ABSTRACT
Windows are the most energy-transmissive elements in the envelope. Even the highest performance glazing has a U-value at least five times greater than typical insulated opaque elements. When in direct sun, windows will transmit around 400W/m2, 40 times greater than a 20°C temperature difference across a wall with a U-value of 0.5W/m2. As well as this, windows provide useful daylight that can reduce the dependence on artificial light, one of the main energy consumers in non-domestic buildings.
