Field summer performance of interior reflective screen shades for residential windows

Recent statistics published by Natural Resources Canada estimates that the energy demand for heating and cooling accounts for about 60% of the total energy use of an average Canadian home. Although the overall demand for cooling energy is much lower than the demand for heating, many populated areas experience a peak demand for electricity on summer afternoons. Interior reflective window shading devices have the potential to reduce solar overheating and electricity peak demand in summer, and to improve the thermal comfort of house occupants when seated near windows. This work is part of a project to develop guidelines for effective exterior, mid-pane (inside the window) and interior shading devices in Canadian residences. This paper presents the results of three weeks of summer field measurements of interior highly reflective perforated shading screens installed on the windows of a typical two-storey detached house compared to typical interior Venetian blinds installed in an identical neighbouring house.  The shading devices were closed in both houses during both daytime and night-time in order to assess the maximum possible savings in cooling energy on a 24-hour basis. The results showed that the daily total electric energy used by the air-conditioning unit and the furnace circulation fan in the house equipped with interior screen shadings was on average ~8±2% lower than in the house equipped with interior typical blinds. The savings in daily energy used by the air-conditioning unit alone ranged between 10-18%. The interior screen shadings also reduced the hourly electricity demand for cooling by up to 45% during a sunny day, which represents one of the most important benefits of this window shading strategy by having reduced the demand load on the electricity supply system during high-peak demand hours.