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Substitutes for R22 in A/C and heat pumps Resulting design criteria With regard to system technology, previous experience with R22 can only be utilized to a limited extent. The distinctive temperature glide requires a particular design of the main system com- ponents, e.g. evaporator, condenser, ex- pansion valve. In this context it must be considered that heat exchangers should preferably be laid out for counterflow opera- tion and with optimized refrigerant distribu- tion. There are also special requirements with regard to the adjustment of control devices and service handling. Furthermore, the use in systems with flood- ed evaporators is not recommended as this would result in a severe concentration shift and layer formation in the evaporator. BITZER can supply a widespread range of semi-hermetic reciprocating, screw and scroll compressors for R407C. Converting existing R22 plants to R407C Because of the above mentioned criteria, no general guidelines can be defined. Each case must be examined individually. Because of the negligible temperature glide (< 0.2 K), the general usability is similar to that of a pure refrigerant. The material compatibility is comparable to the previously discussed blends, the same applies to the lubricants. However, the pres- sure levels and the higher specific loads on the system components need to be taken into account. Resulting design criteria The fundamental criteria for HFC blends also apply to the system technology with R410A. However, the high pressure levels have to be considered (43°C condensing temperature already corresponds to 26 bar abs.). Compressors and other system components designed for R22 are not suitable for this refrigerant (or only to a limited extent). Though, suitable compressors and system components are available. When considering to cover usual R22 appli- cation ranges, the significant differences in the thermodynamic properties (e.g. pres- sure levels, mass and volume flow, vapour density) must be taken into account. This also requires considerable constructional R410A as substitute for R22 In addition to R407C, the near-azeotropic mixture listed by ASHRAE as R410A is available and widely used for medium-sized capacities in air conditioning and heat pump applications. An essential feature indicates nearly 50% higher volumetric refrigerating capacity (Fig. 21) compared to R22, but with the conse- quence of a proportional rise in system pressures (Fig. 22). At high condensing temperatures, energy consumption/COP initially seems to be less favourable than with R22. This is mainly due to the thermodynamic properties. On the other hand, very high isentropic efficiencies are achievable (with reciprocating and scroll compressors), so that the real differences are lower. Another aspect are the high heat transfer coefficients in evaporators and condensers determined in numerous test series, result- ing in especially favourable operating con- ditions. With an optimized design, it is quite possible for the system to achieve a better overall efficiency than with other refriger- ants. Fig. 21 R410A/R22 – comparison of performance data of a semi-hermetic compressor Fig. 22 R410A/R22 – comparison of pressure levels 21PDF Image | REFRIGERANT REPORT 21
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