Influence Of Chilled-water With Large Temperature Difference On Performance Of Fan-coil Unit

As one of the large temperature difference techniques in air conditioning, common chilled water system with large temperature difference has been applied in actual projects. It goes without saying that the application of chilled water system with large temperature difference can save energy efficiently. However, increasing the temperature of chilled water can also influence the performance of terminal units. So far research achievement with quantitative analysis has been very few. As a result, the extent of influence of large temperature difference on terminal units can not be assessed quantitatively.At present, fan coil units (FCU), which are representative, are widely used terminal units in air conditioning systems. According to the data of typical samples available, the regression equation of FCU has been gotten. The performance equation of FCU under large temperature difference has been found. The transformation laws of total cold capacity, sensible cold capacity, latent cold capacity, humid release coefficient and heat-to-humid ratio line of FCU under conventional large temperature difference have been analyzed quantitatively. In order to apply large temperature difference system better, the water flow path of present FCU is altered tentatively. The test method for thermodynamic characteristic of FCU using "room air enthalpy method" is investigated, and test devices are developed, and the calculation program for thermodynamic characteristic of FCU is compiled. In order to make the transformation law from performance equation applicable to the selection of project design, the law is verified through experiment, and results between experiment and theoretical calculation are fit very well. The shortcomings of present assessment criteria for FCU performance are analyzed, then the exergy efficiency analysis upon the second law of thermodynamics are evaluated for FCU performance. Upon full consideration of effect on heat transfer and flow resistance, the maximum exergy efficiency is arrived when the temperature difference is about 6°C. In addition, the exergy efficiency of improved FCU is a little bigger than that under the same temperature difference, which provides theoretical ground and guidance for selection of the temperature difference and optimal design and research of the structure of FCU.