Thermal bridge..

Thermal bridge, also called a cold bridge, heat bridge, or thermal bypass, is an area or component of an object which has higher thermal conductivity than the surrounding materials, creating a path of least resistance for heat transfer. Thermal bridges result in an overall reduction in thermal resistance of the object. The term is frequently discussed in the context of a building's thermal envelopewhere thermal bridges result in heat transfer into or out of conditioned space.

Thermal bridges in buildings may impact the amount of energy required to heat and cool a space, cause condensation (moisture) within the building envelope, and result in thermal discomfort. In colder climates (such as The United Kingdom), thermal heat bridges can result in additional heat losses and require additional energy to mitigate.

There are strategies to reduce or prevent thermal bridging, such as limiting the number of building members that span from unconditioned to conditioned space and applying continuous insulation materials to create thermal breaks.

Heat transfer occurs through three mechanisms: convection, radiation, and conduction. A thermal bridge is an example of heat transfer through conduction. The rate of heat transfer depends on the thermal conductivity of the material and the temperature difference experienced on either side of the thermal bridge. When a temperature difference is present, heat flow will follow the path of least resistance through the material with the highest thermal conductivity and lowest thermal resistance; this path is a thermal bridge. Thermal bridging describes a situation in a building where there is a direct connection between the outside and inside through one or more elements that possess a higher thermal conductivity than the rest of the envelope of the building.

Surveying buildings for thermal bridges is performed using passive infrared thermography (IRT) according to the International Organization for Standardization(ISO). Infrared Thermography of buildings can allow thermal signatures that indicate heat leaks. IRT detects thermal abnormalities that are linked to the movement of fluids through building elements, highlighting the variations in the thermal properties of the materials that correspondingly cause a major change in temperature. The drop shadow effect, a situation in which the surrounding environment casts a shadow on the facade of the building, can lead to potential accuracy issues of measurements through inconsistent facade sun exposure. An alternative analysis method, Iterative Filtering (IF), can be used to solve this problem.

In all thermographic building inspections, the thermal image interpretation if performed by a human operator, involving a high level of subjectivity and expertise of the operator. Automated analysis approaches, such as Laser scanning technologies can provide thermal imaging on 3 dimensional CAD model surfaces and metric information to thermographic analyses. Surface temperature data in 3D models can identify and measure thermal irregularities of thermal bridges and insulation leaks. Thermal imaging can also be acquired through the use of unmanned aerial vehicles (UAV), fusing thermal data from multiple cameras and platforms. The UAV uses an infrared camera to generate a thermal field image of recorded temperature values, where every pixel represents radiative energy emitted by the surface of the building.

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