The color of heat — Part 1

Back in 1963, during the Vietnam War effort, the American forces were being overwhelmed by the jungle and its ability to hide the jungle wary Viet Cong army forces. The enemy had not only learned how to disguise themselves with the local flora, but had also become quite adept at digging tunnels underground, creating literal underground highways, which allowed them to move around undetected by the intervening forces. Enter the U.S. Air Force and forward looking infrared radiation (FLIR). This technology gave pilots the opportunity to see the heat from the bodies of the enemy even though they were covered with camouflage from the jungle, making them virtually invisible to the naked eye. This was a major turning point in the war effort, and the technology was even employed into the field in the form of hand-held units that allowed the ground troops to monitor enemy troop movement.

Since its inception, FLIR has made huge leaps and bounds as it pertains to its potential application in the industrial and mechanical fields. Energy in general, has different “ranges” in the spectral field. They now have infrared detectors that can actually “see” gas vapors escaping into the atmosphere, making visual inspection of large mechanical complexes a virtual snap. The thermal imaging portion of the technology has been used for performing inspections of electrical and mechanical systems for many years. The early detectors had a mechanically cooled sensor array that was required to cool the sensor array down to an extremely cool temperature. When I was first introduced to the technology, through an infrared thermography contractor, it took about 20 minutes for the sensor array to cool down to the point that the camera would work properly. It was also quite noisy when the cooling system was running.

My first application of this wonderful technology was for a municipal swimming pool. The Olympic-sized swimming pool had developed leaks in its piping distribution system, and none of them were visible from outside of the pool’s gunite exterior surface. We plugged off all of the pool’s supply and return lines, and began pressurizing the distribution system using hot water from the building domestic hot water system. We started pressurizing the pool approximately two hours before the arrival of the thermographer because at that time, it was $350 per hour, and you didn’t want the thermographer standing around doing nothing, waiting for the ideal conditions to arrive, hence the need for critical timing and coordination.

As the thermographer prepared his equipment in the parking lot of the swimming pool, he pointed his camera towards the swimming pool and told me he could see at least three leaks from the parking lot. I was amazed. He took three long range IR photos, as well as conventional light photos, and then moved closer and did the same. We were able to locate the leaks and effect repairs without having to completely destroy the interior of the pool finish. The customer was extremely happy as well because they were due to open the pool in a week, and we helped them meet their goal.

Timing and saturation are critical when considering the use of this technology. I once had a leak in a hot water space heating system on the bottom floor of a three-story building. The bottom floor was a concrete slab on grade application with ¾-in. copper lines running between hot water base-board heaters. The underground leak had been occurring for a long period of time (several months) and when the thermographer showed up, the slab was so saturated with heat that there was not enough temperature differential to allow us to locate the leak.

Temperature differential is critical in employing this technology. If there is no difference in temperature, i.e. everything is extremely warm, then it is virtually impossible to see where the leak is coming from.

We ended up having to resort to other technologies (Doppler leak detection and ultrasonic leak detection) to find that particular leak. I bring this up because it is important to understand exactly what it is that drives this technology, and it is temperature differential that is critical. If you attempt to use the technology too early, before heat has had a chance to migrate to the leak, there may not be enough differential to show the heat traces, or if you flow heat to the area for too long, the target area may become saturated, causing the temperature differential to be washed out, eliminating the possibility of being able to see where the leak is coming from.

Bear in mind, that the degree of leakage will also dictate the differential that will be seen. In other words, larger leaks will have a tendency to “pool” faster and greater than will a smaller leak. In fact, it may not be possible to “see” the smaller leaks until the larger leaks have been repaired.

Tune in next month as we continue our journey into the colorful world of infrared thermography and its application to our wonderful trade.

Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at [email protected] or by phone at 303-936-7606.

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