Research On Energy-saving Optimization Design Of Digital Variable-capacity Direct Expansion Air-conditioning Units

In recent years,with the rapid development of variable capacity air conditioning in China,variable capacity technology has also been widely used in the field of clean air conditioning.At present,the digital variable capacity direct expansion air conditioning unit is more and more widely used in hospital operation room,biopharmaceutical,microelectronics and other places.In this paper,on the basis of the standard digital variable capacity direct expansion air conditioning unit,the design is optimized by adding the heat exchanger with reheat to the indoor machine.Furthermore,the experimental analysis and validation of standard unit and condensing unit with reheat are carried out.By comparing and analyzing the data of the two kinds of models,it is concluded that under the refrigeration condition,the condensing unit with reheat is better than the standard unit in terms of refrigeration capacity and energy efficiency ratio while the refrigerating capacity of standard unit is slightly larger than that of the condensing unit with reheat during the ultra high temperature refrigeration(The temperature of dry ball in outdoor environment is higher than 46).When the dry-bulb temperature outdoors is at the range of 18?43 C,the refrigerating capacity of the condensing unit with reheat is larger than that of the standard unit.When the refrigerating condition is 34/28 C and 30/24 C,the advantage of refrigeration capacity is the most prominent.Under the nominal refrigeration condition of the new air system,the refrigerating capacity of the condensing reheat unit is 1.72kW larger than that of the standard unit,and the energy efficiency ratio is increased by 0.26.Defrosting time is 3min 10s?3min40s,accounting for 7%?7.9%of defrosting period as the unit operates in the mode of defrosting.The frosting time of standard unit is 4min30s to 4min50s,accounting for 10 to 10.5%.It can be seen that compared with standard unit,defrosting time of the condensing unit with reheat is shortened by 50s to 1min40s.Experiment is operated for optimizing the control of opening of the electronic expansion valve of the internal machine.The optimal opening of the internal valve is obtained by changing the valve opening under condensation and low temperature refrigeration conditions.Under condensation conditions(27/24 C),the most reasonable opening of the electronic valve EXVi2 of the exchanger with reheat is 80P,and the most reasonable opening of the electronic valve of indoor exchanger with reheat is 40P under the condition of low temperature refrigeration(21/15 C).At 30/26 C,when EXVil=320P and EXVi2=60P,the cooling capacity reaches the maximum.Setting indoor temperature to 26 degrees,when EXVi2=60P,EXVi1=320,400 and 480P while if EXVi2=80P,EXVi1 should be fully opened(EXVil=480P).When EXVi2=100P,the EXVi1 is adjusted to 240P.On the basis of the above experiments,the system consumes the least power and its performance is best when the opening of the indoor electronic expansion valve is set to above values.