Exergy Analysis Of Radiant Cooling System Based On Evaporative Cooling

Semi-central air conditioning system of radiant cooling based on evaporative cooling was introduced. The practical application of this hybrid sytem was summarized. Theoretical exergy analsis on this hybrid system was performed from viewpoint of both energy quantity and quality to determine the weak part of the system and propose corresponding measures in order to provide theoretical basis for system design and optimization.The theoretical research progress of exergy analysis at home and abroad was reviewed. The theoretical investigation of humid air exergy was studied systematicly. The basic theory of exergy analysis and as well as exergy calculation formula of moist air were introduced in detail. The exergy function in evaporative cooling application and transformation were analyzed. The development of exergy analysis method was briefly discussed.The exergy analysis models of each component in the semi-central air conditioning system of radiant cooling based on evaporative cooling were established using the theoretical exergy analysis method. By exergy equilibrium principle, the consumed exergy and obtained exergy of various components were analyzed in detail. Systematical exergy analysis of theree-stage indirect evaporative cooling unit, high-temperature evaporative cooling chillers and radiant cooling were investigated and the exergy analysis models of each component were established. The exergy analysis of three-stage indirect evaporative cooling unit involes the indirect evaporative cooling section, the surface air cooling section, the direct evaporative cooling section and the air supply section. The related influence factors to the exergy efficiency of each component were obtained. The exergy efficiency of indirect evaporative cooling section reaches its maximum when the tube diameter equals18～21mm, and the ratio between tube diameter and tube spacing equals1.8～2.1. In the surface air cooling section, its exergy efficiency decreases with increasing air volume. In the direct evaporative cooling section, the exergy efficiency decreases with increasing inlet air temperature and relative humidity. In the high-temperature evaporative chillers, this provides the high-temperature cold water for the surface cooling section and the radiation cooling section, the exergy efficiency of the chiller increases with the NTUd number. Improved air velocity and water mass flow rate can improve NTUd number, so does the mass transfer coefficient. Pad with greater specific surface area or larger volume should be chosen for increasing exergy efficiency. The temperature of the chilled water produced by the high-temperature evaporative chillers have directly effects on the exergy efficiency of surface air cooling section and the radiation cooling section. The lower the temperature of the chilled water, the higher exergy efficiency of the two sections.On the basis of these, according to the energy balance principle, the exergy analysis of the semi-central air conditioning system of radiant cooling based on evaporative cooling was carried out, which established the exergy analysis model of this hybrid system. The exergy loss coefficient, the influence factor formula of the system as well as their relationship to the exergy efficiency of the system were_analyzed and calculated. The calculated exergy efficiency of the studied air conditioning system is53.76%. The theree-stage indirect evaporative cooling unit and high-temperature evaporative chillers are the weak parts of the system due to their higher exergy influence factors and higher irreversible loss to the system exergy loss efficiency. Compared with the exergy analysis results of radiant cooling system based on ground-source heat pump the advantages of evaporative cooling unit applied in northwest China are illustrated. Suggestions for the improvement of system design were puts forward.