Optimum Design Of The Dew Point Indirect With Direct Evaporative Cooling Air Conditioning Unit

Today,the energy conservation and emission reduction has been the mainstream trend for the international world.And the air conditioning as the large building energy consumption, along with the development of society, continues to increase. Therefore the energy saving in HVAC systems is particularly important. Evaporative cooling air conditioning, as an energy saving, environmental protection and high efficient way to get more and more attention.So how to improve the heat transfer efficiency of the existing evaporative cooling equipment in order to maximize efficiency of energy utilization is the problem which we put forward to the air conditioning.Compared with the traditional form of air conditioning,the heat transfer efficiency of the dew point indirect evaporative is greatly improved.But there is still a gap in the ideal dew point temperature.This paper, aiming at high humidity region climate condition, propose the dew point direct with indirect evaporative cooling air conditioning. We have done the optimization design and experimental studies on the whole unit from the structure of the dew point indirect section and the selection of fillers.First,we analysed the principle, characteristics and the reinforcement in heat and mass transfer of the air conditioning unit in theory.What's more, design and process the experimental prototype according to the inventive patent dew point plate indirect evaporative cooler.Then we do the experiments on the five fillers of GLASdek,CELdek, aluminum foil, the porous ceramic filler used in cooling towers, and the blue PVC fill.AndThe experimental results show that:(1) The efficiency of PVC decreases with the increasing of spray density. When the spray density is 1600kg/m2h in this experiment,we achieve a maximum in efficiency.(2) The efficiency on porous ceramic is higher than aluminum foil but lower than CELdek.However,the resistance on porous ceramic is larger in practical application.(3) The over-current resistance of all the five fillers changes with air velocity in a power-law,but a smooth linear regularity with spray density.The impact of air velocity on resistance is significantly larger than that of spray density.(4) Every filler has its own best spray density and air velocity.We take the factors of efficiency and resistance into account comprehensively,so the best spray density and air velocity in the experiment range is1600kg/m2h and 2.5m/s,respectively.In order to analyze the performance of the unit in depth,we built the test bed and compare the unit to the traditional dew point indirect evaporative cooler,the result show that:(1) Under the experiment,when we just open the second and the main fan of precooling section,the secondary /primary air ratio up to 1.2,the highest value of the efficiency reaching 0.72.And the primary air resistance decrease with primary air flow.(2) When we open the the second and the main fan of cooling section alone,the best ratio of the secondary /primary air is 1.69.And with the increasing of secondary /primary air ratio,the primary air velocity is decresed.At the same time,the secondary air velocity is changed passivly,which is slightly increased.The primary air resistance changed as the same as precooling section,secondary air resistance is on the contrary.(3) When the best ratio of secondary/primary of the precooling and cooling section is 1.2 and 1.5,respectively.Open all the fan and pump in the unit,we find that the total temperature drop is 10.24℃.(4) In Fuzhou,the efficiency of the dew point evaporative cooling unit is increased obveriously than the traditional dew point indirect cooler.Its temperature drop is close to the effect of direct evaporative cooler and does not increase the amount of air humidity.(5) In Fuzhou,such a high humidity region,when the unit is in the joint operation model,Its exit temperature is lower than the local outdoor air wet bulb temperature,close to the dew point temperature.And the temperature drop incresed greatly than just using direct evaporative cooling.Therefore,in middle humidity area and dry area,its final temperature will be more closer to the dew point temperature of out air.