This Web exclusive comes from Jack Sine, a freelance writer who specializes in IAQ matters.
Refrigerant leaks have always been a concern for facility managers, but it was a problem that could be easily discovered and corrected. For several years, refrigerant leak detection, while not perfect, was a fairly settled technology. Almost everyone used a heated sensor detector. There were other methods on the market—sound amplification, soap bubbles, fluorescent dyes in the refrigerant, and corona discharge—but by far the most successful and most popular defense was heated diode technology.
For anyone unfamiliar with heated diode technology, it is an approach that relies on a ceramic substrate doped with a reactive element and heated to a high temperature. When the surface makes contact with a halogen-bearing gas, the chlorine, fluorine, or bromine atoms separate from the molecule and are ionized. This activates an electric current that alerts the instrument user to the presence of a refrigerant. The portable hand-held technology was developed originally by GE as a plug-in device and then refined by Inficon as a smaller, battery powered, more accurate instrument more than 10 years ago.
“We made what we thought were the best refrigerant leak detectors and the market responded,” says Jerry Wander, general manager at Inficon.
But, as with all technologies, there were problems as well. Temperature variations and a variety chemicals and gasses could trigger false alarms. The sensors also have a short life span and must be replaced often.
Enter The Blends
Then came the blended refrigerants.
“When the blends like R404a and R507 came out, heated diode could identify them, but it wasn’t sensitive enough to be truly effective,” said Wander. “We turned to infrared technology, which proved to be much more sensitive not only for blends, but for all the CFCs, HCFCs, and HFCs as well.”
Infrared radiation is electromagnetic radiation with a wavelength longer than that of visible light but shorter than radio waves. The term literally means “below red.”
For leak detection, the sensor is an infrared absorption filtometer consisting of an infrared emitter at one end, an infrared energy detector at the other, and an optical filter in between. Since most materials absorb specific and known wavelengths of infrared energy, the sensor in an infrared refrigerant leak detector focuses on the wavelengths absorbed by refrigerant.
All refrigerants and blends have similar absorption spectra between 7.5 and 14 micrometers. The optical filter in the sensor limits the infrared spectrum emitted by the instrument to that range.
When activated, the emitter creates a high intensity infrared stream containing all the wavelengths in the infrared spectrum. The optical filter blocks all of those except the ones in the refrigerant spectra. The remaining infrared energy strikes the detector and causes it to heat up.
When refrigerant passes through the sampling cell, some of the infrared energy is absorbed by the refrigerant. There is an immediate decrease in the amount of infrared energy reaching the detector and a corresponding drop in the detector’s temperature which triggers an alarm, either visual or audible, to alert the user of the presence of a leak.
“It’s simply the best way to find refrigerant leaks in air conditioning systems,” said Rey Harju, president of Fieldpiece Instruments who just introduced its own infrared detector. “It makes a maintenance engineer’s job a lot easier. They are also more cost effective. Although the initial cost is more than the heated diode detectors, the life of our sensing system is more than 10 years. When you figure the cost of sensors for heated diode detectors, the cost of the infrared instrument is less over the long run. And, more important, over the long run they’re more reliable.”
The first infrared refrigerant leak detectors were wall mounted units used inside walk-in coolers and freezers. In recent years, electronic technology has advanced to the point that they can now be made small enough to be hand-held.
No More False Alarms
“The beauty of infrared detectors is that they eliminate false alarms,” say Jim Mowery, vice president of sales at Bacharach. “Other technologies are sensitive to other background gases such as cleaning products. Heated diode detectors are affected by breezes and changes in air temperature. Infrared detectors only react to refrigerant and they are very sensitive.”
Bacharach manufactures the H25-IR, a complex infrared detector designed for heavy industrial operations where there is a possibility of catastrophic leakage. At eight pounds and with a price tag of more than eight thousand dollars, it is not designed for home or commercial HVAC environments.
“It’s effective in an industrial setting because it not only detects, it also quantifies,” explains Mowery. “That’s important, because you can determine the seriousness of the leak and either schedule repair or shut down for emergency servicing. That makes it important for assembly lines producing such things as refrigeration racks, automobiles, fire extinguishers, and any production environment that uses process cooling. It can pick up and eliminate all trace gasses and be set to look for one specific refrigerant. Then, after that refrigerant has been identified in the air, the unit can be used to detect where the leak is and how much refrigerant is escaping.”
A Versatile Detector
A smaller and more affordable infrared detector that is useful in many applications has been offered by Inficon for more than three years.
“We designed our D-TEK Select so it could be used in a variety of environments,” said Wander. “It is used in automotive, refrigeration, and HVAC.”
Significantly smaller than the Bacharach detector, this one is much easier to transport and use in tight spaces, weighing only one pound three ounces. To solve the need to change sensor with the heated diode detector, the Select’s sensor lasts for 800 hours.
“One important thing with infrared,” Wander says, “is to keep the infrared path clean. To assure that happens, we’ve designed in a series of filters to keep out anything that would interfere with accurate operation.”
The D-TEK Select also features sensitivity to 0.10 ounce per year, two sensitivity settings (high and low), and a battery life of 6.5 hours.
The Power Of Infrared
But the question still remains – “How good are infrared leak detectors and do they justify the higher cost?
Bobby Rosser is the outside salesman at B & T Heating and Air in Tulsa, OK. He recently had reason to try out his company’s new infrared leak detector.
“I was over at a friend’s house a few weeks ago,” he said, “and he was complaining that his split system was loosing refrigerant. I asked him what he had done about it, and he said he had had three separate service companies come over the last six months, but they couldn’t find the leak. They all three thought it was probably in the evaporator. It was a small one, about half a pound a year, but this is one meticulous guy and he wanted it fixed. It just so happened that I had our new Fieldpiece SRL2 in the car, so I said ‘let me give her a go.’ It was an R-22 system, so the other companies heated diode detectors should have found it, but it must have been too small. I used the infrared and found the leak within minutes. It was at the first U-bend going into the compressor. He was impressed and so was I.”
With the emergence of blended refrigerants, the infrared leak detector is definitely here to stay, but Rosser would probably contend that it does very well with the old refrigerants as well.