Effects of the types of double-skin facades on sunlight availability and potential food self-sufficiency for agri-facades in temperate climate

Hunger and malnutrition will continue to be global issues due to increased global population, climate change, and resource scarcity. There is an ever-growing interest in urban agriculture in response to addressing potential food security issues and problems arising from the decline of natural areas in cities. Building-integrated agriculture, such as agri-facades developing agricultural activities along the building’s vertical spaces, can utilize soilless cultivation or vertical farming techniques to conserve water resources and improve crop productivity per unit area without occupying additional land, while simultaneously enhancing building energy efficiency. Studies have demonstrated the potential of food production of agri-facades and assessed the impact of urban forms, building typologies, and weather conditions on the sunlight availability, known as daily light integral (DLI) – a critical factor for photosynthesis and the overall plant growth. However, there is a lack of studies investigating the influence of facade form on DLI levels for agri-façades. Hence, the aim of this study is to explore how the form of double-skin facades influences DLI values necessary for plant growth and to calculate the potential self-sufficiency in terms of food in four typical types of apartments, ranging from studios to 3-bedroom units, in Sydney. 3D computer graphics software was used to obtain quantifiable indicators of vegetable production based on the DLI conditions between double-skin facades. Air cavities, glazing properties (exterior and interior), ventilation types, and the ratio of vegetables to facades were considered.

The results show that glazing properties present a greater impact on the DLI levels and food self-sufficiency. To maintain indoor lighting comfort while maximizing the available DLI within the cavity, the inner layer of glass should utilize low-emissivity coated glass, while the outer layer should be clear glass. In those cases, food self-sufficiency is achieved in the 1-bedroom unit with one family (2 adults and one child). Besides, vegetables are able to serve as shading devices to reduce solar heat gain. Although the air cavity (box window and corridor facades) and ventilation types (supply air, exhaust air, outdoor air, and indoor air) have a relatively minor impact on DLI, they may influence the relative humidity and temperature necessary for optimum plant growth. Prospective studies should expand to how façade types affect relative humidity and temperature to assist the development of future agri-façade designs.