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Servicing of refrigeration systems. Substitution of R502 for R404A or R507

R404A refrigerant is accepted as an alternative to R502 in the new equipment. It can be used also for charging of some systems operating on R502, such as commercial refrigeration equipment of big universal shops, refrigeration facilities of food industry factories, transport refrigeration facilities. As to its characteristics, R404A, as it has been stated before in chapter 7, is the best to correspond to R502 refrigerant of all CFC, and it can be used within all the working range of temperatures and pressures characteristic for R502. Discharge temperatures of the compressor operating on R404A, is lower than while using R502, which contributes to increasing of reliability and service life of the compressor.

R507 refrigerant also serves as an alternative to R502 refrigerant in the new equipment, and it can be used for retrofit of the systems operating on R502. Characteristics of R507 are also close to characteristics of R502, their working ranges coincide. Discharge temperatures of the compressor where R507 serves as a refrigerant is lower than that in the compressors with R502.

Composition of vapors of R404A and R507, contained in the ballon, slightly differ from the composition of the liquid refrigerant. These insignificant differences can effect operational efficiency of the systems with flooded evaporators.

As practical experience shows, in some systems, where R502 is substituted for R404A or R507, the level of leakage can become higher due to using of sealing made of elastomers. But substitution of elastomers can lead to additional costs and cause time waste for re-equipment.

Methods of retrofit of refrigeration systems during transfer from R502 to R404A or R507 are analogous to the methods of substitution of R12 refrigerant for R134a.

R404A and R507 refrigerants have good compatibility with polyester oils. When charging of the liquid refrigerant into the system, it is necessary to be poured out of the charging ballon only. Ballons are provided with immersion legs with the help of which it's possible to drain liquid out of the ballon being in vertical position. Proper position of the ballon at liquid drainage is shown by arrows on the ballon and on the box for the ballon. Refrigerant can be charged into the system either in the state of liquid or in the gaseous state. If it's necessary to transfer the liquid into tyhe gaseous state, there is used a valve of collecting pressure gage or throttling device. Disposable ballons with R507 do not have immersion leg, and therefore they have to be turned for liquid drainage.

Usually for charging of the refrigeration system there is required less (mass) of refrigerant R404A or R507, than that of R502. Optimal mass of the charging dose depends on the system structure and its operational conditions. For the majority of ystems optimal mass of the alternative refrigerant when charging constitutes 75-90 % of mass of the initial one.

When starting the system, they correct the volume of the refrigerant being charged. For comparison of pressures and temperatures of the initial refrigerant and alternative refrigerants it is necessary to use the table.

Comparative indicators of refrigerants R502, R404A and R507 on the saturation line
Pressure, kPa Temperature Pressure, kPa Temperature
R502 R404A R507 R502 R404A R507
25 -72 -71 -72 1000 19 17 16
50 -60 -59 -61 1050 21 19 17
75 -52 -52 -53 1100 23 20 19
100 -46 -46 -47 1150 25 22 21
125 -41 -41 -43 1200 26 24 22
150 -37 -37 -39 1250 28 25 24
175 -33 -34 -35 1300 29 27 25
200 -30 -30 -32 1350 31 28 27
225 -27 -28 -29 1400 32 30 28
250 -24 -25 -26 1450 34 31 30
275 -22 -22 -24 1500 35 32 31
300 -19 -20 -22 1550 37 34 32
325 -17 -18 -19 1600 38 35 34
350 -15 -16 -17 1650 39 36 35
375 -13 -14 -15 1700 41 37 36
400 -11 -12 -14 1750 42 38 37
425 -9 -10 -12 1800 43 40 38
450 -8 -9 -10 1900 46 42 41
475 -6 -7 -9 2000 48 44 43
500 -4 -6 -7 2100 50 46 45
550 -1 -3 -4 2200 52 48 47
600 2 0 -2 2300 54 50 49
650 4 2 1 2400 56 52 51
700 7 5 4 2500 58 54 53
750 9 7 6 2600 60 56 54
800 11 9 8 2700 62 57 56
850 13 11 10 2800 64 59 58
900 15 13 12 2900 65 61 59
950 17 15 14        

 

Expected values of operational parameters of the refrigeration system after substitution of R502 for R404A or R507 are given in the table.

Expected values of operational parameters of the refrigeration system after substitution of R502 for R404A or R507
Indicator R404A R507
Changing of pressure, kPa:
charging
suction

137,9
Remained unchanged

206,8
Remained unchanged
Changing of discharge temperature -5,6 8,3
Changing of overheat on suction 1,1 2,2

 

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