Centrifugal-chiller and method for controlling the same

Abstract

Provided is a centrifugal-chiller including one variable-speed centrifugal-compressor and one constant-speed centrifugal-compressor and capable of high-efficiency operation. A centrifugal-chiller comprising a variable-speed centrifugal-compressor whose rotational frequency can be varied by an inverter and which compresses a refrigerant; a constant-speed centrifugal-compressor connected in parallel with the variable-speed centrifugal-compressor and operated at a constant rotational speed to compress the refrigerant; and a control unit that controls the operations of the variable-speed centrifugal-compressor and the constant-speed centrifugal-compressor, wherein in the case where a required load factor of the centrifugal-chiller is less than a predetermined value, the control unit selects a variable-speed-compressor priority operating mode in which only the variable-speed centrifugal-compressor is activated, and in the case where the required load factor of the centrifugal-chiller is the predetermined value or greater, the control unit selects a combined-use operating mode in which the variable-speed centrifugal-compressor and the constant-speed centrifugal-compressor are activated.

1 . A centrifugal-chiller comprising:
 a variable-speed centrifugal-compressor whose rotational frequency can be varied by an inverter and which compresses a refrigerant;   a constant-speed centrifugal-compressor connected in parallel with the variable-speed centrifugal-compressor and operated at a constant rotational speed to compress the refrigerant;   a condenser that condenses the refrigerant compressed by the variable-speed centrifugal-compressor and/or the constant-speed centrifugal-compressor into a liquid using cooling water supplied thereto;   an expansion valve that expands the refrigerant that is condensed into a liquid by the condenser;   an evaporator that evaporates the refrigerant expanded by the expansion valve; and   a control unit that controls the operations of the variable-speed centrifugal-compressor and the constant-speed centrifugal-compressor,   wherein, in the case where a required load factor of the centrifugal-chiller is less than a predetermined value, the control unit selects a variable-speed-compressor priority operating mode in which only the variable-speed centrifugal-compressor is activated, and in the case where the required load factor of the centrifugal-chiller is the predetermined value or greater, the control unit selects a combined-use operating mode in which the variable-speed centrifugal-compressor and the constant-speed centrifugal-compressor are activated.   
     
     
         2 . The centrifugal-chiller according to  claim 1 , wherein the predetermined value of the load factor of the centrifugal-chiller is set to 30% or higher and less than 50%. 
     
     
         3 . The centrifugal-chiller according to  claim 1 , wherein
 an inlet guide vane that controls the flow rate of the refrigerant flowing to an impeller of the constant-speed centrifugal-compressor is provided upstream of the impeller in the flow of the refrigerant; and   a wall facing the inlet guide vane has a sealing portion that minimizes leakage of the refrigerant through the gap between the inlet guide vane and the wall when the inlet guide vane is fully closed.   
     
     
         4 . A method for controlling a centrifugal-chiller including
 a variable-speed centrifugal-compressor whose rotational frequency can be varied by an inverter and which compresses a refrigerant;   a constant-speed centrifugal-compressor connected in parallel with the variable-speed centrifugal-compressor and operated at a constant rotational speed to compress the refrigerant;   a condenser that condenses the refrigerant compressed by the variable-speed centrifugal-compressor and/or the constant-speed centrifugal-compressor into a liquid using cooling water supplied thereto;   an expansion valve that expands the refrigerant that is condensed into a liquid by the condenser; and   an evaporator that evaporates the refrigerant expanded by the expansion valve,   the method controlling the operations of the variable-speed centrifugal-compressor and the constant-speed centrifugal-compressor, wherein   in the case where a required load factor of the centrifugal-chiller is less than a predetermined value, the control unit selects a variable-speed-compressor priority operating mode in which only the variable-speed centrifugal-compressor is activated, and in the case where the required load factor of the centrifugal-chiller is the predetermined value or greater, the control unit selects a combined-use operating mode in which the variable-speed centrifugal-compressor and the constant-speed centrifugal-compressor are activated.