Patent Publication Number: US-2023152018-A1

Title: Method of operating a refrigerant compressor

Description:
BACKGROUND 
     Exemplary embodiments pertain to the art of vapor compression systems. More particularly, the present disclosure relates to methods of starting compressors of vapor compression systems. 
     A vapor compression cycle can be deployed in air conditioning, refrigeration, and heat pump systems. These systems can utilize a variable speed refrigerant compressor that adjusts the compression rate to meet the thermal output demanded from the system. Although these systems can be designed to follow the thermal demand, e.g., deploy active control methods to compensate for changing thermal demand, under some conditions the operating boundaries can be more restrictive in order to prevent unwanted conditions from developing or persisting in the vapor compression cycle. Accordingly, there remains a need in the art for methods of operating vapor compression systems that maintain cycle conditions within the desired ranges to reduce undue wear on system components. 
     BREIF DESCRIPTION 
     Disclosed is a method of operating a vapor compression system configured for environmentally conditioning a space comprising: providing a compressor of the vapor compression system with a variable speed drive configured to control a speed of the compressor and correspondingly a flowrate of a refrigerant flowing through the compressor, operating the compressor at a first speed in response to a start command, determining a demand speed of the compressor based at least in part on a user selected target value for an environmental condition within the space, determining a maximum allowable compressor speed of the compressor based at least in part on a condition of a parameter of the vapor compression system, reducing the speed of the compressor from the first speed to a second speed corresponding to the maximum allowable compressor speed when the maximum allowable compressor speed is less than the first speed, maintaining the speed of the compressor below the first speed when the maximum allowable compressor speed is greater than the first speed, and operating the compressor at the demand speed once a startup condition is satisfied. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the maintaining the speed of compressor below the first speed further comprises operating the compressor at the demand speed when the demand speed is greater than the second speed. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the maintaining the speed of the compressor below the first speed further comprises operating the compressor at the second speed when the demand speed is less than the second speed. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the startup condition comprises increasing a discharge superheat value of the vapor compression system to a threshold discharge superheat value. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the startup condition comprises waiting for a first time period to expire. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the startup condition comprises increasing a discharge superheat value of the vapor compression system to a threshold discharge superheat value and waiting for a first time period to expire. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the determining the maximum allowable compressor speed of the compressor further comprises comparing at least one of a suction pressure of the compressor, a discharge pressure of the compressor, a compression ratio of the compressor, a compressor discharge temperature, or a combination comprising at least one of the foregoing to a threshold condition. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the reducing the speed of the compressor further comprises decreasing the speed of the compressor according to a downward ramp rate. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein operating the compressor at the demand speed further comprises adjusting the speed of the compressor according to an upward or downward ramp rate from the second speed to the demand speed. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the upward ramp rate and the downward ramp rate have the same magnitude but opposite signs. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the condition of the parameter of the vapor compression system comprises a high suction pressure of the compressor, a low suction pressure of the compressor, a high discharge pressure of the compressor, a low discharge pressure of the compressor, a high compression ratio of the compressor, a low compression ratio of the compressor, a low compressor discharge temperature, a high compressor discharge temperature, or a combination comprising at least one of the foregoing. 
     Also disclosed is a vapor compression system configured for environmentally conditioning a space comprising: a compressor, an indoor heat exchanger, and outdoor heat exchanger, and an expansion valve disposed in a closed loop in operable communication with one another, wherein the indoor heat exchanger is disposed in thermal communication with the space, a variable speed drive disposed in operable communication with the compressor and configured for adjusting a speed of the compressor, and a controller in operable communication with the variable speed drive and a sensor configured to determine a condition of a parameter of the closed loop, wherein the controller is configured to operate the vapor compression system according to the method of any one of the preceding claims. 
     Also disclosed is a vapor compression system configured for environmentally conditioning a space comprising: a compressor, an indoor heat exchanger, and outdoor heat exchanger, and an expansion valve disposed in a closed loop in operable communication with one another, wherein the indoor heat exchanger is disposed in thermal communication with the space, a variable speed drive disposed in operable communication with the compressor and configured for adjusting a speed of the compressor, a controller in operable communication with the variable speed drive and a sensor configured to determine a condition of a parameter of the closed loop, wherein the controller is configured to determine a demand speed of the compressor based at least in part on a user selected target value for an environmental condition within the space, determine a maximum allowable compressor speed of the compressor based at least in part on the condition of the parameter, reduce the speed of the compressor from a first speed to a second speed corresponding to the maximum allowable compressor speed when the maximum allowable compressor speed is less than the first speed, maintain the speed of the compressor below the first speed when the maximum allowable compressor speed is greater than the first speed, and operate the compressor at the demand speed once a startup condition is satisfied. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the controller is configured to operate the compressor at the demand speed when the demand speed is greater than the second speed. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the controller is configured to operate the compressor at the second speed when the demand speed is less than the second speed. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the startup condition comprises a discharge superheat value of the vapor compression system being greater than or equal to a threshold discharge superheat value. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the startup condition further comprises waiting for a first time period to expire. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the startup condition comprises a discharge superheat value of the vapor compression system being greater than or equal to a threshold discharge superheat value and waiting for a first time period to expire. 
     In addition to one or more of the above disclosed aspects or as an alternate, wherein the controller is configured to determine the maximum allowable compressor speed by comparing at least one of a suction pressure of the compressor, a discharge pressure of the compressor, a compression ratio of the compressor, a compressor discharge temperature, or a combination comprising at least one of the foregoing to a threshold condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG.  1    is a schematic illustration of a vapor compression system configured as an air conditioning system. 
         FIG.  2    is a schematic illustration of a vapor compression system configured as a heat pump system. 
         FIG.  3    is a schematic illustration of a method of operating a vapor compression system. 
         FIG.  4    is a graphical illustration of operating parameters of the vapor compression system over time with and without implementation of the disclosed method. 
         FIG.  5    is a graphical illustration of operating parameters of the vapor compression system over time with and without implementation of the disclosed method where the demand speed is less than the second speed. 
         FIG.  6    is a graphical illustration of operating parameters of the vapor compression system over time with and without implementation of the disclosed method where the demand speed is greater than the second speed. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
       FIG.  1    is a schematic illustration of a vapor compression system  100  configured as an air conditioning system for providing cooling to an interior space  200  of a building  210 . The vapor compression system  100  can have a compressor  130 , an outdoor heat exchanger  150 , an expansion valve  160 , and an indoor heat exchanger  170  disposed in operable fluid communication sequentially around a refrigerant loop  110 . The outdoor heat exchanger  150  can be placed in thermal communication with the ambient outdoor environment  220  and the indoor heat exchanger  170  can be placed in thermal communication with the interior space  200  to be environmentally conditioned within the building  210 . An indoor air mover  175  (e.g., a fan or blower) can be configured to provide a return air stream  177  from within the building  210  to the indoor heat exchanger  170 . The return air stream  177  can be cooled by the indoor heat exchanger  170  (correspondingly heating a refrigerant flow in the refrigerant loop  110 ) and distributed as a supply air stream  179  to the interior space  200  to be environmentally conditioned within the building  210 . An outdoor air mover  155  (e.g., fan or blower) can be configured to provide an outdoor air supply stream  157  from the outside environment  220  to the outdoor heat exchanger  150  which can heat the air (correspondingly cooling the refrigerant flow) before it is returned to the outside environment  220  as an outdoor air exhaust stream  159 . For example, the indoor heat exchanger  170  can be located within a furnace coil, fan coil, air handler, or the like, while the outdoor heat exchanger  150  is located on a rooftop, yard, or the like. 
     During operation of the vapor compression system  100 , the compressor  130  can compress vapor phase refrigerant flow to a higher pressure and supply it to the outdoor heat exchanger  150 . Outside air can be blown, or pulled, through the outdoor heat exchanger  150  to cool the refrigerant flow which can condense vapor phase refrigerant to a liquid phase. The cooled liquid refrigerant flow exiting the outdoor heat exchanger  150  can be expanded to a lower pressure as it passes through the expansion valve  160  and enters the indoor heat exchanger  170 . This expansion can cause a portion of the refrigerant flow to vaporize and result in a vapor-liquid two-phase mixture exiting the expansion valve  160 . Warmer air from the interior space  200  to be conditioned within the building  210  can be directed through the indoor heat exchanger  170  as return air stream  177  where it can be cooled and returned to the building  200  as a conditioned supply air stream  179  by heat transfer with the cold refrigerant passing through indoor heat exchanger  170 . 
       FIG.  2    is a schematic illustration of a vapor compression system  100  configured for operation as a heat pump system for providing cooling and heating to an interior space  200  of a building  210 . The vapor compression system  100  can have a compressor  130 , an outdoor heat exchanger  150 , an expansion valve  160 , and an indoor heat exchanger  170 , and a four-way valve  140 , disposed in operable fluid communication sequentially around the refrigerant loop  110 . The heat pump can operate in a heating mode or a cooling mode depending on the direction of refrigerant flow around the refrigerant loop  110 . The four-way valve  140  can be utilized to change the flow direction of a portion of the refrigerant loop  110  when changing from the heating mode to the cooling mode or vice versa. For example, when in a cooling mode, the four-way valve  140  can be set in a first position  141  (shown in detail A) where the refrigerant can be directed along a cooling mode flow path as indicated by cooling mode directional arrows  111  and mode independent directional arrows  115  and when in heating mode, the four-way valve  140  can be set in a second position  142  (shown in detail A) where the refrigerant can be directed along a heating mode flow path as indicated by heating mode directional arrows  112  and independent directional arrows  115 . 
     The compressor  130  of the vapor compression system  100  can be configured for operation with input from a variable speed drive  135 . Such a drive can vary its output speed (e.g., by varying output frequency) and consequently the speed of the compressor  130  and the flow rate of refrigerant through the compressor  130 . Allowing for compressor speed adjustment can provide for more efficient system operation, e.g., under off-design conditions, partial thermal output conditions, startup conditions, full rated thermal output conditions, and the like. Additionally, use of the variable speed drive  135  to drive compressor  130  can allow for adjustment to the compressor speed in response to system events or disturbances. 
     A system controller  120  can be configured in operable communication with the variable speed drive  135  to control the compressor  130 . The controller  120  can be configured to adjust the speed of the compressor  130  when one or more system parameters deviate from their predetermined operating envelop. For example, the system controller  120  can limit the compressor speed or command the variable speed drive  135  to limit the compressor speed to a maximum allowable compressor speed  440  when one or more system parameters deviate from their predetermined operating envelop. The one or more system parameters that can deviate from their predetermined operating envelop can include a suction pressure of the compressor  130  reaching a minimum value for a specified time duration, a discharge pressure of the compressor  130  reaching a maximum value for a specified time duration, the compression ratio of the compressor  130  reaching a minimum value for a specified time duration, the compression ratio of the compressor  130  reaching a maximum value for a specified time duration, the discharge pressure of the compressor  130  reaching a minimum value for a specified time duration, the discharge temperature of the compressor  130  reaching a minimum temperature for a specified time duration, or a combination including at least one of the foregoing. 
     Several different strategies for starting up the vapor compression system  100  having a variable speed driven compressor  130  can be employed. A method which can be implemented during startup operation can include operating the compressor  130  at a fixed speed, for a fixed time duration, until a startup condition is satisfied (e.g., until a target discharge superheat value is reached for a predetermined duration), or a combination including at least one of the foregoing. In situations where parameters of the vapor compression system  100  deviate from their predetermined operating envelop (e.g., stored in a memory storage device in operable communication with the controller  120 ) during startup, the controller  120  can be configured to command the compressor  130  to a different speed (e.g., lower speed) such that the parameter returns to within its predetermined operating envelop. For example, one situation that can arise is low compressor suction pressure (e.g., as measured at the inlet of the compressor  130 ). Under this condition the controller  120  can reduce the speed of the compressor  130  until the suction pressure returns to the predetermined operating envelop. However, a consequence of this, or other corrective actions, is they can further exacerbate the underlying issue that resulted in the low suction pressure to begin with. For example, by lowering the speed of the compressor  130  followed by returning to a higher, fixed, startup speed the discharge pressure of the compressor  130  can cycle from relatively lower to higher pressure. This pressure difference between high pressure and lower pressure can have a significant effect on the refrigerant solubility in lubricating oil used in the refrigerant loop  110  for lubricating the components of compressor  130 . As a result, refrigerant in solution in the liquid oil phase can vaporize as the refrigerant solubility in the lubricant oil drops. Rapid volume expansion due to vaporization within the liquid oil phase can lead to oil foaming, a condition which can lead to premature failure of the compressor  130  due to reduced viscosity and lubricity of the lubricating oil. 
     During such startup operation, the controller  120  can be configured for operating the compressor  130  at a first speed until the startup condition is satisfied. For example, the startup condition can include achieving a target discharge superheat value greater than or equal to about 25° F., or greater than or equal to about 24° F., or greater than or equal to about 23° F., or greater than or equal to about 22° F., or greater than or equal to about 21° F., or greater than or equal to about 20° F., or greater than or equal to about 19° F., or greater than or equal to about 18° F., or greater than or equal to about 17° F., or greater than or equal to about 16° F., or greater than or equal to about 15° F., or greater than or equal to about 14° F., or greater than or equal to about 13° F., or greater than or equal to about 12° F., or greater than or equal to about 11° F., or greater than or equal to about 10° F., or greater than or equal to about 9° F., or greater than or equal to about 8° F., or greater than or equal to about 7° F., or greater than or equal to about 6° F., or greater than or equal to about 5° F., or greater than or equal to about 4° F., or greater than or equal to about 3° F., or greater than or equal to about 2° F., or greater than or equal to about 1° F. 
       FIG.  3    is a schematic illustration of a method  300  of operating the vapor compression system  100  which is configured for environmentally conditioning a space  200 . The method  300  can include a first aspect  310  including receiving a request for environmental conditioning the space  200  (e.g., from a user, a master device, or the like). For example, the method can include receiving a setpoint for an environmental condition (e.g., temperature, humidity, or the like) from a user interface (e.g., thermostat, mobile device, or the like), a supervisory controller, or the like. 
     The method  300  can include a second aspect  320  including starting the compressor  130  (e.g., following receiving the request for environmental conditioning of the space  200 ). Starting the compressor  130  can include operating the compressor  130  at a first speed (e.g., set to maintain a constant, fixed speed, setpoint within control tolerances of the variable speed drive  135 ). The first speed can be set to a percentage of the maximum speed. For example, the first speed can be greater than or equal to about 10% of the maximum speed of compressor  130 , or greater than or equal to about 25% of the maximum speed of compressor  130 , or greater than or equal to about 50% of the maximum speed of compressor  130 , or greater than or equal to about 60% of the maximum speed of compressor  130 , or greater than or equal to about 70% of the maximum speed of compressor  130 , or greater than or equal to about 75% of the maximum speed of compressor  130 , or greater than or equal to about 80% of the maximum speed of compressor  130 , or greater than or equal to about 85% of the maximum speed of compressor  130 . The maximum speed of the compressor  130  can correspond to the maximum rated speed of the compressor  130  as supplied by the manufacturer of the compressor  130 . 
     The method  300  can include a third aspect  330  including determining a demand speed of the compressor  130 . The demand speed of the compressor  130  is the speed that the compressor  130  of the vapor compression system  100  would run at based on the thermal demand placed on the vapor compression system  100 . This thermal demand can be based, at least in part, on a user selected target value for an environmental condition within the space  200  (e.g., temperature, humidity, or the like). Determining the demand speed of the compressor  130  can include interpreting with the controller  120  the demand speed from a predefined relationship between thermal output of the vapor compression system  100  and at least compressor speed. Such relationship can be stored in the memory disposed in operable communication with the controller  120 . The relationship can be stored in the form of a series of data points, an equation, or a combination thereof. Further, the relationship can be empirically determined as a function of one or more operating parameters of the vapor compression system  100 , e.g., by testing or simulating operation (e.g., using a physics-based computer aided model) over a variety of environmental conditions. 
     The method  300  can include a fourth aspect  340  including determining a maximum speed of the compressor  130 . The maximum speed of the compressor  130  can be based at least in part on a condition of a parameter of the vapor compression system. For example, the controller  120  can monitor one or more parameters of the vapor compression system  100  for deviation from expected ranges. If a parameter reaches a threshold condition then the controller  120  can reduce the operating window of the compressor  130  to prevent damage to the compressor  130  (e.g., liquid ingestion). For example, the condition of a parameter can include a suction pressure of the compressor  130  reaching a minimum value for a specified time duration, a discharge pressure of the compressor  130  reaching a maximum value for a specified time duration, the compression ratio of the compressor  130  reaching a minimum value for a specified time duration, the compression ratio of the compressor  130  reaching a maximum value for a specified time duration, the discharge pressure of the compressor  130  reaching a minimum value for a specified time duration, the discharge temperature of the compressor  130  reaching a minimum temperature for a specified time duration, or a combination including at least one of the foregoing. The condition of these parameters can therefore influence the determination of the maximum allowable compressor speed at any given time during operation. 
     The method  300  can include a fifth aspect  350  including reducing the speed of the compressor  130  from the first speed to a second speed corresponding to the maximum allowable compressor speed when the maximum allowable compressor speed is less than the first speed. If, during operation at the first speed, the controller  120  determines the maximum allowable compressor speed is reduced below the first speed then the controller  120  can reduce the speed of the compressor  130  to be equal to or less than the maximum allowable compressor speed, e.g., by reducing the speed of the variable speed drive  135 . However, instead of allowing the compressor  130  to return to the first speed to finish the startup when the parameter returns within the expected operating range, the applicants have found that maintaining the speed of the compressor  130  at or near the second speed can at least reduce the occurrence of compressor pressure cycling and resultant oil foaming. 
     Accordingly, the method  300  can include a sixth aspect  360  including maintaining the speed of the compressor  130  below the first speed when the maximum allowable compressor speed is greater than the first speed. For example, after the speed of the compressor  130  is reduced to the second speed, the controller  120  can operate to maintain the speed of the compressor  130  (e.g., through the variable speed drive  135 ) at or near the second speed even when the maximum allowable speed of the compressor  130  returns to values greater than the first speed. By maintaining the speed of the compressor  130  at or near the second speed, pressure disturbances throughout the refrigerant loop can be reduced and consequent changes in refrigerant solubility in lubricant oil can be minimized while the startup operation proceeds until satisfying the startup condition. Furthermore, in instances where the demand speed is near the second speed, the controller  120  can be configured to operate the compressor  130  at the demand speed. For example, the controller  120  can be configured to operate the compressor  130  at the demand speed when the difference between the demand speed and the second speed is less than or equal to about 10% of the maximum speed of the compressor  130 , such as less than or equal to about 9% of the maximum speed of the compressor  130 , or less than or equal to about 8% of the maximum speed of the compressor  130 , or less than or equal to about 7% of the maximum speed of the compressor  130 , or less than or equal to about 6% of the maximum speed of the compressor  130 , or less than or equal to about 5% of the maximum speed of the compressor  130 , or less than or equal to about 4% of the maximum speed of the compressor  130 , or less than or equal to about 3% of the maximum speed of the compressor  130 , or less than or equal to about 2% of the maximum speed of the compressor  130 , or less than or equal to about 1% of the maximum speed of the compressor  130 , or such as less than or equal to about 1000 rpm, or less than or equal to about 800 rpm, or less than or equal to about 600 rpm or less than or equal to about 500 rpm, or less than or equal to about 405 rpm, or less than or equal to about 300 rpm, or less than or equal to about 200 rpm, or less than or equal to about 100 rpm, or less than or equal to about 50 rpm. 
     Still further, maintaining the speed of the compressor  130  below the first speed can include operating the compressor  130  at the demand speed when the demand speed is greater than the second speed. For example, maintaining the speed of the compressor  130  below the first speed can include operating the compressor  130  at the demand speed when the demand speed is greater than the second speed and less than the first speed. Maintaining the speed of the compressor  130  below the first speed can further include operating the compressor  130  at the demand speed when the demand speed is less than the second speed and less than the first speed. As disclosed herein, the controller  120  can be configured to operate the compressor  130  at the demand speed when the demand speed is near the second speed and below the first speed. Operating at the demand speed can include increasing or decreasing the speed of the compressor  130  to follow the thermal demand of the vapor compression system  100 . During the startup operation, e.g., before the startup threshold condition is satisfied, operating the compressor  130  at the demand speed can further include operating the compressor  130  at a speed less than or equal to the first speed. 
     The method  300  can include a seventh aspect  370  of operating the compressor  130  (e.g., via the variable speed drive  135 ) at the demand speed S D  once the startup condition is satisfied. The startup condition can include achieving the target discharge superheat value (e.g., as discussed above) which can be a function of the architecture of the vapor compression system  100 , the type of compression technology employed in the compressor  130 , the specific design of the compressor  130 , or a combination including at least one of the foregoing. 
       FIG.  4    is a schematic illustration of a graph of operating parameters of the vapor compression system  100  over time with and without implementation of method  300 . The compressor speed without implementation  405  is denoted by the solid line, the maximum allowable compressor speed  440  (e.g., as determined by the controller  120  based on conditions of the refrigerant loop  110 ) is denoted by the dot-dashed line, and the compressor speed with implementation  410  is denoted by the dashed line. The demand speed is indicated by S D  and the first speed is indicated by S 1 . At the time to the compressor  130  starts and the speed of the compressor  130  is increased to the first speed, S 1 . Both the compressor speed without implementation  405  and the compressor speed with implementation  410  initially track the first speed until at t 1  the maximum allowable compressor speed  440  drops below the first speed S 1 . The two traces ( 405  and  410 ) continue to follow the maximum allowable compressor speed  440  as it decreases until t 2  when the maximum allowable compressor speed  440  becomes greater than the first speed S 1 . At that point, the compressor speed without implementation  405  increases back to the first speed S 1  while the compressor speed with implementation  410  remains at the second speed S 2  (e.g., the speed that the compressor  130  was operating at just before the maximum allowable compressor speed became greater than the first speed S 1 ). There are numerous ways that the second speed S 2  can be determined and stored in the memory in operative communication with the controller  120 . For example, this second speed S 2  can be determined through a rolling multi-point average of the compressor speed over a predetermined time interval (e.g., such as about 30 second or less), the second speed S 2  can be substantially equal to the minimum speed of the compressor  130  over a predetermined time interval, the second speed S 2  can be substantially equal to the maximum allowable compressor speed  440  when the maximum allowable compressor speed  440  is less than the first speed S 1  (e.g., such as in region  415 ), the second speed S 2  can be substantially equal to the demand speed of the vapor compression system  100 . The second speed S 2  can change with time. The second speed S 2  can be less than the first speed S 1  at all times. 
     Both the compressor speed without implementation  405  and the compressor speed with implementation  410  trace the maximum allowable compressor speed  440  when it decreases below the first speed S 1  for a second time at t 3 . The two traces ( 405  and  410 ) continue together, following the maximum allowable compressor speed  440  until it becomes greater than the first speed S 1  at t 4 . Here, again the two traces diverge as the compressor speed without implementation  405  increases back to the first speed S 1  and the compressor speed with implementation  410  remains at a newly established second speed S 2n  (e.g., established as the maximum allowable compressor speed  440  just prior to it becoming greater than the first speed). Although the newly established second speed S 2n  can be numerically different than the initial second speed S 2 , both remain below the first speed S 1 . 
     Once the startup condition is satisfied, the speed of the compressor  130  can be adjusted to the demand speed S D  to balance the thermal output of the vapor compression system  100  with the demanded thermal output. For example, once the startup condition is satisfied at t 5 , both the compressor speed without implementation  405  and the compressor speed with implementation  410  can be adjusted to the demand speed S D . By maintaining the speed of the compressor  130  at a speed less than the first speed S 1  and not increasing back to the first speed S 1 , pressure pulses in the vapor compression system  100  such as those associated compressor speed spikes  412  can be avoided. 
       FIG.  5    is a schematic illustration of operating parameters of the vapor compression system  100  with and without implementation of method  300 . Again, the compressor speed without implementation  405  is denoted by the solid line, the maximum allowable compressor speed  440  (e.g., as determined by the controller  120  based on conditions of the refrigerant loop  110 ) is denoted by the dot-dashed line, the compressor speed with implementation  410  is denoted by the dashed line, the first speed is denoted S 1 , the second speed is denoted S 2 , and the demand speed is denoted S D . In this example, the compressor  130  is operating at the first speed S 1  until a system parameter causes the maximum allowable compressor speed  440  to drop below the first speed S 1  at t 0  to a second speed S 2 . Both the compressor speed without implementation  405  and the compressor speed with implementation  410  then are reduced and track the maximum allowable compressor speed  440  until it increases above the first speed S 1  at t 1 . Once the maximum allowable compressor speed  440  increases above the first speed S 1  the compressor speed without implementation  405  increases back to the first speed S 1  while the compressor speed with implementation  410  stays at the seconds speed S 2 . By maintaining the speed of the compressor at the second speed, pressure pulses in the vapor compression system  100  such as those associated compressor speed spikes  412  can be avoided. Once the startup condition is satisfied at t 2 , both the compressor speed without implementation  405  and the compressor speed with implementation  410  can be adjusted (e.g., decreased) to the demand speed S D . 
       FIG.  6    is a schematic illustration of operating parameters of the vapor compression system  100  with and without implementation of method  300 . Again, the compressor speed without implementation  405  is denoted by the solid line, the maximum allowable compressor speed  440  (e.g., as determined by the controller  120  based on conditions of the refrigerant loop  110 ) is denoted by the dot-dashed line, the compressor speed with implementation  410  is denoted by the dashed line, the first speed is denoted S 1 , the second speed is denoted S 2 , and the demand speed is denoted S D . In this example, the compressor  130  is operating at the first speed S 1  until a system parameter causes the maximum allowable compressor speed  440  to drop below the first speed S 1  at t 0  to a second speed S 2 . Once both the compressor speed without implementation  405  and the compressor speed with implementation  410  ramp their speed down after to they track the maximum allowable compressor speed  440  while it is less than the first speed S 1  until it increases above the first speed S 1  at t 1 . Once the maximum allowable compressor speed  440  increases above the first speed S 1  then compressor speed without implementation  405  increases back to the first speed S 1  while the compressor speed with implementation  410  increases to the demand speed S D . By maintaining the speed of the compressor  130  at a speed less than the first speed S 1 , pressure pulses in the vapor compression system  100  such as those associated compressor speed spikes  412  can be reduced. Once the startup condition is satisfied at t 2 , the compressor speed without implementation  405  can be adjusted (e.g., decreased) to the demand speed S D  while the compressor speed with implementation is already operating at the demand speed S D . Following startup, the compressor  130  can operate to maintain a parameter of the vapor compression system, such as temperature of the space  200 , by following the demand speed S D . 
     Optionally, the variable speed drive  135 , the controller  120 , or both can include a rate limiter to limit the rate at which the speed of the compressor  130  can be changed. For example, one of the variable speed drive  135  or the controller  120  can be configured to limit the rate at which the speed of the compressor  130  is changed to less than or equal to about 100 rpm/sec, or about 90 rpm/sec, or about 80 rpm/sec, or about 70 rpm/sec, or about 60 rpm/sec, or about 50 rpm/sec, or about 40 rpm/sec, or about 30 rpm/sec, or about 20 rpm/sec, or about 10 rpm/sec, or about 5 rpm/sec. Further, the rate limiter can be applied to either increases or decreases in the speed of the compressor  130 . Still further, the magnitude of the rate limit for speed increases can be different than the magnitude of the rate limit for speed decreases. For example, a speed increase rate limit can be set to 50 rpm/sec while a speed decrease rate limit can be set to 25 rpm/sec, or 75 rpm/sec, or any such combination as is deemed appropriate for the compressor  130  and the overall design and operation of the vapor compression system  100 . When rate limiting is not implemented the controller  120  can utilize other control approaches to bring controlled variables within desired range such as proportional, integral, or differential controllers or combinations including at least one of the foregoing. These control approaches can generate an output speed signal having a magnitude corresponding to the deviation of a system parameter from its set point (e.g., output air temperature). 
     The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof. 
     While the present disclosure has been described with reference to an exemplary embodiment or embodiments, 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 present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.