Buying a Thermal Imager for Building Applications What Equipment Specifications Should You Consider Introduction Over the past few years there have been considerable breakthroughs in the market for thermal imagers including the fact that prices have dropped considerably. Infrared cameras are also finally being designed with the end user in mind. Advances in technology and materials get a lot of credit for this, but it once seemed that the comfort and sanity of the operator was an afterthought when it came to the camera s form factor and menu layout. The reality is that today s imagers are also lighter and easier to use. Matt Schwoegler The Snell Group Regarding the cost of an infrared camera, when I first started with The Snell Group back in 2002, you really could not find a new, fully-featured, imager for much less than $20,000 USD. Today, there are many fantastic choices out there for building applications with a wide range of features in prices ranging from $2,000 to $9,000 USD. Even better, the ideal thermal imager for today s building thermographer does not necessarily need to be top-ofthe-line or most expensive. Whether you are a home performance contractor, weatherization crew member or energy auditor there are many fine choices in the $2,000- $5,000 USD range that will certainly meet your needs. If you conduct moisture investigations, are a building inspector or work in pest detection this information is for you as well. What IR Camera Features are Important? As complex as some systems may seem, infrared cameras are comprised of some basic components: lens, detector, processing electronics, display, controls and power supply. One would not think that, however, if you were to take a quick glance at a typical technical data sheet for a camera. Thermal imager specification sheets can be confusing and difficult to understand. Some features such as thermal sensitivity and detector size are useful in evaluating performance, but a data sheet is not going to tell you how the camera functions and feels while you are in the field. If you are considering purchasing any type of infrared camera be sure to try it before you buy and compare it to others. That said, the good news is there are many great products available with some that represent an amazing value. There are a number of factors to consider in addition to cost and after-sales service. Please keep in mind as you read this that The Snell Group is vendor-neutral. We do not sell equipment nor are we a subsidiary of any infrared camera manufacturer. As such, I am not going to recommend a specific brand or model of thermal imager. What I am going to do, however, is summarize which equipment specifications are important for you to consider and which ones maybe are not. Ultimately it is you who will know best which camera is the right one for your job. Thermal Sensitivity: For buildings work this is probably one of, if not, the most important specification to evaluate. Be certain that your thermal imager is able 322 N Main St. Suite 8 Barre Vermont 05641 Tel: +1.802.479.7100 Fax: +1.802.479.7171 1.800.636.9820 (toll-free in the US and Canada)
to resolve temperature differences of at least 0.1 C or lower. This is also often stated as 100mK ( millikelvin, see Glossary on page 7 for more definitions) on a specification sheet. Keep in mind that the smaller the number the better (i.e. more sensitive) the system. Strong consideration should be given to cameras with even lower thermal sensitivities such as 70mK (0.07 C). A handful of 40-50mK (0.04-0.05 C) systems are also available and provide fantastic image quality and clarity. A better thermal sensitivity allows you to work more hours in a day and more days in a year. The lower sensitivities are capable of discerning smaller temperature variations typically encountered in marginal inspection conditions (such as when the inside to outside wall surface temperature difference is low). In other words the additional cost of improved sensitivity is an investment that can have real returns. Detector Array Size: This relates to the number of pixels or sensors on your camera s detector. While IR imagers available for the civilian market are a long way from the 5-8 megapixel visual arrays we are used to seeing on most smartphone cameras today, many out there are more than adequate for most building diagnostic work. More pixels generally means greater detail. Excellent infrared systems for home weatherization are now being made with 120 x 120 (14,400 detectors), 160 x 120 (19,200) and 320 x 240 (76,800) focal plane arrays (FPAs). FPAs smaller than 120 x 120, while financially attractive, do not provide sufficient spatial resolution for building diagnostics and are not recommended. FPAs larger than 320 x 240, such as 640 x 480 (307,200), do produce an impressive image but cost more and are bigger than what is needed for most residential work. If, however, you are primarily inspecting larger buildings (multifamily units, high rise apartments/offices, or industrial facilities) the bigger array size is worth considering. Infrared cameras come in all shapes and sizes, so be sure to test them out in the field and get a feel for their weight and balance. Ergonomics/Ease of Use: Often overlooked, but important, the camera must be simple and easy to use. What I mean is that image adjustment, focusing and basic operation must be intuitive. Avoid complicated menu systems or cameras that make the most important, and often used, adjustments such as focus, level/span and image capture cumbersome to execute. Do you feel you would be able to comfortably hold it for an hour or two? Is it balanced properly or is your wrist or arm strained? Does it allow for one hand operation when you are in a tight space or have a poor viewing angle? Can you wear a glove and still operate the imager when working outside in colder climates? These are just some of the important questions to consider. Visual Image Capture/Viewer: A useful and common feature of many imagers is a built-in visual camera that captures a visual picture and links it to the saved infrared image a must for complete reports. If the camera has a built in light to help illuminate the scene, that is a plus too. Some visual cameras are better than others but most will provide decent, visual documentation, of where the infrared image was captured. The visual border of a picture-in-picture feature helps thermographers identify what the infrared camera is pointing at as they pan around a scene. Having a separate digital visual camera is still something to consider given that the quality of the visual camera on some infrared imagers is still somewhat low. The benefit of taking a good, high-quality visual image is being able to blow it up and clearly see some essential detail you may have overlooked at the job site. Know this will add considerable time to generating your report, however, as you match up the separated thermal and visual images.
That is time which eats into your bottom line and might not be worth the trade off. On some models the visual camera allows for a picture-inpicture feature that shows a thermal view in the center of the display screen surrounded by a visual image that frames the infrared shot. Be aware, though, that the alignment of the visual and thermal images on some models are better than others, however new parallax alignment techniques used by the manufacturers are helping address this issue. Voice or Text Annotation: Stand-alone digital voice recorders have been around for a while, but it is the integrated voice recorder (now available on a number of models) that allows building thermographers to work more efficiently. This facilitates note taking in the field, but can also expedite report writing back at the office. Since the voice file is tied to the captured thermal and visual images, all that one has to do is just open the file in the report software, play back their notes, and type those into the report. No pens, clipboards or separate voice recorders that can be cumbersome to carry around. It also helps you keep your notes organized. No longer will you have trouble deciphering hand written notes nor will you be confused by what audio file goes with what thermal image if using a standalone digital voice recorder. Current text annotation capabilities do not offer nearly the same benefit or flexibility, but can be helpful for basic note taking, especially if set-up in the camera s software prior to the inspection. You can create categories and tag these labels to the images with pre-set information as you save them. Having said that, until cameras start coming with an on-screen keyboard, voice annotation is the way to go. Image Analysis and Reporting Software: Most infrared cameras today work with a free, basic software package provided by the manufacturer. With these you can typically perform simple image adjustments, add analysis and comments, export individual shots with adjusted temperature scales, change color palettes and generate basic reports of multiple images at a time. You may find with some manufacturers that they offer a more robust software program at an additional cost, but typically these packages offer far more features than what is really needed to generate effective reports. Also know that many might at the very least require Word or Adobe installed on your computer as the report wizards typically export the final report file to either one of these formats. Image Display: A high-quality LCD display screen is essential to diagnosing an image. The size of these vary considerably from model to model so be sure to try at least a couple of different brands/units. Larger displays are helpful if more than one person is viewing an image (the homeowner, crew member or auditor) and you are trying to communicate the problem or facilitate on-the-job training. One downside to an LCD display screen is that they can be challenging to use outdoors whether on a sunny or cloudy day. Many manufacturers are providing sun shields/visors that can easily be slipped over the camera s display to help reduce issues with glare. You will also still find some models that offer both an LCD display and a viewfinder. This is something to consider if you find that you will be working outside more often than not. Instantaneous Field of View (IFOV): First, the Field of View (FOV) is a measure of the angular view path of what the camera sees. Usually measured in degrees, it determines the thermal imager s overall viewing area and is defined by horizontal and vertical angles. For building inspections a normal FOV of somewhere around 20 x 20 can work well. The IFOV describes the spatial resolution capability of a camera. Simply defined, IFOV is the smallest target size an infrared imager can discern at a given distance with a given lens and detector array. IFOV represents the size of the projection of the detector through the lens onto the scene. It is usually specified in a camera s technical data sheet as an angle of measurement in milliradians or mrad. The smaller the mrad value, the tighter the angle and the better the spatial resolution of the imager.
Except for work on large buildings, spatial resolution is typically not a concern nor is it a limiting factor because we can easily move closer to increase resolution. The item to consider here, though, is what spatial resolution will you require? What is the smallest level of detail you are going to need to resolve at your inspection distances? What types and sizes of buildings are you inspecting? If your answer is mostly greater distances (where simply moving closer is not possible) or larger structures, a lower mrad value would be worth considering. Optional Lenses: While telephoto lenses are not typically necessary for residential work, the option to add a wideangle lens can be helpful for inspections in tight spaces or where your perspective is not wide enough. This would include a scenario on the interior where you are not able to view enough of a wall in a small bedroom without standing in the hallway. An example outside is if you are in a high-density residential neighborhood where yards are small (or the spacing between buildings is tight) which limits the viewing distance. On average, though, the ability to change lenses might not be worth the additional cost. focus imagers, while convenient, can have trouble with clarity when looking at objects either very near or far. Motorized/Auto focus cameras are nice for their simple function which allows for quick, one-hand, operation on some models. One drawback is that you might find it difficult to fine tune the image to your liking. Many thermographers seem to enjoy the control one has over image clarity with a manual focus where the operator is able to dial it in. This is something you need to test for yourself and is often a personal preference. There is really no wrong type of focus method as long as you get the right focus. The image above was taken with a standard lens while the one below was captured with a wideangle lens. Focus: Cameras come in several varieties including Fixed Focus, Manual Focus and Motorized/Auto focus. Fixed Here we see examples of three different types of color palettes; grayscale, ironbow and rainbow. It is important to note that some systems work better in one palette versus another, so be sure to check what kinds of color palettes are offered on the camera you are considering.
Batteries: It used to be that most infrared cameras did not last more than 60-90 minutes before needing a fresh battery. This is no longer the case for most thermal imaging systems out there. Almost all new cameras on the market have run-times that average 3-4 hours, maybe more, depending on the model, the user s inspection habits and the camera s settings such as the brightness of the LCD screen. Batteries may be either removable or builtin. If given a choice, I would suggest an infrared camera with a removable battery for those long inspection days where only one battery is not sufficient to finish the job. Image Palettes: Many thermographers prefer either using a grayscale or monochromatic (shades of a few colors) type palette. We generally recommend to avoid working in a rainbow color palette in the field as 1) these can make it difficult to focus and 2) are not as intuitive as monochromatic palettes set to positive polarity where lighter is hotter and darker is colder. When inspecting with rainbow palettes in the past, I found myself often struggling with Is yellow warmer than red or is red hotter than orange? Make it easy on yourself, less is more when it comes to colors and palettes. Frame Rate: 9 Hz systems have become widely available and can work just as well as 30 Hz and 60 Hz systems if you take care to hold the camera steady. The higher the frame rate value, the better the camera s ability to render and capture moving targets. Lower frame rates are less tolerant to movement and will blur the image if you pan across a scene too quickly. While an important consideration for industrial thermographers who are inspecting certain types of rotating equipment (motor shafts, bearings or couplings), it is far less of a concern in building applications where our targets are stationary. Know that any movement during the exact moment that an image is saved can blur the captured picture on pretty much any infrared system, regardless of its frame rate. Laser Pointer: This feature is certainly not required, but the laser pointer can help visually guide you around a room, giving thermographers a general idea of where Here we see, qualitatively (i.e. without temperature measurement), the effects of warm air infiltration while depressurizing with a blower door in warm-weather conditions. they are looking. While the laser does not necessarily line up with the spot temperature displayed on the screen, it can be useful for both beginner thermographers or building owners who like to see where they are pointing to on a wall or ceiling. Image Storage: Images are saved electronically either on a small removable SD, (seen here, left) or compact flash memory card or on internal storage. Both can work but make sure you can download it to your computer. When considering a camera, think realistically about how many images you need to store before downloading. Most SD cards now are 2 gigabytes at a minimum; more than enough space for your typical inspection day. Digital video capture in MPEG4 format or similar is a feature that is starting to show up on some systems and will certainly add another useful dimension to reporting and analysis. You will find a few that also offer a composite video output. This is nice to have for conducting demonstrations with your thermal imager and LCD projector. With the right couplers you can also record this feed to either a camcorder or some type of digital video recorder. Granted the captured data does not have radiometric or span/level adjustment capabilities, but is still useful for some reporting needs. Radiometric Measurements: It used to be that you could chose between having a system that was either radiometric (displays a thermal image and provides temperature measurements) or non-radiometric (just displays a thermal image). Today, most models are radiometric and come with at least one fixed temperature spot in the center of the screen, if not more. Generally speaking, radiometric temperature measurements are not
necessary for most buildings work. That said, having at least one spot measurement can be useful. The problem I have with temperature measurements in building applications is that new thermographers often pay far too much attention to the temperature value and not enough attention to what the image is actually telling them. Not to mention the fact that temperature measurements can be wrought with error too. Infrared in building inspections is most often about qualitative differences on the wall surface is that area hot or not (or cool or not)? That the wall happens to be 72.3 F (22 C) at a particular point does not really tell me anything if I am trying to evaluate insulation performance or air leakage. The dew point indicator operates in a similar way and takes into account relative humidity and temperature that the thermographer enters to highlight points on the wall where condensation may form or be present. These features are overly simplistic and attempt to take critical thinking out of the inspection process. While I have heard from some thermographers out there that they are having success with the dew point option, great caution is strongly advised when using either of these features. Proper Training and Qualification Insulation/Dew Point Indicators: In a way a subset of radiometric measurements, these two features (found on some models) require data input from the user that may be inaccurate making it potentially misleading and dangerous to use. The insulation indicator is supposed to locate areas in the building where there is inadequate or deficient insulation. The operator is directed to enter into the camera the outdoor temperature, indoor temperature and insulation level percentage. The imager then calculates an insulation temperature value and places a colored isotherm over the suspect area on the display screen. There are a number of variables that are not being considered with this feature. Ambient air temperature is by no means the only driver of heat transfer through a wall. It is the surface-to-surface temperature difference across the wall system and ambient air temperature is not wall surface temperature in many instances. Also, does the thermographer understand what the state of heat transfer is through the wall? Is it steady state or transient? The wall could still be in a state of thermal flux due to differences in the thermal capacitance of building materials. It is also possible that the temperature difference from inside to outside might have flipped during the day and has not yet stabilized in the opposite direction. How about solar loading on the outside wall surface? What type of insulation is in the wall? What is its density? These questions are not being sufficiently considered with this feature. This is why a thermographer needs to be trained and qualified to think critically during an inspection and not have some computer with limited information make the decisions for you. Infrared cameras today are certainly easy to use and affordable, however, operators still need to be qualified to use them properly. That includes having the right training and experience. I am not concerned with whether or not someone is certified as a building thermographer. I am far more interested in that they are a qualified building thermographer. Those that are do better work, get better results, and work more efficiently. Unfortunately, as imagers have now broken below the $2,000 barrier and continue to drop, some are calling into question whether similarly priced infrared training is still necessary. My response? Well, anyone can buy a framing hammer. They too are easy to use and inexpensive, but it takes a skilled carpenter to know how to frame a wall correctly. The same is true with an infrared camera. Just like the hammer, one can do quite a bit of damage if it is used improperly. Being successful with this technology not only requires great camera skills, but also an indepth understanding of heat transfer, radiation physics, inspection conditions and building science.
Buildings are complex. In fact, it could be argued that an infrared building inspection is one of the most, challenging applications of infrared thermography. In many instances you will have to conduct an inspection with conditions that are often less than ideal in buildings that are in a transient, and confusing, state of thermal transfer (early morning vs. sunny afternoon), built with different materials (wood vs. concrete) and that have highly varied surface emissivities (windows vs. glass, shiny metal, painted walls, etc.). The thermographer must understand how that affects what they are seeing and not seeing in the thermal image. Without a solid foundation in training and experience, expect to make mistakes. Some may be costly. Good training options are available, but make sure the one you choose specifically covers the camera you have and the needs of your applications. For groups, specialized onsite training that allows your team to avoid travel, lodging and meal costs probably makes the most sense. Be wary too of training organizations that purport to certify those who attend just their training class or perhaps purchase one of their products. Those types of certifications are more of a marketing and sales product than a service that actually qualifies thermographers. ISO 6781: Thermal Insulation, Qualitative Detection of Thermal Irregularities in Building Envelopes, Infrared Method (www.iso.org) ASTM C-1060: Thermographic Inspection of Insulation Installations in Envelope Cavities of Frame Buildings (www.astm.org) ASTM E-1186: Air Leakage Site Detection in Building Envelopes and Air Barrier Systems (www.astm.org) RESNET: Interim IR Guideline for Thermographic Inspections of Buildings (www.resnet.us) Canadian GSB 149-GP-2MP: Manual for Thermographic Analysis of Building Enclosure (http://www.tpsgc-pwgsc.gc.ca/ ongc-cgsb/index-eng.html) Canadian NMS Section 02 27 13: Thermographic Assessment Building Envelope (www.pwgsc.gc.ca) The Future is Bright for Infrared The number of choices today for fully-featured, inexpensive, infrared systems are astounding. Now is the time to analyze your current needs and see if investing in a thermal imager makes sense. Do your homework, look at and try! several systems. If you are considering buying an infrared camera give us a call or drop us an e-mail as we are more than willing to help you through the decision making process. We are not going to tell you which brand or model of infrared camera to buy, but we will work with you to ensure that the camera you do end up getting meets both your needs, and more importantly, your budget. Infrared Equipment Glossary Infrared Standards for Building Inspections There are a handful of standards for conducting infrared building inspections that thermographers should know. In addition to proper training, all thermographers should be familiar with these: Background, also known as Reflected Temperature: The source of radiation that reflects off of the target the IR instrument is viewing. FOV: Field of view, a measurement of the angle seen by the camera; the specification is typically given in degrees horizontal and vertical, such as 20 x 20.
FPA: Focal Plane Array infrared system that has a matrix of individual detectors. Detector Array: The detector array is a composed a number of individual detectors, typically 320 x 240 or 160 x 120 in size. Emissivity: A property of a material that describes its ability to radiate energy by comparing it to a blackbody (a perfect radiator) at the same temperature. Emissivity settings range from zero to one. IFOV: Instantaneous Field of View; the smallest sized area that can be seen by the infrared camera at any one instant. Also known as Spatial Resolution. IFOVmeas: Instantaneous Field of View-Measurement; the smallest sized area that can be measured by the system at any one instant. Isotherm: A software function that outlines or highlights areas of apparent similar temperature or radiosity in the image. Level: The position of the thermal span in the particular thermal range to which the radiometric thermal imaging camera is set. Similar to visual brightness. Measurement Resolution: See IFOVmeas. MilliKelvin (mk): One thousandth of a Kelvin (or centigrade) degree. Range: The term used with many IR systems that describes the preset range of temperatures that can be viewed and/or measured. Many infrared cameras offer several ranges allowing the user to select the proper temperature range for the scene being viewed, although most cameras marketed for building applications have just one range. Spatial resolution: A measure of the ability of the detector to resolve small-sized details; the term Instantaneous Field of View (IFOV) may be used with the specification quoted as an angular measurement in milliradians (mrad). Span: The difference between the high and low temperature settings displayed on the color scale of the thermal image. Similar to visual to contrast. Spot Radiometer: Also known as point radiometer. A non-imaging radiometric device that outputs a temperature or other radiometric measurement. Also called an infrared thermometer. While useful, these devices can have severe limitations with regard to spatial resolution and emissivity correction. Spot Size: The size of an area that can be measured at a given distance by a radiometric system. Thermal Sensitivity: A measure of the minimum temperature difference (in millikelvin or mk) that can be detected at a given temperature, typically 30 C (86 F). Qualitative Thermography: Thermal imaging without radiometric temperature measurement. Comparing surface thermal patters, not temperature differences. Quantitative Thermography: Thermal imaging with radiometric temperature measurement. Radiometric: The response of the detector to IR radiation is calibrated so that temperatures can be inferred from the amount of radiation detected. If a camera is fully radiometric, temperatures can be read anywhere in the image. Others have only a center spot that is calibrated for measurement. 322 N Main St. Suite 8 Barre Vermont 05641 Tel: +1.802.479.7100 Fax: +1.802.479.7171 1.800.636.9820 (toll-free in the US and Canada)