Servicing of refrigeration systems. Substitution of R22 for R407C
General information. Below there is considered the procedure of substitution of R22 in the refrigeration system by the alternative refrigerant R407C. In the same way they realize charging of the refrigeration system with R410 and other alternative refrigerants.
Before performing operations on substitution of traditional blend of a refrigerant + mineral oil for the blend of R407C + polyester oil, it is necessary to pay attention on chemical compatibility of the latter with the used sealing materials (plastics and elastomers).
It is recommended before substitution of the refrigerant and introduction of structural changes into the refrigeration system as to such elements like pads and sealings to consult with the equipment manufacturer.
During charging of the equipment with R407C refrigerant there are used gage cylinders. Cylinders for R407C are provided with liquid and vapor valves. Liquid valve is installed on the branch pipe fixed in the cylinder dished end in such a way that in case the cylinder is in vertical position, the refrigerant would be delivered in the liquid phase.
In the operating refrigeration equipment, R22 refrigerant can be substituted for R407C with the use of simple devices and tools being used in practice of servicing.
In the majority of refrigeration systems it is enough during transfer from a traditional refrigerant to R407C to substitute only oil in the compressor, filter-dehydrator, and, possibly, to change the temperature of the refrigerant overheat on suction (for the systems with TEV). Before performing the operations on substitution of the refrigerant in the systems being on warranty, it is necessary to address to the manufacturers of the compressor and other equipment, since warranty for some kinds of the refrigeration equipment initially designed for operation on traditional refrigerants and oil, can lose its force after their substitution.
Determination of operating parameters of the refrigeration system operating on R22. They put down information on the system operation on R22 (temperatures and pressures in the condenser, evaporator, before TEV, etc.) First it's necessary to make sure that the system has been properly charged with thee refrigerant, and also that it is operating in normal working conditions.
Substitution of mineral or alkylbenzene oils on polyester oil. For drainage of the oil it can be necessary to disassemble the compressor. Especially it is related to small hermetic compressors, which do not have openings for the oil drainage. Il can be drained out of such compressors through the suction line. In the majority of the systems with low productivity one can remove 90...95 % of the oil using the described method. In larger systems In bigger systems there can occur necessity of additional drainage out of the other points of the system, especially out of the lower parts placed close to the evaporator. If the system contains the oil eliminator, then all the oil contained there should also be drained off. In any case, they measure the quantity of the oil removed from the system. Then the obtained result is compared with passport data of the system to make sure that bigger amount of the oil has not been drained off. In order to have resolvability of polyester oil in R407C in the system being equivalent to resolvability of the removed oil in R22, residue quantity of mineral or alkylbenzene oil should not exceed 5 % of the total quantity of the oil in the system. In big systems one can obtain residue content of mineral or alkylbenzene oil using so-called methods of backwashing.
Back washing includes the following operations:
- Removal of mineral or alkylbenzene oil out of the system;
- Selection of polyester oil whose viscosity is equivalent to viscosity of the oil being removed;
- Charging of polyester oil into the system in the quantity being equal to the quantity of the removed oil;
- Start of the system with R22 for thorough mixing of polyester oil with mineral or alkylbenzene oil (for this there can be required 48 - 72 hours).
The above-mentioned actions are repeated twice. After the last backwashing R22 is substituted for R407C.
Removal of R22 refrigerant out of the refrigeration system and it is utilization. R22 refrigerant is removed out of the system and collected into the cylinder (ballon) for utilization with the help of special device (developed vacuum is 34...67kPa).
If the required quantity of the charged R22 is unknown, it is necessary to weigh the ballon with the removed refrigerant; initial quantity of the charged R407C should be determined after the quantity of the removed R22.
Repeated assembly of the compressor. If the compressor has been removed, its assembly is realized using usual methods.
Substitution of the filter-dehydrator. This operation is a simple procedure which is performed during technical maintenance of the system. In the equipment on R22 there are used two types of filters-dehydrators: the one with bulk extender -adsorbent; the one with the inner cassette containing the adsorbent.
Adsorbent of HN type for the filters with the bulk extender can be used with R407C (for example, HN-11 of UOP company). Extenders being used in the systems with R22, cannot be used, as a rule, in the systems with R407C, because they absorb R32.
Vacuumization of the refrigeration system and checking of its hermiticity. In order to eliminate the air and other permanent gases out of the system, the system is vacuumized till residue 0.14 kPa pressure. During checking of the system hermiticity they use simple methods accepted for maintenance of refrigeration systems.
Charging of the system with R407C refrigerant. Charging is performed with the refrigerant in the liquid phase. Ballons for R407C are provided with special branch pipe installed in the dished plate which allows to deliver the liquid out of it in case it is in vertical position. It is possible to perform charging with the liquid refrigerant out of disposable ballons (13,6 kg).
If it is necessary to perform charging from the vapor phase, they use a reducing gear with the sight glass (it is necessary so that at charging by means of the refrigerant delivery into the suction pipe of the compressor, no liquid would come inside). R407C refrigerant should be delivered out of the ballon only in liquid phase.
Usually mass of R407C in the system is smaller than mass of R22. Optimal quantity of the refrigerant being charged depends on many factors: working conditions, dimensions of the evaporator and condenser, dimensions of the receiver (if available), the length of pipelines in the system. For the majority of the systems optimal mass of the refrigerant being charged constitutes 90...95 % of R22 mass, recommended by the factory-manufacturer of the equipment.
It is recommended first to charge 80 % of the refrigerant mass which is determined by R22 mass. Initially the system is charged with the refrigerant on the high pressure line (compressor is off). After pressures in the system and ballon become equal, the residue refrigerant is delivered to the suction line of the compressor (compressor is on). Liquid refrigerant should not enter the compressor suction pipe.
Start and adjustment of the system. The system is started and working mode is waited for to be stabilized. If the system is undercharged, the refrigerant should be added in small portions until working parameters have not reached desired values. During charging of the refrigerant, it is necessary to use the table of pressures and temperatures on the saturation line for R407C, in order to compare suction pressure and boiling temperature at operation on R22 and R407C. Usually increasing of discharge pressure compared to that of R22 constitutes 103...276kPa; decreasing of discharge temperature is 0...10 oС.
Marking of the system elements. After performing operations connected with substitution of the initial refrigerant for the alternative R407C, on the visible place they stick the label indicating what refrigerant and lubricating oil are contained in the system. It will help to perform maintenance operations of the system in the future properly.