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01722 A fault detection and diagnosis strategy of VAV air-conditioning systems for improved energy and control performances
10 Space heating and cooling~heat pumps
SPACE HEATING AND COOLING/HEAT PUMPS
10
06/01721 A comparative study of water as a refrigerant with some current refrigerants Kilicarslan, A. and Miiller, N. International Journal of Energy Research, 2005, 29, (11), 947-959. Water as a refrigerant (R718) is compared with some current natural (R717 and R290) and synthetic refrigerants (R134a, R12, R22, and R152a) regarding environmental issues including ozone depletion potential (ODP) and global warming potential (GWP), safety (toxicity and flammability), operating cost, refrigeration capacity and coefficient of performance (COP). A computer code simulating a simple vapour compression cycle was developed to calculate COPs, pressure ratios, outlet temperatures of the refrigerants from the compressor, and evaporator temperatures above which water theoretically yields better COPs than the other refrigerants investigated. The main difference of this study from other similar studies is that both evaporator temperature and condenser temperature are changed as changing parameters, but the temperature lift, which is the temperature difference between condenser and evaporator, are held constant and the irreversibility during the compression process is also taken into consideration by taking the isentropic efficiency different from 100%. It is found that for evaporator temperatures above 20°C and small temperature lift (5 K), R718 gives the highest COP assuming exactly the same cycle parameters. For medium temperature lifts (20-25 K), this evaporator temperature is above 35°C, whereas for even greater temperature lifts it decreases again. Furthermore, with increased values of polytropic efficiency, R718 can maintain higher COPs over other refrigerants, at lower evaporator temperatures.
06/01722 A fault detection and diagnosis strategy of VAV air-conditioning systems for improved energy and control performances Qin, J. and Wang, S. Energy and Buildings, 2005, 37, (10), 1035-1048. This paper presents the results of a site survey study on the faults in variable air volume (VAV) terminals and an automatic fault detection and diagnosis (FDD) strategy for VAV air-conditioning systems using a hybrid approach. The site survey study was conducted in a commercial building. 20.9% VAV terminals were ineffective and 10 main faults were identified in the VAV air-conditioning systems. The FDD strategy adopts a hybrid approach utilizing expert rules, performance indexes and statistical process control models to address these faults. Supported by a pattern recognition method, expert rules and performance indexes based on system physical characteristics are adopted to detect 9 of the 10 faults. Two pattern recognition indexes are introduced for fault isolation to overcome the difficulty in differentiating damper sticking and hysteresis from improper controller tuning. A principal component analysis (PCA)-based method is developed to detect V A V terminal flow sensor biases and to reconstruct the faulty sensors. The FDD strategy is tested and validated on typical VAV air-conditioning systems involving multiple faults both in simulation and in situ tests.
06101723 coil
A model for the dynamic response of a cooling
Yu, X. et al. Energy and Buildings, 2005, 37, (12), 1278-1289. The purpose of this study is to develop and evaluate simulation models for the dynamic performance of dry and wet cooling coils. The energy consumed by a building air conditioning system is directly related to that in the cooling coil. A dry-area model without consideration of condensation is established with three energy equations, and a wet-area model is developed based on a mass balance equation for moist air and three energy equations for the air, tube/fin, and working fluid. The derivatives with respect to the time variable are approximated using an explicit method, and the upwind approximation is used for the spatial variables. The results of the dry-area model show good agreement with those for the effectiveness method and the dynamic responses have reasonable physical meaning. The wet-area model is first compared to the dry-area model, and then the wet conditions are applied. A new factor called the mass transfer efficiency as a parallel to the total fin efficiency is introduced in the mass balance equation for the wet-area model to produce consistent results. The dynamic responses for several practical operations related to changing inlet conditions are reported. Comparisons indicate that the model predictions show good agreement with experimental data.
06/01724 A model-based online fault detection and diagnosis strategy for centrifugal chiller systems Cui, J. and Wang, S. International Journal of' Thermal Sciences, 2005, 44, (10). 986-999.
264
Fuel and Energy Abstracts July 2006
The paper presents an online adaptive strategy for the fault detection and diagnosis of centrifugal chiller systems. The strategy is developed based on six physical performance indexes. These performance indexes have the capability to describe the health condition of centrifugal chillers and particularly to account for existing chiller faults. A set of rules for faults and their impacts on the six performance indexes are deduced from theoretical analysis, and then serve as the fault classifier. The benchmarks of the performance indexes are provided by simplified reference models, whose parameter identification is simple. In addition, an online adaptive scheme is developed, by analysing uncertainty coming from both model-fitting errors and measurement errors, to estimate and update the thresholds for detecting abnormal performance indexes. The FDD strategy is validated by both field data collected from a real building chiller system and by laboratory data provided by an A S H R A E research project.
06/01725 Air-side heat transfer enhancement of a refrigerator evaporator using vortex generation Sommers, A. D. and Jacobi, A. M. International Journal of Refrigeration, 2005, 28, (7), 1006-1017. In most domestic and commercial refrigeration systems, frost forms on the air-side surface of the air-to-refrigerant heat exchanger. Frosttolerant designs typically employ a large fin spacing in order to delay the need for a defrost cycle. Unfortunately, this approach does not allow for a very high air-side heat transfer coefficient, and the performance of these heat exchangers is often air-side limited. Longitudinal vortex generation is a proven and effective technique for thinning the thermal boundary layer and enhancing heat transfer, but its efficacy in a frosting environment is essentially unknown. In this study, an array of delta-wing vortex generators is applied to a plain-finand-tube heat exchanger with a fin spacing of 8.5 ram. Heat transfer and pressure drop performance are measured to determine the effectiveness of the vortex generator under frosting conditions. For air-side Reynolds numbers between 500 and 1300, the air-side thermal resistance is reduced by 35-42% when vortex generation is used. Correspondingly, the heat transfer coefficient is observed to range from 33 to 53 W m 2 K - 1 for the enhanced heat exchanger and from 18 to 26 W m 2 K i for the baseline heat exchanger.
06101726 An implicit curve-fitting method for fast calculation of thermal properties of pure and mixed refrigerants Ding, G. et al. btternational Journal of Refrigeration, 2005, 28, (6), 921 932. Calculations of refrigerant thermal properties are desired to be very fast and stable in cases of simulation of refrigeration system, etc. The traditional method based on equation of state cannot meet such requirement because of unavoidable iterations in calculation. In this paper, a new calculation method for refrigerant thermal properties is presented. Low order implicit polynomial equations are got by using curve-fitting method at first, and then explicit formulae for calculating refrigerant thermal properties quickly are obtained by getting the analytical solution of these implicit equations, Explicit fast calculation formulae for thermal properties of R22 and R407C, covering the saturated temperature of - 6 0 ~ 8 0 ° C and superheat of 0-65°C, are presented as examples. The calculation speeds of the formulae of R22 are about 140 times faster than those of R E F P R O P 6.01 while the formulae of R407C are about 1000 times faster. The total mean relative deviations of the fast calculation formulae for R22 and R407C are less than 0.02%.
06/01727 Application of integrating multi-zone model with CFD simulation to natural ventilation prediction Tan, G. et al. Energy and Buildings, 2005, 37, (10), 1049-1057. Predicting the performance of natural ventilation is difficult, especially for large-scale naturally ventilated buildings, due to the lack of accurate and efficient prediction tools. This paper presents a strategy, integrating a multi-zone model and computational fluid dynamics (CFD), to improve natural ventilation prediction and design methods. Large openings and atrium configurations are broadly used in naturally ventilated buildings to promote buoyancy force and optimize air movement. How to properly deal with this typical configuration for a multi-zone model and integrated simulation is discussed and compared in this paper. In order to validate a newly developed multi-zone model program, MMPN, this paper investigated both buoyancy ventilation and wind-buoyancy combined ventilation. Integration strategies, transferring data (velocity or pressure) from a multi-zone model program to CFD as boundary conditions, are also studied.
06/01728 Application of multi-output ARX models for estimation of the U and g values of building components in outdoor testing Jim6nez, M. J. and Heras, M. R. Solar Energy, 2005, 79, (3), 30~310.
SPACE HEATING AND COOLING/HEAT PUMPS
10
06/01721 A comparative study of water as a refrigerant with some current refrigerants Kilicarslan, A. and Miiller, N. International Journal of Energy Research, 2005, 29, (11), 947-959. Water as a refrigerant (R718) is compared with some current natural (R717 and R290) and synthetic refrigerants (R134a, R12, R22, and R152a) regarding environmental issues including ozone depletion potential (ODP) and global warming potential (GWP), safety (toxicity and flammability), operating cost, refrigeration capacity and coefficient of performance (COP). A computer code simulating a simple vapour compression cycle was developed to calculate COPs, pressure ratios, outlet temperatures of the refrigerants from the compressor, and evaporator temperatures above which water theoretically yields better COPs than the other refrigerants investigated. The main difference of this study from other similar studies is that both evaporator temperature and condenser temperature are changed as changing parameters, but the temperature lift, which is the temperature difference between condenser and evaporator, are held constant and the irreversibility during the compression process is also taken into consideration by taking the isentropic efficiency different from 100%. It is found that for evaporator temperatures above 20°C and small temperature lift (5 K), R718 gives the highest COP assuming exactly the same cycle parameters. For medium temperature lifts (20-25 K), this evaporator temperature is above 35°C, whereas for even greater temperature lifts it decreases again. Furthermore, with increased values of polytropic efficiency, R718 can maintain higher COPs over other refrigerants, at lower evaporator temperatures.
06/01722 A fault detection and diagnosis strategy of VAV air-conditioning systems for improved energy and control performances Qin, J. and Wang, S. Energy and Buildings, 2005, 37, (10), 1035-1048. This paper presents the results of a site survey study on the faults in variable air volume (VAV) terminals and an automatic fault detection and diagnosis (FDD) strategy for VAV air-conditioning systems using a hybrid approach. The site survey study was conducted in a commercial building. 20.9% VAV terminals were ineffective and 10 main faults were identified in the VAV air-conditioning systems. The FDD strategy adopts a hybrid approach utilizing expert rules, performance indexes and statistical process control models to address these faults. Supported by a pattern recognition method, expert rules and performance indexes based on system physical characteristics are adopted to detect 9 of the 10 faults. Two pattern recognition indexes are introduced for fault isolation to overcome the difficulty in differentiating damper sticking and hysteresis from improper controller tuning. A principal component analysis (PCA)-based method is developed to detect V A V terminal flow sensor biases and to reconstruct the faulty sensors. The FDD strategy is tested and validated on typical VAV air-conditioning systems involving multiple faults both in simulation and in situ tests.
06101723 coil
A model for the dynamic response of a cooling
Yu, X. et al. Energy and Buildings, 2005, 37, (12), 1278-1289. The purpose of this study is to develop and evaluate simulation models for the dynamic performance of dry and wet cooling coils. The energy consumed by a building air conditioning system is directly related to that in the cooling coil. A dry-area model without consideration of condensation is established with three energy equations, and a wet-area model is developed based on a mass balance equation for moist air and three energy equations for the air, tube/fin, and working fluid. The derivatives with respect to the time variable are approximated using an explicit method, and the upwind approximation is used for the spatial variables. The results of the dry-area model show good agreement with those for the effectiveness method and the dynamic responses have reasonable physical meaning. The wet-area model is first compared to the dry-area model, and then the wet conditions are applied. A new factor called the mass transfer efficiency as a parallel to the total fin efficiency is introduced in the mass balance equation for the wet-area model to produce consistent results. The dynamic responses for several practical operations related to changing inlet conditions are reported. Comparisons indicate that the model predictions show good agreement with experimental data.
06/01724 A model-based online fault detection and diagnosis strategy for centrifugal chiller systems Cui, J. and Wang, S. International Journal of' Thermal Sciences, 2005, 44, (10). 986-999.
264
Fuel and Energy Abstracts July 2006
The paper presents an online adaptive strategy for the fault detection and diagnosis of centrifugal chiller systems. The strategy is developed based on six physical performance indexes. These performance indexes have the capability to describe the health condition of centrifugal chillers and particularly to account for existing chiller faults. A set of rules for faults and their impacts on the six performance indexes are deduced from theoretical analysis, and then serve as the fault classifier. The benchmarks of the performance indexes are provided by simplified reference models, whose parameter identification is simple. In addition, an online adaptive scheme is developed, by analysing uncertainty coming from both model-fitting errors and measurement errors, to estimate and update the thresholds for detecting abnormal performance indexes. The FDD strategy is validated by both field data collected from a real building chiller system and by laboratory data provided by an A S H R A E research project.
06/01725 Air-side heat transfer enhancement of a refrigerator evaporator using vortex generation Sommers, A. D. and Jacobi, A. M. International Journal of Refrigeration, 2005, 28, (7), 1006-1017. In most domestic and commercial refrigeration systems, frost forms on the air-side surface of the air-to-refrigerant heat exchanger. Frosttolerant designs typically employ a large fin spacing in order to delay the need for a defrost cycle. Unfortunately, this approach does not allow for a very high air-side heat transfer coefficient, and the performance of these heat exchangers is often air-side limited. Longitudinal vortex generation is a proven and effective technique for thinning the thermal boundary layer and enhancing heat transfer, but its efficacy in a frosting environment is essentially unknown. In this study, an array of delta-wing vortex generators is applied to a plain-finand-tube heat exchanger with a fin spacing of 8.5 ram. Heat transfer and pressure drop performance are measured to determine the effectiveness of the vortex generator under frosting conditions. For air-side Reynolds numbers between 500 and 1300, the air-side thermal resistance is reduced by 35-42% when vortex generation is used. Correspondingly, the heat transfer coefficient is observed to range from 33 to 53 W m 2 K - 1 for the enhanced heat exchanger and from 18 to 26 W m 2 K i for the baseline heat exchanger.
06101726 An implicit curve-fitting method for fast calculation of thermal properties of pure and mixed refrigerants Ding, G. et al. btternational Journal of Refrigeration, 2005, 28, (6), 921 932. Calculations of refrigerant thermal properties are desired to be very fast and stable in cases of simulation of refrigeration system, etc. The traditional method based on equation of state cannot meet such requirement because of unavoidable iterations in calculation. In this paper, a new calculation method for refrigerant thermal properties is presented. Low order implicit polynomial equations are got by using curve-fitting method at first, and then explicit formulae for calculating refrigerant thermal properties quickly are obtained by getting the analytical solution of these implicit equations, Explicit fast calculation formulae for thermal properties of R22 and R407C, covering the saturated temperature of - 6 0 ~ 8 0 ° C and superheat of 0-65°C, are presented as examples. The calculation speeds of the formulae of R22 are about 140 times faster than those of R E F P R O P 6.01 while the formulae of R407C are about 1000 times faster. The total mean relative deviations of the fast calculation formulae for R22 and R407C are less than 0.02%.
06/01727 Application of integrating multi-zone model with CFD simulation to natural ventilation prediction Tan, G. et al. Energy and Buildings, 2005, 37, (10), 1049-1057. Predicting the performance of natural ventilation is difficult, especially for large-scale naturally ventilated buildings, due to the lack of accurate and efficient prediction tools. This paper presents a strategy, integrating a multi-zone model and computational fluid dynamics (CFD), to improve natural ventilation prediction and design methods. Large openings and atrium configurations are broadly used in naturally ventilated buildings to promote buoyancy force and optimize air movement. How to properly deal with this typical configuration for a multi-zone model and integrated simulation is discussed and compared in this paper. In order to validate a newly developed multi-zone model program, MMPN, this paper investigated both buoyancy ventilation and wind-buoyancy combined ventilation. Integration strategies, transferring data (velocity or pressure) from a multi-zone model program to CFD as boundary conditions, are also studied.
06/01728 Application of multi-output ARX models for estimation of the U and g values of building components in outdoor testing Jim6nez, M. J. and Heras, M. R. Solar Energy, 2005, 79, (3), 30~310.