Thermally improved spacers As set out by the window product standard EN 14351-1 clause 4.12, one of the methods to determine the thermal transmittance UW of windows is by calculation as per EN ISO 10077-1. The quantities required for this calculation are the thermal transmittances of the frame and the glazing, Uf and Ug, respectively as well as the linear thermal transmittance Psi. The Psi-value describes the heat loss caused by fitting the glass in the frame. The amount of this Psi-value depends largely on the type of spacer inserted in the insulating glass unit. In this context we distinguish between ‘conventional‘ and thermally improved spacers. The definition of a thermally improved spacer is included in EN ISO 10077-1 and has again been summarised in the scope of this Guideline.weiterlesen