Infrared Thermography

Everything on Earth contains thermal energy and therefore has a specific temperature. This thermal energy is emitted from the surface of the material. This energy is called is infrared radiation (IR). The amount of IR radiation emitted at a certain wavelength, from the surface of an object, is a function of the object’s temperature. This is a very important concept, since it implies that one can calculate the temperature of an object by measuring the infrared radiation emitted from it.

A thermal bridge, also called a cold bridge, is an area of a building construction which has a significantly higher heat transfer than the surrounding materials. This is typically where there is either a break in the insulation, less insulation or the insulation is penetrated by an element with a higher thermal conductivity.

A qualitative report presents high quality thermal images using comparisons of energy levels to evaluate the data.

A quantitative report presents high quality images but includes temperature data (typically spot temperatures) to identify the energy levels and evaluate the data.

Infrared Thermography is a non-destructive technique which uses an infrared camera to produce visible images of infrared energy (invisible radiated heat energy) emitted by objects. The thermal image produced by an infrared camera is called a thermogram and shows a temperature distribution of the surface of an object.

Infrared energy (IR):- is part of the electromagnetic spectrum and behaves similarly to visible light. It travels through space at the speed of light and can be reflected, refracted, absorbed, and emitted. Thermography uses the middle infrared region or ‘shortwave region’ (3 to 5 microns) and infrared region (8 to 14 microns) or ‘longwave infrared region’. These regions are collectively known as the ‘thermal infrared region’ or ‘thermographic range’. In the region of 6-7 microns the atmosphere absorbs and weakens infrared signals so they cannot accurately be measured by IR cameras.

Other common forms of electromagnetic radiation include radiowaves, ultraviolet, microwaves and x-rays – see Electromagnetic Spectrum chart below

Electromagnetic Spectrum chart

Emissivity describes how effective a material is at emitting infrared energy from its surface. Emissivity is dependent on material properties, the surface finish and the temperature of the object. Determining the emissivity of an object is crucial in obtaining accurate temperature results on infrared cameras and often trained Thermographers have to employ specific techniques to obtain this. For example clean, unoxidised, bare metal polished surfaces have very low emissivity values whilst oxidised or painted surfaces have a higher emissivity.

It’s easy to see how full these tanks are in infrared because of the temperature difference on the metal surface caused by the liquid inside.

Any condition when the thermal gradient of the surface temperature deviates from the normal uniform thermal pattern that should exist for that particular component.

Using infrared cameras, Thermography measures the radiated heat emitted from the surface of an object. Infrared radiation is the energy that forms part of the electromagnetic spectrum and is normally invisible to the human eye. By measuring the heat signature of a surface, discontinuities and/or hotspots can be observed.

Although the origins of Thermography date back to 1800 it was not until 1965 that the first liquid nitrogen cooled infrared cameras were commercially available. Luckily, the Infrared cameras on the market today use advanced detector technologies, electronics and microprocessors to produce high quality infrared images without the requirement to carry around liquid nitrogen to cool them.

The most widely used application of Thermography is the inspection of electrical distribution systems. Many commercial and industrial organisations have introduced this non-intrusive technique as part of their preventative maintenance (PM) programmes. By identifying/detecting thermal anomalies early the advantages of this are as follows:-

• Prevent the risk of fire resulting in injury or death, equipment damage and financial loss
• Reduce the risk of equipment failure
• Prevention of lost production
• Predictive method of anticipating equipment failure

Mechanical systems applications include:

• AC/DC motors
• Pumps and fans
• Compressors
• Engines
• Gears
• Couplings
• Bearings
• Hydraulics
• Valves
• Drives

Air leakages in buildings which are caused by convection losses either open loop or closed loop – are almost impossible to identify using smoke detection methods. but can easily be identified by Thermography.

“Closed loop” convection losses may be observed where the air mass remains largely unchanged but temperature differences exist at the boundaries causing re-circulatory air flow whereby the air moves in a loop. A good example of this could be an unventilated cavity wall.

“Open loop” convection losses allows an air mass to be replaced by other air and therefore includes air gaps that permit air flow, and thus heat transfer, between two regions. This form of heat loss is the result of failures in airtigthness and windtightness.

Convection loops can reduce the effectiveness of insulation by up to 40% and account for up to 15% of total heat loses within a new or existing building structure

The following is a list of typical areas where open loops can be present in a building:

• Attic to ceiling soffits
• Attic to interior walls
• Pipes/ducts to outside
• Flow through vertical shafts of Attic to stairwell ceiling
• Flow behind wall/ceiling insulation
• Party wall systems
• Flow through finger spaces in masonry veneer walls
• Fireplace chimneys

The following is a list of typical areas where closed loops can be present in a building:

• Short circuit wall insulation
• Party wall system
• Basement wall system
• Ducting into unheated areas
• Within loose insulation
• Rock bed systems

Convection loses caused by either external ‘open loop’ or internal ‘closed loop’

The temperature of an object is a good indicator of its condition or health, for example if a machine is running too hot it maybe in imminent danger of failure. Detectors inside the infrared camera convert incoming infrared energy from the infrared spectrum, which is normally invisible to the human eye, to the visual spectrum so we can see the infrared energy as an image. These visual maps co-relate image intensity or colour to the amount of infrared radiation received from that object. The amount of radiation received, along with other parameters, is used to calculate the actual surface temperature of the target object. The detectors are extremely sensitive to small temperature differences so trained Thermographers in conjunction with IR software can produce valuable and accurate reports.

No despite what is depicted in movies thermal cameras cannot see through walls. Walls are generally, thick and insulated enough to block any infrared radiation from the other side. If you point a thermal camera at a wall, it will detect heat from the wall, not what’s behind it. However, if something inside the wall causes enough of a temperature difference, a thermal imager will be able to sense it on the surface of the wall.

Trained Thermographers can assist building professionals, home owners, insurance companies, building surveyors etc.. using thermal image cameras to detect issues like water leaks or missing insulation without needing to tear down walls to assess the problem.

Studs inside the wall (vertical lines) are colder than the insulation, causing a temperature difference on the surface of the wall. Note also the integrity of the insulation which is not uniform.

The answer to this question is basically the same as the question for walls no, but a thermal camera might be able to detect something inside the concrete like a pipe or radiant heating that causes a temperature difference on the surface of the concrete.

Radiant underfloor heating is clearly visible under a concrete floor. Note – since the underfloor pipework has not been evenly laid, localised hotspots mean the floor is unbearable to stand on for its users in certain places’