Heat conduction happens when the temperature differs between two given points of a solid structure. In this case, heat moves from the warmer structure towards the colder one. If the difference in temperature maintains, constant heat conduction can be observed. Heat conduction is marked with λ; its unit of measurement: W/mK.
When a liquid media or a gas form comes into contact with a solid structure, the heat exchange developing on the verge of the two structures is called heat transmission. For instance, the air traveling in front of our windows draws or transfers heat to them.
Each structure with T>0 K emits electromagnetic waves. This phenomenon is called heat radiation. The most common example is the radiation of the Sun, the intensity of which is 1,4kW/m2. In case of an insulating glass, 2/3 of the energy gets through by heat radiation. Consequently, the application of glasses with low emission (Low-e) has a great importance since they remarkably improve the heat insulating ability of the glass.
Ug (g=glass), thermal transmission value of glass
Unit of measurement: W/m2K
It shows the amount of energy traveling through the glass between indoors and outdoors (on a given surface, at a given difference in temperatures).
The lower value we receive, the better glass we have.
The Ug value can be improved by:
- using more layers (triple layered glasses are recommended)
- choosing the optimal distance between the glasses (spacers)
- applying glasses with soft coating (Lowe, superlowe)
- using spacers filled with noble gas (Argon, Krypton)
The evolution of Ug value (EN 673)
4 mm thick single-layer glass 5,8 W/m2K
4-16 spacer-4 2,7 W/m2K
4-16 spacer -4-16 spacer -4 1,8 W/m2K
4-16 spacer -4 Planibel G (hard coating) 1,7 W/m2K
4-16 spacer -4 Low-e (soft coating) 1,4 W/m2K
4-16 argon (90%)-4 Low-e 1,1 W/m2K
4-16 argon (90%)-4 Super Low-e 1,0 W/m2K
4 Low-e-16 spacer -4-16 spacer -4 Low-e 0,8 W/m2K
4 Low-e-16 argon (90%)-4-16 argon (90%)-4 Low-e 0,6 W/m2K
4 Low-e-18 argon (90%)-4-18 argon (90%)-4 Low-e 0,5 W/m2K
4 Super Low-e-16 argon (90%)-4-16 argon (90%)-4 Super Low-e 0,5 W/m2K
4 Super Low-e-16 krypton (90%)-4-16 krypton (90%)-4 Super Low-e 0,4 W/m2K
Lately, we are able to construct quadruple-layer insulating glasses as well. These glasses can achieve a 0.3 Ug value if they are filled with argon, and even a 0.27 Ug value if we fill them with krypton.
Although, the price of a 4-layered glass is quite high:
- at least 20mm thick spacers must be used; consequently the glass becomes 76mm thick
- the two glasses in the middle of the structure must be tempered.
The technology of CE Glass is modern enough to produce such quadruple-layer glasses, what is more, even the production of 100mm thick insulating glasses is possible.