Method for increasing efficiency of a vapor compression system by compressor cooling

#The present invention relates generally to a method for increasing the efficiency of a vapor compression system by removing heat in the compressor from the system with the heat accepted by the heat sink of the heat rejecting heat exchanger.

#Chlorine containing refrigerants have been phased out in most of the world due to their ozone destroying potential. Hydrofluoro carbons (HFCs) have been used as replacement refrigerants, but these refrigerants still have high global warming potential. “Natural” refrigerants, such as carbon dioxide and propane, have been proposed as replacement fluids. Unfortunately, there are problems with the use of many of these fluids as well. Carbon dioxide has a low critical point, which causes most air conditioning systems utilizing carbon dioxide to run transcritical, or above the critical point.

#When a vapor compression system runs transcritical, the high side pressure of the refrigerant is typically high so that the refrigerant does not change phases from vapor to liquid while passing through the heat rejecting heat exchanger. Therefore, the heat rejecting heat exchanger operates as a gas cooler in a transcritical cycle, rather than as a condenser. The pressure of a subcritical fluid is a function of temperature under saturated conditions (where both liquid and vapor are present). However, the pressure of a transcritical fluid is a function of fluid density when the temperature is higher than the critical temperature.

#The various features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:

#FIG. 1 illustrates a schematic diagram of a prior art vapor compression system;

#FIG. 2 illustrates a schematic diagram of a vapor compression system employing a stream of cooling fluid to cool the compressor;

#FIG. 1 illustrates a schematic diagram of a prior art vapor compression system 20. The system 20 includes a compressor 22 with a motor 23, a first heat exchanger 24, an expansion device 26, a second heat exchanger 28, and a reversing valve 30 to reverse the flow of refrigerant circulating through the system 20. When operating in a heating mode, after the refrigerant exits the compressor 22 at high pressure and enthalpy, the refrigerant flows through the first heat exchanger 24, which acts as a gas cooler, and loses heat, exiting the first heat exchanger 24 at low enthalpy and high pressure. A fluid medium 38, such as water, flows through the heat sink 32 and accepts heat from the refrigerant passing through the first heat exchanger 24. The cooled fluid medium 38 enters the heat sink 32 at the heat sink inlet or return 34 and flows in a direction opposite to the direction of flow of the refrigerant. After accepting heat from the refrigerant, the heated fluid medium 38 exits at the heat sink outlet or supply 36. The refrigerant then passes through the expansion device 26, and the pressure drops. After expansion, the refrigerant flows through the second heat exchanger 28, which acts as an evaporator, and exits at a high enthalpy and low pressure. The refrigerant passes through the reversing valve 30 and then re-enters the compressor 22, completing the system 20. The reversing valve can reverse the flow of the refrigerant to change the system 20 from the heating mode to a cooling mode.

#In a preferred embodiment of the invention, carbon dioxide is used as the refrigerant. While carbon dioxide is illustrated, other refrigerants may benefit from this invention. Because carbon dioxide has a low critical point, systems utilizing carbon dioxide as a refrigerant usually require the vapor compression system 20 to run transcritical.

#FIG. 2 illustrates a vapor compression system 120 employing a stream of cooling fluid 140 to cool the compressor motor 123. Like numerals are increased by multiples of 100 to indicate like parts. The stream of cooling fluid 140 flows in or near the compressor motor 123, accepting heat generated by the compressor motor 123. Preferably, the stream of cooling fluid 140 is water. After accepting heat from the compressor motor 123, the stream of cooling fluid 140 merges with the heated fluid medium 138 exiting the heat sink 132 at the heat sink outlet 136. The merged flows of the heated cooling fluid 140 and the heated fluid medium 138 exit the vapor compression system 120, removing both the heat generated by the compressor motor 123 and the heat rejected by the refrigerant flowing through the first heat exchanger 124. The heated merged flows can then be used by the customer.