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Heat losses through the building envelope is one of the key factors in thecalculation of the building energy balance. If steady-state heat conduction isobserved, which is commonly used to assess the heat losses in building, thereis an analytical solution for one-dimensional problem. For two andthree-dimensional problems, especially for the complex geometry cases, one mustuse numerical methods to solve the heat conduction equation. To standardise twoand three-dimensional calculation of heat losses through building elements, ISO10211 standard can be used. The standard has four benchmark examples withcriteria that must be satisfied to declare a method as a high-precisioncalculation method. A problem occurs for Case 1 of benchmark test because theanalysed problem has a singular point due to discretely assigned Dirichletboundary conditions. The reliability of the results around the singular pointcould be improved by the refinement of the mesh in the area around the singularpoint, but as a point of interest is the total heat flux that is entering thebuilding element, and it must converge between subdivisions, this method is notgood since the reliable result cannot be reached. The problem for theconvergence is in the marginal node because the temperature gradient in itincreases as the temperature difference remains constant and the distancebetween the corresponding nodes decreases. For that reason, Case 1 from thebenchmark is inadequate because even if there is a discontinuity in temperaturefield on the boundary, there is an interval in which this change is to happen,and the heat flux has a theoretical limit which is not infinity. From theresults of this research, it is shown that one should neglect a certain numberof singular points in order to achieve the tolerance given by the standardsince the temperature further from the marginal node is stable for anysubdivision.

Total heat flux convergence in the calculation of 2d and 3d heat losses through building elements