An Appraisal of Simple Shading Devices to Mitigate the Effects of Urban Heat Islands on Buildings in Nigeria

Abstract

With the effects of global warming and urban heat islands, the maintenance of thermal comfort in houses is likely to be challenging in some Nigeria states without relying on active cooling systems. This paper proffers simple shading components which can reduce heat gain in houses due to solar radiation, which in turn has the potential to reduce the use of air-conditioning systems for thermal comfort purposes. Trees make ideal shading devices generally because they provide a pleasant shade and relief from intense sunlight, especially if utilized intelligently. The transpiration which occurs in the trees, provide additional cooling to their immediate outdoor environment by as much as 5.4 °C when compared to a similar unshaded building. A draught resistant tree such as the Umbrella Thorn is ideal for Nigeria, they have high canopies which have the tendencies to shade both the roof and sides of the building. But because trees are living organisms, they have certain drawbacks which include time to mature, intrusive root systems and initial nurturing process. Another shading component with impressive results is a Sierpinski tetrahedron fractal canopy. A typical fractal object with a fractal dimension of 2 is a Sierpinski tetrahedron while that of a natural tree is “approximately” 2, meaning that Sierpinski tetrahedron fractal canopies mimic natural trees and provide shade from sunlight without being heated themselves. Results showed that the fractal roofs were effective in reducing surface temperatures in sunlight. The ground surface temperatures under the fractal roofs were also significantly reduced by as much as 10 °C even though they did not provide complete shade. Consequently, they provide a comfortable environment and significantly reduce thermal stress in urban areas. The canopies also provide an open-air feeling by allowing nice breeze to flow through while creating a luminous environment. Because fractal membranes are porous, they are not swollen with the wind and do not suffer from strong wind drag force. This property makes it possible to use thin frames to support fractal roofs. This paper recommends that trees and fractal canopies be employed to mitigate against the effect of urban heat islands in a manner that is green. In certain instances, where trees cannot be used for shading purposes, Sierpinski Tetrahedron fractal canopies can be adopted as an equally effective alternative.