Seeing the light on solar control

Adrian Adams of Saint Gobain Building Glass UK explains how the latest solar control glass can help create bright interiors without the heat or glare.

Maximising daylight is now considered fundamental to good design as it enhances the comfort of the occupants and has a direct impact on their well-being. This is often achieved through the use of large glazed areas in facades, atriums and roofs, or the installation of curtain wall systems where the glass is a structural component of the building.

Designing-in attractive large elevations of glass can however hinder the thermal performance of a building by allowing in too much natural daylight, so the effects of solar gain must be addressed during the design process.

Building orientation is one of the key factors that can mitigate excessive sun exposure. The Royal Institute of British Architects (RIBA) advises that for any site, knowledge of ‘sunpaths’ is “fundamental in designing building facades to let in light and passive solar gain, as well as reducing glare and overheating to the building’s interior.”

It is important to carefully consider the strategy for handling solar gain as it will have an impact on the building appearance. Common solutions such as brise soleil can provide external shading, while window blinds may be adopted for internal shading – although their effectiveness would depend on how often building occupants use them.

However, if architects envisage designing a building with uninterrupted sightlines and smooth elevations while also aiming to maximise daylight, it is the type of glass they specify that holds the key to success.

How solar control glazing works

The secret to the performance of solar control glazing lies in the microscopically-thin coating that is applied to the glass substrate that forms the basis of these products. The coatings are applied to clear float glass under controlled conditions and consist of single, double or triple layers of silver.

The coating is positioned on the inside face of the outer pane of glass (also known as face two) within a double or triple glazed unit. It reflects sunlight to reduce the amount entering the building and also works to reduce uncomfortable glare. The coating delivers an optimum balance between the amount of light transmittance that penetrates the glass and the amount of solar heat that is reflected, the ratio of which is described as a coating’s “selectivity index.”

Insulating capabilities

The latest generation of solar control glass delivers higher levels of selectivity than ever before. SGG Cool-Lite Xtreme 50/22 Ii for example has a selectivity of 2.24, which is believed to be the most selective triple silver product available in Europe – and comes with the added benefit of maintaining neutrality of colour.  This also delivers another important aspect to the performance of the glass – its insulating capabilities.

Products such as these deliver glass facades with a centre pane U-value as low as 1.0 W/m²K, while optimising the solar control performance. This ability to combine the solar control and insulating benefits into one glass product puts the performance of the facade at the heart of a building’s energy saving strategy.

In terms of assessing how the energy consumption of a building can be minimised, the predictability of the way the glass coatings will perform over time, without degradation, provides a ‘fit-and-forget’ element for specifiers.

Knowing that the glass will perform to a given level reflecting heat in summer months means mechanical engineers and building managers can focus their efforts on managing other issues, such as the heat generated as a result of building use and occupancy using other mechanical and passive cooling solutions. With the solar control glass doing its job efficiently – maintenance-free – the reliance on such cooling solutions is reduced and energy consumption cut as a result.

During colder months, the solar control glass aids thermal retention with its insulating properties. The low U-value of the glass gives architects the scope to use glazed facades as part of a highly insulated building envelope – and model the insulating qualities in exactly the same way as for roofing, floors and walls.

The energy saving benefit comes with reduced reliance on heating systems given that the glass reflects heat back into the building.  It also ensures that cold spots are reduced close up to the facade, something that building occupiers will often notice in buildings featuring earlier generations of glass. This helps stabilise internal temperatures, with fewer variations in performance to manage and consider.

The product’s ability to harness good levels of light transmittance also means less reliance on artificial lighting during daytime hours which will help to significantly reduce energy consumption.  This energy saving benefit is, of course, in addition to the health and well-being benefits associated with maximising natural daylight in the workplace, including reduced absenteeism and improved productivity.

Adrian Adams is Saint-Gobain Building Glass UK’s commercial market manager