Figure 1. Static approaches to energy efficient glazing

The figure details different static approaches to energy efficient glazing.

The top left spectra come from a sputtered silver product. the spectra show that the glazing is highly reflective in the near infra-red portion of the spectrum, effectively this works as a heat mirror and stops heat entering a building thus reducing the need for air conditioning and lowering the buildings energy demand. This type of coating works best in warmer climates.

The top right spectra are from a self cleaning product. Essentially this type of product is not significantly different from standard float glass and allows the transmission of solar heat right accross the solar spectrum.

The bottom left spectra corresponds to a low emmisivity or low-e product. Low-e coatings are reflective in the far infra-red portion of the solar spectrum. Thus this type of coating allows solar heat into a building but prevents blackbody radiation (re-radiated absorbed solar radiation, a surface for example) from escaping; essentially acting as an insulator and reducing the need for internal heating. This type of product works best in cooler climates.

The bottom right spectra are from an absorbing product. Absorbing products do not transmit or reflect heat in the near infra-red and often not in the red or yellow protion of the visible spectrum - hence these products appear coloured, usually blue or green. As a result solar heat can only enter a building as black body radiation (re-radiated heat) which places less demand on cooling and heating systems. Products of this type are usually body tinted glasses rather than coated glass and they find major application in commercial building glazing in both hot and cool climates.