Influence Of Clearness Index On Indoor Thermal Environment Of Residential Buildings Under Typical Conditions

The outdoor meteorological parameters is an important factor causing the change of indoor thermal environment.In this paper,the clearness index(0.2～0.7,changed by 0.1)is used to characterize the changes of solar radiation intensity and outdoor air temperature,and the FLUENT is used to simulate the heat transfer process of residential buildings in Nanchang area in summer under natural ventilation and air conditioning conditions with different clearness index.The relationship between indoor thermal comfort and clearness index under the two conditions is analyzed,and the influence of clearness index on building energy consumption under air conditioning condition is analyzed.Finally,the building environment control strategy considering indoor thermal comfort and building energy saving is given.The main conclusions of this study are as follows:(1)As predictive mean vote(PMV)is suitable for indoor thermal comfort evaluation under steady-state conditions,this paper uses the modified PMV(e PMV)to evaluate indoor thermal comfort under natural ventilation conditions.The results show that the duration ratio of e PMV>0.5 increases with the increase of clearness index K_t.When the clearness index is0.2,0.3,0.4,0.5,0.6,0.7,the proportion of duration with e PMV>0.5 in the whole day is 1.3%,23.6%,38.5%,63.9%,76.4%and 81.9%respectively.(2)In this paper,through the monitoring window of fluent,the temperature and speed of the air conditioning air supply outlet are monitored,and the air supply volume of the air conditioning is calculated by using the hourly speed monitored,and then the cooling capacity of the air conditioning under different weather conditions is obtained.The results show that the supply air volume and cooling capacity of the air conditioner increase with the increase of the clearness index because the air speed at the air supply outlet of the air conditioner increases with the increase of the clearness index.When the clear sky index is 0.2,0.3,0.4,0.5,0.6 and 0.7,the cooling capacity of the air conditioner is 1.19×10~5kJ、1.30×10~5kJ、1.44×10~5kJ、1.59×10~5kJ、1.71×10~5kJ、1.80×10~5kJ respectively.According to the relationship between air conditioning cooling capacity and clear sky index,the semi empirical formula is fitted,and the coefficient of determination R~2 is 0.999.(3)Under the action of air conditioning,the indoor air temperature is maintained at about26°C.However,with the increase of solar radiation intensity and outdoor air temperature,the indoor thermal environment will also overheat.And the proportion of predicted mean vote under air conditioning conditions(PMV)greater than 0.5 also keeps a positive proportional relationship with the clearness index.Therefore,for air conditioning conditions,the control of indoor air temperature alone is not enough to maintain the comfort of indoor thermal environment in the range of-0.5≤PMV≤0.5.(4)It is found that when the clearness index is 0.2,the indoor thermal comfort maintained by air conditioning is even worse than that maintained by natural ventilation.When the clearness index is 0.3～0.7,compared with the indoor thermal comfort under natural ventilation,the improvement rates of this scheme are as follows:0.3:2.9%,0.4:19.2%,0.5:38.6%,0.6:44.5%,0.7:48.6%.Compared with the building energy consumption under air conditioning conditions,the effect of the scheme on reducing energy consumption under different clearness index conditions is as follows:0.3:8.46×10~4kJ,0.4:6.51×10~4 kJ,0.5:3.89×10~4 kJ,0.6:2.63×10~4 kJ,0.7:2.16×10~4 kJ.