Effects of green façade retrofitting on thermal performance and energy efficiency of existing buildings in northern China: An experimental study

• Three rooms with green façades with removable metal frames and one reference room without green façades were set up. • The effect of different types of green façade and different plants on improving the thermal performance of buildings in a hot and dry summer climate was investigated. • The experiments were carried out in both cooled and uncooled conditions. • The green façade reduces the room’s air temperature and achieves significant building energy efficiency. • Indirect green façades can better improve the thermal performance of the building and have a higher building energy efficiency than direct green facades. In recent years, vertical greenery systems have gradually entered public attention, and more and more people are beginning to know it. This study aims to explore the impact of green façade retrofitting on building thermal performance and building energy consumption under hot summer conditions in northern China and to derive detailed data for future building energy efficiency retrofitting. This article used a comparative experiment to complete this research. Four laboratories of the same structure were constructed in Shandong Province, China. A movable metal frame was installed on the outside of the laboratory, and the green façades could be adjusted to direct green façades or indirect green façades according to the need of the experiment. In addition, two different plants were studied. This study was carried out under two experimental conditions: cooling and no cooling. The experiment was carried out from July to August 2024. According to the data obtained from the experiment, the green façade well reduced the surface temperature of the walls around the experimental room and the average temperature level in the room. The most significant temperature drop of 23.1 °C was observed on the surface of the external walls of the room with the indirect green façade covered with Parthenocissus quinquefolia. The data show that the average temperature in several experimental rooms decreased by 1–5 °C. The indirect green façade improves the thermal insulation of the building envelope better than the direct green façade. In the cooling experiments, the room with indirect green façades covered with Parthenocissus quinquefolia has the highest energy-saving rate of 45.75 %. However, the room with direct green façades covered with Humulus scandens only has an energy saving rate of 6.43 %.