Energy performance of venetian blinds in south-oriented residential spaces in Cairo: Impact of three parameters: location, reflectivity and slat angle

The Egyptian capital, Cairo, has a massive building stock and it is currently experiencing mega-scale urban extension projects that will lead to a significant increase in the city’s built-up area, and consequently, in the energy needed to run those buildings, making it a necessity to rationalise energy use. Although window shading can help reduce energy consumption, it is rarely implemented in both existing and newly proposed residential building designs. End-users, then, usually install internal shading devices either to achieve privacy and indoor aesthetics or to block the sun. However, inappropriate shading may cause an increased use of artificial lighting and, in turn, an increase in internal loads on the HVAC (Heating, ventilation and air conditioning) system. Thus, a careful selection and adjustment of shading devices becomes crucial. Venetian blinds (VBs) are a type of adjustable shading device that can be installed to the interior, exterior or in between glass panes of a window and that can be easily employed in both new and existing buildings. VB attributes are expected to affect the blind’s energy performance. This study investigated the impact of three VB parameters: location, slat angle and reflectivity on the overall energy consumption of a residential space with a south-facing facade in the climate of Cairo. A test room was modelled for energy simulation with a 20% window-to-wall ratio. A venetian blind was assigned with alternatives being located to the indoor, outdoor or in between double glazed panes. High, medium and low reflectivity values were applied at each location at slat angles of 15o, 30o, 45o, 60o, 75o and 90o. Results showed VB performance across slat angles, where up to 22% energy savings were achieved by mid-pane high reflectivity VBs, while the value exceeded 33% where they were externally located.