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One of the reliable methods to make more use of energy production sources, is to use power generation units that use a fuel source, and by utilizing any wasted energy, bring the temperature of the exhaust gases closer to the ambient temperature. The use of waste energy of exhaust gases increases the efficiency and improves the performance of the system. The purpose of this paper is to make optimal use of gas turbine exhaust gases and use them to produce cooling in absorption chillers. And then analyze the thermodynamic and exergy performance of a triple hybrid system to generate electrical, heating and cooling energy. In this research, a hybrid cycle of a gas turbine and a fuel cell is considered as the primary actuator, and two single-effect and double-effect absorption chillers are considered as the secondary actuator. To perform this research, two proposed hybrid systems with their peripherals have been analyzed from a thermodynamic point. To have high accuracy results, in addition to thermodynamic analysis, the thermal and the electrochemical analysis has also been performed in order to the importance of the fuel cell in the hybrid system in this component. In the following, the effect of compressor pressure ratio, turbine inlet temperature, evaporator inlet water temperature, cooling tower inlet temperature and generator inlet temperature on energy and exergy efficiency, as well as exergy destruction rate in the system has been checked with the parametric study of the mentioned hybrid system. The results show that the increase in compressor pressure ratio causes the increase of electrical efficiency and exergy efficiency and the decrease of exergy destruction rate of the system. Also, if a double-effect absorption chiller is used instead of a single-effect absorption chiller, the energy efficiency and exergy will increase by 8% and 2%, respectively, and the exergy destruction rate will decrease by 5.4%. [ABSTRACT FROM AUTHOR]

Machine- and deep-learning methods are used for industrial applications in prognostics and health management (PHM) for semiconductor processing and equipment anomaly detection to achieve proactive equipment maintenance and prevent process interruptions or equipment downtime. This study proposes a Pruning Quantized Unsupervised Meta-learning DegradingNet Solution (PQUM-DNS) for the fast training and retraining of new equipment or processes with limited data for anomaly detection and the prediction of various equipment and process conditions. This study utilizes real data from a factory chiller host motor, the Paderborn current and vibration open dataset, and the SECOM semiconductor open dataset to conduct experimental simulations, calculate the average value, and obtain the results. Compared to conventional deep autoencoders, PQUM-DNS reduces the average data volume required for rapid training and retraining by about 75% with similar AUC. The average RMSE of the predictive degradation degree is 0.037 for Holt–Winters, and the model size is reduced by about 60% through pruning and quantization which can be realized by edge devices, such as Raspberry Pi. This makes the proposed PQUM-DNS very suitable for intelligent equipment management and maintenance in industrial applications. [ABSTRACT FROM AUTHOR]

• A novel method modifying suction port based on non-uniform pressure was proposed. • The suction delay was studied with different radial ports and speeds. • The effect mechanism of suction bearing distance was clarified. • Two modified machines with new suction arrangement were tested to prove the method. To improve the efficiency of the twin-screw refrigeration compressor at a high speed of about 3000 rpm, the suction arrangement was investigated in this paper. Several simplified CFD models of a twin-screw refrigeration compressor for chillers were established to parametrically analyze the influence of the suction delay, rotor wrap angle, and suction bearing distance. The parametric studies showed that the volumetric efficiency could be improved by 3 % by a suction delay of 18°, and more volumetric efficiency could be improved by shortening the length of it. The optimal delay angle was found to be linear with the rotational speed. Increasing the wrap angle from 300° to 330°, the volumetric efficiency decreased by 2–3 %, and the adiabatic efficiency increased by about 0.2 %. By increasing the distance between the suction bearings and the rotor end face from 5 mm to 80 mm, the isentropic efficiency increases by about 1.4 %. Based on the parametric studies, two modified machines were built and tested by experiments. Experimental results showed that the volumetric efficiency of machines #1 and #2 increased by 1.5 % at 3000 rpm. The isentropic efficiency of machine #2 increased by 0.78 % at 3000 rpm and 1.27 % at 3300 rpm. [ABSTRACT FROM AUTHOR]

The present study focuses on modeling the solid oxide fuel cell power plant combined with an absorption-ejection refrigeration cycle. First, a comparison is made between the absorption chiller refrigeration cycle and the absorption-ejection chiller to connect the superior cycle to the solid oxide fuel cell as an auxiliary cycle. Then, the solid oxide fuel cell cycle, the combustion of the output product, the heat recovery unit combined with the refrigeration cycle, and freshwater production are modeled. Next, the sensitivity analysis is presented in order to study the effect of the design parameters on objective functions, which simplifies the justification of the optimization results based on the genetic algorithm. In order to perform optimization, machine learning methods have been employed to reduce computational time and cost. The optimization of this cycle shows that the exergy efficiency is enhanced up to 68%, whereas the overall cost rate is in within 9.7–10.4 dollars per hour. • An integrated gSOFC cycle power plant is proposed, modeled, and designed. • A parametric study is conducted to study the effect of design variables. • Using ejector absorption chiller to increase the efficiency. • Optimal design is performed through a multi-objective optimization method. [ABSTRACT FROM AUTHOR]

The latent heat storage of phase change materials (PCMs) can be used in refrigeration and air conditioning systems. Storing cool energy during the nighttime (off-peak hours) and releasing the cool energy during the daytime (on-peak hours) to reduce the number of starts of the chiller and pumps is a practical approach for achieving energy saving and carbon reduction. Therefore, selecting PCMs is vital for improving energy efficiency and preventing future energy shortages. However, selecting PCMs is complicated by their unique characteristics and types. The purpose of this study was to establish a PCM selection model by combining the Delphi, analytic hierarchy process (AHP), and VIseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) methods to select the optimal PCM type applied in cold storage. A numerical example was used to verify the model's usability, confirming that A9 is the optimal PCM for the cold storage of an air conditioning system. This three-stage PCM selection model combining the Delphi, AHP, and VIKOR approaches provides a more suitable selection model and considers the selection method of material criteria. Moreover, it can solve the problem of difficult PCM selection. Simultaneously, it considers mechanisms to incorporate a company's primary considerations into material selection for real-world applications. These results can facilitate material evaluation and selection during system design and material qualification, helping companies achieve the goals of energy saving, carbon reduction, and sustainable management in the future. [ABSTRACT FROM AUTHOR]

Featured Application: Electric Vehicle, Data Center, Simulink, etc. This study examines the use of meta-heuristic algorithms, specifically particle swarm optimization and genetic algorithms, for optimizing thermal systems, addressing a research gap on their efficacy in larger systems. Utilizing MATLAB's Simulink and Simscape, the research initially targets an electric vehicle thermal system model, emphasizing the optimization of a Li-ion battery pack and associated cooling components, like chillers, pumps, and cooling plates, during operation. One consideration is the use of a glycerol–water mixture in the chiller pump, which demands the use of an optimal control algorithm that adjusts to outdoor temperatures and control strategies. This study focuses on computational efficiency reflecting the complexity of system simulations. Challenges related to applying particle swarm optimization and genetic algorithms to these systems are scrutinized, leading to the establishment of a new objective function to pinpoint target values for system optimization. This research aims to refine design methodologies for engineers by harmonizing optimal design with computational expediency, thereby enhancing the engineering design process in thermal management. This integrative approach promises to yield practical insights, benefiting engineers dedicated to the advancement of thermal system design and optimization. The results show that, compared to the base model, 1% of the overall state of charge could be saved, and the battery temperature could also be cooled by more than 4 °C compared to the initial temperature. [ABSTRACT FROM AUTHOR]

Energy crisis in developing countries is worrisome, and this has made the preservation and transportation of medical and perishable food items a common problem. Most conventional refrigeration systems operate with electricity; however, there are regions where it is difficult or not cost efficient to provide electric service. Therefore, this research seeks to solve the problems of inconsistent, irregular and complete non availability of power supply required to keep food products and drugs refrigerated over a long period of time by designing a tricycle mounted solar-powered cold room. The tricycle mounted solar-powered cold room designed consists of a refrigeration system having a compressor, a condenser, an expansion valve and an evaporator; a solar system having a photovoltaic (PV) module, charge regulator, storage battery and DC to AC inverter; and a tricycle for easy distribution and safe delivery of refrigerated items. A comprehensive analytical design was performed on each of the systems and the design results showed that the solar-powered cold room has refrigerating cooling load, PV array size, battery cap, and inverter power of 986 W, 275 W, 94 kWh, and 8000 W respectively. A structural analysis was also carried out on the tricycle chassis using the finite element method on Autodesk Inventor software. The results showed that the maximum von misses stress experienced by tricycle chassis was 56.96 MPa which is significantly lower than the yield strength of the chassis material used in the design, indicating a robust structural integrity and can therefore be used to carry the loads that it will be subjected to without deformation. [ABSTRACT FROM AUTHOR]

Knowing the right moment when an asset must be replaced is highly relevant to the economic efficiency of any industry. The main objective of this work was to determine the opportune moment to replace an asset, based on an economic approach, which allowed making the best decision between continuing to operate the asset and carrying out the corresponding maintenance actions, or opting for its replacement. For this, the method used was the calculation of the Replacement Profitability Index, which determines if it is necessary to replace the existing asset, or if it is better to wait one more year to proceed with the change. The investigation focused on a 200-ton refrigeration water chiller, from one of the Biocubafarma companies, essential equipment for the efficient production of medicines. The value obtained from the Replacement Profitability Index was 82.88%. This result allows us to conclude that it is economically feasible to replace this equipment with a new one, instead of keeping it in operation for longer. The Replacement Profitability Index constitutes a feasible economic model to assess the opportune moment of asset replacement. [ABSTRACT FROM AUTHOR]

• Characteristics of non-uniform pressure in a twin-screw compressor are revealed. • A new phenomenon of pressure waves inside a twin-screw compressor is discovered. • A fast method to estimate the influence of pressure waves is proposed. • A novel direction for the compressor design is suggested. To achieve higher efficiency of twin-screw compressors for refrigeration, the non-uniform internal pressure distribution in the rotor chamber and the flat section in the p-θ diagram were investigated in this paper. A three-dimensional CFD model of a twin-screw refrigeration compressor for chillers was established to analyze the generating mechanism of the flat section in the p-θ diagram. The p-θ diagrams of the compressor were compared under different rotational speeds and working fluids. Analysis results showed that the flat section in the p-θ diagram is caused by the periodic pressure wave propagation and reflection along the working chamber, and the pressure along the chamber is non-uniform when the sound speed is relatively slow compared with the chamber length in one compression cycle. A dimensionless ratio of chamber length and pressure wave travel distance is proposed to estimate the pressure distribution in the working chamber, based on which the flat section is prone to appear in large-scale compressors with low sound speed refrigerants like R134a. Some improvement directions were put forward to avoid efficiency losses, i.e., appropriately delaying the suction end angle and modifying the discharge port to match the pressure distribution. [ABSTRACT FROM AUTHOR]

Cogeneration and trigeneration systems have been broadly employed as part of the strategies oriented toward rational energy use. The assessment of these systems must include simultaneous considerations of costs, irreversibility, energy losses, and their causes. This work presents a step-by-step thermoeconomic analysis of a microcogeneration unit, composed of an internal combustion engine and an NH3-water single-effect absorption refrigeration chiller. The research employed the Theory of Exergetic Cost method to determine monetary and energy costs and the exergy efficiency of equipment. It is therefore, possible to identify which pieces of equipment present the highest impact and focus on these to improve the overall performance of the energy system. Although not part of the Theory of Exergetic cost, exergoeconomic parameters can be calculated to expand the assessment further. The highest specific exergy cost is associated with the endothermic reaction inside the absorber (282 $/GJ), while the lowest specific exergy cost is due to electricity consumed by the pump of the refrigeration system (2.16 $/GJ). The highest exergy efficiency was identified at the condenser (almost 90%, while values under 40% were obtained for the engine, pump, and absorber. The combined analysis of exergoeconomic results indicates that the lowest performances are related to the generator, the absorber, the evaporator, and the regenerator. [ABSTRACT FROM AUTHOR]

Dehumidification is one of the key challenges facing the air conditioning (AC) industry in the treatment of moist air. Over many decades, the dual role of heat exchangers of AC chillers for the sensible and latent cooling of space has hindered the thermal-lift reduction in the refrigeration cycle due to the requirements of water vapor removal at dew-point and heat rejection to the ambient air. These practical constraints of AC chillers have resulted in the leveling of energy efficiency of mechanical vapor compressors (MVC) for many decades. One promising approach to energy efficiency improvement is the decoupling of dehumidification from sensible processes so that innovative but separate processes can be applied. In this paper, an advanced microwave dehumidification method is investigated in the laboratory, where the microwave (2.45 GHz) energy can be irradiated onto the dipole structure of water vapor molecules, desorbing rapidly from the pores of adsorbent. Results show a significant improvement in performance for microwave dehumidification, up to fourfold, as compared to data available in the literature. [ABSTRACT FROM AUTHOR]

The energy consumption prediction of the chiller is an important means to reduce the energy consumption of buildings. Therefore, a novel energy consumption prediction model for chillers based on an improved support vector machine (ICA-DE-SVM) is proposed. The imperialist competitive algorithm (ICA) is used to optimize the penalty coefficient and kernel function width of SVM, greatly improving the generalization ability and prediction accuracy of the SVM model. The assimilation process is very important in ICA. Colonies of empires move randomly toward imperialists during the assimilation process in ICA, which decreases population diversity and can lead to premature convergence. Therefore, to create more new locations for colonies and increase population diversity, the idea of differential mutation proposed by differential evolution (DE) was applied to ICA. The established model was experimentally verified in an actual multi-chiller system in a building, and the results showed that the ICA-DE-SVM model could obtain good prediction results. Finally, the proposed model was compared with SVM model, PSO-SVM model, GA-SVM model, WOA-SVM model, and ICA-SVM model. With an MAPE of 0.6%, an MSE of 2.3, and an R2 of 0.9998, the findings demonstrate that the ICA-DE-SVM model has a greater prediction accuracy than the other models. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Refrigeration Technology is the property of Shanghai Society of Refrigeration and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Central air-conditioning systems account for the largest share of energy consumption in public buildings, wherein the chiller room is the main source. The current empirical strategies of chiller room group control have difficulty realizing integrity, timeliness, and equipment adjustment accuracy and lead to energy wastage. Therefore, the operation strategy optimization model is of great value for achieving energy savings. This study proposed a stepwise optimization method for central air-conditioning systems, which is divided into the chilled side (the chiller and chilled water pump) and the cooling side (the chiller, cooling water pump, and cooling tower). The optimal points of the two sides are calculated sequentially and integrated as the global optimization result. To construct the stepwise optimization model, mathematical power models of the equipment in use were established to provide mathematical support for objective functions, and a short-term load prediction model with a matching optimization step size was established for energy constraints. The TRNSYS simulation model was developed to verify the energy-saving effects of the stepwise optimization model according to the energy-saving rates of 6.41% and 13.56% attained in both cases. The stepwise optimization strategy can more effectively guide practical applications and provide another way of thinking with respect to the group control optimization of chiller rooms in public buildings. [ABSTRACT FROM AUTHOR]

Considering vibration of centrifugal air-conditioning chillers at working conditions of 300Hz and 386Hz, a vibration reduction method for centrifugal air-conditioning chillers based on particle damping is proposed. Firstly, the vibration transfer path of the chillers is determined based on dynamic characteristics analysis of the chillers. Secondly, the vibration sensitive area of the compressor is determined by finite element analysis. Then the energy dissipation is calculated by the discrete element method (DEM) to determine the optimal installation scheme of the damper. Finally, the vibration reduction effect of the chillers after arranging the damper is verified by experiments. [ABSTRACT FROM AUTHOR]

The operation of chillers plant in the HVAC system is not ideally efficient in major academic buildings because the chillers are operated without accounting for the cooling load demand of the air-conditioning area of the building. The current operation of the chillers plant may fall under two cooling effects, namely excessive cooling effect that will reduce the efficiency of the chillers and inadequate cooling effect that may create an unpleasant environment inside the air-conditioning area. This is because the cooling load demand of the air-conditioning area of the building is unknown and is not numerically measured. The main aim of this study is to find the optimal operation of chillers plant in HVAC system by formulating an optimization framework with the main goal of minimizing energy consumption and electricity costs. The formulation of the optimization framework for chillers plant operation is modelled as Linear Programming (LP) to establish real representation of the chillers plant. The energy consumption profile, cooling load demand, cooling capacity and COP can be obtained by using historical data analysis. The optimization framework is modelled in GAMS v38.2.1 and solved by CPLEX solver to obtain the optimum input for the chillers plant in the HVAC system. The minimum total power consumption can be achieved by optimally coordinating the operation of chillers, cooling towers and AHUs while maintaining room temperature. From the cost comparison analysis between the current and optimal chillers plant, considerable cost reduction is expected to be less than 5 % if the chillers plant is operating efficiently or greater than 30 % if the chillers plant is not functioning effectively. Therefore, this study is beneficial to the administration of academic building to find a strategic action plan to promote cost optimization in the operation of the chillers plant. [ABSTRACT FROM AUTHOR]

A low-cost medium-power carbon dioxide (CO2) laser system is designed, constructed, and characterized to produce coherent, monochromatic laser radiation in the infrared region. The laser cavity is simulated and designed by using ZEMAX optic studio. A switch-mode high-tension pump source is designed and constructed using a flyback transformer and simulated using NI Multisim to study the voltage behavior at different node points. A prototype cooling system/chiller is designed and built using thermo-electric coolers (TEC) to remove the excess heat produced during laser action. Various parameters, such as pumping mechanism, chiller stability, efficiency, output power, and current at different applied voltages, are studied. The chiller efficiency at different output powers of the laser is analyzed, which clearly shows that the chiller's cooling rate is good enough to compensate for the heat generated by the laser system. The center wavelength of the carbon dioxide laser is 10.6 μm with an FWHM of 1.2 nm simulated in the ZEMAX optic studio. The output beam penetration through salt rock (NaCl), wood, and acrylic sheet (PMMA) at various output powers is analyzed to measure the penetration depth rate of the CO2 laser. [ABSTRACT FROM AUTHOR]

Aiming at the issues of unreasonable cooperation schemes and inappropriate setting of parameters of the refrigeration system with multi-chiller plants, this paper presents a cooperative optimization method to improve the energy performance of the system composed of water-cooled chillers and air-cooled heat pumps. The cooperative optimization process includes scheme optimization and parameter optimization. To content the dynamic cooling load, the working sequence of air-cooled heat pumps and water-cooled chillers with variable frequency chilled water pumps is first optimized. Based on the optimal scheme, a back-propagation neural network (BPNN) coupled with particle swarm optimization (PSO) is implemented to explore the preferred operating parameters of multiple chiller plants corresponding to the best coefficient of performance (COP). Compared with the performance of the initial operation module, the energy consumption of the water pump and fan decreases by over 50%, and the COP of the refrigeration system is improved by 16% (COP = 3.85) through the scheme operation. After parameter optimization, the total energy consumption is reduced by 21.7%, and COP is increased by 26.5% (COP = 4.20). Therefore, the proposed cooperative optimization method can provide useful operation guidance for the refrigeration system with multi-chiller plants. [ABSTRACT FROM AUTHOR]

In building HVAC systems, a chilled water flowmeter is an important sensor. Its reading can be used to measure the real-time cooling load, which is a critical variable for the automated control of building HVAC systems, especially central chiller plants. To maintain accurate reading data, fault detection and diagnosis (FDD) of flowmeters are necessary. The available FD/FDD methods for chilled water flowmeters have several common disadvantages: (1) high requirements on sensor integrity: multiple sensors are usually involved in the construction of energy balance models; (2) complex methodology: the fault of any monitored sensor could trigger a detection hit, and a diagnosis procedure must be used to isolate the faulty sensor; and (3) the more sensors that are involved, the more difficult it is to collect fault-free historical data for the establishment of a fault-free benchmark. To address these problems, a user-friendly fault detection (FD) method for building chilled water flowmeters is proposed in this study. The proposed method requires three types of variables to function: the pump frequency, the pump power, and the measured chilled water flow rate on the header pipe. The real-time pump frequency and electrical power data that are collected by VFDs/power meters are used to estimate the true value of the chilled water flow rate with random forest regressor. An auxiliary alarm rule is proposed to tackle the tradeoff issue between detector sensitivity and false alarm rate. Field data of a real HVAC system are used in a case study to evaluate the performance of the proposed method in comparison with three existing FD methods. The results of the validation case study suggest that compared to existing FD methods, which are based on the physical pump model, ensemble learning and clustering techniques, the proposed method could realize higher hit rates and higher alarm rates when confronting different faults (bias, noise and drift) at various levels. Besides, due to the proposed alarm rule, false alarms caused by occasional data errors are completely evaded. Sensitivity analysis to the proposed method indicates that the random forest with default hyperparameters is good enough for the FD task. In brief, the good features of the proposed method (i.e., the simple workflow, low sensor requirements, accessible robust input variable data, handy estimation model, auxiliary alarm rule with tight detection threshold) render the proposed method feasible and user-friendly for engineering practice. [ABSTRACT FROM AUTHOR]

A solar cooling and heating plant with a 1000 l hot water storage tank has been operated since 2018. Two main problems were observed: (1) a fluctuating operation of the absorption chiller due to a high number of stat-up and shut-down procedures; (2) high electricity consumption caused by a low solar fraction SFn of 50.9% during the cooling period. In 2021, the solar plant was retrofitted by employing a shell and tube heat exchanger based on a PCM melting at 64 °C and by adjusting the control strategy. The system performance was evaluated and compared before and after retrofitting based on the operational data in 2021 and 2022. The total number of switch-on times of the chiller shrank by 33.5% and the operation time was increased by 65% in 2022 due to the stable hot water inlet temperature. Contributing to the high heat storage capacity of the PCM storage, more solar thermal energy was utilized and the average SF n reached 75.6% during the cooling period in 2022, leading to a 24.4% reduction in the total electricity consumption compared to 2021. • A fluctuating operation of the absorption chiller was observed before retrofitting due to a higher number of stat-up and shut-down procedures. • A high electricity consumption was caused by a low solar fraction SF n of 50.9% during the cooling period before retrofitting. • After retrofitting, the total number of switch-on times of the chiller shrank by 33.5% and the operation time was increased by 65% due to the stable hot water inlet temperature. • Contributing to the high heat storage capacity of the PCM storage, the average SF n reached 75.6% during the cooling period in 2022, leading to a 24.4% reduction in the total electricity consumption compared to 2021. [ABSTRACT FROM AUTHOR]

This article provides an insight into the numerical simulation of an ammonia-water solution-based plate heat absorber, which is a crucial part of an absorption chiller. These chillers could be used as part of a stratified chilled-water storage tank configuration for coupling to a small modular reactor. The common approach utilized in the process of designing the chiller is to call the absorber a "black box" without considering the processes inside. It follows that the resulting design must be highly oversized to ensure reliable operation of the system. This article focuses on the obstacles that needs to be overcome in order to simulate the processes inside the absorber, such as stream breakup into separate droplets or absorption of ammonia. Unfortunately, we do not have any experimental data we could use to validate our simulations and thus this article should be looked at as a "proof of concept" and a possible guideline for simulations of similar phenomenon. [ABSTRACT FROM AUTHOR]

Several faults affect heating, ventilation, and air conditioning (HVAC) chiller systems, leading to energy wastage, discomfort for the users, shorter equipment life, and system unreliability. Early detection of anomalies can prevent further deterioration of the chiller and energy wastage. In this work, a data-driven approach is used in order to detect faults that usually plague chiller systems. In particular, the proposed approach employs a kernel principal component analysis (KPCA) in order to capture the normal operative conditions of the system; the learning method turns out to be effective in handling nonlinear phenomena through the use of the Gaussian kernel, which, by means of a self-tuning procedure, ensures good accuracy properties while maintaining enough generalization characteristics. The effectiveness of the proposed fault detection method is evaluated by means of tests on emulated and real chiller data. The KPCA approach is first proved to exhibit better detection performances than linear PCA, and then, it is corroborated through the comparison with local outlier factor, one-class support vector machine, and isolation forest. [ABSTRACT FROM AUTHOR]

This paper presents a case study for measuring and simulating the vibration and radiated sound for a large complex industrial chiller. We describe a simulation framework based on statistical energy analysis (SEA), which is populated using a hybrid mix of analytic, numerical, and measurement techniques. This hybrid approach was motivated by preliminary measurements of vibration and sound from the operating chiller, as well as a series of vibroacoustic transfer functions measured during quiescent non-operating conditions. Some components, like the chiller condenser shell, are modally dense and well suited to statistical estimates of SEA parameters like modal density and coupling between the shell modes and internal and external acoustic spaces. Other components, like the discharge pipe between the compressor and condenser shell, have only a few well separated modes with low damping. This component is better modeled using mobilities either measured or calculated using finite element analysis. We estimate other parameters like internal and coupling loss factors using a mix of analytics and measurements where appropriate. We validate the general model by comparing simulated and measured transfer functions between the discharge pipe and condenser shell — the components that radiated the most sound. We estimate structure-borne and fluid-borne input powers from the compressor using inference techniques based on transfer function measurements at quiescent conditions and averaged surface vibrations measured at operating conditions. This inference approach allows for estimating input powers over any chiller operating condition. Simulated vibrations and radiated sound are generally within 3 dB of measurements for several operating conditions. This case study provides a useful general methodology for modeling and measuring the vibroacoustics of chillers and other complex machinery. [ABSTRACT FROM AUTHOR]

[Display omitted] • The solar still by PCM, HP and HPET methods was assessed. • These methods increase thermal efficiency and productivity of the solar stills. • Comparing various solar stills using CO 2 , SO 2 and NO reduction was studied. • CPL and produced water of SSHP-PCM-2 was about 0.0458 $/L and 2248 ml/m2. This study comparatively assesses the efficiency of various single-slope solar stills employing thermosyphon and pulsating heat pipe evacuated solar collectors, integrated with phase change material. The evaporator of the thermosyphon/pulsating heat pipe system is affixed to the evacuated tube, while the condenser is immersed in water to assist the transfer the solar irradiation heat energy. Paraffin wax is utilized as the PCM, positioned at two filling ratios within the thermosyphon/pulsating heat pipe evacuated tube at two filling ratios of 50 % and 100 %, to investigate its impact on water production during periods of low solar irradiation. The thermal energy of the solar radiation stored in the PCM and remove it to the thermosyphon/pulsating heat pipe system. The findings demonstrate that the highest daily freshwater production was 2248 ml/m2, showcasing a notable 40.7 % increase in productivity compared to conventional solar stills (CSSs). Moreover, the system employing pulsating heat pipe and full PCM showcased significant reductions in CO 2 , SO 2 , and NO emissions, approximating 19.53 tons, 117.1 tons, and 449.2 tons, respectively. Additionally, solar stills utilizing heat pipes (SSTHP) and solar stills employing pulsating heat pipes (SSPHP) exhibited energy efficiencies of 19.4 % and 20.3 %, respectively. Furthermore, the exergy-economic factors for CSS, SSTHP, and SSPHP were approximately 1.27 kWh/$, 1.56 kWh/$, and 1.62 kWh/$, respectively. [ABSTRACT FROM AUTHOR]

• Stirling engine and ICE are combined in a CCHP system to produce power. • COP of absorption chiller is improved by weak solution recycling to absorber. • Net electrical efficiency of over 37 % and total efficiency > 60 % can be achieved. • Payback period is < 6 years if the rotational speed is > 4000 rpm and the working time is > 4000 h/year. This work proposes a combined cooling, heating and power (CCHP) system based on biomass gasification with an internal combustion engine (ICE), a Stirling engine and an absorption chiller. The energy and exergy efficiencies and economic performance of the CCHP are evaluated under different working conditions by thermodynamic model and net present value method. The Stirling engine recovers the high temperature potential of syngas during cooling process and improves the CCHP output power by 14 % along with ICE, while the thermal efficiency of ICE reaches 39 % at 5000 rpm. In this work, about half of the total exergy destruction comes from ICE rather than gasifier due to the utilization of Stirling engine as an additional mover to produce electricity. The recycling of weak solution in absorber is adopted in order to increase the COP (Coefficient of performance) of single-effect absorption chiller. The COP could be increased by 7 % and reach 76 % as half of the weak solution recycling to absorber. The electric efficiency and total CCHP efficiency of this system reach 37 % and more than 60 %, respectively. The payback period is estimated to be less than 6 years at an ICE rotational speed of over 4000 rpm and an operation time of more than 4000 h/year. [ABSTRACT FROM AUTHOR]

The aim of the study was to analyze the total microflora in aerobically packed buffalo meat stored under chiller (4±1oC) condition using chemical indicators of spoilage. Buffalo meat was kept in chiller (4±1oC) and analyzed on alternate days from 1st day to 7th day. Various chemical indicators analyzed were pH, TVBN, free amino acids (FAA), FDA hydrolysis and D-glucose concentration. Standard plate count (SPC) values of meat sample were also evaluated on each experimental day. Except D-glucose concentration, all other parameters including SPC increased significantly (P<0.05) as storage advanced. The SPC values of buffalo meat increased from 3.44 log cfu/g on day zero to 6.96 log cfu/g on day 7. The SPC showed a correlation coefficient (r) of 0.943 with both pH and TVBN, 0.953 with FAA, 0.978 with FDA hydrolysis and -0.919 with D-glucose concentration. Further. regressions equations were generated to predict SPC using correlated chemical indicators. Based on correlation coefficient and standard error of estimate, the suitability of regression equation to predict SPC using various chemical parameters as independent variable was found to be, FDAFAApH=TVBND-glucose. [ABSTRACT FROM AUTHOR]

• Development of an improved (torque free using VRF) solar powered milk cooling system. • Thermal calculation of cooling load for various milk cooling systems. • Determination of PV, battery bank and inverter capacities for solar milk cooling. • A comparative study for three vapor compression technologies in terms of power, torque load and chilling time. • T-s and p-h diagrams plotting by experimentally evaluating the developed solar milk chiller refrigeration system. The improper post milking handling and storage results in a complete wastage due to the microorganisms and bacterial multiplication present in raw milk. The torque load minimalizing in the chilling unit using a solar photovoltaic (PV) is indeed a challenging task for the smooth functioning of the milk chilling system especially for the conventional (reciprocating) type of compressors. The variable refrigerant flow (VRF) technology not only solves the toque load problem but also reduces the size of peak power requirement of PV array. The present study enables the design of an improved solar chilling system consists of a chilling tank (200 L capacity) coupled with one tonne of refrigeration unit powered by PV panels (2 kWp) and employing VRF technology to make system more energy efficient by reducing the torque load. Experiments were conducted using different batch sizes (50, 100, 150 and 200 L) to decrease the raw milk temperature from 30 °C to 4 °C. During optimization phase the comparative power required to run various types of compressors (reciprocating, rotary with capacitor and rotary with VRF) were found to be 1.8 kW, 1.2 kW and 0.8 kW, respectively whereas the torque loads were noted to be 3.3 kW, 1.6 kW and zero kW for respective compressor type. The experimental and modeled predicted power consumption and chilling time under different batch sizes revealed excellent correlation coefficient (R2 = 0.99, P < 0.0001). Around one tonne of refrigeration unit is sufficient to chill 200 L of milk up to 4 °C within less than two hours. [ABSTRACT FROM AUTHOR]

Conventional solar heat-driven single stage two bed chillers demand a large area for installation of solar thermal collector to activate the chiller, but in a highly populated tropical country open spaces is insufficient. In the intention to utilize accessible solar energy with better performance, a mathematical investigation is carried out with a three bed adsorption cooling unit working with silica gel-water pair. The studied chiller is powered by direct solar heat collected by a series of compound parabolic concentrator solar thermal collectors without any heat or mass recovery. The working principal of the chiller is, in principle, the same as the conventional two-bed adsorption chiller. However, instead of two half cycles, there are three one third cycles in the proposed chiller in which at every cycle the former desorber is kept in the precooling mode and as an adsorber for the next two one third cycles, respectively. As desorption kinetic is faster than the adsorption kinetics, this longer precooling mode helps the silica gel granules to adsorb more water molecules and increase evaporation rate. Hence, a better cooling effect of at least 1°C can be observed, increases chiller working hour after sunset for almost a further one hour. [ABSTRACT FROM AUTHOR]

• Dimensionless energy-matching parameters and map are established, respectively. • ESR, CO 2 ER and CostR of two cooling supply modes based systems are compared. • FOL strategy is proposed and the comprehensive operation strategy maps are drawn. • Boundaries (ESR > 15%) of the suitable user demands in different seasons are applied. Albeit some studies discussing the performance of the hybrid chiller based CCHP systems and the only an absorption chiller (AC) based CCHP systems from different perspectives, however, there is still lack of theoretical studies focus on the comparison of these two types CCHP systems and screen out the suitable users for CCHP systems. In this research, instead of the case study, the dimensionless energy-matching parameters and map are extracted and designed to quantitative analyses the matching performance for these two systems. Energy saving rate (ESR), CO 2 emission reduction (CO 2 ER), and operation cost reduction (CostR) for these two systems under different operation strategies are compared based on two situations: 1) the redundant electricity that systems produced neither can sold back to the grid, nor can used by the electric chiller; 2) the redundant electricity can used by the electric chiller. According to the comparison, the comprehensive operation strategy maps are drawn to guide systems running in the off-design condition, which are suitable for different energy-matching performance in ESR, CO 2 ER, and CostR. Meanwhile, an optimisation operation strategy (FOL) is proposed for the hybrid chiller based CCHP systems and its suitable application scenario is also calculated based on the operation strategy map. Finally, boundaries of suitable user demands for CCHP systems (ESR > 15%) in China are applied during summers and winters. [ABSTRACT FROM AUTHOR]

Chillers are responsible for nearly 30–40% of the energy consumption of an HVAC system. To enhance the efficiency of HVAC systems, it is necessary to optimize the operation of chillers. Conventional chiller operation strategies are mostly intended to save energy by suitably distributing the chiller cooling load in accordance with the measured cooling system data, which is typically considered noise-free. In other words, the uncertainty of the cooling system measurement and the necessity of customized optimization—as different buildings require different tradeoffs between energy-saving and indoor comfort—are usually not considered. This paper proposes a stochastic optimized chiller operation strategy based on multi-objective optimization and measurement uncertainty. The strategy consists of five steps: (1) Quantify the indoor comfort utility and energy consumption utility by using utility functions; (2) integrate these two utilities into one comprehensive utility using user-defined weights; (3) specify the measurement uncertainty distribution in the cooling system; (4) traverse each possible operation plan, and calculate the mean value (i.e., mathematical expectation) of its corresponding comprehensive utility (expected utility, EU); and (5) determine the optimal operation plan to be the one corresponding to the maximum EU value. The performance of the proposed strategy is validated by establishing a cooling system model on TRNSYS and comparing the findings with those of two conventional chiller operation strategies commonly adopted in Shanghai: the cooling load control strategy and coefficient of performance (COP) optimization strategy. Moreover, the robustness of the proposed strategy is validated by performing a comparison with the deterministic multi-objective strategy, which assumes that the measured system data is noise-free. The simulation results suggest that the proposed strategy can be customized to satisfy different optimization requirements such as less energy consumption or a high level of indoor comfort. [ABSTRACT FROM AUTHOR]

As one of the substitutes for R134a in chillers, the refrigeration performance of R450A is poor. Heat exchanger structural improvement is proposed to improve its refrigeration performance in chillers. In this article, the heat transfer characteristics, resistance characteristics, and stress characteristics of shell-and-tube heat exchangers (STHXs) with different baffles (segmental baffles [SB], plane helical baffles [PB], fold helical baffles [FB]) are numerically investigated based on the fluid–solid coupling. The results show that the shell-side flow velocity and temperature difference of STHXsSB are the highest, and those of STHXsPB are the lowest. The heat transfer coefficient and pressure drop of STHXs increase gradually with the increase of the shell-side volume flow, but h/ΔP decreases gradually. Compared with h/ΔP of STHXsSB, that of STHXsPB increases by 62.2–65.7%, and that of STHXsFB increases by 73.9–76.1%. The stresses around the holes of the baffles are higher than other parts of the baffles. Besides, the effect of temperature on the baffle stress distribution is much greater than that of pressure. Although the maximum stress of STHXsFB is the highest, it is in the allowable stress range of the material. Hence, STHXsFB is suitable for water chillers due to its excellent comprehensive performance. [ABSTRACT FROM AUTHOR]

In this paper, the effects of various compressor inlet air cooling methods to increase the performance of Shahid Hashemi-Nezhad gas turbines refinery were investigated. These methods included media, fogging, and absorption chillers as common inlet air cooling methods and pressure drop station as novel cooling method. By using the exergy, environmental, and economic analysis, the best method for compressor inlet air cooling was selected. Based on the results, the absorption chiller system had the highest compressor inlet air temperature drop and increased the thermal and exergy efficiencies of cycle by about 2.5 and 3%, respectively, in hot season. Using absorption chiller, pressure drop station, fogging, and media had further reduction in CO2 and CO than simple gas turbine, respectively. Finally based on the net present value and internal rate of return coefficients, the pressure drop station method is the most economically feasible option. [ABSTRACT FROM AUTHOR]

The objective of this paper is the comparison of two dedicated subcooling methods, after the gas cooler, in a CO2 transcritical refrigeration system. The use of vapor compression refrigeration with R134a for subcooling is the first method, and the second is the use of an absorption chiller that operates with a LiBr-H2O working pair. The examined systems are compared energetically and exegetically with the reference transcritical CO2 refrigeration cycle without subcooling. The analysis is conducted for different operating scenarios and in every case, the system is optimized by selecting the proper temperature and pressure levels. The analysis is performed with a developed and validated model in Engineering Equation Solver. According to the final results, the use of the absorption chiller is able to decrease the system electricity consumption by about 54% compared to the simple transcritical cycle, while the decrease with the mechanical subcooling is 41%. Both systems with dedicated subcooling are found to have an important increase in the system exergy performance compared to the simple transcritical cycle. However, the system with the mechanical subcooling is found to be the best choice exegetically, with a small difference from the system with the absorption chiller. [ABSTRACT FROM AUTHOR]

Highlights • A novel modeling approach of feature-recognition was proposed. • The chiller models were developed based on feature-recognition. • The models were validated by comparisons between simulations and experiments. • Relative errors of simulations and experiments are all within 10%. Abstract With the absence of structure parameters of chillers, it is difficult to simulate the chiller performance by the conventional precise modeling approach. Thus, a novel modeling approach is proposed, which makes unknown structure parameters lumped and obtains them (i.e. the characteristic parameters, which are unique for each chiller) based on measured data of chillers. The modeling principle of feature recognition is described, based on which then the chiller models were developed. An experimental platform of chiller was established, and the relevant chiller models were established on basis of measured data. Moreover, to verify the chiller models, simulations and experiments were compared under variable water flow rate and variable water temperature conditions respectively. Results show that with the feature recognition method, the chiller models can function quickly and efficiently, and achieve a high accuracy. Compared with experimental results, relative errors of simulated performance parameters, such as refrigerating capacity and COP (coefficient of performance), are all within 10%. This study provides a new and efficient approach for chiller modeling. [ABSTRACT FROM AUTHOR]

Thermally driven absorption chillers have the advantage of being powered by renewable or waste heat as well as using environmentally friendly refrigerants. However, micro scale capacities suitable for residential and office applications are still lacking. This study presents the experimental evaluation of a developed 3 kW capacity, single effect, hot water fired absorption chiller prototype. The chiller operates on the lithium bromide - water pair. To enhance wettability in the absorber, a double - tube configuration was employed to aid the falling film mode. Experimental test on the chiller showed the chilled water outlet temperatures from the evaporator ranged between 16.3 to 20.5oC. The chiller response time to cooling was about 15 minutes from the commencement of evaporation process at the evaporator. The chiller pressures stayed below 9 kPa throughout the experiment. Maximum cooling power of 2.01 kW was recorded, representing 67% of nominal cooling capacity. Maximum coefficient of performance (COP) of 0.47 was recorded, while an average COP of 0.43 was recorded. [ABSTRACT FROM AUTHOR]

Abstract Over the last decade, building engineers have begun implementing sensible-latent de-coupled air-conditioning systems in non-residential buildings in hot-humid climates. Typically, a de-coupled system consists of a dedicated outdoor air sub-system for ventilation and high-temperature radiant cooling sub-system for space cooling. This approach has lowered cooling energy demands and fan energy consumption in buildings. However, the complete energy saving potential of de-coupled systems, specifically high-temperature space cooling sub-systems, can only be realized by using low-lift chillers that supply chilled water which matches the high-temperature radiant cooling application. This paper discusses the results of a retro-installation of a prototype modular low-lift chiller to provide high-temperature chilled water (at 17 °C) to the radiant cooling units. The paper presents temperature and cooling load profiles, control methodology and energy efficiency improvements of the low-lift cooling system. The paper also further discusses the influence of various parameters on the performance of the chiller. Despite having a cooling capacity of only 20 kW, the modular low-lift chiller is consistently able to achieve a Coefficient of Performance (COP) of 8. By operating at a low-lift (20 K) compared to a high-lift (29 K), the sensible cooling electrical consumption (at the chiller) is reduced by 23% despite being compared to a high-lift low-temperature chiller with 100 x higher cooling capacity. When normalized for cooling capacities, this reduction is between 29–30%. The project is the first known installation of low-lift cooling for building comfort control in hot-humid climates, and first reported publication of low-lift cooling in a real-life scenario - i.e., non-laboratory conditions or modelling exercise. [ABSTRACT FROM AUTHOR]

Highlights • FAPO 4 -5 adsorbents synthesized and characterized. • Adsorption properties of adsorbents examined by binder type. • Adhesion strength determined by cross-cut tests. • Addition of 5.0 wt% epoxy binder found to be optimum. Abstract To overcome the problem of peak electricity demand caused by the use of air-conditioning in the summer, researchers have been focusing their interest on adsorption chillers, which are an environmentally friendly technology in that they use waste heat as their power source and water as a refrigerant. In the present study, to improve the performance of an adsorption chiller, FAPO 4 -5 adsorbents were synthesized using two hydrothermal synthetic methods, and then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N 2 adsorption/desorption isotherms and water adsorption isotherms. Coatings of the adsorbent were applied to an aluminum substrate. Six different coating solutions were used, with a 5.0 wt%, 10.0 wt%, and 15.0 wt% content of epoxy-based and silicone-based binders, respectively. The surface features of adsorbent coating were observed with scanning electron microscopy (SEM). To determine the variation in the water adsorption properties of the adsorbents according to the binder type, each adsorbent was subjected to water adsorption isotherm analysis at 25 °C. The coating thickness was calculated by three dimension coordinate measuring machine. Cross-cut tests (performed according to ISO 2409:2013) were carried out to assess the strength of the adhesion of the coating to the aluminum substrate. [ABSTRACT FROM AUTHOR]

In this study, the performance of a solar cooling system, composed of a water–lithium bromide vapour absorption chiller fed by thermal solar flat-plate collectors and an external heater, has been investigated in Italy, pointing out the difference in heating energy saving related to the efficiency of the heat transfer fluid. In particular, two working fluids, water and nanofluid (3·0 vol% aluminium oxide (Al2O3) nanoparticles in bidistilled water), have been simulated, showing a significant increment, up to 36·54%, of the heating energy saving, when the nanofluid was employed. Therefore, this work demonstrated that the working fluid can be a key factor for performance improvements in solar cooling systems. Furthermore, in view of the need to increase the efficiency of renewable energy systems, these results suggest the possibility of using nanofluids in several systems characterised by closed-loop working fluids, in order to improve their performance. [ABSTRACT FROM AUTHOR]

Abstract In the paper, a solar driven ammonia-water chiller is investigated, as one of the systems having potential for reduction of resources depletion. An energy and exergy analysis is proposed for correct diagnostics while designing and operating the cycle. The boundary conditions for the analyses are set in accordance with Professor Szargut's primary instructions. They are however widened to solar collector component. Solar radiation is treated as the driving energy or exergy, respectively. The analyses are supplemented with a sensitivity diagnosis revealing the most significant parameters modifying the efficiency and irreversibilities distribution. According to the findings, design COP of the chiller equals 0.444 while its net exergy efficiency is 0.026. Solar collector component is the most burdened with exergy destruction and loss in the whole cycle. Highlights • Energy and exergy analysis of 23 kW solar NH3 H2O absorption chiller is performed. • Balance boundary is widened and includes solar collector field component. • Under wide balance boundary COP = 0.444 and exergy efficiency ( η e x n e t ) equals 0.0262 • Lower cooling water temp. increases η e x n e t but induces higher losses in evaporator and sol. collector. • Decreasing exergy destruction in solar collector means higher irreversibilities in absorber. [ABSTRACT FROM AUTHOR]

Highlights • Cox regression was used to assess transitional statuses. • Survival curves showed variable ranges to limit transitional statuses. • Pair-up operation of system components gave the highest COP. • The COP rose by 2.72% by limiting undesirable statuses. Abstract The coefficient of performance (COP) of chiller systems drops when their operating statuses change frequently and deviate from the conventional pair-up operation of chillers, pumps and cooling towers. This paper analyses the chance of having transitional and unconventional operating statuses when the operating variables vary. 12,541 sets of operating conditions were collected from a chiller system at 15 min intervals over 8 months. 1901 sets of transitional statuses and 1565 sets of unconventional statuses were identified. Cox regression models were developed to analyze the impacts of ambient variables, flow- and temperature-related operating variables on transitional statuses. The temperatures of water entering and leaving the condensers were significant variables influencing the chance of switching on/off an extra cooling tower. Survival curves suggested the throttling range of significant variables to identify the chance of transitional statuses causing a COP fluctuation. Minimizing unnecessary transitional and unconventional statuses increased the average system COP by 2.72%. [ABSTRACT FROM AUTHOR]

Highlights • Entransy analysis is used to indicate the ways to improve the energy efficiency of the DET chiller. • Influences on the heat transfer of the heat exchangers are analyzed for the DET chiller. • Lowest entransy dissipation rate and EDTR are achieved at the ratio of 40%: 60% (R32:R236fa). • Suggested temperatures of low and high temperature chilled water are concluded at 7 °C and 16 °C. • Differences between entransy anlysis and exergy analysis are discussed for the DET chiller. Abstract The double evaporating temperature (DET) chiller has been considered as a credible method to realize temperature and humidity independent control (THIC). Energy performance optimization is of great significance for the extensive application of the DET chiller. In this paper, entransy method is employed to analyze heat transfer performance of heat exchangers based on the extremum principle of entransy dissipation (EPED) and the minimum entransy dissipation-based thermal resistance (EDTR). The entransy dissipation rate and EDTR are discussed in detail to indicate the impacts of t l,c , t h,c (i.e., temperature of low temperature chilled water, high temperature chilled water), MC(R32): MC (R236fa) (i.e., mass concentration ratio of R32 to R236fa), and structural parameters on heat transfer performance of heat exchangers. The results indicate that the lowest entransy dissipation rate of heat exchangers are achieved when MC (R32): MC (R236fa) is 40%: 60%. The design t l,c /t h,c are suggested to be set at 7/16 °C to reduce the entransy dissipation rate and EDTR of heat exchangers, which is beneficial to strengthen energy utilization of the chiller for energy saving. Considering the significant effect of heat capacity ratio of two steams on the EDTR, m r (i.e., mass flow rate of refrigerant) and m l,c /m h,c /m c (i.e., mass flow rates of low/high temperature chilled water/cooling water) should be increased and decreased, respectively. [ABSTRACT FROM AUTHOR]

This article compares two modeling approaches for optimal operation of a turbo chiller installed in an office building: (1) a machine learning model developed with artificial neural network (ANN) and (2) a hybrid machine learning model developed with the ANN model and available physical knowledge of the chiller. Before developing the ANN model of the chiller, the authors used Gaussian mixture model in order to check the validity of measured data. Then, the hybrid model was developed by combining the ANN model and physics-based regression equations from the EnergyPlus engineering reference. It was found that both the ANN and hybrid ANN model are satisfactory to predict the chiller's power consumption: mean bias error (MBE) = −2.63%, coefficient of variation of the root mean square error (CVRMSE) = 8.05% by the ANN model; MBE = −3.99%, CVRMSE = 11.98% by the hybrid ANN model. However, the hybrid model requires fewer inputs (four inputs) than the ANN model (eight inputs). The energy savings of both models are similar coefficient of performance (COP) = 4.32 by the optimal operation of the ANN model; COP = 4.44 by the optimal operation of the hybrid ANN model. In addition, the hybrid ANN model can be applied where the ANN model is unable to provide accurate predictions. [ABSTRACT FROM AUTHOR]

Highlights • Thermally drive refrigeration integrated with low temperature FC. • Thermo chemical modeling of half effect absorption chillers. • The behavior of the energy systems is studied in real energy management scenarios. • The control strategy optimized through a graph-based methodology. • Absorption chiller boosts environmental and economic benefits of cogeneration. Abstract Fuel cell based trigeneration plants, that utilize absorption chillers to convert waste heat into cooling energy, are a promising technology to satisfy heat, power, and cooling demand in warm climates. Polymer electrolyte membrane fuel cells, that operate at low temperature (< 100 ° C), are the most technologically mature among the several types of fuel cells. Thermally activated cooling technologies are widely utilized in trigeneration plants to improve their efficiency. However, absorption chillers require relatively high grade thermal energy and their coupling with low temperature fuel cells is relatively untapped. Herein, we perform a techno-economic analysis of a trigeneration plant based on low temperature polymer electrolyte membrane fuel cells and half-effect absorption chillers. A thermo-chemical model is developed to estimate the performance of a cogeneration plant based on low temperature fuel cells and of the half-effect absorption chiller. The behavior of such combined heat, cooling, and power plant is also analyzed within real energy management scenarios, considering different energy demands, climatic conditions, energy costs, and plant layouts. The control strategy of the power plant is optimized through a graph-based methodology previously developed and validated by the authors. Total energy cost and CO 2 emissions are then compared to those of a reference scenario where electricity is acquired from the distribution grid, thermal energy is produced through a natural gas boiler, and a mechanical chiller is used for cooling. The results show that the utilization of half-effect absorption chillers boosts the environmental and economic benefits for all the considered scenarios. We also demonstrate that the utilization of the absorption chiller reduces the imbalance between the results obtained for the different scenarios (i.e. climates), although economic and environmental benefits associated to distributed generation are strongly influenced by the energy context. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the various optimized generators for H 2 O/LiBr absorption chiller with multi-heat sources are discussed. While the previous optimization has been mainly conducted for a single element, the integrated generation system including high/low temperature generator and waste heat recovery generator is optimized in this paper. A practical modeling method is proposed for the high/low temperature generator and it has been verified by comparing with experimental results. Meta-models for the volume and the generation rate are built with kriging method, and the generators are optimized by multi-objective optimization technique using the meta-models. The total volume is minimized and the total generation rate is maximized according to five design variables of the generators. It is found that from the optimization process the total volume is decreased by 59.06% and the total generation rate is increased by 31.46% compared to the baseline point. It is concluded that the contribution of the waste heat recovery generator and the high temperature generator are dominant for the total volume reduction and the total generation rate improvement, respectively. Moreover, the effects of the key variables on the performance of each generator are analyzed according to the optimization of the integrated generation system. Highlights • A practical modeling method is proposed for generators with multi-heat sources for tri-generation systems application. • The generators are optimized by multi-objective optimization technique using the meta-models. • The total volume is decreased by 59.06% while total generation rate is increased by 31.46% by the optimization. • The waste heat recovery generator is dominant for the total volume reduction. • The high temperature generator is dominant for the total generation rate improvement. [ABSTRACT FROM AUTHOR]

Highlights • An enhanced PCA sensor fault detection method was presented for screw chillers via EEMD. • EEMD was applied for signal decomposition and noise elimination of raw sensor measurements. • 11 sensors were chosen for PCA modeling by quantifying the chiller energy performance. • Field operating data from real screw chillers at summer seasons were used for validation. • EEMD significantly improved the PCA-based sensor fault detection performance. Abstract In heating, ventilating and air conditioning (HVAC) systems, sensor faults cause improper control strategy resulting in both energy penalty and service costs. As the first and foremost step of an entire on-line fault-tolerant control strategy, sensor fault detection is crucial for maintaining system operation performance. Principal component analysis (PCA) is a widely studied sensor fault detection method in HVAC area. However, the noise information contained in field sensor measurements may confuse the PCA model training process and deteriorate the sensor fault detection performance. To address the problem, this study presented an enhanced PCA-based sensor fault detection method using ensemble empirical mode decomposition (EEMD) denoising. The proposed EEMD-PCA method includes two steps: (1) EEMD is adopted to decompose and denoise the raw measured data, namely eliminating the possible noise information and extracting the possible useful information; (2) PCA is employed to establish the Q -statistic with threshold for sensor fault detection. A case study on a real screw chiller system was conducted to validate the proposed method. 11 sensors were chosen for modeling by qualifying chiller energy performance. Field operating data were used for validation with various magnitudes of added biases. Results revealed that EEMD-PCA showed better detection performance than PCA for 8 critical sensors. The fault detection ratios of the 8 sensors were increased by 22% at average. After pre-processed by the EEMD method, the denoised data were smoother than the raw data. Data distributions in the PCA residual subspace indicated that EEMD-PCA is sensitive to the smaller biases since the denoised data can separate faulty data from the normal data. [ABSTRACT FROM AUTHOR]

Highlights • Mass fraction difference as the driving force for the mass transfer. • New variable to fit experimental data for absorption chillers. • Linear relation of cooling capacity to mass fraction difference. • Less deviation compared to characteristic temperature function. Abstract Absorption chillers are considered as heat transfer devices and hence most commonly modeled as heat transfer processes. The absorption of the refrigerant vapor though inherently involves mass transfer into the absorbent, which in comparison to the heat transfer usually is a slow transport process. Modeling absorption chillers, however, usually does not include this mass transfer process. This in fact neglects the dominant process in absorption chillers which is addressed in the present paper. [ABSTRACT FROM AUTHOR]

Highlights • Two new arrangements of series and parallel absorption chillers are proposed. • The effects of operating temperatures on cooling capacity and COP are estimated. • The effect of mass ratio on COP in parallel cycle is studied. • The proposed parallel cycle has a wider operation range than series cycle. • The COP is optimized based on GA method with condition of no crystal formation. Abstract In this paper the effect of some key parameters on coefficient of performance (COP) in two novel arrangements of double effect lithium bromide–water absorption chillers with series and parallel flow have been studied. The main components of these cycles are generators, absorber, condensers, evaporator and heat exchangers. The mass, concentration, and energy balance equations are used for both cycles and performances of the systems are analyzed at different conditions with the condition of no formation of lithium bromide crystal. Also, the effects of temperatures and mass flow rates of inlet vapor of generator and inlet water of absorber on evaporator cooling capacity, absorber heat transfer rate and COP are investigated. In addition, two new parameters based on mass ratio of solution splitters are defined (R 1 and R 2) and their effects on the system performance are analyzed. The results show that the series cycle at inlet vapor temperature to the high temperature generator (HTG) below 150 °C has higher COP than the parallel cycle. In addition, with increase of inlet vapor temperature to HTG and rise of mass flow rate of inlet water to absorber, the COP increases in both parallel and series cycles. In addition, with increase of R 1 , the COP increases at first and reaches to a maximum value, and then decreases. Furthermore, the Genetic Algorithm (GA) method has been used to optimization of the system COP at series and parallel cycles. [ABSTRACT FROM AUTHOR]

The design of the absorber of absorption chillers is still subject to great uncertainty since the coupled processes of heat and mass transfer as well as the influence of systemic interactions on the absorption process are not fully understood. Unfortunately, only a few investigations on the transport phenomena in the absorber during operation in an absorption chiller are reported in the literature. Therefore, experimental investigations on the heat and mass transfer during falling film absorption of steam in aqueous LiBr-solution are carried out in an absorber installed in an absorption chiller in this work. An improvement of heat and mass transfer due to the increase in convective effects are observed as the Ref number increases. Furthermore, an improvement of the heat transfer in the absorber with increasing coolant temperature can be identified in the systemic context. This is explained by a corresponding reduction in the average viscosity of the solution in the absorber. A comparison with experimental data from literature obtained from so-called absorber-generator test rigs shows a good consistency. Thus, it has been shown that the findings obtained on these simplified experimental setups can be transferred to the absorber in an absorption chiller. However, a comparison with correlations from the literature reveals a strong deviation between experimental and calculated results. Hence, further research activities on the development of better correlations are required in future. [ABSTRACT FROM AUTHOR]

Highlights: • A directly solar-driven diffusion absorption chiller is designed and built up. • Development of a directly solar-heated generator integrated into a collector. • The solar-driven diffusion absorption chiller is tested in a solar simulator. • The start and operational behavior of the chiller was investigated in outdoor tests. • A bubble pump unit with a plate heat exchanger (PHX) generator is investigated. Abstract Nowadays, the diffusion absorption process is well known and mainly used as refrigerators in hotels and caravans. The huge advantage of this process is the noiseless and wear-free operation due to the absence of moving parts. There are few studies where the diffusion absorption process is combined with solar cooling. The main disadvantages are the low efficiency and the high weight in relation to the cooling capacity. This paper presents a diffusion absorption chiller directly heated by a solar collector with enhanced efficiency. The generator, acting as the bubble pump of the diffusion absorption process, is integrated into a double-glazed flat plate collector. The design and build-up of the solar-driven diffusion absorption chiller is presented. Measurement results of the solar-driven diffusion absorption chiller recorded in a solar simulator as well as in outdoor tests are shown. Maximum cooling capacities of 226 W and 228 W are reached. The maximum efficiency of the whole process and therefore the percentage of the insolation incident on the solar collector, converted into cooling capacity, is 11.4 %. Thus, the efficiency is higher than in similar concepts. Finally, an outlook is provided on further improvements using a bubble pump unit with a plate heat exchanger (PHX) generator to increase the cooling capacity. [ABSTRACT FROM AUTHOR]