Patent Publication Number: US-10775070-B2

Title: Method for solving charge imbalance in existing split heat pump

Description:
TECHNICAL FIELD 
     The present disclosure is directed to reversible HVAC systems and in particular to charge compensators. 
     BACKGROUND OF THE INVENTION 
     HVAC systems can comprise an indoor heat exchanger, an outdoor heat exchanger, a compressor, an expansion device, and other components. Some HVAC systems may comprise a reversing valve, enabling the system to function both as a heat pump and as an air conditioner. During heating modes the indoor heat exchanger functions as a condenser and the outdoor heat exchanger functions as an evaporator. During cooling modes the roles of the heat exchangers are reversed. The indoor and outdoor heat exchangers are typically the same size, but not always. Different sized heat exchangers may be due to space constraints, material differences, or other reasons. The volume ratio of indoor to outdoor coils may lead to charge imbalances, leading to high pressure and other problems. 
     BRIEF SUMMARY OF THE INVENTION 
     One possible embodiment under the present disclosure can comprise a compensator for an HVAC system operable in both a cooling mode and a heating mode, comprising: an inlet configured to be coupled to a liquid line of a heat exchanger; a tank configured to receive refrigerant from the liquid line when the HVAC system is in a heating mode; and a heater electrically coupled to the HVAC system, wherein when the HVAC system is in a cooling mode then the heater is turned on, wherein the heater is operable to cause refrigerant in the compensator to migrate out of the compensator. 
     Another possible embodiment under the present disclosure can comprise an HVAC system operable in both a heating mode and a cooling mode comprising: an indoor heat exchanger operable to receive a refrigerant and transfer heat between the refrigerant and another medium; a compressor operable to receive the refrigerant from the indoor heat exchanger when the HVAC system is in a cooling mode; an outdoor heat exchanger operable to receive the refrigerant from the compressor when the HVAC system is in a cooling mode, an outlet of the outdoor heat exchanger comprising a liquid line when the HVAC system is in a cooling mode; an expansion valve operable to receive the refrigerant from the outdoor heat exchanger and to direct the refrigerant toward the indoor heat exchanger when the HVAC system is in a cooling mode; and a compensator comprising: an inlet configured to be coupled to the liquid line of the outdoor heat exchanger; a tank configured to receive refrigerant from the liquid line when the HVAC system is in a heating mode; and a heater electrically coupled to the HVAC system, wherein when the HVAC system is in a cooling mode then the heater is turned on, wherein the heater is operable to cause refrigerant in the compensator to migrate out of the compensator. 
     Another possible embodiment under the present disclosure can comprise a method of alleviating charge imbalance in an HVAC system that is operable in both a cooling mode and a heating mode, comprising: circulating a refrigerant through an indoor heat exchanger, an outdoor heat exchanger, a compressor and an expansion device, wherein a compensator is coupled to a liquid line of the outdoor heat exchanger; allowing refrigerant to flow into the compensator when the HVAC system is in a heating mode; and heating the compensator when the HVAC system is in a cooling mode in order to cause the refrigerant to migrate out of the compensator. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram of a possible embodiment under the present disclosure. 
         FIG. 2  is a diagram of a possible embodiment under the present disclosure. 
         FIG. 3  is a flow chart diagram of a possible method embodiment under the present disclosure. 
         FIG. 4  is a flow chart diagram of a possible method embodiment under the present disclosure. 
         FIG. 5  is a diagram of a possible embodiment under the present disclosure. 
         FIG. 6  is a flow chart diagram of a possible method embodiment under the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     When aluminum components are used to replace copper ones in HVAC systems, the load carrying capacities of the components may change, leading to charge imbalance issues and high pressure. A typical HVAC system comprises both an indoor and an outdoor heat exchanger. Copper has historically been the preferred material for heat exchanger tubes. Aluminum is being used more and more frequently however. The move from copper to aluminum may be for environmental, cost, or other reasons. Typically, the same material is used for both the indoor and outdoor heat exchangers. Sometimes however, existing HVAC systems are repaired or updated by replacing a copper component with an aluminum one, or another material switch. When an aluminum coil replaces a copper coil an installer usually keeps the same physical size due to pre-existing space constraints. Because aluminum is weaker than copper, a similarly sized (same outside diameter) aluminum heat exchanger tube will have a smaller inner diameter than a copper tube. This is because the aluminum walls must be made thicker to provide an equivalent amount of strength. But this means that the aluminum coil can circulate less refrigerant than a similar copper coil. One consequence of combining, for example, an indoor aluminum coil with an outdoor copper coil can be a charge imbalance, i.e. the heating and cooling modes require different amounts of refrigerant. During heating operations there may be too much refrigerant passing through the indoor aluminum coil creating high pressure. The removal of refrigerant can help relieve the pressure. But when the system is switched to cooling mode the larger amount of refrigerant is needed to achieve greater heat transfer and provide sufficient cooling to the conditioned space. Similar problems can occur when space constraints force an indoor or outdoor coil to be smaller than the other, even if both coils are made of the same material. 
     Embodiments under the present disclosure can help solve the charge imbalance problems described above. A possible embodiment can be viewed referring to  FIG. 1 . HVAC system  100  comprises an indoor heat exchanger or coil  110 , a compressor  120 , an outdoor coil  130 , and an expansion device  140 . Typically an indoor unit  150  comprises expansion device  140  and inside heat exchanger  110 . Outdoor unit  160  typically comprises outside heat exchanger  130  and compressor  120 . As displayed here, during a cooling mode the refrigerant flows in a counter-clockwise direction. During cooling mode the indoor coil  110  will comprise an evaporator. Refrigerant will flow from the evaporator, through the compressor  120 , and to the outdoor coil that is serving as a condenser. Refrigerant leaving the outdoor coil will enter liquid line  133 , pass through an expansion device  140 , and return to the evaporator. During heating operations the refrigerant will reverse course and flow clockwise. The indoor coil  110  will become a condenser and the outdoor coil  130  will become an evaporator. Fans/blowers  112 ,  132  can provide airflow across heat exchangers  110 ,  130 . 
     During heating operations it may be desirable to remove refrigerant from the system  100 . Compensator  170  comprises a connection to liquid line  133 . During heating operations, high pressure drives an amount of refrigerant into compensator  170 , relieving the pressure. During cooling operations, it is desired to retrieve the extra refrigerant within compensator  170  so that the cooling demand can be met. This is achieved by applying heat to compensator  170  via heater  172 . Heater  172  can comprise a belly band heater similar to compressor crank case heaters, or another appropriate type of heater. Heater  172  can be coupled to a controller/processor/electronics  135  in the outdoor unit  160 . Optionally, the heater  172  can be coupled to another controller/processor/server/electronics  180 , such as a thermostat. When the controller  135  receives a command to begin cooling operations, then the heater  172  can receive a signal to turn on. Turning on heater  172  causes the temperature within compensator  170  to rise higher than the temperature of the indoor coil  110 . Refrigerant migrates to cooler locations and refrigerant will therefore leave compensator  170 . As refrigerant circulates in the system it will pass by the inlet to the compensator  170  and migrate toward the indoor coil  110  (because the indoor coil is lower temperature than the compensator). The preferred location for plumbing the compensator  170  into the refrigerant line is at the liquid line  133 , or anywhere between the outdoor heat exchanger  130  and the expansion device  140 . 
     A possible retrofit embodiment can be seen in  FIG. 2 . System  200  comprises a building  210  and associated indoor  220  and outdoor  240  units of an HVAC system. Outdoor unit  240  may have been preexisting and indoor unit  220 , or the indoor coil, may be newly installed to replace an old unit. The new indoor unit  220  may comprise an aluminum coil, causing charge imbalance issues. To remedy this, compensator  250  can be installed. Compensator  250  comprises a plumbed connection  255  to the liquid line from the outdoor unit  240 . Electrical connection  260  connects a heater  265  on compensator  250  to electronics or a controller in the outdoor unit  240 . 
     A preferred embodiment under the present disclosure comprises a retrofit solution. The teachings could also be implemented in newly-built systems. Solutions under the present disclosure will be particularly helpful when aluminum coils are used to replace copper coils in indoor units. Other embodiments under the present disclosure can be retrofit onto HVAC systems undergoing pressure or charge imbalance issues, even if both indoor and outdoor coils are built from the same materials. Even when copper coils replace copper coils, operating conditions may affect the new coil size or geometry, leading to possible charge imbalance issues. Sometimes an outdoor unit has to be replaced instead of the indoor unit. In these situations and others, the present disclosure can provide help in solving charge imbalances. 
       FIG. 3  displays a possible method embodiment  300  for constructing a compensator under the present disclosure. At  310 , a compensator tank is provided. At  320 , a heater is coupled to the compensator tank. At  330 , the compensator is plumbed into the liquid line of an outdoor heat exchanger. At  340 , the heater is coupled to a controller, such that when the HVAC system is in cooling mode then the heater is turned on. 
       FIG. 4  displays another possible method embodiment  400  for constructing an HVAC system under the present disclosure. At  410 , an indoor heat exchanger, outdoor heat exchanger, reversing valve, compressor, and expansion valve are provided. At  420 , a refrigerant flow path is provided for connecting the indoor heat exchanger, outdoor heat exchanger, reversing valve, compressor, and expansion valve. At  430 , a compensator tank is provided. At  440 , a heater is coupled to the compensator tank. At  450 , a fluid coupling is provided from the compensator to the liquid line of the outdoor heat exchanger. At  460 , the heater is coupled to a processor operable to turn on the heater when the HVAC system is in cooling mode. 
       FIG. 5  displays another possible system embodiment under the present disclosure.  FIG. 5  is similar to  FIG. 1  but shows a reversing valve in more detail. System  500  comprises an indoor heat exchanger  510 , compressor  520 , outdoor heat exchanger  530 , and expansion valve  540 . Fans  512 ,  532  provide airflow over the heat exchangers. Reversing valve  550  is disposed between the heat exchangers  510 ,  530  and is fluidly coupled with compressor  520 . A compensator  570 , heater  572 , and controller  535  are shown in a manner similar to  FIG. 1 . The direction of refrigerant flow in cooling and heating modes is shown in  FIG. 5 . Reversing valve  550  can change the direction of refrigerant flow, going from cooling mode to heating mode and vice versa. Valve  550  can comprise a connection to a thermostat/controller/electronics  551  that direct the flow of refrigerant. Heater  572 , controller  535  can alternatively comprise a connection to thermostat/controller/electronics  551 . 
     Embodiments under the present disclosure can comprise a variety of heat exchanger types, such as tube and fin, microchannel, and others. Other components such as expansion devices, compressors, reversing valves, and others, are not limited to one type of component but can take a variety of forms known to those skilled in the art. 
       FIG. 6  displays another possible method embodiment  600  under the present disclosure. Method  600  comprises a process for operating an HVAC system and/or alleviating charge imbalance in an HVAC system that is operable in both a cooling mode and a heating mode. At  610  a refrigerant is circulated through an indoor heat exchanger, an outdoor heat exchanger, a compressor and an expansion device. At  620  a compensator is coupled to a liquid line of the outdoor heat exchanger. At  630 , an amount of refrigerant is directed into the compensator when the HVAC system is in a heating mode. At  640 , the amount of refrigerant is heated when the HVAC system is in a cooling mode in order to cause the amount of refrigerant to migrate out of the compensator. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.