Experimental Study Of The Performance Of A Small Plate-type Dew Point Indirect Evaporative Cooler With Counter Cross Flow

Recently,the energy consumptions of HVAC systems in buildings are widely concerned.Air conditioning with traditional compressor usually cost a large amount of electricity.Therefore,it is necessary to develop new air conditioning method with high energy-saving potential.Indirect evaporative cooler(IEC)can lower the air temperature by consuming the latent heat of evaporation,which is more energy-saving,environmental protection and economical,compared to traditional cooling methods.However,the lowest supply air temperature with IEC can only reach the wet bulb temperature of incoming working air,even under the ideal operating condition.The low cooling capability limit the applications of this kind of technique.For this reason,a new dew point IEC method was recently developed,which can cool the supply air temperature to the dew point temperature of incoming working air approximately.Nevertheless,the cooler size is usually too large to be applied in residential buildings.In this study,the key influencing parameters for the performance of the dew point IEC were comprehensively analyzed.Then we further improved the internal flow pattern and heat/mass transfer medium material in the cooler,which laid a good foundation for applying the dew point IEC in residential buildings.The main research content can be summarized as: Firstly,a small plate-type dew point IEC with counter cross flow was developed,which has an internal flow pattern similar to the counter flow dew point IEC,but much lower system resistances.Secondly,a composites medium was introduced,which combined hygroscopic wicked polyamides on the wet side,and hydrophobic plastics on the dry side.Thus,the composites medium has a better water-retaining capability than the commonly-used Aluminum foil medium on the wet side.Thirdly,a mathematical model was established to theoretically study the heat/mass transfer in the dew point IEC.The calculated results were used to determine the optimal size and operating parameters of the cooler,which was helpful for designing the experimental prototypes.Then the cooling capabilities of the two cooler prototypes were tested,using the Aluminum foil and composites as the medium material,respectively.Finally,the key influencing parameters for the cooling capabilities of the two cooler prototypes were examined,including the secondary/primary airflow ratio,the primary airflow volume,and the dry bulb temperature and humidity ratio of the incoming working air.The research mainly led to following conclusions: When the incoming working air temperature ranged from 23.8oC-28.0oC,the cooler prototype with Aluminum foil medium had a wet bulb efficiency of 65.6%-95.4% and a dew point efficiency of 46.9%-68.3%.Meanwhile,the cooler prototype with composites medium had a wet bulb efficiency of 66.3%-108.8% and a dew point efficiency of 46.7%-79.4%,with the incoming working air temperature ranged from 23.1oC-27.3oC.The cooler prototype with composites medium showed a better cooling capability,which could supply air below the wet bulb temperature of the incoming working air.Moreover,it is suggested to intermittently operate the recycling spray water pump,when using the composites medium with a hygroscopic material on the wet side.Lastly,the unit primary airflow volume of the cooler prototypes with Aluminum foil medium and composites medium were 0.38(m3/s)/m3 and 0.95(m3/s)/m3,respectively.Consequently,the cooler size can be dramatically reduced using the composites medium.