On which surface would you recommend applying a ‘Low-E’ coating to achieve the best solar performance?
Currently, the industry offers ‘Low-E’ coatings on both the #2 surface and the #3 surface. On which surface would you recommend applying the coating to achieve the best solar performance?
Ultimately this depends upon the type of ‘Low-E’ coating. When referring to coatings whose primary function is solar control (such as Guardian SunGuard products) then these should be applied on surface #2, or rather on the outer pane facing the building interior. Solar control coatings by necessity are spectrally selective, and as such comprise of a complex layer of materials to provide the varying levels of solar control performance as well as the low U Values required by todays designers. These coatings are also designed to have a specific aesthetic when viewed from the exterior and another when viewed from the interior. For this reason if the solar control coating was placed on surface #3 it would not look as intended.
When referring to a ‘Low-E’ coating whose primary function is thermal insulation (such as Guardian ClimaGuard products) these are normally applied to surface #3, or on the inner pane facing the building exterior. Unlike the solar control coatings they are not as spectrally selective which results in a more neutral appearance and so can be placed on surface #2 without altering the aesthetic dramatically, however the performance characteristics will change, with the solar factor reducing.
By way of some examples, a ‘Low-E’ coating is often on surface #3 in residential applications to achieve a higher solar heat gain and positive energy balance in the colder seasons. Conversely, reducing solar factor is most important in commercial buildings where air conditioning costs can be high. This can be achieved with a thermal insulation ‘Low-E’ coating on surface #2 or by using solar control ‘Low-E’ coatings such as SunGuard HP, SunGuard SN and SunGuard SNX. The silver functional layer of these coatings reflects both the longwave heat radiation for a good thermal insulation and the shortwave solar radiation for a good solar protection.