Study Of Human Thermal Comfort In Large Space Radiant Floor Cooling Enviroments In Terminal Bulidings

With the development of the aviation industry and the growth of passenger flow,passengers’stay time during waiting or connecting flights has been extended,and the comfort level of the indoor environment in terminal buildings has also become increasingly prominent.The Terminal 3 of Xi’an Xianyang International Airport adopts a floor cooling+independent displacement ventilation system to control the indoor thermal and humid condition in the large space areas,in order to create air stratification and achieve building energy efficiency.This is the first time in China that a floor radiation cooling composite system has been applied in high space buildings.This research took the Terminal 3 of Xi’an Xianyang International Airport as the research object,measured the indoor thermal and humid environmental parameters under different weather conditions in summer,studied the distribution law of environmental parameters,e.g.temperature,relative humidity,mean radiant temperature,and used PMV-PPD indicators and on-site questionnaire survey methods to objectively and subjectively evaluate the indoor thermal environment and comfort level of the large space.The investigation and research found that the indoor air temperature at the heights of 0.1～1.1m on high temperature days is generally higher than the air temperature on typical day in summer.After 12:00,the indoor air temperature was higher than 28℃,which did not meet the demand of comfort level II for air conditioning in summer.The vertical height temperature gradient distribution was more obvious in high temperature days,and 65%of the PMV value was greater than 1,and the PPD value was up to 58%,which did not meet the requirements of human thermal comfort.Subjective voting results showed that during the extream hot days,more testers felt that the indoor environment is"hotter",and the number of people who felt that the environment was uncomfortable increased.More people hoped that the current indoor environment should be"cooler".The applicability of PMV indicators in floor radiantion cooling environment for tall spaces was verified through comparative analysis of PMV and TSV values.In addition,through the sensitivity analysis of air temperature and mean radiant temperature to PMV value,it was found that the impacts of these two environmental parameters on PMV value depended on the air supply speed of displacement ventilation device and the surface temperature of radiant cooling floor.In order to solve the problem of overheating in the large space during high temperature days,this study adopted a numerical simulation method to explore some measures to improve the indoor environment.Airpak simulation software was applied to establish a computational model.The results showed that from a single change of air conditioning system parameters,reducing the floor temperature more effectively reduce the overall space mean radiant temperature,air temperature,and thus reduce the PMV value to achieve the effect of improving thermal comfort.When the floor temperature was 19℃,the PMV value of most indoor areas was close to 1,basically meeting the indoor comfort requirements,and the indoor temperature distribution was relatively uniform.The required heat exchange rate was 200W/m~2,which is 33.6%higher than the original space heat exchange rate.Based on the simulation results of single parameter optimization,it was found that the spatial heat transfer of the tall space in the terminal building varies with the floor temperature and supply air temperature at high temperatures.The corresponding mathematical relationship was established,and the total heat transfer coefficient of the cold surface of the floor in the tall space was calculated to be 10.26W/m~2 K.For a given PMV value,the heat exchange required to only reduce the cold surface temperature of the floor was greater than that required to only reduce the supply air temperature.To achieve a PMV value of 1,the supply air temperature needs to be reduced to 16℃.A multi-parameter optimization simulation was conducted to further improve the indoor thermal comfort level.The results showed that when the air supply temperature was set to 18℃and the floor temperature was 22℃,the average PMV value was 0.87,and the required heat exchange was still 200W/m~2.The results of this study can supplement the research on the comfort of large spaces and provide some reference for the optimization of indoor thermal environment in radiation cooling rooms.