Temperature and heat flow analysys in Thermal Bridges with a Finite Element Model

The purpose of this paper is to analyze some thermal bridge typologies not proposed in the ISO Standard prEN ISO 14683 and in the Italian Standard UNI 7357, but nearly always used in the building practice: inside or outside corners between walls of the same material with a column represent one of the most heavy condition that can take place. Using a finite difference program, the minimum temperature factors, the linear thermal coefficients and the heat flows in both directions x and y have been evaluated. This work has been repeated with three different insulating materials commonly used (expanded polystyrene, polyurethane and glass wool) considering three different positions of the insulating material in the structure (at the outside of the wall, at the inside of the wall and in the middle of the wall). The simulations have been done also considering different relative humidity conditions (from 50% to 80%) because most building materials absorb moisture from the air. The insulating materials are not influenced by humidity but, on the contrary, the thermal behavior of building materials (both high and medium density) depends on moisture contents because, usually, the absorption of the moisture from the air influence the thermal conductivity of the material. For each of the proposed thermal bridges, the graphics related to the temperature factors, the linear thermal coefficients, the isotherms and the heat flows will be shown. Some relations are also proposed to predict the linear thermal transmission without doing any measurement, according to the Italian Standard UNI 7357 FA-3.