Influence Of Structural Optimization Of Built-in Finned Trombe Wall On The Indoor Thermal Environment Of Buildings

In the context of the"carbon peak and carbon neutrality"target,utilizing multi-energy complementary to reduce traditional heating energy consumption is of great significance in reducing the carbon emission intensity of building operation.Trombe wall is a traditional solar building integrated structure,which can effectively reduce the energy consumption of building operation and improve the indoor thermal environment through its auxiliary heating function.And the addition of fins on the absorptive surface can strengthen the heat transfer capability of the wall,thus achieving efficient utilization of solar energy.Xining,in Qinghai Province,is located in severe cold region.And the total amount of solar radiation during the heating season,from October to April of the next year,is about 2707.9 MJ/m².In this paper,a floor heating room with built-in finned Trombe wall in Xining is taken as the research object.By using ANSYS 2021 R1,the three-dimensional fully coupled numerical simulation of Trombe wall and indoor space was realized.On the basis of studying the influence of fin arrangement and fin structure on the heat transfer performance of the absorptive surface,the effects of the improved Trombe wall on indoor thermal comfort were analyzed,and the energy-saving perfomance of the optimization scheme was discussed.The main work in this paper is as follows:（1）The physical model of a residential building in the severe cold region in accordance with"Energy-saving design of residential buildings in Qinghai Province-75%energy conservation"DB63/T1626-2020 was constructed.On the basis of calculating the daily and hourly average values of solar radiation intensity and the outdoor sol-air temperature for each orientation,the influence law of the dual effect of the outdoor sol-air temperature fluctuation and solar radiation in winter in Xining,on the internal surface temperature of the building envelope was obtained based on the unsteady heat transfer theory,which was used as the boundary condition of numerical analysis.（2）The effects of fin height（e）,fin transverse distance（a）and fin longitudinal distance（b）on the heat transfer performance of the absorptive surface of Trombe wall with equilateral triangular brass fins aligned vertically and horizontally were investigated.The results show that the optimal fin heights of vertical fins and horizontal fins are e=20 mm and e=15 mm,respectively.Compared with Trombe wall without fins,the convective heat transfer efficiency of the absorptive surface can be increased by 1.18%and 7.75%respectively,which indicates the enhancement effect of horizontal fins on the convective heat transfer of the absorptive surface is greater than that of vertical fins when the fin height is low.The optimal fin transverse distance of vertical fins and horizontal fins are a=0.20 m and a=0.34 m,respectively.And compared with Trombe wall without fins,the convective heat transfer efficiency of the absorptive surface can be increased by 13.65%and 13.33%respectively,indicating that the enhancement effect of vertical fins on the convective heat transfer of the absorptive surface is more affected by the fin transverse distance.The optimal fin longitudinal distance of vertical fins and horizontal fins are b=0.53 m and b=0.40 m,respectively.And compared with Trombe wall without fins,the convective heat transfer efficiency of the absorptive surface can be increased by 13.65%and 13.78%respectively,indicating that the enhancement effect of horizontal fins on the convective heat transfer of the absorptive surface is more affected by the fin longitudinal distance.On this basis,the effects of fins in aligned arrangement and staggered arrangement on the thermal performance and ventilation performance of Trombe wall were compared.The results show that compared with fins in aligned arrangement,fins in staggered arrangement can achieve a higher upper vent temperature,and the ventilation capacity of the upper vent increases when fins are arranged vertically and decreases when fins are arranged horizontally.（3）Based on the optimization of the height,longitudinal distance and transverse distance of horizontal fins,and the change of fins from aligned arrangement to staggered arrangement,the effects of fin inclined angle（β）,fin shape,perforated shape and the opening area ratio of perforated fin on the heat transfer performance of the absorptive surface of Trombe wall were investigated.The results show that when the base edges of fins are perpendicular to the height direction,the average heat transfer coefficient of the absorptive surface reaches the maximum value of 5.89 W/（m²·K）atβ=45°.Under the condition that the area of the upstream surface of fins is the same,the four shapes of fins,in descending order of enhancement effect on the heat transfer of the wall,are equilateral triangular fins,semicircular fins,isosceles triangular fins,and rectangular fins,among which,the average heat transfer coefficient of the wall under the action of equilateral triangular fins is 5.89 W/（m²·K）.Compared with solid fins,fins with circular holes can obtain better convective heat transfer effect only when the opening area ratio is 1:6.While the fins with equilateral triangular holes can obtain better convective heat transfer effect when the opening area ratio is 1:3,1:4,1:5 and 1:6.For fins with elliptical holes,the heat transfer effect of fins on the wall is not significantly improved regardless of whether the long axes are parallel to the base edges or the short axes are parallel to the base edges.（4）Based on the completion of fin arrangement and fin structure optimization,the thermal performance of improved Trombe wall and its effect on the indoor thermal comfort during the period of 8:00～16:00 were investigated.And the energy saving rate of the scheme was discussed.The results show that compared with Trombe wall without fins,the temperature of the upper vent,the average heat transfer coefficient of the absorptive surface,the convective heat supply and the convective heat supply efficiency are greater and the ventilation capacity of the upper vent is smaller for the improved Trombe wall at different time.Moreover,changes in solar radiation intensity have a relatively smaller effect on the average heat transfer coefficient of the absorptive surface,the convective heat supply and the convective heat supply efficiency for improved Trombe wall.At the same moment,there is little difference in PMV and PPD between the room with improved Trombe wall and the room with traditional Trombe wall.The local dissatisfaction rates（LPD₃）caused by the temperature of the floor surface in both cases are less than 10%.Compared to the room with traditional Trombe wall,the temperature difference between 0.1 m and 1.1 m above the ground（ankle position and head or shoulder position of human body in sitting position）is smaller,the wind speed at 1.1 m above the ground is smaller,and the wind speed at 0.1 m above the ground is greater in the room with improved Trombe wall.In terms of energy efficiency,compared with Trombe wall without fins,optimizing the arrangement of additional fins on the absorptive surface and the fin structure can increase the heating energy-saving rate by 30.71%during the daytime.