What is Heat Gain and how can you control it?

What is the G Factor?

The G Factor is a coefficient for measuring the amount of solar radiation that enters a building through a glazed unit. In simpler terms the G Factor represents the amount of heat entering the building through the glass.

The sun's light can be broken down into 3 main parts; ultra-violet rays, infra-red radiation and visible light. It is the ‘infra-red’ element of the sun’s light that causes overheating in highly glazed areas. Short wave infra-red radiation from the sun can penetrate through glass but when this radiation heats internal surfaces within a space they emit long wave infra-red radiation which cannot pass through glass units as easily. This causes the infra-red radiation to be trapped within the space and cause overheating, referred to as Solar Gain.

The G Factor is sometimes also known as the solar factor and is represented as a percentage of the total incident radiation that enters through the glass. This includes the direct radiant influx as well as the infra-red radiation that is absorbed by the glass and then re-emitted internally.

For example a 53% total radiant influx will be a G Factor of 0.53. The G Factor is measured using a standard testing method EN 410 under the assumption of standard daylight light settings with the internal and external temperatures equal.

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Reduce Heat Gain

There are many elements that can alter the G Factor of glass panels if required.

Using a tinted glass will mean that more of the sun’s rays will be reflected than emitted but this will include the visible light as well. For a modern glazing technology using a transparent coating, such as a solar control coating, will reduce the G Factor of the glazing, therefore reduce the amount of infra-red radiation from entering a space causing overheating, with only a small reduction in the visible light transmission.

More advanced options for solar control from your architectural glazing include the innovative Electro Chromic Glass which allows the user of a space the ability to change the glass G Factor from 0.47 all the way down to a minimum of 0.04, which means that only 4% of the solar infra-red radiation hitting the external face of glass will transmit into the internal spaces.

Alternatively you could shade large elevations of glazing from solar radiation using external louvre systems such as Umbris by IQ.

Luke Brindley
Expert in Aluminium Systems
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