After covering thermal transmittance U and resistance R of opaque assemblies, and insulated glass, we now cover one of the most critical areas of the thermal envelope: window frames. Good windows are the cornerstone of a performing building for both comfort and energy efficiency, specially if it is a passive house.
To achieve thermal comfort and energy efficiency in buildings, a primary role is played by the thermal envelope: this is required to thermally decouple the indoor environment from the ever-changing external conditions, both in summer and in winter. The structures of the thermal envelope need to be able to control the amount of heat migrating through them: the thermal resistance and the thermal transmittance are two ways to describe this phenomenon.
For new builds as well as energy retrofits, worldwide the construction industry is shifting more and more towards zero energy buildings and Passive Houses. With the thermal envelope becoming more and more advanced, the correct evaluation of thermal bridges becomes critical: with this article, we explain the PSI value.