Infrared thermography uses specially designed infrared video or still cameras that convert the infrared radiation into images that show surface heat variations. The technique has applications in a variety of fields, including medicine, electrical installations, cold storage facilities, etc. When applied to buildings, it can be used to examine the whole or part of the exterior envelope, or it can be used to look at surface temperatures within a building. When used to identify thermal bridges, it is usual to take images of the exterior of the building. Such images, when combined with an air pressurisation test, can also indicate points at which air is leaking from the building.
However, although thermographic scans of the outside of a building are more convenient, especially if the building is large, they have a number of drawbacks. Warm air escaping from a building does not always move through the walls in a straight line, and heat loss detected in one area of an outside wall might originate at some other hard-to-find location inside the wall. Wind conditions also affect the thermal image. On windy days, it is harder to detect temperature differences on the outside surface of the building. The most accurate thermo-graphic images usually occur in calm conditions when there is a large temperature difference (at least 14°C) between inside and outside air temperatures. For this reason, in the UK, thermographic scans are most effective when done in winter. Unfortunately, even in ideal conditions, the temperature differences between different parts of the exterior surfaces of a building are not large, and the thermal imaging equipment must have a very high resolution in order to detect them.
Further information on the application of infrared thermography to building inspections is given by Hart .
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