Heat pump

Abstract

A heat pump ( 100 ) is described having an evaporator ( 50 ) for evaporating a fluid in order to obtain an evaporated fluid; a condenser ( 60 ) for condensing a compressed fluid; a compressor with a first compressor stage ( 10 ) and with a second compressor stage ( 20 ), wherein the compressor is arranged in the direction of flow of the evaporated fluid between the evaporator ( 50 ) and the condenser ( 60 ) during operation of the heat pump ( 100 ) and is designed to compress the evaporated fluid in order to obtain the compressed fluid; a value recording device ( 95 ) for recording a first value (P 1 ) which corresponds to a first pressure ratio between an inlet of the first compressor stage ( 10 ) and an outlet of the first compressor stage ( 10 ) or is dependent on the first pressure ratio; and a controller ( 96 ) for controlling a first rotational speed of the first compressor stage ( 10 ) and a second rotational speed of the second compressor stage ( 20 ), wherein the controller ( 96 ) is designed to control the second rotational speed of the second compressor stage ( 20 ) depending on the first value (P 1 ). Furthermore, methods for operating and producing the heat pump are described.

1 . A heat pump having the following features:
 an evaporator for evaporating a fluid, in order to obtain an evaporated fluid;   a condenser for condensing a compressed fluid;   a compressor having a first compressor stage and a second compressor stage, wherein the compressor is arranged in the flow direction of the evaporated fluid, during operation of the heat pump, between the evaporator and the condenser, and is configured to compress the evaporated fluid, in order to obtain the compressed fluid;   a value acquisition device for acquiring a first value, which corresponds to a first pressure ratio between an inlet of the first compressor stage and an outlet of the first compressor stage, or is dependent on the first pressure ratio; and   a controller for controlling a first rotational speed of the first compressor stage and a second rotational speed of the second compressor stage, wherein the controller is configured to control the second rotational speed of the second compressor stage depending on the first value.   
     
     
         2 . The heat pump according to  claim 1 , wherein the value acquisition device is configured for acquiring a second value, which corresponds to a second pressure ratio between an outlet of the second compressor stage and an inlet of the first compressor stage, or is dependent on the second pressure ratio, and wherein the controller is configured to furthermore control the second rotational speed depending on the second value. 
     
     
         3 . The heat pump according to  claim 2 , wherein the controller is configured to use the first value as the actual value and the second value as the target value. 
     
     
         4 . The heat pump according to  claim 3 , wherein the controller is configured to increase the rotational speed of the second compressor stage when the actual value is greater than the target value, or to reduce the rotational speed of the second compressor stage when the actual value is less than the target value. 
     
     
         5 . The heat pump according to  claim 1 , wherein the value acquisition device is furthermore configured to ascertain an actual temperature of a cooling fluid discharged on the evaporator side, and wherein the controller is configured to set the rotational speed of the first compressor stage in a manner dependent on the actual temperature of the cooling fluid and a predefined target temperature of the cooling fluid. 
     
     
         6 . The heat pump according to  claim 1 , wherein the controller is configured to operate the first compressor stage at a higher pressure ratio than the second compressor stage, depending on a power requirement in a first power region, wherein a difference between the pressure ratios of the first compressor stage and the second compressor stage reduces at increasing power requirements, and, in order to operate both the first compressor stage and the second compressor stage, in a second power region, in such a way that pressure ratios of the two compressor stages are approximately identical, in the second power region, and/or increase identically as the power requirement increases, wherein the second power region has higher power requirements than the first power region, and a boundary between the first power region and the second power region is set by the first compressor stage and/or by the second compressor stage. 
     
     
         7 . The heat pump according to  claim 6 , wherein the first compressor stage and the second compressor stage comprise radial wheels of different sizes, and wherein the controller is configured to control the first compressor stage, in the first power region, to a constant first pressure ratio as the target value, and to control the second compressor stage, with increasing power requirement, to an increasing second pressure ratio as the target value, and to fulfil, in the second power region, an increasing power requirement both by the first compressor stage and also by the second compressor stage-. 
     
     
         8 . The heat pump according to  claim 7 , wherein the controller is configured to use a maximum value from a function of the second value or a predefined constant as the target value for controlling the second rotational speed of the second compressor stage. 
     
     
         9 . The heat pump according to  claim 8 , wherein the function is a root function, and the predefined constant is the boundary between the first and the second power region. 
     
     
         10 . The heat pump according to  claim 1 , wherein the value acquisition device comprises a first temperature sensor for acquiring a first temperature with respect to the evaporator, and a second temperature sensor for acquiring a second temperature with respect to an outlet of the first compressor stage, and wherein the value acquisition device is configured to determine the first value from the first temperature and the second temperature. 
     
     
         11 . The heat pump according to  claim 10 , wherein the first temperature sensor is arranged in an evaporator sump of the evaporator, in order to acquire the first temperature before the first compressor stage, and the second temperature sensor is arranged in an intermediate cooling sump, in order to acquire the second temperature after an outlet of the first compressor. 
     
     
         12 . The heat pump according to  claim 11 , wherein a vapour duct is provided between the first compressor stage and the second compressor stage, in order to conduct compressed fluid out of the first compressor stage into the second compressor stage, wherein the intermediate cooling sump is arranged in the vapour duct. 
     
     
         13 . The heat pump according to  claim 1 , wherein the value acquisition device comprises a third temperature sensor for acquiring a third temperature with respect to the condenser, and wherein the value acquisition device is configured to determine the second value from the third temperature and the first temperature. 
     
     
         14 . The heat pump according to  claim 13 , wherein the third temperature sensor is arranged in the condenser sump, in order to acquire the third temperature after the second compressor stage. 
     
     
         15 . The heat pump according to  claim 14 , wherein a fluid conducting channel extends from the condenser sump into the intermediate cooling sump, in order to conduct fluid out of the condenser sump into the intermediate cooling sump, and wherein a further fluid conducting channel extends from the intermediate cooling sump into the evaporator sump, in order to conduct fluid out of the intermediate cooling sump and into the evaporator sump. 
     
     
         16 . The heat pump according to  claim 1 , wherein a bridging channel is arranged between the first compressor stage and the condenser, in order to bridge the second compressor stage, wherein a cross-section reducing element is arranged in the bridging channel, in order to set a cross-section of the bridging channel for controlling a flow of compressed fluid out of the first compressor stage to the condenser, wherein the cross-section reducing element assumes a closed position during operation of the second compressor stage. 
     
     
         17 . A method for operating a heat pump comprising: an evaporator for evaporating a fluid, in order to obtain an evaporated fluid; a condenser for condensing a compressed fluid; and a compressor having a first compressor stage and a second compressor stage, wherein the compressor is arranged in the flow direction of the evaporated fluid, during operation of the heat pump, between the evaporator and the condenser, and is configured to compress the evaporated fluid, in order to obtain the compressed fluid, said method comprising the following steps:
 acquiring a first value, which corresponds to a first pressure ratio between an inlet of the first compressor stage and an outlet of the first compressor stage, or is dependent on the first pressure ratio; and   controlling a first rotational speed of the first compressor stage and a second rotational speed of the second compressor stage, wherein the second rotational speed of the second compressor stage is controlled depending on the first value.   
     
     
         18 . A method for producing a heat pump comprising: an evaporator for evaporating a fluid, in order to obtain an evaporated fluid; a condenser for condensing a compressed fluid; and a compressor having a first compressor stage and a second compressor stage, said method comprising the following steps:
 arranging the compressor in the flow direction of the evaporated fluid, during operation of the heat pump, between the evaporator and the condenser, in order to compress the evaporated fluid, in order to obtain the compressed fluid; and   connecting a value acquisition device, for acquiring a first value, which corresponds to a first pressure ratio between an inlet of the first compressor stage and an outlet of the first compressor stage, or is dependent on the first pressure ratio, to the compressor, the evaporator or the condenser; and   connecting a controller, for controlling a first rotational speed of the first compressor stage and a second rotational speed of the second compressor stage, to the compressor, wherein the second rotational speed of the second compressor stage  9  is controlled depending on the first value.