Verifying adequate oil level
The compressors must be at a standstill before proceeding as described below!
The most common method of determining if oil needs to be added to the compressor is to observe the sight glasses.
- In tandem/trio units of Orbit 6 and 8, or mixed tandems Orbit 6 with Orbit 8, the oil level can be monitored directly at the sight glass of the individual compressors.
- In Orbit 8 trios, a sight glass is available in the oil equalisation line itself.
During commissioning, a technician can observe the oil level in the sight glasses and determine if oil needs to be added to the compressor (example even ORBIT 6 trio).
The oil level should be checked prior to system operation, after the initial start, during normal operation, and also periodically when the system is off to ensure that it is within the acceptable limits.
Prior to commissioning the system
In case of tandem and trio arrangements, all compressors mus be rigidly mounted on the fixing rails and placed on a level surface, so that the oil equalisation line is kept as horizontal as possible for a reliable operation. Once the compressors are installed and all pipes are connected, the oil level should be at least 1/2 of sight glass as shown in the following figure. If the oil level is not visible, the recommended oil type should be added to one of the compressors through the oil maintenance connection until the oil level is at 2/3 of the sight glass. This procedure is exactly the same for single scroll compressor assembly, see
- ESB-130: Operating instructions Hermetic scroll compressors Orbit 6 and Orbit 8
The compressors are factory-charged with oil. Therefore, the initial compressor oil charge should be sufficient in most compact installations. However, additional oil may be required in the following cases:
- systems with long pipe works >20 m
- systems with suction accumulators
- systems that tend to log oil in the evaporator during extended operation at low load
- systems with potentially large variation in mass flow, which may result in greater oil logging in the system
Risk of compressor damage!
Bitzer scroll compressors may only be operated with the indicated original Bitzer oils!
Oil with high water content may damage compressor and refrigeration system!
Avoid air intake into the system and oil containers.
Use only originally sealed oil containers. Opened oil containers should be closed tightly and their content be used up as quickly as possible.
For used oils: Observe the warning values on water content.
For more information on oils for scroll compressors:
- EST-500: BITZER refrigeration compressor oils for scroll compressors, stationary applications (ORBIT, ESH7)
Commissioning
Commissioning is a very critical period for any compressor because all load-bearing surfaces are new and require a short break-in period to carry high loads under adverse conditions. The oil heater must be turned on at least 12 h prior to compressor start – this will prevent increased refrigerant solution in the oil and bearing stress on initial start-up. Energise the oil heater during compressor off cycles.
Operate the system for at least 1 h at nominal conditions. The oil may fluctuate during operation:
- During operation a minimum oil level at 1/4 of the sight glass is acceptable for single compressors,
- for a BAHT primary compressor (explanation: Tandem and trio operation), a visible oil level at the bottom of the sight glass is also admissible in operation.
Consult Bitzer for drawings of Orbit 6 and Orbit 8 tandems and trios. They indicate the primary compressor, as the correct compressor position is essential for the BAHT function.
After operation at nominal conditions for at least 1 h, switch off the system. Wait for 5 min until the oil level accumulated and check it according to the above figure for standstill (Sight glass prior to system operation). Compressors may lose some oil during normal operation because some of it inevitably leaves the compressors with the discharge gas. If the refrigerant pipes are properly sized and configured, this oil will eventually return to the compressors, but some of it will always circulate with the refrigerant. When commissioning a new system, additional oil may be needed to compensate for the oil in circulation, mainly in oil traps and accessories such as suction accumulators and liquid receivers. The oil level should be checked at the maximum and minimum mass flow of the system.
- At maximum mass flow, most oil is circulating in the system, therefore sufficient oil has to be in the compressor.
- At minimum mass flow, the oil still needs to come back from the system although it is transported with low velocity and force.
If the oil level is too low after these tests and 5 min of standstill, add some oil in order to get within the recommended oil level according to the above figure for standstill (Sight glass prior to system operation).
After additional oil has been added, run the compressors for 20 min. During operation, the second figure (Sight glass during system operation) can be used as a guidance to estimate the oil return.
Shut off the system to recheck the oil level at standstill according to the first figure (Sight glass prior to system operation). The compressors must be off when checking the oil level – the reference for the level during operation (Sight glass during system operation) is simply a guidance. With BAHT for tandems and trios, oil may be above the sight glass in systems where a lot of oil was added. If a certain amount of oil has already been added and the oil level in the sight glass keeps decreasing, oil return in the system is insufficient. Possible causes for oil loss of the compressors need to be checked, some examples are explained in the following.
Draining oil may be necessary when exchanging compressors.
When exchanging a compressor from the system, oil is already in the system, so it may be necessary to drain a part of the oil charge. If there is a large quantity of oil in the system, there is also a risk of a liquid slugging at start. Adjust the oil level within the recommended sight glass range.