Abstract:
A heat pump is provided with a component that has a pulse width modulation control to adjust system capacity. Thus, by utilizing a pulse width modulation technique to control this component, the present invention is able to closely tailor the delivered capacity of the heat pump to that which is demanded, without cycling the unit. In one embodiment, the component has a suction pulse width modulation valve. In another embodiment, the component which is modulated is the compressor pump unit, and, in particular, a pair of scroll members that are allowed to move into and out of contact with each other. The pulse width modulation control device can also be utilized in combination with a heat pump having an economizer function and/or an un-loader function.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to a heat pump that is operable in both a cooling and a heating mode, and wherein at least one component is controlled by pulse width modulation techniques to vary the capacity of the heat pump. 
         [0002]    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. 
         [0003]    The above description is of a refrigerant system being utilized in the 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 exchanges 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 design, with the valve located downstream of the compressor discharge port. The four-way reversing valve selectively directs the refrigerant flow through the indoor or outdoor heat exchanger when the system is in the heating or cooling mode of operation, respectively. Furthermore, if the expansion device cannot handle the reversed flow, than, for example, a pair of expansion devices, each along with a check valve, can be employed instead. 
         [0004]    The operation and control of refrigerant systems faces many challenges. One challenge is that the capacity for either cooling or heating demanded by an environment to be conditioned can vary. It would be desirable to only provide the required capacity, as the energy efficiency and comfort are then improved as the amount of unit cycling is reduced or eliminated. However, heat pumps have typically not been provided with the features assuring sufficient variability as may be desirable, in order to continuously match the required capacity to the capacity delivered by the unit without frequent cycling. 
         [0005]    In air conditioning systems, a technique known as a pulse width modulation control has been provided. In this technique, various components are provided with a pulse width modulation control that rapidly cycles the component “on” and “off” to change the capacity. As an example, a suction pulse width modulation valve may be rapidly opened and closed to restrict the amount of refrigerant delivered to a compressor. While such pulse width modulation controls provide sufficient performance variability for air conditioning systems, they have not been incorporated into heat pumps to date. 
       SUMMARY OF THE INVENTION 
       [0006]    In a disclosed embodiment of this invention, a four-way reversing valve selectively controls the flow of refrigerant from a compressor discharge to either an outdoor heat exchanger in a cooling mode, or to an indoor heat exchanger in a heating mode. As explained above, the refrigerant flows through a complete cycle under either mode, and returns to the compressor. The refrigerant flow, on its way back to the compressor, once again, passes through the four-way reversing valve. 
         [0007]    To provide greater variability in capacity delivered by the heat pump system to match external load demands, at least one component within the heat pump system is equipped with a pulse width modulation control. In a disclosed embodiment, this component may be a suction pulse width modulation valve controlling the amount of refrigerant flowing through a suction line to the compressor. In another embodiment, the component which is provided with a pulse width modulation control may be a compressor pump unit. In one disclosed example, in a scroll compressor, a pair of scroll members is selectively held into contact, or allowed to move away from each other in a pulse width modulated manner, thus controlling the amount of refrigerant compressed by the compressor and delivered to other system components. 
         [0008]    By utilizing the pulse width modulation control, the present invention is able to tailor the delivered capacity to meet desired capacity requirements for the refrigerant heat pump system. In these arrangements, heat pumps are provided that are better able to match the delivered system capacity and the conditioned environment demanded capacity (and its latent and sensible components) either in the heating or cooling mode of operation. 
         [0009]    In other embodiments, an economizer cycle is incorporated into the heat pump schematic to provide additional capacity control. As is known, the economizer cycle essentially taps a portion of the refrigerant flow through an auxiliary expansion device. That portion of the refrigerant flow is passed through an economizer heat exchanger along with the main refrigerant flow. Heat is exchanged between the two refrigerant flows, with the tapped refrigerant cooling the main refrigerant. The tapped refrigerant exits the economizer heat exchanger typically in a vapor state. This vapor is returned to the compressor at some intermediate point in the compression process. The main refrigerant flow passes to a main expansion device and then to a downstream heat exchanger (evaporator), having a greater cooling potential due to additional cooling obtained by passing through the economizer heat exchanger. Various embodiments for configuring and incorporating the economizer cycle in a heat pump system are disclosed in this invention. 
         [0010]    The present invention thus allows several additional steps of capacity control. In one embodiment, an unloader function allows for at least a portion of the partially compressed refrigerant to be diverted to the compressor suction to reduce capacity. 
         [0011]    The several embodiments disclosed in this application thus allow the use of full capacity with pulse width modulation. The control also has access to the unloader function and the economizer function in combination with a modulation of one of the components to further control system capacity. 
         [0012]    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  
         [0013]      FIG. 1A  is a schematic of a first view. 
           [0014]      FIG. 1B  shows an alternative method. 
           [0015]      FIG. 2  shows an alternative schematic. 
           [0016]      FIG. 3  shows an alternative schematic. 
           [0017]      FIG. 4  shows an alternative schematic. 
           [0018]      FIG. 5  shows an alternative for a standard economizer heat exchanger. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]      FIG. 1A  shows a heat pump refrigerant system  20  incorporating a compressor  22  having a discharge line  23  supplying a compressed refrigerant to a four-way reversing valve  26 . The four-way reversing valve  26  selectively communicates the refrigerant from the discharge line  23  either to an outdoor heat exchanger  24 , when the system is operating in a cooling mode, or to an indoor heat exchanger  30 , when the system is operating in a heating mode. In either case, the refrigerant passes from the heat exchanger it first encounters after leaving the compressor to a main expansion device  28 . From the main expansion device  28 , the refrigerant passes through to the second heat exchanger, and back to the four-way reversing valve  26 . The four-way reversing valve  26  routes the refrigerant into a suction line  31  leading back to the compressor  22 . This is a very simplified schematic for a heat pump system. It should be understood that much more complex systems are feasible. A pulse width modulation valve  40  is positioned on the suction line  31 . As is known, the pulse width modulation suction valve  40  can be rapidly cycled to control the amount of refrigerant flowing through the compressor. In this manner, the capacity of the refrigerant system can be controlled. As mentioned, such controls are known for use in the air conditioning systems, but have not been utilized in the heat pumps. By incorporating this type of control into the heat pump system, the capacity (and power) of the heat pump in either heating or cooling mode of operation can be precisely tailored to a demanded capacity in a very efficient manner. Typically, cycling times on the order of 3 seconds to 30 seconds are utilized. 
         [0020]      FIG. 1B  shows an embodiment  301 , schematically. It is known that the orbiting scroll member  302  and the non-orbiting scroll member  304  of a scroll compressor may be biased together by means of gas pressure in a chamber  306 . Opening and closing the valve  310  can control pressure in the chamber  306 . As shown, the valve  310  communicates via a refrigerant line  308  with another pressure source that is at different pressure than pressure in the chamber  306 , when the valve  310  is closed. When the pressure in the chamber  306  is reduced below a certain level, the scroll members will separate from each other, and the amount of refrigerant pumped by the compressor is then reduced. When the pressure in the chamber  306  is increased above certain level, the scrolls will come into contact with each other, and then the normal compression process will resume. The valve  310  can be controlled by a pulse width modulation control  312 . Thus, by modulating the pressure in the chamber  306 , the two scroll members  302  and  304  can be allowed to periodically move away from, and come into contact with, each other. It should be noted that the schematic shown in  FIG. 1B  is presented for an illustration purpose only. For example, instead of allowing the scroll  304  to move axially in and out of contact with the scroll  302 , the scroll  302  can be allowed to move axially while the scroll  304  remains essentially stationary in the axial direction. Further, the valve  312  can be located internal or external to the compressor. 
         [0021]    The control  42  (or  312 ) is operated to provide variation in the amount of refrigerant delivered by the compressor based upon any number of factors. As the capacity demand on the system  20  changes, then the pulse width modulation control can change the amount of refrigerant flowing through the compressor. Moreover, it may well be that less refrigerant would be desirably passed through the compressor in one of the cooling or heating operating modes. Again, the inventive control easily allows such a modification. In addition, as will be discussed below, the unloader bypass feature (if available) provides further variation in the capacity of the entire system, and the ability to better tailor the control to either the heating or cooling modes of operation. 
         [0022]      FIG. 2  shows another embodiment system  100  wherein a second routing valve  102  is positioned to selectively route refrigerant from the heat exchangers  24  and  30  either into a main liquid line  103 . Refrigerant flows through the routing valve  102  from either of the heat exchangers  24  or  30  into the liquid line  103 . In both heating and cooling modes of operation, the refrigerant passes from the heat exchanger  30  or the heat exchanger  24  to the liquid line  103  initially, through an economizer heat exchanger  104  and then through the main expansion device  28 . This refrigerant then flows back through the routing valve  102  downstream to the heat exchanger  24  or the heat exchanger  30  accordingly. 
         [0023]    As is known, a tap line  106  selectively taps a portion of the refrigerant from the liquid line  103  and passes that tapped refrigerant to an economizer expansion device  108 . This refrigerant flows through the economizer heat exchanger  104  and cools the main refrigerant flow. A vapor injection line  110  returns the tapped refrigerant back to an intermediate compression point in the compressor  22 . While the flow of the tapped refrigerant and the main refrigerant flow through the economizer heat exchanger  104  are shown in the same direction, in practice, it is typically preferable that they be in counter-flow relationship. However, for simplicity of illustration, they are shown flowing in the same direction. Also, it has to be noted that the auxiliary expansion device  108  and the economizer flow diversion point can be located downstream of the economizer heat exchanger  104 . 
         [0024]    As is known, an economizer function allows the provision of increased capacity (and efficiency) by additional cooling of the refrigerant in the main liquid line. Again, the pulse width modulation valve  40  positioned on a suction line  31  may be controlled using pulse width modulation techniques to tailor the provided capacity with the demanded capacity. The economizer feature, along with the optional unloader feature, and the pulse width modulation control, allows the system to operate with minimal amount of cycling to meet particular cooling/heating capacity demands. 
         [0025]      FIG. 3  shows another embodiment, wherein the economizer function is achieved somewhat differently. In the economized cooling mode, tapped refrigerant having passed through a cooling mode economizer expansion device  204  located on a tap line is returned through a vapor injection line  110  to the compressor  22 . The refrigerant from the main liquid line passes through a cooling mode economizer heat exchanger  202 , the main expansion device  28 , and a heating mode economizer heat exchanger  206  to the indoor heat exchanger  30  and back to the compressor  22 . Since the tapped refrigerant would not be flowing through the heating mode economizer expansion device  208  in this mode of operation, there is no heat exchanged in the heating mode economizer heat exchanger  206 . 
         [0026]    When the system  200  operates in the economized heating mode, the refrigerant flow direction throughout the system is essentially reversed, and the tapped refrigerant flows through the heating mode economizer heat exchanger  206  but not through the cooling mode economizer heat exchanger  202 . A control controls the economizer expansion devices  204  and  208  such that they also provide a shutoff valve function. When the system  200  is operating in a cooling mode, the expansion device  204  is open and the expansion device  208  is closed. When the system  200  operates in a heating mode, the position of the valves is reversed. Once again, similar to the  FIG. 2  embodiment, the economizer function along with the suction pulse width modulation valve  40  controlled by the control  42  allows for precise matching of the capacity provided by the heat pump system in either heating or cooling mode of operation to the demanded capacity. 
         [0027]      FIG. 4  shows another embodiment  220  wherein a single economizer heat exchanger  230  is provided. A pair of main expansion devices  224  is provided on each side of the economizer heat exchanger. A bypass line  202  and a check valve  226  are also provided around each main expansion device  224 . Now, the refrigerant will pass through one of the selective main expansion devices  224  depending on the mode of operation (cooling or heating) and the refrigerant flow direction, since the flow of the refrigerant around this expansion device will be blocked by the respective check valve  226 . At the same time, the refrigerant flow will be allowed around another expansion device but not through it. An economizer expansion device  228  and heat exchanger  230  operate in a manner similar to the  FIG. 3  embodiment, with the only difference that the economizer flow is tapped either upstream or downstream of the economizer heat exchanger  230 . Again, the valve  40  positioned on the suction line  31  and controlled by the control  42  using pulse width modulation techniques, along with the economizer function, allows tailoring the provided capacity to the demanded capacity. 
         [0028]      FIG. 5  shows an embodiment  260  wherein the economizer heat exchanger is replaced with a flash tank  262 . As is known, an inlet line  264  is the main liquid line. It passes into the flash tank  262 , where a refrigerant liquid  266  is separated away from a vapor. The vapor is returned through the vapor injection line  268  back to the compressor intermediate port. A return liquid line  270  passes downstream to a heat exchanger or additional expansion device. 
         [0029]    In each of the above embodiments, the unloader function may also be incorporated as shown in the  FIG. 2  embodiment. 
         [0030]    The present invention thus provides the ability to not only control capacity with an unloader function, and the economizer function, as known. However, the present invention also provides the increased ability to control capacity by operating either the suction pulse width modulation valve  40 , or modulating the scroll members by separating them from each other, to control the amount of refrigerant pumped by the compressor (see  FIG. 1B ) to further control the delivered capacity. A worker of ordinary skill in the art would recognize when such control over capacity would be desirable. By closely matching the delivered capacity and required capacity either in cooling or heating mode of operation, the invention allows reduction in system “on” and “off” cycling and thus enhance its performance and improve comfort in the conditioned space. Normally, the pulse width modulation duty of the refrigerant system component is rapid enough not to cause substantial temperature fluctuations in the conditioned environment. For typical applications, the pulse width modulation cycle is between 3 and 30 seconds. 
         [0031]    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.