| With the improvement of living standards,people's requirements for indoor environment comfort have been increasing,and ventilation and air conditioning equipment and systems have been widely used.Although the traditional ventilation methods(upper air supply or downside air supply)are widely used for heating,there are still problems such as airflow short circuit,serious stratification of indoor temperature and more,which not only increases the thermal discomfort,but also a waste of heating energy consumption.As an energy-saving ventilation method,stratum ventilation is widely concerned because of its excellent summer cooling effect.However,the research on stratum ventilation are mostly concentrated in summer cooling,and winter heating researches are still in its infancy.According to previous studies on the indoor thermal environment and thermal jet characteristics in winter,it is found that stratum ventilation has the potential to create a reasonable indoor air distribution for heating.Therefore,the research on air supply angle of stratum ventilation on heating will use as the basis in this paper.The thermal comfort of stratum ventilation for heating will study through theoretical analysis,experimental research and CFD numerical simulation.The supply air velocity and supply air temperature are optimized combined with muti-objective optimization algorithm in this paper.Firstly,according to the thermal air jet theory,the trajectory of the stratum ventilation is theoretically solved.The difference of the thermal air jet trajectory under different supply air parameters is compared.It is proved that supply air velocity and supply air temperature have a significant influence on the thermal air jet trajectory.Compared with the vertical stratification characteristics of various ventilation heating modes,it is proved that stratum ventilation heating mode is beneficial to reduce the indoor temperature stratification and bring a small vertical temperature difference.According to the theoretical analysis of thermal comfort research,the thermal comfort evaluation index that can be applied to the thermal environment of the stratum ventilation on heating is determined.Secondly,six groups of stratum ventilation heating conditions and one group of mixing ventilation heating conditions were studied experimentally,and the distribution characteristics of the velocity and temperature of the occupant zone were measured.The results show that the velocity distribution and temperature distribution of the front and rear rows in occupant zone are significantly different when stratum ventilation used for heating.The velocity distribution in the front row is similar with summer cooling,which shows a “V” shape distribution,and the velocity peak appears at the height of 1.1 m.The velocity in the rear area is lower than that in the front row,and the velocity increases from low to high in the rear area.The calculation results of draft at the height of 1.1 m in each working condition are all lower than 15%,indicating that there will be no discomfort due to the draft when stratum ventilation uses on heating.The temperature distribution in the front row area is greatly affected by the supply air velocity and the supply air temperature.The combination of high supply air temperature and low supply air velocity easily aggravates the indoor temperature stratification,in which the vertical temperature difference in the experiment can reach up to 4.66 °C.However,the combination of low supply air temperature and high supply air velocity is beneficial to reduce the vertical temperature difference of the front row.The lowest vertical temperature difference in the experiment is-0.32 °C,and the phenomenon of "inverse temperature difference" occurs.The temperature distribution in the rear row above 0.6m is relatively uniform,but the foot temperature is low.The effect of supply air velocity and temperature on the rear row area is not as significant as that in the front row.In the experiment,the vertical temperature difference in the rear row area is between 1 and 3 °C,which meets the comfort standard.In the experiment,the calculation results of the energy utilization efficiency of stratum ventilation are all higher than 1.2,and the highest reached 1.66.Compared with the stratum ventilation and mixing ventilation under the same supply air conditions,it is found that the energy utilization efficiency of the stratum ventilation is 48.6% higher than that of the mixing ventilation,indicating that the energy saving effect of the stratum ventilation on heating is better.Thirdly,the subjective questionnaire surveyed 23 subjects who voted for the five stratum ventilation heating conditions and one mixing ventilation heating conditions for indoor thermal comfort.The results show that,except one stratum ventilation conditions,the average voting value of the thermal sensation is 0.35~0.5,which indicates that the thermal sensation of the stratum ventilation heating can meet the thermal comfort requirements.The average voting results of thermal comfort are between 0~0.2,which also indicates the indoor thermal comfort during stratum ventilation on heating.Combined with the calculation results of draft and the airflow sensation,it is found that the subject is able to feel the slight airflow when the stratum ventilation uses for heating,but there no discomfort due to the draft.The statistical results of perceived air quality under six working conditions are between 0.51~0.77,which indicates that the indoor air quality can be accepted when the stratum ventilation is on heating.The average vote results of humidity sensation under each working condition are between-0.13 and-0.33,indicating that indoor environment is relatively dry and humidity needs to be improved.Then based on the CFD model which verified by experimental data,42 groups of stratum ventilation heating conditions with different air supply parameters were simulated numerically.Then the effects of supply air velocity and supply air temperature on PMV,vertical temperature difference,draft and energy utilization efficiency were analyzed.The results show that the increase of supply air temperature can improve the value of PMV in the occupant zone and reduce the draft,but it is easy to cause the increase of vertical temperature difference and aggravate the indoor temperature stratification.When the supply air velocity increases,it is beneficial to reduce the indoor temperature stratification and reduce the vertical temperature difference,but it will enhance the draft.For the PMV,when the supply air temperature is below 24 ?,the increase of the supply air velocity can make the PMV showed a trend of decrease.When the supply air temperature is 26 ?,the increase of the supply air velocity will not make the PMV appeared significant change.When the supply air temperature is higher than 28 ?,the increase of the supply air velocity will cause PMV increases gradually.The above analysis shows that the influences of supply air parameters on PMV,vertical temperature difference,draft and energy utilization efficiency are obviously different.Therefore,it is necessary to introduce an optimization method to calculate the optimal combination of supply air velocity and supply air temperature.Finally,according to the constraint interval of thermal comfort and energy utilization efficiency,23 feasible supply air parameters was selected,which could be able to maintain indoor comfort with energy utilization efficiency above 1.Finally,the TOPSIS method(Technique for Order Preference by Similarity to an Ideal Solution)was adopted in this paper.According to the four indexes of PMV,vertical temperature difference,draft and energy utilization efficiency,the 23 feasible air supply parameters were ranked in the order of heating performance through TOPSIS.Finally the supply air velocity of 1.6 m/s and supply air temperature of 28 ? is the best supply air parameter.Based on the above research results,it can be concluded that stratum ventilation can be applied in winter,and its air distribution can bring lower vertical temperature difference and lower draft to the indoor,which is conducive to creating a satisfactory indoor thermal comfort environment,and can efficiently use the air supply energy.The research results in this paper can provide data support and theoretical basis for the designs of stratum ventilation on heating,and provide guidance for the stratum ventilation heating design. |
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