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Understanding Building Infrared Thermography |
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Written by mikeSITS
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Sunday, 04 November 2007 |
By Gregory R. Stockton
Infrared Imagery in General Infrared imagery is often a grayscale picture whose scales (or shades of gray) represent the differences in temperature and emissivity (opposite of reflectivity) of objects in the image. As a general rule, objects in the image that are lighter in color are warmer, and darker objects are cooler. No object is detected in visible light wavelengths (400-700 nm) rather, it detects infrared wavelengths (3000-5000nm & 8000-14000 nm). Lights and other relatively hot objects are evident, but as a result of their heat--not light emissions.
When an image is taken with an infrared camera, it is often recorded onto videotape and/or digitally saved to an on-board storage device. The images are downloaded, opened in specialized software and modified in a number of ways to enhance their value to the end user, like colorizing the images or adjusting the span and temperature to highlight a particular object in the image. Applications There are many applications for infrared thermography, such as:
- Predictive Maintenance of Electrical and Mechanical Equipment
- Research and Development
- Manufacturing Process Quality Assurance
- Non-Destructive Testing
- Building Thermography
Building Thermography To be an effective tool, an infrared thermographer must know the limitations of the imager, the way that buildings absorb and radiate heat energy, and the best time to perform a given IR survey. He must have an imager capable of finding and documenting problems and more importantly, understand building physics. Building IR applications can actually be one of the most demanding on imager thermal sensitivity and spatial resolution, the two most important factors in an imager’s ability to focus in on sometimes physically small and/or thermally miniscule problems. For example, there is a different methodology for surveying the wood framing, missing insulation, heat loss, air leakage and moisture intrusion in the same building. IR can only detect surface temperatures, but differences in surface temperatures and the patterns they leave (IR signatures) can indicate what is going on inside the building.
There are four types of buildings by use: Residential-houses and apartments dwellings of all types Commercial-office buildings, retail stores, malls Industrial-manufacturing facilities and plants Institutional-college and universities, hospitals, government buildings
Inspection Motivation Factoids Even though examining a building with infrared thermography can often pinpoint problems, owners of have different reasons for wanting to know (or not know) about the condition of a given building. Here are some examples:
-Buildings are often owned by one company or person and leased to another. If the tenant is paying the utility bills, he wants the building to be energy efficient, but the lease may not be long enough to enjoy an appreciable return on the investment of re-insulating the building. The owner is not worried about utility bills unless he is paying them or can use the fact that the building energy costs are low as a sales advantage.
-Industrial building owners [manufacturers] care about one thing...how many of their products get shipped that day. Unless it affects the bottom line (like a refrigerated warehouse or a building that needs to maintain exact temperature control), most are not concerned about heat loss until it starts to; a) damage the building from condensation, b) affect the operation, or c) make the people so uncomfortable that they revolt. In a plant where 85% of the kilowatts are consumed by machinery, the heating/cooling bills are not an issue.
-There is nothing remedial about infrared thermography itself, or any other type of testing for that matter. I have been looking at buildings with infrared cameras for 17 years and not once has a building I scanned repaired itself. IR can pinpoint and document problems. Often the repairs cost many times the testing costs and sometimes it opens a “can of worms” that the owner would rather not have opened.
-Residential building owners may not be willing to pay the cost of surveying and repair if they move every few years, because they figure that they can live with problems for a while, then they will become someone else’s.
Building owners want both low prices and high quality…nothing new about that. So what has changed to make building thermography viable now?
• Energy costs are on the rise. Money talks. Everyone is shelling out more money for energy and by inspecting a building with IR and other techniques, the owner can determine what needs to be done to maintain the building using less energy.
• “Green” thinking is becoming more popular with the public. It looks like earthlings actually can affect the planet’s climate. Over the years, people in North America have become more conscious of the fact that even if we can afford to pay the higher energy costs, the Earth suffers as a result of its inhabitants being inefficient and wasteful.
• Liability issues are becoming a problem for sellers, buyers and insurers, as the costs of construction repairs and renovation increase and our litigious society brings suits against each other.
• Mold issues are a giant problem for insurance companies as occupants increasingly ask for more “healthy” buildings in which to work and live.
• "You get what you pay for" is not a new concept, but perspective building owners are increasingly concerned about the quality and efficiency of their investment.
Building IR applications can be divided into categories such as: - Heat Loss Surveys
- Moisture Intrusion Surveys
- Insulation Q/C Surveys
- Structural Surveys
- Insect and Rodent Surveys
Infrared thermography can be used as a building quality assurance tool. All building materials will absorb, retain and radiate heat energy at a different rate, therefore building components can be checked for quality of installation using IR. In very cold climates, poorly installed insulation and vapor barriers can lead to condensation problems and the degradation of the building itself. In warm climates, as more “fresh” moist outside air is mechanically introduced into buildings in an attempt to make the building healthier, condensation and its side effects - mold and mildew, become a real threat to building owners and managers, in reality and in the form of health-related lawsuits.
Improperly installed insulation and air seals in buildings can be seen, documented and measured using IR and blower door testing. Building components “inside” the walls, ceilings and floors are recognizable using infrared because the surface temperatures are affected by their differences in mass. For example, infrared thermography can be used to determine the presence and correct placement of grouted cells in concrete block walls. If the owner of a new block building spends a little money checking the building work with infrared thermography, the contractor will be forced to build the building to specifications, or face the added direct cost of repairs and resulting loss of schedule repercussions.
Inspecting buildings for heat loss was one of the first commercial uses for infrared thermography. As we decide to become less dependent on fossil fuels, IR will again be used as it was in the 1980’s to monitor the energy efficiency of buildings, but now with the newer IR cameras and more thermographers, more and more buildings will become energy efficient and better-built.
We will publish many more articles in detail about applications in the coming months...
-Greg Stockton
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Last Updated ( Thursday, 08 November 2007 )
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