When designing an enclosure solution, it is important to consider the thermal transmittance value. Therefore, the choice of carpentry and glass will depend to a large extent on the heat lost or gained through these elements.
The Uw is the name given to the thermal transmittance of the window, where the U-value represents the W/m2K (watts per square meter and degree Kelvin). For its calculation, the following formula must be applied:
Where:
Ag: is the surface of the glass in the window.
Af: is the surface of the blind part of the window frame.
Ug: which is the thermal transmittance of the glass.
Uf: what is the thermal transmittance of the frame?
Ap: which is the surface of the blind part of the blind box and Up which is the thermal transmittance of the blind, if available.
The lower the thermal transmittance, the better the thermal insulation and, therefore, the more energy efficient the window.
To illustrate this, a performance comparison between Extrugasa’s XP-50 and XP-80 HO HI is shown below:
For the matching between two-pane windows, we define the model of these, their measurements and those of the glass, in addition to specifying whether they will have a shutter box or not. Likewise, it is necessary to indicate the climatic zone in which the window will be installed since each one will have specific requirements.
| Data | XP-50 | XP-80 HO HI |
| Air permeability | 4 | 4 |
| Water tightness | E-1950 | E-1650 |
| Wind resistance | 5 | 5 |
| Section view of the frame | 99.60 mm | 65.70 mm |
| Inverse view section | 159.20 mm | 94.40 mm |
| Frame transmittance | 2.40 W/m2K | 1.10 W/m2K |
With this information we solve the thermal transmittance formula, taking into account the values of Uf and Ug, together with those of their areas, in addition to the linear thermal transmittance coefficient of the interlayer, the Ψg and the glazing perimeter (g).
Thus, the result is obtained for both series in the defined climatic zone, which in this case is E, for a window with a width of 1,480 mm and a height of 2,200 mm, and a triple glazing Ug of 0.5 W/m2K with Warm Edge interlayer profile:
| XP-50 | XP-80 HO HI | |
| Uw | 1,2 | 0,7 |
Therefore, although both comply with the Technical Building Code in all climatic zones, the XP-80 HO HI has a better thermal transmittance and, therefore, there is a higher energy efficiency of the enclosure.
*All tests are carried out in an external laboratory that guarantees the quality of our products and materials.
