THERMAL imaging (infrared) CAMERA$ 1,000+
Another branch of military research to bear ever more peacetime fruit is the THERMAL IMAGING CAMERA. These tools detect thermal energy— specifically infrared radiation (IR), a range of wavelengths often expe
rienced as heat. Along with visible light, IR is part of the electromagnetic spectrum, but like X-rays, microwaves, and radio waves, it cannot be seen with the naked eye. Thermal imaging cameras employ sensors that change electrical resistance, voltage, or current when heated by IR, then display this information as an image called a thermogram that can be viewed and analyzed.
Thermal imaging came into practical use during the Korean War for identifying targets and foes through battlefield smoke or darkness, and later to fight fires on ships. Expensive and security-sensitive, it remained in the military until after the 1991
Gulf War, when reduced equipment sizes and costs opened it up to the public. Law enforcement put thermal imaging to work in surveillance and security, and municipal firefighters adopted it for search and rescue and to identify fire hot spots. Since the 2000s, even more compact and economical cameras have become standard inspection tools. Utilities use thermal imaging cameras to look for overheating in high-voltage power lines, and the building industry relies on them to find heat leaks and improve HVAC-system efficiency.
Today’s thermal imaging cameras come in many forms and complexities, from helmet mounts for firefighters to handhelds for building inspectors. Basic cameras just read the temperature under crosshairs on the image, then display the temperature as a number, or multiple numbers for comparison. More sophisticated cameras display relative temperatures as colors, typically as [ text cont. on p. 40]
either a black/white/grey range or, in the most sensitive cameras, a palette of multiple colors—say, white for hottest, reds and yellows for intermediate, blue or black for cold. Specialized cameras can offer a color alarm feature that only displays an image where the temperature is above or below a user-selected range, for example displaying only the hot spots around a window or on mechanical equipment.
Like conventional photography, the quality of a thermogram depends on the design, cost, and operation of the camera. At the top of the list is detector—that is, the number of pixels and thereby temperature data points. The higher the resolution, the clearer the image. A thermal imaging camera can cost from $1,000 to $10,000, with resolution commonly the biggest difference between an expensive camera and a
cheaper one. Also important is thermal sensitivity, or to what degree the camera can distinguish a difference in temperature between two surfaces.
Better cameras also allow the user to adjust for emissivity (how well a material radiates infrared energy, compared to a perfect radiator); reflective temperature (compensating for temperature reflected from surroundings); and thermal tuning (adjusting the temperature range the camera detects).
Thermal imaging cameras can’t see through walls, but they can tell a great deal about the condition of a building by “taking the temperature” of its surfaces in multiple ways:
>Energy Audit Also called a thermographic inspection, this survey of the building’s exterior or preferably its interior (where temperature differences are less affected by air movement and more accurate) can determine the effectiveness of insulation—whether a
building needs it and where. Thermographic inspections are also valuable before a house purchase to evaluate its condition, and after adding insulation to assure it was done correctly. Inspections even can reveal the condition of existing insulation, such as settling or saturation from a roof leak.
>Building Leakage Thermographic inspection also will zero in on air leaks that allow heat to escape or infiltrate the building. When combined with a blower door (a fan attached to a door that tests airtightness by exaggerating air leaks), an inspection can locate air leaks around windows and doors or through building defects (such as wall penetrations or faulty siding) when they show up in the thermogram as black streaks.
>Mechanical Systems As with utilities, thermal scans of electrical systems can detect overly warm connections or circuit breakers, indicating potential problems. Similarly, scans of HVAC equipment and the like can point to areas of friction or wear.
>Moisture Detection The non-invasive nature of thermal imaging cameras coupled with their ever-growing sophistication and affordability has made them increasingly popular for moisture detection. Rather than measuring electrical resistance or capacitance like a traditional moisture meter, thermal imaging cameras can identify areas of moisture when they show up as anomalies in a thermogram, due to the effects of evaporative cooling.
>Material Defects In high-level inspections, such as structural investigations, thermal imaging is also a tool for finding defects in materials. For example, moisture trapped in a porous material such as wood increases its thermal conductivity, and shows up in a thermogram as a cooler area.
Thermal imaging cameras may be obtained through a service (some utilities do work for a nominal charge or for free), rented, or purchased outright. gordon bock is an architectural historian, instructor at the National Preservation Institute (npi.org), and in-demand speaker: gordonbock.com