Operation Characteristics Analysis Of Cooling Tower And Pipe Network Of Chilled-water System In Central Air-conditioning System And Experimental Study

The optimization of air-conditioning system is the key to energy saving for publicbuildings.For chilled water system and cooling water system,their performance are directlyrelated to the performance of air-conditioning system.This article mainly theory analyzed andexperiment researched operation characteristics of cooling tower and pipe network ofchilled-water system, which will provide a theoretical basis for optimizing operation to thewhole system.Cooling tower is an important equipment in the cooling water system. It is very importantfor the performance of condenser,thus impacting on the efficiency of the entire airconditioning system.The thermodynamic models based on mechanical draft counterflowcooling tower and mechanical draft cross cooling tower were set up and validated by test withthe fully consideration of circumfluence, evaporation loss,Lewis number and the actualcharacteristic number. These studies revealed that the relative error of outlet watertemperature is below3.5%for cross cooling tower.And for counterflow cooling tower therelative error is below2%.The influenceon on the operation of cooling tower by Lewis number,the change ofcharacteristic number,circumfluence and floating water was analysed. Results show that,forlarge temperature difference using Lewis relation can result in a large deviation between thesimulated results and the experimental results especially for the outlet air temperature andrelative humidity.So the Lewis relation need to revise on this condition. The more the actualcharacteristic number deviates from standard condition value, the greater the impact onperformance of cooling tower. The analysis shows that when the change of characteristicnumber falls to0.5from1, the heat exchange capacity decreases23.5%.And when it falls to0.1, the heat exchange capacity decreases as much as74.3%. The exist of reflux ratio oncooling tower can affect on cooling capacity and the surrounding population’s intimacy.Theheat exchange capacity decreases40.68%when the reflux ratio increases50%.Meanwhile theoutlet water temperature increases2.7°C and the variation of comfort index is1.92.The operation of chilled water system directly affects energy consumption of the wholesystem and air condition comfort.Basing on pressure difference control the static and dynamiccharacteristics of chilled water sysytem was analyzed and researched.The results show thatpressure difference characteristic of chilled water system and energy cost characteristic ofwater pump from experiment are in agreement with theory.The choice of pressure differencevalue of bypass control valve and control pressure difference value does not much affect on air conditioning host power but affect greatly on pump power,and it influence stability andprecision of pressure difference control.When control pressure difference value is less than orslightly greater than pressure difference value of bypass control valve,the pipe network hasgood dynamic stability.But when it is greater than pressure difference value of bypass controlvalve and different from each other,the pipe network will occur concussion and difficult torealize dynamic stability.When control pressure difference value is approach pressuredifference value of bypass control valve,the actual pressure difference value is close to controlpressure difference value and it has high controlling accuracy.But when it deviates frompressure difference value of bypass control valve, the actual pressure difference value deviatesfrom control pressure difference value and it has poor controlling accuracy.And the larggerthe deviation,the more the actual pressure difference value deviates from control pressuredifference value and the poorer the controlling accuracy.