Infrared Thermography: The Detective in Your Toolbox Stephanie M. Robinson, PEng WSP Canada, Inc. 300-2611 Queensview Drive, Ottawa, ON K2B 8K2 613-690-3888 • stephanie.robinson@wsp.com and Harry W. Koyle, RRO WSP Canada, Inc. 237 4TH Avenue SW, Suite 3300, Calgary, AB T2P 4K3 587-482-0313 • harry.koyle@wsp.com IIBEC 2020 Virtual International Conve ntion & Trade Show | June 12-14, 2020 R obi nson and Koyle | 199 200 | Robi nson and Koyle IIBEC 2020 Virtual International Conve ntion & Trade Show | June 12-14, 2020 Stephanie Robinson is the manager for the building sciences team of her company’s Ottawa office. Robinson leads technical decisions for roofing and cladding projects across Canada and manages her firm’s Roofing Centre of Excellence, a national team that connects the roofing business by sharing knowledge, managing internal company processes and documents, and promoting industry reputation. She is a Level 2 Certified Thermographer. Robinson has served on the board for the Building Envelope Council Ottawa Region (BECOR) and currently serves as the secretary and National Capital Region Branch Liaison for the IIBEC Southern Ontario Chapter. Harry Koyle is currently a project director for the building sciences team of his company’s Calgary, AB, office. With over 35 years of experience in the roofing and building enclosure industry, he has extensive experience in all fields related to these important components of a building. Koyle is a Registered Roof Observer, an ARCA Approved Inspector, and a Certified Infrared Thermographer. He is a charter member of the IIBEC Canadian Prairies Chapter and has served on the executive committee of the Alberta Building Envelope Council for six years. ABSTRACT SPEAKERS Infrared thermography is a non-invasive testing method for detecting infrared energy radiated from building surfaces. Its ability to identify thermal patterns indicative of heat loss and trapped moisture enables the accurate location of compromised building enclosures and roof assemblies. This presentation will examine the capabilities and limitations of thermography, as well as the conditions required to attain useful results when scanning walls and roofs. The presenters will use case studies that exhibit the benefits of infrared thermography as an investigative tool, referencing images that show solid examples of challenges and eureka moments. Practical examples from real projects will help attendees learn how a thermographer’s ability to interpret images—and not necessarily the caliber of the equipment— drives a successful analysis. The objective of this presentation is to demonstrate how a comprehensive understanding of the equipment, thermodynamics, and building enclosure systems is required to generate quality results and how a lack of understanding can lead to completely different conclusions. Our intent here is not to train the reader to become a thermographer, an expert in infrared (IR) technology, or an adept building enclosure consultant. Instead, we hope to help you to understand the advantages and limitations of an IR thermography scan in the context of building enclosure investigation so that you might better realize how and when a thermal scan will assist you on a project and, more importantly, when it will not. Like all tools in our investigation toolboxes, thermography is not a magic wand. While it can be a powerful tool, it can lead to inaccurate conclusions if used without an appropriate appreciation and understanding of its limitations based on current technology, quality of the equipment, environmental factors, and subject matter. All of this comes back to the training and qualification of the thermographer or the person interpreting the results of the IR scan. This paper intends to demonstrate the importance of a comprehensive understanding of scanning processes by discussing some of the most common misunderstandings of IR thermography scans that will lead to misdiagnosis of building enclosure performance. A BRIEF HISTORY OF IR THERMOGRAPHY To start with, what are we measuring with an IR camera? An IR camera measures heat energy radiating from the surface of a subject. It is a nondestructive device that does not affect the target subject. It captures a thermal image or “thermogram” that visualizes heat patterns. Studies into detecting and measuring IR radiation began in the 1800s, with the first non-contact detector developed in 1835.1 By the early 1900s, IR detection technology was being used in military operations, and the first thermal imaging cameras—along with handbooks describing how to apply the technology— were available on the commercial market by the mid-1960s. In the field of building diagnostics, IR thermography has been used for decades. The first units were very large and heavy, mounted on vehicles to make them mobile, required a truck to move them, and used an oscilloscope to display radiation on a two-dimensional plot output. In the 1970s, manufacturers removed the power cord and reduced the weight, providing portable cameras (Figure 1). They were large, cumbersome, heavy portable cameras that required a back brace for the operator and additional considerations for the safe transport of liquid nitrogen for the coolant, but they were portable nonetheless. Fast forward to today. We now have cameras with very high resolution, digital photography capabilities, adjustable input menus, multiple color palettes, laser pointers, interconnected reporting software, and built-in WiFi and Bluetooth links (Figure 2). As an added bonus, we don’t even need to hold the camera anymore if we mount it to an unmanned aerial vehicle Infrared Thermography: The Detective in Your Toolbox IIBEC 2020 Virtual International Conve ntion & Trade Show | June 12-14, 2020 R obi nson and Koyle | 201 Figure 1 – Examples of early thermography cameras.3 Figure 2 – Examples of modern thermography cameras. 4 or drone. A technology that boasts that it can keep the user out of danger, measure hundreds of temperature points in one image, and speed up the investigative process is certainly attractive, but remember that improved technology will only provide improved results if you know how to use it and what to look for. UNDERSTANDING A THERMOGRAM An IR camera detects heat energy as IR radiation and converts it into an electronic signal, which is then further processed to produce a thermogram, or visualization of the radiation patterns, on a monitor/screen (Figure 3). The camera will display a scale, which defines which colors represent a low level versus high level of radiation detected; the differences between the low and high temperatures shown is the span. Most devices also perform real-time temperature calculations and display them to the user; the accuracy of these temperature calculations relies on input of various environmental conditions and subject material properties by the camera user. Thermograms can be saved as a digital file for further analysis and reporting. APPLICATION OF IR THERMOGRAPHY TO BUILDING ENCLOSURE INVESTIGATION In the world of building enclosure consulting, IR thermography is most often used as a nondestructive diagnostic tool to identify heat anomalies that could indicate air leakage, thermal bridging, and/or concealed moisture. The important thing to remember is that the camera only detects radiation at the surface of the subject; the camera cannot “see” into the concealed layers of an assembly. It cannot see through materials at all—even materials that are transparent to visible or ultraviolet (UV) light, such as glass. It only detects and illustrates heat patterns at the surface of a subject located closest to the camera operator. It is therefore up to investigators to determine the optimal conditions that will produce heat patterns at the surface of the subject and to interpret what those patterns mean. A common misunderstanding is that the camera sees wet or missing insulation, thermal bridging, air leakage, mold, etc. IR thermography is able to detect the symptoms of these conditions (heat loss or heat absorption) because they influence heat transfer. Air infiltration/exfiltration contributes to convective heat transfer, and thermal bridging/moisture accumulation contributes to conductive heat transfer. These conditions will affect the rate at which heat moves through the layers of a building enclosure. When the rate of heat flow varies within the concealed components of an assembly, patterns in temperature or IR radiation variances are detected at the surface closest to the camera operator. Areas that show up as warmer or cooler than the surrounding assembly are identified as “thermal anomalies,” and these anomalies may indicate that conditions at one particular location do not match the surrounding conditions. The camera illustrates the surface temperature of the enclosure, and it is up to the skill of the investigative team to determine the cause. For a thermograph to become anything more than a colorful image, the team must possess a comprehensive understanding of a multitude of factors which can be summarized into three categories: • Environmental conditions at, and leading up to, the time that an image is captured • Composition and material characteristics of the building enclosure being photographed • The presentation/manipulation of the digital image 202 | RobiBInson and Koyle IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Figure 3 – Examples of thermograms; temperature span (scale) on right. The thermogram in Figure 4 has no fewer than eight types of exposed exterior cladding materials. Each of these materials has a different emissivity (ability to radiate energy) and a different thermal conductivity (ability to transfer heat). Though they are all exposed to most of the same environmental conditions (temperature, wind, solar radiation, humidity, etc.), they will each act differently under these conditions. In addition, there is no way to know which conditions they are subjected to without accurate documentation at the time the image is captured. Public Works Canada defines three levels of IR technology as follows:2 • Level 1 Thermographic: Locating thermal anomalies and interpreting problem mechanisms. Both activities are performed by a para-professional (thermographer, a trained IR camera operator with a para-professional knowledge level of building science) and produce qualitative results. • Level 2 Thermologic: Interpreting the significance of the identified problem mechanisms to the construction, and recommending appropriate action to correct the problem. Both activities are performed by a thermologist (a trained IR camera operator with a professional knowledge level of building science) and produce quantitative results. • Level 3 Building Science: Interpreting the cause and effect of building problems and detailing design recommendations to correct existing complex problems and prevent future occurrences. All activities are performed by a building scientist (a trained IR thermal image interpreter with a specialist knowledge level of building science) and produce quantitative results. Though all three roles may not necessarily be performed by one person on a given project, the authors argue that all of these roles must be filled by the project team as a whole in order to appropriately capture an image, interpret that image, and provide a conclusion. Keep in mind that “additional investigation required” may often be a perfectly valid conclusion given some of the technology’s limitations. Thermography is a qualitative tool and may often require pairing with additional quantitative testing or destructive openings in order to arrive at accurate conclusions regarding the magnitude, source, and consequential risk for heat loss or wet materials within the building enclosure. In order to achieve consistent results and support diagnosis activities, the team should understand and follow the guidelines of industry-recognized standards such as: • CAN/CGSB 149-GP-2MP, Manual for Thermographic Analysis of Building Enclosures • ASTM C1060, Standard Practice for Thermographic Inspection of Insulation Installations in Envelope Cavities of Frame Buildings • ASTM E1186-98, Standard Practices for Air Leakage Site Detection in Building Envelopes and Air Retarder Systems • ANSI-ASHRAE Standard 101, Application of Infrared Sensing Devices to the Assessment of Building Heat Loss Characteristics • ISO Standard 6781, Thermal Insulation – Qualitative Detection of Thermal Irregularities in Building Envelopes – Infrared Method These standards typically lay out methodologies for data collection and analysis and discuss the effects of environmental conditions on scan results, but they do not, in many cases, dictate specific environmental conditions under which a scan must be completed. This is because environmental conditions encountered while scanning building enclosures are difficult to control and are variable. In fact, camera operators may be forced to measure and account for varying conditions throughout the course of one scan. ENVIRONMENTAL CONDITIONS INFLUENCING BUILDING ENCLOSURE SCANS The following environmental conditions are the most influential on the results and diagnosis of thermal anomalies related to building enclosures. The entire team needs to understand these and agree on appropriate measurement and documentation IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 R roBInson and Koyle | 203 Figure 4 – Thermogram of typical multifamily townhouse displaying a variety of cladding materials. In the world of building enclosure consulting, IR thermography is most often used as a nondestructive diagnostic tool to identify heat anomalies that could indicate air leakage, thermal bridging, and/or concealed moisture. techniques so that information is not lost between the camera operator and the thermogram interpreter. We are at the mercy of Mother Nature, and the team must understand that it is not always possible to complete a scan under the optimal conditions for each category listed below, but in understanding the optimal conditions, the team can adjust their methods and compensate by exaggerating the conditions that they can control (such as interior operating conditions). Environmental conditions may also change during the course of the IR scan, which will alter what the thermographer is viewing and affect the interpretation. At the end of the day, the team must be adaptable and diligent in their recording and communication protocol. Interior/Exterior Temperature Interior and exterior temperature are most influential if you are trying to assess heat transfer through the building enclosure via air leakage or thermal bridging. The greater the temperature difference between the interior and the exterior, the easier it will be to see local surface temperature changes due to air infiltration/exfiltration or thermal bridging. In an ideal world, the authors aim to schedule a scan when there is a temperature differential of at least 18°C (64°F). In northern climates, this is very easily accomplished during winter; in southern climates, you might have more success during the summer. Solar Radiation All materials will absorb, reflect, and transmit heat energy that they are exposed to in different ratios, depending on their physical properties (absorption + reflection + transmission = 100% heat energy). In a thermography scan, we are trying to detect the amount of heat energy absorbed and then emitted (absorptivity = emissivity) by a material while ignoring heat energy that is reflected back at the camera. Exposure to solar radiation as a source of heat energy can be either a help or a hindrance to your thermal scan, depending on what you are looking for and the emissivity/absorptivity of your subject. If you are looking for evidence of thermal bridging or air leakage, solar radiation is a distraction, as it can mask any heat loss occurring through the building enclosure by heating up highly absorptive exterior cladding surfaces or bouncing off of highly reflective cladding surfaces. A clear, sunny day will warm the south and west exposures more than the north and east exposures, which needs to be taken into consideration when conducting the scan. To eliminate this distraction, it is best to scan the walls at night after the exterior surface of the cladding has cooled; this may take several hours, depending on the exterior temperatures and the thermal conductivity of the cladding material. Figure 5 is a good example of the results you will see if you do not wait long enough for the heat from solar radiation to dissipate before completing your scan. The image shows elevated temperatures (yellow hues) at the masonry tower on the left and the concrete foundation at the bottom of the frame. This image, captured of the southwest elevation, was within 20 minutes of sunset, and there is a risk that the patterns shown are demonstrating heat retention in materials with greater thermal mass that have absorbed solar radiation throughout the day. These patterns could be masking thermal anomalies resulting from heat loss through the enclosure that would be expected to display in similar yellow colors. If you are looking for evidence of moisture in the walls or roof, solar radiation is your friend. We are usually able to detect heat patterns indicative of moisture due to the variance in thermal conductivity between wet and dry materials. Wet materials will warm and cool more slowly than dry materials. This type of scan is best conducted immediately after sundown following a warm sunny day as your subject begins to cool or just after sunrise as your subject 204 | RobiBInson and Koyle IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Figure 5 – Thermogram captured shortly after sunset on southwest elevation. Masonry tower (left), asbestos panels, and concrete foundation wall with heat signatures resulting from solar radiation absorption; varies by material. Figure 6 – Thermal anomaly indicative of wet insulation in a conventional roof assembly. begins to warm so that you can observe the temperature difference between the wet and dry materials. Figure 6 shows the temperature difference between wet insulation and dry insulation as the materials cool at different rates after sundown. Wind Wind has arguably the greatest potential effect on scan results. A 4.83-km/h (3-mph) wind can cut the temperature rise of a hot spot in half. It creates a “washing” effect that, through convection, carries the heat signature away from the cladding surface. In the authors’ opinion, wind speeds less than 16 km/h (10 mph) are desirable; risk for thermal anomalies being undetectable increases as wind speeds increase beyond this. Anything greater than this increases the risk that heat patterns will be difficult or impossible to detect, resulting in false negatives. Air Pressure While we cannot see air leakage itself, we can see the symptoms as heat patterns. It can often be difficult to ascertain the difference between heat loss due to air leakage versus heat loss due to thermal bridging. One trick that we use in our diagnosis between the two is to complete a dual-stage scan. Scan the building once while using the HVAC systems to create a positive pressure on the building enclosure to exacerbate any air exfiltration, and once under neutral or negative pressure to minimize air leakage. Under these two conditions, heat loss due to thermal bridging will generally maintain a consistent visual pattern (air pressure does not significantly affect conductive heat flow), but heat loss due to air leakage will vary between the images. Figure 7 demonstrates an example of air leakage observed through ladder support penetrations through the air barrier under positive and neutral pressure. The greater the air pressure differential, the easier it is to capture heat loss due to air leakage. A building with a minimum positive air pressure of 25 to 30 Pa (0.5 to 0.6 psf) is desirable. While this dual-stage scanning approach does require additional time for data collection on site, it can improve the accuracy of the analysis and thermogram interpretation. The scan team must also be mindful of natural environmental factors that can influence air pressure differential across the building enclosure: wind pressure and stack effect. Wind acting on the windward side of an enclosure will counteract any positive pressure differential that you are creating with HVAC systems, while wind acting on the leeward side of an enclosure will enhance a positive pressure differential. In tall buildings, stack effect will typically counteract positive pressures that the building operator is trying to exert on the building enclosure at lower levels while enhancing the positive pressure differential at the top of the building. The camera operator and image interpreter must be aware of the impact that the HVAC systems, wind, and stack effect all have on the pressure differential across the enclosure in order to appropriately ascertain the risk for air leakage. The team must also accept that they often may not have control over any of these aspects, which makes arriving at a conclusion using thermography alone more difficult. Humidity Everything needs to be dry. Humidity (including precipitation) in the air will affect the accuracy of temperature measurements and generally affect focus and image quality taken by the camera. Moisture on the surface of the cladding subject will mask any heat radiation of the concealed materials below due to the factors described above (Figure 8). Similar to glass, thermographic cameras cannot see through water; they detect heat patterns on the surface of the subject closest to the camera. If the closest surface is water, the heat characteristics of the water will be measured and obscure any footprint of heat loss on cladding elements beyond. IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 R roBInson and Koyle | 205 Figure 7 – Thermal anomaly indicative of air leakage. Left image captured with positive air pressure differential across building envelope; right image captured with neutral air pressure differential. Figure 8 – Standing water on a conventional roof reflects the temperature of the night sky and displays as much colder than surrounding roof surface. Recommended Scan Conditions When we have the luxury of unlimited time and resources and can choose, within reason, the conditions under which a scan is performed, the authors would prefer the following to achieve optimal results: 1) For scans aiming to identify heat loss (thermal bridging or air leakage): • Temperature differential: 18°C (64°F) between interior and exterior • Solar radiation: no direct exposure • Wind: less than 16 km/h (10 mph) • Air pressure: dual stage; first stage with +25 to +30 Pa (+0.52 to +0.63 psf) and second stage with neutral or -5 to -10 Pa (-0.11 to -0.21 psf) • Humidity: no precipitation within 48 hours prior to scan 2) For scans aiming to identify concealed moisture: • Temperature differential: 10°C (50°F) between day and night to allow temperature change of materials; temperature between interior/exterior is irrelevant • Solar radiation: direct exposure desired during the day with scan completed after sundown • Wind: less than 16 km/h (10 mph) • Air pressure: neutral so as not to influence scan with air leakage • Humidity: no precipitation within 48 hours prior to scan Given that we don’t always have control over some of these conditions, the authors often find it more useful to understand the influences and limitations of the environmental conditions and compensate for them as well as possible rather than to strive for the “perfect” scan scenario. Of course, the material properties of the subject also contribute to the scan results. MATERIAL PROPERTIES WITH GREATEST INFLUENCE ON BUILDING ENCLOSURE SCANS Emissivity and Reflectivity As discussed above, we rely on emissivity of a material to measure the amount of heat radiating from its surface. Highly reflective materials have a lower emissivity. Highly reflective subjects, such as glass towers, will also show areas of thermal bridging and air leakage, but it is more difficult to detect as they also reflect radiation from all adjacent sources; trees, surrounding buildings, people, and the night sky will show up in the image (Figure 9). Consideration of material emissivity and reflectivity is even more important when an image is captured at viewing angles greater than 90 degrees. Thermogram quality will always be greatest when the camera lens is perpendicular (at a 90-degree angle) to the subject. When trying to scan a subject at greater angles, surface patterns/temperatures can become distorted, less accurate, and harder to detect. An example of this challenge is attempting to scan the top floors of a tall building from grade with a handheld camera. An improved method would be to scan the upper floors using an unmanned aerial vehicle (drone) or from atop a neighboring building. If these options are not viable, the camera operator should try to get as far from the building base as possible and understand that there will be limitations in scanning the upper floors. Heat Conductivity Understanding a material’s conductivity and how quickly it will heat or cool will help in determining the most appropriate time and the most appropriate conditions under which to complete your scan. This can help to determine how long after sunrise (as materials begin to heat) or sunset (as materials begin to cool) you should wait to complete your scan or how long after creating a positive pressure differential you should wait to be able to see symptoms of air leakage behind a cladding material. UNDERSTANDING ASSEMBLY COMPOSITION AND INFLUENCE ON BUILDING ENCLOSURE SCANS In a cold climate, application of IR technology on single-dwelling wood-framed buildings can be very appropriate for identifying heat loss. Since the surface being scanned is relatively close to the thermal barrier, the paths for heat movement are more direct, and areas of concern will reveal themselves very readily. These types of assemblies are often more forgiving to scan under less than optimal temperature or air pressure differential conditions. 206 | RobiBInson and Koyle IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Confidently identifying the cause and source of the thermal anomaly becomes very difficult, and additional investigation—often including destructive openings—may be required for a definitive diagnosis. Figure 9 – Reflections on a glass building. In contrast, buildings with a rainscreen masonry-type cladding surface (brick, granite, stone, etc.) are more difficult to obtain accurate information about due to the air space behind the cladding. If there is a breach in the air barrier, the air that exfiltrates will diffuse behind the panel as it seeks a path to the exterior. If a scan is being completed from the building exterior and the air barrier is located inboard of the insulation layer, there is an added material for heat to move and diffuse through before heat patterns appear on the exterior cladding surface. In a cold climate, if an air leak is large enough and the air is moist enough, ice may form within the assembly; this can sometimes be much easier to detect than the air leakage itself. Figure 10 shows patterns of heat loss at precast concrete panel cladding; without further investigation, we do not have enough information to diagnose a potential source for these patterns. Metal-clad buildings typically have similar issues to stone cladding, with the added complexity that metal is highly conductive as well as reflective. A typical wall assembly with gypsum board, a self-adhered air/vapor barrier membrane, mineral wool insulation, air gap, and metal panel will typically have poor readings. This is not to say that the scan is without merit. Thermal bridging and air leakage will still translate to thermal anomalies on the exterior surface of the subject cladding, but heat transfers comparatively quickly in this type of cladding. Confidently identifying the cause and source of the thermal anomaly becomes very difficult, and additional investigation—often including destructive openings—may be required for a definitive diagnosis. Figure 11 demonstrates this scenario. CASE STUDIES OF MISDIAGNOSIS THROUGH MISUNDERSTANDING One of the environmental conditions discussed above that will affect the results of a vertical cladding scan is differential air pressure between the interior and exterior under building heating conditions. A hole in the building enclosure will only result in heat loss if there is a positive differential pressure between the interior and exterior environment that creates air leakage and convective heat transfer. The image in Figure 12 was captured at an old warehouse-type building clad with asbestos panels. Without understanding the context of the environmental conditions at the time of the scan, it would be tempting to state IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 R roBInson and Koyle | 207 Figure 10 – Thermal patterns indicative of heat loss at precast concrete panel rainscreen assembly; potential source(s) of heat loss unknown without further investigation. Figure 11 – Thermal anomaly behind metal panel rainscreen assembly; pattern shows the assembly warming quickly beyond the original sources. Figure 12 – Thermogram with minimal evidence of heat loss at pipe penetrations. that there are no anomalies indicative of significant air leakage in this thermograph; while we expect some temperature differential at pipe penetrations due to thermal bridging, there are no significant “flares” that would typically accompany air leakage. However, a daytime photograph of the same location shows an obvious hole through the enclosure (Figure 13). And before you give credit to any concealed sealants, it is worth mentioning that light from the interior was clearly visible around the entire perimeter of these pipe penetrations at night during the scan and the camera operator was able to put a finger through the gap to the interior space. The HVAC system at this 65-year-old building was not capable of creating a positive air pressure from the interior, and at the time the thermograph was captured, these penetrations were on the windward elevation of the building, resulting in an overall negative air pressure differential. These were not ideal conditions for a scan intended to identify potential air leakage through the enclosure in the first place, but also risky in that the thermograph interpreter would not recognize that the image is showing a false negative. Just because there is no anomaly present does not mean that there are no problems, unless you fully understand the context under which the image is captured. This highlights the importance of documenting environmental conditions at the time of the scan and communicating these between the camera operator and the thermograph interpreter. Similarly, misunderstanding or miscommunication of the physical condition of the building components can result in misinterpretation of thermographs. Figure 14 208 | RobiBInson and Koyle IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Figure 13 – Daytime photograph of location shown in Figure 13; obvious holes through building enclosure at pipe penetrations. Figure 14 – Thermal anomalies at localized punched windows in multi-unit residential high rise. shows a number of thermal anomalies, but the more prominent of these are distinct anomalies at isolated punched windows. So the interpreter asks, what would cause these anomalies at some windows but not others? Is there significant thermal bridging or missing insulation at the frames? Failed insulated glass units? Failed sealant joints resulting in air leakage? A heat source behind the windows? Or has someone left their windows open overnight on a balmy -25°C Canadian night? In the case of this image, the answer is open windows, which is not an intuitive diagnosis given the exterior weather conditions at the time of the scan. Without this visual observation recorded by the camera operator, the interpreter can easily misdiagnose the source of the anomaly as any of the other possibilities presented because they did not understand the physical building component condition. The final factor that will affect interpretation of a thermograph is the manipulation of the digital image. Most thermographic cameras produce images in an output that can be further refined and manipulated by adjusting various inputs—either on the camera or in post-imaging software. This image processing is useful in accentuating thermal anomalies when the thermographer understands the environmental conditions and material characteristics as described above, but it can influence a diagnosis in the wrong direction if there is a lack of understanding. Figure 15 above shows the exact same digital file with the temperature span adjusted to a different range between images. The narrower temperature span in the second image results in a greater contrast in the heat patterns, making the anomalies at the top of the wall easier to identify. An understanding of the overall enclosure is required to determine whether magnifying such anomalies is appropriate. CONCLUSION IR thermography can be an invaluable tool that can add substantial information to an evaluation of building enclosures when used properly. The physical and technical parameters of the equipment, subject, and surrounding environment need to be fully understood by the thermographer and the interpreter to produce reliable results and conclusions. To ensure success the team must: • Observe, understand, document, and appropriately communicate the environmental conditions (both interior and exterior) under which the scan took place • Understand the material properties and the assembly construction of the scanned subject • Understand the input parameters and values applied to the digital image Misunderstanding any of these items can result in misdiagnosis. And remember that thermography scans are just one of the many tools in our toolboxes; it is a qualitative tool that will not always provide a stand-alone definitive answer. REFERENCES 1. History of Infrared Thermography by Infrared Training Institute; infraredtraininginstitute.com. 2. Peter A.D. Mill. The Principles of Building Science and Thermography Needed to Diagnose the Performance of Building Enclosures. Architectural Sciences Division, Public Works Canada, Ottawa, Ontario. 3. Photo references: Thermal Imaging from the Beginning of the Thermographer’s Camera to the Present by Ed Kochanek, IRINFO.org. 4. Photo References: www.flir.ca and www.fluke.com. IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 R roBInson and Koyle | 209 Figure 15 – Temperature span manipulation to cccentuate thermal anomalies.
