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The purpose of this study was to develop mathematical models for air-cooled chillers and their components using innovative varied row configurations as a parameter analysis model followed by a simulation of actual operational performance. In this manner, we were able to observe the increase in performance of air-cooled chillers and the energy transfer efficiency of individual components. This study found that the innovative varied row configuration (Type C) can increase the COP of air-cooled chiller by 6.7% over that of traditional condensing-coil configuration (Type A) with an increase in total irreversibility and the irreversibility of the condenser of 8.4% and 4.1%, respectively; Type C can increase the COP of air-cooled chiller by 3.3% over that of the best condensing-coil configuration (Type B) with an increase in total irreversibility and the irreversibility of the condenser of 1.6% and 4.6%, respectively. We believe that the results of this research can provide an important basis of reference for future design of air-cooled chiller units.
Wu Chieh Wu; Tzong Shing Lee; Chich Hsiang Chang. Improved Energy Performance of Air-Cooled Liquid Chillers with Innovative Condensing-Coil Configurations. Applied Mechanics and Materials 2013, 284-287, 785 -789.
AMA StyleWu Chieh Wu, Tzong Shing Lee, Chich Hsiang Chang. Improved Energy Performance of Air-Cooled Liquid Chillers with Innovative Condensing-Coil Configurations. Applied Mechanics and Materials. 2013; 284-287 ():785-789.
Chicago/Turabian StyleWu Chieh Wu; Tzong Shing Lee; Chich Hsiang Chang. 2013. "Improved Energy Performance of Air-Cooled Liquid Chillers with Innovative Condensing-Coil Configurations." Applied Mechanics and Materials 284-287, no. : 785-789.
This study evaluates the performance prediction ability and model suitability of eleven empirically-based performance models for centrifugal water chillers. Specifically, this study uses over 2000 datasets with a constant or variable chilled water flow rate for fixed or variable speed drive centrifugal liquid chillers. The best regression coefficients for each empirical-based model were obtained using the ordinary least squares (OLSs) method. The model prediction accuracy of each empirical-based model is based on the coefficient of variation of root-mean-square error (CV). The evaluation for model suitability is based on the considerations of prediction ability, the complexity in training datasets, the effort needed to calibrate, the generality of the model, and its ability to physically interpret the model regression coefficients in this study. Results show that among the eleven empirical-based models, the BQ (CV = 0.54%), MP (CV = 0.61%), SMP (CV = 0.70%), and MDOE-2 (CV = 0.63%) models have overall prediction CV values under 1% for all kinds of datasets and achieve extremely good prediction accuracy. Because the MDOE-2 model has a more complicated datasets training process than the BQ, MP, and SMP models, and it has no ability to physically interpret the model regression coefficients, the BQ, MP, and SMP models have the best suitability. The results of this study provide important reference values for selecting empirically-based performance models for energy analysis, optimal operating control, energy efficiency measurement and verification (M&V), and the development of fault detection and diagnosis (FDD) systems in centrifugal water chillers.
Tzong-Shing Lee; Ke-Yang Liao; Wan-Chen Lu. Evaluation of the suitability of empirically-based models for predicting energy performance of centrifugal water chillers with variable chilled water flow. Applied Energy 2012, 93, 583 -595.
AMA StyleTzong-Shing Lee, Ke-Yang Liao, Wan-Chen Lu. Evaluation of the suitability of empirically-based models for predicting energy performance of centrifugal water chillers with variable chilled water flow. Applied Energy. 2012; 93 ():583-595.
Chicago/Turabian StyleTzong-Shing Lee; Ke-Yang Liao; Wan-Chen Lu. 2012. "Evaluation of the suitability of empirically-based models for predicting energy performance of centrifugal water chillers with variable chilled water flow." Applied Energy 93, no. : 583-595.
This study constructed a parameter analysis for improving the energy performance of air-cooled water chillers by altering the angle configuration of the condenser coils. The mathematical models for energy and exergy analyses of the individual components and overall system of air-cooled water chillers are presented. This study investigated the potential enhancement of performance efficiency in air-cooled chillers and the energy conversion efficiency of each component, in order to determine how the angle configuration of condenser coils influences chiller performance. This study found that the overall performance of an air-cooled chiller could be improved by approximately 3.4%, and the total irreversibility could be reduced by approximately 2.7%. With each 1% increase in average wind speed over the condenser coils, the overall performance of an air‑cooled chiller was found to be enhanced by approximately 0.43%, and its total irreversibility was reduced by approximately 0.35%. The results of this study can be effectively applied to air-cooled condenser units, and can provide an important basis of reference for developing and enhancing the energy efficiency of air-cooled chillers.
Wu-Chieh Wu; Tzong-Shing Lee; Chich-Hsiang Chang. Energy and Exergy Analysis for Improving the Energy Performance of Air-Cooled Liquid Chillers by Different Condensing-Coil Configurations. Entropy 2012, 14, 517 -532.
AMA StyleWu-Chieh Wu, Tzong-Shing Lee, Chich-Hsiang Chang. Energy and Exergy Analysis for Improving the Energy Performance of Air-Cooled Liquid Chillers by Different Condensing-Coil Configurations. Entropy. 2012; 14 (3):517-532.
Chicago/Turabian StyleWu-Chieh Wu; Tzong-Shing Lee; Chich-Hsiang Chang. 2012. "Energy and Exergy Analysis for Improving the Energy Performance of Air-Cooled Liquid Chillers by Different Condensing-Coil Configurations." Entropy 14, no. 3: 517-532.
Mal-distribution of airflow is an important factor for the performance of air-cooled multi-coil air-cooled condensers. This study is an attempt to investigate the effects of different included angles between the coils of the condenser. It has been found in this study that it can be a mean to improve the performance of multi-coil condensers without using larger heat transfer surfaces. A commercially used four-coil condenser of an air-cooled water chiller was used as the base case in the tests and analysis. The results show that the variation of the included angle can increase the airflow rate by 7.85%, which corresponds to 5.29% increase in heat transfer. The improvements were found to be due to the reduction of the stagnant flow regions of the heat exchanger coils, and more even flow distribution through the coils. Test data were used to verify the computer model of the four-coil heat exchanger. The same tested fan performance characteristic was used in all of the analyses. The research results are important as air-cooled condensing units can be designed to better performance merely by changing the configuration of the coil arrangements.
Tzong-Shing Lee; Wu-Chieh Wu; Yew-Khoy Chuah; Sheng-Kai Wang. An improvement of airflow and heat transfer performance of multi-coil condensers by different coil configurations. International Journal of Refrigeration 2010, 33, 1370 -1376.
AMA StyleTzong-Shing Lee, Wu-Chieh Wu, Yew-Khoy Chuah, Sheng-Kai Wang. An improvement of airflow and heat transfer performance of multi-coil condensers by different coil configurations. International Journal of Refrigeration. 2010; 33 (7):1370-1376.
Chicago/Turabian StyleTzong-Shing Lee; Wu-Chieh Wu; Yew-Khoy Chuah; Sheng-Kai Wang. 2010. "An improvement of airflow and heat transfer performance of multi-coil condensers by different coil configurations." International Journal of Refrigeration 33, no. 7: 1370-1376.
This paper presents an evaluation of six empirically-based models for predicting water chiller energy performance using over 1000 chiller data sets from chiller manufacturers and field measurements. The data sets comprise three broad classifications, including (1) constant condenser and constant chilled water flow, (2) constant condenser and variable chilled water flow, and (3) variable condenser and variable chilled water flow. The regression parameters for each performance model are obtained using least squares method. The criteria for evaluating the predictive ability of models are based on the coefficient of variation of root-mean-square error (CV). Results show that among the six empirically-based performance models for water chillers in this study, the bi-quadratic regression model (CV = 2.2%) and the multivariate polynomial regression model (CV = 2.25%) have the best prediction accuracy for all kinds of data sets. The results of this study can be used as a reference for selecting empirically-based models for the purposes of energy analysis, performance prediction, evaluation of energy-efficiency improvements, and fault detection and diagnosis of water chillers. Keywords Water chiller Performance Energy consumption Model Accuracy Comparison Nomenclature B vector of estimated parameters β i of the regression models COP coefficient of performance CV coefficient of variation of root-mean-square error, defined by Eq. (11) . CV overall overall coefficient of variation of root-mean-square error, defined by Eq. (14) . E vector of residual N total number of data sets n number of data sets Q ˙ e chiller cooling capacity (kW) RMSE root-mean-square error, defined by Eq. (12) . T temperature (K or °C) V mass flow rate (kg s −1 ) W ˙ c electrical power input to compressor X vector of the independent variables Y vector of observations on the true dependent variable Y ˆ vector of observations on the estimated dependent variable Z 95% confidence interval Greek symbols ε vector of errors between target and fitted outputs β estimated parameters Subscripts ci water inlet to condenser i independent variable ( i = 1,…,m) m measured p predicted wi water inlet to evaporator wo water outlet from evaporator 1 Introduction Vapor-compression water chillers have been widely used to cool water or secondary coolant for air-conditioning and refrigerating applications in both commercial and industrial fields. Fig. 1 shows that the main components of a vapor-compression water chiller include compressor and its driver, condenser, throttling device, and evaporator (liquid cooler). The coefficient of performance (COP) for water chillers is defined as the ratio of the evaporator cooling capacity to the compressor input power. Practically, it is more convenient to express chiller performance COP in terms of readily measured water-side data rather than refrigerant-side data. This is especially true for the purposes of performance prediction, evaluation of energy-efficiency improvements, and fault detection and diagnosis of water chillers [1–8] . Measurable water-side data include condenser inlet and outlet water temperatures, evaporator inlet and outlet water temperatures, and condenser and evaporator water flowrates. Therefore, developing chiller performance model by using water-side data has been a subject of many studies over the last decade. Previous empirically-based models for water chillers can generally be classified into two categories: gray-box (semi-empirical) and black-box (empirical) models [3,9] . In a gray-box approach, the functional form of the chiller model allows the parameter estimates be traced to actual physical principles that govern the performance of the water chillers being modeled. Model parameters or fitting coefficients are determined using a regression method applied to a set of training data obtained from chiller manufacturers, laboratory and field measures. Examples of gray-box studies include Gordon et al. [10] , Ng et al. [11] , and Lee [5] . The functional form of black-box models is developed by either statistical or non-statistical methods. However, the estimated model parameters of the models have no physical interpretations. Black-box models often require less time and effort to develop and use compared to gray-box approaches, but they cannot be used to extrapolate performance beyond the data range for which they were developed [9] . A number of researchers have used a black-box approach to predict performance of water chillers [1,2,4,12,13] . A review of the literature shows that comprehensive comparison studies on empirically-based model for predicting performance of water chillers are still lacking. To fill this gap, this study evaluates the suitability of empirically-based performance models for water chillers available in the literature. The empirically-based performance models selected in the study include the (1) simple linear regression model [13] ; (2) bi-quadratic regression model [12] ; (3) multivariate polynomial regression model [2,4,14] ; (4) Gordon–Ng universal model [15] ; (5) Gordon–Ng simplified model [16] ; and (6) Lee’s simplified model [5] . This study uses over 1000 chiller data sets from major chiller manufacturers and field measurement to test these models in previous studies. The data sets comprise three broad groups, including (1) constant condenser and constant chilled water flow, (2) constant condenser and variable chilled water flow, and (3) variable condenser and variable chilled water flow. The regression parameters or fitting coefficients for each empirically-based model are estimated using the least squares method. The criteria for evaluating model suitability are based on the coefficient of variation of root-mean-square error (CV), an assessment for predictive ability. The results obtained in this work could be served as a reference when selecting an empirically-based...
Tzong-Shing Lee; Wan-Chen Lu. An evaluation of empirically-based models for predicting energy performance of vapor-compression water chillers. Applied Energy 2010, 87, 3486 -3493.
AMA StyleTzong-Shing Lee, Wan-Chen Lu. An evaluation of empirically-based models for predicting energy performance of vapor-compression water chillers. Applied Energy. 2010; 87 (11):3486-3493.
Chicago/Turabian StyleTzong-Shing Lee; Wan-Chen Lu. 2010. "An evaluation of empirically-based models for predicting energy performance of vapor-compression water chillers." Applied Energy 87, no. 11: 3486-3493.
This work applies the second-law analysis of thermodynamics to quantify the exergy destruction of the components of screw liquid chiller, and to identify the potential for each component to contribute to improve the overall energy efficiency of the system. Three screw liquid chiller units were built to demonstrate the feasibility of the model presented herein. Unit A was a 100 RT water-cooled screw liquid chiller. Unit B was modified from Unit A by switching the old condenser for a new one with a greater heat transfer, and Unit C was modified from Unit B by exchanging the compressor for a more efficient one. The results indicate that the compressor has the largest potential to improve energy efficiency, followed in order by the condenser, and then the evaporator. The second law analysis may help engineers to focus on the components with higher exergy destruction and quantify the extent to which modifying such components can influence, favorably or unfavorably, the performance of other components of the screw liquid chiller.
Tzong-Shing Lee. Second-Law Analysis to Improve the Energy Efficiency of Screw Liquid Chillers. Entropy 2010, 12, 375 -389.
AMA StyleTzong-Shing Lee. Second-Law Analysis to Improve the Energy Efficiency of Screw Liquid Chillers. Entropy. 2010; 12 (3):375-389.
Chicago/Turabian StyleTzong-Shing Lee. 2010. "Second-Law Analysis to Improve the Energy Efficiency of Screw Liquid Chillers." Entropy 12, no. 3: 375-389.