Outdoor measurements of G-values for external, interpane and internal sunshades

Solar shading devices can significantly improve thermal comfort and reduce cooling loads and potential glare problems in highly glazed buildings. This paper describes results from an extensive measurement program that started in 1997, covering external shading devices, products placed between two panes (interpane), and internal shading devices. Measurements of the total solar energy transmittance (g-value) have been performed using a double hot-box arrangement placed in a real climate. One box was equipped with the solar shading device, while the box with a bare window was used as a reference. Thus, the g-value of each product (g-sunshade) has been estimated as g-system/g-window. In general, external shading devices have a larger potential to reduce cooling loads since the absorbed solar heat is mostly dissipated to the outdoor air. Interpane products have a slightly higher g-value and internal products show the highest g-values. This is demonstrated within the project, although the variation among each group is large. The average g-value within each group (g-sunshade) was 0.3 for external products, 0.5 for interpane products and 0.6 for internal products. Thus, on average, external products are twice as good as internal products in reducing peak cooling loads.