One of the commonly used materials in the building industry is glass. This material is quite versatile which was introduced long ago and mostly used for windows and doors. Through the advancement of time, glass has been used in many areas like for interior partitions, railings for stairs and balconies, skyscrapers, roofing as well as glass facades of commercial and large buildings. Through the use of glass, both solar and thermal performance is greatly improved.
Why Low-E Glass Is Handy to Make Energy Efficient Windows
Low-E glass, which is also known as low-emissivity glass, is a clear glass that has exemplary thermal insulation properties. To make energy-efficient windows, the use of low-E glass comes in handy. The low-E glass has a low-E coating which allows only visible light to enter into the room, while offering protection from harmful UV and infrared lights.
Another reason to use low-E glass is the fact that during summer there is so much heat and the use of low-E glass helps to block most of the infrared radiations. Thereby, the heat coming into the house is greatly reduced and the interior of the house is kept cool. This cuts down the costs one may incur in installing air conditioners.
During the winter, the low-E glass does not allow heat from the interior of the house to escape. Hence, the house is kept warm. This is an efficient way of conserving the energy in the house as the low emissivity glass comes in handy to act as a barrier between the interior temperature and the exterior temperature.
One of the disadvantages of using low-E glass is the fact that they are costlier than normal glass.
The coating applied to the glass is microscopically as thin as human hair and it is developed to minimise the amount of UV as well as infrared light that is transmitted in and out of the house without compromising the visible light that passes to the building. In order to understand the different types of coating, it is vital to understand solar energy and the rays from the sun: Ultraviolet light (UV) and the infrared light (IR), which occupy different parts of the solar spectrum.
- Ultraviolet light is mostly what causes the walls and other materials like fabrics to fade and have a wavelength reaching up to 380 nanometers.
- Infrared light is also known as heat energy that enters the building and has wavelengths of up to 780 nanometers.
Types of Low-E Coating
There are two different types of low emissivity coating. These are passive low-E coatings, also known as the hard coat, and the other one is solar control low-E coatings, also known as the soft coat.
1. Passive Low-E Coatings (Hard Coat)
These are developed to maximise the heat that is gained into the building or home and this creates effective heating which is “passive”, and this greatly reduces the reliance and the costs involved in the use of artificial heating.
This is created using the pyrolytic or hard coat process. The coating is applied to the glass in its production stage when it is in a molten state, which creates a strong bond as it fuses with the glass. This type of coating is long-lasting and very durable. The hard-coated low-E glass is then cut into sheets of different pieces and then shipped.
2. Solar Control E Coatings (Soft Coat)
This type of coating – sometimes referred to as off-line coating – is mostly applied after the glass has been manufactured. This type of coating uses the magnetron sputter vacuum deposition (MSVD). The soft coated low-E glass coating is normally applied in vacuum chambers at room temperature.
Advantages of Passive Low-E Coatings
- One of the major advantages of this coating is that it is not easily susceptible to scratches or even easily breakable. They are durable and can be permanently bonded with the glass.
- They act as barriers to the UV light and infrared light hence minimising the fading of materials.
Disadvantages of Passive Low-E Coatings
- They are more costly than the normal glass.
- They limit the amount of condensation that occurs due to temperature changes.
Advantages of Soft Coat Low-E Glass
- One of the major advantages of the soft coat low-E glass is the fact that they are more efficient in reflecting heat energy as compared to the hard coat low-E glass. This brings the concept of retaining heat in the interior during winter and reflecting the heat during summer.
- Soft coat low-E glass is mostly used in double pane windows in the form of insulated glass. This is because it provides better thermal insulation as compared to the hard-coated low-E glass.
Disadvantages of Soft Coat Low-E Glass
- One of the major disadvantages of this type of coating is that it is very delicate and very vulnerable to oxidisation when exposed to air. That’s why it must be applied in a vacuum chamber.
- It is susceptible to scratches as compared to hard coat low-E glass.
Checking Low-E Coating Performance of the Glass
Some measures are used to check the performance of low-E coating glass and these measures determine the effectiveness of the glass. These include:
- U-value – this is the rating that is given to a glass which is mostly based on how much heat loss it allows.
- Visible light admittance – this determines how much light can pass through the glass.
- Solar heat gain – this measures the amount of solar radiation that can be admitted through a glass.
- Light to solar gain – this measures the ratio between the glass solar heat gain and its visible light admittance.
All these measures are carried out to minimise the amount of UV light and infrared light that passes through the glass without compromising the visible light that is transmitted in and out of the house.