Study On Annual Heat And Mass Transfer Characteristics And Suitable Operating Conditions Of Cooling Tower

As an important heat and mass transfer equipment for air conditioning system,cooling tower (CT) has been more applied to the cooling system out of summer.However, most CT factory only gives out the thermal performance curve in summercondition, rather than the whole year performance curve. However, changes inmeteorological parameters directly affect the heat and mass transfer capacity of theCT. As the changing of seasons,outdoor air wet bulb temperature, imported watertemperature, water-air ratio etcl, the operating conditions of the CT will deviate fromits rated operating conditions, and heat and mass transfer capacity of the CT willdeviate from rated conditions. But this problem has not caused enough attention,people are still accustomed to follow the technical parameters given in the relatedoperating conditions when the non-summer conditions to run the CT, which leads tolow efficiency of CT in actual project..In order to grasp the factors affecting the efficient operation of the CT andappropriate operating conditions in a non-rated conditions (especially in the transitionseasons, winter), this study presents evaluation of non-rated conditions of the coolingtower, and select the four-variable model of the CT as an analysis model, and throughMatlab programming model calculated and measured values were compared, theresults show that both the relative error is less than5%, the validity of themodel.Based on the four-variable model, the paper analyz the annual heat and masstransfer performance of the CT, the results showed that: the outdoor wet bulbtemperature changes directly affect the heat and mass transfer capacity of the CT andthe VWV (variable water volume) operation mode for CT contributes more inimproving the energy efficiency than VAV (variable air volume) operation mode.Then the year-round operation of CT in Nanjing is studied on the base of VWVoperation mode. The results show that the suitable water-air ratio condition of CT isμ=0.5~1（μ=W/G0，W=0.67W0~1.33W0）during July and August, and when it comesto June and September, the suitable value is μ=0.3~1（μ=W/G0，W=0.4W0~1.33W0）.During transition season and in winter (from December to February), the suitablewater-air ratio condition of CT is μ=0.5~0.76（μ=W/G0，W=0.67W0~W0）. Base on the above result, the suitable operation condition for CT applied tonormal air conditioning system is studied using the example of Nanjing. The resultsshow that, in the summer for normal air conditioning system, the VWV (variablewater volume) operation mode for CT contributes more in improving the energyefficiency. And the suitable water-air ratio condition of CT is μ=0.5~1during July andAugust, and when it comes to June and September, the suitable value is μ=0.3~1.While in the transition seasons and winter, CT is used the free cooling system, theoutdoor wet bulb temperature is lower than9degree in Nanjing. Then the suitableoperation condition for CT applied to normal air conditioning system in31provincialcapital cities are given, which may provide reference on the design and operation ofcooling tower free-cooling system. In addition, in order to solve the thermalaccumulation problem of GSHP system in a residential building in Nanjing, thisstudy present a novel method based on the cooling tower cool-stage, and gives thesuitable operation condition of CT using this new method. The results indicate that inNanjing, the suitable water-air ratio condition of CT is μ=0.3~1in low-load period(June, September), and in transition season (March, Late October and November), thesuitable water-air ratio condition of CT is μ=0.5~0.76. The results show that thethermal accumulation problem can be well restrained using the new method, whichcan provide reference on optimized system design and energy-saving operation forCT.