湿热地区遮阳形式对校园热环境的影响研究

Impact of shading form on campus thermal environment in humid and hot areas

受气候变暖与热岛效应影响,城市热环境正在恶化,对人居环境和居民健康造成严重威胁。校园是一种重要的教育类社区,亦受到高温威胁。改善夏季校园热环境,营造凉爽宜居校园环境,对保障师生健康、丰富户外活动、提高学习效率、节约能源等方面具有积极意义。本研究旨在探究遮阳对室外热环境的调节能力及机制。选取重庆大学校园内常见的遮阳空间(树荫遮阳、遮阳篷遮阳、亭子遮阳),对其热环境(黑球温度(Tg)、空气温度(Ta)、相对湿度(Rh)、地面温度(Ts))进行现场实测,分析不同遮阳形式对夏季校园室外热舒适(生理等效温度(PET)、通用热气候指数(UTCI))的影响程度。研究表明:遮阳可以有效阻挡太阳辐射,改善室外环境的热舒适。无遮阳空间的Ta、Tg、Ts、PET、UTCI均高于有遮阳空间;在湿热环境下,遮阳篷遮阳与亭子遮阳的热舒适优于树荫遮阳;在遮阳条件下,不同地面材质对室外热舒适的影响无明显差异;不同遮阳形式的天空可视因子(SVF)对室外热环境有明显影响,SVF对Tg、Ts、PET、UTCI的影响较大,对Ta和Rh的影响较弱。研究结果将对营造健康安全的校园热环境提供理论支撑。

Urban thermal environment is deteriorating due to global warming and heat islands,posing a serious threat to the quality of life and health of residents.Campus is an important type of educational precinct and is also threatened by extreme heat.Improving campus thermal environment and creating a cooler and more liveable campus environment are of significance to secure the health of students and teachers,enrich outdoor activities,improve learning efficiency,and improve energy efficiency.However,microclimatic regulation for a safe,healthy and comfortable built environment is complicated and context-specific.For instance,the regulatory effect of microclimatic parameters on outdoor thermal comfort varies with climatic and geographical conditions.The influence of shading on outdoor thermal environment varies significantly with a specific shading form adopted.Even though,most of the existing studies on shading cooling have focused on a single shading form,and the background climatic and weather conditions of these studies are mostly different,limiting the optimal selection of shading forms due to the lack of effective reference for comparison.In view of this,this study,contextualized in an educational precinct of Chongqing University,explored the influence of different shading forms on campus thermal environments.This paper(1)analyzed the impact of different shading forms on campus thermal environment and compared the outdoor thermal comfort levels in different shaded areas;(2)investigated to what extent the flooring materials and shading forms could affect the campus thermal environment;and(3)investigated the correlation between sky view factor(SVF)and thermal environment parameters,and that between SVF and thermal comfort indices.The area for field experiment is in Area A of Chongqing University.The measurement points were near the playground and around the Democracy Lake.The SVFs of the five measurement points(e.g.A,B,Ctrees,Csun,and D)around the Democracy Lake,with diverse shading forms(i.e.shaded by trees,shaded by pavilions,shaded by trees,shaded by trees,and shaded by trees),were 0.018,0.012,0.014,0.460 and 0.056,respectively.There were four measurement points(e.g.E,F,G,and H)the playground.Such four points were characterized by the same flooring materials,while the shading forms were different such as awnings.The measurement points of E,F,G,and H were shaded by awnings,trees,bare,and bare,so that their SVFs were 0.028,0.101,0.509 and 0.810,respectively.Moreover,the field experiment requires a sunny day to well reveal the outdoor thermal environment and the regulating effect of shading forms.The experiment was conducted from 09:00 to 19:00 on July 26,2021,and the weather during the experiment was sunny and mostly cloudless.The thermal environmental parameters such as black bulb temperature(Tg),air temperature(Ta),relative humidity(Rh),and soil temperature(Ts)were measured in situ.To what extent different shading forms affect outdoor thermal comfort was also analyzed based on two indicators of Physiological Equivalent Temperature(PET)and Universal Thermal Climate Index(UTCI).The results show that(1)Shading could effectively block solar radiation and improve outdoor thermal comfort in summer.Ta,Tg,Ts,PET and UTCI in unshaded spaces were all higher than those in shaded spaces.(2)In hot and humid environments,awning shading and pavilion shading had a better ability to regulate thermal comfort than shade shading.(3)Under shaded conditions,there was no significant difference in the effect of flooring materials on Ta,Rh and outdoor thermal comfort.(4)The SVFs of different shading forms were significantly correlated with outdoor thermal environment,where SVF was more strongly correlated with Tg,Ts,PET and UTCI,and less strongly correlated with Ta and Rh.Accordingly,two suggestions were proposed to improve summertime campus thermal environments.First,shading can effectively improve outdoor thermal environment.Natural shading facilities(e.g.vegetation)and artificial shading facilities(e.g.sunshades,umbrellas,awnings)should be planned and designed to improve campus thermal environments.Artificial shading can be further combined with highly radiant,highly reflective,permeable materials,plant,and water bodies to create a“ground permeable,top reflective”shading system.Natural shading is also dependent on the diurnal and seasonal cooling patterns of vegetation,tree planting area,and tree spacing.Second,a low-reflectivity,highly permeable underlayer is recommended to reduce pedestrian heat stress.Overall,the results of this paper can enhance the understanding of shading and cooling mechanisms on the one hand,and provide theoretical references for architects to design and optimize campus shading systems to enhance the thermal environment and improve outdoor thermal comfort on campuses in hot and humid regions on the other.