Energy performance for interior shadings

Figure 9.6.12 shows the performance of some internal shading devices. The white roller blind with high reflectance (83 per cent) shows the best performance with a gsystem of 22 per cent to 26 per cent. The beige screen (reflectance 52 per cent) has a gsystem of 26 per cent to 32 per cent. White Venetian blinds are effective and better than blue ones. Note that for the two screens, the gap between window and screen is assumed ventilated to the room (convection).

In general, interior sunshades are better when they are in a light colour, reflecting more of the shortwave radiation to the outside. This is especially true for highly insulating windows that can

Source: Maria Wall

Figure 9.6.12 Monthly mean g-values for the combination of window and interior shading: Triple-glazed window with argon and 2 low-e coatings (4 per cent); south orientation in a cold Stockholm climate reflect shortwave solar radiation back out, but more effectively trap long-wave heat inside the room. The purpose of low-emissivity coatings, often used in high-performance windows, is to reduce heat losses and thus give rise to a low U-value. A drawback is that heat absorbed in the interior shading will be hindered in retransmitting to the outside. This is also the case for interpane shading when a low-e coating is positioned outside the shading, on the outmost glass pane.

Figure 9.6.13 shows values for gsystem for different interior sunshades in relation to the reflectance of the sunshade. There is a strong correlation between the reflectance of the sunshade and the g-value.

Source: Maria Wall

Figure 9.6.13 G-values for the combination of window and interior shading in relation to the reflectance of the fabric: Triple-glazed window with argon and 2 low-e coatings (4 per cent); south orientation in a cold Stockholm climate

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