Patent Publication Number: US-11035357-B2

Title: System and method for controlling a system that includes variable speed compressor

Description:
The embodiments disclosed herein relate generally to a system and method for controlling a system that includes at least one variable speed compressor. 
     BACKGROUND 
     Generally, certain factors such as a minimum operating speed are required for prolonging the life of a variable speed compressor. Such requirements can affect energy efficiencies. Improvements in control of systems that include a variable speed compressor are desirable. 
     SUMMARY 
     The embodiments described herein are directed to a system and method for controlling a system that includes for example at least one variable speed compressor. The method can provide improved accuracy in the control of a system, for example, a heating, ventilating, and air condition (HVAC) system that includes at least one variable speed compressor, and can reduce a compressor cycling frequency of the compressor when a required capacity is below a minimum capacity of the compressor. 
     Generally, the improved accuracy and reduction in compressor cycling frequency are achieved by simultaneously controlling the variable speed compressor and a supply fan that are included in the system. The system and method described herein can advantageously lead to improved energy efficiencies. That is, in general, cycling between startup and shutdown can not only help prolong the life of the compressor, but also can improve energy efficiencies. The system and method described herein also can lead to a higher percentage latent capacity for improved space dehumidification so that an additional reheating of the supply air which is typically conducted by traditional air-side products for dehumidification is not required. 
     In general, a different fan speed and compressor speed combination can provide the same unit or required capacity. The system and method described herein can determine the fan speed from the current compressor speed based on predetermined equations or maps. An energy efficiency equation/map can be setup so that the system will achieve maximum energy efficiency when provided the same unit or required capacity. 
     In some examples, the dehumidification map can have a lower fan speed than the energy efficiency map does when the same compressor speed is used. In this instance, controlling based on the dehumidification equation/map can remove more moisture and improve space dehumidification. In some instances, the controller can choose to run based on an energy efficiency map when space humidity is not high and to run based on a dehumidification map when space humidity is too high. 
     In some embodiments, the system includes a variable speed compressor, a condenser, an evaporator, and a supply fan. In some examples, the system can further include a controller that is configured to control the system by executing a control program or algorithm that is stored in a memory of the controller. In some examples, the controller is configured so that the variable speed compressor can operate in four different operational states: a unit off state, a startup state, a running state and a shutdown state. 
     In the unit off state, the variable speed compressor stays off at the off position so that the speed of the variable speed compressor is at 0 revolutions per second (rps). In some instances, the fan also can be off so that the speed of the fan is at 0 rps. 
     In the startup state, the speed of the variable speed compressor can ramp up at a constant rate from 0 rps until the speed reaches a startup speed of the compressor. In some instances, the fan can run at a minimum speed. 
     In the running state, the variable speed compressor is modulated between a minimum speed and a maximum speed. In some instance, the fan also can be modulated between a minimum speed and a maximum speed. 
     In the shutdown state, the variable speed compressor can ramp down from the minimum speed to 0 rps. The shutdown is complete when 0 rps is reached. In some instances, the fan can run at a minimum speed. 
     In one embodiment, the algorithm that is executed by the controller includes determining a required capacity and comparing the determined required capacity with a minimum capacity of a variable speed compressor. 
     If the determined required capacity is greater than the minimum capacity of the variable speed compressor, then the variable speed compressor operates in the running state. 
     If the determined required capacity is less than the minimum capacity of the variable speed compressor, then the variable speed compressor will cycle between the four different operating states based on the determined required capacity. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings in which like reference numbers represent corresponding parts throughout. 
         FIG. 1  is a schematic illustration of a system for controlling a variable speed compressor and a supply fan, according to one embodiment. 
         FIGS. 2A and 2B  are flow charts of the overall processes involved in controlling the variable speed compressor, according to one embodiment. 
         FIG. 3  shows a schematic representation of the cycling process, according to one embodiment. 
         FIG. 4  shows a block diagram of a feedback control system using a PI controller, according to one embodiment. 
         FIG. 5  shows a graph of how the speeds of the supply fan and the compressor are modulated simultaneously, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments described herein are directed to a system and method for providing control in a system that includes a variable speed compressor. The system can be any system that utilizes a variable speed compressor, including water source heat pumps, unitary equipment, air handlers and terminal units. 
       FIG. 1  provides a schematic illustration of one embodiment of the disclosed system (see system  100  in  FIG. 1 ). The system  100  includes a conditioned space  104  and a ductwork  113  that is in fluid communication with the conditioned space  104 . The term “conditioned space” herein means a single space or a group of spaces, where the single space or the group of spaces can be defined as a zone or zones. The conditioned space  104  can include a thermostat  119  that measures a dry-bulb temperature of the conditioned space  104 . The term “dry-bulb temperature” herein means a temperature of air measured by the thermostat  119  that is freely exposed to the air but shielded from radiation and moisture. 
     The ductwork  113  can include a cooling coil  126  and a supply fan  131 . The ductwork  113  can include other components that are typically included in a HVAC system, including a relief fan (not shown). The ductwork  113  and the conditioned space  104  can be configured so that needed airflow can flow from the ductwork  113  into the conditioned space  104 , back into the ductwork  113  and then out of the ductwork  113  as generally known in the art. 
     Generally, air flows past the cooling coil  126  so as to be cooled. The cooled air then is delivered by the supply fan  131  into the conditioned space  104  as supply air. The supply fan  131  also can be used to draw air out of the conditioned space  104  as return air. Some outdoor air for ventilation can be mixed with the recirculated portion of the return air. The remaining return air, that which has been replaced by outdoor air, can be then exhausted as exhaust air by a relief fan. 
     In some examples, the cooling coil  126  can be in fluid communication with a condenser  142  and a compressor  137 . In  FIG. 1 , the system  100  is illustrated as having one compressor, but it is to be realized that more than one compressor can be used. In the instance where more than one compressor is used, the compressors can operate, for example, parallel to one another. 
     In one example, the compressor  137  is a variable speed compressor. The term “variable speed compressor” means a compressor whose speed can be controlled, for example, by a controller, as generally understood in the art. The variable speed compressor  137  can include components that are generally known in the art, including a variable speed drive and a motor. The speed of the compressor  137  is generally controlled by controlling the speed of the motor that is driven by the variable speed drive. The variable speed compressor  137  can be any compressor type that is suitable for use in a HVAC system, and can include, but is not limited to reciprocating, scroll, rotary, screw, centrifugal, etc. It is to be realized that some deviation or enhancements may be required depending on the type of compressor used, e.g., for a screw or centrifugal compressor. 
     The variable speed compressor  137  generally functions to compress refrigerant gas and feed the resulting high-pressure and high-temperature refrigerant gas to the condenser  142 . As is generally understood in the art, a capacity of the variable speed compressor  137  is based on the operating speed of the variable speed compressor  137 . That is, the capacity of the variable speed compressor  137  will generally increase as compressor speed increases when other variables in the system stay the same. In the description that follows, a variable speed compressor will be described. However, it is to be realized that the concepts herein can apply to any suitable modulating capacity compressor. Note that a variable speed compressor is understood to be an example of a modulating capacity compressor. The other variables may include condenser fan speed, condenser ambient conditions and evaporator entering air conditions. 
     Generally, the variable speed compressor  137  has a minimum capacity. The term “minimum capacity of the variable speed compressor  137 ” means the lowest operating speed or capacity of the variable speed compressor  137  necessary to prevent damage to the variable speed compressor  137 . That is, in general, as the load of a variable speed compressor decreases, the compressor becomes less efficient, which can lead to increased internal compressor temperatures. This can in turn lead to overheating of the rotor temperature and the radial expansion or radial growth of the rotors. This radial growth can result in a radial rub with the compressor housing, subsequently causing a failure. Also, damage can result from a lack of compressor lubrication at lower operating speeds. The minimum capacity of the variable speed compressor  137  is the lowest operating speed or capacity of the variable speed compressor  137  necessary to prevent such failure of the variable speed compressor  137 . It is to be appreciated that the minimum capacity of the variable speed compressor  137  can be determined and/or set by a user. 
     In some instances, the minimum capacity of the variable speed compressor  137  is dependent on factors such as the type of variable speed compressor  137  used. In some examples, the minimum capacity of the variable speed compressor  137  is predetermined, e.g., by the manufacturer of the variable speed compressor  137 . In some other examples, the minimum capacity of the variable speed compressor  137  is set by a user. In some other examples, the minimum capacity of the variable speed compressor  137  can be calculated in a manner that is generally known in the art, e.g., based on readings from a temperature sensor  169  of the fluid that is discharged from the compressor  137  and/or a temperature sensor  172  of the compressor  137 . 
     The cooling coil  126 , the condenser  142  and the compressor  137  can utilize a refrigeration cycle that is generally known in the art. In some instances of the refrigeration cycle, the variable speed compressor  137  can feed high-pressure and high-temperature refrigerant gas to the condenser  142 . The refrigerant vapor that is delivered to the condenser  142  then can enter into a heat exchange relationship with a fluid, for example, air. The condensed liquid refrigerant from the condenser  142  then can flow through an expansion device (not shown) to an evaporator  132 . A secondary liquid, e.g., water, that has flowed into the evaporator  132  then can enter into a heat exchange relationship with the low pressure/low temperature liquid refrigerant to chill the temperature of the secondary liquid. The chilled secondary liquid can then run through the cooling coil  126 , and the refrigerant liquid in the evaporator  132  can undergo a phase change to a refrigerant vapor as a result of the heat exchange relationship with the secondary liquid. The refrigerant vapor then can return to the variable speed compressor  137  to complete the refrigeration cycle. 
     The system  100  further can include a controller  175 . The controller  175  generally can include a processor, a memory, a clock and an input/output (I/O) interface and can be configured to receive data as input from various components within the system  100 , and send command signals as output to various components within the system  100 . 
     In some examples, during operation, the controller  175  can receive information, for instance, from the variable speed compressor  137 , the supply fan  131 , the thermostat  119 , the temperature sensor  169 , and/or the temperature sensor  172  through the I/O interface, process the received information using the processor based on an algorithm stored in the memory, and then send command signals, for instance, to the components involved in the refrigeration cycle including the compressor  137  and/or the supply fan  131 . For example, the controller  175  can receive information regarding the dry-bulb temperature from the thermostat  119  and the current operating speed of the variable speed compressor  137 , process the data, and then based on the data, send a command signal to the variable speed compressor  137  so as to control the speed of the compressor  137 . It is to be realized that the controller  175  can be configured to receive information and send command signals to other components that are generally known to be included in a system that utilizes a variable speed compressor. 
     Details of the various algorithms that can be stored in the memory will now be provided below. 
     Generally, the controller  175  can be configured to implement the disclosed method of controlling the system  100  as illustrated in  FIGS. 2A and 2B . In general, the processes described in  FIGS. 2A and 2B  are executed by the processor executing program instructions (algorithms) stored in the memory of the controller  175 . The process can be initiated at any time during the four different operating states of the variable speed compressor  137 . In some examples, the process can be initiated manually by a user, or initiated automatically, for example, by a preprogrammed instruction stored inside the memory. 
     With reference to  FIG. 2A , in one embodiment, the disclosed method or algorithm  200  initiates at step  106  and proceeds to step  109  where a determination is made as to a required capacity of the conditioned space  104 . The term “required capacity” means a capacity or speed of the variable speed compressor  137  that is necessary to achieve a predetermined temperature and/or a predetermined relative humidity. 
     The determination of the required capacity can involve the use of certain parameters and calculations that are generally known in the art. For instance, the determination of the required capacity can be based on a prediction algorithm that involves calculations using a current reading of a dry-bulb temperature of the thermostat  119  and a predetermined temperature of the conditioned space  104 . The predetermined temperature may be a temperature of the conditioned space that is desired by a user. The predetermined temperature may be manually set by a user, e.g., as input to be processed by the controller  175 . 
     In one example, a PI controller can be used to determine the required capacity. In this instance, when the space temperature is above a set point, the PI controller will increase the capacity value, and when the space temperature is below the set point, the PI controller will decrease the capacity value. The adjustment will continue until the temperature reaches set point. The final capacity value is the “required capacity”. In one example, passive dehumidification is employed. In this instance, when relative humidity is high, a dehumidification map is used to coordinate the fan and the compressor, which will remove more moisture from conditioned air. The required capacity is calculated in the same manner as described above. 
     After step  109 , a determination is made as to whether the required capacity is larger than a minimum capacity of the variable speed compressor  137 . In some examples, the minimum capacity of the variable speed compressor  137  can be predetermined. In some other examples, the minimum capacity of the variable speed compressor  137  can be set by a user, e.g., as an input to be processed by the controller  175 . In some other examples, the minimum capacity of the variable speed compressor  137  can be calculated by the controller  175  in a manner that is generally known in the art, e.g., based on readings from a temperature sensor  169  of the fluid that is discharged from the compressor  137  and/or a temperature sensor  172  of the compressor  137 . 
     If the required capacity is the same as the minimum capacity, then the variable speed compressor  137  will remain at the minimum speed. 
     If the required capacity is less than the minimum capacity, then the algorithm proceeds to a cycling process {circle around ( 1 )} (further described/illustrated in  FIG. 3 ). In some examples, conducting the cycling process {circle around ( 1 )} based on the comparison between the determined required capacity and the minimum capacity can lead to improvement in space comfort control accuracy and reduction of compressor cycling frequency as compared to those of dead band based cycling by anticipating the load requirement and its dynamic changes. One example of dead band based cycling is when the space temperature is 1° F. above the set point, the compressor is turned on, and when the space temperature is 1° F. below the set point, the compressor is turned off. 
     In one example, the load requirement and its dynamic changes is anticipated by the PI controller, for instance, using the current temperature and the previous temperature to calculate the required capacity, and accordingly, taking the change in speed into consideration to predict what may happen in the future. 
     An overview of the cycling process {circle around ( 1 )} is illustrated in  FIG. 3 . Generally, the cycling process {circle around ( 1 )} involves cycling between four different operational states: operating in a unit off state  202 , operating in a startup state  207 , operating in a running state  212  and operating in a shutdown state  218 . 
     In the unit off state  202 , the variable speed compressor  137  stays off at the off position so that the speed of the variable speed compressor  137  is at 0 revolutions per second (rps). In some instances, the supply fan  131  also can be turned off so that the speed of the fan  131  is at 0 rps. In some examples, the supply fan  131  is turned off unless it is on fan off delay. “Fan off delay” means that the fan will not turn off until the compressor is turned off for a predetermined amount of time, e.g., about 30 seconds. 
     In the startup state  207 , the speed of the variable speed compressor  137  can ramp up at a constant rate from 0 rps until the speed reaches a startup speed of the compressor  137 . In some examples, the constant rate can be predetermined. In one implementation, the constant rate is an increase of about 2 revolutions per second. It is to be realized that the constant rate can vary depending on the allowable speed defined by the system components and the compressor specification. In other examples, the constant rate can be determined based on the required capacity determined in step  109  at  FIG. 2 . In some examples, the variable speed compressor  137  will ramp up at a constant rate from 0 rps until a startup speed of 25 rps, which is 25% of the maximum speed of 100 rps, is reached. Note that both the minimum and maximum speed values can vary depending on the allowable speed defined by the system components and the compressor specification. In some examples, after the startup speed is reached, the compressor  137  will operate at the startup speed for a predetermined amount of time. In some implementations, the predetermined amount of time is about 120 seconds. 
     In some instances in the startup state  207 , the supply fan  131  can run at a minimum speed where a variable speed fan is used for the supply fan  131 . 
     In the running state  212 , the variable speed compressor  137  is modulated between a minimum speed and a maximum speed. In some examples, the minimum speed is a function of entering water temperature (EWT) of the condenser. In some instances, the fan  131  also can be modulated between a minimum speed and a maximum speed. 
     In the shutdown state  218 , the variable speed compressor  137  can ramp down from the minimum speed to 0 rps. Shutdown is complete when 0 rps is reached. In some instances, the fan can run at a minimum speed. 
     The algorithm of the cycling process {circle around ( 1 )} is illustrated in  FIG. 2B . The cycling process {circle around ( 1 )} initially involves determining the operating state of the variable speed compressor  137  (step S 100 ). The operating state of the compressor  137  can be determined to be in the unit off state  202 , startup state  207 , running state  212  or shutdown state  218 . Note that at power-up, the controller  175  will start from the off state and use the logic in  FIG. 2B  to determine the next operating states. 
     If the operating state of the compressor  137  is determined to be in the startup state  207 , then a determination is made as to whether startup is completed (step  220 ). 
     In some examples, startup is completed when the speed of the variable speed compressor  137  reaches the startup speed of the compressor  137 . 
     If startup is determined to be incomplete, then the algorithm goes back to startup  207 . If the startup is determined to be complete, then the algorithm goes to step  228 . 
     In step  228 , a determination is made as to whether the required capacity determined in step  109  is greater than 0. If the required capacity is greater than 0, then the algorithm proceeds to operating the compressor  137  in the running state  212 . If the required capacity is equal to zero, then the compressor  137  proceeds to operate in the shutdown state  218 . 
     Note that in some examples, the algorithm can involve the step of determining whether the required capacity determined in step  109  is greater than 0 before the step of determining whether startup is completed. In this instance, the outcome would be the same as conducting the steps  220  and  228  in that order as described above. For example, if the required capacity is determined to be 0 at the running state, the algorithm goes to the shutdown state  218 . If the required capacity is detected to be 0 at the startup state, then the algorithm goes to the shutdown state  218  as well. 
     If the operating state of the compressor  137  is determined to be in the running state  212 , then the algorithm proceeds to step  235  where a time calculation is made. In one example, the time calculation involves calculating an amount of time the compressor will be turned on. In one instance, the time calculation is based on the required capacity calculated in step  109 . 
     After step  235 , a timer comparison is made (step  242 ). In this step, the time that the compressor will be turned on as determined in step  235  is compared with the current time, and the compressor is turned on for an amount of time based on the comparison. 
     After the compressor  137  is turned on for the determined amount of time, the compressor  137  then operates in the shutdown state  218 . 
     If the operating state of the compressor  137  is determined to be in the shutdown state  218 , the algorithm proceeds to step  254  where a determination is made as to whether shutdown is complete. In one example, shutdown is complete when the speed of the compressor reaches 0 rps. If shutdown is determined not to be complete, then the algorithm returns to the shutdown state  218 . If shutdown is determined to be complete, then the compressor  137  proceeds to operate in the unit off state  202 . 
     If the operating state of the compressor  137  is determined to be in the unit off state  202 , then the algorithm proceeds to step  265  where a time calculation is made. In one example, the time calculation involves calculating an amount of time the compressor will be turned off. In one instance, the time calculation is based on the required capacity calculated in step  109 . 
     After step  265 , a timer comparison is made (step  272 ). In this step, the time that the compressor will be turned off as determined in step  265  is compared with the current time, and the compressor is turned off for the determined amount of time. 
     After the compressor  137  is turned off for the determined amount of time, the compressor  137  then proceeds to operate in the startup state  207 . 
     Referring back to step  114  in  FIG. 2A , if the required capacity is greater than the minimum capacity, then the algorithm proceeds to step  121 , where the compressor  137  operates in the running state  212 , and then proceeds to step  135  where a time calculation is made. In one example, the time calculation involves calculating an amount of time the compressor will be turned on. In one instance, the time calculation is based on the required capacity calculated in step  109 . 
     After step  135 , a timer comparison is made (step  145 ). In this step, the time that the compressor will be turned on as determined in step  135  is compared with the current time, and the compressor is turned on for the determined amount of time. 
     In some examples, a feedback control system using a PI controller can be used to calculate the required capacity as in step  109 , execute the time calculation as in steps  135 ,  235  and  265 , and execute the timer comparison as in steps  145 ,  242  and  272 . A block diagram of a feedback control system  380  using a PI controller  402  is illustrated in  FIG. 4 . 
     The PI controller  402  can receive as input a current reading of a dry-bulb temperature of the thermostat  119  and a predetermined temperature of the conditioned space  104 . The predetermined temperature may be a temperature of the conditioned space  104  that is desired by a user. The PI controller  402  then can be used to calculate the required capacity, and provide as a controller output if there is a disparity between the current reading of a dry-bulb temperature of the thermostat  119  and the predetermined temperature of the conditioned space  104 . The controller output then can be used for calculating the amount of time the compressor needs to be turned on or off (block  405 ) as in steps  135 / 235  and  265 , respectively, make a timer comparison (block  411 ) as in steps  145 ,  242  and  272 , and turn the compressor  137  on or off for the determined amount of time. 
     In one example, the speed of the supply fan  131  can be modulated at the same time as the speed of the compressor  137 . In one instance, the supply fan  131  is a variable speed fan. In this instance, the fan speed increases or decreases with the compressor speed following a predetermined map(s). In some examples, the predetermined map(s) is an energy efficiency map(s) and/or a dehumidification map(s). In one example, the “energy efficiency map” and “dehumidification map” are lookup tables where the fan speed is calculated based on the compressor speed. Generally, there are many combinations of fan speed and compressor speed that can provide the same capacity. The energy efficiency map will provide the best overall energy efficiency, while the dehumidification map will provide the best moisture removal performance. In some instances, the fan speed will be lower in the dehumidification map than in the energy efficiency map when the same compressor speed is required. 
     In some examples, the energy efficiency map is a compressor efficiency map as described in U.S. Pat. No. 5,537,830, which is herein incorporated by reference. 
     In some examples, the predetermined map(s) coordinate the speeds of the fan  131  and compressor  137 . In some instances, the predetermined map(s) are different for the heating mode and the cooling mode. In one example, the heating and cooling mode transition is determined by the controller  175 . For example, heating is enabled when the space temperature stays below a set point for an extended period of time, while cooling is enabled when the space temperature stays above a set point for an extended period of time. 
     In other instances, the predetermined map(s) can change based on operating conditions such as the entering water temperature for a water-source unit. In this instance, the system  100  would further include a sensor (not shown) for the entering water for the water-source unit. In yet some other instances, the predetermined map(s) includes a dehumidification map. In some implementations, the dehumidification map has a lower fan speed to provide a higher percentage of latent capacity for improved space dehumidification. In one example, with the same compressor speed and the same entering air condition, the lower fan speed can result in a lower discharge air temperature and a lower saturate humidity. As such, a humidity ratio of the discharge air can be decreased. 
     In another instance, the supply fan  131  is a fixed speed fan. In this instance, the supply fan  131  is turned on or off at the same time the speed of the compressor  137  is modulated. In one instance, the fan  131  is turned on or off for a certain amount of time depending on the predetermined map(s) described above. In one example, the fan will be turned on when the compressor is on, and the fan will be turned off after the compressor is turned off for a period of fan off delay. 
     One example of how the speed of the supply fan  131  can be modulated at the same time of the speed of the compressor is illustrated in  FIG. 5 .  FIG. 5  depicts a graph, where the x-axis of the graph represents the required capacity and the y-axis of the graph represents the speeds of the supply fan  131  and the compressor  137 . In the graph, region “a” represents the startup state  207  and region “b” represents the running state  212 . 
     In the example shown in  FIG. 5 , during the startup state  207 , the compressor  137  ramps up speed at a constant rate from 0 rps to a minimum speed of the compressor  137 . During this time period, the supply fan  131  runs at a certain minimum speed. After the compressor  137  reaches its minimum speed, the compressor  137  enters the running state  212 , where the compressor  137  continues to ramp up speed at a constant rate. At the point where the compressor  137  reaches its minimum speed and enters the running state  212 , the fan  131  begins to increase in speed together with the speed of the compressor  137 . The speeds of the fan  131  and compressor  137  increase together at a constant rate until a maximum speed for the fan  131  and a maximum speed for the compressor  137  are reached. 
     Aspects 
     
         
         Any of aspects 1-8 can be combined with any of aspects 9-14. Any of aspects 1-8 can be combined with aspect 15. Any of aspects 1-8 can be combined with aspect 16.
       Aspect 1. A system, comprising:
           a compressor having the following operational states: a unit off state, a startup state, and a running state, and   a controller that is configured to   (a) determine a required capacity of a conditioned space;   (b) compare the required capacity determined in (a) with a minimum capacity of the compressor,   wherein if the required capacity determined in (a) is greater than the minimum capacity of the compressor, then
               (c1) operate the compressor in the running state; and   
               wherein if the required capacity determined (a) is less than the minimum capacity,
               (c2) cycle between each of the operational states based on the required capacity determined in (a).   
               
           Aspect 2. The system of any of aspects 1 and 3-8, further comprising a supply fan, wherein the compressor is a variable speed compressor, and the supply fan and the variable speed compressor are controlled simultaneously.   Aspect 3. The system of any of aspects 1-2 and 4-8, wherein operational state of the compressor further comprises a shutdown state, wherein in the unit off state, the compressor stays off at the off position so that the speed of the compressor is at 0 revolutions per second (rps), wherein in the startup state, the speed of the compressor ramps up at a constant rate from 0 rps until the speed reaches a startup speed of the compressor, wherein in the running state, the compressor is modulated between a minimum speed and a maximum speed, and wherein in the shutdown state, the compressor ramps down from the minimum speed to 0 rps.   Aspect 4. The system of any of aspects 1-3 and 5-8, wherein in the unit off state, the supply fan is off so that the speed of the supply fan is at 0 rps, wherein in the startup state, the supply fan operates at a minimum speed, wherein in the running state, the supply fan is modulated between a minimum speed and a maximum speed, and wherein the shutdown state, the supply fan operates at a minimum speed.   Aspect 5. The system of any of aspects 1-4 and 6-8, wherein the supply fan is a variable speed fan.   Aspect 6. The system of any of aspects 1-5 and 7-8, wherein the supply fan operates at a fixed speed.   Aspect 7. The system of any of aspects 1-6 and 8, wherein in (c2), a determination is made as to the operating state of the compressor.   Aspect 8. The system of any of aspects 1-7, wherein in (a), the required capacity is based on a current reading of a dry-bulb temperature of the conditioned space and a predetermined temperature of the conditioned space.   Aspect 9. A method of controlling a heating, ventilating and air conditioning system that includes a compressor, the compressor having the following operational states: a unit off state, a startup state, and a running state, the method comprising
           (a) determining a required capacity of a conditioned space;   (b) comparing the required capacity determined in (a) with a minimum capacity of the compressor,   wherein if the required capacity determined in (a) is greater than the minimum capacity of the compressor, then
               (c1) operate the compressor in the running state   wherein if the required capacity determined (a) is less than the minimum capacity of the compressor,   (c2) cycle between each of the operational states based on the required capacity determined in (a).   
               
           Aspect 10. The method of any of aspects 9 and 11-14, wherein the system further comprises a supply fan, wherein the compressor is a variable speed compressor, and wherein the compressor and the supply fan are controlled simultaneously.   Aspect 11. The method of any of aspects 9-10 and 12-14, wherein the operational state of the compressor further comprises a shutdown state, wherein in the unit off state, the compressor stays off at the off position so that the speed of the compressor is at 0 revolutions per second (rps), wherein in the startup state, the speed of the compressor ramps up at a constant rate from 0 rps until the speed reaches a startup speed of the compressor, wherein in the running state, the compressor is modulated between a minimum speed and a maximum speed, and wherein in the shutdown state, the compressor ramps down from the minimum speed to 0 rps.   Aspect 12. The method of any of aspects 9-11 and 13-14, wherein in the unit off state, the supply fan is off so that the speed of the fan is at 0 rps, wherein in the startup state, the supply fan operates at a minimum speed, wherein in the running state, the supply fan is modulated between a minimum speed and a maximum speed, and wherein the shutdown state, the supply operates at a minimum speed.   Aspect 13. The method of any of aspects 9-12 and 14, wherein in (c2), a determination is made as to the operating state of the compressor.   Aspect 14. The method of any of aspects 9-13, wherein in (a), the required capacity is based on a current reading of a dry bulb temperature of the conditioned space and a predetermined temperature of the conditioned space.   Aspect 15. A method for controlling a compressor and a supply fan in a heating, ventilating and air conditioning system, wherein the compressor and the supply fan are controlled based on an efficiency map and/or a dehumidification map.   Aspect 16. A system, comprising:
           a variable capacity compressor having the following operational states: a unit off state, a startup state, and a running state, and   a controller that is configured to   (a) determine a required capacity of a conditioned space;   (b) compare the required capacity determined in (a) with a minimum capacity of the compressor,   wherein if the required capacity determined in (a) is greater than the minimum capacity of the compressor, then
               (c1) operate the compressor in the running state; and   
               wherein if the required capacity determined (a) is less than the minimum capacity,
               (c2) cycle between each of the operational states based on the required capacity determined in (a).   
               
           
     
       
    
     With regard to the foregoing description, it is to be understood that changes may be made in detail, especially in matters of the construction materials employed and the shape, size and arrangement of the parts without departing from the scope of the present invention. It is intended that the specification and depicted embodiment to be considered exemplary only, with a true scope and spirit of the invention being indicated by the broad meaning of the claims.