Calculation of thermal bridges: general aspects, characteristics of the phenomenon and their calculation
In this article, we’ll be taking a look at the general aspects and methods of calculating thermal bridges.
Thermal bridges: general aspects
Thermal bridges (often referred to as cold bridges) are well identified areas where weaknesses within a building’s structure cause heat and/or cold to be transferred at a substantially higher rate than through the surrounding envelope area.
Thermal bridges can generally be divided into:
• structural based thermal bridges (or material related) where the presence of heterogeneous elements of different conductivity increases the thermal flow;
• form based thermal bridges (or geometrically related), where the presence of variations in the shape of a material (edges, restraints, etc.) results in a thickening of the flow lines with a consequent increase in thermal flow.
Typical examples of material discontinuities are found in reinforced concrete structures. When using cladding blocks without any particular insulation technique, especially at the contact points between the two different materials.
Geometric discontinuities refer to issues related to the geometry and shape of the element. Typically, geometric discontinuities occur in the following areas:
• at the edges between the walls;
• between walls and floor slabs;
• between walls and fixtures;
• at interruptions of the thermal insulation layer.
Thermal bridges are generally located at the connection points between building elements or where the building’s structure is modified, producing the following effects:
• a change in the thermal flow (amount of thermal energy absorbed in the unit of time)
• a change in the internal surface temperature
The thermal bridges are located near columns, beams, balconies, sills or even at mortar joints between bricks, which represent points of heterogeneity of the structure.
Effects of thermal bridges on living comfort
The presence of thermal bridges in buildings is a serious threat to a number of factors such as:
• living comfort
• the home’s overall wellbeing
• energy efficiency aspects
• energy consumption
• the home’s quality
It therefore becomes obvious that avoiding the formation of thermal bridges in buildings, starting right from the design phase, is essential and can only be achieved by means of special calculations.
Calculating thermal bridges
The EN ISO 13789 standard (transmission heat transfer coefficient) and EN ISO 13790 (Calculation of energy use for space heating) specify the standard for calculating thermal bridges:
• Numerical calculations (finite element analysis) according to EN ISO 10211:2008
Numeric Calculation (Finite Elements Analysis)
To calculate thermal bridges without any limitations, a finite elements solver is therefore essential.
Finite element analysis software allows you to draw and define thermal bridges of any type or form and calculate results (linear thermal transmittance, thermal coupling coefficient, thermal flow, etc.) in a numeric (analytic) and graphical form.
When dealing with Thermal Bridges in buildings, the Finite element numerical calculations method is the only way to evaluate thermal bridges and analyze virtually infinite combinations as well as the various design possibilities that the professional faces.