With the formula
ψ = L2D – (Σ Ui*li*Fxi)
the Ψ values can be changed depending on the reference lengths assigned to the respective U values.
There are situations where this is necessary:
– with other normative conditions (keyword external dimension reference / internal dimension reference)
– for differences between the dimensional references of the thermal bridge taken from the thermal bridge catalogue and the lengths defined in the heat requirement calculation (example: difference between the upper edge of the raw ceiling and the upper edge of the finished floor).
In the following you will find various blog posts on the subject of “Changing the reference lengths of the U-values”:
04 Example basement ceiling (unheated basement)
05 Example basement ceiling (heated basement)