Has anyone applied Thermography to HVAC cooling coils and if so how did it go and what did you find?

Can it detect impending leakage from HVAC cooling coils?

Liquid leakage is one of the easiest things to detect with thermography. Typically liquids (depending on conditions) will begin to evaporate once they escape, and of course you have evaporative cooling which is easily detected. I was thinking in terms of both refrigerant flow and proper airflow across the coils. I'm just wondering if anyone has been doing it.

Woops, you said "impending" leakage. That is another question. I think you would have better luck with eddy current testing, if that is possible on a cooling coil. I'm not sure since I do not do that kind of testing, but I know it is done on heat exchangers and other tubes.

We just had a good paper presented at our conference, Thermal Solutions 2007, on stratified air flow in HVAC systems. I'd be happy to send you (and others) a complimentary copy.

It is possible to see the effects of air flow through the coil and filter and thus visualize the flow patterns. It is also possible to see flow restrictions or imbalances in the coil side and leaks from the coil itself, as you say, due to evaporative cooling. Dust build-up in the filters or coils can also typically be seen.

I too would concur with Martin that IR is not the technology to find "impending" leaks.

Thanks John, I would appreciate that paper if you could send it to mmm@gene.com.
Thanks!

The question came up int the field yesterday, I was doing standard electrical system Thermography and was looking around while the electrician was opening panels. I noticed an air conditioner coil with an obvious imbalnce in temp and went to inspect it. It turned out that the "excess load" fan was off by design, but there were other qualities of the image which got me thinking of both air flow and refrigerant flow.

This message has been edited. Last edited by: Martin Moore,

Does it make sense to set up a peridic program of inspection of HVAC coils. i.e. is anyone doing it programatically. I figured it is technically possible, I just haven't explored the practicality of it. HVAC people seem to be skeptical. Dust can be seen, leaks can be seen, damage can be seen during regular visual inspections which are more frequent. I guess I am asking what can IR bring to this inspection which regular visual inspection cannot?

If possible I would also like to view your report. bhelton@eastman.com

Thanks,

quote:

Originally posted by Martin Moore:
Has anyone applied Thermography to HVAC cooling coils and if so how did it go and what did you find?

Look in this months Uptime I have used IR for many HVAC problems as a Mechanical contractor
www.infraredsurvey.com

I have used thermography to assess HVAC coils. There are numerous considerations:

-The coils are typically finned with a very low emissivity material. However, because of the spacing, cavity effect can be used to obtain meaningful surveys. Angle of inspection can be important, and you can get some reflection depending on the design.

-Safety: for AHUs, there is typically significant airflow past the coils (by design) and since the inspection can only be done with the unit in operation, the effect of this airflow on safely avoiding any rotating components must be considered.

-Stacked coils: Many AHUs have an arrangement with double coils, meaning that you can only look at one set of the coils because the other is hidden behind the one you see. I once suggested that a hidden coil was blocked in one section because there were cool spots in the visible coil but obvious flow of steam/condensate through that coil. This is not always obvious, though, and deficiencies in the hidden coil can be easily overlooked.

Emissivity: Any previous leaks that causes staining, any growth of mold, etc., can have an impact on emissivity of the surface and produce apparent temperature differences that are false. This must be carefully considered.

Flow of steam and chilled water: Inspection of steam traps and steam flow control valves is a very effective tool for IR, provided these are not hidden from view or insulated (shouldn't be, but I've seen it). Chilled water or refrigerant flow can also be imaged in some cases, but it really takes an understanding of what the unit is calling for at any given point in time. Your inspection must be accompanied by an individual knowledgeable about the system design, and having access to the building controls in near real time, so that the building heating/cooling requirements and the appropriate coolant/heating fluid flows are known. IR is then used to confirm these conditions/lineups. No flow may be what the system is calling for at a given point in time, so you need to know that to properly assess.

Leaks: I don't think it is possible to predict future leaks (from wall thinning, etc), but I do think that you can see very early leaks before they become visually obvious. Pinhole refrigerant leaks will allow a tiny amount of evaporative cooling on the surface of the coil, which can make an area much cooler. Likewise leaking condensate on a steam coil will be cooler as well due to evaporative cooling, and I've been able to pick these up before the significant leaks that are seen in drip pans, etc. Finding some of these leaks early can prevent the catastrophic flooding that can occur later.

Rich Wurzbach
ASNT PdM Level III - #117658
Infrared and Thermal Testing
Maintenance Reliability Group, LLC