Impacts Study Of Personal Nozzle Air Supply System On Human Thermal Comfort In Aircraft Cabin

Sincethe aircraft has become the most favorite mode of transportfor people inlong-distance trips, the time people are exposed to the thermal environment of aircraftcabin has been longer and longer. Compared with the buildings indoor environment,aircraft cabin isa typical special micro environment withits obvious features, which arenarrow space, and high density of staff without movement. It is said that about25%ofthe passengers feel unsatisfied in the cabin, which is far higher than that in the buildingenvironment (5%~10%).Therefore, creating a "safe" and "comfortable" aircraft cabinenvironment has become the main focus of competition of large civil aircraft. Two airsupply systems have a strong relationship with the thermal environment of the aircraftcabin. One is the main air supply system, another is the personal airflow system. Mainair supply system is mainly to create a more stable thermal environment to meet thepassengers’ health and comfort requirements. The personal airflow system providespassengers a self-control and regulation of air supply which can meet the individualpreferencesbased on passengers’ demand. The personal airflow system is more special.However, previous studies,in this field havenot been reported,especially on theinfluence to the passengers’ comfort. Therefore, it is necessary to analyze the personalairflow system affecting human thermal comfort tooptimize the air-condition system ofaircraft. This paper is based on the National Basic Research Program of China (973Program)”Research on the key scientific issues in the control of air environment in largeaircraft cabin”, and conduct research focus on individual nozzle ventilation system’sinfluence on human thermal comfort.Firstly,air temperature and relative humidity were measuredfor one and half yearsin the aircraft cabin of23flights under different flight conditions in different seasons.Based on the measured data, the changes of main thermal environment parameters withthe running time have beenanalyzed. The results show that: in the state of cruising, airtemperature and relative humidity keep relatively stable, air temperature keeps in therange of25℃~28℃, relative humidity keeps in the range of20%~30%. More than60%of the passengers deem that it is necessary to set the personal airflow nozzle. Themain reason is stuffiness. Most passengers choose to open nozzle partly for regulatingthe upper body.Secondly, three row seat aircraft simulation cabin wasbuiltwith real nozzles which are used on actual aircraft cabin. A similar cabin thermal environment was created asthe actual operation of the aircraft, the thermal reaction of the passengers and the usebehavior of personal airflow nozzle wereanalyzed by simulating the whole process fromboarding the cabin to steadying. The results show that: under different attendance rates,the maximum value of mean overall thermal sensation vote appears at the beginning,and then gradually reduces with time. However, the minimum value of mean airmovement sensation vote appears in the start time, and increases withtime. Both of themwill remain relatively stable in the end. In the thermal environment, More than50%ofthe subjects opened the personal airflow nozzles to improve their thermal comfort byadjusting their upper body part. The nozzle using rate and degree are increased first andthen decreased with time, and tended to be stable. Open degree is kept in the partialopen station in most cases. Based on the above result, test and analysis of the flowcharacteristic of personal airflow nozzle weredone in isothermal air supply conditions.The result shows that the nozzle jet axis velocity decrease with an increase of distancefrom the section to the outlet section; the distribution of air speed in different sections isapproximately symmetrical pattern, being similar to the attenuation law of circular jet;combined with empirical formulae, the turbulent coefficient values and spread angles ofthe isothermal jet flow are established with the vents fully open and half open; the axialvelocity attenuation rule is also confirmed.Thirdly, using the three row seat aircraft simulation cabin, the investigation of theaffect human thermal comfort wascarried out while the nozzle blows the main parts ofthe body with testing the main physiological index in isothermal air supply andnon-isothermal air supply conditions. The results show that: when the nozzle adjusts theupper part of body, human thermal sensation changes, air movement sensation and theaverage skin temperature is maximum. In the same regulation part of body, theinfluence of2/3open and full open nozzle on overall thermal sensation and skintemperature are stronger with the same degree, the1/3open’s impact is minimal.Howeverthe influence of the2/3open is basically the same as the full open. Isothermaland non-isothermal air supply the experimental results were analyzed using the pairedt-test. The result shows no significant difference between the two conditions. Combinedwith the mean skin temperature and thermal sensation, there is an obvious linearrelationship between both of them. In addition, the mean air movement sensation andmean thermal sensation also has a positive linear relationship.Finally, based on the Principal component analysis, all of the local part of body was classified to two parts, head part and other parts (trunk and extremity), and theirthermal sensation was calculated. Path analysis method was adopted.The direct andindirect impacts of two parts of the body mean thermal sensation on overall thermalsensation wereanalyzed. The results show that the whole other parts of body thermalsensation have a greater direct impact on overall thermal sensation. In the indirect effect,head has the indirect effect by whole other parts ofbody to the overall thermal sensation,but the whole other part of body has feebly indirect impact on overall thermal sensationby head. Based on analysis of physiological mechanism of thermal sensation, combinedwith the distribution density of cold spots and hot spots in human body and the weightcoefficient of mean skin temperature, the weight coefficient of two main parts isconfirmed. And then combined with the weight coefficient from regression analysis, thefinal prediction model of head, the whole other body of mean thermal sensation to theoverall thermal sensation is obtained and the weight coefficient is respectively0.31, and0.69. The model is verified by experimental data.This paper proposes the better adjusting angle and opening degree of the personalairflow nozzle, which provide evidences for setting personal airflow nozzle morereasonably. Comparing different air supply conditions, reducing the temperaturedifference is promoted which has certain effect on saving energy for the actualoperation of the air conditioning system. The prediction model of overall thermalsensation in aircraft simulation cabin is also reported, which provides the reference forcontrol and evaluation of aircraft cabin environment.