The potential of external shading devices for comfort extension and energy savings in Kenya

The use of shading systems for climate control in tropical climates is well documented. Previous research has indicated that if shading devices are installed on the exterior of the building, they are able to block solar radiation effectively before it passes through glazing and in so doing reduce the overheating potential. A review of contemporary office buildings in the warm humid city of Mombasa, Kenya reveals the predominance of highly glazed buildings which often rely on active air conditioning systems for cooling purposes. Following an initial study of suitable design strategies for warm-humid climates, the authors found that responsive sun shading could be used to significantly improve indoor thermal comfort conditions and in so doing reduce the need for electricity for cooling. In this paper, using results obtained from the dynamic simulations of a typical office building in Mombasa, the authors focus on quantifying the effect of external shading devices on indoor thermal comfort and energy use. First, the performance of horizontal, vertical and egg crate sun shading devices was investigated. The results indicated that the egg crate shading has the most significant impact in decreasing discomfort hours by up to 50% more than horizontal or vertical shading. Next, solar heat gain coefficients were derived for various shading types (horizontal, vertical and egg crate) and their impact on indoor thermal comfort and energy savings calculated. The solar heat gain coefficients (as a result of external shading) and curve fit equations/graphs suitable for use with various projection factor ratios (a simple ratio used to define the relationship between the shading element depth and window size) were derived for the four cardinal compass orientations. Using these equations and graphs, it was possible to estimate the potential annual energy savings (of up to 120kWh/m² or 74.68% improvement) with building information of the glazing area, orientation of the window and the PF ratio. It was suggested that these solar heat gain coefficients, equations and graphs show potential for use by local building practitioners in deriving the potential comfort and energy savings during early design stages of similar type buildings.