Study On The Indoor Thermal Comfort Of Stratum Ventilation With Pulsating Air Supply

Ventilation strategy determines the quality of indoor environment,which is directly related to the thermal comfort,health and work efficiency of indoor personnel.This study innovatively proposes a new ventilation strategy which combines stratum ventilation with pulsating air supply.On the one hand,stratum ventilation has a high thermal neutral temperature and a good ability to remove pollutants,thus can reduce indoor energy consumption and maintain good indoor air quality.On the other hand,pulsating air supply has the potential to reduce the percentage of draft while improving the thermal comfort uniformity.Therefore,pulsating air supply combined with stratum ventilation has the potential to achieve good thermal comfort while ensuring good energy efficiency and indoor air quality.Firstly,the air distribution in the room was measured by objective experiments.The airflow characteristics of steady air supply and pulsating air supply were analyzed and compared.Four pulsating air supply cases were designed,including different combinations of room air temperatures(27 and 28 °C),supply airflow rates(7.9 and 9.0air changes per hour),and cycle durations(2 and 5 min).One steady air supply case was also considered for comparison.The pulsating air supply created different velocity conditions between the low(i.e.,< 0.4m/s)and high pulses(i.e.,> 0.4m/s)and a temperature fluctuation of approximately 1 °C in the occupied zone.For dynamic characteristics,according to the results of turbulence intensity,kurtosis and skewness,power spectral density function,and one-dimensional continuous wavelet transform,pulsating air supply was closer to natural wind than steady air supply.In short,on the one hand,pulsating air supply created fluctuations in air temperature and air velocity near the head level,bringing dynamic thermal sensations,which can improve thermal comfort;On the other hand,the airflow characteristics of pulsating air supply were more similar to that of natural wind.These characteristics have the potential to improve thermal comfort compared with steady air supply.Secondly,the study investigated the thermal comfort level of 25 subjects under the same cases as the objective measurement by subjective questionnaires.The results showed that,stratum ventilation combined with a pulsating air supply could provide acceptable air movement and good thermal comfort at elevated room air temperatures,which can satisfy the requirements for Categories A and B of thermal environments stipulated in ISO 7730.The difference in the mean overall thermal sensation votes between the two rows was reduced from 0.6 to 0.2 scale on the ASHRAE 7-pointscale.The PD due to draft under the steady air supply was greater than 30%,but it decreased to8% with the pulsating air supply.Thermal comfort was improved by approximately 0.2scale on the scale of-1(very uncomfortable)to 1(very comfortable).This study innovatively proposed the dynamic thermal comfort evaluation index,namely TAPMV,TAPPD and TAPD,and used the results of subjective questionnaires to verify the accuracy.Finally,this study used three-dimensional transient computational fluid dynamics(CFD)calculation model and gained the data of 26 cases.Based on the evaluation index validated above,this study explored the effect of the supply air parameters(i.e.,total cycle length,the ratio of duty period length and idle period length,the supply air velocity)on thermal comfort.The results showed that the higher the supply air velocity,the lower the TAPMV and the higher the TAPD.The greater the ratio of duty period length and idle period length,the greater the TAPD of duty period.In order to keep the TAPMV between-0.5～0.5 and TAPD below 20%,the total cycle time(i.e.,300 s and 120 s)and the ratio of duty period length and idle period length(i.e.,from 0.25 to 4)were satisfying,while the supply air velocity should be kept between 1 and 2.4 m/s.When the ratio of the duty period length and the idle period length was 1,the supply air velocity of the duty period was 1.95 m/s,and the supply air velocity of the idle period was 1.05 m/s,the comprehensive evaluation of thermal comfort was the best.The results of this study can provide guidance for the design of pulsating supply air coupled with stratum ventilation,improve the thermal comfort level of stratum ventilation,so as to promote the implementation of elevating the air conditioning room temperature in summer,reduce the energy consumption,and alleviate the increasingly severe energy and environmental problems.