Thermodynamic evaluation of triple effect absorption chiller

Water lithium bromide vapour absorption cooling systems, both single and double effect, are being used extensively for air conditioning. However, relatively few works are available on triple effect absorption cooling system and the published literatures are silent on the exergetic analysis of this system. This paper deals with the exergy analysis of the triple-effect LiBr-water absorption refrigerating system. The exergy analysis is carried out for each component of the system. All exergy losses that exist in triple effect lithium bromide/water absorption system are calculated. In addition to the coefficient of performance and the exergetic efficiency of the system, the number of exergy of each component of the system is also estimated. The effect of HPG temperature was analysed for a commonly used chilled water temperature (12° C/7°C). The maximum coefficient of performance (COP) and exergy efficiency (ηexergy), are obtained for a maximum value of LPG and MPG temperatures. For a given MPG temperature there is an interval of LPG temperature for which the triple effect absorption cooling system can operate. Out from this interval of temperature the system does not function any more. For commonly used condenser and absorber cooling water temperature (25°C/30°C) and chilled water temperature (12°C/7°C) the maximum exergetic efficiency value of the triple effect refrigeration system is about 35.1 % Triple-effect chillers can achieve even higher efficiencies than the double-effect chillers. These chillers require still higher elevated operating temperatures that can limit choices in materials and refrigerant/absorbent pairs. The second law analysis used in this study facilitates the identification of the system components with high exergy loss. The results of the exergy analysis presented in this paper can be used in thermo-economic optimization of triple effect absorption cooling system.