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Service blends as hydrocarbons have especially good solu- bility characteristics. For these blends two variations are offered in each case. When optimizing the blend variations with regard to identical refriger- ating capacity as for R502 the laboratory measurements showed a significantly in- creased discharge gas temperature (Fig. 13), which above all, with higher suction gas superheat (e.g. supermarket use) leads to limitations in the application range. On the other hand a higher proportion of R125 or R218, which has the effect of re- ducing the discharge gas temperature to the level of R502, results in somewhat higher refrigerating capacity (Fig. 14). With regard to material compatibility the blends can be judged similarly to (H)CFC refrigerants. The use of conventional re- frigeration oil (preferably semi or full syn- thetic) is also possible due to the R22 and R290 proportions. Apart from the positive aspects there are also some disadvantages. These substan- ces are alternatives only for a limited time. The R22 proportion has (although low) an ozone depletion potential. Furthermore, the additional components R125, R143a and R218 have a high global warming potential (GWP). Resulting design criteria/ Converting existing R502 plants The compressor and the components which are matched to R502 can remain in the sys- tem in most cases. The limitations in the application range must however be consid- ered: Higher discharge gas temperature than R502 with R402B**, R403A** and R408A** or higher pressure levels with R402A** and R403B**. The good solubility characteristics of R22 and R290 increase the risk that, after con- version of the plant, possible deposits of oil decomposition products containing chlorine are dissolved and find their way into the compressor and control devices. Systems where chemical stability was already insuf- ficient with R502 operation (bad mainte- nance, low drier capacity, high thermal loading) are particularly at risk. Thus, generously dimensioned suction gas filters and liquid line driers should be in- stalled for cleaning before conversion, and an oil change should be made after approxi- mately 100 hours operation. Further checks are recommended. * When using blends containing R22, legal regula- tions are to be observed, see page 8. ** Classification according to ASHRAE nomenclature. Service blends with the basic component R22* as substitutes for R502 As a result of the continued refurbishment of older installations, the importance of these refrigerants is clearly on the decline. For some of them, production has already been discontinued. However, because of the development history of service blends, these refrigerants will continue to be cover- ed in this Report. These refrigerants belong to the group of "Service blends" and have been offered under the designations R402A/R402B* (HP80/HP81 – DuPont), R403A/R403B* (formerly ISCEON® 69S/69L) and R408A* (“Forane®” FX10 – Arkema). The basic component is in each case R22, the high discharge gas temperature of which is significantly reduced by the addi- tion of chlorine free substances with low isentropic compression exponent (e.g. R125, R143a, R218). A characteristic fea- ture of these additives is an extraordinarily high mass flow, which enables the mixture to achieve a great similarity to R502. R290 (Propane) is added as the third com- ponent to R402A/B and R403A/B to im- prove miscibility with traditional lubricants Fig. 13 Effect of the mixture variation upon the discharge gas temperature (example: R22/R218/R290) Fig. 14 Comparison of the performance data of a semi-hermetic compressor 15PDF Image | REFRIGERANT REPORT 21
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