Insulation performance caught on camera

External thermal insulation systems are gaining popularity in European construction, driven by need to maximise the energy efficiency of buildings. Unfortunately, says FLIR Systems, best practise in their installation is lagging behind take-up, often compromising the effectiveness of this new technology  

Thermal imaging is a suitable technology for establishing the integrity of internal and also external insulation. The aim of the study was therefore to establish benchmark thermal data that will guide thermographers in the correct interpretation of the nature of faults when inspecting external insulation installations.

For this purpose a test structure was built, covered on three sides with thermal insulation panels made from expanded polystyrene (EPS) with graphite additives.  In the top half of the structure, the walls were covered replicating the laying mistakes that are commonly made. In the bottom half the external insulation was correctly laid, with and without EPS dowels.

The thermal performance of the entire wall was then captured by a FLIR T640bx thermal imaging camera which took and stored periodic radiometric images during the solar cycle.  The method used for this work is known as active thermography, when the thermal effects of the solar radiation on the substrate are analysed during the discharge phase, in other words, when the sun goes down.

ANIT chose the FLIR T640bx camera – one of the company’s dedicated building models – because of its suitability for the variety of technical requirements involved in this project.  For example, the camera had to be able to discern small temperature differences, typically 0.5°C, and to record superficial temperature variations automatically during different time lapses. The camera’s ability to generate good quality video images was another factor in its favour.

Findings

Analysis of the characteristics of the materials shows different behaviour in terms of energy charging caused by solar radiation and subsequent discharge when the structure was in the shade.  In the first graph it is clear that the PVC and adhesive have greater effusivity than EPS.

Thermal effusivity is a measure of the material’s thermal energy penetration ability.  This is an important parameter as the surface temperature of the external thermal insulation is strongly influenced by how the material conducts heat to the various sub-layers combined with the material’s capacity to accumulate heat and therefore warm-up. The lower the effusivity value, the lesser amount of energy is required to heat the material.

In the second graph the structure is allowed to cool in the shade.  The PVC and adhesive have a greater volumetric heat capacity so they have accumulated more thermal energy and will be initially hotter than the EPS.  The EPS itself cools down more rapidly with the dowels and the adhesive joints being the hottest points.

The thermal analysis makes it clear that there are two distinct types of surface layers; the insulating material with low thermal conductivity and limited thermal capacity and the adhesive and PVC dowels which have higher thermal conductivity and greater heat capacity. 

This information is key for any building inspector using thermography to determine whether external insulation has been correctly installed and the nature of any fault. As with all thermal findings, a thorough understanding of the physics involved in the technology and the anomalies that are specific to the application are vital components in its effectiveness.  

These research findings are now being applied by both ANIT and training bodies such as FLIR Systems’ ITC to ensure building thermographers are better prepared for the inspection of external insulation.