Patent Application
20050166614
The present invention relates generally to a vapor compression system that uses the cold condensate from an evaporator to further subcool refrigerant exiting the condenser to increase system capacity and efficiency.
In a vapor compression system, refrigerant is compressed to a high pressure in a compressor. The refrigerant then flows through a condenser and rejects heat to a secondary fluid medium. The high pressure and relatively low enthalpy refrigerant is then expanded in an expansion device. The refrigerant then passes through an evaporator and accepts heat from another secondary fluid medium, such as air. The relatively high enthalpy and low pressure refrigerant then reenters the compressor, completing the cycle.
When refrigerant flows through the evaporator, moisture is removed from the air stream, and cold condensate forms on the surface of the evaporator coil. The cold condensate typically drips from the evaporator surface into a drain pan and is discharged from the system through a drain, for example.
It is desirable to further subcool the refrigerant exiting the condenser before expansion to increase system capacity and efficiency. In a prior art system, the cold condensate is collected and randomly sprayed directly on the surface of the condenser coil to assist heat rejection from the refrigerant in the condenser and reduce the discharge pressure of the refrigerant.
A drawback of this prior art system is that it is not effective, particularly in high efficiency vapor compression systems having large condenser coils, since the heat rejected in the condenser is still limited by the outdoor air temperature. As the size of the condenser coil increases, the amount of heat rejected in the condenser coil does not increase proportionally. Therefore, the cold condensate has little cooling effect on the large condenser coils. Thus, the driving force for the heat rejection diminishes, establishing a limit for further refrigerant temperature reduction.
There is a need in the art for a vapor compression system including additional heat rejection in the condenser and to further subcool the liquid refrigerant exiting the condenser to increase system capacity and efficiency.
In general terms, this invention utilizes condensate produced during system operation for further subcooling of the refrigerant in the system.
One example system includes a compressor, a condenser, an evaporator an expansion device between the condenser and the evaporator, and refrigerant lines connecting these components. The system further includes a subcooling portion that facilitates subcooling of the refrigerant flowing between the condenser and the expansion device using the condensate that forms on the evaporator.
One example vapor compression system includes a compressor, a condenser, an expansion device, and an evaporator. Refrigerant is circulated though the closed circuit system. The compressor compresses the refrigerant to a high pressure and a high enthalpy state. As the refrigerant flows through the condenser, the refrigerant rejects heat to a secondary fluid medium and exits the condenser at a relatively low enthalpy and a high pressure. The liquid refrigerant exiting the condenser is further subcooled by condensate formed on the evaporator surfaces and delivered for a heat transfer interaction with this refrigerant. When refrigerant in the evaporator exchanges heat with the air, moisture is removed from the air stream, forming a cold condensate on the evaporator surfaces collected in a condensate pan. The further subcooled refrigerant is then expanded to a low pressure in an expansion device. After expansion, the refrigerant flows through an evaporator and accepts heat from the air stream. The refrigerant exits the evaporator at a relatively high enthalpy and a low pressure. After evaporation, the refrigerant reenters the compressor, completing the cycle.
In one inventive example, the cold condensate flows by gravity onto the refrigerant line between the condenser and the expansion device or onto a subcooling portion of the condenser coil to further subcool the liquid refrigerant before expansion.
In another inventive example, the refrigerant line exiting the condenser is located in the condensate pan. The refrigerant in the refrigerant line exiting the condenser rejects heat to the cold condensate in the condensate pan, further subcooling the refrigerant.
In another inventive example, the cold condensate collected in the condensate pan is selectively sprayed on the refrigerant line exiting the condenser or on the subcooling portion of the condenser to further subcool the refrigerant.
In another inventive example, the refrigerant flows through a condensate heat exchanger positioned between the condenser and the expansion device and is further subcooled by the cold condensate that is removed from the indoor air stream. After accepting heat from the refrigerant in the condensate heat exchanger, the condensate is discharged from the system through a drain.
These and other features of the present invention will be best understood from the following specification and drawings.
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 drawing that accompanies the detailed description can be briefly described as follows:
The refrigerant then passes through the expansion device 26, which expands the refrigerant, reducing its pressure and temperature. The expansion device 26 can be a mechanical expansion device (TXV), an electronic expansion valve (EXV) or other type of known expansion device.
After expansion, the refrigerant flows through the evaporator 28 and exits at a relatively high enthalpy and a low pressure. In the evaporator 28, the refrigerant absorbs heat from the air stream 44. When the refrigerant exchanges heat with the air stream 44 in the evaporator 28, moisture is removed from the air stream 44 and forms a cold condensate 58 that collects in a condensate pan 60. In one example, the condensate pan 60 is positioned under the evaporator 28.
In the embodiment illustrated in
Subcooling the liquid refrigerant using the condensate 58 increases the capacity and efficiency of the system 20.
The cold condensate 58 in the condensate pan 60 accepts heat from the refrigerant in the refrigerant line 78. When the collected condensate 58 is heated, it becomes less effective in subcooling the refrigerant in the refrigerant line 78. Moreover, the condensate 58 collected in the condensate pan 60 is heated by the refrigerant, and therefore precautions must be taken to prevent an unlikely event of condensate 58 re-evaporating and reentering the air stream 44 flowing through the evaporator 28. In one example, the system 20 includes a temperature sensor 76 to detect the temperature of the condensate 58 collected in the condensate pan 60. When the temperature sensor 76 detects that the temperature of the condensate 58 in the condensate pan 60 is above a threshold value, the temperature sensor 76 sends a signal to a control 74. The control 74 sends a signal to open a drain 72 and drain the warm condensate 58 from the condensate pan 60. After draining the warm condensate 58, cold condensate 58 is again collected in the condensate pan 60 during heat exchanger between the air stream 44 and the refrigerant flowing through the evaporator 28. One skilled in the art would know what threshold temperature to employ.
Alternately, the system 20 includes a level sensor 68 to detect the amount of the condensate 58 collected in the condensate pan 60. When the level sensor 68 detects that the amount of the condensate 58 collected in the condensate pan 60 is above a threshold value, the level sensor 68 sends a signal to a control 74. The control 74 sends a signal to open the drain 72 and drain the warm condensate 58 from the condensate pan 60. After draining the warm condensate 58, the cold condensate 58 is again collected in the condensate pan 60. One skilled in the art would know what threshold temperature to employ. Also, it should be understood that both the temperature sensor 76 and the level sensor 68 can be utilized simultaneously.
Alternately, the cold condensate 58 collected in the condensate pan 60 is directed into the condensate heat exchanger 56 when a level sensor 68 detects that the amount of cold condensate 58 collected in the condensate pan 60 is within a selected range. The level sensor 68 then sends a signal to a control 66 to activate a flow control device 62, such as a valve or a pump, to direct the cold condensate 58 collected in the condensate pan 60 into the condensate heat exchanger 56 to accept heat from the refrigerant exiting the condenser 24. Given this description, one skilled in the art would know what the threshold amount of the cold condensate 58 to employ.
When the level sensor 68 detects that the amount of cold condensate 58 collected in the condensate pan 60 is below the threshold amount, the control 66 deactivates the flow control device 62 to stop the flow of the cold condensate 58 into the condensate heat exchanger 56. When the flow control device 62 is deactivated, the liquid refrigerant exiting the condenser 24 and flowing through the condensate heat exchanger 56 is not subcooled because the cold condensate 58 does not flow into and through the condensate heat exchanger 56.
The amount of subcooling obtained by the refrigerant entering the expansion device 26 is no longer limited by the temperature of the secondary fluid (e.g., air) 30. The amount of subcooling is enhanced due to a heat transfer interaction between the refrigerant exiting the condenser 24 and the cold condensate 58 removed from the air stream 44, formed on the surface of the evaporator 23 and collected in the drain pan 60.
The amount heat transferred in the condensate heat exchanger 56 between the refrigerant exiting the condenser 24 and the cold condensate 58 is determined by the temperature and the amount of the cold condensate 58 collected in the system 20. Therefore, the significantly increased temperature difference between the high pressure liquid refrigerant exiting the condenser 24 and the cold condensate 58 drives the heat transfer process and determines the amount of subcooling of the refrigerant.
It should be understood that the described embodiments can be also used in conjunction or in addition to refrigerant systems where the condensate is applied to the condenser coil as a whole.
The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.
