An experimental study of a direct expansion ground‐coupled heat pump system in heating mode

In this paper, an experimental performance evaluation of a direct expansion ground‐coupled heat pump (DX‐GCHP) system in heating mode is presented. The DX‐GCHP uses R134a as the refrigerant, and consists of three single U‐tube copper ground heat exchangers (GHEs) placed in three 30 m vertical boreholes. During the on–off operations from December 25, 2007, to February 6, 2008, the heat pump supplied hot water to fan‐coil at around 50.4°C, and its heating capacity was about 6.43 kW. The energy‐based heating coefficient of performance (COP) values of the heat pump and the whole system were found to be on average 3.55 and 3.28 at an evaporating temperature of 3.14°C and a condensing temperature of 53.4°C, respectively. The second law efficiency on the DX‐GCHP unit basis was around 0.36. The exergetic COP values of the heat pump and the whole system were obtained to be 0.599 and 0.553 (the reference state temperature was set equal to the average outdoor temperature of ?1.66°C during the tests), respectively. The authors also discussed some practical points such as the heat extraction rate from the ground, refrigerant charge and two possible new configurations to simultaneously deal with maldistribution and instability of parallel GHE evaporators. This paper may reveal insights that will aid more efficient design and improvement for potential investigators, designers and operators of such DX‐GCHP systems. Copyright © 2009 John Wiley & Sons, Ltd.     

Solar adsorption refrigeration (SAR) system modeling

The solar adsorption refrigeration (SAR) system has economical and environmental aspects that motivate many researches to investigate its capability in cooling system design. In this study, multi-dimensional mathematical models have been generated to predict the coefficient of performance (COP) value of the SAR system as function of the evaporator, condenser, and generator temperatures. Fuzzy logic and regression analysis approaches were implemented to construct a mathematical model for this purpose from one-dimensional collected data that relates COP value separately to condensation, evaporation, and generation temperatures, respectively. The results of COP calculation from the two models were agreed quite well with the measured values. However, the fuzzy logic technique showed excellent accuracy than the regression model when compared to the calculated COP value, as its steps have the optimum nature in constructing the required model.     

基于全局信息融合粒子群算法的水轮发电机模型参数辨识

针对粒子群(PSO)优化算法辨识发电机模型参数时存在局部最优和后期收敛速度慢很难准确获取具有强泛化能力的模型参数的问题,提出了一种基于多粒子全局信息共享和变权重的全局信息融合PSO算法(GPSO),并通过IEEE3机9节点系统算例验证了该算法的有效性。结果表明,与常规PSO算法相比,该算法具有泛化能力强、辨识精度高和后期收敛速度快的优点。     

Study on hybrid ground-coupled heat pump system for air-conditioning in hot-weather areas like Hong Kong

The ground-coupled heat pump (GCHP) system is becoming attractive for air-conditioning in some moderate-weather regions due to its high energy efficiency and reliable operation capability. However, when the technology is used in buildings where there is only cooling load in hot-weather areas like Hong Kong, the heat rejected into the ground by the GCHP systems will accumulate around the ground heat exchangers (GHE). This heat accumulation will result in degradation of system performance and increment of system operating costs. This problem can be resolved by using the hybrid ground-coupled heat pump (HGCHP) system, which uses supplemental heat rejecters to reject the accumulated heat. This paper presents a practical hourly simulation model of the HGCHP system by modeling the heat transfer process of the system’s main components. The computer program based on this hourly simulation model can be used to calculate the hour-by-hour operation data of the HGCHP system. As a case study, both a HGCHP system and a traditional GCHP system are designed for a hypothetic private residential building located in Hong Kong, and the economic comparisons are conducted between these two types of systems. The simulation results show that the HGCHP system can effectively solve the heat accumulation problem and reduce both the initial costs and operating costs of the air-conditioning system in the building.     

On-line monitoring the performance of coal-fired power unit: A method based on support vector machine

This paper introduces a novel on-line monitoring performance method of coal-fired power unit. Support vector machine (SVM) is used to predict the unburned carbon content of fly ash in the boiler and the exhaust steam enthalpy in turbine, which are two difficulties in the real time economic performance calculation model in coal-fired power plant. Comparison between the output of SVM modeling and the experimental data shows a good agreement, and compared with conventional artificial neural network techniques, SVM can achieve better accuracy and generalization. This presented monitoring method is proven by the results of application cases in a practical coal-fired power plant.     

Finite time thermodynamics study and exergetic analysis of ammonia–water absorption systems

This paper presents an optimization study of a single stage absorption machine operating with an ammonia–water mixture under steady state conditions. The power in the evaporator, the temperatures of the external fluids entering the four external heat exchangers as well as the effectiveness of these heat exchangers and the efficiency of the pump are assumed fixed. The results include the minimum value of the total thermal conductance UA_tot as well as the corresponding mean internal temperatures, overall irreversibility and exergetic efficiency for a range of values of the coefficient of performance (COP). They show the existence of three optimum values of the COP: the first minimises UA_tot, the second minimises the overall irreversibility and the third maximises the exergetic efficiency. They also show that these three COP values are lower than the maximum COP which corresponds to the convergence of the internal and external temperatures towards a common value. The influence of various parameters on the minimum thermal conductance of the heat exchangers and on the corresponding exergy efficiency has also been evaluated. From an exergetic viewpoint it is interesting to reduce the temperature at the desorber and at the evaporator and to raise the values of that parameter at the condenser and the absorber. However these changes must be accompanied by an important increase in the total UA if it is desired to conserve a constant COP. The internal heat exchangers between the working fluid and the solution improve both the overall exergy efficiency and the coefficient of performance of the absorption apparatus.     

PCA-PSO/GS-SVM组合方法在风电齿轮箱故障预测中的应用研究

在标准支持向量机(SVM)的基础上,引入主成分分析法(PCA)、粒子群算法(PSO)以及网格算法(GS),构建针对风力机故障的PCA-PSO/GS-SVM组合预测模型。相对于标准SVM,该模型采用PSO以及GS算法寻优参数,能够更准确地建立各变量间的相关关系以提高模型的预测准确性。以中国北方某风场2 MW风电齿轮箱在2017年上半年某2个月的SCADA监测数据为例进行分析。结果表明,对于以齿轮箱输出功率为例的骤变信号的预测,采用PSO算法寻优后的绝对误差均值是采用GS算法的3.0647倍,而对于以高速侧轴端温度为例的缓变信号的预测,则采用PSO算法更加合理;同时发现剔除训练样本数据中的奇异点能够有效提高模型的预测精度及其泛化能力。     

Performance comparison of natural refrigerants based cascade systems for ultra-low-temperature applications

Theoretical analyses and optimisation are carried out with ethane, ethylene and nitrous oxide as the low-temperature (LT) fluids in a cascade system for ultra-low-temperature refrigeration applications to examine the effects of design and operating parameters. Finally, performance improvement has been investigated employing an internal heat exchanger. Optimal intermediate temperature (IT) correlations have been developed. Ethane is superior in terms of coefficient of performance (COP), whereas nitrous oxide is superior in terms of volumetric cooling capacity as an LT fluid. With increase in compressor efficiency, COP increases; however, with little influence on the optimum IT. Using an internal heat exchanger in the LT circuit, the cooling COP can be increased for ethane and ethylene; however, there is marginal decrease in COP for N ₂O. Ammonia is not suitable as a HT fluid for some operating conditions where the optimum IT is lower than the normal boiling point and propylene may be a suitable substitute with a penalty on COP.     

Analysis and assessment of a nanoparticle seeded small scale absorption refrigeration system driven by a low‐grade waste heat source

The thermoeconomic behaviour of a nanoparticle seeded single effect LiBr‐H₂O absorption refrigeration system (ARS) is investigated for a small scale application. In the proposed method, alumina nanoparticles with volume concentrations of 3%, 5%, and 7% are dispersed into an aqua lithium bromide solution. The multiobjective heat transfer search algorithm is employed to examine the design trade‐off between the coefficient of performance (COP) and total annualized cost (TAC). To analyze the overall performance of the system, the influence of five design parameters, namely the temperatures of the generator, absorber, evaporator, condenser and heat exchanger pipe diameter, are studied. It is found that with an increase in the COP, the TAC of the system is initially raised marginally, and after that, raised rigorously with further increment. The comparative results indicate that the COP and TAC of the nanofluid based ARS system are increased by about 7% and decreased by about 3.2%, respectively, corresponding to the Pareto points of the base ARS system. A lower break‐even point of about 2.6 years is achieved for the ARS system containing nanoparticles compared to the base ARS system. Overall, the ARS system containing 5% nanoparticles is the best solution from a thermodynamic and economic point of view.     

Experimental performance investigation of a horizontal ground source compression refrigeration machine

In this paper, the effect of various system parameters on horizontal ground source compression refrigeration machine (CRM) performance is studied experimentally in Bursa, Turkey. A ground heat exchanger (GHE) system connected to CRM in a test room in the air conditioning and refrigeration laboratory of Uludag University has been designed and constructed. This system was tested for space cooling in August and September 2004 and performance tests were performed during this period. Overall, system mainly consists of the GHE (GHE–water circuit) and CRM (CRM–refrigerant circuit). Refrigerant is R134a. Hourly variations of inlet and outlet water temperatures, extracted heat from test room, rejected heat to ground, compression ratio, total power consumption, and coefficient of performance (COP) values for both whole system and only CRM are obtained. Thermal properties of soil are also estimated by using experimental data and theory. Cooling load of test room and rejected heat to ground, and all COP values are also presented. Finally, heat rejection rate to ground with respect to leaving water temperature from GHE is given. The COP of the overall system changes between 2 and 2.5, also CRM COP values are in the range of 3 and 3.86. Copyright © 2007 John Wiley & Sons, Ltd.     

A novel predicting method on degree of catalytic reaction in fuel cells

An accurate assessment of the utilization of a catalyst for fuel cells is beneficial for guiding the optimization of working conditions and adjustment of parameters. In this study, a composite model containing the numerical model of catalyst layers and improved support vector machine (SVM) is proposed to predict the catalyst utilization. The effectiveness factor of the field of catalytic reaction engineering is introduced into the numerical model. The adaptive learning factor and the differential evolution strategy are introduced to improve the ability of generalization and robustness of the distinguishing method in the SVM. The results indicate that the radial basis function is well-suited as the kernel function of the SVM, and the accuracy of the prediction in the anode and cathode can be increased up to 99.31% and 99.65%, respectively. The increasing transfer coefficient leads to an enhancement of the catalytic reaction, and the particle size of the catalyst impacts the catalytic reaction mainly by changing the pattern of internal diffusion. Pressure has little impact on the Knudsen diffusion.     

Optimization and analysis of a novel hydrogen liquefaction process for circulating hydrogen refrigeration

In industrial engineering, hydrogen is usually transported and stored after being liquefied, which is an energy-intensive process. Aiming to liquefy hydrogen with high efficiency and low consumption, a novel hydrogen liquefaction process based on dual-path hydrogen refrigeration is proposed innovatively and simulated by Aspen HYSYS to determine the key parameters. Taking the specific energy consumption (SEC) as the objective function for the optimization by genetic algorithm (GA), optimum parameters could be obtained. Meanwhile, the single variable method is conducted to analyze the impact of key parameters on process characteristics. Under the premise of complete liquefaction, the SEC, coefficient of performance (COP) and exergy efficiencies (EXE) of the proposed system are 7.041 kWh/kg _LH2, 0.1834, 0.5413, respectively. Compared with the other three hydrogen liquefaction systems simulated under the same conditions, they are decreased by 22.16% and increased by 33.58% and 42.37%, respectively. The results show that the proposed system shows better performance under lower consumption.     

Increase of COP for heat transformer in water purification systems. Part I – Increasing heat source temperature

The integration of a water purification system in a heat transformer allows a fraction of heat obtained by the heat transformer to be recycled, increasing the heat source temperature. Consequently, the evaporator and generator temperatures are also increased. For any operating conditions, keeping the condenser and absorber temperatures and also the heat load to the evaporator and generator, a higher value of COP is obtained when only the evaporator and generator temperatures are increased. Simulation with proven software compares the performance of the modeling of an absorption heat transformer for water purification (AHTWP) operating with water/lithium bromide, as the working fluid–absorbent pair. Plots of enthalpy-based coefficients of performance (COP_ET) and the increase in the coefficient of performance (COP) are shown against absorber temperature for several thermodynamic operating conditions. The results showed that proposed (AHTWP) system is capable of increasing the original value of COP_ET more than 120%, by recycling part of the energy from a water purification system. The proposed system allows to increase COP values from any experimental data for water purification or any other distillation system integrated to a heat transformer, regardless of the actual COP value and any working fluid–absorbent pair.     

Comparative analysis of thermodynamic performance of CO2 cascade refrigeration system assisted with expander and mechanical subcooling

In order to discuss the feasibility of using R744/R744 cascade refrigeration system (CRS) instead of R744/R717 CRS, six configurations of R744/R744 CRS assisted with expander and mechanical subcooling system (MS) are analyzed. Based on the thermodynamic analysis, the results show that the high pressure, the condensing temperature of the low‐temperature cycle (LTC), and the degree of subcooling of LTC and the high‐temperature cycle (HTC) are three important operating parameters with an optimum value corresponding to the maximum coefficient of performance (COP). Compared with other CRSs, CRS with HTC throttling valve and MS of HTC (CTS_H) and CRS with HTC expander and MS of HTC (CES_H) show an excellent performance. CES_H has the highest COP and is improved by an average of 13.8% compared with the COP of R744/R717 CRS. The COP of CTS_H is improved by an average of 4.2% compared with the COP of R744/R717 CRS. In conclusion, it is an efficient way to improve performance that CRS combines MS in HTC and HTC expander. And it is possible R744/R744 CRS instead of R744/R717 CRS.     

Increase of COP for heat transformer in water purification systems. Part II – Without increasing heat source temperature

The integration of a water purification system allows a heat transformer to increase the actual coefficient of performance, by the reduction of the amount of heat supplied by unit of heat. A new defined COP called COP_WP is proposed for the present system, which considers the fraction of heat recycled. Simulation with proven software compares the performance of the modeling of an absorption heat transformer for water purification (AHTWP) operating with water/lithium bromide, as working fluid–absorbent pair. Plots of enthalpy-based coefficients of performance (COP_ET) and water purification coefficient of performance (COP_WP) are shown against absorber temperature for several thermodynamic operating conditions. The results showed that the proposed (AHTWP) system is capable of increasing the original value of COP_ET up to 1.6 times its original value by recycling energy from a water purification system. The proposed COP_WP allows increments for COP values from any experimental data for water purification or for any other distillation system integrated to a heat transformer, regardless of actual COP_A value or working fluid–absorbent pair.     

Exergetic analysis of an absorption/compression refrigeration unit based on R124/DMAC mixture for solar cooling

This work presents an energetic and exergetic analysis of an upgraded frigorific production unit, operating with a novel organic mixture: DMAC/R124 (N, N′-dimethylacetamide/2-chloro-1,1,1,2-tetrafluoroethane). Investigated parameters are the COP (performance coefficient), the irreversibility and the exergetic efficiency. Performances of the proposed mixture system are compared with those relative to the classical water/ammonia system. Results show that the COP obtained with the new fluids is similar to that relative to the old one, it is about 64% for a compression ratio about 2, while the same optimum value is achieved with a compression ratio about 3.3 when working with ammonia/water. Furthermore, the system using the new proposed couple uses lower threshold temperatures, between 60 °C and 80 °C as optimum COP, which allows the use of low temperature energy sources.Results of the exergetic analysis indicate that irreversibility of the R124/DMAC system is lower than that of the ammonia/water system by about 5 kW and so is the exergetic efficiency. It is noted from this study that the major gain brought by this new couple is the diminution of the operating temperatures of this type of heat pumps from temperatures going to 120 °C–80 °C and even 60 °C. We retain the advantages of introducing this organic absorbent (DMAC) in the refrigeration production field.     

Applying support vector machine to predict hourly cooling load in the building

In this paper, support vector machine (SVM) is used to predict hourly building cooling load. The hourly building cooling load prediction model based on SVM has been established, and applied to an office building in Guangzhou, China. The simulation results demonstrate that the SVM method can achieve better accuracy and generalization than the traditional back-propagation (BP) neural network model, and it is effective for building cooling load prediction.     

Experimental investigations of a small-scale solar-assisted absorption cooling system

The present study deals with a small-scale solar-assisted absorption cooling system having a cooling capacity of 3.52 kW and was investigated experimentally under the climatic conditions of Taxila, Pakistan. Initially, a mathematical model was developed for LiBr/H₂O vapor absorption system alongside flat-plate solar thermal collectors to achieve the required operating temperature range of 75°C. Following this, a parametric analysis of the whole system was performed, including various design and climate parameters, such as the working temperatures of the generator, evaporator, condenser, absorber, mass flow rate, and coefficient of performance (COP) of the system. An experimental setup was coupled with solar collectors and instruments to get hot water using solar energy and measurements of main parameters for real-time performance assessment. From the results obtained, it was revealed that the maximum average COP of the system achieved was 0.70, and the maximum outlet temperature from solar thermal collectors was 75°C. A sensitivity analysis was performed to validate the potential of the absorption machine in the seasonal cooling demand. An economic valuation was accomplished based on the current cost of conventional cooling systems. It was established that the solar cooling system is economical only when shared with domestic water heating.     

基于改进GA-CPSO融合算法的1 000 MW机组给水系统建模

为解决现有方法对1 000 MW机组给水系统建模复杂、算法收敛速度慢、精度低等问题,提出一种改进遗传算法融合混沌粒子群算法(Genetic Algorithm-Chaotic Particle Swarm Optimization, GA-CPSO)。首先,粒子群算法(Particle Swarm Optimization, PSO)中引入了自适应权重和收缩因子,提升粒子寻优能力;在一维Logistic的基础上提出二维Logistic混沌映射,避免寻优过程中陷入局部最优解;采用轮盘赌选择方法,选取粒子进行下一步的遗传算法优化,提升了全局寻优能力。其次,通过实验仿真数据和现场实际数据验证了改进GA-CPSO算法的精度。将该算法用于1 000 MW机组给水系统,建模精度提高了88.65%,仅需要迭代7次左右即完成收敛。然后,利用数据中加干扰实验进一步挖掘改进GA-CPSO算法的抗干扰能力。实验表明：加入外部大扰动建模误差仅有0.385,算法抗干扰能力强。最后,用皮尔逊相关系数方法验证了机组直流阶段模型间的相关性,相关系数达到了0.9以上,可用一个模型代表。