Screw compressors use up to 200 tons capacity. once you need more than 6 units of scroll compressors it is time to switch to screw. Screw have the ability to vary the cooling output 100% to 20% via the use of a slide vane to limit refrigerant delivery to the compressor and provide smooth transition. There can only be one Screw compressor in the chiller. the screw compressors are fixable and has less vibration compared to the scroll chiller.