Conference Year

2014

Keywords

Manifolding, Active Solution, Passive Solution, Oil Balance, Vibration

Abstract

Manifolded compressors are widely used in existing refrigeration systems such as cold rooms, display windows and ice machines. Scroll compressors are increasingly used in refrigeration systems, hence manifolded scroll compressors are easily found in the current market. The manifolding of two, three or even four compressors provides many benefits. It can provide capacity modulation; it can offer lower starting load of the system; it also enables the change of one compressor when it is tripped without shutting down the whole system. The key success factor of design of the manifold is to ensure the right balance of the oil between compressors in different running conditions. It is vital for the compressor to maintain the proper level and quantity of oil for its reliability. Two kinds of oil management solutions are predominant. One is the active solution which includes a mechanical or electronic oil level control device (oil level regulator) to control the oil feeding in order to maintain the oil level inside of the compressor crankcase. This solution is maturely used in the market. The other is the passive solution which relies on the piping design to achieve a good oil balance. The passive one is more interesting for its cost effectiveness and robustness due to fewer components, however, it is more difficult to handle. In this paper, three different passive oil management solutions for even tandem systems are studied. The first solution is that each compressor has its own respective oil separator; oil separated in the oil separator is returned back to the corresponding compressor crankcase, and the oil balance line is installed to avoid that one compressor oil level is much higher than the other if OS(oil separator) efficiency is different or any OS is blocked. The second solution consists of two compressors sharing one common oil separator; oil separated from the OS is fed back to the common suction line, and is then led back to each compressor with refrigerant gas. The oil return has to be split equally between the running compressors; the oil state could be as spray with the gas and as droplets along the length and bend of the piping. Since the oil is returning back together with the suction gas, gas balance is critical and gas velocity in the suction line is very important. Suction header and suction branch design is described in detail in the paper to ensure the gas balance and oil return. The oil balance line is installed between two compressors in order to balance the oil level. The third solution is that two compressors share one oil separator; oil is returned back to one compressor crankcase and then through the oil balance line to feed another compressor’s crankcase. All of the above three passive solutions are working but have their own advantages and disadvantages. Test results for each solution are shown in the paper. Also, the vibration analysis and the tests are described to optimize the piping design for good acoustic result.

1348_presentation.pdf (903 kB)
Oil Management Solutions for Manifolding Scroll Compressors for Refrigeration Systems

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