The defects of the building envelope are mainly divided into external surface thermal defects and internal surface thermal defects, including thermal bridge defects, ring beams, columns, corners and other parts. They are the weak parts of the thermal performance of the building's external envelope and are affecting the building Important energy saving effects and thermal comfort of buildings. At the same time, most of these wall thermal defects are hidden, and engineering data and conventional field testing methods alone are not enough to judge their location and severity, which affects the evaluation of the building's thermal performance and energy saving status. The use of infrared cameras can quickly and comprehensively judge the thermal conditions of buildings, find out the parts with thermal defects, and have an overview of the overall situation. Therefore, prior to the detailed inspection of the building envelope, the inspection of building thermal defects should be prioritized.
I. The concept of thermal bridge
• Thermal bridge refers to: some parts of the building envelope structure, due to the temperature difference between indoor and outdoor, form a region with relatively dense heat flow and low internal surface temperature. These parts become bridges with more heat transfer, so they are called thermal bridges, sometimes called cold bridges. The reason is that the place where this phenomenon occurs can always feel the existence of cold air, and the temperature is lower. .
• Heat is a kind of energy. The conduction of thermal energy requires a channel and a bridge, and those parts with low thermal resistance and large thermal conductivity provide thermal conduction bridges. Therefore, these parts are called "thermal bridges". The special term in the "Building Thermal Design Code" (GB50176-93) is "thermal bridge".
• Thermal bridges are often caused by a much larger heat transfer coefficient at this location than at adjacent locations and much worse thermal insulation performance. This is a very common phenomenon in envelope structures. Such as metal built in brick walls or aerated concrete walls, beams, columns, slabs and ribs of concrete or reinforced concrete, ribs in prefabricated insulation, metal joints in sandwich insulation walls for the two walls inside and outside the tie knot In the external thermal insulation wall, metal anchors are installed for fixed thermal insulation panels, the keels set in the internal thermal insulation layer, the connection parts of the selected balcony panels and the main structure, the door and window frames in the thermal insulation doors and windows, especially the metal door and window frames .
• In the cold season, the heat dissipation area of the corner of the outer wall is larger than the heat absorption area. The air velocity in the corner is slower, the indoor heat is less than that of the adjacent straight parts, and it is also a heat bridge part with dense heat flow and low inner surface temperature.
• Due to the low temperature of the inner surface of the thermal bridge, when the temperature is lower than the dew point temperature during the winter, water vapor will condense on the surface and form condensation.
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