The Effects of #4 Surface Low-E Coatings on Fenestration Condensation Resistance

As the focus on improving building envelope thermal performance continues to grow so too have alternative solutions for improving the thermal transmittance (U-factor) of glazed fenestration systems. Lately, particular attention has been paid to achieving “R5” performance in glazed window systems; these systems having U-factor ≤ 1.14 W/m2-K (0.20 BTU/hr-ft2-°F) for fixed units and ≤ 1.25 W/m2-K (0.22 BTU/hr-ft2-°F) for operable. The traditional solution for achieving this level of performance is through the use of triple glazed insulating glass. Such construction utilizes two glazing cavities and can incorporate multiple low-e coatings for significantly improved thermal performance. An alternative is to use a suspended low-e film inside the IGU construction for similar performance results. Recently introduced is a dual glazed IGU construction that utilizes a high performance, soft-coat low-e coating on surface #2 and a hard-coat, pyrolytic low-e coating on surface #4. This construction is designed to reflect long wave infrared radiation back to the interior environment thereby decreasing thermal transmittance and achieving a U-factor approaching 1.14 W/m2-K (0.20 BTU/hr-ft2-°F). This paper highlights the degradation of condensation resistance performance of #4 surface low-e insulating glass configurations of a variety of coating and spacer constructions.

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