Patent Publication Number: US-7584625-B2

Title: Compressor capacity modulation system and method

Description:
FIELD 
     The present teachings relate to compressors and, more particularly, to a capacity-modulated compressor. 
     BACKGROUND 
     Compressors may be used in a wide variety of industrial and residential applications to circulate refrigerant within a refrigeration, heat pump, HVAC, or chiller system (generically “refrigeration systems”) to provide a desired heating or cooling effect. In any of the foregoing applications, the compressor may be used in conjunction with a capacity modulation system that adjusts a capacity of the compressor based on system demand. 
     Conventional capacity modulation systems selectively adjust the ability of the compressor to circulate refrigerant through the refrigeration system and therefore adjust the ability of the refrigeration system to absorb and reject heat. Conventional capacity modulation systems may therefore be used to adjust a capacity of the refrigeration system based on a required heating and/or cooling demand. Regulating compressor capacity based on system demand improves the efficiency of the compressor as only that amount of energy that is required is consumed. 
     Conventional capacity modulation systems may adjust compressor capacity by regulating a pressure within a compressor housing to prevent operation of a compression chamber disposed within the housing. For example, in a scroll compressor application, a conventional capacity modulation system may permit a non-orbiting scroll member to separate from an orbiting scroll member. Such separation creates a leak path between the non-orbiting scroll member and the orbiting scroll member and therefore reduces the ability of the compressor to compress refrigerant. 
     Leak paths may be accomplished by exposing the non-orbiting scroll member to low-pressure vapor (i.e., vapor at suction pressure) or to intermediate-pressure vapor or high-pressure vapor (i.e., vapor at discharge presue) through actuation of a valve. Pulse width modulation may be used to cycle the valve between an open state and a closed state to achieve a desired capacity of the compressor. Typically, the valve is cycled at a rate such that the valve is closed when the compressor is loaded and is open when the compressor is unloading. 
     During loading of the compressor, suction pressure at an inlet of the compressor steadily decreases, while during unloading of the compressor, suction pressure steadily increases. The decrease in suction pressure over time results in a reduction in capacity as the compressor is required to consume additional energy to compress the low-pressure vapor to discharge pressure when compared to the energy consumed in compressing vapor at a higher pressure (i.e., earlier during loading of the compressor). Therefore, the efficiency of the compressor decreases with decreasing suction pressure. 
     SUMMARY 
     A compressor system includes a compressor having an inlet, a first conduit fluidly coupled to the inlet, an accumulator fluidly coupled to the inlet by a second conduit, and a first valve disposed in the second conduit that prevents fluid communication between the accumulator and the inlet in a closed state and permits fluid communication between the accumulator and the inlet in an open state. 
     The first valve permits communication between the accumulator and the inlet of the compressor during loading of the compressor to increase the pressure of vapor received by the compressor generally at the end of an loading cycle (i.e., when vapor pressure is lowest). The increase in vapor pressure allows the compressor to consume less energy in compressing the vapor to discharge pressure and therefore increases the capacity and efficiency of the system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present teachings will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a schematic view of a heat pump or cooling system incorporating a capacity modulation system including a first capacity modulation circuit in accordance with the principles of the present teachings; 
         FIG. 1A  is a schematic view of a second capacity modulation circuit for use with the capacity modulation system of  FIG. 1 ; 
         FIG. 2  is a waveform diagram illustrating variable duty cycle signals of a first valve and a second valve for use with the capacity modulation system of  FIG. 1 ; and 
         FIG. 3  is comparison of suction pressure versus time for a conventional capacity modulation system and a capacity modulation system of the present teachings. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the drawings, a capacity modulation system  10  is provided for use with a compressor  12 . The capacity modulation system  10  selectively loads and unloads the compressor  12  to tailor compressor capacity with system demand. The compressor  12  may be a scroll compressor incorporating an intermediate-pressure biasing system as shown in Assignee&#39;s U.S. Pat. No. 6,821,092 or may be a scroll compressor incorporating a discharge-pressure biasing system as shown in Assignee&#39;s U.S. Pat. No. 6,213,731, the disclosures of which are hereby incorporated herein by reference. While a scroll compressor is described in association with the capacity modulation system  10 , the capacity modulation system  10  may be used with other compressor types, including a reciprocating compressor, such as the compressor shown in Assignee&#39;s U.S. Pat. No. 6,206,652, the disclosure of which is hereby incorporated herein by reference 
     With particular reference to  FIG. 1 , the capacity modulation system  10  and compressor  12  are incorporated into a system  14  having an evaporator  16 , a condenser  18 , an expansion valve  20 , and an accumulator  22 . The system  14  may be a heat pump system, refrigeration system, chiller system, or HVAC system depending on the location of the evaporator  16  and the condenser  18 . 
     The compressor  12  is fluidly coupled to the evaporator  16 , condenser  18 , expansion valve  20 , and accumulator  22  by a main conduit  24 . The compressor  12  and main conduit  24  cooperate to circulate refrigerant between the various components  16 ,  18 ,  20 ,  22  of the global system  14  to produce a cooling effect. The main conduit  24  extends between the various components  16 ,  18 ,  20 ,  22  and is fluidly coupled to an inlet  25  of the compressor  12  to provide the compressor  12  with vaporized refrigerant. 
     In operation, the compressor  12  receives vapor refrigerant from the evaporator  16  and compresses the vapor prior to discharging, the compressed vapor to the condenser  18 . The condenser  18  extracts heat from the refrigerant, thereby causing the vapor refrigerant to change state from a vapor to a liquid. The liquid refrigerant is pumped from the condenser  18  to the expansion valve  20  under pressure from the compressor  12 . 
     The expansion valve  20  expands the liquid refrigerant prior to the refrigerant entering the evaporator  16  to increase the ability of the refrigerant to absorb heat. The evaporator  16  extracts heat from its surroundings, thereby converting the liquid refrigerant from a liquid to a vapor. Once in the vapor state, the refrigerant is returned to the compressor  12  to start the cycle anew. 
     The capacity modulation system  10  generally includes a vapor compensation circuit  11  and a capacity modulation circuit  13 . The vapor compensation circuit  11  is generally disposed between the evaporator  16  and the compressor  12  and selectively supplies the compressor  12  with vaporized refrigerant at a slightly higher pressure than the suction pressure being supplied through the main conduit  24 . 
     The vapor compensation circuit  11  includes an input conduit  26 , an outlet conduit  28 , and a valve  30 . The input conduit  26  fluidly couples the accumulator  22  to the main conduit  24  and includes a check valve  32 . The check valve  32  is disposed proximate to an inlet of the accumulator  22  to prevent refrigerant from exiting the accumulator  22  and traveling into the evaporator  16 . The outlet conduit  28  fluidly couples the accumulator to main conduit  24  and includes valve  30 . Valve  30  may be an ON-OFF valve such as, for example, a solenoid valve. While a solenoid valve is disclosed, any valve capable of selectively preventing flow from the accumulator  22  to the compressor  12 , such as a thermal expansion valve or an electronic expansion valve, may be used. 
     A check valve  34  is generally disposed at a junction of outlet conduit  28  and main conduit  24 . The check valve  34  prevents vapor from the accumulator  22  from traveling along main conduit  24  generally toward the evaporator  16 . The check valve  34  ensures that vapor from the accumulator  22  is directed away from the evaporator  16  and toward the compressor  12 . 
     The capacity modulation circuit  13  may be a pressure biasing circuit, such as an intermediate-pressure biasing system  36  or a discharge-pressure biasing system  38 , to selectively load and unload the compressor  12 , as described in Assignee&#39;s U.S. Pat. No. 6,821,092 and Assignee&#39;s U.S. Pat. No. 6,213,731, respectively. The discharge-pressure biasing system  38  is shown schematically in  FIG. 1  while the intermediate-pressure biasing system  36  is shown in  FIG. 1A . While either pressure biasing system  36 ,  38  may be used in conjunction with the capacity modulation system  10 , the capacity modulation system  10  will be described hereinafter as including the discharge-pressure biasing system  38 . 
     As shown in the drawings, operation of the capacity modulation system  10  includes converting refrigerant from a liquid to a vapor at the evaporator  16 , whereby the vaporized refrigerant travels from the evaporator  16  toward the compressor  12  along the main conduit  24  to the inlet  25  of the compressor  12  and the inlet conduit  26  of the accumulator  22 . 
     The accumulator  22  receives the vaporized refrigerant and collects vaporized refrigerant in a tank  40 . Once in the tank  40 , the vaporized refrigerant is separated into a low-pressure liquid and a vapor at a slightly higher pressure, but at a lower pressure than both intermediate pressure and discharge pressure of the compressor  12 . The liquid refrigerant collects at a bottom of the tank  40  while the vapor refrigerant rises to a top of the tank  40 . The vapor refrigerant exits the accumulator  22  via conduit  28  and enters the compressor  12  at inlet  25  when the valve  30  is in an open state. The vapor refrigerant remains in the accumulator  22  when the valve  30  is in a closed state. 
     Operation of the valve  30  may be controlled using pulse width modulation to cycle the valve  30  between the open state and the closed state. The valve  30  is timed with operation of the discharge-pressure biasing system  38  such that when the discharge-pressure biasing system  38  loads the compressor  12 , the valve  30  is in the open state for at least a portion of the compressor loading. 
       FIG. 2  depicts an exemplary duty cycle for the discharge-pressure biasing system  38  and the valve  30 . The duty cycle depicts the discharge-pressure biasing system  38  as loading the compressor  12  for five seconds and unloading the compressor for five seconds for a total cycle time of ten seconds. While a duty cycle of ten seconds is disclosed, the discharge-pressure biasing system  38  and the valve  30  may include a shorter or longer duty cycle. 
     In a scroll compressor application, the discharge-pressure biasing system  38  selectively supplies vapor at discharge pressure to a biasing chamber  42  of the compressor  12  to maintain engagement of a non-orbiting scroll member with an orbiting scroll member. Maintaining engagement between the non-orbiting scroll member and the orbiting scroll member allows the non-orbiting scroll member to cooperate with the orbiting scroll member to compress fluid therebetween. 
     During unloading of the compressor  12 , vapor refrigerant at suction pressure is supplied to the biasing chamber  42  to allow the non-orbiting scroll member to separate from the orbiting scroll member. Separation of the non-orbiting scroll member from the orbiting scroll member creates a leak path between the non-orbiting scroll member and the orbiting scroll member. The leak path reduces the ability of the non-orbiting scroll member and the orbiting scroll member to compress fluid. 
     In a non-scroll compressor application, such as a reciprocating compressor, the valve may be disposed in fluid communication with main conduit  24  and is selectively actuated between an ON state permitting vapor refrigerant at suction pressure to enter a compression chamber  43  of the compressor  12  and an OFF state preventing vapor refrigerant at suction pressure from entering the compression chamber  43  of the compressor  12 . Restricting vapor refrigerant to the compression chamber  43  reduces the capacity of the compressor  12  when system demand is low and therefore improves the efficiency of the compressor  12  and system  14 . 
     The duty cycle of the valve is shorter than the duty cycle of the discharge-pressure biasing system  38 , but is timed such that when suction pressure being introduced to inlet  25  through main conduit  24  is at its lowest (e.g., the last 2.5 seconds of the five second loading period), the valve  30  is opened to allow vaporized refrigerant to enter the compressor  12  at inlet  25 . The influx of vaporized refrigerant at a suction pressure higher than suction pressure on main conduit  24  increases the capacity of the compressor  12  without requiring the compressor  12  to consume additional energy. 
     The compressor  12  consumes additional energy in compressing reduced-pressure vaporized refrigerant to discharge pressure. Because suction pressure decreases with time during loading of the compressor  12 , the compressor  12  consumes additional energy in compressing the reduced-pressure vapor refrigerant to discharge pressure. The additional energy consumption reduces the efficiency of the compressor  12  and therefore increases operational costs. When the valve  30  is in the open state (i.e., in the exemplary duty cycle at 2.5 seconds), suction pressure at the compressor inlet  25  increases when compared to a conventional system. The increase in suction pressure reduces the work required by the compressor  12  in compressing the vaporized refrigerant to discharge pressure. Reducing the work required by the compressor  12  in providing vaporized refrigerant at discharge pressure reduces energy consumption of the compressor  12  and therefore increases compressor efficiency. 
       FIG. 3  provides an exemplary plot illustrating the additional capacity realized by the compressor  12  when the valve  30  is in the open state during loading of the compressor  12 . The plot of  FIG. 3  indicates an increase in suction pressure from roughly 70 psig to roughly 78 psig when the valve  30  is open. The increase in suction pressure increases the capacity of the compressor  12  without requiring additional energy consumption. 
     In operation, the valve  30  is in the closed state when the compressor is initially loaded. When the compressor  12  is loaded for a predetermined time (i.e., 2.5 seconds in the exemplary duty cycle of  FIG. 2 ), the valve  30  is opened and high-pressure vaporized refrigerant is permitted to flow from the accumulator  22  to the compressor inlet  25  via outlet conduit  28 . While the vaporized refrigerant from the accumulator  22  also encounters the discharge-pressure biasing system  38 , it does not affect the ability of the system  38  to maintain the compressor  12  in the loaded state as the high-pressure vaporized refrigerant from the accumulator  22  is at a lower pressure than the vaporized refrigerant at discharge pressure applied to the compression chamber  42 . 
     Once the discharge-pressure biasing system  38  has loaded the compressor  12  for a predetermined time (i.e., five seconds in the exemplary duty cycle of  FIG. 2 ), the compressor  12  is unloaded. At approximately the same time, the valve  30  is closed such that the compressor  12  only receives vaporized refrigerant from main conduit  24 . At this point, the compressor  12  remains in the unloaded state until the discharge-pressure biasing system  38  returns the compressor  12  to the loaded state and the cycle is started anew. 
     The capacity modulation system  10  works in conjunction with the pressure biasing system  36 ,  38  to tailor compressor capacity with demand. The capacity modulation system  10  controls vaporized refrigerant from the accumulator  22  through pulse width modulation of the valve  30  generally disposed between an outlet of the accumulator  22  and the inlet  25  of the compressor  12 . Such valve control increases the capacity and efficiency of the compressor  12 . 
     The description of the teachings is merely exemplary in nature and, thus, variations that do not depart from the gist of the teachings are intended to be within the scope of the teachings. Such variations are not to be regarded as a departure from the spirit and scope of the teachings.