Building thermography: including blower door and heat flux meter by Lanzoni Davide

Author:Lanzoni, Davide [Lanzoni, Davide]
Language: eng
Format: epub
Publisher: Davide Lanzoni
Published: 2015-01-08T16:00:00+00:00

On the other hand, if within the wall there is a defect consisting of a conductive element, for example consisting of metal or thermal bridge (shown in grey in the figure below), with a greater thermal conductivity, the trend of the isotherms will no longer be regular and the surface temperature of the wall will be greater on the opposite side (red line).

The heat capacity (m * c) acts as "slower" for propagation of the heat flow, since Q = m*c*ΔT. The thick walls heat up slowly and remain hot for longer when the heat source ceases, with the same transmittance with respect to lighter elements.

If the defect is superficial and consists of detachment of the plaster, in the area of the detachment between the plaster and the rear masonry, there is an air layer which constitutes an insulator with lower thermal capacity. It will cause that plaster heats up very quickly and could give rise to false interpretations, but its irregular form facilitates identification as a surface defect of the plaster and not as a region with different rear mass masonry.

Similar considerations apply to the detachment of façade covering tiles; in this type of survey, essentially qualitative in nature, an element of difficulty can be constituted by specular reflectivity of the tiles, so that in this case it is advisable to take the same picture from different angles in order to recognise any reflections, and to repeat the survey while the façade is heating or cooling.

The image below, with temperatures in degrees F, taken in the summer during heating of the south east façade, shows 3 areas of measurement:

• AR01: an apparently normal area

• AR02: a colder area thus probably wet: the greater thermal capacity of the water slows its heating

• AR03, a warmer area, thus probably with removal of the coating: the presence of a blade of air behind the sunny surface slows down the transfer of heat and thus causes a faster increase in surface temperature

Note on the right-hand portion of the façade parts of the covering of a darker colour and how these parts become much warmer and faster because of the greater solar absorptivity, making it very difficult to compare them with the other areas.

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