Ambient heat transfer can occur via three methods; convection, conduction and radiation, the weakest resistance to these mechanisms, in a building envelope, is the glazing material.
By nature, a single piece of glass has little resistance to either heat gain or loss; however, an IG unit containing two or more panes of glass with hermetically sealed air spaces in between, slows down the rate of heat exchange between the ambient hot and cold air masses either side of the unit. The resultant reduction in heat transfer minimizes the capital cost, and subsequent operating cost of heating or cooling equipment.
In the Uniglass I.G. unit, the glass panes can be annealed, heat-strengthened, tempered or laminated, as required, to meet building code requirements, safety glazing standards and design requirements. The panes can be of equal or unequal thickness.
The most common insulating glass unit is constructed with two plies of glass and one sealed air space.
Insulating glass is used due to the improvement in solar performance it provides. The most significant improvement is thermal performance (u-value) which improves by approximately 50% when compared to a monolithic glass ply. This improvement occurs whether the glass is coated or uncoated.
In addition to the improved solar performance, insulating glass offers a greater availability of coatings. Low-E coatings which cannot be exposed, and therefore cannot be used with monolithic glass, can be used inside the insulating unit where they are protected by the hermetically sealed space.
Insulating units also have more aesthetic possibilities than monolithic glass. The Low-E coating and silk-screen pattern, if desired, are applied to the exterior ply of glass leaving the interior ply available for additional treatment. For a spandrel location, a full coverage opaque ceramic frit can be applied to the inner face (surface #4). For vision areas where daylight is desired but view through needs to be minimized, a translucent ceramic frit can be applied to the surface facing the airspace (surface #3)