Using calculated PSI values for the thermal bridging energy loss can improve a buildings energy rating (DER or BER) by up to 16% compared to using the default PSI values. An improvement that otherwise may need to be achieved using better performing heating and cooling equipment, renewable energy or improved insulation and air tightness.
The calculation of ψ-value(s) is specialist work requiring dedicated software, able to perform 2D and 3D thermal modelling. Our specialists have an excellent grasp of BR 497: 2007 Conventions for calculating linear thermal transmittance and temperature factors is essential for performing modelling at an appropriate level and an outstanding knowledge of calculating U value(s) of plain elements. We use software that is in line with the requirements of BS EN ISO 10211: 2007.
Using calculated PSI values for the thermal bridges in a proposed new building makes sense for almost any project. But for large buildings, standardised construction details and buildings that are required to demonstrably achieve very high energy performance levels the cost benefit analysis will undoubtedly be in favour of using calculated psi values to represent the thermal bridged in the energy model.