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Refrigerants – the future is ‘natural’

By Ilana Koegelenberg

As efforts to phase down HCFCs intensify and the end of HFCs looms not too far in the distance, the search for alternative refrigerants is the order of the day.

Natural refrigerants are nothing new to our industry, but they are becoming more viable as replacements for synthetic refrigerants insofar as equipment, technology, and skills improve. In this article, we take a look at how the industry is adapting (and hopefully embracing) natural options such as ammonia, CO2, and hydrocarbons in particular.

General Background credit AHAM

As usual, this was once again a much bigger topic than I initially anticipated. I was overwhelmed by the information available and the work done by the various industry associations. The world seems to be accepting these more environmentally friendly alternatives with open arms. Even in South Africa, we finally seem to be catching on. I have definitely seen an increase in projects with plants running on CO2 and ammonia. Retail in particular seems to be warming up to the idea of CO2.  

I could fill an entire magazine on each of the refrigerants I have selected to look at in this article (hydrocarbons, ammonia, and CO2). The sheer amount of content I got on hydrocarbons from Lyndsay Pelser in Australia (an engineer specialising in hydrocarbon refrigerant conversions at AAPT Group) was enough to short-circuit my brain!

So here follows some form of an ‘executive summary’ on my take on natural refrigerants. Although I have spoken to quite a few experts on the matter, once again, the untapped pool of resources remains vast. So, consider this my disclaimer — this is by no means an exhaustive article.

Why go natural?

As world economies grow, the application of HVAC&R systems also grows, which leads to a proliferation in refrigerant production by virtue of the ‘banked’ refrigerant existing in deployed equipment and a greater quantity of refrigerant needed for servicing and maintenance. Both factors result in a greater potential for refrigerant emissions to the environment, with the potential adverse impacts.

At the same time, as the need for refrigerants grows, the world’s societies are becoming more concerned about the environmental consequences of the refrigerants being used and the systems that use them. Through the Montreal Protocol, the world developed an unprecedented response to the environmental problem of stratospheric ozone depletion by phasing out the manufacture and the eventual use of ozone depleting refrigerants.

Synthetic refrigerants such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) have a negative impact on the earth’s atmosphere. The CFCs and HCFCs destroy the protective ozone layer so that the sun’s aggressive ultraviolet rays can reach the surface. The radiation causes genetic damage in the cells of people, plants, and animals. Therefore, the international Montreal Protocol started the phase out of ozone depleting substances in 1987 — with success. According to the latest scientific assessment by the World Meteorology Organisation and the United Nations Environment Programme (UNEP), the ozone layer could recover to a large extent by 2050.

However, the ozone-friendly successors, the synthetic hydrofluorocarbons (HFCs), contribute to global warming up to 4 000 times more than CO2 does. Even though they are specified as greenhouse gases under the Kyoto Protocol, they are still widely used in refrigeration appliances. The concentration of greenhouse gases in the atmosphere is at an all-time high and the contribution of HFCs is growing.

In the search for alternatives that have low global warming potential (GWP) and reduced likelihood of other environmental impacts, natural refrigerants are gaining increased interest. Natural refrigerants are substances that can be found naturally occurring in the environment. Natural refrigerants include ammonia, carbon dioxide, hydrocarbons, water, and air. Some of the natural refrigerants have been used in the marketplace for many decades, although at varying degrees of application.

According to the US Environmental Protection Agency (EPA), who have been driving the phase down of harmful refrigerants globally, although environmentally superior, natural refrigerants are not free of other concerns, such as corrosion, toxicity, high pressures, flammability or, in some cases, lower operating efficiencies. Selection of the correct refrigerant for an application requires careful review of such criteria as capital cost, operating cost (including energy and maintenance), equipment size and location, operating temperatures/pressures, facility staff capability, and local, national, and international regulations.

What are natural refrigerants?

Natural refrigerants include a range of organic and inorganic compounds suitable for use in a variety of refrigeration and air-conditioning system applications and presenting a variety of issues and challenges. Thus, the successful application of these refrigerants will vary depending on the compound. A useful definition is “Natural refrigerants occur in nature's biological and chemical cycles without human intervention. These materials include ammonia, carbon dioxide, natural hydrocarbons, water, and air.”

"In the search for alternatives that have low global warming potential (GWP) and reduced likelihood of other environmental impacts, natural refrigerants are gaining increased interest."

The advantages of natural refrigerants have led to a significant increase in their use in recent years in applications traditionally served by fluorocarbons.


Note: I’ll be skipping over water (R718) and air for this article as they tend to be quite inefficient and not widely used in South Africa. They are more for niche applications.

Ammonia (R717)

Ammonia has a longstanding and widespread use in food and beverage processing and preservation, and a growing adoption in HVAC chillers, thermal storage systems, process cooling and air conditioning, district cooling systems, supermarkets, and convenience stores. Since the middle of the nineteenth century, there have been many changes in types of refrigerants, but ammonia is unique because it has seen continued use over this 150-year period.

Ammonia has an ozone depletion potential (ODP) and a GWP equal to zero. It has inherently high refrigeration system energy performance, excellent thermodynamic properties, and high heat transfer coefficients. In a vapour state, it is lighter than air. It is easily detected by smell, or by a variety of electrochemical and electronic sensors, and is readily available at a relatively low price.

The primary disadvantage of ammonia is its toxic effect at higher concentrations (that is to say, above 300ppm); however, this risk is somewhat mitigated by its pungent smell alerting humans to its presence so that even at lower concentrations (5ppm) it is self-alarming in the event of a leak.

Ammonia provides useful cooling across the range of temperatures from air conditioning to low-temperature applications.

Carbon dioxide (R744)

Like ammonia, CO2 was also used in the mid- to late-nineteenth century, particularly on-board ships and in shops and theatres where the smell of ammonia was not acceptable. However, as ammonia system safety and efficiency improved at the beginning of the twentieth century, CO2 systems became less common.

With the introduction of fluorocarbons in the 1930s, CO2 fell out of use by the 1950s. However, the low toxicity, non-flammability, zero ODP, and low GWP properties of CO2 attracted the attention of system designers, beginning in the early 1990s when alternatives to CFCs were being sought. Since then, CO2 has found widespread acceptance in the full range of vapour-compression systems from low-temperature freezers to high-temperature heat pumps. It has also been widely used as a secondary refrigerant, offering significant improvements in efficiency compared with traditional water, glycol, or brine systems.

One major difference between CO2 and other refrigerants is in its pressure/temperature characteristics, because the pressures experienced are approximately 10 times higher than those in ammonia or R404A systems. This high pressure requires special equipment designs, but it also offers many advantages over other refrigerants.

Exceptionally good system performance has been noted in low-temperature plate freezers and multi-chamber blast freezers where improvements in efficiency and reductions in freezing times have been reported.

The unusual fluid properties of carbon dioxide, including its high density and low critical point, make it particularly well suited for cooling very intense heat loads, such as those found in IT applications.

Hydrocarbons

In nature, hydrocarbon (HC) refrigerants are constituents of oil and natural gas. HC refrigerants have excellent environmental, thermodynamic, and thermo-physical properties; however, they are highly flammable. As a result of these factors, HC are the molecular basis for the halocarbon refrigerants wherein some or all of the hydrogen atoms have been replaced by halogens such as chlorine, fluorine, and bromine, which reduce flammability but can cause unwelcome effects on the environment.

NR006

The ozone hole before and after the Montreal Protocol (signed in 1987). The phase down of refrigerants has a huge impact on the healing of the ozone layer.
Image credit: NASA

In the past, HCs have had limited applications primarily within the petrochemical industry to provide industrial chilling and process refrigeration. With the phase out of the CFCs, hydrocarbon refrigerants are entering into new arenas.

There are many benefits in using HCs. “Mainly, they work better in hot climates, offer lower operating pressures, half the amount of refrigerant used compared to HFC/HFO, and the cost is very low compared to HFC refrigerants which will now increase even more forcing people to move away from HFC refrigerants,” explains Pelser. “A hydrocarbon system will use up to 40% less energy than any HFC/HFO system.”


Note: There are very comprehensive manuals and documents on the dos and don’ts of working with HC — and doing it safely. So, make sure you do your research before you venture into this field.

South African context

What refrigerants will be used in South Africa in the future? Where are we going with natural refrigerants?

CFCs like R11 and R12 are now officially phased out and a thing of the past. We are currently busy with the phase down of HCFCs, which started in 2014. It is now illegal to build any new plants containing these refrigerants such as R22. As such, we have been moving towards HFCs as replacements — unfortunately, not a very sustainable solution.

South Africa will (eventually) ratify the Kigali Amendment to the Montreal Protocol (there may be a funding problem as the US threatens to pull out) and by 2024, must start the phase down of high GWP refrigerants. This includes HFCs, many of which we have become quite reliant on, such as R410A, R134a, R507A, R404A, and R407C.

Many of the developed countries have already started the phase down of HFCs under the EU F-Gas regulation (for example) and as such we might soon be experiencing price increases and shortages on these refrigerants. Chemours has already announced that as of next year, it will no longer produce R410A, and there have been various accounts of shortages of R410A globally.

Therefore, the sooner we move away from HFCs (rather than towards it), the better. There simply is no longevity in these systems and suggesting them to clients is no longer a feasible solution.

“The problem with replacing with HFCs instead of using naturals is that in 20 years or quite probably even earlier), everything installed today will have to be changed again,” explains Wynand Groenewald of Commercial Refrigeration Services (CRS).

Current situation

There is a lot of movement in terms of natural refrigerants — globally and in South Africa. Various associations and industry bodies are hard at work refining regulations and standards to keep up with all the refrigerants that are now on the rise. The South African Qualification and Certification Committee (SAQCC) for Gas now even offers a separate registration category for working on HCs and CO2.

As the safety properties and risks vary, it is vital to keep industry professionals working with these gases up to date to ensure not only safety on site, but also maximum efficiency in terms of system operation.

It comes back to education. “I believe many misunderstand the issue of refrigerants and GWP,” says Marius La Grange of Refrigeration Solutions, a local contracting company and division of Energy Partners. The direct GWP of a refrigerant would only have an impact if refrigerant leaks out, which makes it vital to ensure leak-proof systems. That is also why it is so important that refrigerant be recovered from a system whenever you do repairs or decommissioning. Refrigerant securely in a functioning system only has an indirect GWP from the energy consumed to get the cooling or heating effect. Many clients do not realise this and it is important that contractors factor this into budgets when doing refurbishments, La Grange says. “Releasing refrigerant into the atmosphere is illegal.”

According to Michael Labacher of A-Gas, they have definitely seen an increase in the popularity of CO2 and HCs like R290 and R600a. “The Hydrocarbons section is growing rapidly and we believe it will grow even more in future,” says Labacher. “It will never replace synthetic refrigerants, but it is definitely gaining ground. There is a massive enquiry for HC in the rest of Africa in particular.”

The rise of CO2 can be seen across the board. “We have definitely noticed an increase in interest in terms of using CO2 in projects from both the consultants and contractors’ side,” says Groenewald.

Especially on the contractors’ side, there are some who want to stay ahead of the game and upskill themselves in terms of working with CO2 systems. “With all the industry changes happening lately, contractors want to retain their clients and not be absorbed by bigger companies. This is where we can support such contractors by training them on the use of CO2 and assisting in supplying the system.”

According to A-Gas, ammonia sales seem to be slowing down.

Nigel Amschwand, engineering consultant at GEA, says this could also be explained by the fact that industry is constantly working at finding ways to improve the system and use a smaller refrigerant charge. So, while ammonia sales might be down, there are in fact more ammonia systems going up — they are just using a smaller refrigerant charge to help reduce some of the safety concerns.

Through careful design, it is often possible to reduce the required quantity of refrigerants in systems by the application of design techniques such as plate heat exchangers and dry expansion evaporators — both of which are already common in a number of applications, explains Pelser. Another way to decrease the refrigerant charge is the use of indirect refrigeration systems with secondary coolants.

Applications – horses for courses

Table 1 is a handy table put together by Amschwand on what refrigerant works in which application.

 Number  Name   Class*  GWP  Main applications
 R 170  Ethane   A3  3  Ultra-low temperatures
 R 290  Propane  A3  <4  RAC, beverage coolers, water chillers
 R600a  Isobutane  A3  3  Domestic refrigerators/ freezers
 R 717  Ammonia  B2L  0  Industrial refrigeration, water chillers
 R 744  Carbon dioxide  A1  1  Supermarket refrigeration
 R 1 270  Propylene  A3  <4  Alternative to propane with higher efficiency

Table 1.
*In terms of class, the letter refers to the toxicity and the number to flammability.

The mainstream refrigerant for supermarkets will be CO2 in cascade arrangements with HFO blends such as R513A, predicts Amschwand. In South Africa, transcritical CO2 uses too much energy due to the high ambient temperatures compared to that of Northern Europe where the systems can run sub-critical for long periods. The drop-in replacements for R404A/R507A are very expensive and as supermarket systems are generally very leaky, often due to poor installation practices, CO2 will be preferred. CO2 , due to its high working pressures, necessitates better workmanship.

“Industrial refrigeration will continue using ammonia, perhaps with CO2 as a volatile brine where required,” predicts Amschwand.

Subcritical systems are used more frequently in a cascaded arrangement with R134a in many retail applications, according to La Grange; this being a strategic decision from some local retailers.

“Popularity is on the increase, but not as rapid as some European countries. Ambient conditions are one factor and there is a  longer return on investment when compared to HFC, but the running costs and lifespan need to be factored in as well,” says La Grange. The longer return on investment outlook might well end up being a good call in 20 years from now should energy costs continue to increase at the current rates. The service regime for a subcritical CO2 system needs a planned preventative programme to keep the system in healthy state.

NR005The global warming potential (GWP) of natural refrigerants show just how much less harmful they are than HFCs.
Image credit: www.pddnet.com

“An ammonia installation typically needs a bigger capital investment with a longer payback period and this might well influence decisions towards larger HFC installations that have a shorter return on investment within what many could view as an uncertain environment to operate in,” says La Grange.

Ammonia (R717) and CO2 subcritical combines very well, but the skill sets and qualifications required from one service team to attend to this combination is a challenge, says La Grange. “Often, the R717-qualified tradespeople know very little about an HFC or other synthetic vapour compression systems and vice versa. Few people have both sets of skills,” says La Grange. The combination R134a and CO2 subcritical is, however, more popular, with none of the strict R717 safety regulations needing to be factored in. “Ideally, these skills need to be better integrated without lowering the safety standards required when working with R717.

“Ammonia installations can be very efficient in medium-temperature applications (in many ways the best), but it comes under competition for that spot when used in low-temperature applications — CO2 being a strong contender,” says La Grange.

Although HCs are good on a small scale, Groenewald believes that when it comes to retail applications, CO2 is always a viable option. Although cost of equipment is still a bit of a barrier, this will soon change, as the phase down of HFCs is already affecting the price of synthetic refrigerants while the price of CO2 comes down due to volumes increasing. “CO2 is also moving more into the industrial playing field, globally now.”

Choosing which natural refrigerant to use is quite easy, says Pelser. “With an existing plant, the only way forward is hydrocarbon. If you are looking at a new plant, then it would depend on the project.” Ammonia is good for large cold rooms and freezers, while HC works well for air conditioning, he recommends.

Concerns/ dangers

In South Africa, the skill set is putting a damper on the use of natural refrigerants and HCs in particular, explains Labacher. “We cannot control our leaks. Our leak rates in South Africa are exorbitant and with HC, this is a high risk as you cannot smell it and it is highly flammable.”

“The use of A2L and A3 refrigerants require greater safety due to their flammability, and training methods must improve,” says Amschwand. “Regulations such as SANS 10147 are being updated to cater for A2L refrigerants which I’m sure are already being installed in centrifugal water chillers.” The safety requirements are similar to ammonia, a B2L class.

There is international pressure to increase the upper limit for A3 refrigerants from 150g to 1.5kg, explains Amschwand. There are already regulations (EN 378) for the use of A3 and A2L (R32) refrigerants in room air conditioners (RACs) and one leading UK supermarket group is already using propylene in water cooler self-contained display cases.

It is important to note here that it is illegal to import (or use) any flammable refrigerants (such as HCs) in disposable (non-refillable) canisters. This is not only dangerous, but could have legal implications.

Although HC manufacturers have their own service technicians who can service the product and have been trained in-house, this only applies while the product is still under warranty. After that, the risk is quite high that an unskilled person could work on the system — someone who does not understand how to work with a flammable refrigerant. And this is a huge risk, explains Amschwand.

“It is time to introduce sustainable and economical natural refrigerants in developing countries to provide environmentally friendly cooling for comfort and productivity.”

Skills in general are also a concern when it comes to HCs and the other natural refrigerants. This makes maintenance costlier, as it is more specialised and technicians would need to get extra training to work on these systems. Whether a toxicity risk or flammability or any of the others, maintenance and repair will not be as straightforward as with the synthetic refrigerants we have become accustomed to.

“While climate change is the most important challenge of our days, it is still important to pay attention to how the conversions to environmentally friendly HC refrigerants are taking place to avoid unnecessary accidents due to ignorance and neglect,” says Pelser.

With the phase out of high GWP refrigerants, it will be advantageous to introduce natural refrigerants. Once countries start to adopt the use of HC as refrigerants, enterprises as well as individual technicians and engineers will find some barriers to their implementation. “Many of these are related to a lack of information about the flammability issue, leading to fear and reluctance,” says Pelser.

“Despite this, an increasingly rapid uptake of HCs in developing countries is taking place; unfortunately, often with little know-how, resulting in rather dangerous equipment operating conditions. While we cannot assume responsibility for any individual conversion, it is essential to contribute the best available safety information to ensure a safe and sustainable shift to natural refrigerants,” says Pelser.

People are scared of change. And a lot of the old contractors are only used to working with synthetic refrigerants and won’t bother to learn about the new options, as they will probably retire before they are forced to switch over, explains Labacher. “I don’t think people are going to embrace natural refrigerants very quickly,” he says. “Although industry is spending a lot of time educating the end user about refrigerants and things like recovery, they are still slow on the uptake.”

Groenewald agrees. “The contractors are not always familiar enough with the system to sell it to the end user,” he explains. “Sometimes, if they do not know how to install a natural system, they will scare the end user to convince them not to go for it, rather than lose the contract.”

“The end users themselves also do not always keep up to date with what is happening globally with refrigerants and technology,” says Groenewald. They tend to focus only on their products and not the back-of-house. “As contractors, it is our responsibility to ensure we inform the end user so as to make the correct choice for their refrigeration needs.”

CRS is doing a lot of work on the CO2 training side. Although they are currently focusing on training up their internal team, they are planning on expanding to train the rest of the industry as well — not just from a theory point of view, but including the practical side, too. This course will teach them the basics, but it is important that they get training in the field as well.

Then there is the issue of cost. As mentioned, equipment has to be completely changed to use any natural refrigerant. You cannot retrofit from synthetics to naturals. For example, CO2 works at much higher pressures, so the compressors have to be a lot stronger. Ammonia is a very low-density gas, which means the compressor valves have to be designed for low-pressure drops.

HCs do not fall into this category, though. “There is no difference in cost of plant when looking at hydrocarbon or HFC/HFO plant,” explains Pelser. “The same design work needs to take place in plant rooms as both refrigerants will be flammable, or toxic flammable in the case of HFC/HFO refrigerant blends. Installation of an HC plant is cheaper when installing large chillers into a building.” However, the use of HCs in larger systems is not yet very popular in South Africa ...

Over the years, ammonia systems have been improved to use a smaller refrigerant charge to improve safety. Pictured here, the Massmart ammonia plant installed by MRE. 
Image credit: Ilana KoegelenbergAn ammonia skid for an ice rink, ready to go at the Multistage Cooling offices. Ammonia systems (like all natural refrigerant systems) require highly skilled technicians for maintenance.
Image credit: Ilana KoegelenbergIt is important to recover all refrigerant when doing maintenance or retrofitting a system, as it is illegal (and very harmful to the environment) to simply vent it into the atmosphere.
Image credit: IE3media
Hydrocarbons such as R290 are on the rise in South Africa. This truck is part of a pilot study to trial R290 in refrigerated transport.                      
Image credit: John AckermannTraining is crucial when it comes to the uptake of natural refrigerants in South Africa. Here is the world-class CO2 plant that was built at the OTTC training centre.
Image credit: Ilana KoegelenbergReplacing HCFCs with HFCs is not a long-term solution, as these too are being phased down globally.
Image credit: Ref Gas China

It is this initial high cost of equipment which means that many still favour HFC retrofits instead of natural refrigerants. But, this is changing. These systems may be more expensive initially, but the gas itself is much cheaper. As the price of synthetic refrigerants slowly creeps up, this is making natural refrigerants more viable, explains Amschwand. There is no patent on natural refrigerants, so they are cheap and easy to manufacture and you can get them from a variety of suppliers.

“Because the capex is much higher than on synthetic refrigerant systems, people are hesitant to look at natural refrigerants in such an uncertain environment as the one in which we find ourselves currently,” explains La Grange. “Decision makers aren’t always looking long term.”

Finding the right components can also be a challenge. “Initially, when we started putting in subcritical CO2 systems we had a problem with finding components for the higher pressure ratings required,” explains La Grange. “Many suppliers have these as standard stock items now.”

HC applications are still challenging, with few options from which to source compressors, explains La Grange. Long lead times from Europe dampen prospects of these applications at the moment when competing with HFC-type installations.

Another challenge is the sheer variety of options currently in the market, explains Amschwand, particularly in the supermarket arena. There is no standardisation in terms of what type of system (and refrigerant) is being used. Everyone is coming up with very clever alternatives. But this makes maintenance an even bigger challenge. It is impossible to train all technicians on all systems. This is not only costly but makes availability of service technicians a challenge.

Future

“It is time to introduce sustainable and economical natural refrigerants in developing countries to provide environmentally friendly cooling for comfort and productivity. A change from the ozone depleting HCFCs directly to HC refrigerants will contribute to a ‘greener’ growth of developing economies,” says Pelser.

Although this seems so logical, it is easier said than done.

“When you are more concerned with humanity as a whole than with your back pocket, that is when we will see more natural refrigerants,” explains Amschwand.

In the end, we still have a long way to go — but at least we are slowly moving towards a more ‘natural’ future. It is unavoidable after all. The sooner we get on board, the better.

Sources

  • Refrigerants Naturally
  • EPA
  • ASHRAE

Click below to read the March 2018 issue of RACA Journal

RACA MARC 2018

02 Sep 2018
08:00AM - 05:00PM
1st IIR International Conference on the Application of HFO Refrigerants
04 Sep 2018
08:00AM - 05:00PM
ATMOsphere Asia
05 Sep 2018
08:00AM - 05:00PM
Mostra Convegno Expocomfort (MCE) Asia
16 Oct 2018
08:00AM - 12:00AM
Chillventa 2018 - 16-18 October

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