An insulated wall can be supported internally by thin steel girders. There will be an extra heat loss caused by the metal U-girders perpendicular to the heat flow direction reduces this heat loss.
Calculation of the heat transmittance is a difficult numerical problem due to the high ratio of the thermal conductivity between the insulation and the steel.
The study presents results of calculations in three dimensions. The proper choice of the numerical mesh is discussed.
Simplified equations for the U-value are derived and implemented in a PC-program. The heat transmittance is quickly calculated for different parameters: thermal conductivity of insulation and steel, steel thickness, distance between girders, and additional insulated layers (with or without cross-laid steel grinders).