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- EXTRA EDITION
The refrigeration industry has supported global efforts to protect the environment by phasing out chlorine-containing refrigerants in accordance with the Montreal Protocol. These actions have significantly reduced chlorine in the atmosphere and are starting to repair the ozone layer.
Today there is increased attention on global warming and the reduction of greenhouse gases. To the extent that refrigeration equipment consumes energy, refrigeration systems design and the corresponding choice of refrigerants also contribute to this global warming. Equipment manufacturers have significantly improved energy efficiency.
For a refrigerant to be considered a long-term option, it must meet three criteria: It must be safe, it must be environmentally friendly, and it must provide excellent performance benefits, thus resulting in zero ozone depletion and low global warming potential (GWP).
Several nonhalogen substances, including ammonia, carbon dioxide, and hydrocarbons, will work as refrigerants. All of these substances can be viable refrigerants for the right application if the system can be designed to meet key selection criteria.
HFCsHydrofluorocarbons (HFCs) are nonozone-depleting, nonflammable, recyclable, and energy-efficient refrigerants of low toxicity that are currently used safely throughout the world.
The global sustainability of HFCs requires a focus by the industry on the real environmental issues of refrigerant containment and energy efficiency. Research has shown that properly designed and maintained systems using HFC refrigerants provide the lowest overall GWP and zero ozone depletion. They are also a safe and cost-effective solution that will serve us well into the future.
As we consider the refrigerants available to manufacturers and the potential global warming impact of each, we believe it is likely that commercial refrigeration applications will eventually move to HFC options like R-134a, -404A, -507, -134a, -407C, and -410A. Initial results show that the efficiency performance and cost advantages of these refrigerants outweigh the disadvantages associated with higher pressures and direct GWP.
R-134aThis was the first nonozone-depleting fluorocarbon refrigerant to be commercialized. Developed more than 20 years ago to have characteristics similar to R-12, it is a viable candidate for use in medium- and high-temperature applications in which R-12 has been used. R-134a has the benefit of being a single-component refrigerant, and therefore, does not have any glide.
In addition, its direct Halocarbon Global Warming Potential (HGWP) is low relative to other options that have been evaluated.
The disadvantage of R-134a lies in its relatively low capacity compared to HCFC-22. To use this refrigerant, all of the tubing within the heat exchangers and between the components of a system would need to be significantly larger to minimize pressure drop and maintain an acceptable operating efficiency.
R-404AEquipment manufacturers have chosen R-404A as the long-term replacement for CFC-502. R-404A is an excellent low- and medium-temperature refrigerant with high energy efficiency and zero ozone depletion potential (ODP). R-404A is a near-azeotropic blend of HFC refrigerants R-125, -143a, and -134a. It is commercially available from numerous sources and is becoming the most popular refrigerant in its class.
R-507This refrigerant is an azeotropic mixture of R-143a and -125, with characteristics also very similar to R-502. (Emerson compressors developed for R-404A have been approved for R-507, with the exception of a few hermetic reciprocating models.) Both R-404A and -507 operate at slightly higher pressures and slightly lower discharge temperatures than R-502.
R-407CThis blend of R-32, -125, and -134a is one of the higher-temperature HFC options. R-407C was designed to have operating characteristics similar to R-22. The major concerns surrounding R-407C are its relatively high glide (approximately 10 degrees F) and its efficiency degradation when compared to R-22. However, the use of the refrigerant provides the simplest conversion of the HFC alternatives.
Take care applying R-407C in any applications in which glide can impact system performance by fractionation, such as in flooded-evaporator or multievaporator designs. Also, R-407C should not be viewed as a drop-in for R-22 systems or applications.
R-410AAmple research has shown that R-410A is the best replacement for R-22 refrigerants in high-temperature systems. Most major residential air conditioning manufacturers already offer R-410A product lines. With new residential energy-efficiency regulations going into effect in 2006, significantly more air conditioning manufacturers will have implemented the transition to more energy-efficient units using R-410A.
It has quickly become the refrigerant of choice for use in residential air conditioning applications, because the refrigerant delivers higher efficiency and better Total Equivalent Warming Impact (TEWI) than other choices. The refrigerant also has many benefits that make it an ideal refrigerant for use in commercial refrigeration applications.
R-410A operates at 50 percent higher pressure than R-22. However, this higher pressure allows the system to run at a lower temperature.
Because of these differences, anyone handling these units should receive training on the technical aspects of R-410A systems, where they can learn proper joint brazing and critical maintenance tips.
Carbon DioxideThe use of carbon dioxide (CO2) as a refrigerant has been considered for various refrigeration applications, especially smaller systems. CO2 has been given the designation R-744. It is environmentally benign versus other refrigerants, is nonflammable, has low toxicity, is widely available, and is a low-first-cost substance.
These are the reasons it was one of the original refrigerants, used nearly 100 years ago. Although thermodynamic performance of a simple CO2 cycle
is very poor (30 to 50 percent worse than HFCs), "poor" refrigerants such as CO2 tend to have very good heat transfer characteristics and respond well to cycle modifications.
Achieving decent CO2 system performance depends on CO2's substantially higher heat transfer coefficient (two to five times that of R-22) and the addition of a high- to low-side auxiliary gas heat exchanger or expander. The performance benefits of these factors offset some of the poor cycle efficiency of CO2.
Service ConsiderationsEmerson actively promotes the idea that responsible use is a key to safety and environmental stewardship. HFC refrigerants are the key to energy-efficient refrigeration equipment. However, other factors also figure into optimized energy efficiency (Figure 1).
Prompt maintenance is important to keeping systems running not only longer, but also more efficiently. Preventive maintenance routines can help extend the life of equipment, as well as increased energy efficiency.
Containment is one way to promote the responsible use of refrigerant. Equipment manufacturers are working to design systems that require less charge and have fewer leaks. There can be no direct impact on the environment from any refrigerant that is contained in a well-designed system. Early leak detection and repair will reduce refrigerant consumption.
Finally, all refrigerants should be recovered, reclaimed, and recycled at the end of the system's life.
Publication date: 12/05/2005