Research Of The Living Wall System In Hot And Cold Climate

Living Wall Systems can enhance the thermal performance of buildings by adding an extra layer of "insulation". Unlike building walls, living walls consist of variable materials such as living plants, substrates, and water. Plant canopies exchange heat with the environment through transpiration. Substrates contain mixed lightweight materials. Water within substrates is supplied by a dripping system and is uptook by plants. Since the state of the living wall is changing constantly, its thermal properties are difficult to define and quantify. For this reason, existing energy simulation tools can hardly simulate the living wall's thermal behavior. As a result, the living wall's energy saving effect is usually not fully evaluated and none of the current green building rating systems in different nations issue large credits for living walls. On the other hand, there is no special and comprehensive technique standard for living walls yet. A detailed technical guidance is in need.This paper studies the tectonics and the thermal behavior of living walls.Firstly, after a comprehensive review of the history and the development of the green wall technology in general and the living wall in specific, this paper provided a classification of the different green wall technologies in which the living wall is an important part. Then the living wall's prototype is extracted and defined from the historical study and case studies. Three types of living wall system are derived from its prototype and their tectonics are fully explored and refined in terms of containers, substrate, structures, the air layer, and irrigation systems. The outcome is a comprehensive lay out of the different fabrication methods of living wall systems.Secondly, this paper studied the thermal performance of the living wall system through physical experiments. Two identical thermal labs are constructed with adjustable living walls installed on the west-facing walls in Wuhan, China. Three series of experiments were carried out. Results show that the living wall has a notable cooling effect to the building surface and the indoor space. The microclimate created by the living wall features in a cool layer of air with identical mean relative humidity as the ambient air. Instead of gaining heat, the exterior building surface is losing heat to the microclimate between the surface and the living wall all day. The living wall with a sealed air layer performs better in cooling the building surface than the living wall with a naturally ventilated air layer. Lastly, three comparison experiments tested the living wall with different air layer depth: 30 mm, 200 mm, 400 mm, and 600 mm. Results show that the thinner air layer has better cooling effect but higher relative humidity in the air layer.Lastly, this paper established a mathematical model to simulate the thermal behavior of the living wall system. The energy exchanges at the plant canopy and substrate surface are analyzed and calculated. Then the finite difference method is used to calculate the unstable heat transfer through the living wall and the building wall. Finally the living wall's contribution to the building's energy saving can be calculated. This mathematical model is able to simulate living walls in any location and climate, including adjustable parameters like plants characteristics(such as leaf area index, leaf width, stoma conductance, etc.), substrate characteristics(such as depth, materials), irrigation schedules, and so on.