Insulated Glass, often called double glazing, is a combination of two or more panes of glass spaced apart with a spacer bar and hermetically sealed with a primary and secondary sealant to form a single unit with one or more air spaces in between. IG units improve the thermal performance, thus significantly reducing heating and air-conditioning costs. IG units also reduce interior condensation in cold climates, and increase comfort near windows, thus maximizing the usable interior space.

By combining Low-E coatings, tinted glasses, reflective coatings, silk-screened patterns, laminated glass products and more, a wide variety of insulating glass configurations are available to satisfy a wide range of performance and aesthetic requirements. IG units can be fabricated to meet state energy codes, sound control requirements, seismic requirements, impact resistance, bullet resistance, and hurricane and blast resistance requirements. IG units can be designed to reduce heat loss and solar heat gain entering the building, with a minimal reduction of visible light transmittance.

IGU Surfaces:

The IG unit consists of four surfaces. Surface 1 is that side of the glass lite that faces the exterior of the building. Surface 2 is other side of the Surface 1. Surface 4 is the side of the glass lite that faces the interior of the building. And the Surface 3 is the other side of surface 4.

IGU: The Process
Insulating glass is a glazed unit composed of two or more glass panes separated by spacers filled with dehydrated air or gas. The various machines used in the process of making insulated glass are washing unit, drying unit, spacer conveyor, butyl extruder, and pressing unit, which is vertical. The insulated glass is constructed in the following ways.

Components of IGU

Glass lites:
An IGU consists of at least two panes (or lites) of glass. Though IG units typically use monolithic glass, other types of coated and laminated glasses may be used depending on the application to enhance the performance of the unit.

Frame:
Frame, or the spacer bar, is the material used to separate the two glass lites in an IGU. Usually made of aluminium and filled with desiccant, it holds the unit together, provides thickness and mechanical resistance, and plays a key role in ensuring optimum performance of the unit.

Frames are of two types - ones joined with corner keys, and bent frames. In the first type, the spacer material is cut to the specific size and desiccant is filled. Then the four sides are assembled together using corner keys. As the frame created in this process has four joints, the heat loss is more. To address this, the frame or the spacer bar is bent at 90 degree angles and the frame is assembled with only one joint - this is referred to as a bent frame.

Desiccant:
Desiccants are used to remove any moister trapped within the IG unit. The different types of desiccants are silica, molecular sieve and zeolites.

The desiccants need to have the following characteristics to perform the function:

Sealant:
Sealants are very important in the manufacture of insulating glass. They are easy to handle, efficient, safe and environment friendly. They are good adhesives, elastic and durable. Their moisture vapour transmission rates are low and have good cure profile. There are two types of sealants - primary and secondary.

Poly Iso Butylene, or Butyl, is the most common primary sealant used. Silicone and Polysulfide are commonly used secondary sealants.

The primary sealant helps in fixing the insulating glass unit at the time of assembly.

Secondary sealants are structural adhesives, binding the glass panes in multi-pane IG units (MIG) together. The sealant comprises of two components which are mixed before application and applied by a robot or manually.

Secondary sealant protects the gas filled spaces from influences of moisture vapour penetration, chemical attack from cleaning fluids and glazing products, and liquid water penetration due to rain or condensation.

Filling:
There are three different types of IG units based on the type of gas filled between the glass lites. The most commonly used type is the regular IG unit with no filling - it has dry air inside. The second type is the one with inert gas filling. Inert gases such as argon, krypton, and xenon are used as a filling in this type of IG unit. They are more efficient than dry air, but expensive. The third type of IG unit is where vacuum exists between the glass lites.

The formula used to calculate the amount of gas to be filled into the IGU is given here.

IGU Features:

Benefits of IGU:

Energy Conservation:
The table given below shows, how insulating glass helps in conserving energy in hot climate, as compared to monolithic glass.

Perfect Transparency:
Insulated glass units help in reducing the incidence of condensation on the warm air side and bring about transparency. IG can be used in larger glazed areas without increasing energy consumption and still bring about perfect transparency. For example, insulated glass is used in soft drink chillers in retail stores, airports, etc.

Sound Insulation:
Monolithic glass resonates when high frequency sound comes in because it cannot withstand the high frequency. IG units are highly effective in reducing sound transmission. Air inside the IG will prevent the resonance from passing through. For example, buildings near airports, railway stations, and main roads are constructed using IG to prevent noise from entering the building.

Reduced Infiltration:
In cold climates, the aim is to reduce infiltration of the cold, maintain internal heated temperature and reduce the cost of heating.

Reduced Condensation:
Water from condensation build-up and the resultant water run-off can damage window sills and frames, and seep into walls and adjoining areas. Condensation will form when the moisture in the air condenses out on surfaces that are cooler. Window surfaces being colder than other surfaces in the building are more prone to condensation build up. An IGU reduces the likelihood of condensation forming by providing a thermal barrier between the inside and the outside.

Applications of IGU:
Insulating glass (IG) units are used in a wide range of applications including: