Recently Building Multi System Air-Conditioners (VRF: Variable Refrigerant Flow) are continuously widening their market share in the global air conditioning marketplace, as commercial buildings are required to reduce building energy consumption due to global warming issue. In building multi system air-conditioner (VRF), because of the long distance or high elevation gap between outdoor unit and indoor unit and the wide variable speed range with various cooling and heating loads, the oil in the compressor sump can be dropped below minimum level before the discharged oil returns to compressor. In order to improve the compressor reliability, it is desirable to develop the technology for sensing and controlling oil level of compressor in real time. This paper introduces the principle of real-time oil level sensor and its application to control oil level of scroll compressor.
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