Thermal Bridge Calculation

Thermal bridge is an area of a building, which has a significantly higher heat transfer than the surrounding materials (where a heat transmission is added to the 1D flux approximation usually computed).

The bigger building envelope insulation is the bigger impact of the thermal bridge effect is. Better insulated buildings are in fact the current trend.

In Romania, thermal bridge effect in the building energy performance calculation is required even when producing Energy Performance Certificates (EPCs). Romanian legislation, Annex K: “Catalogue with thermal bridges specific to buildings” of Normative C 107/3-2005 amended and supplemented by Order no. 1590 of August 24, 2012, provides values of the linear thermal transfer coefficients for a limited number of construction details. But the various details encountered in reality are of course different in many cases.

Thermal bridge simulation examples are presented in the below figure for two building details.


Wall terrace roof joint detail: a) architectural detail, b) heat flux density


Overhang detail: a) architectural detail, b) conventionally colored isotherms

The thermal bridges generated by windows are very important, especially for high efficiency buildings. In a super insulated and airtight building, selecting highly efficient energy window models is not enough. Careful detailing of the window mounting, window position depth and attachment to the wall structure is necessary too, in order to achieve energy performance of the integral wall.

Making decisions about adequate windows for a (new or retrofitted) building design may be decisively important for success. Windows lose important energy through heat transmission during the cold season, but they also can give valuable solar gains, with proper orientation.

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