Heat reflecting and heat absorbing glazing

These products are usually considered for application in situations where overheating poses a risk. Visible light and solar heat gain are both parts of the electromagnetic spectrum of energy emitted by the sun. The interaction of glazing with light and solar heat has three components: reflection, absorption and transmission.

Modifications in the proportions of reflected, absorbed and transmitted radiation could be engineered by changing the glazing system properties. There are several ways of achieving this:

• using 'body tinted' glass, which increases absorption;

• using reflective coatings, which increase the reflected component and, usually, the absorbed component;

• using combinations of body tinted and reflective coatings.

It must be remembered that a reduction in solar heat gain can only be achieved at the cost of reducing daylight transmission, though some tinting and reflective products are more selective than others. The reflected component can be increased by changing the angle of incidence - the more acute the angle, the greater the reflection.

Body tinted glass is normally available in a range of colours including grey, green, bronze and blue. The tinting is produced by the addition of small amounts of metal oxides during production, and it is present throughout the thickness of the glass. The effect is to increase the absorption of the radiation within the glazing, reducing the directly transmitted component. However, the heat absorbed must be dissipated as the glass temperature increases. The warmth of the glass transmits heat inwards as well as outwards. Because of this the body tinted layer would normally be installed as the outer pane of a multi-pane unit. Though body tinted glass has an effect on heat transmission it also has aesthetic implications.

For improved solar heat gain attenuation, reflective coated glass has a better performance. The coating is applied to the surface of the glass which must be installed on the side facing in towards the cavity of a sealed unit, or by applying a second laminating layer.

Reflective coatings are available in a wide range of colours and with a wide range of performance specifications. It is easier to specify and produce a glass with specific properties for a specific application than with body tinted varieties. In hot climates, glazing is specified to reduce heat gain, both by direct solar transmission, which can be as low as 10 per cent in some cases, and by conduction. To achieve this second aim, a double glazed unit with a reflective outer layer is combined with a low emissivity coated inner layer to reflect outwards the heat which is transmitted. Avoidance of glare and the provision of some natural light and view, are also considerations. In temperate climates a balance must be struck between control of summer heat gain and the benefits of winter sun, plus the fact that higher levels of natural daylight are required. No two situations are quite the same and it is important to consider the full range of options before choosing a particular product or glazing system.

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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