Optimisation of the VRF test rig to eliminate oil trapping in the evaporator

Abstract

Refrigeration is a hot topic when the summer months arrive on the Maltese Islands. The refrigeration cycle is dealt with during the thermodynamics lectures. However, without practical knowledge of the subject, it is difficult to envision how the process works. In this final year project, the VRF test rig in the thermodynamics labs was optimised due to trapping oil in evaporator. An oil separator was added to the system to aid in the oil return to the compressor due to the design of the heat exchangers. The caps at each end of the heat exchangers were re-manufactured from acrylic to add better transparency to the rig. Moreover, sensors on the system, such as the flow and temperature sensors, had faults with interpretation of the data. As a result, the flow sensor was redesigned such that it can read the small flow rates generated by the Aspen 4-24-0000X compressor. The electrical circuit was rebuilt, such that a 5 volts, voltage regulator was added, to eradicate the loss in power to the +5 volts power line, connecting the temperature sensors. The installation of submersible water pumps was also required to be able to drain the new glass water tanks. The water tanks were changed since plastic crazing and yellowing were noted at the beginning of the year. The control algorithm for the rig was altered to accommodate the new Ethernet shield. A GUI was created such that it can be accessible over the web. The GUI was designed with features to manually control the system by varying the speed of the compressor and EEV steps. Testing concerning the rig’s capacity with the flow rate of water was performed. The COP of the system could be obtained which later on was cross-checked with the performance chart of the system. The results obtained were all on a positive note, as long as the speed of the compressor is below 5500RPM, since prolonged duration at the mentioned speed would result in an abrupt motor lock. The transparent heat exchangers also helps in giving a better understanding of the Vapour Compression cycle used in most domestic and commercial A/C units.