Finding the best solution
The versatility of thermal imaging has prompted its take-up across virtually all industry sectors but there can be no doubt that building science is one the greatest beneficiaries of this technology. It is the ideal tool for so many diagnostic tasks in the built environment and its scope is considerably enhanced by the availability of dedicated thermal imaging cameras. Hardware and software have been developed in parallel to provide cameras that are optimally suited to building inspection.
Today’s thermal imaging camera is easily portable and year on year the technology is being developed to provide better image quality and the necessary software tools to make the job easier, quicker and more efficient. This is also a fast growing and competitive market and as a result there is a wealth of infrared camera choices available.
Finding the right model to suit both budget and application can be daunting. So, how do you find the best solution for you? In essence, you need to address five factors. These are camera resolution, camera sensitivity, additional function, software and training.
Resolution and sensitivity
The big growth in the thermal imaging market has been in the compact, torch style cameras that cost as little as £1,300. These are great troubleshooting tools but are not designed to provide the image clarity that is necessary for more detailed analysis. For this you need a thermal imaging camera with a minimum resolution of 320 x 240 pixels or better still, 640 x 480 pixels.
An infrared camera with 640 x 480 pixels has 307,200 measurement points in one image, four times as many as a model with a 340 x 240 pixel detector and 76,800 measurement points. The increased number of pixels results in a much clearer picture in which small details are clearly visible and the temperature measurement is much more accurate.
This order of performance is vital for pinpointing hot spots and determining their status in terms of urgency and danger.
It is so much easier to understand and interpret a scene when all the image details are crisp and easily defined.
Higher resolution also means you need fewer images as you can often cover a larger object with just one image. With lower resolution more images are required for the same area and image detail. With a 640 x 480 camera equipped with a 45 degrees lens, a wall area of about 4m x 3m can be inspected in a single image at a distance of 5m. To inspect the same wall with a 340 x 280 camera four images, taken at a distance of 2.25m are required.
Using a larger array camera represents a significant increase in efficiency as not only do fewer images need to be captured in the field, but also evaluating the results is far less complicated during the documentation phase.
High camera sensitivity is particularly important in building inspection as temperature differences are generally smaller than in other applications. It allows the camera to capture greater detail and therefore enable the thermographer to provide a more accurate diagnosis so the appropriate action can be taken.
As a rule of thumb, the more advanced the infrared camera the greater number of dedicated and special functions are included in the standard package. Almost all professional cameras and also some less advanced models have a built-in digital camera. Many will have features such as thermal fusion and picture-in-picture functions that merge visual and infrared images for enhanced analysis and reporting.
GPS is available for tagging the thermal image to its geographic location and clever image stitching software is another development that allows every pixel to be dragged and dropped to the composite image complete with its own radiometric data. The more advanced camera will also have interchangeable optics so that the optimal lens can be selected to the application.
A tiltable viewfinder is another feature to look out for. It is especially useful for outdoor inspection as it enables a sharp image to be shown with any influence from ambient light and reflections.
Specific alarm functions are a real boon for building inspectors. A relative humidity alarm, for example, alerts you to the areas where there is risk of condensation. An insulation alarm shows areas below or above a pre-set temperature. In figure 1 areas under the 17.5°C pre-set are clearly shown in green.
The ability to present results of a thermal imaging survey clearly and succinctly is of considerable importance. Findings not only need to be interpreted by tradesmen who subsequently undertake the repair or correct the fault, but also by others involved in the building process that may not be conversant with technicalities.
Many thermal imaging cameras are supplied with basic reporting software and naturally the more sophisticated cameras have in-built features that make reporting even better and more efficient when out in the field. They will also offer possibilities such as inputting text and voice comments, either directly or via a PDA as part of the image. The infrared and digital images are linked together and automatically presented side by side in a report.
Professional reporting software provides advanced image analysis and report creation. It supports interval
and blending fusion, picture-in-picture, imaging stitching, trending and GPS. Other advanced features include digital zoom, colour palette change, playback of voice comments recorded in the field and the automatic conversion of report to Adobe pdf format. Look for those that are Microsoft Word based as they make it intuitive and easy for users to create reports and email using industry-standard functions.
Other dedicated software packages work together with the thermal imaging camera to visualise and quantify building related problems such as air infiltration, insulation defects, thermal bridges and moisture build-up and present them in a professional report. New software developments have made it possible to produce an energy cost comparison report that calculates achievable cost savings when the identified structural problems are fixed.
Thermal imaging is a hugely valuable technology for those involved in building inspection but don’t just buy a camera and stop there. Dedicated training provides the knowledge for the operator to interpret the results more effectively and to spot more faults before they become expensive failures.
In order to interpret thermal images in the correct way you need to know how different materials and structure influence the temperature readings on the surface. For example, concrete is thermally slow whereas metals change temperature quickly. The camera user must take into account any big change in outside or inside temperature prior to the inspection as very clearly this has a bearing on the validity of the reading.
How the structure is built and the influence of sunshine and shadows must be considered. So too must reflection from surroundings. The reflection could be from the body heat of the camera operator or some other heat source in the area such as machinery, a light bulb or transformer. Reflections will result in incorrect data in the thermal image and, if this potential is not recognised by the camera user, results will be misleading.
Dedicated training in thermal imaging isn’t an extra cost; it’s an investment in payback. Anyone using thermal imaging must have a thorough grounding in the principles and application of infrared regardless of their professional qualifications. Trying to make savings on this important element can compromise the substantial cost and time saving potential of the technology.
Dedicated foundation courses for those involved in building science thermal imaging are provided throughout the UK or indeed in-house if required. And for those wishing to gain a professional qualification in thermal imaging certification to ISO/PCN standards, this can be achieved up to Level 3.