HPAC Magazine

The Art Of Leak Detection

By DAVE DEMMA   

Refrigeration

The key to success is to institute programs that require regular checks.

One of my customers had a recent problem with his home air conditioning unit. He is a smart guy…a professional engineer with a fair amount of experience in our industry, but he has no field experience. Being in the business, his wife expected that he would be able to determine what the problem was and then repair it in a timely manner. For a couple of weeks he was able to put her off while he was attempting to solve the problem.

During this couple of weeks his coworkers and I took great pleasure in hounding him on a near daily basis, asking “So, did you get the problem solved yet…”. At one point I suggested that he ask one of his company’s technicians to come over after work one night and take a look at it, but given the extreme workload in the summer, he did not have any takers.

Eventually his wife became weary of his inability to deliver the “cold air,” so he was left with no other alternative then to call a residential air conditioning contractor. When it became common knowledge that he finally called a professional, we (his coworkers and I) were more than a little interested in what problem the contractor discovered.

Here is where it gets interesting. Apparently, the contractor determined that his unit was low on refrigerant. He added three lbs of R-410A and by that evening all was well in their household, as cold air was abounding.

As my customer was relaying the events to me I asked what anyone with a technician’s background would ask: ”Where did he find the leak”?

My customer asked that very question to his contractor and this was his response: “Well, normally you’d see some oil at the leak location. I did a visual inspection and didn’t find any oil. Also, it’s really tough to check for leaks everywhere, so I didn’t check anywhere but the condensing unit. Don’t worry. It was a little short of charge, but I don’t think there’s a big leak anywhere.”

Post Script: In preparation for writing this article I revisited my customer. I asked him if his air conditioning unit was still maintaining temperature, to which he responded “It’s starting to get a little warm in the house, like it was before the contractor came out in the first place.”

Let me share another experience regarding leaks, this one supermarket related. A certain pressure regulating valve that is frequently used in multi-compressor supermarket racks was “allegedly” experiencing leak issues, and the gasket was blamed. This was “allegedly” occurring in several locations and it was blamed for 100 lbs to 150 lbs of leakage every several weeks. I was dispatched to investigate the reported leaks in these stores.

Upon arrival at the store the technician directed me to the valve in question. He brought out his electronic leak detector, checked the gasket joints on the valve, and sure enough the detector indicated a leak.

I always like to verify/pinpoint the leak location with soap bubbles, so I asked the technician to bring his bottle of bubbles in. We generously lathered the gasket joints with leak detector soap and after several minutes we found the tiniest of tiny buildup of foam at one of the gasket joints.

Was there a leak? Yes.

Was this the leak that was responsible for 100 lbs to 150 lbs of leakage every several weeks? No and no – not even close.

Now, the leak detector screams at the same volume whether this is a small leak or a large leak. When sensing a leak with a leak detector capable of sensing a leak in the range of 1/10 to 1/2 ounce per year, how big a leak are we really talking about? 1/10 of an ounce per year equates to one pound every 160 years. Yes, it is a leak but it is not the leak in question, causing up to 150 lbs of leakage every few weeks. If there were 50 such leaks on a rack, the resulting refrigerant loss would be of such minimal consequence that it could be considered a nuisance.

This is not to say that these small leaks should be overlooked or ignored. They absolutely should be addressed and repaired. A small leak today might develop into a larger leak next month/year.

Now here is the potential problem which resulted in my being called to this jobsite: a technician determines that the refrigerant level has slowly dropped over the course of months, adds refrigerant and then proceeds to leak check the rack. He will undoubtedly take the path of least resistance, and start in the machine room. When his electronic leak detector finds a leak at a regulating valve or a solenoid valve on the rack, how often does he determine that his job is finished? Unless the technician leak checks the entire rack, fixtures piped to the rack, the condenser and perhaps the piping too, then the leak check is insufficient. How often does an insignificant leak take the blame for substantial refrigerant loss, while the real leak goes undetected because a technician has not completely leak checked the entire system?

When an electronic leak detector senses a leak, it should then be verified with soap bubbles. An alleged leak that cannot produce any visible soap bubbles is not the culprit in major repetitive refrigerant losses. Once a leak is identified (and ultimately repaired), the question should be asked: “Is this leak large enough to have resulted in any significant loss of refrigerant to the system?” If the answer is no, then the logical conclusion should be that there is still a leak somewhere in the store.

“How often does an insignificant leak take the blame for substantial refrigerant loss, while the real leak goes undetected because a technician has not completely leak checked the entire system?”

POSTSCRIPT: After discussing this situation with the contractor owner, he directed his technician to leak check the entire store in question. Admittedly, this is a herculean task. It requires a technician with patience, and an unquenchable thirst for finding any and all leaks.

Here is what the technician found after a full-day of leak checking the store: two ball valve leaks, one case hand valve leak, two TEV leaks and a liquid line with a loose clamp, resulting in a hole from constant rubbing against the strut. 

Moral of the story:

1. If a system that was once properly charged is now short of refrigerant, there is a leak somewhere in the system. Adding refrigerant without finding/repairing the leak(s) does not address the root cause of the problem.

2. In large systems with longer piping runs, multiple compressors and/or evaporators, there might be more than one leak contributing to the loss of refrigerant.

Now, let’s talk prevention. While the data is a little old, it serves the purpose of this discussion. In 2011, EPA reported that the annual refrigerant leak rate in a super-market was 23 per cent of its total charge. I find this mind-boggling.

Imagine going to your bank to make a deposit, to which they undoubtedly would thank you for patronizing their fine institution. Before leaving though, your teller feels compelled to offer the following disclaimer: “You know that sometime during the coming year we will likely be robbed and you’ll lose approximately 23 per cent of your account balance.&
rdquo; No way would you remotely tolerate that. You would immediately withdraw your funds and close your account.

So, why is a 23 per cent (or 20 per cent, or 17 per cent or 12 per cent, or…) annual leak rate acceptable? Certainly with the long piping, multiple fixtures and multiple control valves present in the typical supermarket there is a substantial amount of potential for refrigerant leaks to occur. But are there not any ways to proactively reduce the expected amount of leaks a system might see?

I recall working with a grocery chain that employed a team of technicians to maintain their own stores. Any equipment problems/failures could only be blamed on them, since no outside contractor was involved in maintaining their equipment. After a particular year where their annual leak rate was substantially above the national average and their annual refrigerant purchases were cause for alarm, they decided to implement some standards for reducing their refrigerant leakage. Management instituted a quarterly leak check program and this included leak checking the entire store. They had a specific set of technicians who became their leak checking “champions” because they realized that some technicians were better suited for the lengthy and repetitive job of leak checking. The results were phenomenal. They reduced their refrigerant consumption nearly 50 per cent the year that program was instituted.

There is no way to completely eliminate refrigerant leaks. Vibration and pulsation will occur and occasionally will result in broken/cracked fittings, capillary tubes, and so on. Clamps will occasionally come loose, resulting in lines that rub against strut and develop leaks. Seals and gasketed joints will leak at some point in time. There are some environments that will cause the copper tubing to erode, resulting in a refrigerant leak.

The key to keeping leaks at a minimum is to institute programs that require regular leak checks. As part of a program of this sort, it is imperative that the person who is performing the leak check do a completely thorough job.   <>

Dave Demma holds a degree in refrigeration engineering and worked as a journeyman refrigeration technician before moving into the manufacturing sector where he regularly trains contractor and engineering groups. He can be reached at ddemma@uri.com. For more information on leak detection see The Quest For The Smoking Gun, HPAC May 2014 at www.hpacmag.com.

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