Alternatives to HCFCs in the Refrigeration and Air Conditioning Sector 59 S ection 02 keep the machine running. The VRF technology uses a special lubricating oil and a special expansion valve, in order to allow the compressors to run at only a few hundred RPMs for extended periods. Oil separators are fitted to each compressor. The return of oil to the compressor crank-cases is vital and given that the large shell and tube evaporator is below the compressors, the lift of this oil via adequate suction pipe velocity and miscibility was very important to consider. 2.5.1 Description of conversion procedures Prior to retrofit, the performance of the chiller was documented with a ClimaCheck™ Performance Analyser to ensure that the system was in good shape. To initiate a retrofit if the compressor has a low efficiency already or heat exchangers are fouled can risk that the contractor would assume responsibility for a problem already existing but not detected in the system. It is also interesting to have a baseline performance to compare before and after retrofit. Recovery of the R-22 refrigerant was first undertaken to make the machine ready for the first stage of work, which included the replacement of a number of peripheral items such as shut off valves, oil line pipe work, oil line filters, high and low pressure switches, etc. These measures was done partly in line with normal maintenance and partly to upgrade the system to minimize leaks. To change filters are good practice in connection with oil and refrigerant change. The replacement of tubes an pressure switches were done as many lines to controls were old capillary tubes that are vulnerable to vibrations and not considered good practice. Old pressure switches are a significant risk for large losses of refrigerant as the bellows can burst often with loss of total charge so it was deemed worth to replace these lines and switches in connection with the change of refrigerant. Some of the old valves had O-rings that are not optimal for HFCs which can result in increased leakage (Viton™ that was commonly used for CFC/HCFC is not a preferred solution with HFC). The replacement refrigerant lines were run in copper with suitable anti-vibration loops or were run in flexible plastic tubing. Flexible plastic tubing is quick and easy to use to connect, i.e. pressure switches gauges and similar equipment and they will not break because of vibrations. It is a more expensive solution, but it is one way of reducing the problem of loss of refrigerant from broken capillary tubes. The replacement of certain equipment components described above was not inevitable in the operation of changing the R-22 refrigerant to a drop-in blend, but inspection of the equipment before conversion revealed that certain components would need replacement even if the refrigerant was not changed. Once all the replacement of auxiliary components and interconnecting pipe work had been fitted, a pressure tightness test was applied to the system as a whole. However, the compressors were isolated via their service valves for the following reasons: The compressors were known to be sound in terms of their ■■leak-tightness as a result of recent and regular service visits. It had been previously noted that the compressor shaft ■■seals can leak when subject to nitrogen pressure testing, yet do not leak when under refrigerant/oil pressure. It was decided that these would be checked with an electronic leak detector, once the system had been charged, re-commissioned and put into service. After the pressure test of the refrigerant system the condenser water flow switch had been observed sticking on occasion and this was replaced. A leak test pressure of 8 bars was applied over an extended time period and, in addition, all new joints were checked with leak test solution. A minor leak was detected at a compression joint at a T-connection for the flexible tubing. This was repaired and the system again pressurised for the final pressure tightness test. Once all the joints had been leak tested, the leak test solution residue was carefully cleaned up. Three high performance vacuum pumps were used to evacuate and dehydrate the system to less than 4 mbar / 6 Torr. Having achieved a satisfactory vacuum and having held this for a Vacuum Rise Test, charging with the new refrigerant R-422D started. The refrigerant was supplied in cylinders with a single valve/single port type arrangement with a dip tube to enable liquid to be drawn from the cylinder without the need to invert.