Assessment of the energy efficiency of a window system with a shading device of the egg-crate type

Introduction. The article proposes a new energy efficiency assessment method based on a new technique used to calculate the window heat gain. The proposed method takes account of the coefficient of irradiance reduction by the sun shading device. The study was carried out for the shading device of the egg-crate type. Materials and methods. Calculations are based on the projection of a sunbeam performed for a fraction of a window area in the shade. They take account of the coefficient of irradiance reduction applied due to the presence of the sun shading device. A shading device reduces the irradiance, caused by diffused solar radiation, and coefficient Kbt is applied to demonstrate this process. This coefficient was identified in an experiment and expressed in the form of regression equations. To evaluate the energy efficiency with regard for the effectiveness of shading devices, coefficient of solar radiation gain reduction β was developed. This coefficient is described by the ratio of the value of solar radiation incoming through a glazed window in the presence of shading device QK to the value of solar radiation incoming through a glazed window that has no shading QKo. The software programme was used to verify the calculations of the heat gain from the solar radiation incoming through the window system with regard for the shading device in various geographical regions in summer (in Hanoi and Moscow). Results. The results, obtained using the proposed methodology and the observation data, show an insignificant difference in the relative value of β; and they demonstrate a major error when qwindow, or the absolute value of heat entering the room, is taken account of. The heat load, incoming through the window system, is down by 42–45 % in Moscow and by 45–53 % in Hanoi in the hottest period of the year if shading devices are used. Conclusions. The proposed methodology and computer software, used for a quick assessment of the energy efficiency of a window system equipped with shading devices, allow to design building envelopes that feature high energy efficiency in terms of air conditioning systems, given that coefficient of radiation gain reduction β is taken account of.