Research On Energy-saving And Cost-effectiveness Of Vertical Greening Renovation Of Existing Buildings

The number of existing buildings in China is huge,and more than 60% of the buildings are high-energy-consumption buildings.The thermal performance of building exterior walls is the main reason that affects bu ilding energy consumption.The vertical greening of building exterior walls can reduce the air-conditioning load,improve the urban greening rate,and alleviate the urban heat island effect.Therefore,this paper will use the methods of experimental testin g and numerical simulation to study the energy-saving and cost-effectiveness of vertical greening renovation of existing buildings.The main research contents include:（1）The heat transfer process of the vertical green vegetation layer is analyzed.The thermal insulation effect of the vertical greening wall is determined by the vegetation layer,the air layer between the plant and the outer wall,and the outer wall structure.The heat transfer process of the vegetation layer includes reflection,heat conduction,convection,transpiration,photosynthesis and respiration.In terms of function and other aspects,the optical characteristics,biological characteristics of plants and the external atmospheric environment are the main factors affect ing the heat transfer of the vegetation layer.（2）The effect of vertical greening on the indoor thermal environment of the building and the outdoor near-wall microenvironment was measured and studied.Two rooms with or without greening on the exterior wall of an incomplete vertical green building in Mianyang City were selected for comparative test research,and parameters such as the indoor air temperature,the temperature of the interior and exterior surfaces of the exterior wall,the air temperature near the wall,and the solar radiation were measured.The average shading rate of the solar radiation on the outdoor near-wall surface by the vertical greening is above 53%,the average temperature of the outer surface of the green exterior wall is reduced by 1.8°C,and the maximum temperature drop is 4.7°C,the temperature drop is 1.2°C,and the air temperature near the outdoor wall is reduced by 0.9°C on average.Vertical greening also has a certain impact on the wind speed near the outdoor wall.When it is cloudy,the test data of each measuring point in the room with or without vertical greening is very small,indicating that vertical greening has a significant effect on indoor air.The external thermal environment has little influence.（3）The numerical simulation method is used to study the energy-saving performance of vertical greening of different walls in different building climate zones.The building energy consumption model was established based on the measured buildings,and the air-conditioning load be fore and after the vertical greening transformation of the external walls was simulated and calculated.The implementation of vertical greening renovation for small concrete hollow block walls and concrete walls can reduce the annual air-conditioning load by 8.1%,9.1%,7.3% and 5.9%;in Guangzhou,which is hot in summer and warm in winter,the buildings with the above four types of walls are retrofitted with vertical greening,and the annual air-conditioning load of the buildings is reduced by12.0%,11.1%,10.3% and 9.1% respectively;in Xi’an,the annual air-conditioning load of buildings decreased by 7.4%,7.1%,6.7% and 5.6% respectively.（4）Based on the theory of building life cycle cost,the cost-benefit of vertical greening renovation of existing buildings is analyzed.The vertical greening transformation of the above four types of walls is carried out.In Mianyang City,which is hot in sum mer and cold in winter,the dynamic investment recovery period is 9.5 years,8.5 years,10 years and 10.9 years respectively;in Guangzhou,the payback period is 7.6 years,7.3 years,9.2 years and 10.3 years;and in Xi’an,the cold zone B,the payback per iod is 10 years,9.8years,11.4 years and 12.0 years.From the perspective of engineering economy,the scheme of implementing vertical greening is acceptable.（5）Research on regional adaptability of vertical greening renovation of existing buildings.By analyzing the energy-saving potential and cost-effectiveness of building vertical greening in different building climate zones,a second-level fuzzy comprehensive ev aluation system was established to analyze the adaptability of vertical greening applications in different climate zones.Guangzhou City in the hot summer and warm winter area has an excellent adaptability rating for implementing vertical greening renovati on,while Xi’an,which is located in the cold zone B,has a good adaptability rating for implementing vertical greening renovation.Energy-saving benefits,economic benefits and environmental benefits are important factors affecting the implementation of v ertical greening.This paper studies the energy-saving and cost-effectiveness of vertical greening in the energy-saving renovation of existing buildings,and analyzes the adaptability of vertical greening in different building climate zones.The research methods and conclusions can be used for the application of vertical greening technology in different regions and promotion to provide reference and reference.