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A CCHP‐ORC system consisting of a MGT, an ORC and an absorption refrigeration chiller was proposed in this study. A verified simulation model based on specific mass, energy conservation and exergy destruction was built. Thermodynamic analysis was applied to the system. A parametric study was carried out to investigate the impacts of the ORC's evaporating temperature and, turbine efficiency, and the ARC's generating temperature on the system's performance. Six different organic working fluids (R141b, Toluene, D4, n‐Octane, n‐Heptane and MM) were selected in this study, and their impact on the system's performance was also analyzed. The results showed that the CCHP‐ORC system's primary energy efficiency and exergy efficiency could reach a maximum of 76.89% and 54.95% respectively, with toluene as the organic working fluid. The MGT accounted for a large part of exergy destruction in both the CCHP‐ORC and reference system. Compared to the reference system, the total exergy destruction of the CCHP‐ORC system decreased, for all six organic working fluids. The main exergy reduction occurred in the GEN, ABS and DHW. A T‐Q diagram method was conducted to analyse the heat transfer process in the CCHP‐ORC and reference system. The results showed that the CCHP‐ORC system can significantly reduce the mean heat transfer temperature difference in the heat transfer process, which helps to decrease the exergy destruction in GEN, and improves the system's exergy efficiency. Hence, it is beneficial for the system's efficiency and exergy destruction to introduce ORC as a middle cycle into the CCHP system. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1513–1522, 2018 [ABSTRACT FROM AUTHOR]

The energy consumption in a multi-chiller system is very significant and its consumption will be increased by inappropriate operating of the chillers. Accordingly, the economic dispatch in multi-chiller systems becomes an important issue for saving energy. Such issue is known as optimal chiller loading, which is solved by applying different optimization methods. This study employs exchange market algorithm to obtain optimal set points of the economic dispatch problem on chiller plants, which is inspired by trading the shares on a stock market. Exchange market algorithm is proposed for solving continuous non-linear optimization problems and it is comprised of two searching and two absorbing operators. The decision variable of the optimal chiller loading is partial load ratio of each chiller and the objective function of the optimal chiller loading problem is minimizing the power consumption while satisfying the cooling demand. This paper adopts three case studies to evaluate the performance of exchange market algorithm and compares it with other optimization methods applied on the optimal chiller loading problem. Results show that exchange market algorithm is an efficient method for solving optimal chiller loading problem in chiller plants, and is adaptable for usage in air-conditioning systems. In addition, the comparison results show that the exchange market algorithm provides better solutions than previous optimization methods applied on the optimal chiller loading method in terms of convergence speed and total consumption of electrical energy. [ABSTRACT FROM AUTHOR]

Chiller plants use more than 50% of the total energy consumed by heating ventilation and air conditioning (HVAC) systems. Adjustments to the interactions between components could reduce the total power used, in the premise of helping systems to meet building thermal load targets. Studies have shown that significant power reduction can be achieved by adopting different kinds of optimisation techniques to different variables. However, it is difficult to apply these optimisation strategies into industry, as frequent simultaneous updates of different variables with large fluctuations harm the operational stability of chiller plants. In practice, making fewer and more moderate variable updates is a more practical optimisation strategy. To address this problem, this study proposes using varying searching bounds in the optimisation processes. To determine the contribution of each variable to power reduction, the effect of each optimised variable is analysed. The results show that applying varying searching bounds is an effective way to avoid frequent large fluctuations in optimised variables without sacrificing much optimisation performance. The optimisations of the condenser water mass flow rate and condenser water supplying temperature make the greater contributions to power reduction. [ABSTRACT FROM AUTHOR]

Cold Thermal Energy storage systems (TES) present opportunities for offsetting peak demand from chillers. An assessment of the TES system at the University of Idaho was performed to quantify the current exergy efficiency of the single phase, water based, cold TES that typically operates under the full capacity. Internal temperatures within the TES vary from 7 °C and 15.5 °C throughout the summer months. Measurements were taken on internal temperatures and flow rates and were used to create a model in TRNSYS. Comparison of Richardson, Fourier Peclet, and Biot numbers show the influence of internal and external conditions on TES performance and stratification characteristics. The Richardson number indicates that the turbulence effect of the inlet geometry is very small and it has negligible effect on the stratification within the TES. The Peclet and Fourier numbers show that prediction of the stratification profile of a TES can be done with minimal measurements. The Biot number shows that the temperature variation only occurred vertically within the TES. Using the data obtained, as well as an analysis of the model, showed the TES is determined to have an overall energy efficiency of 75% and an exergy efficiency of 20%. The individual layers of the TES were evaluated to conclude that the upper half of the TES is the most exergy efficient layers of the TES and steps to maximize their usage should be taken without reducing the overall CAPACITY. [ABSTRACT FROM AUTHOR]

In this paper, the potential of a small scale concentrated solar Organic Rankine Cycle unit coupled with an absorption chiller for trigeneration purposes is investigated using a simulation analysis. At the moment, only few research works encompass small-scale solar trigeneration systems and most of them do not refer to real plant. On the contrary, in this work electric, heating and cooling maximum generation of a real and experimental small scale prototype system composed of a 50 m 2 CPC solar field, a 3.5 kWe ORC plant and a 17 kWc absorption chiller is investigated by means of TRNSYS. In particular, this work relies on the evaluation of the dynamic performance of the mentioned plant varying some selected system parameters to provide proper modifications of its design configuration and operation. More precisely, working temperature ranges, heating and intermediate fluid flow rates as well as volume of the storage tanks and size of the solar field have been varied within the simulation model. Results have shown that operating temperature ranges of the storage tanks considerably affect the overall performance of the system; by appropriately choosing these ranges the primary energy production can be increased by 6.5% compared to the baseline configuration without any additional investment costs. Moreover, setting suitably some design parameters can significantly contribute to extend the operating hours and the feasibility of a such small scale integrated system for residential applications. [ABSTRACT FROM AUTHOR]

A standalone absorption chiller based on microchannel heat exchanger technology was developed with a cooling capacity of 7 kW. A review of recent advances in microscale heat and mass exchangers and vapor absorption technology guided this development. Thermodynamic and heat and mass transfer design procedures are discussed. A control system for standalone operation was developed. Experimental evaluation demonstrated the achievement of target cooling capacities. An overall system COP of 0.44, and an ammonia–water cycle COP of 0.51 were achieved. Reasons for differences between model predictions and actual performance are discussed. This development validates scalability and application of microscale heat exchanger technology for absorption heat pumps at residential-scale capacities. In contrast to conventional absorption systems, core heat and mass exchangers require only small portion of overall system volume and weight, which significantly improves the prospects of this technology for small capacity applications. [ABSTRACT FROM AUTHOR]

This paper presents the approach of thermoeconomic analysis of centralized cold generation in trigeneration system integrated with steam-powered absorption chillers (ACs). The analysis was conducted for real back-pressure combined heat and power (CHP) unit BC-50 and single-effect absorption refrigerators using water and lithium bromide as the working fluids. It has been assumed that the heating medium supplied to the chiller generator is technological steam from the existing steam bleeding. The calculations take into account changes of energy demand for heating and cooling for each month of the year. Mathematical simulation models of cogeneration and trigeneration systems have been developed with the commercial program for power plant simulation EBSILON PROFESSIONAL. System effects of heat and electricity cogeneration and cogeneration with additional cold production have been calculated compared to separate production of heat, electricity, and cold (replaced heating plant and power unit). The effect of trigeneration has been assessed quantitatively by the coefficient of the increasing cogeneration effects, which has been calculated as a ratio of chemical energy savings of fuels to the demand for heat by the consumers in the cases of trigeneration and cogeneration. This paper includes also analysis of economic effectiveness of a trigeneration system with ACs for cold agent production. The results of economic calculations show that an acceptable payback period of approximately 13 yr for a CHP and absorption system may be achieved. Discounted payback (DPB) is equal to the half of assumed operating time of the system. Sensitivity analysis shows that the most important impact on profitability is the selling price of cold and the purchase of fuel--hard coal. [ABSTRACT FROM AUTHOR]

Temperature and humidity independent control (THIC) has been demonstrated as an effective way to improve the performance for air-conditioning systems. As an alternative option of THIC method, a double evaporating temperature (DET) chiller using zeotropic mixture refrigerants of R32 and R236fa has been proposed to substitute the traditional water-cooled chiller. The low temperature chilled water of 7 °C and high temperature chilled water of 17 °C will be produced simultaneously by this DET chiller, and the latent and sensible cooling loads of buildings can be afforded by the produced low temperature chilled water and high temperature chilled water respectively. In this paper, the experiments with different concentration ratios of R32 to R236fa are carried out on a 4.0-kW DET chiller. To further improve the energy performance of the DET chiller, the exergy analysis is used to investigate the effects of chilled water temperature and mass concentration of zeotropic mixture on the DET chiller. The exergy loss for each component is discussed in detail to identify the inefficient components, and then indicate the ways to improve the performance of DET chiller. The results show that the DET chiller achieves the lowest exergy loss and highest exergy efficiency when the mass concentration ratio of R32 to R236fa is 40%: 60%. Furthermore, the design temperature of high temperature chilled water should be at 16 °C to improve the energy utilization of DET chiller. This study will help to understand the design and operation for the DET chiller based air-conditioning systems. [ABSTRACT FROM AUTHOR]

This paper presents an analytical methodology of evaluating the economic viability of a CCHP system, over three alternative configurations: (1) boiler and electric chiller, which have been extendedly analyzed in literature, (2) boiler and gas driven absorption chiller and (3) reversible heat pump, which have been slightly investigated in comparison with CCHP systems. An adjusted Levelized Cost of Electricity (LCOE) is defined for those cases and used as a decision-making criterion. A sensitivity analysis is carried out to explore the effect of technical and economic data and load characteristics on the LCOE. The viability of the CCHP system is determined by comparing the LCOE with the electricity market prices. Two different economic viability problems are considered: (1) investing viability for new CCHP systems, and (2) operating viability for existing CCHP systems. The results demonstrate interesting interactions and encouraging perspectives, especially when CCHP system is used in combination with conventional technologies like boilers and chillers. [ABSTRACT FROM AUTHOR]

The current article presents an analysis conducted upon the sensor data gathered from the distribution control system of a central heating and cooling plant in Ottawa, Canada. After observing that the performance of four boilers and five chillers of this plant vary substantially in time under steady-state conditions, data-driven models were developed to explain this variability from the archived sensor data. By employing a forward stepwise regression and a repeated random sub-sampling cross-validation approach, two-layer feed-forward artificial neural network models with 7 to 15 hidden-nodes were selected for each boiler and chiller. The selected boiler models could explain 84% to 95% of the variability in a boiler's efficiency, and the selected chiller models could explain 65% to 94% of the variability in a chiller's coefficient of performance. Among studied nine variables, the most informative ones to predict a boiler's efficiency were identified as follows: flue gas O2 concentration, pressure, part-load ratio, forced draft fan state, and return water flow rate. Unlike boilers, all four studied variables were found useful in predicting a chiller's coefficient of performance. These four variables were the return water flow rate, part-load ratio, outdoor temperature, and return water temperature. A residual analysis was conducted to verify the appropriateness of the selected models to the datasets. In addition, potential use cases for the selected models were discussed with illustrative examples. [ABSTRACT FROM AUTHOR]

The objective of this study was to develop a strategy for miniaturizing heat exchangers (HXs) used for the thermal management of sorbent beds within adsorption refrigeration systems. The thermal mass of the microchannel heat exchanger (MCHX) designed and fabricated in this study is compared with that of commercially available tube-and-fin HXs. Efforts are made to quantify the overall effects of miniaturization on system coefficient of performance (COP) and specific cooling power (SCP). A thermal model for predicting the cycle time for desorption is developed, and experiments are used to quantify the effect of the intensified HX on overall system performance. [ABSTRACT FROM AUTHOR]

Energy saving is an open point in most European countries where energy policies are oriented to reduce the use of fossil fuels, greenhouses emissions and energy independence, and to increase the use of renewable energies. In the last several years, new technologies have been developed and some of them received subsidies to increase installation and reduce cost. This article presents a new sustainable trigeneration system (power, heat and cool) based on a solid oxide fuel cell (SOFC) system integrated with an absorption chiller for special applications such as hotels, resorts, hospitals, etc. with a focus on plant design and performance. The proposal system is based on the idea of gasifying the municipal waste, producing syngas serving as fuel for the trigeneration system. Such advanced system when improved is thus self-sustainable without dependency on net grid, district heating and district cooling. Other advantage of such waste to energy system is waste management, less disposal to sanitary landfills, saving large municipal fields for other human activity and considerable less environmental impact. Although plant electrical efficiency of such system is not significant but fuel utilization factor along with free fuel, significant less pollutant emissions and self-sustainability are importance points of the proposed system. It is shown that the energy efficiency of such small tri-generation system is more than 83% with net power of 170 kW and district energy of about 250 kW. [ABSTRACT FROM AUTHOR]

Currently, water-cooled screw chiller is widely applied in commercial and industrial buildings, and the energy consumption of water chiller even could cover 70% of air-conditioning energy consumption in the most adverse operating conditions. Moreover, a number of chillers are running at a low rate under part-load state. In order to reduce the energy consumption of water-cooled screw chillers under part-load state, the paper presents the paralleling throttle mechanism. Through experimental study, under part-load state, it can be found that the by-pass tube diameter Ø16 has the most positive effect on the performance of water-cooled screw chiller in four by-pass tube diameters. The oblique access mode is better than the vertical access mode, while the spiral access mode has little influence on the chiller performance. Because of paralleling throttle using, the exergetic loss of the evaporator and chiller is able to be reduced by 3.4%-15.5% and 0-6.7%, respectively. Meanwhile, the coefficient of performance of chiller can be enhanced by 0.2%-1.6%, and discharge temperature can be reduced by 0.4-2.7 °C. In addition, the economic and environmental benefits of the advanced water-cooled screw chiller are more evident than the conventional water-cooled screw chiller's. [ABSTRACT FROM AUTHOR]

When receiving an urgent request from a smart grid, shutting down part of operating chillers directly in the air-conditioning system in a building can achieve immediate power reduction. However, no study has addressed how to determine the number of chillers/pumps to be shut down and how to regulate the load of retained equipment systematically during DR events. This paper presents a new approach to address these issues based on three schemes. A power demand optimization scheme predicts the building cooling demand and the power limiting threshold in response to a received DR request. A system sequence control resetting scheme determines the number of operating chillers/pumps to be retained. An online control/regulation scheme ensures the system power following the expected profile by regulating the total chilled water flow delivered to the building and therefore the chiller load. It also employs a cooling distributor to distribute chilled water to individual zones concerning different sensitivities/sacrifices to temperature increases. Case studies are conducted on a simulated dynamic building air-conditioning system. Results show that, during DR events, the proposed strategy can achieve the expected power reduction (i.e., about 23%) and also maintain acceptable zone temperature even though uncertainties exist in the prediction process. [ABSTRACT FROM AUTHOR]

The necessity of limitation of carbon dioxide emissions, which also concerns the energy sector, causes that more and more effective and efficient methods of CO2 capture from the flue gas are being tested. Among these technologies are adsorption ones, which have been used for a gas separation for many years. The characteristic features of adsorption separation are: long life of the sorbents used, low energy expenditure, and minim effect on the environment; however, their application requires adequate initial preparation of the flue gas fed into the system of CO2 separation so that the flue gas temperature is as low as possible, and there is no water content in it. The study presents the concept and numerical calculations of the system for preparation of the flue gas feeding the CO2 adsorption (vacuum pressure swing adsorption (VPSA)) separation unit, using the absorption chiller (AC). In the presented concept, the AC is driven by the flue gas which is used as both: upper and lower heat source for AC; however, due to the amount of energy being carried out with the flue gas, which is larger than required by the AC, the additional heat exchangers must be implemented. The calculations presented in the study show that owing to the application of AC, flue gas may be cooled down to temperatures even about 5 °C. Moreover, the simultaneous process of flue gas cooling and drying in such system is realized at low energy expenditure which leads to improvement of the overall energy efficiency of the system of CO2 separation from flue gas and also to reduction of its dimensions. [ABSTRACT FROM AUTHOR]

A three dimensional numerical scheme has been developed to examine geometrical configuration effects on the performance of a single bed adsorption chiller with a trapezoidal aluminum finned flat-tube heat exchanger (FFT HEx). A mathematical distributed model along with the linear driving force (LDF) model and Darcy’s law have been considered to take into account the effects of heat and both intra/inter-grain mass transfer resistances. The developed numerical scheme has also been validated experimentally by using a composite sorbent SWS-1L and water as a working pair. Additionally, rectangular beds with identical working conditions and bed dimensions as the tested trapezoidal beds have been examined in similar details to identify, which type of the fin geometry provides a superior performance. It was found that in this particular HEx, the heat transfer resistance is mainly influenced by both of the fin pitch and height, while the inter-grain mass transfer resistance is independently controlled by the bed length. This fact makes the role of the fin pitch and fin height almost interchangeable with respect to the cycle time and specific cooling power ( SCP ) especially in rectangular beds. However, the coefficient of performance ( COP ) is more influenced by the fin height than the fin pitch. In addition, higher SCP can be achieved at smaller bed dimensions at the expense of lower COP . Moreover, it was found that using rectangular bed is more appropriate, since its SCP is either the same or higher than its corresponding trapezoidal bed especially at shorter bed lengths, while COP remains almost the same for both bed types in all considered ranges of bed dimensions. Finally, a bed designing procedure has been proposed for proper designing of effective adsorption HExs based on the performed parametric studies. [ABSTRACT FROM AUTHOR]

The present work focuses on the design of a novel tri-generation system based on gasification of municipal solid wastes, a solid oxide fuel cell and an ammonia-water absorption chiller. Tri-generation systems can be implemented in buildings such as hospitals and hotels, where there is a continuous and large demand for electricity, heating and cooling. The system is modelled in Aspen Plus and the influence of different operating parameters on the system performance was studied. The findings suggest that low air equivalent ratios and high gasification temperatures enhance the overall system performance. Syngas cleaning with metal sorbents zinc oxide and sodium bicarbonate for the removal of hydrogen sulfide and hydrogen chloride concentrations proved to be very effective, reducing the concentration of contaminants to < 1 ppm (part per million) levels. The possibility of covering the demand profiles of a specific building was also investigated: the system could fully meet the electricity and cooling demands, whereas the heat requirements could be satisfied only up to 55%. Moreover, assuming 20 years of operation, the payback period was 4.5 years and the net present value exceeded 5 million euros. [ABSTRACT FROM AUTHOR]

Combined cooling, heating and power (CCHP) systems, which have the advantages of energy saving and environmental protection, have attracted more and more attentions. Great deals of works have been done, but most of them are theoretical research. It is still lack of experimental research for large scale CCHP system in practical application, and an overall off-design thermodynamic model is also desired to simulate or exam the system performance. In this work, a novel CCHP system integrated with dehumidification system is proposed for further utilizing waste heat, in which an internal combustion engine (ICE) is used as prime mover, its heat of flue gas and the heat of jacket water above 81 °C are used to drive absorption chiller, and the heat of jacket water below 81 °C is used to drive absorption dehumidifier. A comprehensive off-design thermodynamic model and evaluation of the system is established. The tested results of a MW CCHP system integrated with dehumidification system are used to validate the model, and the thermodynamic performance analysis is also carried out. The thermodynamic performance comparison between the CCHP system integrated with dehumidification system and conventional CCHP system has been done. The results show that: the simulated values are basically in keeping with those experimental results; when the output power of ICE is 1200 kW, the primary energy rate of the MW CCHP system can go up to 84.0%, the primary energy saving ratio achieves 32.77%, and exergy efficiency is 42.45%; the thermodynamic performance of the proposed CCHP system is better than conventional CCHP system. [ABSTRACT FROM AUTHOR]

In this study, an improved invasive weed optimization ( EIWO ) algorithm is investigated to solve the optimal chiller loading ( OCL ) problem for minimization of the power consumption. In the proposed algorithm, several components are developed, such as decimal-based representation, reproduction approach, spatial dispersal method, and competitive selection mechanism. Then, the local search strategy for elite weed is proposed, which can improve the searching ability of the algorithm. To verify the efficiency and effectiveness of the proposed algorithm, three well-known instances based on the OCL problem in air-conditioning systems are tested with the comparison with other recently published algorithms. The experimental results show that the EIWO algorithm can find equal or better optimal solution compared with other algorithms. The convergence ability, stability and robustness are also verified after the detailed comparisons. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate a solar cooling system with an absorption chiller driven by nanofluid based flat plate collectors. Pure water and water/Cu nanofluid (2% volumetric concentration) are the examined working fluids on the solar field and they are compared for steady-state conditions, as well as for daily operation. The system is optimized for steady-state conditions using a multi-objective procedure with energetic and exergetic criteria. The mean thermal efficiency enhancement by the use of nanofluids it is found close to 2.5%. The optimized system is further examined on a daily basis for operation with pure water and nanofluid. According to the final results, the use of nanofluids in the solar collector is able to enhance the exergetic performance of the system close to 4.0% and to increase the refrigeration production approximately 0.84% on a daily basis. The analysis is conducted with a developed model in Engineering Equation Solver. [ABSTRACT FROM AUTHOR]

This paper presents a multi-objective optimization model for estimating the cooling capacity of refrigeration in a trigeneration system for both grid on and off operating modes. In trigeneration systems, the cooling demand can be provided by single effect absorption and compression chillers (as the refrigeration system). Genetic Algorithm and LINMAP selection procedure are used for obtaining the final optimum point considering four-E analysis (energy, exergy, economy and emission) with the help of net future worth benefit difference (NFWBD) and global exergy efficiency objective functions. It was found that the NFWBD and exergy efficiency with cooling capacity of 1800 and 5600 kW for absorption and compression chillers, respectively, are 330 × 10 6 $ and 41.9% for grid on mode, while they reduce to 232 × 10 6 $ and 32.7% for grid off mode. Sensitivity analysis in grid on mode shows that the increase in the number of equipment (gas engine and chillers) leads to the decrease in both NFWBD and exergy efficiency, while selecting two similar absorption chillers (with cooling capacity of 900 kW), has payback period of 5.1 years, and provides the maximum NFWBD (321 × 10 6 $) and exergy efficiency (40.02%). [ABSTRACT FROM AUTHOR]

Thermally-driven absorption refrigeration technology is currently being discussed as possibly contributing to a more climate-friendly refrigeration supply. However, factors beyond technological and economic aspects influencing a broader diffusion of this technology have not yet been considered. This article presents results of a socio-technical constellation analysis identifying barriers against and drivers of a fortified dissemination of innovative low-temperature absorption chillers in a more comprehensive way. Results show that future perspectives of absorption refrigeration arise from a coincidence of mutually influencing factors, also including (lacking) know-how, experience, standard solutions, developed supplier structures and political framework conditions. Due to interdependencies with developments in the heat and electricity sector, targeted intervention requires integrated approaches. Future promotion of absorption refrigeration should be part of an optimised overall energy system perspective (electricity, heat, cold). [ABSTRACT FROM AUTHOR]

In this paper the experimental testing of a cascade chiller composed of an adsorption unit and a vapour compression unit is reported. The operation of the cascade under realistic operating conditions, differing for the temperature of the heat source available and the environmental temperature is analysed. A comparison was made between the application of the cascade and a vapour compression chiller only for air conditioning applications. According to the heat source temperatures, an increase in the electric COP of the system ranging from 25% to 50% was measured, with a maximum value of 8. An optimization of the system was subsequently proposed, by evaluating different adsorbent materials and refrigerants through the use of thermodynamic models. The theoretical study revealed that a performance up to 110% higher with respect to traditional chillers could be obtained if the cascade was used in refrigeration applications. [ABSTRACT FROM AUTHOR]

Mist is increasingly applied to precool outdoor air in heat rejection. This study investigates how the coefficient of performance of an air-cooled chiller varies with a mist precooler at different levels of cooling effectiveness. A multi-variate regression model was developed to simulate the operating variables of an aircooled chiller with mist precooling. The model was validated with typical performance data of an air-cooled centrifugal chiller. The coefficient of performance would increase by up to 30%, depending on the cooling effectiveness and the wet bulb depression -- the difference between the dry bulb and wet bulb temperatures of outdoor air. At a large wet bulb depression, the percentage increase of coefficient of performance tended to correlate linearly with the chiller capacity. Yet at a small wet bulb depression, the dynamic control of condensing temperature resulted in a non-linear relationship between the percentage change of coefficient of performance and the cooling effectiveness. Further experimental work is required to optimize cooling effectiveness for the maximum coefficient of performance. [ABSTRACT FROM AUTHOR]

A chiller plant consists of chiller, cooling tower, and pump subsystems. Two major configurations, primary-only and primary–secondary systems, are often used. Given the high energy costs of a plant, chiller plant operation optimization is important to save energy. For both configurations, chilled/condenser water supply temperatures are critical in improving chiller efficiency and should be considered as decision variables. However, nonlinearity of the problem is increased since chiller power consumption is a highly nonlinear function of these temperatures. Additionally, the problem is combinatorial considering the number of active units (e.g., chillers). In this paper, primary-only systems with identical units in each subsystem and primary–secondary systems with units of two sizes are studied, and both supply temperatures are optimized for energy savings. To obtain near-optimal solutions efficiently, a recent decomposition and coordination approach with little multiplier zigzagging and fast reduction of coupling constraint violations combining with sequential quadratic programming (SQP) is used. Penalties for the constraints that are difficult to be satisfied (e.g., mass balance constraints between fixed-speed pumps and variable-speed chillers) are added. After decomposition, complexity and nonlinearity of a subproblem are reduced drastically as compared with the original problem so that SQP is used. Numerical testing demonstrates that our approach is efficient in obtaining near-optimal solutions, and major energy savings are achieved as compared with benchmark strategies. The approach is scalable and can be used for chiller plant optimization and beyond. Note to Practitioners—Traditionally, chiller plant operation is often based on rules. For example, the number of active chillers is the minimum number that satisfies cooling requirements, and chilled water supply temperature is constant. Chiller power consumption is a nonlinear function of chiller cooling load and chilled/condenser water supply temperatures. Energy is wasted since chiller efficiency is low with fixed supply temperatures, and sometimes energy consumption of two chillers is less than that of one chiller. To save energy, chiller plant optimization with good decision variables such as the number of active units and chilled/condenser water supply temperatures is studied. The problem is challenging with high nonlinearity caused by considering such temperatures as decision variables. Furthermore, with discrete variables (e.g., the number of active chillers), the problem is combinatorial. To efficiently solve the problem for high-quality solutions, a novel decomposition and coordination approach is developed. Complexity and nonlinearity of a subproblem are reduced drastically after decomposition as compared with the original problem so that appropriate nonlinear methods are used to solve the subproblems. The results show that the solutions are near-optimal with short computational time and the approach is scalable. Additionally, major energy savings are achieved as compared with benchmark strategies. The approach provides a new and powerful way to solve chiller plant optimization problems and beyond. [ABSTRACT FROM AUTHOR]

The simulation studies of conventional small-scale adsorption chillers reported so far in literature incorporate a pre-determined user-defined cycle time which remains constant with the increasing number of cycles. This study presents the first attempt of the numerical simulation of a two-bed solar adsorption chiller with “adaptive” cycle time based on the temporal variations of temperatures and pressures existing inside the beds, the evaporator and the condenser. A water-stable metal organic framework (MOF), MIL-100(Fe), has been selected as the adsorbent while water has been chosen as the refrigerant. A flat-plate solar collector with three different glaze configurations, namely single-glazed (S-G), double-glazed (D-G) and single-glazed with transparent insulation material (TIM), has been employed. The performance of the two-bed adsorption chiller has been evaluated in terms of the variations of the specific cooling power ( SCP ), the coefficient of performance ( COP ) and the solar coefficient of performance ( COP sc ) with increasing number of cycles. [ABSTRACT FROM AUTHOR]

Air-cooled chillers normally operate under head pressure control without minimizing the electric power at part load operation. This study considers logistic regression to implement optimal control for an air-cooled chiller. Random forest models were developed for the chiller operating under two modes: the normal mode – switching on and off condenser fans at constant speed based on a fixed condensing temperature set point; the VSD mode – controlling all condenser fans at variable speed based on an adjustable set point instead. Genetic algorithm was then applied to simulate the maximum coefficient of performance (COP) with optimal operating variables. The COP at a low chiller load could increase by up to 110% and 67% in the normal and VSD modes, respectively. Logistic regression ascertained that the optimal control depended highly on the condensing temperature and the condenser airflow rate. The regression models served to adjust the condensing temperature set point to achieve maximum COP. [ABSTRACT FROM AUTHOR]

An absorption refrigeration system is environmental friendly a technology with zero ozone depletion and global warming potential. The LiBr-H2O solution in the generator is heated by any renewable source or industrial waste heat. In the present study the analysis of a parallel flow LiBr-H2O double-effect absorption refrigeration system is performed to compute the optimum system conditions from the point of maximum exergetic efficiency and coefficient of performance (COP), minimum exergy destruction. This analysis is also provides to more develop efficiencies of an absorption driven chiller system by using avoidable exergy analysis. For this purpose of an avoidable and unavoidable exergy destruction analysis is also conducted for each of absorption chiller component. Effect of main temperature difference on the conductance (UA), COP, exergetic efficiency is lent assistance to recover absorption refrigerant system. This study also is showed that how the changing the temperature difference effects total thermal conductance, COP and exergetic efficiency. [ABSTRACT FROM AUTHOR]

Configuring the number and size of chillers in a multiple-chiller plant properly is an efficient way to improve the plant energy efficiency. At the design stage, the optimal configuration can be achieved through matching the capacity to load as closely as possible across the full-load profile. However, in spite of the fact that current literature offers practical recommendations, a systematic method to optimize the configuration of multiple-chiller plants is lacking. Due to the lack of accurate information at the design stage and only limited knowledge of the eventual realization it is hard to predict the building’s cooling load. Moreover, there is no operational data to predict the system performance. Both explain the existence of uncertainty in the HVAC plant design process. This paper, therefore, proposes a strategy to optimize the configuration of multiple-chiller plants, which takes account of the load side uncertainty as well as the COP uncertainty and selects the optimal configuration through a life-cycle analysis. Both the load side uncertainty and the COP uncertainty are quantified using statistical distributions. To facilitate applications, the distributions of the cooling load profile of different types of buildings under different weather conditions are investigated and are classified into four categories, and the optimal configuration schemes under each type of cooling load distribution are analyzed and summarized in a tabulated form. [ABSTRACT FROM AUTHOR]

The refrigeration and air-conditioning system contribute significantly to building energy consumption. Therefore, it is necessary to develop new technologies that can achieve a higher coefficient of performance (COP). Employing a magnetic field (MF) on the condenser tube (between the condenser outlet and the capillary tube) is a new technique that helps in improving efficiency and cooling capacity of air-cooled vapour compression cycle (VCC) water chiller. In this work, four pairs of the permanent magnet of 3000 G field strength were installed on the condenser tube (between exit of the condenser and inlet of the capillary tube) of the VCC water chiller test setup. The performance of the test setup was compared by applying and removing an MF from the condenser tube to estimate an enhancement in the VCC water chiller system with an MF. Experiments were carried out using R404A as a primary refrigerant in the VCC system. This work discusses the outcomes of magnetic flux applied to the condenser tube at various locations of VCC on COP and power consumption of the water chiller unit. The percentage growth in refrigeration effect ranged between 0.58 and 8.82, and a higher value of the refrigeration effect of 8.82 was found by using the first magnet pair. Experimental outcomes show that compressor power consumption decreased by 4.43% with an increase in the number of magnet pairs from 1 to 4. The VCC system performance was improved by 8.94%. [ABSTRACT FROM AUTHOR]

A variable refrigerant flow (VRF) system is convenient to install and manage as well as the operability via occupants is superior compared to a chiller system. Thus, the use of the VRF system has increased in East Asia and Europe in recent years. In particular, a water-cooled VRF system can solve a space problem of installation for outdoor units in existing air-cooled systems. Thus, it can be applicable to large-sized buildings. However, most cooling tower operations are done with the same setup regardless of the changes in outdoor conditions during the operating period, which is a conservative method for a water-cooled mode. The present study aims to improve the performance of outdoor units in the VRF by reducing the temperature of cooling water to a lower temperature than the existing setup value and verify this through actual measurements. To do this, a new algorithm for a cooling tower operation was developed and applied to a six-week operation during the summer to analyze the effect of the change in setup value. The result showed that power consumption of the cooling tower system and VRF outdoor unit was reduced by 24% and 5.9%, respectively due to the new setup and the coefficient of performance (COP) of the outdoor unit and system was improved by 7.3% and 12.7%, respectively thereby reducing an operation cost by 11%. [ABSTRACT FROM AUTHOR]

This study investigates electricity saving potentials of mist coolers for air-cooled chiller systems in commercial buildings in a subtropical climate. Extensive operating data were collected from an experimental chiller with mist cooling of condenser air. The chiller had a nominal capacity of 282 kW and was retrofitted with dual condenser fan controls: constant speed with fixed condensing pressure and variable speed with floating condensing temperature. The variation of the cooling effectiveness of the cooler was identified to depend mainly on the wet bulb temperature, followed by the relative humidity and the multiplication of dry bulb temperature and relative humidity under fixed condensing pressure control. While under floating condensing temperature control, the significant independent variables for modelling cooling effectiveness were the wet bulb temperature, followed by the relative humidity and the condensing temperature. Simulation was conducted to find the hourly chiller system load distributions of a reference office building and a hotel in a subtropical climate. The probabilistic distribution of cooling effectiveness was examined with the hourly system load distributions under two system configurations with 6 chillers and 8 chillers. Using mist coolers improved the coefficient of performance of chillers by 0.70–9.35%, resulting in an annual electricity saving of 2.50–2.94% under the diverse patterns of weather and system load distributions. Mist coolers complemented the advanced condenser fan control and improved system configurations with 8 chillers. Higher electricity savings were achieved by prolonging the operation of chillers near full capacity. [ABSTRACT FROM AUTHOR]

Solar assisted absorption chiller is one of efficient cooling production systems for large cooling capacities. The main drawback of this system is that in addition to the electricity consumption, it demands for a lot of heat in relatively high temperature range of 90–120 °C, though the solar system may provide a significant portion of this heating demand. On the other hand, in gas transmission systems, there are some expansion stations in which gas pressure is reduced considerably and this pressure drop causes temperature collapse in gas stream. Power productive gas expansion station (PPGES) is the most recent design proponed for these stations in which the unit is equipped with power generation systems. In this work, taking advantage of this temperature fall for cooling production is proposed by coupling the station with an absorption chiller. In this case, the chiller could also provide the heating demand of the expansion station. In order to evaluate the effectiveness of the proposed configuration, it is simulated for a case study in Denmark, i.e. Aarhus University (AU) hospital absorption chiller and Viborg gas station. The results show that the expansion station could provide an annual cooling production contribution of 27%. In addition, the paper presents an extensive economic assessment to prove the impact of the proposed system economically. The results show a great enhancement in the levelized cost of energy (LCOE) of the case study in case of employing the hybrid system instead of the conventional chiller. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for systematic energy efficiency evaluation and optimization in turning operations, combining spindle, chiller and material removal models. Framing a joint machine-process design approach, the proposed study aims at selecting optimal combinations of cutting parameters (feed rate, depth of cut and spindle speed) for a given spindle-chiller assembly, able to minimize the energy consumption. Contrary to most of the literature, where the efficiency analysis is fully empirical, relying on extended cutting test campaigns, here a model-based approach is adopted. The goal is to characterize a key subsystem of modern machine tools, often used in both turning and milling machines, composed by a permanent magnet brushless direct-drive spindle with a dedicated chiller unit. Analytical relationships are identified, producing efficiency maps as a function of various process parameters. Physic-based models are exploited, reproducing electrical and mechanical energy dissipation occurring in the spindle and chiller units and in the material removal process. The models parameters are identified by a reduced set of spindle ramp-up and cutting tests, executed in an industrial context. Then, an overall process efficiency optimization is performed and discussed. [ABSTRACT FROM AUTHOR]

Summary: In this study, we present a novel teaching‐learning‐based optimization (TLBO) algorithm for solving the optimal chiller loading problem. The proposed algorithm uses a novel integer‐based encoding and decoding mechanism that is efficient and easy to implement. The teaching phase can improve the quality of learning process and thus enhance the exploitation ability. In addition, a well‐designed learning phase procedure is developed to enhance the learning process between one another in the population. A novel exploration and self‐learning procedures are embedded in the proposed TLBO algorithm, which can enhance the exploitation and exploration capabilities. The proposed algorithm is tested on several well‐known case studies and compared with several efficient algorithms. From the experimental comparisons, the efficient performance of the proposed TLBO is verified. [ABSTRACT FROM AUTHOR]

To implement the condenser water set point optimization, one can employ a regression model. However, existing regression-based methods have difficulties to handle non-linear chiller plant behaviour. To address this problem, we develop a Bayesian network model and compare it to both a linear and a polynomial regression model via a case study. The results show that the Bayesian network model can predict the optimal condenser water set points with a lower root mean square deviation for both a mild month and a summer month than the linear and the polynomial models. The energy-saving ratios by the Bayesian network model are 25.92% and 1.39% for the mild month and the summer month, respectively. As a comparison, the energy-saving ratios by the linear and the polynomial models are less than 19.00% for the mild month and even lead to more energy consumption in the summer month (up to 3.73%). [ABSTRACT FROM PUBLISHER]

The study described in this paper results from the observation that, when dealing with solar-driven absorption chillers, a compromise situation very likely exists between the collector efficiency and the coefficient of performance (COP) of the absorption cycle. An idea of a control strategy pursuing this objective, and thereby increasing the solar fraction for a solar absorption cooling cycle is consequently presented. The advantage of operating the solar chiller on a variable driving temperature is demonstrated. The theoretical analysis considers a solar chiller operated under moderate climate conditions of Poland. The model of the ammonia-water absorption chiller is described in detail, and the main assumptions of the iterative control procedure are explained. The effects of its application are computationally tested for one location and one type of solar collector, for representative days of three months during the cooling season. The results of the simulation are compared with the reference case of fixed driving temperature. According to the simulation results, it is possible to increase the cooling power yield at various levels, up to 34 W per 1 m 2 of solar collector, by adjusting the chiller driving temperature throughout the cooling season. The same, it is possible to more than double the cooling effect for some hours, with respect to fixed-temperature control operation. [ABSTRACT FROM AUTHOR]

Chilled water plants with multiple chillers are commonly used to provide cooling in large commercial buildings. Optimization offers a significant opportunity for improving the energy efficiency of such plants. Model based approaches used for control and optimization require accurate models, which can be difficult and/or expensive to obtain in practice due to large variations in equipment characteristics and operating conditions. In this paper, a model-free optimization strategy based on multivariate Extremum Seeking Control (ESC) with penalty terms is proposed for maximizing the energy efficiency of a chilled-water plant with parallel chillers. The feedback to ESC is the total power consumption of the plant consisting of chiller compressors, cooling tower fan, and condenser water pumps, in combination with penalty terms for input-saturation. The control inputs include the cooling tower fan airflow, condenser water flows and evaporator leaving chilled-water temperature setpoint. A band-pass filter array, instead of the high-pass filter in the standard ESC, is adopted to reduce the coupling among the input channels. The proposed strategy is evaluated with simulation study using a Modelica based dynamic simulation model of a chilled-water plant with two parallel chillers. Six cases are presented that demonstrate real-time optimization capability of ESC for this application. [ABSTRACT FROM AUTHOR]

In the solar absorption cooling systems, concentrating collector can be adopted to achieve higher driven temperature and improve the system performance. The Compound Parabolic Concentrator (CPC) is a good option with both concentrating and stationary features. With higher working temperature, solar absorption cooling system with concentrating collector has more choices of absorption chillers than the system with non-concentrating collector. The aim of this paper is to find the better chiller choice for solar absorption cooling systems with CPC. The analyzed LiBr-water absorption chillers include the single effect chiller, the double effect absorption chiller and a novel variable effect chiller built by the author. Simulation is carried out in TRNSYS. Model of the variable effect absorption chiller is first derived from MATLAB artificial neural network (ANN) toolbox based on experimental data, and then built in TRNSYS. Performance of the three systems is calculated under the same condition. Performance of the three systems is compared to get the better choices. The impacts of the solar collector area, cutoff driven temperature and storage tank volume on the solar cooling fraction, auxiliary heat input, average chiller COP and average solar efficiency are analyzed. The variable effect system has high solar cooling fraction, low auxiliary heat input and high solar efficiency. The single effect system has medium solar fraction, high auxiliary heat input and medium solar efficiency. The double effect system has low solar cooling fraction, low auxiliary heat input and low solar efficiency. [ABSTRACT FROM AUTHOR]

Absorption chillers are a viable option for providing waste heat-powered cooling or refrigeration, thereby improving overall energy efficiency-less primary energy input, lower emissions, and cost savings. This study focuses on the assessment of aqueous lithium-based salt solutions as working fluid for absorption chiller in exploring the possibility of developing new mixtures for absorption chillers to improve the performance of the absorption refrigeration systems (ARSs). In this paper, the coefficient of performance (COP) of a single-effect absorption chiller using aqueous lithium-based salt solutions (LiF-H2O, LiCl-H2O, LiBr-H2O, and LiI-H2O) as working fluid was assessed using Aspen Plus®. The simulation results obtained showed that the mass and energy were well balanced for all systems. Furthermore, a direct proportionality relationship between COP of absorption chillers and the van't Hoff factor, i of dissociated aqueous salt solutions was observed. The highest COP value is 0.8930 for LiI-H2O among others. [ABSTRACT FROM AUTHOR]

We synthesized a series of silico-aluminophosphates with a CHA-type microporous structure (SAPO-34) under hydrothermal conditions with different silicon to aluminum (Si/Al) ratios and systematically studied the effect of the Si/Al ratio on the structural properties and the water-adsorption capacity of the SAPO-34 adsorbents. The crystallinity, pore volume and surface area of the SAPO-34 increased with an increasing the SiO2/Al2O3 up to 1.0, and the amount of water adsorption also increased with the same trend. However, as increasing the ratio more, these properties became worse. SAPO-34 with SiO2/Al2O3 = 1 exhibited the highest water adsorption amount (0.359 gwater/gsorbent) at 308 K and 30% relative humidity. In order to enhance the water-adsorption capacity further, we impregnated the SAPO-34 with hygroscopic salts, LiCl and CaCl2. The amount of water adsorption at 308 K and 30% relative humidity was increased up to 0.584 and 0.664 gwater/gsorbent for the LiCl@SAPO-34 and CaCl2@SAPO-34 respectively. However, after several cycles of adsorption (308 K, 12 Torr)-desorption (353 K, 42 Torr) conditions of typical adsorption chiller, the CaCl2@SAPO-34 lost more than 81% of its working capacity. On the other hand, LiCl@SAPO-34 maintained well the working capacity during five cycles. SAPO-34 impregnated with LiCl is a highly promising water adsorbent for the application of adsorption chiller. [ABSTRACT FROM AUTHOR]

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The configuration, design and operation strategy are the main factors that can affect the technical, economic and environmental performances of combined cooling, heating and power (CCHP) system. In this paper, the operation of a CCHP system with fired heat recovery steam generator (HRSG), electric chiller, absorption chiller and a boiler is classified into one of three scenarios which are determined by gas turbine size and magnitude of thermal and electric loads. The optimal operating strategies are presented for these scenarios. For scenario with high cooling loads, we derive analytical expressions for calculation of ratio (electricity price/natural gas price) values which delimit three optimal modes for providing cooling demand in summer, thereby enabling selection of optimal operating strategy without numerical optimization. We examine the optimal design of CCHP system in three climate zones based on the proposed strategy. Supplementary firing as well as a higher coefficient of performance (COP) of the absorption chiller increase system efficiency and enable reduction of gas turbine size. Our case studies show that supplementary firing, (for some values of price ratio, absorption chiller COP and climate zone) the electric chiller and/or the boiler are necessary components to achieve optimal system performance. [ABSTRACT FROM AUTHOR]

Power grids connected to renewable energy sources must cope with fluctuating output by those sources. One method to do so is for the power grid company to accept bids to increase grid stability. These bids are accepted via capacity market auction of increasing grid stability. These offers are to increase the maximum power capacity by using power stations (both utility and non-utility stations) and by reducing electricity consumption via demand response. One candidate for achieving this is a district heating and cooling (DHC) system installed with combined heat and power. However, the electricity adjustment (EA) operation needed by the DHC for the auction is complicated because the system consists of boilers, water heaters, chillers, generators, and other items. To investigate the possibility of using DHC systems for capacity market auctions, this paper proposes two models for operating a DHC system: electricity-adjustment capacity (EAC) provision and EA operation. In addition, to develop methods for evaluating the cost of the proposed operational methods, a model DHC system is formulated with an actual DHC system as a basis. Using the models, numerical simulations are conducted by particle swarm optimization. Then, the running costs of EAC, EA, and normal operation are calculated. The results show that the running costs of the proposed operations are relatively stable by day and season, not varying beyond the range of ±10%. Nevertheless, the running costs in spring and fall are be lower than those in summer and winter. The cost of providing EAC is no more than 1% the cost of normal operation, and the cost of EA itself is no more than 2% that of normal operation. [ABSTRACT FROM AUTHOR]

District cooling system (DCS) is recognized to be highly energy efficient compared to equivalent conventional systems being operated at individual buildings. In this paper, it was verified from the performance analysis of a DCS plant based on current operation data. The seasonal coefficient of performance (COP) for the centrifugal chillers was 5.16. The value was lower compared to the design one but still higher with respect to the conventional system. Furthermore, the seasonal energy efficiency ratio of the cooling source system (EER sys ) reached 3.85. The analysis showed that the lower value associated with the low occupancy ratio and lower temperature difference between the supply and return water. Our work was much significant in the planning and operation for the plant at the next stage. On the other hand, the operation experience was also worth considering for other projects. [ABSTRACT FROM AUTHOR]

As an important part of urban public transport, how to reduce energy consumption of rail transit becomes a focused issue. Considered with the operating characteristic of air conditioning in subway station, solution method with large temperature difference and high outlet temperature of 10/17 Celsius in evaporator is put forward. Two condensers and evaporators are linked in series and both of them are in countercurrent form, in which condition the energy efficiency can be improved greatly. Simultaneously high efficiency chiller with two different capacities of compressor heads is designed to improve the energy efficiency in part load. Experimental research of high efficiency chiller is conducted and the results show that: With the decrease of load percentage, COP (coefficient of performance) is fluctuated from 6.2 to 7.0. With the increase of outlet chilled water, COP increases greatly; while with the increase of outlet cooling water, COP decreases greatly. In this system at the design condition, COP can reach as high as 7.01, which can supply database for utilization of chiller in subway station air conditioning system. [ABSTRACT FROM AUTHOR]

Chiller consumes a significant power ratio in HVAC system. In order to minimize the power consumption of chiller, many efforts have been made on load predictions and optimal control strategies. The performance of chiller (e.g., COP) and dedicated devices (e.g., operation variables) play very important roles in chiller power consumption. However, it is difficult to find proper model to predict accurate chiller COP chiller in practice. Moreover, how the operating variables of the chiller system affects the over power consumption need to be identified. This paper therefore aims to find out a simple and accurate COP prediction model for chiller and investigates the optimal values of operating variables related to the chiller system. By com-paring kinds of models (e.g., SL, BQ, MP, GNU, QHP and BP-ANN), BP-ANN is considered as the proper model in predicting COP of chiller accurately. By adopting GA-based operating variables identification, optimal values of the variables can be found in specified ranges as well. This study evaluates the performance of different COP prediction models by using actual operation data of chiller plant in a commercial building. Furthermore, optimal settings for operating variables have also been identified in resulting of minimum power consumption of chiller plant. [ABSTRACT FROM AUTHOR]

Hybrid Ground Source Heat Pump (HGSHP) system has been widely used for mitigating the heat accumulation problem of conventional GSHP systems. This paper proposes a wet-bulb temperature-based control method for a HGSHP system which comprises a GSHP and a conventional water-cooled chiller (WCC) by using a cooling tower. With this method, the operation priority between the GSHP and the water-cooled chiller is determined according to the outdoor web-bulb temperature. A TRNSYS platform of the system is developed and simulations are carried out to investigate the system performance under the proposed control method. Meanwhile, simulations with two other control methods (reference methods), i.e., the GSHP-prioritized method and WCC-prioritized method, are also conducted. The study results show that the proposed control method has obvious advantage in controlling the heat balance of the ground source heat exchangers, and at the meantime no more energy is consumed when compared with the two reference control methods. [ABSTRACT FROM AUTHOR]

Chiller plants are often operated in drastically different conditions other than the design. Consequently, the optimal control has to be developed and implemented based on the real operation conditions to improve the efficiency. This study presents a Web-based online control system implementation in a chiller plant for a hospital as a case study. The primary optimization measures include an optimal number of chillers in operation, optimal chilled water and condensing water pump speeds, and optimal cooling tower fan speed. The measured chiller plant savings is 24.6%. [ABSTRACT FROM AUTHOR]

Chiller sequencing control is a vital function for the feasible and energy-efficient operation of multiple-chiller plant in a centralized HVAC system. Various control strategies have been developed and applied to achieve overall energy efficiency of chiller plant with guarantying sufficient cooling for indoor thermal comfort. However, these control strategies suffer from various uncertainties and usually fail to achieve the expected control and/or energy performance. Therefore, this study presents a robustness analysis of chiller sequencing control in order to understand the robustness of the typical control strategies under uncertainties. Based on the robustness analysis, a simple and applicable control method is developed to enhance the robustness and reliability of chiller sequencing control under uncertainties. [ABSTRACT FROM AUTHOR]