Method and device for controlling operation of heat pump unit

Abstract

The temperature of high-temperature water at the exit of a condenser is maintained to be within a setting range by control of, under an operation with all cylinders, capacity of a reciprocating compressor in the period between a maximum allowable load and a minimum load for lubrication, at which the flow of a lubrication oil pump is ensured, based on the revolution-speed control of a drive motor that drives the reciprocating compressor and by control of the capacity of the reciprocating compressor at the minimum load for lubrication or less based on the combination of the control of decreasing the number of operation cylinders and the revolution-speed control of the drive motor. In addition, a heating mechanism is provided on an inlet path of the reciprocating compressor to prevent the liquefied refrigeration flow of a refrigerant liquid to the reciprocating compressor during the operation or at the start.

1 . A method for controlling an operation of a heat pump unit that uses NH 3  as a refrigerant, has a compressor, a condenser, an expansion valve, and an evaporator, and constitutes a heat pump cycle,
 the compressor being a reciprocating compressor having a plurality of cylinders, a drive motor that drives pistons of the cylinders, and also having a lubrication oil pump driven by the drive motor,   the method comprising:   a first step of detecting temperature of heat-exchanging fluid at an exit of the condenser or the evaporator, the heat-exchanging fluid being heat-exchanged with the NH 3  refrigerant at the condenser or the evaporator;   a second step of maintaining the temperature of the heat-exchanging fluid at the exit of the condenser or the evaporator to be within a setting range by control of, under an operation with all the cylinders, capacity of the reciprocating compressor in a period between a maximum allowable load and a minimum load for lubrication, at which a flow of a lubrication oil pump is capable of being ensured, based on revolution-speed control of the drive motor that drives the reciprocating compressor; and   a third step of maintaining the temperature of the heat-exchanging fluid at the exit of the condenser or the evaporator to be within the setting range by control of the capacity of the reciprocating compressor at the minimum load for lubrication or less based on a combination of control of decreasing the number of operation cylinders and the revolution-speed control of the drive motor.   
     
     
         2 . The method for controlling the operation of the heat pump unit according to  claim 1 , comprising:
 a fourth step of maintaining the NH 3  refrigerant flowing into a refrigerant inlet path at temperature not less than a saturation temperature by a heating mechanism provided on the refrigerant inlet path of the reciprocating compressor in order to prevent liquefied refrigeration flow of the NH 3  refrigerant to the reciprocating compressor.   
     
     
         3 . The method for controlling the operation of the heat pump unit according to  claim 1 , wherein the inlet path is shut off at a stop of the heat pump unit by a shut-off valve provided on the inlet path of the reciprocating compressor in order to prevent the liquefied refrigeration flow at a start of the reciprocating compressor. 
     
     
         4 . The method for controlling the operation of the heat pump unit according to  claim 1 , comprising:
 a fifth step of making, at a stop of the reciprocating compressor, pressure of high-pressure refrigerant gas of an outlet path of the reciprocating compressor equal to pressure on a side of the evaporator in order to prevent liquefaction at a high-pressure part of the reciprocating compressor.   
     
     
         5 . The method for controlling the operation of the heat pump unit according  claim 1 , comprising:
 a sixth step of making, at the start of the reciprocating compressor, pressure of high-pressure refrigerant gas of an outlet path of the reciprocating compressor equal to pressure on a side of the evaporator in order to decrease a start torque of the reciprocating compressor.   
     
     
         6 . A unit for controlling an operation of a heat pump unit that uses NH 3  as a refrigerant, has a compressor, a condenser, an expansion valve, and an evaporator, and constitutes a heat pump cycle,
 the compressor being a reciprocating compressor having a plurality of cylinders, a drive motor that drives pistons of the cylinders, and also having a lubrication oil pump driven by the drive motor,   the heat pump unit comprising:   a temperature sensor that detects temperature of heat-exchanging fluid at an exit of the condenser or the evaporator, the heat-exchanging fluid being heat-exchanged with the NH 3  refrigerant at the condenser or the evaporator; and   a controller that maintains the temperature of the heat-exchanging fluid at the exit of the condenser or the evaporator to be within a setting range by controlling capacity of the reciprocating compressor in a period between a maximum allowable load and a minimum load for lubrication, at which a lubrication state of the reciprocating compressor is capable of being ensured with a flow of the lubrication oil pump, based on revolution-speed control of the drive motor that drives the reciprocating compressor and by controlling the capacity of the reciprocating compressor at the minimum load for lubrication or less based on a combination of the revolution-speed control of the drive motor and cylinder-number control.   
     
     
         7 . The unit for controlling the operation of the heat pump unit according to  claim 6 , wherein a heating mechanism is provided on a refrigerant inlet path of the reciprocating compressor to maintain the NH 3  refrigerant flowing into the refrigerant inlet path at temperature not less than saturation temperature thereby preventing liquefied refrigeration flow of the NH 3  refrigerant to the reciprocating compressor. 
     
     
         8 . The unit for controlling the operation of the heat pump unit according to  claim 7 , wherein the heating mechanism is a heater provided on the inlet path of the reciprocating compressor. 
     
     
         9 . The unit for controlling the operation of the heat pump unit according to  claim 7 , wherein the heating mechanism has the inlet path of the reciprocating compressor formed into a dual-pipe structure, introduces refrigerant gas outlet from the reciprocating compressor or a refrigerant liquid on a side of the exit of the condenser into an outer pipe of the dual-pipe structure, and heats the inlet path with heat retained in the refrigerant gas or the refrigerant liquid. 
     
     
         10 . The unit for controlling the operation of the heat pump unit according to  claim 7 , wherein the heating mechanism causes part of refrigerant gas outlet from the reciprocating compressor to be divided and poured into the inlet path thereby heating the inlet path with heat retained in the refrigerant gas. 
     
     
         11 . The unit for controlling the operation of the heat pump unit according to  claim 7 , wherein the heating mechanism covers the reciprocating compressor with a detachable heat-insulating jacket. 
     
     
         12 . The unit for controlling the operation of the heat pump unit according to  claim 6 , wherein a pressure-equalizing mechanism is provided that makes pressure of high-pressure refrigerant gas in an outlet path of the reciprocating compressor equal to pressure on a side of the evaporator at a stop or start of the reciprocating compressor. 
     
     
         13 . The unit for controlling the operation of the heat pump unit according to  claim 12 , wherein the pressure-equalizing mechanism has a heat exchanger provided on the outlet path of the reciprocating compressor or the condenser, causes a cooling medium to flow into the exchanger at the stop of the heat pump unit, and condenses and liquefies the refrigerant gas to decrease the pressure of the refrigerant gas of the outlet path. 
     
     
         14 . The unit for controlling the operation of the heat pump unit according to  claim 6 , wherein
 a second heat pump unit having a heat-pump-cycle constituting apparatus is provided, the evaporator is incorporated in a high-pressure side refrigerant path of the second heat pump unit to be constituted as a cascade condenser that uses heat retained in a refrigerant of the second heat pump unit as a heat source, and   pressure of the high-pressure side refrigerant path of the second heat pump unit is regulated in order to maintain the temperature of the heat-exchanging fluid at the exit of the condenser to be within the setting range.   
     
     
         15 . The unit for controlling the operation of the heat pump unit according to  claim 14 , wherein a condensed refrigerant liquid of the second heat pump unit is supercooled by the cascade condenser, and the supercooled refrigerant liquid is caused to return to a low-pressure side refrigerant circulation path of the second heat pump unit. 
     
     
         16 . The unit for controlling the operation of the heat pump unit according to  claim 14 , wherein the cascade condenser is arranged in parallel with a condenser of the second heat pump unit, and a flow of the refrigerant of the condenser is regulated to regulate condensing pressure of the condenser. 
     
     
         17 . The unit for controlling the operation of the heat pump unit according to  claim 14 , wherein the cascade condenser is arranged in series between the condenser of the second heat pump unit and the compressor, and either a flow of the refrigerant of the condenser is regulated or condensing pressure of the condenser is regulated by an outlet pressure regulation valve provided between the cascade condenser and the condenser.