In 2006, the Technical Building Code (CTE) was enacted, and therefore windows entered into the world of energy efficiency: energy now has to be taken advantage of from the outside to minimise energy use.
First of all, the solar factor means measuring the solar radiation that is let in through a specific enclosure, into the rooms inside.
Depending on the type of climate where the windows are installed and the direction which they face, a high or a low solar factor may be preferable.
The best way to achieve high energy efficiency is by using a variable solar protection system. This may be in the form of a set of shutters, or through a system of moving slats, which makes it possible to take full advantage of the sun’s energy in winter, while reducing the need for cooling in the summer.
Knowing the air permeability of enclosures is a decisive factor in a window’s energy efficiency and in the comfort of a building’s interior. It also provides information on unwanted air renewals which take place on the inside of buildings. These have a negative influence on the energy efficiency of buildings and tend to even out the indoor and outdoor temperatures, causing greater energy use through heating or air conditioning.
Last of all, thermal conveyance is a measurement of the heat flow that is conveyed through a material, due only to the difference in temperature between the inside and outside, without bearing in mind any solar radiation or air flows through enclosures.
The decisive factor in the thermal conveyance of an enclosure is glass, because it is the material which occupies the greatest percentage of the surface area in a window. The savings entailed by replacing existing windows that have performance levels prior to the CTE rules with windows that have a Thermal Bridge Break is nearly 36% (demand shift from 111 to 71 kWh/m2).