The vast majority of refrigeration and air-conditioning systems, both residential and commercial, rely on vapor compression systems to remove heat. For decades, ozone-depleting chlorofluorocarbons (CFC) were the refrigerant of choice for such systems. CFCs, however, were banned in the 1990s because of their ozone depletion potential (ODP). This led to an often costly and painful conversion to non-ozone depleting, hydrofluorocarbon (HFCs) refrigerants. For some, especially Europeans, this transition was only a bridge to other refrigerants because of the high global warming potential (GWP) of HFCs. Further research and development has led to increased use of these natural refrigerants, which had once been popular, were displaced, and are now back. These include carbon dioxide (R-744) and hydrocarbons such as isobutane (R-600a) and propane (R-290a).

Now, change might again be brewing as the phase out of HFCs for use in European mobile air conditioning (MAC) applications begins in 2011 and completes in 2017. And, looming on the horizon is the possibility that HFCs for stationary applications might be next on the list. Already, many countries tax HFCs at levels of $70 to $80/lb. to discourage use, and this can price HFCs out of installations where 2,000 lbs. of refrigerant are used. Pressure on the use of these gases, known as F-gases (fluorine gases), is popping up in countries around the world, including Canada.

Traditionally, the use of natural refrigerants has been staunchly resisted in the U.S., but that resistance has started to wane, according to some select OEMs, refrigerant suppliers, compressor manufacturers, and industry experts.

Two companies, GE Appliances and Ben & Jerry’s, a subsidiary of Unilever, have petitioned the EPA for approval to use hydrocarbon refrigerants. If they get this approval, the interest will increase considerably and more companies in the U.S. may explore the use of natural refrigerants, says Reinhard Radermacher, professor of mechanical engineering at the University of Maryland who conducts research in this area. In addition, hydrocarbons have the potential of being a bit more energy efficient. This would be helpful to companies that sell into both the U.S. and European markets.

The Danfoss CO2 TN compressor can operate at up to 2,000 psig.

Additionally, the EPA has already approved one new hydrocarbon refrigerant for use in home appliances such as refrigerators and small window air conditioners, and Carrier Commercial Refrigeration, a unit of the Carrier Corp., is developing both CO2 and hydrocarbon-based refrigerated cases and displays.

Hydrocarbons, most notably isobutane and propane, are the most widely used alternative refrigerants in the world. They have zero ODP and a negligible GWP and can be found in appliances worldwide. Isobutane is currently used in more than 300 million refrigerators with manufacturers such as Bosch, Samsung, Haier, and Siemens producing them.

If the EPA approves GE’s petition, it would make the company the first major U.S. appliance maker to use alternative refrigerants in a residential refrigerator. This is noteworthy, because GE’s primary market is the U.S. To this point, the company has no plans to develop additional appliances that use the alternative refrigerants. A date for a ruling from the EPA is also uncertain, but the company is still shooting for a 2010 launch.

The GE Monogram refrigerator uses 2 oz. of isobutane refrigerant. This is about the amount of isobutane that is found in a large lighter and is the standard amount of charge used in hundreds of millions of refrigerators around the world, says Eckhard Groll, professor of mechanical engineering, at Purdue University, West Lafayette, Ind.

Enlarge this picture A comparison by The Coca Cola Co. of CO2 and H-134a refrigerants at 40.6 DegC and 75 percent RH.

This amount of refrigerant would also be acceptable in the European market, but it is not known if GE plans to sell its product in that market. In Europe, companies follow an IEC standard that allows up to 150 g of hydrocarbons to be used in a stationary cooling system. UL has developed a similar standard for the U.S., says Alan Gerrard, director of the Center for Policy at Unilever’s UK headquarters.

The UL standard, a supplement to the UL 471 standard, was published in October 2008. It contains requirements applicable to commercial refrigerators and freezers employing a flammable refrigerant and so far only the ice cream freezer from Ben and Jerry’s has been listed. At this point, the SNAP program has not officially recognized flammable refrigerants for use with commercial refrigerators, says Randy Haseman UL’s principal engineer for refrigeration and room air conditioning. So, while the standard exists, EPA approval is still required to use these gases.

Unilever wants to use propane in its ice cream cabinets in the U.S. as it does in other parts of the world. Unilever sells most of its ice cream at small outlets that display the product in cabinets operating at -18 DegC. Currently, they use propane in more than 330,000 cabinets, out of the 2 million cabinets that they own. As refrigeration cases are retired, they are being replaced with cabinets that operate with propane.

Of those 330,000, only 50 of them are found in the U.S. The EPA allowed the company to install the cabinets in Ben & Jerry locations in Washington, D.C., and Boston, to conduct trials of the propane refrigerant cabinets. During in-house testing, these cabinets typically achieved a 10 percent greater efficiency level than cabinets that were charged with HFCs, says Gerrard. He expects the results to be the same in the U.S.

The Embraco EK compressor is designed to be used with CO2.

What sets hydrocarbons apart from other natural refrigerants is that they are a near drop-in replacement for current refrigerants, says Markus Draeger, strategic marketing director at Danfoss, Baltimore. For example, the company markets its Apexx SLV compressor for use with both R-404a, an HFC used in refrigerator applications, and propane. Moreover, Draeger says Danfoss sees significant energy savings just by switching the refrigerant toward hydrocarbons.

The density of hydrocarbons compared to HFCs is a big advantage, agrees Groll. For instance, the density of isobutane is about 40 percent that of R-134a. For a same size refrigerator, a refrigerator that uses 150 g of HFCs, might be able to use about 60 g of isobutane.

The tradeoff for hydrocarbons is that they are flammable, and, to a lesser degree, there are toxicity concerns for exposure to the gas at high concentrations. Because of the flammability concerns, designers of the refrigerant systems must ensure that no ignition sources are present. Potential sources of ignition are switches including manual, pressure, thermostatic, timed, relays, contactors, and overloads. These sources should be addressed by using components that are sealed, enclosed, solid state, or specially positioned, says Daniel Colbourne, a consultant for Refrigerants Naturally!, a European advocacy group for natural refrigerants.

Groll says that hydrocarbons are well suited for small applications such as refrigerators and ice cream cabinets that use hermetically sealed compressors. They are not as well suited for larger-scale systems, field-installed systems, or systems that have open drives, because there is more opportunity for leaks that could encounter ignition sources.

Enlarge this picture In Honeywell’s internal testing, direct emissions were combined with indirect emissions from refrigeration systems using HFO-1234yf and other refrigerants.

A Hawaiian inventor has developed a new hydrocarbon blend and has received EPA approval to sell it for use in appliances such as refrigerators and small window units. The agency approved HCR-188c, which was developed by Richard Mayura, a former auto mechanic who was experimenting with the refrigerant at his home in Hawaii. He tested the refrigerant in a 20 year-old-car and used the refrigerant in the air conditioner for more than 10 years.

Maruya, who founded the company, A.S. Trust & Holdings, Kaneohe, Hawaii, says the refrigerant is a blend of propane, isobutane, ethane, and pentane gases, with variations that include hexane, methane, and heptane.

Maruya had the refrigerant tested by Intertek, a testing and certification services company, which found that HCR-188c, has zero ODP and GWP of <5 over 100 years. Intertek also tested the refrigerant in a common brand of refrigerator. Initially, it tested R-134a at a 113 g charge. The appliance was evacuated and then charged with 28.3 g of HCR-188c (25 percent by weight of the original formulation) and tested. The results showed that the refrigerator/freezer, when running with HCR-188c, drew only 68 percent of the total power required when running with the original R-134a. The refrigerator had a temperature differential of 1 percent, and the average freezer temperature was lowered by more than 5 DegF.

Maruya is continuing to work to get HCR-188c approved for use in commercial freezers, commercial air conditioners, vending machines, and other products. He says it is a natural replacement for any applications that can use R-12 or R-134a.

Unilever’s ice cream freezer cabinet that uses propane refrigerant. The cabinet is one of 50 that are in trials in the U.S.

Carrier is also working with its refrigerant suppliers to develop a hydrocarbon refrigerant that can be used in display cases, says Kevin Mattimoe, sales manager, Carrier Commercial Refrigeration.

Interestingly, Carrier, a United Technologies company, Farmington, Conn., has developed carbon dioxide refrigeration systems for supermarkets and other large applications. As of November 2008, plans called for a 2009 full-scale product rollout of its CO2-based turnkey refrigeration system, CO2OLTEC.

Mattimoe says that Carrier has been developing CO2 systems for nearly 10 years as a response to the pressures seen around Europe to find an alternative to HFC refrigerants. The company recently won an Environmental Pioneer Award for CO2 systems in the Refrigeration category at the 2008 Cooling Industry Awards. The award recognized Carrier’s work in Europe in developing transcritical CO2 refrigeration systems.

In one store, at a large market in Northern Germany, three high-temperature packs with a total capacity of 670 kW, and two low temperature packs with a capacity of 130 kW, were installed. In addition, Carrier developed a two-step technology with the refrigerant that allows the pressure on the supermarket shop floor to be kept at around 40 bar with only the plant areas requiring higher pressures. Mattimoe says that the high operating pressures of a CO2 system can pose a challenge for compressors. This two-step process helps alleviate this concern.

The cooler from Coca-Cola runs on carbon dioxide refrigerant.

Compressor manufacturers have several products that will work with carbon dioxide refrigerants. Danfoss invested in a hermetic compressor technology as one possible option to provide environmental solutions for selected applications. As a result, the Danfoss TN compressor is used today in some of The Coca Cola Co.’s CO2-based vending machines around the world.

Another company, Embraco, also recently released a new product, the EK compressor for use with CO2 refrigerants. At the AHR Expo in January in Chicago, Embraco displayed a CO2 vending machine, which operated throughout the 3-day show.

Ricardo Maciel, product leader, commercial refrigeration, says that because of the high operating pressure of CO2 refrigerants, the company developed a new compressor with enhanced features. The refrigerant characteristics affected the shell of the compressor the most, he says. The shell was developed to withstand load requirements mandated by international codes like UL 984. The load is the result of a design pressure (saturation pressure associated to 27 DegC) multiplied by a fixed constant (regardless of the refrigerant fluid). In the case of the CO2 application, the hydrostatic pressure can reach 350 bar. This requires special demands for construction material, geometry, tubing design, and electrical connection development.

These demands will need to be met in many different applications, as CO2 is not only seen as an alternative refrigerant for stationary HVAC systems, vending machines, and other appliances, it is being considered as an alternative refrigerant for use in European MAC applications.

Enlarge this picture A comparison of the flammability of various refrigerants. Graphic: DuPont

In a joint effort between Honeywell and DuPont, the two companies are working to develop a low-GWP, synthetic refrigerant that can compete with CO2 in terms of efficiency (see Chart), and beat CO2 on ease of replacement.

The refrigerant, HFO-1234yf, is based on hydro-fluoro-olefins. Its initial target application is automotive, but David Diggs, global business director for Honeywell, believes that the refrigerant will eventually migrate into stationary operations. He could not give a timeframe for this other than to say that the work has begun, and there is a long way to go. The companies believe that HFO-1234yf can be a replacement for R-134a, but does not consider it a replacement for other refrigerants such as R-410a because that refrigerant has a higher operating pressure.

When developing the product, Diane Iuliano Picho, global business manager for DuPont, says that they were looking to create a refrigerant that balanced low GWP with performance and overall economic attributes. Its disadvantage revolves around flammability issues. Picho says that the auto OEM industry wanted to make sure HFO-1234yf’s mild flammability was not going to be an issue, and this was accomplished. The Society of Automotive Engineers validated that HFO-1234yf as safe for use in automotive applications.

In terms of the environment, Diggs says that HFO-1234yf has a GWP of 4 and it has an atmospheric lifetime of just 11 days, as opposed to 13 years for R-134a. (While the gas contains some of the same chemical elements as an HFC, it has an unsaturated, or olefin, carbon backbone. The olefin backbone allows the HFO to quickly decompose if it is released into the atmosphere, unlike conventional HFC molecules.)

As a result of all these changes, OEMs have a number of possible design decisions they may need to make going forward. They can stay with HFCs for as long as the regulations will allow and wait for synthetic alternatives such as HFOs to arrive, but this could lay them open to criticisms of not being environmentally friendly. Or they can begin a conversion to a natural refrigerant now. They can convert to hydrocarbons and deal with flammability and regulatory issues, or they can convert to CO2 and be faced with significant redesign of their systems.

Calculations involved in the decision will include technical issues, cost, politics and government, and changing customer attitudes. The result of these calculations may come out differently for different companies or different types of equipment, but one observation is likely to made across the board. In the realm of refrigerants, there are more changes to come.

For more information, email:
Danfoss: solutions@danfoss.com
DuPont: dimc@usa.dupont.com
Embraco: accs@embraco.com.br
Honeywell: david.diggs@honeywell.com
Re-Phrige: d.colbourne@re-phridge.co.uk