Refrigerant leak detection – the right tool for the job

Leaks cause major problems in HVAC&R systems. Susanne Dobelin of Toolsense looks at the various methods of refrigerant leak detection and how they compare.

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 lesser quality in workmanship and inferior installation materials, as well because 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 is a major industry concern.

In the United States, the gravity of refrigerant leakage has evoked a stern warning from the Environmental Protection Agency (EPA) authorising fines up to USD25 000 per day for each violation for contractors and service people who vent chlorofluorocarbons (CFCs), hydro chlorofluorocarbons (HCFCs), or hydrofluorocarbons (HFCs).

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.

A single leak detection method that locates every leak in every possible situation simply does not exist. So, how do we determine which method is most appropriate for different air conditioning and refrigeration systems?

To answer that question, let’s look at some of the more common leak detection methods available to make an informed decision about selecting the one that’s best for your application.

Common leak detection methods

  • Visual inspection
    The first inspection should be to investigate any unusual markings or grime / oil build-up around joints or on piping.
  • Bubble solutions
    The oldest method of leak detection is the bubble solution. In short, soap solution is applied at suspected leak points, usually with a squeeze bottle, brush or dauber. Theoretically, the escaping refrigerant will produce bubbles at the leak sites. However, very small leaks or windy conditions may make this method ineffective.
  • Nitrogen pressurisation hold test
    Recovering a system’s refrigerant and then pressurising it with nitrogen at 150psi is a good method of leak detection. The holding process should be observed for at least 10 minutes. If the system loses any pressure over the course of 30 minutes or more, then it is a sure indication the system is leaking. Nitrogen pressure hold tests can also indicate a small leak or if the system has large or multiple leaks. A 10% or larger psi drop most likely indicates large or multiple leaks. Some leaks are not detectable until the system operates, therefore nitrogen is not always the best solution.

    Safety note: never leave an unattended nitrogen tank pressurised on the regulator.
  • Halide torches: Halide torches are more sophisticated than bubble solutions. This method is based on the torch’s flame will turn green when exposed to refrigerants containing chlorine atoms (CFCs and HCFCs). However, not all refrigerants contain chlorine atoms.

    Safety note: never use a halide torch on systems containing flammable / combustible refrigerants such as R600a or R290.
  • Electronic detectors
    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, electrolyte sensor and E_Mos (enhanced metal oxide semiconductor).

    Here is a brief explanation of the different technologies:

Corona-suppression One of the earliest electronic leak detectors to be introduced to the industry was the negative corona discharge model. The instrument works by creating a high voltage corona in the sensing tip. When the corona senses refrigerant, the device will sound an alarm.

Corona suppression technology measures variations in the conductivity of gases passing between two electrodes. The instrument creates a high-voltage dc spark that jumps from one point to another in the sensor, establishing a baseline current between the two points. A drop in current between the two points indicates the presence of an insulating gas. The greater the current drop, the higher the concentration of gas.

Negative corona leak detectors 400Negative corona leak detectors

In the sensor of a corona detector, high voltage applied to appointed electrode creates a corona. When refrigerant breaks the corona arc, the degree of breakage generates the level of the alarm. Sensitivity decreases with exposure to dirt, oils and water. False alarms can be triggered by dust, dirt specks, soap bubbles, humidity, and smoke, small variations in the electrode emission, high levels of hydrocarbon vapours and other non-refrigerant variables. Contaminated sensors will have to be replaced periodically.

Heated-diode technology consists of a ceramic element that heats refrigerant and breaks apart the molecules, leaving positively charged chlorine or fluorine ions that are attracted to a negatively charged center collection wire. The flow of chlorine or fluorine ions to the center collection wire creates a small current. As the refrigerant concentration between the electrodes increases, the current increases to a level that sets off an alarm. Generally speaking, heated-diode detectors are more accurate and less prone to false triggering than corona-suppression detectors. Again, contaminated sensors and sensor filters will have to be replaced.

  • Ultrasonic detectors use highly sensitive microphones, these ac- or battery-powered devices ‘listen’ for a high-pitched, inaudible sound caused by the turbulence that results when refrigerant escapes from a leak site. Once detected, an alarm is sounded. Ultrasonic detectors convert and amplify the inaudible sound of a leak into a more natural sound the human ear can easily identify. One of the biggest complications with an ultrasonic leak detector is the possibility of background interference. Some models, especially earlier versions, can pick up other inaudible sounds not associated with the refrigeration system and sound the alarm on the detector.

Modern sensor technology

Electrolyte sensor leak detectors 300Electrolyte sensor leak detectors
When the electrolyte sensing element is exposed to refrigerant, an electrochemical reaction changes the electrical resistance within the element, causing an alarm. The sensor is refrigerant specific with superior sensitivity to all HFCs and HCFCs, and minimal chance of false alarms. When exposed to large amounts of refrigerant which could contaminate other systems, the electrolyte sensor clears quickly and does not need recalibration before reuse.

Enhanced Metal Oxide Semiconductor 300E_Mos® (Enhanced_Metal Oxide Semiconductor)
The E_MOS technology utilised in the latest CPS Products Leak Seekers® takes refrigerant leak detection to a new level. The sensor is an enhanced version of the bulk metal oxide sensors commonly used to detect a wide range of gases and vapors. Laboratory and field tests have confirmed Leak-Seekers made using this new technology are more sensitive, stable and accurate than other detection methods on the market including heated diode, infrared, corona, ultrasonic, halide torches and soap bubbles.

Moreover, the E_Mos® sensor needs minimal warm up, has a longer sensor life (ca. 500 hrs.) and extended battery life (ca.50 hrs.). Other features are: no sensor contamination by R404a, sensitivity remains constant over the life of the sensor, superior sensitivity to R410A and new HFO refrigerants, sensitivity to 35 parts per million (less than 1oz per year) and senses all refrigerants including those with hydrocarbon components.

H2 Detector 300H2 Detector (95% Nitrogen 5% H2 Tracer Gas)
Many countries are now adopting laws that ban the use of refrigerants for system testing. The H2 detector was developed for detection of leaks using a 95% nitrogen and 5% hydrogen tracer gas mixture instead. The unit can detect leak rates less than 5ppm.

 

 

Combustible gas detectors 300

Combustible gas detectors

These are designed to detect all hydrocarbon and other combustible gases including propane, methane, butane, industrial solvents and more. The unit shown here is pre-set at normal sensitivity but can be switched to high or low. Slow beeping indicates that unit is warmed up. Frequency increases when a leak is detected until an alarm sounds when moving into high gas concentration. The Smart Alarm LED indicates leak size.

Fluorescent leak 300Fluorescent leak 02 300

  • Fluorescent leak detection This method requires adding a fluorescent dye to the air conditioning or refrigeration system. The dye then mixes with the lubricant and circulates with the refrigerant throughout the system. Wherever refrigerant leaks out, so does the dye. When the system is scanned with an ultraviolet (UV) or blue light lamp, the dye glows a bright yellow-green colour, pinpointing the location of the leak.
    It is important to use an OEM-approved dye that is compatible with the system’s lubricant.
    Please note, some OEMs prohibit the use of dyes in systems under warrantee.
    Be wary of dyes containing co-solvents because they can adversely affect the lubrication qualities of the system’s oil, which can lead to premature compressor failure. When using fluorescent leak detection, it is best to select a UV or blue light lamp that produces high-intensity output. The greater the light intensity, the brighter the dye will glow, making it easier to find leaks. Depending on the lamp, the glowing dye can be seen from as far away as 6m, which helps to spot leaks in overhead systems. In addition, fluorescent leak detection can be used in preventive maintenance seeing that the dye remains in the system until the lubricant is changed.

    Special dye cleaners are available to clean the detected areas before leaving the system.

Factors to consider when choosing a leak detection method:

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 still must 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?

Environmental factors
Wind and air currents affect the accuracy of electronic detectors and halide torches, which depend on sampling and testing the air near to 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.

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 minimize 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.

Disclaimer: the intention of these articles is to inform the user about the availability of industry relevant tools and equipment and their application, with the understanding that the usage inferred is only undertaken by suitably qualified and competent persons.

Final note on safety

Be responsible and always wear eye protection as well as a good pair of work gloves when it’s appropriate. Be sensible and never compromise on quality tools, your tools put a roof over your head and food on the table. Buy good quality once and look after them.

Credits: Ritchie Engineering Yellow Jacket USA, CPS Products USA


 

08 Jun 2018;
08:00AM -
FRIGAIR Expo 2018 - Day3
16 Oct 2018;
08:00AM - 06:00PM
Chillventa 2018 - 16-18 October
16 Oct 2018;
08:00AM - 06:00PM
Chillventa 2018 - 16-18 October
16 Oct 2018;
08:00AM - 06:00PM
Chillventa 2018 - 16-18 October

 

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