Method for operating a combined heat and power device, combined heat and power device and use of a lubricant

Abstract

This disclosure relates to a method for operating a combined heat and power device, wherein carbon dioxide as a refrigerant ( 17 ) is compressed in a compressor, wherein the carbon dioxide is carried along a refrigerant circuit and routed back to the compressor via a collecting vessel ( 5 ). The method is distinguished by the fact that the compressor is lubricated with a lubricant ( 15 ) which has a density of more than 1004 g/l, and that a hot gas temperature in the compressor is held below a predetermined value, above which overheating and/or ageing of the lubricant occurs.

What is claimed is: 
     
         1 . A method for operating a combined heat and power device, comprising:
 compressing carbon dioxide as a refrigerant ( 17 ) in a compressor;   carrying the carbon dioxide along a refrigerant circuit and routing the carbon dioxide back to the compressor via a collecting vessel ( 5 ); and   lubricating the compressor with a lubricant ( 15 ) which has a density of more than 1004 g/l, and holding a hot gas temperature in the compressor below a predetermined value, above which overheating and/or ageing of the lubricant occurs.   
     
     
         2 . The method according to  claim 1 , wherein the combined heat and power device is operated in a transcritical range, preferably as an air-conditioning system, especially in a motor vehicle, or as a heat pump, especially in a motor vehicle, wherein the cold heat reservoir preferably has a temperature of less than −8° C., preferably less than −15° C., preferably less than −20° C., preferably −30° C. 
     
     
         3 . The method according to  claim 1  wherein the the lubricant ( 15 ) with a density of at most 1100 g/l, preferably of at least 1010 g/l to at most 1080 g/l, preferably of at least 1020 g/l, to at most 1070 g/l, preferably of at least 1030 g/l to at most 1060 g/l, preferably of at least 1040 g/l to at most 1050 g/l, particularly preferably of 1044 g/l, is used. 
     
     
         4 . The method according to  claim 3  wherein a PAG oil with a density of 1044 g/l is used as the lubricant ( 15 ). 
     
     
         5 . The method according to  claim 1  wherein the compressor is cooled by a liquid coolant, wherein the compressor used is preferably one which has a compressor unit and an electric motor that drives the compressor unit, wherein the electric motor is cooled by the liquid coolant, preferably by a water/glycol mixture. 
     
     
         6 . The method according to  claim 6 , wherein a flow of the liquid coolant through the compressor, preferably through a liquid cooling jacket of the electric motor, is subjected to open-loop and/or closed-loop control in such a way that the hot gas temperature in the compressor is held below the predetermined value. 
     
     
         7 . The method according to  claim 5 , wherein a flow of the liquid coolant through the compressor is subjected to closed-loop control in such a way that the carbon dioxide is compressed isentropically in the compressor. 
     
     
         8 . A combined heat and power device, comprising:
 a refrigerant circuit, which has a collecting vessel ( 5 );   a compressor for compressing a refrigerant ( 1 ) and for delivering the refrigerant ( 17 ) along the refrigerant circuit wherein the combined heat and power device has carbon dioxide as a refrigerant ( 17 );   a lubricant ( 15 ) for the compressor which has a density of more than 1004 g/l; and   a temperature limiting device for limiting the hot gas temperature in the compressor, said device being designed to hold the hot gas temperature below a predetermined value.   
     
     
         9 . The combined heat and power device according to  claim 8  wherein the lubricant ( 15 ) has a density of at most 1100 g/l, preferably of at least 1010 g/l to at most 1080 g/l, preferably of at least 1020 g/l to at most 1070 g/l, preferably of at least 1030 g/l to at most 1060 g/l, preferably of at least 1040 g/l to at most 1050 g/l, particularly preferably of 1044 g/l. 
     
     
         10 . The combined heat and power device according to  claim 9  wherein the lubricant ( 15 ) is a PAG oil with a density of 1044 g/l. 
     
     
         11 . The combined heat and power device according to  claim 8  wherein the compressor is cooled by a liquid coolant, wherein it preferably has a compressor unit and an electric motor that drives the compressor unit, wherein the liquid coolant flows around the electric motor, at least locally, wherein the electric motor preferably has a liquid coding jacket, through which the liquid coolant flows. 
     
     
         12 . The combined heat and power device according to one of  claim 8  wherein the temperature limiting device comprises a feed pump, preferably a controllable feed pump, for delivering the liquid coolant. 
     
     
         13 . Use of a lubricant ( 15 ) with a density of more than 1004 g/l in a compressor of a combined heat and power device, which comprises carbon dioxide as a refrigerant ( 17 ), wherein the compressor has a temperature limiting device for limiting the hot gas temperature in the compressor, which is designed to hold the hot gas temperature below a predetermined value, wherein the compressor is preferably cooled by means of a liquid coolant. 
     
     
         14 . Use according to  claim 13 , characterized in that a lubricant ( 15 ) with a density of at most 1100 g/l, preferably of at least 1010 g/l to at most 1080 g/l, preferably of at least 1020 g/l to at most 1070 g/l, preferably of at least 1030 g/l to at most 1060 g/l, preferably of at least 1040 g/l to at most 1050 g/l, particularly preferably of 1044 g/l, is used. 
     
     
         15 . Use according to  claim 14 , characterized in that a PAG oil with a density of 1044 g/l is used as a lubricant ( 15 ).