Overview of Insulated Glass:
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.
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
A hollow aluminium spacer bar is bent into the desired shape.
Holes are drilled in the spacer bar, which is filled with a desiccant such as silica gel or zeolite that helps in absorbing water vapour.
The drilled holes are sealed with a primary sealant such as butyl. Primary sealant is also applied to the sides of the spacer bar.
Two glass panes are placed along the side of the spacer bar and pressed with an automatic presser.
A secondary sealant such as polysulphide or silicon is applied along the sides of the whole unit. The insulating glass unit is ready.
Components of IGU
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.
The desiccants need to have the following characteristics to perform the function:
Absorption of water and hydrocarbons
Non absorption of krypton, argon or other "thermal performance" gases
Should not contain pre-absorbed nitrogen
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.
The formula used to calculate the amount of gas to be filled into the IGU is given here.
Height (cm) x Length (cm) x ID (mm) x 0.001 = Number of Litres (x)
Number of Litres (X) x 1.5 = Number of litres of gas required per window
Optical properties: the visible light transmittance of insulating glazing systems is normally in the range of 7-80% and the visible light reflectance is in the range of 13-48%;
Thermal Properties: the U value is effectively lowered by insulating glazing and can be further reduced by filling of inert gases;
Acoustical insulation: insulating glazing can reduce noise by about 30dB and further reduction is obtainable by filling of inert gases and using laminated glazing.
Condensation: the dew point of CSG insulating glazing systems is below-65C which guarantees no condensation formation under normal applications.
Sealing: aluminum spacer frame is automatically curved and formed with only one joint and two seals are applied in insulating glass production, which ensures excellent sealing characteristics and long application life-time.
Benefits of IGU:
Applications of IGU:
Commercial/Residential Fixed and Operable windows
Non-vision (Spandrel) Locations
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