Systems and methods for defrost control

A system for heating a building via refrigerant includes a coil temperature sensor, an ambient temperature sensor, and a controller. The controller includes a processing circuit configured to record a system operating parameter and a control step of a control process before performing a sacrificial defrost cycle. The processing circuit is configured to cause the system to perform the sacrificial defrost cycle and operate the system at predefined system operating parameters other than the recorded system operating parameters. The system is configured to cause the system to operate at the recorded system operating parameters and generate calibration data in response to the sacrificial defrost cycle ending. The processing circuit is configured to cause the control process to operate at the recorded control step and cause the system to perform a defrost cycle based on the calibration data, the coil temperature, and the ambient temperature.

BACKGROUND

Heat pumps, which operate during winter months, require a method for removing frost that accumulates on an outdoor coil of the heat pump while the heat pump heats a building. The heat pump may be configured to operate a reversing valve to change refrigerant flow from a heating cycle, used to heat the building, to a cooling cycle, used to heat the outdoor coil and thus remove any frost which has accumulated on the outdoor coil.

SUMMARY

One implementation of the present disclosure is a system for heating a building via refrigerant. The system includes a coil temperature sensor configured to measure a coil temperature of an outdoor coil and an ambient temperature sensor configured to measure an outdoor ambient temperature. The system further includes a controller that includes a processing circuit. The processing circuit is configured to record a system operating parameter indicating the current operating status of the system and a control step of a control process before performing a sacrificial defrost cycle. The system operating parameter includes a speed of a compressor. The processing circuit is configured to cause the system to perform the sacrificial defrost cycle and operate the system at predefined system operating parameters other than the recorded system operating parameters. The processing circuit is configured to cause the system to operate at the recorded system operating parameters and generate calibration data in response to the sacrificial defrost cycle ending. The processing circuit generates the calibration data by recording the coil temperature and the ambient temperature. The processing circuit is configured to cause the control process to operate at the recorded control step and cause the system to perform a defrost cycle based on the calibration data, the coil temperature, and the ambient temperature.

In some embodiments, the processing circuit is configured to perform another sacrificial defrost cycle in response to determining that the coil temperature is below a predefined amount during the sacrificial defrost cycle.

In some embodiments, the processing circuit is configured to cause the system to perform the defrost cycle based on the calibration data, the coil temperature, and the ambient temperature a predefined amount of time after the sacrificial defrost in response to determining that the coil temperature is above a predefined amount during the sacrificial defrost cycle.

In some embodiments, the processing circuit is configured to cause the system to perform the defrost cycle based on the calibration data, the coil temperature, and the ambient temperature in response to a predefined amount of time elapsing after the sacrificial defrost cycle in which the coil temperature is below a predefined amount.

In some embodiments, the calibration data includes the recorded ambient temperature and the difference between the recorded ambient temperature and the recorded coil temperature.

In some embodiments, the processing circuit is configured to determine a frost free curve (FFC) based on the recorded ambient temperature, the difference between the recorded ambient temperature and the recorded coil temperature, and a current ambient temperature measured by the ambient temperature sensor.

In some embodiments, the processing circuit is configured to determine a defrost active variable (DAV) based on a temperature dependent variable (TDV) and the FFC. The TDV may be dependent on the coil temperature and perform the defrost in response to determining that a difference between a current ambient temperature and a current coil temperature is greater than the DAV. The current ambient temperature may be measured by the ambient temperature sensor and the current coil temperature is measured by the coil temperature sensor.

In some embodiments, the processing circuit is configured to determine the TDV based on the coil temperature and one or more relationships. Each relationship relates to a range of coil temperatures.

In some embodiments, the processing circuit causes the system to perform the sacrificial defrost in response to a predefined amount of time elapsing while the coil temperature is below a predefined level.

In some embodiments, the processing circuit is configured to cause the system to perform the defrost cycle after a predefined amount of time in which no defrost cycle is performed.

Another implementation of the present disclosure is a method for defrosting an outdoor coil of a heating system. The method includes measuring a coil temperature via a coil temperature sensor and measuring an ambient temperature via an ambient temperature sensor. The method further includes recording a speed of a compressor, a setpoint of an electronic expansion valve, and a control step of a control process before performing a sacrificial defrost cycle. The method further includes performing the sacrificial defrost cycle and operating the heating system at a predefined electronic expansion valve setpoint and a predefined compressor speed other than the recorded compressor speed and the recorded electronic expansion valve position. The method further includes causing the heating system to operate at the recorded compressor speed and the recorded electronic expansion valve setpoint in response to the sacrificial defrost cycle ending. The method further includes generating calibration data based on the coil temperature and the ambient temperature. Generating the calibration data includes recording the coil temperature and recording the ambient temperature. The method includes causing the control process to operate at the recorded control process step in response to the sacrificial defrost cycle ending and causing the heating system to perform a defrost cycle based on the calibration data, the coil temperature, and the ambient temperature.

In some embodiments, the method includes performing another sacrificial defrost cycle in response to determining that the coil temperature is below a predefined amount during the sacrificial defrost cycle.

In some embodiments, the method includes causing the system to perform the defrost cycle based on the calibration data, the coil temperature, and the ambient temperature a predefined amount of time after the sacrificial defrost in response to determining that the coil temperature is above a predefined amount during the sacrificial defrost cycle.

In some embodiments, the method includes causing the system to perform the defrost cycle based on the calibration data, the coil temperature, and the ambient temperature in response to a predefined amount of time elapsing in which the coil temperature is below a predefined amount.

In some embodiments, the calibration data includes the difference between the recorded ambient temperature and the recorded coil temperature.

In some embodiments, the method includes determining a defrost active variable (DAV) based on a temperature dependent variable (TDV) and a frost free curve (FFC) and causing the heating system to perform the defrost cycle in response to determining that a difference between a current ambient temperature and a current coil temperature is greater than the DAV.

The method may further include determining the FFC based on the recorded ambient temperature, the difference between the recorded ambient temperature and the coil temperature, and the current ambient temperature.

In some embodiments, the method further includes determining the TDV based on the coil temperature and one or more relationships. Each relationship may relate to a range of coil temperatures.

Another implementation of the present disclosure is a controller for a heating system configured to heat a building via refrigerant. The controller includes a coil temperature sensor configured to measure a coil temperature of an outdoor coil and an ambient temperature sensor configured to measure an ambient temperature. The controller further includes a processing circuit. The processing circuit is configured to record a speed of a compressor, a setpoint of an electronic expansion valve, and a control step of a control process before performing a sacrificial defrost cycle. The processing circuit is further configured to cause the system to perform the sacrificial defrost cycle and cause the heating system to operate at a predefined compressor speed and a predefined electronic expansion valve setpoint other than the recorded compressor speed and the recorded electronic expansion valve setpoint. The processing circuit is configured to cause the heating system to operate at the recorded compressor speed and the recorded electronic expansion valve setpoint in response to the sacrificial defrost cycle ending. The processing circuit is configured to cause the control process to operate at the recorded control process step in response to the sacrificial defrost cycle ending. The processing circuit is further configured to determine a temperature dependent variable (TDV) based on the coil temperature and one or more relationships between the TDV and the coil temperature. Each relationship may relate to a range of coil temperatures. The processing circuit is further configured to determine a frost free curve (FFC) based on the recorded ambient temperature, the difference between the recorded ambient temperature and the recorded coil temperature, and the ambient temperature. Further, the processing circuit is configured to determine a defrost active variable (DAV) based on the TDV and the FFC and cause the heating system to perform a defrost cycle in response to determining that a difference between a current ambient temperature and a current coil temperature is greater than the DAV.

In some embodiments, the processing circuit is configured to cause the heating system to perform another sacrificial defrost cycle in response to determining that the coil temperature is below a predefined amount during the sacrificial defrost cycle.

DETAILED DESCRIPTION

Referring generally to the FIGURES, systems and methods for determining an ideal time to operate a defrost cycle are shown, according to various exemplary embodiments. In some embodiments, a controller of an outdoor unit (e.g., a heat pump and/or air conditioner) may monitor a temperature of an outdoor coil and outdoor ambient air to determine when to initiate a defrost cycle. In various embodiments, the outdoor controller uses the outdoor ambient air temperature, the outdoor coil temperature, and calibration data to determine when to initiate a defrost cycle.

The calibration data used by the controller to determine when to initiate a defrost cycle may be generated whenever the controller is in an uncalibrated state (e.g., has just been power cycled, has just received a heating call, a heating call has been met before performing a calibration cycle, etc.). To generate the calibration data, the controller may first prepare the outdoor coil by performing a defrost cycle referred to as a “sacrificial defrost.” The sacrificial defrost may last a predefined amount of time (e.g., 12 minutes). The sacrificial defrost may be performed to ensure that there is no frost accumulated on the outdoor coil. The controller can be configured to generate the calibration data once it is confirmed via coil temperature that the sacrificial defrost has removed any frost accumulation.

Once the calibration data has been generated, the controller can monitor the coil temperature and the ambient temperature and use the monitored temperatures in combination with the calibration data to initiate a defrost cycle. In some embodiments, the controller only monitors the temperatures after the coil temperature has been below a predefined amount for a predefined amount of time. The timer responsible for determining this time may be referred to as a defrost run timer. The defrost run timer may record defrost run time only when the temperature is below the predefined amount. Once the defrost run time equals the predefined amount, the controller may begin to monitor the coil temperature, and the ambient temperature to determine when to begin the defrost cycle.

Systems And Methods

FIG. 1illustrates a residential heating and cooling system100. The residential heating and cooling system may provide heated and cooled air to a residential structure, as well as provide outside air for ventilation and provide improved indoor air quality (IAQ) through devices such as ultraviolet lights and air filters. Although described as a residential heating and cooling system, embodiments of the systems and methods described herein can be utilized in a cooling unit or a heating unit in a variety of applications include commercial HVAC units (e.g., roof top units). In general, a residence24includes refrigerant conduits that operatively couple an indoor unit28to an outdoor unit30. Indoor unit28may be positioned in a utility space, an attic, a basement, and so forth. Outdoor unit30is situated adjacent to a side of residence24in some embodiments and is covered by a shroud or housing to protect the system components and to prevent leaves and other contaminants from entering the unit. Refrigerant conduits transfer refrigerant between indoor unit28and outdoor unit30, typically transferring primarily liquid refrigerant in one direction and primarily vaporized refrigerant in an opposite direction.

When the system shown inFIG. 1is operating as an air conditioner, a coil in outdoor unit30serves as a condenser for recondensing vaporized refrigerant flowing from indoor unit28to outdoor unit30via one of the refrigerant conduits. In these applications, a coil of the indoor unit, designated by the reference numeral32, serves as an evaporator coil. Indoor coil32receives liquid refrigerant (which may be expanded by an expansion device, not shown) and evaporates the refrigerant before returning it to outdoor unit30.

Outdoor unit30draws in environmental air through its sides as indicated by the arrows directed to the sides of the unit, forces the air through the outer unit coil using a fan, and expels the air. When operating as an air conditioner, the air is heated by the condenser coil within the outdoor unit and exits the top of the unit at a temperature higher than it entered the sides. Air is blown over indoor coil32and is then circulated through residence24by means of ductwork20, as indicated by the arrows entering and exiting ductwork20. The overall system operates to maintain a desired temperature as set by thermostat22. When the temperature sensed inside the residence is higher than the set point on the thermostat (with the addition of a relatively small tolerance), the air conditioner will become operative to refrigerate additional air for circulation through the residence. When the temperature reaches the set point (with the removal of a relatively small tolerance), the unit can stop the refrigeration cycle temporarily.

When the unit inFIG. 1operates as a heat pump, the roles of the coils are simply reversed. That is, the coil of outdoor unit30will serve as an evaporator to evaporate refrigerant and thereby cool air entering outdoor unit30as the air passes over the outdoor unit coil. Indoor coil32will receive a stream of air blown over it and will heat the air by condensing a refrigerant.

In some embodiments, outdoor unit30can perform a defrost cycle. The defrost cycle may energize a reversing valve and cause an outdoor coil of outdoor unit30to be defrosted by running compressed refrigerant through the outdoor coil. In various embodiments, outdoor unit30initiates a defrost based on calibration data. This calibration data may indicate the proper time to initiate the defrost. Outdoor unit30can be configured to generate the calibration data. To generate the calibration data, outdoor unit30may first perform a sacrificial defrost. The sacrificial defrost may ensure that the outdoor coil is not frosted. After the sacrificial defrost is performed, the outdoor unit30can generate

Referring now toFIG. 2, an HVAC system200is shown according to an exemplary embodiment. Various components of system200are located inside residence24while other components are located outside residence24. Outdoor unit30, as described with reference toFIG. 1-2, is shown to be located outside residence24while indoor unit28and thermostat22, as described with reference toFIG. 1-2, are shown to be located inside residence24.

Thermostat22can be configured to generate control signals for indoor unit28and/or outdoor unit30. Thermostat22is shown to be connected to ambient temperature sensor23while outdoor controller306is shown to be connected to ambient temperature sensor307. Ambient temperature sensor23and ambient temperature sensor307are any kind of temperature sensor (e.g., thermistor, thermocouple, etc.). Thermostat22may measure the temperature of residence24via ambient temperature sensor23. Further, thermostat22can be configured to receive the temperature outside residence24via communication with outdoor controller306. In various embodiments, thermostat22generates control signals for indoor unit28and outdoor unit30based on the indoor temperature (e.g., measured via ambient temperature sensor23), the outdoor temperature (e.g., measured via ambient temperature sensor307), and/or a temperature setpoint.

In various embodiments, thermostat22can cause indoor unit28and outdoor unit30to heat residence24. In some embodiments, thermostat22can cause indoor unit28and outdoor unit30to cool residence24. Further, thermostat22and/or outdoor controller306can be configured to initiate and perform a defrost cycle when system200is operating in a heating mode. When the outdoor temperature approaches freezing, moisture in the outside air that is directed over outdoor coil316may condense and freeze on the coil. Sensors may be included within outdoor unit30to measure the outside air temperature and the temperature of outdoor coil316(e.g., temperature sensor322). These sensors may provide the temperature information to the outdoor controller306which can outdoor controller306can use to determine when to initiate a defrost cycle. A defrost cycle may be the same as a cooling cycle (e.g., same refrigerant flow and position of reversing valve313), however, outdoor fan318may be deactivated during the defrost cycle. In various embodiments, a technician may be able to short out an input to outdoor controller306to immediately exit a defrost cycle. Further, during the defrost cycle, a suction pressure fault (e.g., a fault which is triggered based on the suction pressure measured by pressure sensor328going above a predefined amount) may be ignored. However, there may be an “absolute trip value” in place (e.g., 5 PSI) during the defrost cycle.

In some embodiments, thermostat22and/or outdoor controller306can determine an opportune time to enter a defrost cycle based on one or more sensing methods. The sensing methods may be sensing the refrigerant entering into all circuits (e.g., via temperature sensor324, temperature sensor322, temperature sensor326, temperature sensor314), suction pressure (e.g., via pressure sensor328), determining if the temperature of air being blown over outdoor coil316and/or indoor coil32has been reduced, determining if the current draw of variable speed drive309and/or motor310has increased, etc. In various embodiments, thermostat22and/or outdoor controller306may utilize adapting levels to adjust triggering a defrost cycle based on suction pressure (e.g., via pressure sensor328) and/or coil temperature (e.g., via temperature sensor322).

In some instances, there is a pressure drop in conduits302when outdoor coil316begins to frost and/or the output of motor310begins to drop and the control process for motor310increases the output of motor310to maintain a desired speed (e.g., when motor310is an electrically commutated motor). In this regard, a limit or change limit for pressure and/or motor310output may be monitored at the start of a system cycle to determine when to enter a defrost cycle.

In some embodiments, outdoor unit30may have an outdoor coil with multiple circuits. The circuits may not frost at the same rate. In this regard, a single sensor may not accurately determine the time to enter a defrost cycle. For this reason, multiple sensors may need to be used to determine when to defrost the coil. Also, outdoor unit30may monitor and utilize operating conditions (e.g., stages) and speeds (e.g., speed of compressor311) to determine when to enter into a defrost cycle.

Indoor unit28and outdoor unit30may be electrically connected as described with reference toFIG. 2. Further, indoor unit28and outdoor unit30may be coupled via conduits302. Outdoor unit30can be configured to compress refrigerant inside conduits302to either heat or cool the building based on the operating mode of the indoor unit28and the outdoor unit30(e.g., heat pump operation or air conditioning operation). The refrigerant inside conduits302may be any fluid that absorbs and extracts heat. For example, the refrigerant may be hydro fluorocarbon (HFC) based R-410A, R-407C, and/or R-134a.

Outdoor unit30is shown to include outdoor controller306, variable speed drive309, motor310and compressor311. Outdoor unit30can be configured to control compressor311and cause compressor311to compress the refrigerant inside conduits302. In this regard, the compressor may be driven by variable speed drive309and motor310. For example, outdoor controller306can generate control signals for variable speed drive309. Variable speed drive309(e.g., an inverter, a variable frequency drive, etc.) may be an AC-AC inverter, a DC-AC inverter, and/or any other type of inverter. Variable speed drive309can be configured to vary the torque and/or speed of motor310which in turn drives the speed and/or torque of compressor311. Compressor311may be any suitable compressor such as a screw compressor, a reciprocating compressor, a rotary compressor, a swing link compressor, a scroll compressor, or a turbine compressor, etc.

In some embodiments, outdoor controller306can control reversing valve313to operate system200as a heat pump or an air conditioner. For example, outdoor controller306may cause reversing valve313to direct compressed refrigerant to the indoor coil32while in heat pump mode and to the outdoor coil316while in air conditioner mode. In this regard, indoor coil32and outdoor coil316can both act as condensers and evaporators depending on the operating mode (i.e., heat pump or air conditioner) of system200.

Further, in various embodiments, outdoor controller306can be configured to control and/or receive data from outdoor electronic expansion valve320. Outdoor electronic expansion valve320may be an expansion valve controlled by a stepper motor. In this regard, outdoor controller306can be configured to generate a step signal (e.g., a PWM signal) for the outdoor electronic expansion valve320. Based on the step signal, outdoor electronic expansion valve320can be held fully open, fully closed, partially open, etc. In various embodiments, the outdoor controller306can be configured to generate a step signal for the outdoor electronic expansion valve320based on a subcool and/or superheat value calculated from various temperatures and pressures measured in system200.

Outdoor controller318can be configured to control and/or power outdoor fan318. Outdoor fan318can be configured to blow air over outdoor coil316. In this regard, outdoor controller306can control the amount of air blowing over the outdoor coil316by generating control signals to control the speed and/or torque of outdoor fan318. In some embodiments, the control signals are pulse wave modulated signals (PWM), analog voltage signals (i.e., varying the amplitude of a DC or AC signal), and/or any other type of signal.

Outdoor unit30may include one or more temperature sensors and one or more pressure sensors. The temperature sensors and pressure sensors may be electrical connected (i.e., via wires, via wireless communication, etc.) to outdoor controller306. In this regard, outdoor controller306can be configured to measure and store the temperatures and pressures of the refrigerant at various locations of conduits302. The pressure sensors may be any kind of transducer that can be configured to sense the pressure of the refrigerant in conduits302. Outdoor unit30is shown to include pressure sensor328. Pressure sensor328may measure the pressure of the refrigerant in conduit302in the suction line (i.e., a predefined distance from the inlet of compressor311. Further, outdoor unit30is shown to include pressure sensor332. Pressure sensor332may be configured to measure the pressure of the refrigerant in conduits302on the discharge line (e.g., a predefined distance from the outlet of compressor311).

The temperature sensors of outdoor unit30may include thermistors, thermocouples, and/or any other temperature sensing device. Outdoor unit30is shown to include temperature sensor322, temperature sensor324, temperature sensor326, and temperature sensor330. The temperature sensors (i.e., temperature sensor322, temperature sensor324, temperature sensor326, and/or temperature sensor330) can be configured to measure the temperature of the refrigerant at various locations inside conduits302. Temperature sensor322can be configured to measure the temperature of the refrigerant inside, at the inlet to, and/or at the outlet of outdoor coil316. Temperature sensor324can be configured to measure the temperature of the refrigerant inside the suction line (i.e., a predefined distance from the inlet of compressor311. Temperature sensor326can be configured to measure the temperature of the liquid line (i.e., a predefined distance from the outlet of the outdoor coil316). Further, temperature sensor330can be configured to measure the temperature of the discharge line (i.e., a predefined distance from the outlet of the compressor and/or a predefined distance from the inlet of the outdoor coil316).

Referring now to indoor unit28, indoor unit28is shown to include indoor controller304, indoor electronic expansion valve controller301, indoor fan308, indoor coil32, indoor electronic expansion valve310, pressure sensor312, and temperature sensor314. Indoor controller304can be configured to generate control signals for indoor electronic expansion valve controller301. The signals may be setpoints (e.g., temperature setpoint, pressure setpoint, superheat setpoint, subcool setpoint, step value setpoint, etc.). In this regard, indoor electronic expansion valve controller301can be configured to generate control signals for indoor electronic expansion valve310. In various embodiments, indoor electronic expansion valve310may be the same type of valve as outdoor electronic expansion valve320. In this regard, indoor electronic expansion valve controller301can be configured to generate a step control signal (e.g., a PWM wave) for controlling the stepper motor of electronic expansion valve310. In this regard, indoor electronic expansion valve controller301can be configured to fully open, fully close, or partially close electronic expansion valve based on the step signal.

Indoor controller304can be configured to control indoor fan308. Indoor fan308can be configured to blow air over indoor coil32. In this regard, indoor controller304can control the amount of air blowing over the indoor coil308by generating control signals to control the speed and/or torque of indoor fan308. In some embodiments, the control signals are pulse wave modulated signals (PWM), analog voltage signals (i.e., varying the amplitude of a DC or AC signal), and/or any other type of signal.

Indoor controller304may be electrically connected (e.g., wired connection, wireless connection, etc.) to pressure sensor312and/or temperature sensor314. In this regard, indoor controller304can take pressure and/or temperature sensing measurements via pressure sensor312and/or temperature sensor314. Pressure sensor312may be located on the suction line (i.e., a predefined distance from indoor coil32) while temperature sensor314may be located a predefined distance from the outlet of indoor coil32and/or next to pressure sensor312(e.g., on the vapor line).

Referring now toFIG. 3, a block diagram of outdoor controller306is shown in greater detail, according to an exemplary embodiment. Outdoor controller306is configured to operate outdoor unit30to heat and/or cool residence24. In addition to heating and cooling residence24, outdoor controller306may be configured to perform a defrost cycle. In various embodiments, outdoor controller306uses calibration data to determine the opportune times to perform the defrost cycle. Further, outdoor controller306may be configured to generate the calibration data. Outdoor controller306is shown to include processing circuit329. Processing circuit329can be configured to perform all of the control features of outdoor controller306(e.g., operating in a heating mode, operating in a cooling mode, performing a defrost cycle, generating calibration data, etc.). Processing circuit329is shown to include processor331and memory333.

In addition to containing all the instructions to operate outdoor controller306, memory333may include the instructions to defrost outdoor coil316. These instructions may cause reversing valve313to be energized or de-energized. In some embodiments, processor331executes the defrost instructions stored in memory333. Processor331can be a general purpose or specific purpose processor, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGAs), a group of processing components, or other suitable processing components. Processor331may be configured to execute computer code and/or instructions stored in memory333or received from other computer readable media (e.g., CDROM, network storage, a remote server, etc.).

Memory333can include one or more devices (e.g., memory units, memory devices, storage devices, etc.) for storing data and/or computer code for completing and/or facilitating the various processes described in the present disclosure. Memory333can include random access memory (RAM), read-only memory (ROM), hard drive storage, temporary storage, non-volatile memory, flash memory, optical memory, or any other suitable memory for storing software objects and/or computer instructions. Memory333can include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described in the present disclosure. Memory333can be communicably connected to processor331via processing circuit329and can include computer code for executing (e.g., by processor331) one or more processes described herein. Memory333is shown to include parameter storage346, timer controller338, defrost controller366, sacrificial defrost controller368, system value controller370, demand defrost controller372, frost detector374, calibrator376, and time temperature defrost controller380. The functions of these elements may be combined into a single element, multiple elements, and can be performed by outdoor controller306and/or processing circuit329.

Outdoor controller306and/or processing circuit329are shown to be in communication with ambient temperature sensor307and coil temperature sensor322. In this regard, outdoor controller306is configured to receive ambient temperature334from ambient temperature sensor307and coil temperature336from coil temperature sensor322. Ambient temperature334may be the outdoor temperature measured a predefined distance from outdoor coil316, outdoor controller306, and/or outdoor unit30. Coil temperature336may be the coil temperature of outdoor coil316. The various components of processing circuit329(e.g., processor331and memory333) may receive and utilize ambient temperature334and coil temperature336to initiate a calibration cycle in addition to determining calibration data.

Memory333is shown to include timer controller338. Timer controller338may be any software or hardware module that includes one or more hardware timers (e.g., timer counters, real-time clocks, etc.), software times (e.g., timers emulated from another timer counter, a time stamping mechanism, etc.) and/or any kind of time keeping logic. Timer controller338may record time (e.g., defrost cycle time340, compressor run time342, and defrost run time344) via one or more timers and communicate the recorded time to defrost controller366. Timer controller338may include one or more separate timers which count defrost cycle time340, compressor run time342, and defrost run time344.

Timer controller338may accumulate compressor run time342when outdoor unit30operates in a heating mode based on a heating call received from thermostat22. Timer controller338can be configured to clear compressor run time342after a defrost cycle has been performed. In some embodiments, compressor run time342is cleared after demand defrost controller372and/or time temperature defrost controller380perform a defrost cycle and/or after sacrificial defrost controller368performs a defrost.

Defrost run time344may be the amount of time timer controller338counts when coil temperature336is below a predefined temperature (e.g.,35degrees Fahrenheit). If coil temperature336is above terminate temperature378timer controller338can be configured to reset defrost run time344(e.g., set to zero). Further, when outdoor controller306is performing a defrost cycle, timer controller338may record the amount of time which the outdoor controller306is in the defrost cycle (i.e., defrost cycle time340).

Parameter storage346may be a module of memory333configured to store, retrieve, overwrite, and/or update various system parameters. Parameter storage346may communicate stored values to defrost controller366in addition to saving, overriding, and/or updating a parameter in parameter storage346based on values received from defrost controller366. Parameter storage346may store FFD348(Frost Free DeltaT), a value determined by calibrator376. Further, parameter storage346may store CCS350(Calibrated Compressor Speed). This value may be the compressor speed which is stored by system value controller370and/or calibrator376before entering a sacrificial defrost and outdoor controller306may operate at during a calibration cycle.

Parameter storage346is shown to store AmbT352(Current Ambient Temperature). AmbT352may be the ambient temperature334measured by ambient temperature sensor307which is used by frost detector374to determine when to perform a defrost and/or calibrator376to generate calibration data. AmbTc (Calibrated Ambient Temperature)354stored by parameter storage346may be the ambient temperature334measured by calibrator376during a calibration cycle. DAV356(Defrost Active Variable) may be a variable used to initiate a defrost cycle and is stored by parameter storage346. In various embodiments, DAV356may be generated by frost detector374and/or calibrator376. TDV358(Temperature Dependent Variable) may be a value calculated by defrost controller366based on ambient temperature334and is shown to be stored by parameter storage346.

ODSP360(Calibrated OD EEV Setpoint) may be the setpoint value of outdoor EEV320that is stored before a sacrificial defrost by system value controller370. DCS362(Defrost Compressor Speed) may be a compressor speed which outdoor controller306will operate at during a defrost cycle and/or a sacrificial defrost cycle. DCS362may be dependent on unit tonnage. In various embodiments, system value controller370retrieves DCS362based on unit tonnage of outdoor unit30and causes variable speed drive309, motor310, and/or compressor311to operate at DCS362when outdoor controller306is performing a defrost cycle and/or sacrificial defrost cycle. FFC (Frost Free Curve)364may be a value determined by frost detector374and/or calibrator376based on calibration data and can be used to determine a time at which to enter a defrost cycle.

Terminate temperature378is shown to be stored by parameter storage346. Terminate temperature378may be a temperature set by a user or technician via a jumper, a user interface, a remote connection, etc. In some embodiments, terminate temperature378may be 50 degrees Fahrenheit, 60 degrees Fahrenheit, 70 degrees Fahrenheit, 80 degrees Fahrenheit and/or any other temperature. In some embodiments, timer controller338can be configured to reset defrost run time344if coil temperature336meets and/or exceeds terminate temperature378. Further, a defrost cycle operated by either demand defrost controller372and/or sacrificial defrost controller368may be terminated by sacrificial defrost controller368and/or demand defrost controller372in response to demand defrost controller372and/or sacrificial defrost controller368determining that coil temperature sensor322exceeds and/or equals terminate temperature378.

Defrost controller366can be configured to cause system200, as described with further reference toFIG. 2, to perform a defrost cycle. In this regard, defrost controller366can be configured to send signals to various components (e.g., variable speed drive309, outdoor fan318, indoor fan308, reversing valve313, outdoor EEV320, indoor EEV310, etc.) causing those components to perform a defrost cycle. Further, defrost controller366can be configured to communicate with timer controller338to determine compressor run time342, defrost run time344, and defrost cycle time340. Further, defrost controller366can be configured to communicate with parameter storage346to retrieve and/or store various system values (e.g., terminate temperature378, DAV356, etc.) In some embodiments, defrost controller366can be configured to enter a defrost cycle if timer controller338indicates that compressor run time342equals a predefined amount (e.g., 6 hours) during a heating call without a defrost cycle occurring and ambient temperature334is under a predefined temperature (e.g., 50 degrees Fahrenheit). In some embodiments, this defrost may be a short defrost (e.g., a six minute defrost). This may be a “catch all” defrost which is a periodic defrost.

Defrost controller366is shown to include sacrificial defrost controller368. Sacrificial defrost controller368can be configured to enter a sacrificial defrost cycle (e.g., a defrost cycle) after the outdoor controller306is turned on (e.g., receives a heating call, is power cycled, etc.) and/or is in an uncalibrated state (e.g., has just received a heating call, has been power cycled, etc.). In some embodiments, sacrificial defrost controller368enters the sacrificial defrost cycle when defrost run time344is equal to a predefined amount (e.g., 31 minutes) and outdoor controller306is in an uncalibrated state (e.g., has just received a heating call, has been power cycled, etc.). Sacrificial defrost controller368can be configured to exit the sacrificial defrost if one or more conditions are met. In some embodiments, sacrificial defrost controller368can be configured to exit the sacrificial defrost cycle based on defrost cycle time340equaling a predefined amount (e.g., 10-20 minutes). In some embodiments, sacrificial defrost controller368can be configured to exit the sacrificial defrost if a termination temperature is met (e.g., terminate temperature378).

Based on the method for exiting the sacrificial defrost, sacrificial defrost controller368can enable demand defrost controller372and/or time temperature defrost controller380. If sacrificial defrost controller368exits the sacrificial defrost based on determining that the coil temperature336has reached terminate temperature378(Equation A) or if during the temperature of outdoor coil316has been above a predefined temperature (e.g., 35 degrees Fahrenheit) for a predefined amount of time (e.g., 4 minutes) (Equation B) sacrificial defrost controller368enables demand defrost controller372. If neither of these conditions are met (Equation C), and sacrificial defrost controller368exits the sacrificial defrost based on defrost cycle time340equaling a predefined amount, sacrificial defrost controller368can be configured to attempt another sacrificial defrost in response to defrost run time344being equal to a predefined amount (e.g., 31 minutes) and/or may enable time temperature defrost controller380. If time temperature defrost controller380is enabled and time temperature defrost controller380performs a defrost, sacrificial defrost controller368may be configured to perform another sacrificial defrost after a predefined amount of time (e.g., when defrost run time344is equal to a predefined amount). The following relationships exemplify relationships that sacrificial defrost controller368may utilize to exit a sacrificial defrost and/or enable demand defrost controller372and/or time temperature defrost controller380:
Coil Temperature=Terminate Temperature  Equation A
Coil Temperature>Predefined Temperature for Time B  Equation B
Defrost Cycle Time=Time C and Equations A and B are false  Equation C

Demand defrost controller372is shown to include frost detector374and calibrator376. In response to sacrificial defrost controller368enabling demand defrost controller372, demand defrost controller372may cause calibrator376to perform a calibration. Further, demand defrost controller372can be configured to cause frost detector374to detect frost accumulation and initiate a defrost cycle after calibrator376has performed the calibration and frost is detected.

Calibrator376can be configured generate and/or record calibration data (e.g., FFD348, FFC364, CCS350, ODSP360, and/or AmbTc354). The calibration data may be stored in parameter storage346. Calibrator376can be configured to clear (e.g., erase, overwrite, etc.) calibration data if outdoor unit30receives a call for heating, unit30and/or outdoor controller306is power cycled, etc. Calibrator376may cause outdoor unit30to operate at CCS350and/or ODSP360while determining the calibration data. Calibrator376can be configured to wait a predefined amount of time (e.g., a 5 minute stabilizing period) before determining the calibration data.

Calibrator376can be configured to record ambient temperature334and/or coil temperature336. Based on the recorded values, calibrator376can generate calibration data. In some embodiments, calibrator376measures the values once every time period (e.g., every minute, every thirty seconds, etc.) for a predefined amount of time (e.g., 3 minutes, 4 minutes, 5 minutes, etc.). Calibrator376can be configured to average the readings after the predefined amount of time has expired. In this regard, calibrator376may include any time keeping device (e.g., timer controller338) that can be used to measure time. Calibrator376may not overwrite any calibration data (e.g., AmbTc354and/or FFD348) until the average values for ambient temperature334and coil temperature336are determined. In this regard, any interruption to the calibration cycle (e.g., a heating call ending) will not cause calibration data to be lost. In some embodiments, if a heating call is met during the calibration, outdoor controller306may return to an uncalibrated state and wait for another heating call.

Calibrator376can be configured to generate and store calibration data. The calibration data generated by calibrator376may be AmbTc354and FFD348. AmbTc354may be the averaged ambient temperature334. FFD348may be calculated from the AmbTc354and the averaged coil temperature336. The following equation represents the computation for FFD348:
FFD=(AmbTc−coilT)  Equation 1

Calibrator376can be configured to pause for a predefined amount of time after a calibration has been performed (e.g., 31 minutes). This may prevent any unnecessary defrost for occurring quickly after the sacrificial defrost cycle and the calibration data generation. Further, calibrator376can be configured to pause a predefined amount of time (e.g., a settling time) before generating the calibration data, this may allow system200(e.g., ambient temperature334, coil temperature336) to reach a steady state. In some embodiments, this settling time may be performed while system value controller370operates system200at CCS350and ODSP360.

Frost detector374can be configured to initiate a defrost cycle based on coil temperature336, ambient temperature334, and the calibration data (e.g., FFD348and/or AmbTc354). Frost detector374can be configured to initiate the defrost cycle if the difference between ambient temperature334and coil temperature336is greater than or equal to DAV356. The equation for initiating the defrost cycle can be represented as:
(AmbT−coiln≥DAV if true, initiate defrost  Equation 2

Frost detector374can determine AmbT352by measuring ambient temperature sensor307, determine coilT by measuring coil temperature sensor322, and can calculate DAV356. Frost detector374can be configured to determine DAV356by determining FFC364from the calibration data (e.g., FFD348and/or AmbTc354) (Equation 3), determining TDV358(Equations 4-7), and adding FFC364with TDV358(Equation 8). Frost detector374can determine FFC364with the following relationship, wherein AmbT352is the ambient temperature measured by ambient temperature sensor307, AmbTc354is the ambient temperature determined by calibrator376, FDD348determined by calibrator376, and Defrost DeltaT Change is a predefined value (e.g., 8):

Frost detector374can be configured to initiate a defrost cycle in response to determining that Equation 2 is true and/or has been true for a predefined amount of time (e.g. 5 minutes). In some embodiments, frost detector374initiates a defrost cycle in response to determining that Equation 2 is true and/or in response to determining that defrost run time344is equal to a predefined amount of time (e.g., 31 minutes).

System value controller370can be configured to save a control location (e.g., control step) of a control process prior to entering a defrost cycle, a sacrificial defrost cycle, and/or a calibration, and resume operation of outdoor controller306at the saved control location after the defrost cycle, the sacrificial defrost cycle, and/or the calibration. In this regard, system value controller370can record various system parameters (e.g., EEV setpoint value (e.g., ODSP360), superheat setpoint, compressor speed, fan speed, etc.) of various components of system200as described with reference toFIG. 2. In response to a defrost cycle ending, a sacrificial defrost cycle ending, and/or a calibration ending, system value controller370can be configured to resume at the saved parameters. In various embodiments, system value controller370records a control step location of a control process prior to the sacrificial defrost and resume at the saved control step after the sacrificial defrost has completed (e.g., exited). In some embodiments, the control process may be the process which causes system200, as described with reference toFIG. 2, to heat residence24, as described with reference toFIGS. 1-2. In this regard, recording the step of the heating process may allow outdoor controller306to resume operating heating residence24at the step recorded before operating the sacrificial defrost, defrost, and/or calibration.

System value controller370can be configured to operate various system components at various values before, during, and/or after a defrost cycle (e.g., a defrost commanded by sacrificial defrost controller368, demand defrost controller372, and/or time temperature defrost controller380) and/or a calibration cycle. In various embodiments, when sacrificial defrost controller368and/or demand defrost controller372initiate a defrost cycle, system value controller370may record one or more current operating parameters of the system (e.g., ODSP360, CCS350, etc.). During the defrost cycle, system value controller370can select various operating values for various components of system200as described with reference toFIG. 2. In some embodiments, the values are selected based on unit size (e.g., tonnage). The values may be selected for compressor speed (e.g., DCS362), a setpoint for indoor EEV310, an airflow value for indoor fan308, etc. Further, system value controller370may cause reversing valve313to become energized while operating outdoor EEV320in a fully open position.

In response to the defrost cycle commanded by sacrificial defrost controller368, time temperature defrost controller380, and/or demand defrost controller372ending a defrost cycle, system value controller370may select system values of various components of system200. In some embodiments, the system values may be selected based on the recorded values (e.g., recorded EEV setpoint value (e.g., ODSP360), recorded compressor speed (e.g., CCS350), etc.). Some system values may be predefined after exiting a defrost cycle. In some embodiments, indoor EEV310is fully open, outdoor fan318is commanded to a speed based on the recorded compressor speed (e.g., CCS350), indoor fan308is changed to a proper fan speed, etc.

Time temperature defrost controller380can be configured to perform a defrost cycle. Time temperature defrost controller380may be configured to perform a defrost cycle a predefined amount of time after sacrificial defrost controller368performs a sacrificial defrost. In this regard, time temperature defrost controller380may receive an enable signal from sacrificial defrost controller368. In response to receiving an enable signal from sacrificial defrost controller368, time temperature defrost controller380can be configured to determine if coil temperature336has been under a predefined amount (e.g., 35 degrees Fahrenheit) for a predefined amount of time (e.g., 31 minutes). If time temperature defrost controller380determines that coil temperature336has been under the predefined amount for the predefined amount of time, time temperature defrost controller380may initiate a defrost. After the defrost is concluded, time temperature defrost controller380can cause sacrificial defrost controller368to be enabled, that is, wait a predefined amount of time before performing another sacrificial defrost cycle.

Referring now toFIG. 4, a process400is shown for operating a defrost cycle of outdoor unit30with outdoor controller306, according to an exemplary embodiment. In step402, calibrator376can be configured to clear various system values in response to a power cycle, a unit being commanded into a heating cycle from standby, etc. In some embodiments, the values cleared may be FFD348, FFC364, CCS350, ODSP360, AmbTc354, etc. In step404, sacrificial defrost controller368waits until defrost run time344equals a predefined amount (e.g., 31 minutes). If defrost run time344equals the predefined amount, sacrificial defrost controller368and/or system value controller370can record CCS350, ODSP360, and a control step of a control process prior to a sacrificial defrost and initiate the sacrificial defrost for a predefined amount of time (e.g., 12 minutes) (step406).

In step408, sacrificial defrost controller368determines if demand defrost controller372should be enabled (proceed to step410). Sacrificial defrost controller368may determine if demand defrost controller372should be enabled based on coil temperature336. In response to determining that coil temperature336has been above a predefined amount (e.g., 31 degrees Fahrenheit) for a predefined amount of time (e.g., four minutes) (i.e., Equation B is true) during the sacrificial defrost, sacrificial defrost controller368may enabled defrost controller372(proceed to step410). Also, if sacrificial defrost controller368determines that a predefined coil temperature has been reached (i.e., Equation A is true), sacrificial defrost controller368may enable demand defrost controller372(i.e., proceed to step410). If sacrificial defrost controller368does not enable demand defrost controller372(i.e., Equation C is true), sacrificial defrost controller368can enable time temperature defrost controller380and process400proceeds to step409. In step409, time temperature defrost controller380may perform a defrost cycle if coil temperature336is less than a predefined amount for a predefined amount of time. In response to coil temperature336being less than the predefined amount for the predefined amount of time, time temperature defrost controller380may perform a defrost cycle. Once the defrost cycle concludes, process400may proceed to step404.

In step410, system value controller370and/or calibrator376may cause outdoor unit30to operate at the values recorded in step406(e.g., ODSP360, CCS350, etc.). In step412, calibrator376may wait a predefined amount of time. This may allow ambient temperature334and/or coil temperature336to stabilize. In step414, calibrator376can be configured to record ambient temperature334and/or coil temperature336. Calibrator376can generate the calibration data based on ambient temperature334and coil temperature336. In some embodiments, the calibration data generated by calibrator376is FFD348and/or AmbTc354. Calibrator376may generate FFD348according to Equation 1. In step416, system value controller370can return to the recorded control step of the control process recorded in step406.

In step418, if defrost run time344is equal to a predefined amount of time, step420may be performed, otherwise, step418may be looped. In step420, frost detector374determines if a defrost cycle should be initiated based on coil temperature336, ambient temperature334, and/or the calibration data (e.g., FFD348, AmbTc354, etc.). In some embodiments, frost detector374initiates a defrost cycle in response to determining that Equation 2 is true. In some embodiments, frost detector374may evaluate Equation 2 based on the calibration data (e.g., FFD348, AmbTc354), ambient temperature334, coil temperature336, and Equations 3-8.

Configuration of Exemplary Embodiments