling capacity, the same findings can be applied for the heating capacity. For further experimental investigations of the transcritical cycle, a modular transcritical CO2 heat pump system and its coolant system have been constructed at the MSU Turbomachinery Lab that support cooling, heating, and dehumidification modes. Several parameters' effects on the system performance have been analyzed and the experimental results are reported.
Author: Xin-rong Zhang
Publisher: John Wiley & Sons
ISBN: 1118380061
Category : Science
Languages : en
Pages : 320
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Book Description
A timely and comprehensive introduction to CO2 heat pump theory and usage A comprehensive introduction of CO2 application in heat pump, authored by leading scientists in the field CO2 is a hot topic due to concerns over global warming and the 'greenhouse effect'. Its disposal and application has attracted considerable research and governmental interest Explores the basic theories, devices, systems and cycles and real application designs for varying applications, ensuring comprehensive coverage of a current topic CO2 heat transfer has everyday applications including water heaters, air-conditioning systems, residential and commercial heating systems, and cooling systems
Author: Xin-Rong Zhang
Publisher: Springer Nature
ISBN: 3031225120
Category : Technology & Engineering
Languages : en
Pages : 355
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Book Description
This book covers the fundamentals and applications of carbon dioxide vapor compression refrigeration thermodynamic cycles. In particular, it presents new application areas, such as making ice and snow in the Winter Olympic Games, food cooling and refrigeration. The book explores the physical and chemical characteristics of CO2 fluid, and the unique traits of its thermodynamic cycle. The contributors explain how CO2 refrigeration is a developing, eco-friendly technology, and emphasize its importance for refrigeration and air-conditioning in the current and future market. This book is a valuable source of information for researchers, engineers and policy makers looking to expand their applicable knowledge of high-potential refrigeration technology using carbon dioxide. It is also of interest to postgraduate students and practitioners looking for an academic insight into the industry’s latest eco-friendly technologies.
Author: Xin-rong Zhang
Publisher: John Wiley & Sons
ISBN: 111838007X
Category : Science
Languages : en
Pages : 320
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Book Description
A timely and comprehensive introduction to CO2 heat pump theory and usage A comprehensive introduction of CO2 application in heat pump, authored by leading scientists in the field CO2 is a hot topic due to concerns over global warming and the 'greenhouse effect'. Its disposal and application has attracted considerable research and governmental interest Explores the basic theories, devices, systems and cycles and real application designs for varying applications, ensuring comprehensive coverage of a current topic CO2 heat transfer has everyday applications including water heaters, air-conditioning systems, residential and commercial heating systems, and cooling systems
Author: Ye Yao
Publisher: Springer
ISBN: 3662533138
Category : Technology & Engineering
Languages : en
Pages : 496
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Book Description
This book investigates the latest modeling and control technologies in the context of air-conditioning systems. Firstly, it introduces the state-space method for developing dynamic models of all components in a central air-conditioning system. The models are primarily nonlinear and based on the fundamental principle of energy and mass conservation, and are transformed into state-space form through linearization. The book goes on to describe and discuss the state-space models with the help of graph theory and the structure-matrix theory. Subsequently, virtual sensor calibration and virtual sensing methods (which are very useful for real system control) are illustrated together with a case study. Model-based predictive control and state-space feedback control are applied to air-conditioning systems to yield better local control, while the air-side synergic control scheme and a global optimization strategy based on the decomposition-coordination method are developed so as to achieve energy conservation in the central air-conditioning system. Lastly, control strategies for VAV systems including total air volume control and trim & response static pressure control are investigated in practice.
Author: Umberto Desideri
Publisher: Firenze University Press
ISBN: 8866553220
Category : Energy conservation
Languages : en
Pages : 3218
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Book Description
The 8-volume set contains the Proceedings of the 25th ECOS 2012 International Conference, Perugia, Italy, June 26th to June 29th, 2012. ECOS is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), summarizing the topics covered in ECOS: Thermodynamics, Heat and Mass Transfer, Exergy and Second Law Analysis, Process Integration and Heat Exchanger Networks, Fluid Dynamics and Power Plant Components, Fuel Cells, Simulation of Energy Conversion Systems, Renewable Energies, Thermo-Economic Analysis and Optimisation, Combustion, Chemical Reactors, Carbon Capture and Sequestration, Building/Urban/Complex Energy Systems, Water Desalination and Use of Water Resources, Energy Systems- Environmental and Sustainability Issues, System Operation/ Control/Diagnosis and Prognosis, Industrial Ecology.
Author: Robert Smith Burrus
Publisher:
ISBN:
Category :
Languages : en
Pages : 242
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Book Description
Author:
Publisher:
ISBN:
Category : Refrigeration and refrigerating machinery
Languages : en
Pages : 106
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Book Description
Author: Jun Mei
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The dynamic mathematical models for direct expansion air conditioning (DX A/C) systems with respect to indoor carbon dioxide (CO2) concentration, relative humidity and air temperature and the coupling effects among them have been built in this thesis. To reduce the energy cost and improve the energy efficiency for DX A/C systems while maintaining both indoor air quality (IAQ) and thermal comfort at acceptable levels, a hierarchical control structure is proposed in this thesis. This control structure includes two levels. The upper level is an open loop optimal controller to generate the optimal setpoints of indoor CO2 concentration, relative humidity and air temperature for the lower level controller. The lower level designs a closed-loop model predictive control (MPC) controller to optimize the transient processes reaching the setpoints where the energy efficiency improvement and energy cost savings are achieved. In Chapter 2, the control objective is to improve both IAQ and thermal comfort as well as energy efficiency for a DX A/C system. The details of a hierarchical control structure in this chapter are as follows: In the upper layer, an energy-optimised open loop controller is proposed based on an optimization of energy consumption of the DX A/C system and given reference points of indoor CO2 concentration, relative humidity and air temperature to generate a unique and optimised steady state for the lower layer controller. In the lower layer, the closed-loop MPC controller is proposed such that the indoor CO2 concentration, relative humidity and air temperature follow the steady state computed by the upper layer, whereas the energy efficiency is improved. To facilitate the MPC design, the nonlinear DX A/C control system is linearized around the optimised steady state. In Chapter 3, the control objective is to lower the energy cost and consumption of a DX A/C system while maintaining both IAQ and thermal comfort at comfort levels. To achieve this purpose, an autonomous hierarchical control (AHC) structure is designed and described below. The upper level is an open loop nonlinear optimal controller, which optimizes the predicted mean vote (PMV) index and the energy cost for the DX A/C system under a time-of-use (TOU) price structure of electricity according to the changing environment over a 24-hour period, to generate the tradeoff setpoints of indoor CO2 concentration, relative humidity and air temperature for the lower level controller. The lower layer is formed as a closed-loop MPC to track the trajectory reference points calculated by the optimization layer. This AHC strategy means the upper controller can adaptively and automatically set the setpoints and the lower layer adaptively and optimally tracks them, minimizing energy consumption and costs. In addition, in this chapter, the volumes of outside air allowed to enter the DX A/C system are regarded as varying with the changing circumstance over a day and are optimized by the AHC. Moreover, a supply fan to steer the pressure swing absorption with a built-in proportional-integral (PI) controller is proposed to lower the indoor CO2 concentration such that it would reduce the complexity of computation for the AHC and the cost of hardware. In Chapter 4, the control objective is to reduce energy cost, improve energy efficiency, and reduce communication resources, computational complexity and conservativeness, as well as peak demand for a multi-zone building multi-evaporator air conditioning (ME A/C) system while maintaining multi-zonesaÌ22́Ơ4́Ø thermal comfort and IAQ at comfort levels. To realize this objective and to consider the interaction effects between rooms, we present an autonomous hierarchical distributed control (AHDC) method. The upper level is an open loop nonlinear optimizer, which only collects measurement information and solves a distributed steady state optimization problem to adaptively and automatically generate time-varying and optimised reference points of indoor CO2 concentration, relative humidity and air temperature for the lower-layer controllers, by minimizing the demand and energy costs of a multi-zone building ME A/C system under the TOU price structure of electricity according to the changing circumstance during the day. The lower level also uses local information to track the trajectory references calculated by the upper-layer distributed controller, via distributed MPC controllers. The proposed hierarchical control strategy is distributed in two layers since they use only local information from the working zone and its neighbours. To validate the performance of these hierarchical control strategies for DX A/C systems, simulation tests are performed in this thesis. In Chapter 2, simulations are provided to show that the closed-loop regulation of the MPC controller and the energy-optimised open loop controller can maintain indoor CO2 concentration, relative humidity and air temperature at their desired setpoints with small deviations and reduce the effect of indoor cooling and pollutant loads. The simulations also demonstrate that the controllers are superior to conventional controllers in terms of energy efficiency. In Chapter 3, the simulation tests show that the AHC strategy can reduce more energy consumption and cost than the baseline strategy. In addition, the tests demonstrate that the AHC scheme is not sensitive to the physical parameters of the DX A/C system. In Chapter 4, to show the performance of the two-layer distributed control strategies, a case study is given. The simulation tests demonstrate that the AHDC strategy is capable of shifting demand from peak hours to off-peak hours and reducing the energy cost for a multi-zone building ME A/C system while maintaining multi-zonesaÌ22́Ơ4́Ø IAQ and thermal comfort at comfort levels.
Author: David Zietlow
Publisher: Momentum Press
ISBN: 1606504754
Category : Technology & Engineering
Languages : en
Pages : 216
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Book Description
Most energy systems are suboptimized. Businesses and consumers are so focused on initial costs that they underestimate the effect of operating the energy system over its life. This suboptimization creates a fantastic opportunity to not only make a wise decision financially but also reduce the environmental impact of energy systems. There are three simple tools, known to all mechanical engineers, that when added to traditional thermodynamics, enable an engineer to find the true optimum of an energy system. In this concise book, you will be equipped with these tools and will understand how they are applied to cooling systems. The target audiences for this book are mechanical engineering students in their first semester of thermodynamics through engineers with 20+ years of experience in the design of cooling systems. First semester thermodynamic students will benefit the most from Appendixes A and C in Chapter 1. The rest of Chapter 1 is written at a level where any undergraduate mechanical engineering student who is taking heat transfer will be able to quickly assimilate the knowledge. This book also has the depth to handle the latent load, which will provide the practicing engineer with the tools necessary to handle the complexity of real cooling systems.
