Thermal bridge

Thermal bridge, as known as cold bridge. Thermal bridge is used to describe an area or a material that conducts heat better than surrounding areas, thereby providing a path of least thermal resistance for heat transfer. Therefore, all the heat on the high temperature side is transferred from this area to the low temperature side. The presence of thermal bridges reduces the average thermal resistance across the interface. According to the different causes of thermal bridges, it can be divided into Geometrical Thermal Bridges (thin components compared to other areas) and Material Thermal Bridges (using materials with better thermal conductivity).

In practice, these two types of thermal bridges usually work simultaneously.

The name of the thermal bridge is a vivid description. The surrounding area with high thermal resistance which is like a river people is hard to across it. However, the thermal bridge is like a bridge on the river, which provides convenience for people to cross the river. In addition, the most of the heat tends to be dissipated from the thermal bridge if there is a thermal bridge at some interface, just like when there is a bridge on the river, people are unwilling to wade through the river rather than walk along the river bank first then cross the river from the bridge.

The Concept of thermal bridges is commonly used to describe the construction of building surface. When there is a thermal bridge on the building surface, it is easier for heat to flow into or out of the building interior, making the temperature inside the building more susceptible to the outside temperature, and then increasing the load on the air conditioning system. In the meanwhile, thermal bridges may also cause the temperature of certain surfaces of the building to be too low, causing risks such as condensation that may cause seepage, wetting of insulation materials and other consequences. In conclusion, thermal bridges in buildings usually has a significant negative impact on the thermal comfort of people in the built environment.

The thermal bridge phenomenon can be alleviated or eliminated by some design strategies or construction techniques, which are called thermal bridge design or thermal bridge construction.

Author Professor Wei-Keng Lin Education｜Ph.D., University of Maryland Occupation｜Professor, National Tsing Hua University  Specialty｜Electronic package heat dissipation, Heat pipe, Loop heat pipes(CPL，LHP，PHP), Energy-saving design, Solar heat storage and cooling, Heat flow system, Cooling of electronic components, Two-phase flow, Heat transfer elements of artificial satellite and high-altitude flying object