For the long-term reliable operation of compressors, it is important that there is always the right amount of oil in the compressor – enough, but not too much. Oil shortage quickly leads to mechanical wear and overheating. Too much oil on the other hand may cause liquid slugging that may cause severe damage to the compressor. At the same time, the challenges for the implementation of the oil management are increasing: The use of frequency converters in compressors results in much stronger fluctuations in oil consumption of the compressor, and the increasing use of CO2 systems makes for a much wider spread in both absolute and differential pressure. Foam generation is also changed for the new refrigerants and pressure ranges. This makes it more important to be able to adapt and adjust the oil level regulator more precisely for the specific application. In addition to these more recent challenges, there are also some well-known issues in oil management that require further improvement. For example, run detection is often requested to ensure that the oil level regulator does not seemingly perform a safety shutdown when the compressor is turned off and the high pressure is reduced. Finally, especially, in some regions of the world, contaminated oil remains a cause of many problems.
Refrigeration/AC 4.0 in Oil Management
The Internet of Things and Industry 4.0 are much discussed topics these days. Many aspects of these developments remain rather vague though. With the new INT280 Diagnose, KRIWAN is introducing a product for the refrigeration/AC market that makes Industry 4.0 more practical and concrete. In addition to its basic function – measuring the oil level and adding oil – this regulator is characterised, especially, by the fact that it captures valuable data that it uses for its own operation but is also able to communicate.
The most important value is, of course, the oil level in the compressor. This can be determined in various ways, for example, by optical sensors or floating switches. In the age of Industry 4.0, the KRIWAN optical measuring cell offers a key benefit: It has an active transmitter diode and a passive receiver diode. The transmitter diode sends an infrared beam through a glass prism.
Depending on the oil level, the receiver diode receives a stronger or weaker signal (see Fig. 1). The new product generation exploits the fact that the transmitter diode is an active component. It can receive a stronger or weaker control signal, which enables it to measure additional data with this modulation: Usually, the diode is operated at only 10% of the maximum transmission power. This is enough to reliably measure the oil level. Now the transmission power is periodically raised to 100%. If contamination in the refrigeration circuit has formed deposits on the glass prism, this can be detected by changing the transmission power. For one, the minimum transmission power in the regulator is increased from 10% to compensate for the contamination. On the other hand, the information is also sent via the diagnostic interface. For the first time, the influence of oil on the sensor can be read out on a smartphone or at the refrigeration regulator. In addition to monitoring the glass prism, the INT280 also monitors the correct function of the transmitter diode, the receiver diode, and possible interference of external light. This means that the entire sensor is equipped to monitor itself. Every technical system and every sensor can be damaged or deteriorated and ages. Self-monitoring makes it possible to detect such states early on.
Figure 1: Active optical oil level monitoring
These aren’t all the benefits of the new INT280 Diagnose however: The data interface to the refrigeration/AC controller (circular connector in Fig. 2 to the upper right of the oil nipple) is able to transmit other information as well: Because the Kv value of the oil level regulator (flow in m³/h) is a known constant, the oil consumption rate of the compressor can be calculated when the differential pressure and the oil density are known. This becomes even easier if not the exact value in m³/h is needed, but only the relative ratio of compressors in a rack (e.g., compressor 1 carries over twice as much oil as compressor 2). Then the oil density is an equal parameter, and with properly symmetrical piping, the differential pressure can be assumed to be roughly equal for all oil level regulators. With this method of estimating the oil consumption rate, only the different opening times of the valves in the individual regulators need to be compared, and these times are delivered from the INT280 Diagnose to the controllers via the data interface.
Figure 2: INT280 with diagnostic interface
The interface can be used not only for reading out data from the controller. The INT280 Diagnose can also be set individually: Filling or idle times can be adjusted, as can a specific refill time. This allows the regulator to be adjusted optimally for the various pressure ranges, the oil viscosity, and the operating points of different systems. All this – adapting and reading out data – is easily done in the field using a smartphone, or by factory programming on a PC.
Another option is to combine the new INT280 Diagnose with an INT69 Diagnose compressor protection relay by connecting the two modules using a Y-cable and the two diagnostic interfaces. Other adjustments or settings are not required. The INT280 oil level regulator automatically detects if it is connected to a compressor protection relay.
It continuously receives information whether the compressor is running or whether it has been switched off by the refrigeration/AC controller. In some field applications it may happen that no oil can be refilled when the compressor is switched off because the high pressure is dropping. Even though there still is oil in the collector, it cannot flow through the open valve. The oil level regulator detects what seems to be an error (“oil cannot be refilled successfully despite low oil in the regulator”).
It switches off and locks the compressor. With the new run detection, this can no longer happen: The compressor is not switched off in this situation. The INT280 executes its protective function and switches off only if the compressor is running and no oil can be refilled even though there is pressure.
Oil management is critical for the compressor. The new INT280 Diagnose makes this topic easier and more reliable. When the regulator works not only on a small control circuit but is able to communicate with the refrigeration/AC controller and the compressor protection relay, then that is Industry 4.0: The controller is also used as a sensor and provides valuable data for optimizing the entire refrigeration/AC circuit.
