Thermal radiation, i.e. heat from the sun, plays an important role in heating the interior of a home or building. Special glazing employed to allow the sun's rays to enter the room. They both heat up the air and are absorbed and stored by interior objects like furniture. This heat is slowly released further heating the room.
The benefit of this special coating is that it prevents long-wave radiation from being able to exit, by reflecting it back into the room. This ensures that glass functions as a one-way street, improving heat gain and minimizing heat loss. This is not only true for the sun’s rays but also goes for the heat generated by your home's heating system.
Thus, you retain more free heat from the sun and lose less of the heat you pay for. Today, double and even triple glazing are standard in many countries because of the better thermal performance and energy efficiency.
In plain English, the u-value or u-factor measures heat transfer from an object's warm side to its cold side (e.g. a piece of furniture). It is given W/m²K (Watt per m² Kelvin) for those on the metric system and Btu/h·ft²·°F in the United States.
The lower the value, the better the insulation which translates to less heat loss. A u-factor of 0.6 W/m²K is one of the best possible today. Triple glazing for example, typically produces u-factors between 0.4 and 0.8 W/m²K. The double pane laminated system works using two panes with coatings on the inside.
Thermal performance can be further improved in double glazing and triple glazing by filling the gap between panes with a noble gas such as argon and krypton. They have lower thermal conductivity than air while helping reduce noise and condensation as well.
The main advantages of this glazing type are lower energy bills and reduced heating and cooling. These are both even better when using triple glazing. The special window coating increases performance overall while not affecting natural light. From the outside, it is nearly impossible to see the difference and on the inside, rooms receive the same amount of sunlight as before.
The G-value measures the amount of energy passes through the insulating glass pane. This is also known as the Solar Heat Gain Coefficient, or SHGC, in other parts of the world. In short, it is simply the Greenhouse Effect describing how the interior of your home heats up due to the sunlight passing through windows and doors.
In winter the u-factor will be higher than the g-value during periods of limited sunshine. Once sufficient solar radiation is available the g-value and the U-value will both be higher though in this situation, the higher and somewhat worse u-factor is actually better.