Patent Publication Number: US-11378317-B2

Title: Method and system for compressor modulation in non-communicating mode

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/261,910, filed on Jan. 30, 2019. U.S. patent application Ser. No. 16/261,910 is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to heating, ventilation, and air conditioning (HVAC) systems and more particularly, but not by way of limitation, to utilizing a variable-speed compressor with an HVAC controller adapted for use with a single-speed compressor. 
     BACKGROUND 
     This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. 
     HVAC systems are used to regulate environmental conditions within an enclosed space. Typically, HVAC systems have a circulation fan that pulls air from the enclosed space through ducts and pushes the air back into the enclosed space through additional ducts after conditioning the air (e.g., heating, cooling, humidifying, or dehumidifying the air). To direct operation of the circulation fan and other components. HVAC systems include a controller. In addition to directing operation of the HVAC system, the controller may be used to monitor various components, (i.e. equipment) of the HVAC system to determine if the components are functioning properly. 
     SUMMARY 
     In an embodiment, aspects of the disclosure relate to a heating, ventilation, and air-conditioning (HVAC) system. The HVAC system includes an indoor unit. The indoor unit includes an indoor heat-exchange coil, an indoor circulation fan arranged to circulate air through the indoor heat-exchange coil, and a metering device fluidly coupled to the indoor heat-exchange coil. The HVAC system further includes an outdoor unit. The outdoor unit includes an outdoor heat-exchange coil, an outdoor circulation fan arranged to circulate air through the outdoor heat-exchange coil, a compressor fluidly coupled to the outdoor heat-exchange coil and fluidly coupled to the indoor heat-exchange coil, and a compressor controller electrically coupled to the compressor. A pressure sensor is disposed in a suction line between the compressor and the indoor heat-exchange coil. The pressure sensor is electrically coupled to the compressor controller. An HVAC controller is electrically coupled to the compressor controller. The HVAC controller is configured to transmit a signal to the compressor controller to at least one of activate and de-activate the compressor. The compressor controller is configured to receive a signal from the HVAC controller to activate the compressor, determine a start speed of the compressor, monitor a run time of the compressor, and modulate a speed of the compressor. 
     In an embodiment, aspects of the disclosure relate to a compressor system. The compressor system includes an outdoor heat-exchange coil, an outdoor circulation fan disposed arranged to circulate air through the outdoor heat-exchange coil, a compressor fluidly coupled to the outdoor heat-exchange coil, and a compressor controller electrically coupled to the compressor. The compressor controller is configured to receive a signal from an HVAC controller to activate the compressor, determine a start speed of the compressor, monitor a run time of the compressor, and modulate a speed of the compressor. 
     In an embodiment, aspects of the disclosure relate to a method of modulating a speed of a compressor. The method includes receiving a signal from an HVAC controller to at least one of activate and de-activate a compressor. A start speed of the compressor is determined. The compressor is activated at the determined start speed. A run time of the compressor is monitored. The run time of the compressor is compared to a desired cycle time of an HVAC system. A speed of the compressor is modulated. 
     This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a block diagram of an HVAC system according to aspects of the disclosure; 
         FIG. 2  is a schematic diagram of an HVAC system having a single-speed compressor according to aspects of the disclosure; 
         FIG. 3  is a schematic diagram of the HVAC system where the single-speed compressor has been replaced with a variable-speed compressor according to aspects of the disclosure; 
         FIGS. 4A-4B  illustrate a flow diagram of a process for modulating compressor speed according to aspects of the disclosure; 
         FIG. 5  is a graph illustrating a relationship between HVAC system run time and outdoor temperature; and 
         FIG. 6  is a graph illustrating a relationship between average compressor speed and outdoor temperature. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will now be described more fully with reference to the accompanying drawings. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
     HVAC systems are frequently utilized to adjust both temperature of conditioned air as well as relative humidity of the conditioned air. A cooling capacity of an HVAC system is a combination of the HVAC system&#39;s sensible cooling capacity and latent cooling capacity. Sensible cooling capacity refers to an ability of the HVAC system to remove sensible heat from conditioned air. Latent cooling capacity refers to an ability of the HVAC system to remove latent heat from conditioned air. In a typical embodiment, sensible cooling capacity and latent cooling capacity vary with environmental conditions. Sensible heat refers to heat that, when added to or removed from the conditioned air, results in a temperature change of the conditioned air. Latent heat refers to heat that, when added to or removed from the conditioned air, results in a phase change of, for example, water within the conditioned air. Sensible-to-total ratio (“S/T ratio”) is a ratio of sensible heat to total heat (sensible heat+latent heat). The lower the S/T ratio, the higher the latent cooling capacity of the HVAC system for given environmental conditions. 
     Sensible cooling load refers to an amount of heat that must be removed from the enclosed space to accomplish a desired temperature change of the air within the enclosed space. The sensible cooling load is reflected by a temperature within the enclosed space as read on a dry-bulb thermometer. Latent cooling load refers to an amount of heat that must be removed from the enclosed space to accomplish a desired change in humidity of the air within the enclosed space. The latent cooling load is reflected by a temperature within the enclosed space as read on a wet-bulb thermometer. Setpoint or temperature setpoint refers to a target temperature setting of the HVAC system as set by a user or automatically based on a pre-defined schedule. 
     In situations where there is a high sensible cooling load such as, for example, when outside-air temperature is significantly warmer than an inside-air temperature setpoint, the HVAC system will continue to operate in an effort to effectively cool and dehumidify the conditioned air. When there is a low sensible cooling load but high relative humidity such as, for example, when the outside air temperature is relatively close to the inside air temperature setpoint, but the outside air is considerably more humid than the inside air, an HVAC system having a single-speed compressor will often repeatedly cycle between an active state and a de-activated state in an effort to provide de-humidification air while not over-conditioning the air. In such situations, a variable-speed compressor would allow the HVAC system to run in a more continuous fashion at a lower speed thereby providing more effective de-humidification of air. 
       FIG. 1  illustrates an HVAC system  100 . In various embodiments, the HVAC system  100  is a networked HVAC system that is configured to condition air via, for example, heating, cooling, humidifying, or dehumidifying air within an enclosed space  101 . In various embodiments, the enclosed space  101  is, for example, a house, an office building, a warehouse, or the like. Thus, the HVAC system  100  can be a residential system or a commercial system such as, for example, a roof top system. For exemplary illustration, the HVAC system  100  as illustrated in  FIG. 1  includes various components; however, in other embodiments, the HVAC system  100  may include additional components that are not illustrated but may, in various embodiments, be included within HVAC systems. 
     The HVAC system  100  includes an indoor circulation fan  110  arranged to circulate air over an indoor heat-exchange coil  130 , at least one of a gas heat  120  and an electric heat  122 . The indoor circulation fan  110 , at least one of the gas heat  120  and the electric heat  122 , and the indoor heat-exchange coil  130  are collectively referred to as an “indoor unit”  148 . In a typical embodiment, the indoor unit  148  is located within, or in close proximity to, the enclosed space  101 . The HVAC system  100  also includes a compressor  140 , an associated outdoor heat-exchange coil  142 , and an outdoor circulation fan  210 , which are typically referred to as an “outdoor unit”  144 . In various embodiments, the outdoor unit  144  is, for example, a rooftop unit or a ground-level unit. The compressor  140  and the associated outdoor heat-exchange coil  142  are connected to the indoor heat-exchange coil  130  by a refrigerant line  146 . In various embodiments, as will be discussed in more detail below, the compressor  140  may be, for example, a single-speed compressor, a variable-speed compressor, a single-stage compressor or a multi-stage compressor. In various embodiments, the indoor circulation fan  110 , sometimes referred to as a blower, is configured to operate at different capacities (i.e., variable motor speeds) to circulate air through the HVAC system  100 , whereby the circulated air is conditioned and supplied to the enclosed space  101 . 
     Still referring to  FIG. 1 , the HVAC system  100  includes an HVAC controller  150  that is configured to control operation of the various components of the HVAC system  100  such as, for example, the indoor circulation fan  110 , at least one of the gas heat  120  and the electric heat  122 , and the compressor  140  to regulate the environment of the enclosed space  101 . In some embodiments, the HVAC system  100  can be a zoned system. In such embodiments, the HVAC system  100  includes a zone controller  180 , dampers  185 , and a plurality of environment sensors  160 . In a typical embodiment, the HVAC controller  150  cooperates with the zone controller  180  and the dampers  185  to regulate the environment of the enclosed space  101 . In various embodiments, particularly embodiments where the compressor  140  is a single-speed compressor, the HVAC controller  150  communicates an on/off signal to the compressor  140  via, for example, a 24 Volt alternating-current (VAC) signal. 
     In various embodiments, particularly embodiments where the compressor  140  is a variable-speed compressor, the HVAC controller  150  may be an integrated controller or a distributed controller that directs operation of the HVAC system  100 . In various embodiments, the HVAC controller  150  includes an interface to receive, for example, thermostat calls, temperature setpoints, blower control signals, environmental conditions, and operating mode status for various zones of the HVAC system  100 . For example, in a typical embodiment, the environmental conditions may include indoor temperature and relative humidity of the enclosed space  101 . In various embodiments, the HVAC controller  150  also includes a processor and a memory to direct operation of the HVAC system  100  including, for example, a speed of the compressor  140 . 
     Still referring to  FIG. 1 , in some embodiments, the plurality of environment sensors  160  are associated with the HVAC controller  150  and also optionally associated with a user interface  170 . The plurality of environment sensors  160  provides environmental information within a zone or zones of the enclosed space  101  such as, for example, temperature and humidity of the enclosed space  101  to the HVAC controller  150 . The plurality of environment sensors  160  may also send the environmental information to a display of the user interface  170 . In some embodiments, the user interface  170  provides additional functions such as, for example, operational, diagnostic, status message display, and a visual interface that allows at least one of an installer, a user, a support entity, and a service provider to perform actions with respect to the HVAC system  100 . In some embodiments, the user interface  170  is, for example, a thermostat of the HVAC system  100 . In other embodiments, the user interface  170  is associated with at least one sensor of the plurality of environment sensors  160  to determine the environmental condition information and communicate that information to the user. The user interface  170  may also include a display, buttons, a microphone, a speaker, or other components to communicate with the user. Additionally, the user interface  170  may include a processor and memory that is configured to receive user-determined parameters such as, for example, a relative humidity of the enclosed space  101 , and calculate operational parameters of the HVAC system  100  as disclosed herein. 
     In a typical embodiment, the HVAC system  100  is configured to communicate with a plurality of devices such as, for example, a monitoring device  156 , a communication device  155 , and the like. In a typical embodiment, the monitoring device  156  is not part of the HVAC system. For example, the monitoring device  156  is a server or computer of a third party such as, for example, a manufacturer, a support entity, a service provider, and the like. In other embodiments, the monitoring device  156  is located at an office of, for example, the manufacturer, the support entity, the service provider, and the like. 
     In various embodiments, the communication device  155  is a non-HVAC device having a primary function that is not associated with HVAC systems. For example, non-HVAC devices include mobile-computing devices that are configured to interact with the HVAC system  100  to monitor and modify at least some of the operating parameters of the HVAC system  100 . Mobile computing devices may be, for example, a personal computer (e.g., desktop or laptop), a tablet computer, a mobile device (e.g., smart phone), and the like. In various embodiments, the communication device  155  includes at least one processor, memory and a user interface, such as a display. One skilled in the art will also understand that the communication device  155  disclosed herein includes other components that are typically included in such devices including, for example, a power supply, a communications interface, and the like. 
     The zone controller  180  is configured to manage movement of conditioned air to designated zones of the enclosed space  101 . Each of the designated zones include at least one conditioning or demand unit such as, for example, the gas heat  120  and at least one user interface  170  such as, for example, the thermostat. The zone-controlled HVAC system  100  allows the user to independently control the temperature in the designated zones. In various embodiments, the zone controller  180  operates electronic dampers  185  to control air flow to the zones of the enclosed space  101 . 
     In some embodiments, a data bus  190 , which in the illustrated embodiment is a serial bus, couples various components of the HVAC system  100  together such that data is communicated therebetween. In a typical embodiment, the data bus  190  may include, for example, any combination of hardware, software embedded in a computer readable medium, or encoded logic incorporated in hardware or otherwise stored (e.g., firmware) to couple components of the HVAC system  100  to each other. As an example and not by way of limitation, the data bus  190  may include an Accelerated Graphics Port (AGP) or other graphics bus, a Controller Area Network (CAN) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT) interconnect, an INFINIBAND interconnect, a low-pin-count (LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PC-Express (PCI-X) bus, a serial advanced technology attachment (SATA) bus, a Video Electronics Standards Association local (VLB) bus, or any other suitable bus or a combination of two or more of these. In various embodiments, the data bus  190  may include any number, type, or configuration of data buses  190 , where appropriate. In particular embodiments, one or more data buses  190  (which may each include an address bus and a data bus) may couple the HVAC controller  150  to other components of the HVAC system  100 . In other embodiments, connections between various components of the HVAC system  100  are wired. For example, conventional cable and contacts may be used to couple the HVAC controller  150  to the various components. In some embodiments, a wireless connection is employed to provide at least some of the connections between components of the HVAC system such as, for example, a connection between the HVAC controller  150  and the indoor circulation fan  110  or the plurality of environment sensors  160 . 
       FIG. 2  is a schematic diagram of an HVAC system  200  having a single-speed compressor  220 . For illustrative purposes,  FIG. 2  will be described herein relative to  FIG. 1 . In various embodiments, the HVAC system  200  may operate in a heating mode or an air-conditioning mode. The HVAC system  200  includes the indoor heat-exchange coil  130 , the outdoor heat-exchange coil  142 , a single-speed compressor  220 , and a metering device  202 . In a typical embodiment, the metering device  202  is, for example, a thermal expansion valve or a throttling valve. The indoor heat-exchange coil  130  is fluidly coupled to the single-speed compressor  220  via a suction line  204 . The single-speed compressor  220  is fluidly coupled to the outdoor heat-exchange coil  142  via a discharge line  206 . The outdoor heat-exchange coil  142  is fluidly coupled to the metering device  202  via a liquid line  208 . 
     Still referring to  FIG. 2 , during operation, low-pressure, low-temperature refrigerant is circulated through the indoor heat-exchange coil  130 . The refrigerant is initially in a liquid/vapor state. In a typical embodiment, the refrigerant is, for example, R-22, R-134a, R-410A, R-744, or any other suitable type of refrigerant as dictated by design requirements. Air from within the enclosed space  101  is circulated around the indoor heat-exchange coil  130  by the indoor circulation fan  110 . When the HVAC system  200  operates in the air-conditioning mode, the indoor heat-exchange coil  130  functions as an evaporator. Thus, the refrigerant begins to boil after absorbing heat from the air and changes state to a low-pressure, low-temperature, super-heated vapor refrigerant. Saturated vapor, saturated liquid, and saturated fluid refer to a thermodynamic state where a liquid and its vapor exist in approximate equilibrium with each other. Super-heated fluid and super-heated vapor refer to a thermodynamic state where a vapor is heated above a saturation temperature of the vapor. Sub-cooled fluid and sub-cooled liquid refer to a thermodynamic state where a liquid is cooled below the saturation temperature of the liquid. 
     The low-pressure, low-temperature, super-heated vapor refrigerant is introduced into the single-speed compressor  220  via the suction line  204 . In a typical embodiment, the single-speed compressor  220  increases the pressure of the low-pressure, low-temperature, super-heated vapor refrigerant and, by operation of the ideal gas law, also increases the temperature of the low-pressure, low-temperature, super-heated vapor refrigerant to form a high-pressure, high-temperature, superheated vapor refrigerant. The high-pressure, high-temperature, superheated vapor refrigerant leaves the single-speed compressor  220  via the discharge line  206  and is directed to the outdoor heat-exchange coil  142 . 
     Outside air is circulated around the outdoor heat-exchange coil  142  by an outdoor circulation fan  210 . When the HVAC system  200  is operating in the air-conditioning mode, the outdoor heat-exchange coil  142  functions as a condenser. Thus, in the air-conditioning mode, heat is transferred from the high-pressure, high-temperature, superheated vapor refrigerant to the outside air. Removal of heat from the high-pressure, high-temperature, superheated vapor refrigerant causes the high-pressure, high-temperature, superheated vapor refrigerant to condense and change from a vapor state to a high-pressure, high-temperature, sub-cooled liquid state. The high-pressure, high-temperature, sub-cooled liquid refrigerant leaves the outdoor heat-exchange coil  142  via the liquid line  208  and enters the metering device  202 . 
     Still referring to  FIG. 2 , when the HVAC system  200  is operating in the heating mode, the direction of refrigerant flow is reversed. Thus, in the heating mode, the indoor heat-exchange coil  130  functions as a condenser and the outdoor heat-exchange coil  142  functions as an evaporator. In various embodiments, reversal of refrigerant flow is accomplished by a reversing valve  207 . 
     In the metering device  202 , the pressure of the high-pressure, high-temperature, sub-cooled liquid refrigerant is abruptly reduced. In various embodiments where the metering device  202  is, for example, a thermal expansion valve, the metering device  202  reduces the pressure of the high-pressure, high-temperature, sub-cooled liquid refrigerant by regulating an amount of refrigerant that travels to the indoor heat-exchange coil  130 . Abrupt reduction of the pressure of the high-pressure, high-temperature, sub-cooled liquid refrigerant causes sudden, rapid, evaporation of a portion of the high-pressure, high-temperature, sub-cooled liquid refrigerant, commonly known as “flash evaporation.” The flash evaporation lowers the temperature of the resulting liquid/vapor refrigerant mixture to a temperature lower than a temperature of the air in the enclosed space  101 . The liquid/vapor refrigerant mixture leaves the metering device  202  and returns to the indoor heat-exchange coil  130 . 
     Still referring to  FIG. 2 , an HVAC controller  222  is electrically coupled to the single-speed compressor  220 , the indoor circulation fan  110 , and the outdoor circulation fan  210 . When the HVAC system  200  is operating in the heating mode and the air-conditioning mode, the HVAC controller  222  provides, for example, a 24 VAC signal to the single-speed compressor  220  causing the single-speed compressor  220  to cycle between an activated state and a de-activated state. 
     During the life of the HVAC system  200 , it may be desirable to replace the outdoor unit  144  having the single-speed compressor  220  with an outdoor unit having a variable-speed compressor. In most cases, however, the HVAC controller  222  associated with the single-speed compressor  220  cannot provide the signal required to modulate a speed of a variable-speed compressor. 
       FIG. 3  is a schematic diagram of the HVAC system  300  where the single-speed compressor  220  has been replaced with a variable-speed compressor  320 . For illustrative purposes,  FIG. 3  will be described herein relative to  FIGS. 1-2 . A compressor controller  323  is electrically coupled to the variable-speed compressor  320  and the HVAC controller  222 . A pressure sensor  322  is disposed in the suction line  204  on a suction side of the variable-speed compressor  320  and is electrically coupled to the compressor controller  323 . In various embodiments, the pressure sensor  322  is, for example, a pressure transducer. A temperature sensor  324  is disposed in the discharge line  206  on a discharge side of the variable-speed compressor  320  and is configured to measure a refrigerant temperature in the discharge line  206 . During operation, the compressor controller  323  modulates the speed of the variable-speed compressor  320  in an effort to optimize the run time of the HVAC system  300 . In various embodiments, it is desirable to have the variable-speed compressor  320  run as much as possible in an effort to improve thermal comfort in the enclosed space  101  and to reduce energy consumption due to cycling losses. During operation, the HVAC controller  222  provides a cooling signal (also referred to as a “Y call”) to the compressor controller  323  to activate or deactivate the variable-speed compressor  320 . In various embodiments, the compressor controller  323  may be, for example, a motor control unit, a PID controller, or other appropriate controller. The compressor controller  323  includes a timer unit  325  and a processor  327 . In various embodiments, the timer unit  325  is configured to monitor a run time of the variable-speed compressor  320 . That is, the timer unit  325  measures an amount of time that the variable-speed compressor  320  is activated. The processor  327  is configured to provide a signal to the variable-speed compressor  320  to modulate a speed of the variable-speed compressor  320 . 
     Still referring to  FIG. 3 , when the HVAC system  300  is operating in the air-conditioning mode, as a cooling load in the enclosed space  101  increases, refrigerant pressure in the suction line  204  increases. In various embodiments, a speed of the variable-speed compressor  320  is increased in an effort to lower the refrigerant pressure in the suction line  204 . Similarly, when the cooling load in the enclosed space  101  decreases, the refrigerant pressure in the suction line  204  decreases. In various embodiments, the speed of the variable-speed compressor  320  is decreased in an effort to raise the refrigerant pressure in the suction line  204 . 
     Still referring to  FIG. 3 , when the HVAC system  300  is operating in the heating mode, as a heating load in the enclosed space  101  increases, the refrigerant temperature in the discharge line  206  decreases. In various embodiments, a speed of the variable-speed compressor  320  is increased in an effort to raise the refrigerant temperature in the discharge line  206 . Similarly, when the heating load in the enclosed space  101  decreases, the refrigerant temperature in the discharge line  206  increases. In various embodiments, the speed of the variable-speed compressor  320  is decreased in an effort to lower the refrigerant temperature in the discharge line  206 . 
       FIGS. 4A-4B  illustrate a flow diagram of a process  400  for modulating a speed of the variable-speed compressor  320 . For illustrative purposes,  FIGS. 4A-4B  will be described herein relative to  FIGS. 1-3 . The process  400  begins at step  402 . At step  404 , a start speed of the variable-speed compressor  320  is determined. In various embodiments, the start speed may be determined, for example, as a function of outdoor temperature, suction pressure, and HVAC system  300  cycle time. In one embodiment, the start speed of the variable-speed compressor  320  may be determined utilizing, for example, a lookup table as illustrated at step  404 . At step  406 , the compressor controller  323  signals the variable-speed compressor  320  to activate at the start speed determined in step  404 . In various embodiments, the compressor controller  323  signals the variable-speed compressor  320  to activate responsive to a Y call received from the HVAC controller  222 . In various embodiments, the Y call is, for example, a 24 VAC signal. At step  408 , the timer unit  325  begins to monitor the run time of the variable-speed compressor  320 . At step  410 , it is determined if the compressor controller  323  is receiving a Y call from the HVAC controller  222 . If, at step  410 , the compressor controller  323  is receiving a Y call from the HVAC controller  222 , the process  400  proceeds to step  412 . If, at step  410 , it is determined that the compressor controller  323  is not receiving a Y call from the HVAC controller  222 , the process  400  proceeds to step  414 . At step  414 , the start speed of the variable-speed compressor  320  is reduced. In various embodiments, the start speed may be reduced to a value that is, for example, approximately two thirds of the original start speed of the variable-speed compressor  320  provided that the start speed of the variable-speed compressor  320  remains above a minimum rated speed of the variable-speed compressor  320 . From step  414 , the process  400  returns to step  404 . 
     Still referring to  FIGS. 4A-4B , at step  412 , it is determined if the run time of the variable-speed compressor  320 , monitored by the timer unit  325 , is greater than a minimum threshold. In various embodiments, the minimum threshold may be, for example, five minutes; however, in other embodiments, other time thresholds could be utilized. If, at step  412 , it is determined that the run time of the variable-speed compressor  320  is not above the minimum threshold, the process  400  returns to step  410 . If, at step  412 , it is determined that the run time of the variable-speed compressor  320  is above the minimum threshold, the process  400  proceeds to step  416 . At step  416 , when the HVAC system  300  is operating in the air-conditioning mode, the compressor controller  323  modulates a speed of the variable-speed compressor  320  in an effort to maintain a pressure in the suction line  204  measured by the pressure sensor  322 . In an alternative embodiment, a pressure switch (not shown) may be disposed in the suction line  204 . The pressure switch is electrically coupled to the compressor controller  323 . In such an embodiment, the pressure switch could be calibrated to open when the pressure in the suction line  204  reaches, for example, approximately 140 psig and calibrated to close when the pressure in the suction line  204  falls to, for example, approximately 130 psig. In such an embodiment, the variable-speed compressor  320  would increase in speed until the pressure switch closes at approximately 130 psig. Subsequently, the variable-speed compressor  320  would decrease in speed until the pressure switch opens at approximately 140 psig. In a typical embodiment, a speed of the variable-speed compressor  320  is in the range of approximately 20 Hz to approximately 60 Hz. 
     Still referring to  FIGS. 4A-4B , when the HVAC system  300  is operating in the heating mode, the compressor controller  323  modulates a speed of the variable-speed compressor  320  in an effort to maintain a temperature in the discharge line  206  measured by the temperature sensor  324 . In an alternative embodiment, a pressure switch (not shown) may be disposed in the discharge line  206 . In such an embodiment, the pressure switch could be calibrated to open when the pressure in the discharge line  206  reaches, for example, approximately 400 psig and calibrated to close when the pressure in the discharge line  206  falls to, for example, approximately 350 psig. In such an embodiment, the variable-speed compressor  320  would increase in speed until the pressure switch closes at approximately 350 psig. Subsequently, the variable-speed compressor  320  would decrease in speed until the pressure switch opens at approximately 400 psig. 
     Still referring to  FIGS. 4A-4B , at step  418 , it is determined if the compressor controller  323  is receiving a Y call from the HVAC controller  222 . If, at step  418 , it is determined that the compressor controller  323  is receiving a Y call from the HVAC controller  222 , the process  400  proceeds to step  420 . If, at step  418 , it is determined that the compressor controller  323  is not receiving a Y call from the HVAC controller  222 , the process  400  proceeds to step  428 . 
     Still referring to  FIGS. 4A-4B , at step  420 , it is determined if the run time of the variable-speed compressor  320 , monitored by the timer unit  325  is greater than or equal to a desired cycle time. In various embodiments, the desired cycle time is in the range of approximately 20 minutes to approximately 30 minutes. If, at step  420 , it is determined that the run time of the variable-speed compressor  320  is not greater than or equal to the desired cycle time, the process  400  returns to step  416 . If, at step  420 , it is determined that the run time of the variable-speed compressor  320  is greater than or equal to the desired cycle time, the process  400  proceeds to step  422 . At step  422 , the compressor controller  323  increases the speed of the variable-speed compressor  320 . In various embodiments, the compressor controller  323  increases a speed of the variable-speed compressor  320  by, for example, 1 Hz, provided that the speed of the variable-speed compressor  320  remains below a maximum-rated speed of the variable-speed compressor  320 . At step  424 , it is determined if the compressor controller  323  is receiving a Y call from the HVAC controller  222 . If, at step  424 , it is determined that the compressor controller  323  is receiving a Y call from the HVAC controller  222 , the process  400  returns to step  422 . If, at step  424 , it is determined that the compressor controller  323  is not receiving a Y call from the HVAC controller  222 , the process  400  proceeds to step  426 . 
     Still referring to  FIGS. 4A-4B , at step  426 , the suction pressure and the start speed of the variable-speed compressor  320  are adjusted as a function of the monitored run time of the variable-speed compressor  320 . Likewise, at step  428 , the suction pressure and the start speed of the variable-speed compressor  320  are adjusted as a function of the monitored run time of the variable-speed compressor  320 . That is, if the run time of the variable-speed compressor  320  is short, it is indicative of a target suction pressure that is too low thereby causing the variable-speed compressor  320  to run at a higher speed. In an effort to increase a run time of the variable-speed compressor  320 , the suction pressure target could be increased and the starting speed of the variable-speed compressor  320  could be decreased. From step  426  and step  428 , the process  400  proceeds to step  429  where the lookup table is updated. From step  429  the process  400  returns to step  404 . In various embodiments, the process  400  ends when the Y call ceases. When the Y call ceases, the suction pressure target and the start speed of the variable-speed compressor  320  are updated. 
       FIG. 5  is a graph  500  illustrating a relationship between HVAC system run time and outdoor temperature. An HVAC system having the variable-speed compressor  320  is illustrated by the line  502 . An HVAC system having the single-speed compressor  220  is illustrated by the line  504 . The graph  500  demonstrates that, as outdoor temperature increases, the HVAC system having the variable-speed compressor  320  is capable of more extended run time than the HVAC system having the single-speed compressor  220 . This allows the HVAC system having the variable-speed compressor  320  to increase the run time of the HVAC system while operating the variable-speed compressor  320  at a lower speed that would normally be utilized by the HVAC system having the single-speed compressor  220 . The extended run time of the variable-speed compressor  320  is beneficial for thermal comfort, improved humidity control, and reduced energy consumption. 
       FIG. 6  is a graph illustrating a relationship between average compressor speed and outdoor temperature. The line  602  illustrates that, as outdoor temperature increases, the average compressor speed of the HVAC system having the variable-speed compressor  320  increases. 
     The term “substantially” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. In any disclosed embodiment, the terms “substantially,” “approximately.” “generally.” and “about” may be substituted with “within 10% of” what is specified. 
     For purposes of this patent application, the term computer-readable storage medium encompasses one or more tangible computer-readable storage media possessing structures. As an example and not by way of limitation, a computer-readable storage medium may include a semiconductor-based or other integrated circuit (IC) (such as, for example, a field-programmable gate array (FPGA) or an application-specific IC (ASIC)), a hard disk, an HDD, a hybrid hard drive (HHD), an optical disc, an optical disc drive (ODD), a magneto-optical disc, a magneto-optical drive, a floppy disk, a floppy disk drive (FDD), magnetic tape, a holographic storage medium, a solid-state drive (SSD), a RAM-drive, a SECURE DIGITAL card, a SECURE DIGITAL drive, a flash memory card, a flash memory drive, or any other suitable tangible computer-readable storage medium or a combination of two or more of these, where appropriate. 
     Particular embodiments may include one or more computer-readable storage media implementing any suitable storage. In particular embodiments, a computer-readable storage medium implements one or more portions of the HVAC controller  150 , one or more portions of the user interface  170 , one or more portions of the zone controller  180 , or a combination of these, where appropriate. In particular embodiments, a computer-readable storage medium implements RAM or ROM. In particular embodiments, a computer-readable storage medium implements volatile or persistent memory. In particular embodiments, one or more computer-readable storage media embody encoded software. 
     In this patent application, reference to encoded software may encompass one or more applications, bytecode, one or more computer programs, one or more executables, one or more instructions, logic, machine code, one or more scripts, or source code, and vice versa, where appropriate, that have been stored or encoded in a computer-readable storage medium. In particular embodiments, encoded software includes one or more application programming interfaces (APIs) stored or encoded in a computer-readable storage medium. Particular embodiments may use any suitable encoded software written or otherwise expressed in any suitable programming language or combination of programming languages stored or encoded in any suitable type or number of computer-readable storage media. In particular embodiments, encoded software may be expressed as source code or object code. In particular embodiments, encoded software is expressed in a higher-level programming language, such as, for example, C. Python. Java, or a suitable extension thereof. In particular embodiments, encoded software is expressed in a lower-level programming language, such as assembly language (or machine code). In particular embodiments, encoded software is expressed in JAVA. In particular embodiments, encoded software is expressed in Hyper Text Markup Language (HTML). Extensible Markup Language (XML), or other suitable markup language. 
     Depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. Although certain computer-implemented tasks are described as being performed by a particular entity, other embodiments are possible in which these tasks are performed by a different entity. 
     Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. 
     While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices or algorithms illustrated can be made without departing from the spirit of the disclosure. As will be recognized, the processes described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others. The scope of protection is defined by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.