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Are You Operating Your On-Board Refrigeration System on Borrowed Time?

 


If your refrigeration system is based on refrigerant R-22, then take notice! The life of one of the most successful halocarbon “Freon” refrigerants is coming to an end. Production of the refrigerant is being reduced every year, with a total ban on production in the US by 2020. The result is that an end-of-life rise in the price of refrigerant R-22 as planned by the Montreal Protocol Treaty has already begun, and it will not stop.

Refrigerant R-22 was first developed and marketed as a refrigerant in the mid-1930s, and by the mid-1960s had begun a journey to become one of the most widely used refrigerants across the globe. For over 50 years R-22 has been the workhorse refrigerant for commercial, marine and industrial non-ammonia refrigeration plants, but now the life of this very successful chemical is coming to an end.

A Brief History

The halocarbon refrigerants were developed out of a recognition that common hydrocarbon gases – particularly methane and ethane – were very well suited for use as refrigerants; they could be compressed, liquefied, and evaporated at desirable refrigeration temperatures and at pressures that were easily compatible with existing air compressor technology. They only had one problem – and a formidable problem at that – they are extremely flammable.

From a molecular point of view, methane, for example, consists of a single carbon atom surrounded by four hydrogen atoms. In the presence of oxygen, and a relatively low energy source – a small flame, or electrical spark – methane reacts to produce carbon dioxide and water. That is the nice way of explaining it. More simply put, hydrocarbon gases are dangerously explosive! Explosive because of the ease in which the hydrogen atoms react with oxygen. But what if these hydrogen atoms could be replaced with other types of atoms that would stabilize the molecule and still retain its great refrigeration properties? This was the question that was being asked by researchers back in the 1930s. What these researchers found is that both chlorine and fluorine, which are members of a group of atomic substances commonly referred to as the “halogens”, could easily replace the hydrogens, and produce a very stable chemical that retained many of the great refrigeration properties of the original methane molecule. Hence the formation of the “halocarbons” also known as chlorinated or fluorinated hydrocarbons (HCFCs), chlorofluorocarbons (CFCs), and the like. The commercial trade name “Freon” became the commonplace term for these refrigerants. The new discovery started an avalanche of different halocarbon refrigerants, that didn’t have the problems that contemporary refrigerants of that day, ammonia and sulfur dioxide, had – these new “Freon” refrigerants had no odor, were not acidic or caustic, were inexpensive, could be used indoors – in homes and stores and in automobiles. The refrigeration industry expanded – worldwide, and almost overnight.

In the 1980s there was a growing concern over the use of CFCs and HCFCs. The concern was that although they were very stable at sea level, these chemicals could find their way into the stratosphere, where high-energy radiation could break down the molecule, and leave the chlorine atom available to react with and deplete the “ozone” layer that protects the earth’s surface from excess ultraviolet radiation. It was further believed that these chemicals had the ability to contribute to global warming. While there are a great number of chemicals in use that can have the same effect on the environment, what caused so much alarm with these CFCs and HCFCs was the sheer volume of production. They were used so widely, and their nearly odorless properties and relatively low cost discouraged leak repair in refrigeration systems. Add to that the fact that the high stability of these chemicals gave them a very long atmospheric life – of up to 70 years in some cases. Although there has been much debate over the “Freon vs. ozone” debate, and the impact of global warming, any synthetic gas produced in such great volumes, that has an atmospheric life of up to 70 years should, of course, raise alarming concerns.

At the end of the 1980s, a multi-national treaty, the “Montreal Protocol”, was signed by many of the western nations. It created “phase-out” schedules for most of the CFCs and HCFCs, with the idea that refrigerant producers would research and formulate more environmentally compatible refrigerants. The first refrigerants that were replaced with alternatives were R-12 (refrigerators and auto air conditioners), R-502 (low temperature commercial freezers), and a host of lesser known refrigerants. The action against R-22 was different in that the Montreal Protocol used a longer phase-out that would not be unnecessarily harmful to the economies of the signing nations. The reason for this approach is because R-22 was so widely used in industry, and because the ozone depleting potential was so low.

Since the signing of the Montreal Protocol, the reductions in production have been on schedule, with the final ban in production taking place in 2020. However most R-22 system owners – particularly those with chronically leaky systems – are experiencing the intended effects of the Montreal Protocol today, with R-22 prices approaching $15 per pound, almost three times that of the best replacements.

What replacement options are available?

Currently, the strong leaders in replacement refrigerants are R-404A and R-507. They are not “drop-in” replacements, but their use is so widespread in the new equipment market that future security seems assured. They are both very similar, in composition and characteristics; R-404A seems to be popular with the smaller under 100 HP systems, and R-507 with the larger systems. Both are non-ozone depleting, and they both have a low global warming potential. These are refrigerants that are expected to be around for a long time, and are rapidly becoming standards in both industrial and commercial refrigeration. In fact, the price on these refrigerants has dropped by half as new manufacturers take on the product. A substantial number of marine and industrial design and build refrigeration contractors have been using these two refrigerants as standards in large, direct expansion, flooded, and pump-recirculated systems for more than 10 years now. They have been through all of the necessary engineering changes needed to make them work well, and technicians that are experienced in making them perform to their task are commonplace at this time.

How will your refrigeration system act with the new refrigerant?

There are some differences between R-22 and R-404A/R-507, mostly in the operation of the equipment. For ships engineers and refrigeration plant operators, the most substantial differences are that R-404A/R-507 operates at higher pressures. For example:

• In an R-22 system, if you are used to seeing high side pressure in the 150 PSIG range, you can expect to see around 195 PSIG with R-404a/ R-507.

• If you are chilling seawater with an R-22 system, you are used to seeing low side pressures in the 45-50 PSIG range after pull-down. The same conditions for an R-404a/ R-507 system will give low side pressures in the 60-65 PSIG range.

• Low temperature freezers in R-22 may have low side pressures of around 3-5 PSIG. With R-404a/ R-507, the difference is a little less radical – expect to see 5-10 PSIG.

Some additional impacts to your system – the good and the bad:

• If your existing piping, whether copper or steel, is adequate for R-22, than it will be adequate for R-404A/R-507.

Evaporators in your cold storage will have a slight increase in capacity.

• Both screw compressors, and reciprocating compressors will operate at a higher horsepower requirement for the same refrigeration load (slightly less efficient by approximately 10 percent). Does that mean you need to re-power your compressors? If your system operates with fully loaded compressors at any time in your process, then yes you will; and it may also involve larger motor starters, circuit breakers, and wiring. It will also involve motor mounting changes and different shaft couplings. If your compressors never operate at full capacity, then you may wish to add controls that unload the compressor when the drive motor reaches its maximum amperage.

• Interestingly, the bare screw compressor, and most reciprocating compressors (depending on cylinder valve design) are capable of higher total capacity with the new refrigerant; so that if you up-size the motors, you will have added capacity of around 6 percent in water chilling systems, and up to 15 percent in low temperature freezing systems. In other words, if you need to increase the horsepower size of the compressor drive motor, make sure to select a motor size that will cover the capacity of the existing compressor operating with the new refrigerant. But be aware, that the additional compressor capacity will require additional condensing capacity as well.

• The existing condensers may operate at slightly lower capacity, depending on the type of condenser; that means you may not have enough condenser with the new refrigerant. The need for additional condensing is dependent on how your system currently operates during the warm summer months. If you can easily maintain 140-psig head pressure with R-22 in hot weather or warmer seawater, then you will be in good shape. If your head pressure ranges between 160 psig and higher with R-22, you may have trouble staying below a 250 psig high side relief valve with R-404A/R-507.

• High side components like oil separators, condensers, and liquid receivers will operate at a higher pressure, closer to the design limits, but still below the emergency shut-down limits. You will have to replace the compressor relief valves with a different class of valves that have more precise trip points. This may involve some piping work.

• Finally, some good news: your refrigerant costs will decrease drastically!

What is involved in retrofitting your plant with the new refrigerant?

There are a number of basic tasks required to retrofit your system to the new refrigerant:

• Find a professional to help you decide if you need to re-power your existing compressors, if your existing condensers are adequate, and if your existing high-side components can operate under higher head pressures.

• Identify and change out elastomeric seals – like O-rings, especially in the compressor shaft seals. The existing rubber seals are compatible with the mineral or alkyl-benzene based lubricants, but R-404A/R-507 will require the existing lubricant be changed out to a “polyester” or POE oil. This requires different elastomeric seal material.

• Replace the mineral or alkyl-benzene compressor oil with polyolester compressor oil. This is a critical step that should be done before the refrigerant is changed out because POE oil will do a very good job of “washing out” the dirt and grime in your system. The dirt and grime will be less prevalent in newer screw compressor systems and more prevalent in older low temperature reciprocating compressor systems because of the higher discharge temperatures, as well as metal dust from piston, ring, and cylinder wear. If you have a particularly contaminated system, you will need some time to work through the sludge – so consider operating with POE before the R-22 is changed out – and have refrigerant line filter dryers, oil filters, filter housing gaskets, and compressor crankcase gaskets on hand for one or more cleanup events.

• POE oil is also very “hygroscopic” – that is it absorbs moisture very readily. You will need a substantial amount of dehydration time after the old refrigerant is pumped out, before new is added so that you don’t further contaminate the final charge of clean POE oil.

• Pump out and reclaim the R-22 refrigerant. Keep in mind that the reclaimed R-22 has a substantial market value (lately around $5 per pound) that could pay for the new R-404A/R-507 replacement refrigerant. If you hire a contractor to do the work, make sure that you get paid the full value of the old R-22 refrigerant. It belongs to you, and you have the right to keep the sale price of the refrigerant on the table!

• Re-configure or replace expansion valve devices and pressure limit switches in your system.

• Re-charge with R-404A/R-507, run the system, make adjustments, scour the system for leaks, change filters, clean strainers, and inspect compressors in order to get a good view of how much sludge is returning to the high side. When you are satisfied that the system can operate reliably, return the plant to production.

• Plan for follow up work, including a final strainer cleaning, filter changing, and leak check. At this time, test the oil for residual mineral or alkyl-benzene oil, and replace a final time, if necessary.

Alternatives to retrofit:

The most effective alternative to retrofit is to eliminate all leaks from your system. That is easier said than done with an odorless refrigerant. But if retrofit is a more practical solution, keep a clear view on whether your existing equipment is worth the retrofit labor. The best alternates are assemblies that are engineered for the refrigerant. Whether a new Freon plant, or ammonia for the larger-than-50 HP systems, or the new ammonia/CO2 hybrid systems that keep the ammonia charge to a minimum. Keep an open mind.

Some final advice:

I hope that this article has given you a starting point on the task of migrating away from R-22; and I’m sure that your review of the material will bring up more questions than decisions! The main point is that you can probably use your existing system, as long as you know what to expect, and are willing to go through the process.

Finally, a wise word of caution: don’t wait for the last moment. You will have a number of maintenance issues to get through before your system operates reliably, but once you have worked through the issues, you will have as reliable a plant as you had with R-22, and your days of $15 per pound refrigerant will be over.

Rick Greenquist, an applications engineer with Highland Refrigeration, began his career in the fishing industry unloading king crab in Dutch Harbor, Alaska in the mid 70s but quickly discovered that his true calling was the mechanical aspect of the seafood industry; specifically mechanical refrigeration.

Rick has taught classes as an adjunct instructor through the Seattle Community College Marine Training Center, and through the Dutch Harbor, Alaska chapter of Refrigerating Engineers and Technicians Association. His focus in the last two decades has been in mechanical design of refrigeration systems, electronic controls and energy efficiency.

 
 
 
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