S R C C Alternatives to H F s in the efrigeration and Air Conditioning Sector ection 01 33 problems that should be avoided. Several factors should be taken into account when evaluating the service blend option and when deciding to what extent case studies can be considered relevant for the applications under consideration. TEC HNICAL INFORMATION Factors to consider besides capacity, COCOP and discharge temperature with service blends are: The component (often a hydrocarbon) absorbed by the oil does not make the oil miscible with the refrigerant, but it “adjusts” the viscosity to be more similar to the old oil/refrigerant mixture for which the compressor was designed and to improve oil transport, particularly in the evaporator and suction line where a “thicker” oil increases the risk of poor oil return. Since in most cases the component introduced to decrease the oil’s viscosity is a flammable substance, there are limits on how much of this component can be added before there is a risk of explosion, especially if leakage outside the equipment occurs. At the same time the ratio between oil and refrigerant will affect how diluted the oil is, e.g. if the oil charge is relatively small as compared to the refrigerant charge, the oil-refrigerant mixture will have lower viscosity than if the oil content is significantly higher relative to the refrigerant charge. The oil that is circulated normally has a lower density than the refrigerant and if there are stable liquid levels, e.g. in the receiver, tube or shell condenser, the oil will tend to float on top of the refrigerant liquid and can accumulate to an extent where the compressor will eventually fail. In complex refrigeration systems there are cases that have been reported where the oil accumulated in the evaporator and suction lines. In systems with tubes with rifles/grooves to enlarge tube surface and improve heat transfer, there have been reports where heat transfer was drastically affected due to blocking of the grooves with oil. Therefore, the claims that service blends are easy to use and do not require the same careful evaluation as a retrofit to standard HFC refrigerants can often be questioned. Some of the differences in recommendations between suppliers of different service blends can probably be more related to policies and risk assessment rather than technical differences between the alternatives. Some compressor and/or refrigerant manufacturers recommend that alkylbenzene oils be used with HFC service blends and/or that a part of the old oil is replaced with ester oils. The importance of clean and dry systems and the risks associated with converting old systems of often questionable condition should not be underestimated. The consequence of these aspects is not that service blends cannot be used; rather their suitability should be evaluated versus the system in question to avoid risk of failures. The evaluation of the different commercially-available options is difficult to do as objective information is lacking. All suppliers of service blends are focusing on success stories and there is a tendency to try to minimize any concerns. In operations on mixtures of old and new oils, there is the risk of a chemical break down of the oil caused by contaminants in the old oil. There is also a risk that new oil will dissolve and transport deposits to the compressor. Suction filters during the change over procedure can be used to reduce this problem. to be functional in many systems, but there also have been reports of problems in some applications. There is limited unbiased information readily available and it is obvious that success stories are more widespread than those describing