Abstract:
An automatic self-modulation capacity compressor for an HVAC&amp;R system is disclosed. The system includes a housing, a compressor, a motor, and a pressure sensitive control valve. The HVAC&amp;R system further comprises an expander and a condenser. In the open position, the control valve permits a portion of the pressurized gasses from the compressor to escape, creating a partial capacity compressor within the system. Once a predetermined set point pressure differential is met, the control valve moves to the closed position, where all of the pressurized gasses within the compressor are provided to the system, thereby creating a full capacity compressor. Once the compressor is operating in full capacity, the compressor remains in full capacity mode until the demands of the system are met and the compressor shuts down. Upon restart, the compressor operates in partial capacity until the predetermined set point pressure is met once again and the compressor begins operating in full capacity.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to providing capacity modulation for compressors. More particularly, the present invention relates to automatic capacity modulation in a compressor without any need for external controls. 
         [0002]    Frequently, compressors in heating, ventilation and air conditioning (HVAC) systems are limited to a single output capacity. One problem with the compressor being limited to a single output capacity is that the compressor, especially reciprocating compressors, can produce excess capacity at reduced outdoor ambient temperatures. The excess capacity produced by the compressor adversely affects any system incorporating the compressor during SEER (Seasonal Energy Efficiency Rating) testing and in subsequent operation of the system. 
         [0003]    One attempt to solve the excess capacity problem in a compressor is discussed in U.S. Pat. No. 6,663,358, wherein an internal valve in the compressor is adjusted in response to operating conditions to effect a change in the capacity of the compressor. The output capacity of the compressor is controlled by a valve and biasing member within the motor cavity that responds to the pressure of the gasses. As the pressure builds in the compressor in response to an increasing outdoor temperature, the valve moves to the second position allowing the compressor to operate at the second, higher, output capacity. Once the demand subsides and the pressure drops, the valve then returns to the first position and operates at the first capacity. While this solution allows for the modulation of compressor capacity, the toggle effect between the two operational capacities during operation results in energy and efficiency losses and low reliability of the system. 
         [0004]    Therefore, what is needed is a cost-effective, efficient and easily implemented system to provide for reduced compressor capacity at reduced outdoor ambient temperatures, but that can also provide full compressor capacity at higher outdoor ambient temperatures. 
       SUMMARY OF THE INVENTION 
       [0005]    A method for modulating capacity in a compressor for a heating, ventilation, air conditioning and refrigeration (HVAC&amp;R) system includes providing a control valve having a first position and a second position and configured and disposed to permit full compressor capacity in response to the control valve being in the second position and being configured to permit partial compressor capacity in response to the control valve being in the first position. The method also includes positioning the control valve in the first position upon start up of the compressor, operating the compressor at partial capacity in response to the control valve being in the first position and measuring a pressure differential in the compressor. In addition, the method includes comparing the measured pressure differential to a predetermined pressure differential set point switching the control valve to the second position to operate the compressor at full capacity in response to the measured pressure differential being equal to or greater than the predetermined pressure differential set point and operating the compressor at full capacity in response to the control valve being in the second position until a shut down of the compressor. 
         [0006]    A compressor for an HVAC&amp;R system includes a housing having an inlet and an outlet, a compression mechanism being configured to receive uncompressed fluid from the inlet at a first pressure and provide compressed fluid to the outlet at a second pressure higher than the first pressure and a pressure control valve having a first position and a second position and being configured to be in the first position on startup of the compressor. The pressure control valve is also configured to switch to the second position in response to the difference between the first pressure and the second pressure being greater than a predetermined pressure differential set point, and to remain at the second position until the compressor shuts down. 
         [0007]    An HVAC&amp;R system includes a compressor, a condenser and an evaporator connected in a closed refrigeration loop. The system also includes a temperature control system configured to receive a set point temperature and a corresponding measured temperature for an enclosed space; and the compressor is configured to receive a fluid at an inlet at a first pressure and discharge fluid at a second pressure higher than the first pressure. In addition, the compressor includes a pressure control valve having a first predetermined position and a second predetermined position. The pressure control valve is configured to be in the first position on startup of the compressor and to switch to the second position in response to the difference between the first pressure and the second pressure being greater than the predetermined set point pressure, and to remain at the second predetermined position until the compressor shuts down. 
         [0008]    One advantage of the present invention is increased system performance, efficiency, and capacity control at reduced outdoor temperatures in both heating and cooling modes of operation. 
         [0009]    Still another advantage of the present invention is increased reliability of the system. 
         [0010]    Another advantage of the invention is that the system shuts down once a user-selected set point temperature is satisfied, thereby conserving energy. 
         [0011]    Another advantage of the present invention is that the capacity modulation is automatic without need for external control. 
         [0012]    A further advantage of the present invention is that the self-modulation from partial to full capacity occurs almost immediately, which allows the compressor to operate at partial capacity until the need arises for full capacity, which conserves energy and creates a more efficient compressor. 
         [0013]    Accordingly, the present invention is directed to improved compressors for providing automatic capacity modulation. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIGS. 1 and 2  illustrate schematically a refrigeration system that can be used with the present invention. 
           [0015]      FIG. 3  illustrates a flow chart of one embodiment of the capacity control process of the present invention. 
           [0016]      FIG. 4  illustrates the control valve in the first position. 
           [0017]      FIG. 5  illustrates the control valve in the second position. 
       
    
    
       [0018]    Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    As shown in  FIGS. 1 and 2 , a heating, ventilation, air conditioning and refrigeration (HVAC&amp;R) system  300  includes a compressor  302 , a condenser arrangement  304 , and an evaporator arrangement  306  ( FIG. 1 ) or a compressor  302 , a reversing valve arrangement  350 , an indoor unit  354  and an outdoor unit  352  ( FIG. 2 ). The system  300  can be operated as an air conditioning only system, where the evaporator arrangement  306  is preferably located indoors, i.e., as and indoor unit  354 , to provide cooling to the indoor air and the condenser arrangement  304  is preferably located outdoors, i.e., as an outdoor unit  352 , to discharge heat to the outdoor air. The system can also be operated as a heat pump system with the inclusion of the reversing valve arrangement  350  to control and direct the flow of refrigerant from the compressor  302 . When the heat pump is operated in an air conditioning mode, the reversing valve arrangement  350  is controlled for refrigerant flow as described above for an air conditioning system. However, when the heat pump is operated in a heating mode, the flow of the refrigerant is in the opposite direction from the air conditioning mode, and the condenser arrangement  304  is preferably located indoors, i.e., as an indoor unit  354 , to provide heating of the indoor air and the evaporator arrangement  306 , i.e., as an outdoor unit  352 , is preferably located outdoors to absorb heat from the outdoor air. 
         [0020]    The compressor  302  compresses a refrigerant vapor and delivers the vapor to the condenser  304  through a discharge line (and the reversing valve arrangement  350  if operated as a heat pump). The compressor  302  is preferably a reciprocating compressor. However, it is to be understood that the compressor  302  can be any suitable type of compressor, e.g., scroll compressor, rotary compressor, screw compressor, swag link compressor, turbine compressor, or any other suitable compressor. The refrigerant vapor delivered by the compressor  302  to the condenser  304  enters into a heat exchange relationship with a fluid, e.g., air or water, but preferably air, and undergoes a phase change to a refrigerant liquid as a result of the heat exchange relationship with the fluid. The condensed liquid refrigerant from condenser  304  flows through an expansion device (not shown) to the evaporator  306 . 
         [0021]    The condensed liquid refrigerant delivered to the evaporator  306  enters into a heat exchange relationship with a fluid, e.g., air or water, but preferably air, and undergoes a phase change to a refrigerant vapor as a result of the heat exchange relationship with the fluid. The vapor refrigerant in the evaporator  306  exits the evaporator  306  and returns to the compressor  302  by a suction line to complete the cycle (and the reversing valve arrangement  350  if operated as a heat pump). It is to be understood that any suitable configuration of condenser  304  and evaporator  306  can be used in the system  300 , provided that the appropriate phase change of the refrigerant in the condenser  304  and evaporator  306  is obtained. The HVAC or refrigeration system  300  can include many other features that are not shown in  FIGS. 1 and 2 . These features have been purposely omitted to simplify the drawing for ease of illustration. 
         [0022]    Referring now to  FIG. 3 , in a preferred embodiment of the invention, operation of the self-modulation compressor in the HVAC&amp;R system  300  involves several steps. To begin, in Step  402 , the temperature in an indoor space is measured. Next, the measured temperature is compared to a predetermined temperature set point in Step  404 . If the measured temperature satisfies the predetermined temperature set point requirement, the control returns to Step  402 . Otherwise, the measured temperature does not satisfy the predetermined temperature set point requirement in Step  404 , i.e., the measured temperature is less than the predetermined temperature set point if this system is in a heating mode of operation or the measured temperature is greater than the predetermined temperature set point when the system is in a cooling mode of operation. In other words, for a cooling system, this occurs when the temperature of a space rises above the predetermined temperature set point. For a heating system, this occurs when the temperature of a space falls below the predetermined temperature set point. 
         [0023]    If the temperature set point is not satisfied in Step  404 , the control proceeds to Step  408 , where the compressor is started (if necessary) and the control valve is in the open position to operate the compressor at partial or reduced capacity. Preferably, the partial capacity of the compressor can range from about 70% of full capacity to about 90% of full capacity. As the compressor operates, the pressure within the compressor housing builds if the heating or cooling demand is not being satisfied, thereby creating a need for higher capacity from the compressor. In Step  410 , the pressure in the compressor is compared to a predetermined set point of pressure differential between the suction inlet and the discharge outlet of the compressor. In an alternate embodiment, the pressure in the compressor is compared to a predetermined pressure set point, e.g., suction pressure set point or discharge pressure set point, rather than the differential pressure of the suction inlet and discharge outlet of the compressor. If the pressure differential in the compressor is less than the predetermined pressure differential set point, the control returns to Step  408  to continue operating at partial capacity. Otherwise, the control proceeds to Step  412  to operate the compressor at full capacity. 
         [0024]    In a preferred embodiment, the pressure control valve within the compressor housing is calibrated to perform the comparison Step  410  and to close from the open position to operate the compressor at full capacity when the pressure differential of the compressor reaches the predetermined pressure differential set point. When the pressure differential set point is reached, the control valve activates and closes, which generates full capacity in the compressor. The compressor operates at full capacity until the predetermined temperature set point is reached in Step  414 . If the predetermined temperature set point is not satisfied in Step  414 , the control returns to Step  412  to continue operating the compressor at full capacity. However, if the predetermined temperature set point has been satisfied in Step  414 , the compressor is shut down at Step  406  and the process begins again at Step  402 . Once the compressor is operating at full capacity, the control valve prevents any switching to the lower capacity until after the compressor has been shut down. 
         [0025]    In an alternate embodiment of the invention, the control valve can be arranged to permit operation of the compressor in full capacity mode when the control valve is in the open position and in partial capacity mode when the control valve is in the closed position. In addition, the control valve can be located in any suitable location within the compressor to control the capacity during operation. 
         [0026]    The control valve is activated only by pressure levels within the compressor regardless of the temperature levels within the compressor or surrounding the system. The transition between partial and full capacity occurs almost instantaneously with the control valve moving from the open to the closed position. The almost instantaneous switch from the open to the closed position essentially eliminates a transitional range where the valve is neither fully open nor fully closed. 
         [0027]      FIGS. 4 and 5  illustrate one embodiment of the pressure control valve configuration of the present invention.  FIG. 4  illustrates the pressure control valve  404  in the open position. The pressure control valve  404  is in the open position when the force exerted by the discharge pressure is less than the combined force of the biasing force of the biasing member  470  plus the force exerted by the suction pressure. A suction pressure channel  483  connects the suction side of the compressor to the low-pressure side of the valve  404 . The valve member  464  being in the first, open, position permits flow through the opening  484  and the flow passage  454  to the suction channel  328 . When the valve member  464  is in the first position opening the flow passage  454 , the reciprocating compressor  416  operates in a reduced capacity mode. In this mode, the fluid in the compression chamber  332  flows back through the opening  484  into flow passage  454 , and even into the suction channel  328  in the manifold. The opening  484  and flow passage  454  are in effect combined to provide a reexpansion area in fluid communication with the compression chamber  332 . In effect, the fluid in the compression chamber  332  is not compressed beyond the suction pressure, until the reciprocating piston travels beyond the opening  484 . 
         [0028]    As illustrated in  FIG. 5 , when the discharge pressure reaches a predetermined level, the force exerted by the discharge pressure overcomes the combined force, i.e., the biasing force of the biasing member  470  plus the force exerted by the suction pressure channel  483 , and moves the valve member  464  to the second position and the stem portion  465  prevents flow through the flow passage  454  (and possibly through suction pressure channel  483 ). When the valve member  464  is in the second position preventing flow through the flow passage  454 , the reciprocating compressor  416  operates in a full capacity mode because no fluid exits the compression chamber  332  through the flow passage  454 . In other words, the full stroke length of the reciprocating piston  336  is utilized to compress the fluid entering and exiting the compression chamber  332  through the inlet  340  and outlet  342 . 
         [0029]    Thus, by adjusting the location of the opening  484  relative to the bottom dead center position of the reciprocating piston  336 , the reciprocating compressor  416  achieves a desired capacity modulation. Also, by adjusting the biasing force exerted by the biasing member  470 , the reciprocating compressor  416  controls the discharge pressure at which valve member  464  prevents flow through the flow passage  454 . Accordingly, the system efficiency of an air-conditioning or refrigeration system can be improved by optimizing the combination of the degree of capacity modulation and the pressure at which the valve member  464  prevents flow through the flow passage  454 . Preferably, the location of the opening  484  is adjusted to obtain the desired reduced capacity percentage of full capacity. The valve member may be any suitable valve configuration or multiple valve configuration. 
         [0030]    An alternate embodiment of the invention includes a system with no suction pressure channel  483  connected to the low-pressure side of the valve member  404 . This embodiment allows for a transitional period between the open position and the closed position of the valve member  404 . In one embodiment, the compressor pressure differential is at 0 psi on start-up and builds pressure in the compressor while operating in a reduced capacity mode. Once the compressor reaches the lower limit (e.g., 114 psi) of the predetermined differential pressure range, the control valve begins to close and reaches the fully closed position at the upper limit (e.g., 129 psi) of the predetermined differential pressure range. The pressure in the compressor continues to build until a full capacity steady state differential pressure (e.g., 145 psi) is obtained in the compressor. This transitional period exists during the time it takes the valve member to switch between the open position and the closed position. 
         [0031]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.