Energy saving potential of chiller system with fuzzy logic control

In this study, control algorithm, based on fuzzy logic, for compressor speed and opening percentage of electronic expansion valve (EEV), was investigated. The main aim of this study is to increase efficiency of the chiller system, having variable speed scroll compressor (VSSC) and EEV. Current chiller system has an air cooled condenser, a shell‐tube liquid evaporator, and a vertical scroll compressor. Flow of the refrigerant R134a was controlled by EEV in the system. Chiller systems are designed for working at maximum load conditions; on the contrary, these plants work under partial load conditions most of their life cycle by means of thermostatic control. Refrigeration capacity modulation methods, such as variable speed compressors, allow to match continuously the compressor refrigeration capacity to the load, determining an energy saving according to classical thermostatic control. In this study, compressor speed was controlled with fuzzy logic algorithm according to chiller water output temperature and EEV opening percentage was controlled with fuzzy logic algorithm according to refrigerant superheat value at outlet of the evaporator. Compressor speed has been changed between 30 and 60 Hz and EEV opening percentage has been changed between 10 and 45% of the maximum opening percentage. In fact, the chiller plant was operated as on/off at 50 Hz fixed speed by a thermostat. During the study, it has been operated as variable speed by adding PWM inverter. In the present study, fuzzy logic controlled variable speed chiller system exhibited 17% coefficient of performance increase according to the thermostatic controlled fixed speed system. Also, better water temperature control was obtained via fuzzy controlled VSSC. Copyright © 2009 John Wiley & Sons, Ltd.     

An experimental evaluation of the vapour compression plant performances in presence of R407C leaks using an electronic expansion valve

Chlorofluorocarbons and hydrofluorocarbons (HFCs) used as working fluids in the vapour compression plants, have to be replaced by new substances because of their ozone depletion potential. Zeotropic mixture of HFCs refrigerants that are environment-friendly substances are often employed. The zeotropic mixtures with a large glide temperature could cause problems in the refrigeration control system when a leak occurs because their composition modifies. This paper presents a comparison of the energetic performances, in presence of leaks, when a thermostatic valve and an electronic expansion valve are used in a refrigeration plant, working with the zeotropic mixture designated as R407C (R32/R125/R134a 23/25/52% in mass)—this is the most suitable substitute of the HCFC22. The vapour leaks are simulated at the inlet of the evaporator and at the liquid receiver. Experimental results show that a good adaptability to mixture leaks is related to the electronic expansion valve, while better energetic performances are obtained using the thermostatic expansion valve as long as it is usable.     

Experimental evaluation of electronic and thermostatic expansion valves performances using R22 and R407C

An experimental study to evaluate the energetic performances in steady-state and in transient operating modes of an electronic and thermostatic expansion valve is presented. Both valves have been assembled to feed an air cooled evaporator connected to an experimental vapour compression plant with a water cooled condenser operating with a semihermetic compressor. The performances of the valves have been examined at different conditions when the experimental plant works with R22 and with a substitute as the non-azeotropic blend R407C that is chlorine free. Indeed the HCFC designated as R22 contains chlorine that is harmful for the ozone layer and must be replaced in the future. The final results of this study show an overall better performance of the electronic expansion valve compared with the thermostatic expansion valve under transient conditions while in steady-state conditions both the valves are equal in performance. These results apply to both R22 and R407C.     

Comparison of expansion valve performance

This paper compares the performance of a thermostatic expansion valve, thermoelectric expanison valve, solenoid expansion valve and a motorized type operating as part of an extensively controlled and instrumented refrigeration system. It will be shown that the solenoid expansion valve provides the best contol.     

The control of a refrigeration system using a compact plate heat exchanger as an evaporator

This paper will show some of the problems that may be encountered when using a compact plate exchanger as an evaporator in a refrigeration system which utilizes a thermostatic expansion valve as its controlling device.     

The choice of a thermostatic expansion valve for a CFC12 refrigeration system retrofitted with HFC134a

There is a need to develop a suitably charged thermostatic expansion valve to work with systems charged with HFC134a. The conventional CFC12 cross-charged valve does work, but with a slight loss of superheat sensitivity. A pure HFC134a charged valve lacks a constant superheat over a range of evaporator temperatures, and may require a smaller orifice size than the conventional cross-charged valve.     

Transient modeling of an air-cooled chiller with economized compressor. Part II: Application to control design

Based on the transient modeling developed in the previous paper, the control design of the air-cooled chiller is studied. The main electronic expansion valve (EXV) controls the suction superheat, the compressor controls the leaving water temperature and the sub EXV regulates the injection superheat. Since the system reliability is sensitive to the control of the suction superheat, it is the focus in this paper. Dynamic simulation cases are built to compare two control algorithms, PID and fuzzy logic. The case studies show that the fuzzy controller has higher reliability and performance. Both the two controllers are fully tested and tuned on a chiller test facility and the experiments indicate that the fuzzy controller works better as well.     

Comparison among various energy management strategies for reducing hydrogen consumption in a hybrid fuel cell/supercapacitor/battery system

The aim of this study is to introduce a comprehensive comparison of various energy management strategies of fuel cell/supercapacitor/battery storage systems. These strategies are utilized to manage the energy demand response of hybrid systems, in an optimal way, under highly fluctuating load condition. Two novel strategies based on salp swarm algorithm (SSA) and mine-blast optimization are proposed. The outcomes of these strategies are compared with commonly used strategies like fuzzy logic control, classical proportional integral control, the state machine, equivalent fuel consumption minimization, maximization, external energy maximization, and equivalent consumption minimization. Hydrogen fuel economy and overall efficiency are used for the comparison of these different strategies. Results demonstrate that the proposed SSA management strategy performed best compared with all other used strategies in terms of hydrogen fuel economy and overall efficiency. The minimum consumed hydrogen and maximum efficiency are found 19.4 gm and 85.61%, respectively.     

Particle swarm optimization applied to the co-design of a fuel cell air circuit

This paper presents an optimization approach applied to a whole fuel cell (FC) air supply system including its geometry and its control. The aim is to optimize its power consumption along with its mass. Particle swarm optimization (PSO) algorithm is used to define the design parameters of both permanent magnet synchronous motor (PMSM) and a fuzzy logic controller (FLC). The results are compared with those obtained by a sequential optimization process and advantages of co-design optimization approach are clearly shown. Indeed, a significant reduction of the objective function (made up on both motor mass and energy consumption) on a considered operating cycle can be obtained.     

Power quality improvement using fuzzy logic controller for five-level shunt active power filter under distorted voltage conditions

In this paper, a five-level inverter is used as a shunt active power filter (APF), taking advantages of the multilevel inverter such as low harmonic distortion and reduced switching losses. It is used to compensate reactive power and eliminate harmonics drawn from a thyristor rectifier feeding an inductive load (RL) under distorted voltage conditions. The APF control strategy is based on the use of self-tuning filters (STF) for reference current generation and a fuzzy logic current controller. The use of STF instead of classical extraction filters allows extracting directly the voltage and current fundamental components in the α-β axis without phase locked loop (PLL). The MATLAB fuzzy logic toolbox is used for implementing the fuzzy logic control algorithm. The obtained results show that the proposed shunt APF controller has produced a sinusoidal supply current with low harmonic distortion and in phase with the line voltage.     

Optimal control and performance test of solar-assisted cooling system

The solar-assisted cooling system (SACH) was developed in the present study. The ejector cooling system (ECS) is driven by solar heat and connected in parallel with an inverter-type air conditioner (A/C). The cooling load can be supplied by the ECS when solar energy is available and the input power of the A/C can be reduced. In variable weather, the ECS will probably operate at off-design condition of ejector and the cooling capability of the ECS can be lost completely. In order to make the ejector operate at critical or non-critical double-choking condition to obtain a better performance, an electronic expansion valve was installed in the suction line of the ejector to regulate the opening of the expansion valve to control the evaporator temperature. This will make the SACH always produce cooling effect even at lower solar radiation periods while the ejector performs at off-design conditions. The energy saving of A/C is experimentally shown 50–70% due to the cooling performance of ECS. The long-term performance test results show that the daily energy saving is around 30–70% as compared to the energy consumption of A/C alone (without solar-driven ECS). The total energy saving of A/C is 52% over the entire test period.     

Fuzzy controlled central heating system

In this paper a comparison study was carried out in order to understand how two different systems, classical and fuzzy logic control of central heating affect the economy and comfort of private homes or offices. Also a literature review was done to help decide which one of these systems is more effective. The objective of the fuzzy controller heating system is to estimate the actual heat requirement of the house. It uses a total of five inputs, four of which are derived from energy consumption curve, using conventional digital filtering techniques; the fifth is the average outdoor temperature, whereas, the classical control system burns diesel type fuel in its furnace to heat the water supply (boiler). From the boiler, the hot water is distributed by a pipe system to the individual radiators in the house. Thereby, it is shown that the fuzzy controlled heating system is more effective, also it maximizes the economy and the comfort of the consumer. Copyright © 2002 John Wiley & Sons, Ltd.     

严寒地区住宅建筑热计量的节能潜力分析

本文以大庆市热计量试点项目中三栋建筑作为研究对象,测试了供热期间三栋试验建筑的耗热量,比较了传统建筑和安装温控阀建筑的节能潜力。安装温控阀的建筑单位采暖耗热量为21．8W／m^2,未安装温控阀的建筑采暖单位采暖耗热量为25．5W／m^2,节能潜力为13．3％;未安装温控阀的地板辐射采暖系统建筑单位采暖耗热量为31．2W／m^2,节能潜力达到32．8％。比较发现,只有安装温控阀的建筑单位采暖耗热量没有超过国家标准限值,其它两栋建筑单位采暖耗热量超标率分别为24．5％和41．8％。同时发现,地板辐射采暖系统建筑能源浪费严重,说明了实行供热计量的重要性和必要性。     

A numerical comparison of different methods for optimizing heating-restart time in intermittently occupied buildings

The article starts with a brief recap of the restart time optimization methods: the classical methods, the methods based on fuzzy logic and the methods based on the use of a building model. In order to compare these different approaches, an intermittent heating controller, which makes it possible to define different methods for optimizing heating-restart time, has been developed as part of the TRNSYS software. Two of the six methods under study are new. These are the method based on fuzzy logic and the method using a two time constant building model. The numerical simulations carried out concern a building of which three rooms are studied. The changes in the various variables are presented in the case of the method based on fuzzy logic. Next, the different methods are compared according to restart precision, comfort obtained at the beginning of the occupancy period and energy consumption over the entire period of simulation.     

蒸发器电子膨胀阀过热度模糊控制仿真及分析

建立了蒸发器一电子膨胀阀过热度模糊控制仿真系统，通过仿真分析了量化因子、比例因子及不同的采样时间，对控制效果及参数设置的影响、模糊控制与PID的控制效果比较：同时将带自修正因子参数自调整模糊控制应用到对电子膨胀阀的控制当中。对蒸发器过热度电子膨胀阀模糊控制系统的设计及调试有一定的指导意义。     

Fuzzy control of a bio-hydrogen internal combustion engine generating system

This study proposes a fuzzy control bio-hydrogen internal combustion engine (ICE) generating system. The ICE technology is composed of thermodynamics, mechanical engineering, hydrodynamics, and electrical engineering. Bio-hydrogen can provide clean and efficient power instead of conventional fuels applied in an ICE. The two critical cores of hydrogen ICE generator are ignition time control which can precisely ignite air-fuel mixtures to make generator output stable power and air-fuel ratio control which can adjust output power to satisfy load demand. Fuzzy logic can provide precise control and response fast within various air-fuel ratios.The study establishes a fuzzy control system with an output generator and an ICE with solenoid valve that controls bio-hydrogen injection. The experimental system successfully output stable power and carried out parameters of bio-hydrogen flow rate, air-fuel ratio, injection pressure, and ignition timing. Parameters and experimental data are analyzed in the study and can be references for future development of the bio-hydrogen internal combustion engine generating system.     

Transcritical CO2 refrigerator and sub‐critical R134a refrigerator: A comparison of the experimental results

This paper describes experiments comparing a commercial available R134a refrigeration plant subjected to a cold store and a prototype R744 (carbon dioxide) system working as a classical ‘split‐systems’ to cool air in residential applications in a transcritical cycle. Both plants are able to develope a refrigeration power equal to 3000 W. The R744 system utilizes aluminium heat exchangers, a semi‐hermetic compressor, a back‐pressure valve and a thermostatic expansion valve. The R134a refrigeration plant operates using a semi‐hermetic reciprocating compressor, an air condenser followed by a liquid receiver, a manifold with two expansion valves, a thermostatic one and a manual one mounted in parallel, and an air cooling evaporator inside the cold store. System performances are compared for two evaporation temperatures varying the temperature of the external air running over the gas‐cooler and over the condenser. The refrigeration load in the cold store is simulated by means of some electrical resistances, whereas the air evaporator of the R744 plant is placed in a very large ambient. The results of the comparison are discussed in terms of temperature of the refrigerants at the compressor discharge line, of refrigerants mass flow rate and of coefficient of performance (COP). The performances measured in terms of COPs show a decrease with respect to the R134a plant working at the same external and internal conditions. Further improvements regarding the components of the cycle are necessary to use in a large‐scale ‘split‐systems’ working with the carbon dioxide. Copyright © 2009 John Wiley & Sons, Ltd.     

On-line fuzzy energy management for hybrid fuel cell systems

Fuel Cell Hybrid Vehicles (FCHV) can reach near zero emission by removing the conventional internal combustion from the vehicle powertrain. Nevertheless, before seeing competitive and efficient FCHV on the market, at market prices, different technical, economic, and social challenges should be overcome. A typical hybrid fuel cell powertrain combines a fuel cell stack and a dedicated energy storage system along with their necessary power converters. Energy storage systems are used in order to enhance the well-to-wheel efficiency and thus reducing the hydrogen consumption. An efficient management of power flows on the vehicle, allows optimizing the recovery of energy braking. Moreover, working in the fuel cell maximum efficiency leads to reduced thermal losses and thus to the downsizing of the heat exchangers. This paper presents an enhanced control of the power flows on a FCHV in order to reduce the hydrogen consumption, by generating and storing the electrical energy only at the most suitable moments on a given driving cycle. While the off-line optimization-based on dynamic programming algorithm offers the necessary optimal comparison reference on a known demand, the proposed strategy which can be implemented on-line, is based on a fuzzy logic decision system. The fine tuning of the fuzzy system parameters (mainly the membership functions and the gains), is made using a genetic algorithm and the fuzzy supervisor shows performing results for different load profiles.     

Dynamic simulation of air-to-water dual-mode heat pump with screw compressor

A dynamic model of air-to-water dual-mode heat pump with screw compressor is presented here. The high-pressure and low-pressure segments are divided into three control volumes, including the refrigerant inside tube, the tube wall and the fluid outside tube that is water or air. Time dependent ordinary differential equations are obtained from the mass and energy balances for each control volume. As the compressor, thermostatic expansion valve (TEV) body, and reversing valve have very small thermal inertias, steady-state models are applied for the compression, throttling, and leakage processes. The relationship between the temperature of the saturated liquid–vapor mixture in TEV’s bulb and the temperature of the refrigerant vapor at the evaporator exit is described with a time dependent ordinary differential equation. System simulation is finally carried out with ‘predictor–corrector’ and ‘adaptive integration step’ methods. Simulated results are in good agreement with the measured data, which lead to conclusion that the model can be used as a tool for the product development.     

Knowledge-based versus classical control for solar-building designs

The present paper compares classical control systems with knowledge-based systems in the control of building designs to achieved comfort conditions. Initially the goal has been the minimization of energy usage. For this target, thermostats and PID controllers have been employed. Adaptive and ad hoc first-generation controller implemented for the improvement of specific problems are described next. The achievement of thermal and visual comfort conditions within living and working space fits the application of fuzzy logic expert systems. The structure of a fuzzy control system is described. This paper also discusses the capabilities of the fuzzy logic expert system in the achievement of optimal resource management in passive-building designs.