Until a few years ago, the main refrigerants used in vapor compression refrigeration machines were ozone depleting types, namely R-12, R-22, and R-502; and for special applications, R-114, R-12B1, R-13B1, R-13, and R-503.
CFCs such as 12 and 502 have long been out of the picture as virgin refrigerants. As of the year 2000, R-22 can no longer be used in new systems in Germany. The refrigerant, as well as all other HCFCs, faces phase out in the years ahead. The main reason is because of ozone depletion potential, although such depletion is small.
Although a number of major alternatives have become available — such as 134a, 404A, 507A, 407C, 410A, NH3, and various hydrocarbons — there is still an urgent need for further research and development.
A long history of close cooperation exists with scientific institutions, the refrigeration and oil industries, and component manufacturers, as well as a number of innovative refrigeration companies and users.
A large number of research projects have been completed, and a suitable range of compressors and equipment is available for the various alternative refrigerants.
Following are possibilities for changes to short- and medium-term environmentally benign refrigerants in medium and large commercial refrigeration and ac plants.
Environmental Compatibility and EfficiencyWithin the framework of various studies, all known refrigeration processes and refrigerants were judged according to their environmental compatibility and efficiency. The results confirm that the vapor compression refrigeration plants normally used up to now in the commercial area are far superior to all other processes down to a cold space temperature of around -40Â°C.
Furthermore, it was also established that refrigerants with a low Global Warming Potential (GWP) also show particularly favorable results.
Indeed this point of view has been gaining in importance and will be a significant criteria in future judgments of alternative refrigerants in addition to the Ozone Depletion Potential (ODP) and energy requirements (indirect global warming effect).
In the meantime, methods of calculation are already being used with which the total effect of the direct (due to emission) and the indirect (due to energy requirement) effects can be judged.
In this connection a ‘TEWI’ factor (Total Equivalent Warming Impact) has been introduced. [Editor’s Note: Since this article was written, a methodology similar to TEWI called Life Cycle Climate Performance (LCCP) factor has been introduced in the industry.] The TEWI result is, however, mainly dependent upon the CO2 emission from the energy generation or drive procedure employed. It is therefore imaginable that in the future the assessment of refrigerants with regard to the environment could differ according to the place of installation and drive method.
The evaluation of the (chlorine- free) substitutes shows, however, that the possibilities for directly comparable single substance refrigerants are limited. The situation for R-12 with the substitute R-134a is favorable, as it is for R-502 with the substitutes R-404A and R-507.
Apart from ammonia (NH3) and hydrocarbons, with their special application criteria, as single substances only the refrigerants R-32, R-125, and R-143a remain as direct potential substitutes for R-502 and R-22. These, however, can only be used in a limited way as a pure substance due to their specific characteristics. The most important criteria in this connection are flammability, thermodynamic properties, and global warming effect.
These substances are more promising as components of blends, where the individual characteristics can be largely matched to the requirements according to the mixing proportion.
CALCULATIONSAs already mentioned, methods of calculation have been developed, with which the influence upon the global warming effect can be judged for the operation of individual refrigeration plants.
It should first be noted that all halogenated refrigerants, including the non-chlorinated HFCs, belong to the category of greenhouse gases. An emission of these substances contributes to the greenhouse effect. It should be noted that the emission from 1 kg R-134a is, for example, roughly equivalent to 1,300 kg of CO2 (GWP100 = 1,300).
It is already apparent from these facts that the reduction of refrigerant losses must be one of the main tasks for the future.
On the other hand, the major contributor to a refrigeration plant’s global warming effect is the indirect CO2 emission caused by energy generation. Based on the high percentage of fossil fuels used in power stations, the average European CO2 release is around 0.6 kg per kWh of electrical energy. A significant greenhouse effect occurs over the lifetime of the plant as a result of this release of CO2.
As this is a high proportion of the total balance, it is also necessary to place an increased emphasis upon the use of high-efficiency compressors and associated equipment, as well as optimized system components, in addition to the demand for alternative refrigerants with favorable thermodynamic energy consumption.
When various compressor designs are compared, the indirect CO2 emission (due to the energy requirement) can have a larger influence upon the total effect than the refrigerant losses.
Renz is with Bitzer International of Sindelfingen, Germany. Stateside information can be obtained from Delta Heat Transfer, 4784 Cantrell Road, Flowery Branch, GA 30542; 770-967-0030.
Publication date: 04/02/2001