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We recently came across this interesting article by Ilana Koegelenberg on the RACA Website.
“The percentage of refrigerant leaks on HVAC&R systems is already a much-publicised concern internationally, and in South Africa, this problem appears to be ever greater.
I never really thought much about leaks in terms of refrigeration and air conditioning. Normally, when I think of leaks, it is in the context of plumbing and water leaks. But when I was doing my natural refrigerants feature for the March edition and in chatting to people about refrigerants, the topic of leaks came up time and time again.
Some estimated our local leak rates at exorbitant percentages and, across the board, it seems that everyone is well aware that we have an issue.
International records show that system leaks are becoming more and more prevalent. The factors contributing to this cannot merely be attributed to better record-keeping and policing, but are also direct indicators of lower quality in workmanship and inferior installation materials, as well as a result of the higher pressure of new refrigerants.
Consistent with environmental regulations and consequential penalties starting to be imposed on excessive refrigerant consumption, proper plant management, maintenance, and reduction of refrigerant emission are major industry concerns.
Whether due to poor workmanship, lack of maintenance, or simply inadequate skills and training — leaks are avoidable and should be minimised as far possible. Especially with natural refrigerants becoming more popular and flammable gases on the rise, the stakes are higher than ever to contain leaks.
CO2 leaks in refrigerated spaces have the potential to become dangerous very quickly. Effective CO2 leak detection can be an essential tool in maintaining a safe environment.
What causes leaks, how can they be prevented, and what is the risk really? Can you afford to ignore the problem? Probably not.
“Unfortunately, South Africa does not have a general culture of preventative maintenance. As we know, this saves money in the short run but causes dramatic expenses in the long run,” explains Clement Steenkamp of testo, a global company that provides measuring instruments across a variety of industries. “Many systems may have leaks that no one is even aware of.”
Repairing the leak
Refrigerant leaks are a huge problem in the HVAC&R industry and one of the most frustrating, too. Unfortunately, the tendency of some is to simply recharge the system with refrigerant and hope it lasts the season. This is faulty thinking. If the leak is not repaired, the refrigerant will leak out again and require further service. If this continues for several recharges, consequential loss of oil in the compressor could be enough to damage the compressor and require a major — and expensive — repair. Aside from being costly, a leaking system adds refrigerant to the atmosphere which is not particularly good for the environment.
Repairing the leak is the only option that makes sense. Yes, the cost of repair is higher than simply recharging the equipment, but once the repair is made, the re-occurring costs of recharging because of that leak are eliminated — and you are doing the right thing.
Freon leaks
Most domestic AC and many of the light commercial units are still charged with a synthetic refrigerant. Actually, there are still an incredibly large amount of Freon systems in our industry.
When you are dealing with a Freon leak, understand that things can get a lot worse as time goes by. The hole often starts as a pinhole leak and becomes an even bigger problem if not stopped. The hole can often be detected by observing tiny bubbles in the evaporator coils. This location is where Freon leaks are most often spotted.
Freons are certainly health hazards if they leak out (although some are more dangerous than others). They may contain lethal toxic substances and for this reason, Freon leaks should be handled by an expert repair technician. Inhaling Freons can be highly poisonous and could result in death. In addition, Freon leaks deplete the ozone layer and are unsafe for the environment.
A major cause of Freon leaks is factory defects. If this is the case, it is important to take note that manufacturing companies void the warranty if repairs are made by someone other than a trained technician, so it is important to get the professionals in if you suspect a brand new unit is leaking Freon.
A unit also has the potential to leak Freon if not installed properly. Any sort of damage to your HVAC&R unit can cause separate components to fail.
Vibration can also cause a leak over time — not only in air-conditioning applications, but also refrigeration systems. Wherever there are moving parts, such as compressors and many joints or connections, maintenance and regular inspection are key.
The most common cause of AC Freon leaks is likely to be erosion of the metal over time due to formic acid or formaldehyde corrosion. Small holes are formed when the acid eats away at the metal and the unit eventually releases Freon.
CO2 leaks
Regulations, market drivers, and trends reflect that carbon dioxide (CO2) is increasingly being used as a refrigerant in a variety of applications. This includes applications such as supermarkets/grocery stores, cold rooms, walk-in freezers, industrial cold storage, and food manufacturing/processing.
While beneficial in environmental impact, CO2 is a potentially harmful gas to humans if high concentrations are present. Although it is a non-flammable gas, CO2 is an asphyxiate and can cause both drowsiness and headaches and therefore must be monitored. An additional problem is that, because of the higher pressures involved, any leak of CO2 can quickly cause the loss of all of the refrigerant system gas. Therefore, rapid response is imperative to allow the system to close valves and prevent this loss.
As with all refrigeration systems, over time there is the potential for leaks to occur. Causes can include improper maintenance, mechanical wear, inadvertent damage, or improper installation. With pressurised systems, these factors can contribute to a significantly higher risk of leaks.
CO2 leaks in refrigerated spaces have the potential to become dangerous very quickly. Effective CO2 leak detection can be an essential tool in maintaining a safe environment.
Two key factors that should be considered when looking for a suitable CO2 leak detector relative to the applicable application are response time and operating temperature. The rate at which CO2 can leak and create a dangerous environment makes response time a critical factor. Operating temperature is also a key factor in selecting an appropriate CO2 leak detector for a refrigeration application.
Ammonia leaks
If proper precautions are not taken while working with or around ammonia, serious injury or even death can result. It may not be that harmful to the environment, but it is incredibly harmful to humans.
Ammonia is considered a high health hazard because it is corrosive to the skin, eyes, and lungs. Exposure to 300ppm is immediately dangerous to life and health. Ammonia is also flammable at concentrations of approximately 15–28% by volume in air. When mixed with lubricating oils, its flammable concentration range is increased. It can explode if released in an enclosed space with a source of ignition present, or if a vessel containing anhydrous ammonia is exposed to fire.
Needless to say, leaks on ammonia systems are a big no-no. Unfortunately, they are quite common and we read about explosions and workers being sent to the hospital more regularly than we should. It is a global problem.
People responsible for ammonia refrigeration facilities should be aware of the potential hazards of ammonia releases and of the steps that can be taken to prevent such releases. They should be prepared to respond appropriately if releases do occur.
It is important to establish training programmes to ensure that the ammonia refrigeration system is operated and maintained by knowledgeable personnel. It all comes down to regular maintenance and inspection of the system and making sure that everything is running as it should.
Hydrocarbon leaks
The application of natural refrigerants such as hydrocarbon HCs — propane (R290), propene (R1270), and isobutane (R600a) — are becoming more popular around the world as alternatives for HCFCs and HFCs. These refrigerants are highly flammable and explosive, so that whilst their application as refrigerants may present excellent environmental benefits, their handling with the necessary expertise is essential, cautions Lindsay Pelser, an Australian engineer specialising in hydrocarbon refrigerant conversions at AAPT Group.
“The responsibility for the leak-tightness and the general safety of equipment lies with the manufacturer/producer and installer of the equipment,” says Pelser. Equipment must be designed and constructed so that emissions and the creation of a flammable atmosphere are eliminated as much as possible. This may be achieved through leak-tight design, ventilation, and certain protective systems. “Only engineers and licensed tradespeople who have undergone training and who are competent in the use of these refrigerants should be allowed to design, install, and service systems,” says Pelser.
Once a leak has occurred, the risk becomes a function of the behaviour of the gas with respect to the local environment, according to the GIZ’s Guidelines for the safe use of hydrocarbon refrigerants. In particular, the release may originate from a refrigerant-containing part located external to the confines of the refrigerating equipment, or from a part located within the housing. If the release occurs within the housing, then it may be rapidly transferred out of the equipment, or it may accumulate within. For example, if the conditions are such that the refrigerant exiting the leak hole is immediately mixed with the surrounding air within a very large space, then the amount of flammable material will be small and unlikely to come into contact with a source of ignition. Conversely, if the refrigerant leak enters a relatively small space with minimal air movement, then due to its density being greater than that of air, it may accumulate and exist for a longer period within its flammable limits. The larger this ‘cloud’ and the longer it exists for, then the greater the likelihood that it may come into contact with an active source of ignition.
Detecting the leak
A reduction of refrigerant is not a normal part of the operation of your system and likely signals an AC refrigerant leak. A properly running system circulates and maintains the same amount of refrigerant — it is not like the oil in your car that must be replenished over time.
“The unfortunate reality is that refrigerant leaks are usually discovered only after there has been a loss of cooling due to discomfort, spoilage, or production difficulty,” explains Susanne Dobelin of Toolsense. “Repairing refrigerant leaks is not the problem — finding them is.”
A single leak detection method that locates every leak in every possible situation simply does not exist, she says. So, how do we determine which method is most appropriate for different air-conditioning and refrigeration systems?
Here are a couple of commonly used methods: visual inspections, bubble solutions, Nitrogen pressurisation hold test and Halide torches (not to be used with flammable refrigerants).
The most popular tool of choice to detect refrigerant leaks is the electronic leak detector. There are several types of electronic detectors used to test for escaping refrigerant: corona-suppression (negative corona), heated diode, ultrasonic detectors, electrolyte sensor, E-Mos (enhanced metal oxide semiconductor), H2 detector (95% nitrogen 5% H2 tracer gas), combustible gas detectors, and fluorescent leak detection.
“The perception of many is that digital instruments break easily. For this reason, owners of companies may shy away from purchasing digital equipment for technicians, and leaks are never checked. This though is simply not true,” says Steenkamp.
Currently there are many digital leak detectors on the market. Unfortunately, cheap imports flood the market, as with so many other products in the HVAC&R industry. “If the instrument is not reliable, how can the technician be sure there are no leaks? What is the purpose of testing at all if you are not sure? Really, a company has wasted money if it purchased an unreliable leak detector,” explains Steenkamp.
Many low-cost leak detectors cannot measure far below 0°C. This causes a problem when attempting to measure in a cold room. High-quality instruments can measure in environments from -20°C to 50°C. This allows one instrument to cover many demanding applications, explains Steenkamp.
In rooms that are already contaminated, leak detectors may start producing alarms the moment you walk in. Some more advanced leak detectors can be used in contaminated rooms because they perform an automatic zero in the environment in which they are switched on. “This allows one to pinpoint leaks in contaminated rooms instead of getting false alarms,” says Steenkamp.
Battery life can be an issue as some instruments cannot even perform a full eight hours of testing without a battery change. “If you are out of batteries on site you cannot continue your fault finding,” explains Steenkamp.
Selecting a leak detection method
So, what are the factors to consider when choosing a leak detection method? Dobelin shares some tips …
System factors
The type of refrigerant being used is important when choosing a leak detection method. Not all methods work well with all types of refrigerants. Also, system size and configuration must be considered.
Large systems are more likely to develop multiple leaks, possibly meters apart. In a small unit, multiple leaks are more likely to be next to one another. But every leak must still be precisely located.
If multiple leaks exist, consider what should be done if one is found in an area where there are several leak sites close together. Will a large leak hide smaller leaks from detection until after the large one is repaired? Will the detector be able to precisely identify two or more leaks that are close to each other?
Table 1: Examples of causes of leaks, development rate, and prevention, for HC systems in particular
Environmental factors
Wind and air currents affect the accuracy of electronic detectors and halide torches, which depend on sampling and testing the air in the vicinity of leaks. In outdoor systems, wind can lead to a missed leak or false alarm. Wind also interferes with the accuracy of bubble solutions.
Indoors, ventilation fans and convection currents lead to similar problems. Shutting down fans may eliminate air currents, but convection currents can disrupt readings and cause problems.
“The unfortunate reality is that refrigerant leaks are usually discovered only after there has been a loss of cooling due to discomfort, spoilage, or production difficulty. Repairing refrigerant leaks is not the problem — finding them is.”
Ambient light can wash out the response of visual detectors such as fluorescent leak detectors and halide torches, making leaks difficult or impossible to see. Using high-intensity UV and blue light lamps will help minimise this problem.
Ambient sound, other than that caused by leaks, can adversely affect the performance of some ultrasonic detectors. Noisy environments, such as multiplex refrigeration systems, might influence this type of detector as well.
Human factors
Ease of use and maintenance are also important considerations when choosing a leak detection method. Experience is the best teacher for finding leaks, but the easier a leak detection method is to use and maintain, the better the chances are of pinpointing leaks quickly and accurately.
Due to the high costs of refrigerants, equipment repair, and the time and effort needed to locate leaks, proper preventive maintenance of air-conditioning and refrigeration systems is essential. It is advisable to select a leak detection method that pinpoints leaks quickly and accurately so refrigerant losses are kept to a minimum. By finding and repairing minor leaks early, headaches can often be avoided later.
Preventing leaks
When it comes to leaks, prevention is better than cure. And prevention comes down to three main components: good product, good installation, and good maintenance.
A big cause of leaks on any refrigerant system is poor welding. If your welding is not up to standard, leaks can easily form. It is important to pressure test a system after installation or maintenance to ensure that there are no leaks caused by shoddy workmanship. It is also crucial to hire skilled welders who are trained to do the job properly. Think of installations like ice rinks that require thousands of welds — if these were done by unskilled labour, leaks would spring faster than you could fix them again! It is also important to use suitable flux and welding rods and to weld at the correct temperatures.
As mentioned, vibration of mechanical components, such as compressors, can also cause leaks. A clever idea is installing something like a vibration eliminator on both ends of the compressor to allow for more ease of movement, explains George Thomaides of AERSA, who started his career in refrigeration contracting. The function of a vibration eliminator is to absorb compressor vibration. By installing a vibration eliminator, the risk of damage to system equipment and pipework is reduced. A vibration eliminator can be installed in both the suction and discharge lines of air-conditioning and refrigeration systems. Vibration eliminators are suitable for HCFC, HFC, and CO2 refrigerants, along with their associated oils.
It is also important to ensure that the environment is not corrosive and if it is, that equipment is protected or that the right material is used for piping. For example, in an abattoir, all the blood could create a corrosive environment that could eventually lead to system leaks.
Speaking of materials, you should always make sure to use quality materials from reputable suppliers, advises Thomaides. Don’t just take the first, cheapest import. This could also lead to leaks in the long run.
You should use the right pipe for the right pressure. For example, as mentioned, you need quite high-pressure piping and equipment for a CO2 system.
To prevent leaks, regular leak checks have to be performed. “If unreliable instruments are used for this, the system still loses gas and no one is the wiser. It is important to have an instrument that tests according to international norms,” explains Steenkamp.”
Sources:
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