Patent Publication Number: US-6990826-B1

Title: Single expansion device for use in a heat pump

Description:
BACKGROUND OF THE INVENTION 
   This application relates to a heat pump having a single expansion device coupled with a flow control device to properly route the refrigerant through the single expansion device dependent upon whether the heat pump is operating in a cooling mode or in a heating mode. 
   Refrigerant systems are utilized to control the temperature and humidity of air in various indoor environments to be conditioned. In a typical refrigerant system operating in the cooling mode, a refrigerant is compressed in a compressor and delivered to a condenser (or an outdoor heat exchanger in this case). In the condenser, heat is exchanged between outside ambient air and the refrigerant. From the condenser, the refrigerant passes to an expansion device, at which the refrigerant is expanded to a lower pressure and temperature, and then to an evaporator (or an indoor heat exchanger). In the evaporator, heat is exchanged between the refrigerant and the indoor air, to condition the indoor air. When the refrigerant system is operating, the evaporator cools the air that is being supplied to the indoor environment. In addition, as the temperature of the indoor air is lowered, moisture usually is also taken out of the air. In this manner, the humidity level of the indoor air can also be controlled. 
   The above description is of a refrigerant system being utilized in a cooling mode of operation. In the heating mode, the refrigerant flow through the system is essentially reversed. The indoor heat exchanger becomes the condenser and releases heat into the environment to be conditioned (heated in this case) and the outdoor heat exchanger serves the purpose of the evaporator and exchangers heat with a relatively cold outdoor air. Heat pumps are known as the systems that can reverse the refrigerant flow through the refrigerant cycle, in order to operate in both heating and cooling modes. This is usually achieved by incorporating a four-way reversing valve (or an equivalent device) into the system schematic downstream of the compressor discharge port. The four-way reversing valve selectively directs the refrigerant flow through indoor or outdoor heat exchanger when the system is in the heating or cooling mode of operation respectively. Typically, a pair of expansion devices, each along with a check valve, is employed. 
   One problem with the prior art heat pumps is the complexities associated with the provision of the expansion function. Since in the heat pumps the refrigerant will flow in opposed directions (depending on the mode of operation), it has been difficult to provide a single adequate expansion device. Additionally, since the requirements of enhanced reliability and improved control recently became one of the essential issues in the industry, thermal expansion devices are now frequently found in applications where fixed orifice expansion devices used to be a standard. 
   Another approach is disclosed in co-pending U.S. patent application Ser. No. 10/693,93, owned by the assignee of the present invention. In this concept, a single expansion device is utilized with a movable plunger that is moved to the appropriate position, depending on the mode of operation. 
   Another approach is to utilize an electronic expansion valve. However, electronic expansion valves are expensive and require additional electronics and sensors. 
   SUMMARY OF THE INVENTION 
   In a disclosed embodiment of this invention, there is a refrigerant system utilized as a heat pump, and incorporating a first four-way reversing valve for properly routing the refrigerant from the compressor to the indoor and outdoor heat exchangers. A second four-way valve routes refrigerant between the two heat exchangers in the appropriate direction through a single expansion device. A TXV (thermal expansion valve) bulb is positioned downstream of the first four-way reversing valve on a suction line leading to the compressor. Thus, regardless of the refrigerant flow direction, the TXV bulb will be adequately monitoring the refrigerant characteristics at the compressor suction, and properly controlling and communicating back to the expansion device. Further, the second four-way reversing valve is ensuring that the refrigerant is flowing in the appropriate direction through the expansion device. A control for the system would switch the two four-way reversing valves to the appropriate position, and control the expansion device based upon the refrigerant as sensed by the TXV bulb. 
   The present invention thus provides a heat pump, which is more reliable, less expensive, and easier to manufacture due to the elimination of additional components. Furthermore, an enhanced control is provided. 
   These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of a prior art refrigerant system. 
       FIG. 2  shows the inventive refrigerant system. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In a conventional TXV, a bulb senses a refrigerant condition upstream of the compressor and downstream of the evaporator. This bulb communicates back with the TXV plunger and controls the degree of opening of the TXV port. A TXV is much less expensive than an electronic expansion device and provides improved control over fixed orifice expansion device, however, as mentioned below, in heat pumps to date, two of these TXVs typically have been required. 
     FIG. 1  shows a prior art refrigerant system  20  incorporating a compressor  22  compressing a refrigerant and delivering that refrigerant to a discharge line  23 . A four-way reversing valve  24  is positioned to receive refrigerant from the discharge line  23  and route the refrigerant to a heat exchanger, as appropriate. Should the refrigerant system be operating in a cooling mode, the refrigerant will be initially directed to an outdoor heat exchanger  28  through a line  26 . The refrigerant would then flow through a check valve  32  and a cooling thermal expansion device  30  to the indoor heat exchanger  34 . A cooling TXV bulb  36  would monitor the conditions on a line  38  downstream of the indoor heat exchanger  34  to ensure that the cooling thermal expansion device  30  is controlled to deliver refrigerant to a compressor suction port with desired superheat values. 
   The line  38  leads back to the first four-way valve  24  and the refrigerant is routed back through a suction line  39  to the compressor  22 . Should the four-way reversing valve  24  be moved to the opposite position such that the heat pump  20  is operating in heating mode, the refrigerant would flow from the discharge line  23  into the line  38 , through the indoor heat exchanger  34 , through a check valve  42 , a heating thermal expansion device  40 , the outdoor heat exchanger  28 , and back through the four-way reversing valve  24  to the line  39 . Again, a TXV bulb  44  would sense the conditions on the line  39  and can control the heating thermal expansion device  40  as appropriate to ensure desired conditions at the compressor suction. 
   It has to be understood that a simplified schematic of the prior art cycle presented in  FIG. 1  does not cover a vast variety of different arrangements and system configurations. Additional components such suction accumulators, refrigerant storage receivers, refrigerant distribution devices, refrigerant-side economizers, reheat coils, auxiliary heat exchangers, etc. may be incorporated in the system design. 
   While the prior art does provide a wide variety of cooling and heating applications, it requires additional components. Namely, two distinct thermal expansion valves, two distinct check valves and two distinct bulbs are required. 
   The present invention is illustrated in  FIG. 2 . In this Figure, a heat pump  50  is shown having a compressor  52  delivering a compressed refrigerant to a discharge line  54 . A first four-way reversing valve  56  is positioned to route the refrigerant from the line  54  selectively to one of an outdoor heat exchanger  58  or an indoor heat exchanger  68 . In a cooling mode, the refrigerant would pass through the four-way reversing valve  56  to the outdoor heat exchanger  58 , and to a second four-way reversing valve  60 . The refrigerant, from the second four-way reversing valve  60 , would be routed into a line  64  leading to a single expansion device  62 . Downstream of the expansion device  62 , the refrigerant passes through a line  66 , back through the second four-way reversing valve  60 , and to the indoor heat exchanger  68 . Refrigerant passes from the indoor heat exchanger  68 , to a line  70  leading back to the first four-way reversing valve  56 . The first four-way valve  56  will route this refrigerant into the line  72 , where it returns to the compressor  52 . A single TXV bulb  74  is positioned on the line  72  and can control and communicate back to the thermal expansion device  62 . 
   Should the refrigerant system be operated in a heating mode, the operation of the two four-way reversing valves  56  and  60  is reversed. Refrigerant would now pass from the line  54  into the line  70 , through the indoor heat exchanger  68 , to the four-way reversing valve  60 . Refrigerant would be routed from the four-way reversing valve  60  through a line  64 , single thermal expansion device  62 , line  66 , back through the four-way reversing valve  60  to the outdoor heat exchanger  58 , and back to the first four-way reversing valve  56 . The refrigerant would flow through the first four-way reversing valve  56  to the line  72 , and back to the compressor  52 . 
   The present invention thus provides a heat pump function, and provides a very reliable and simple way of providing the expansion function without requiring at least two separate expansion devices, two check valves and two bulbs. 
   Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.