It is suitable for low temperature refrigeration under evaporating temperature below-25ºC, and the efficiency is significantly higher than that of single-stage compressor unit with economizer;.There are four types of single-machine two-stage screw units, of which high and low pressure stages of compressor have energy adjustment devices, which can ensure the unit is always efficient and economical under low temperature working conditions;·The unit can be customized according to the special needs of users;.The standard configuration control method is automatic.