Study On Human Thermal Comfort And Environmental Distribution Characteristics With Intermittent Air Jet Supply Strategy

Increased air flow has been shown to improve the cooling effect of air conditioning strategies,thus counteracting the negative effects of higher room temperature on human thermal perception,but high-speed airflow could cause draft risk.This has led to dynamic airflow being widely studied.In particular,the intermittent air jet supply strategy has been proved to provide a satisfactory indoor climate.Theoretically,changing the intermittent rate under different temperature conditions can optimize the strategy performance.However,existing studies mainly focus on control factors such as setting temperature and wind speed,and the influence of intermittent rate on the performance of this strategy remains unclear.Therefore,this paper will focus on intermittent air jet strategy providing ventilation cooling in hot and humid summer,experimentally study the thermal,airflow characteristics and thermal comfort after changing intermittent frequency,and discuss indoor air quality and strategic energy saving potential.Objective measurement experiment and subjective subject experiment were set up in this study.By means of objective measurement,the airflow characteristics,power spectrum characteristics and the thermal environment characteristics at different intermittent rates were studied.For the experiment of subjects,four setting temperatures of 24℃,26℃,28℃ and 30℃ were set.Five intermittent rates of 180s-90 s,90s-90 s,90s-180 s,90s-270 s and 180s-180 s were set and steady-state jet conditions as controls,totaling 24 design conditions.A total of 18 subjects were recruited and their subjective evaluation of thermal environment,airflow environment and indoor air quality under different design conditions was recorded in real time by means of questionnaire.At the same time,the subjects’ skin temperature,indoor air temperature and CO2 concentration were recorded throughout.The fan On-Off ratio was introduced to represent the ratio of high pulse duration to low pulse duration during intermittent cycle.The objective measurement results showed that the wind speed alternated between high and low pulses in the intermittent period,and the thermal plume was destroyed periodically.The air temperature in the occupied area could be maintained at the set temperature.The results of power spectral density function analysis showed that the βvalue increased with the decrease of On-Off ratio and reaches a maximum of 0.747,which was larger than the upper limit of the mechanical wind β value.The subjective experimental results showed that reducing the On-Off ratio would significantly reduce the cooling effect,but increased the On-Off ratio would not significantly improve the cooling effect.When the On-Off ratio is both 1,the intermittent rate of 90s-90 s has better cooling effect than that of 180s-180 s.The reduction of On-Off ratio could improve the thermal comfort of occupants at low temperature,but can significantly reduce it in neutral and warm environment,and the range increased with the increase of the setting temperature.At neutral and low temperatures,intermittent air flow with lower β value caused more draft risks.CO2 concentration increased significantly with the decrease of On-Off ratio.Reducing On-Off ratio significantly worsened the subjective perception of air quality,but increasing On-Off ratio had no significant effect on the subjective perception of air quality.At the intermittent rates of 90s-90 s and 180s-90 s,respectively,81% and 83% of subjects could accept the thermal environment of 30℃,which indicated that the setting temperature range could be increased and the energy consumption of refrigeration could be reduced.Changing the intermittent rate could change the running time of the fan,thus reducing the energy consumption of the fan.In conclusion,intermittent jet can simulate airflow characteristics closer to natural wind by changing intermittent frequency.The cooling effect of intermittent air jet strategy depended on the duration of low pulse rather than high pulse during the intermittent cycle.The intermittent frequency of reducing On-Off ratio is suitable for improving thermal comfort in low temperature environment.By changing the intermittent frequency,this strategy can improve the perceived air quality and has potential application at higher room temperature.