The use of thermal imaging in building applications (both residential and commercial) is fairly well known, and it’s one of the topics covered in our Level 1 - Thermographic Applications course. We discuss its use for detecting conduction loss or gain, air leakage, and detection of moisture in building systems. There are several standards associated with these particular applications (see previous blog, Building Inspections), and many home energy agencies recommend it’s use. Here we are discussing one of the areas where IR can be effective but perhaps not as recognized, heating, ventilation, and air conditioning (HVAC) systems.
HVAC systems obviously are powered electrically, and as such there’s the applicability of inspecting those components. A word of caution is worthy of mention here. Inspecting electrical components of any kind should be left to those who are qualified to do so. There are safety concerns that are quite a bit different than what is typical for other aspects of home/building inspections. Also worthy of mention, having sat through the electrical inspections portion of our Level 1 - Thermographic Applications course does not equate to qualification in electrical thermography.
Aside from the electrical aspect, there’s the mechanical portions of the HVAC system. The heat exchange process is what makes these systems work. Flow blockages can be detected in the condenser unit. Not just if blockage exists, but often where it’s occurring. Damaged coils will also show a thermal pattern that’s a departure from those functioning correctly.
It is also possible to detect duct leakage with IR. There are only a few materials that thermal radiation can move through, meaning that the IR imager can see through. One of those is atmospheric air. You won’t see either heated or cooled air leaking from a duct. What you might see, depending on conditions, is the heating or cooling effects of the air leaking from the duct as it passes over the duct surfaces and other nearby surfaces. Obviously, the air leaking needs to be a different temperature than the exterior of the duct and those nearby surfaces.
Additionally, flow blockages in ducts are possible to detect by imaging the duct outputs themselves. Each vent in a single room should have air output at similar temperatures (remember the vent must have a high emmisivity). If you have several vents that are cooler or warmer than other, this could mean that the air flow between them is different. Be careful that you’re not inspecting vents that are fed from two different systems. In some commercial buildings and even larger homes, more than one HVAC unit could be feeding a large space. Ensure that the vents you compare to one another are parts of the same system. You may also want to consider using a "Pocket Weather Station" during these inspections as well (see previous tip, Top 5 Items in Your Camera Case: Building Inspections).
Just one more way you can Think Thermally® when inspecting building systems.