SYSTEM AND METHOD FOR PROVIDING DEMAND DEFROST WITH A VARIABLE SPEED COMPRESSOR

Abstract

A heating system that heats a structure includes a variable speed compressor, an outdoor air temperature (OAT) sensor, and a saturated suction temperature (SST) sensor. A processor connected to the variable speed compressor, OAT sensor, and SST sensor electronically receives a demand to heat the structure and causes the variable speed compressor to operate at a speed determined by the demand. After some time, a current defrost value is determined from the difference between the current OAT and current SST. The current defrost value is compared to a target defrost value that is determined using an initial defrost value, a defrost speed, and the selected speed. When the current defrost value exceeds the target defrost value, the processor causes the heating system to begin performing a defrost cycle by switching a reversing valve and operating the variable speed compressor at a defrost speed.

Description

TECHNICAL FIELD

This disclosure relates generally to a system that provides heat to an enclosed space, either alone or as part of an HVAC (Heating, Ventilation, and Air Conditioning) system. More particularly, this disclosure relates to the system and method for providing demand defrost with a variable-speed compressor.

BACKGROUND

Heating, ventilation, and air conditioning (HVAC) systems regulate environmental conditions within an enclosed space. When functioning as a heater, the air is heated via heat transfer, with refrigerant flowing through the HVAC system and returning to the enclosed space as heated air.

SUMMARY OF THE DISCLOSURE

Heating, Ventilation, and Air Conditioning (HVAC) systems are configured to provide cooling and heating to target spaces inside a structure. One form of an HVAC system is a heat pump where refrigerant moves between an outdoor and indoor unit with a reversing valve controlling the direction the refrigerant flows, depending on whether the heat pump is configured to provide heating or cooling to the target spaces. The heat pump includes a compressor and separate coils for both the outdoor and indoor units. One of the coils serves as an evaporator, and the other serves as a condenser, depending on whether the heat pump operates in a heating or cooling configuration. When operating in a heating configuration, the outdoor coil operates as an evaporator and may begin to accumulate frost or ice while operating. This may cause the compressor to work harder and may cause detrimental strain on the compressor, coils, and other components of the heat pump.

In order to reduce or eliminate the frost or ice when operating in a heating configuration, periodically, the system's controller causes the heat pump to perform a defrost cycle. This causes the outdoor coil to momentarily function as a condenser, heat up, and eliminate the frost, improving performance. The system's controller may cause the heat pump to perform a defrost cycle based on a predetermined schedule. However, this is inefficient and may result in fewer or more defrost cycles than the heat pump actually needs based on ambient conditions. For example, no defrosting may be needed if the ambient temperatures are significantly above freezing. In order to have the defrost cycle performed more efficiently based on the actual needs of the system, the system controller may perform one or more calculations based on the outdoor air temperature (OAT) and the saturated suction temperature (SST) at the outdoor coil to determine when a defrost cycle is needed.

Previous HVAC systems used a single-speed compressor; the compressor always operated at the same speed during a demand for heating. However, this results in inefficiencies in the system. For example, when the compressor operates at too low of a speed, the HVAC system may have to operate longer to cool or heat a target space and may even be insufficient to provide adequate heating or cooling to the target space when the differential between the inside temperature and the OAT is too great. Alternatively, if the compressor is selected that operates at a speed that provides sufficient heating or cooling at the most extreme operating conditions that the HVAC system is expected to operate at, during most operating conditions, that compressor wastes energy operating at a faster speed than what is needed.

The disclosed system provides a solution to these and other technical problems of conventional HVAC systems. In some embodiments, the disclosed system includes a variable-speed compressor, which allows the controller to change the compressor's speed depending on information obtained from a thermostat and/or other sensors in the HVAC system. This allows for more efficient operation of the HVAC system as the compressor provides the level of compression needed for the current demand. However, the use of variable compressors results in the previous calculations on when to perform a defrost cycle being inaccurate due to the effect of the different levels of compression on the refrigerant's saturated suction temperature. Therefore, in order to use a variable speed compressor more efficiently, the HVAC system of the disclosed system uses an updated target defrost value that is calculated based not only on OAT and SST measurements but also on the speed of the compressor. By using calculations that consider the speed of the variable compressor, an HVAC system may be operated more efficiently due to the use of the variable speed compressor while better determining when to perform defrost cycles. This may reduce the number of defrost cycles, decreasing the amount of time that the system is unable to provide heat to the target environment due to running defrost cycles. This results in better heating of the target environment and reduced energy use.

In one or more embodiments, the HVAC system is a heat pump operated as a heating system that is provided for heating inside a structure. The heating system of one or more embodiments includes a variable speed compressor, an outdoor coil, an OAT sensor, an SST sensor, and a controller that includes a processor that is operatively connected to the variable speed compressor, OAT sensor, and SST sensor. The processor controls the variable speed compressor to operate at a selected speed and, when configured to operate as part of a heating system, compresses refrigerant received from an outdoor coil. The OAT sensor is associated with the location of the outdoor coil, and the SST sensor measures the current SST at the outdoor coil. The heat pump may additionally include an indoor coil, a valve, and other components.

The processor is configured to electronically receive a demand for heating in the structure, determine a selected speed for operating the variable speed compressor based on the demand, and cause the variable speed compressor to operate at the selected speed. After a predetermined amount of time passes, the processor receives a current SST from the SST sensor and a current OAT from the OAT sensor. A current defrost value is determined by finding a difference between the current OAT and the current SST. This is compared to a target defrost value that is determined using an initial defrost value, a defrost speed, and the selected speed. When the processor determines that the current defrost value is greater than or equal to the target defrost value, the processor causes the heating system to operate in a defrost cycle, which includes having the variable speed compressor operate at the defrost speed.

The initial defrost value may also be determined prior to the controller receiving a demand or in one or more embodiments; the initial defrost value may be determined when the system is initially run and prior to the formation of frost on the coils. The target defrost value may also be recalculated each time the heating system is caused to operate in the defrost cycle. The defrost cycle is performed by switching a reversing valve and operating the variable speed compressor at the defrost speed. In one or more embodiments, the defrost speed is a predetermined speed selected prior to the controller receiving a demand. Alternatively, the defrost speed may be determined when the processor calculates the target defrost value or may be made the same as the selected speed.

By using a variable-speed compressor and determining when to operate the heating system based on the speed of the compressor as well as the OAT and SST, the heating system may use less energy while providing better heating to a target environment. Certain embodiments of the present disclosure may include some or none of these advantages. These advantages and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a diagram of an embodiment of a Heating, Ventilation, and Air Conditioning (HVAC) system, according to some embodiments of the present disclosure;

FIG. 2 illustrates a flowchart of an example method of operating the HVAC system of FIG. 1 to provide heating; and

FIG. 3 illustrates a flowchart of an example method of performing a defrost of the HVAC system of FIG. 1.

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.

Heating, Ventilation, and Air Conditioning (HVAC) systems are configured to provide cooling and heating to target spaces. An HVAC system operates in a heating mode to provide heating to a target space and in a cooling mode to provide cooling to the target space. The present disclosure is directed towards a heating system that, either alone or as part of a heat pump, provides heating to the target space. In the conventional heating system, the compressor operates at a single speed, and defrost is performed based on measurements of the outside air temperature (OAT) and saturated suction temperature (SST) associated with the outdoor coil. However, when a variable speed compressor is used, which results in the heating system operating more efficiently during heating cycles, the defrost cycles are not triggered at the appropriate time. This results in either additional frost forming, causing more work for the compressor, reduced heating since ice buildup reduces the ability of the outdoor coil to capture ambient heat, or the defrost cycles are performed too frequently, which also reduces the amount of heating. Performing defrost cycles may reduce the amount of heat because when the heating system operates in a defrost cycle, the refrigerant reaching the indoor coil of the heating system has less heat energy due to the energy being added by the compressor being used to heat the outdoor coil instead of the indoor coil.

The disclosed system provides a solution to these and other technical problems of conventional HVAC systems. In some embodiments, the disclosed system uses an updated formula to determine when to perform a defrost cycle. This updated formula considers the speed at which the variable compressor operates during any particular period. By using the speed of the variable compressor along with the OAT and SST as the criteria to determine when to perform a defrost cycle, the disclosed heating system improves the reliability and efficiency of the overall system while reducing stress on the compressor and potential damage to the outdoor coil that may occur due to frost and ice buildup over time. Therefore, the HVAC system that includes the disclosed heating system will function better when configured to operate in a heating mode, use less energy, provide more heating, and potentially have a longer life.

HVAC System, Overview

FIG. 1 illustrates an example HVAC system 100 according to an embodiment of the present disclosure. The HVAC system 100 conditions air for delivery to a conditioned space, e.g., all or a portion of a room, a house, an office building, or a warehouse. In some embodiments, the HVAC system 100 is a rooftop unit (RTU) that is positioned on the roof of a building, and the conditioned air is delivered into the interior of the building. In other embodiments, portion(s) of the HVAC system 100 may be located within a structure or building and portion(s) outside the structure. The HVAC system 100 may be a heat pump, as shown in FIG. 1, and may operate as a heating system when configured to provide heating to the target environment.

The HVAC system 100 may be configured as shown in FIG. 1 or any other suitable configuration. For example, the HVAC system 100 may include additional components or omit one or more components shown in FIG. 1. In one or more embodiments, the HVAC system 100 comprises a working fluid conduit subsystem 102 connecting an indoor unit 120 to an outdoor unit 104. Additionally, the HVAC system 100 may include a thermostat and a controller 160, which is configured to receive information from one or more temperature sensors 114, 116, 134, and pressure sensors 158, 117.

System Components

Working Fluid Conduit Subsystem

The working fluid conduit subsystem 102 comprises refrigerant conduits 150, 152, 154, 156, and 157. The refrigerant conduits 150, 152, 154, 156, and 157 facilitate the movement of a working fluid, e.g., one or more refrigerants, through a cooling or heating cycle within the HVAC system 100 such that the refrigerant flows through the refrigerant conduits 150, 152, 154, 156, and 157 in one of two directions as illustrated by the arrows in FIG. 1 and as determined by the operating mode of the HVAC system 100. The refrigerant or working fluid may be any acceptable fluid including, but not limited to, fluorocarbons (e.g., chlorofluorocarbons), ammonia, non-halogenated hydrocarbons (e.g., propane), or hydrofluorocarbons (e.g., R-410A).

The working fluid conduit subsystem 102 includes tubing, conduits, and pipes, e.g., conduits 150, 152, 154, 156, and 157, that fluidly connect various components of the HVAC system 100. The working fluid conduit subsystem 102 is configured to transport working fluid in vapor or liquid form between these components to enable heat exchange and achieve the desired cooling or heating request: a demand in the conditioned space. The working fluid conduit subsystem 102 is constructed from materials suitable for carrying refrigerants, such as copper, aluminum, or other durable materials that can withstand the pressures and temperatures associated with HVAC operations.

The working fluid conduit subsystem 102 may include pressure sensors 117 and 158 as well as one or more thermal expansion valves 136 and one or more reversing valves 137. When configured as a heating system, the expansion valve 136 causes the refrigerant to expand before passing through conduit 156 to the outdoor coil 108, where the refrigerant absorbs heat from the outside air and passes through conduit 154 to the reversing valve 137. The refrigerant then passes through conduit 150 to compressor 106, which compresses the refrigerant and sends it through conduit 152 to the reversing valve 137, which directs the refrigerant to flow through conduit 157 and back to the indoor coil 126.

Expansion Valve

The expansion valve 136 may take any suitable form and be an expansion valve, flow control valve, solenoid valve, motorized valve, electronic expansion valve (EEV), thermostatic expansion valve (TXV), or any other suitable valve configured to regulate the flow and pressure of the working fluid as it transitions from the outdoor coil 108 to the indoor coil 126. While shown in conduit 156, the expansion valve 136 may be located in any part of the working fluid conduit subsystem 102, including the conduit 157 between the reversing valve 137 and indoor coil 126. The expansion valve 136 may reduce the pressure and temperature of the working fluid as it moves through the expansion valve 136. The expansion valve 136 may also control the flow rate of the refrigerant by varying degrees based on the operating mode and system conditions. In some embodiments, the expansion valve 136 may be active and operably coupled to the controller 160 via wired and/or wireless communication. The controller 160 may send control signals to adjust the opening of the expansion valve 136 based on the operating mode, such as cooling or heating mode. In some embodiments, the expansion valve 136 may be passive and mechanically calibrated to open and close based on a preconfigured pressure differential across the valve to facilitate the movement of the refrigerant working fluid toward the outdoor coil 108.

Indoor Unit

The indoor unit 120 includes a heating element 128, indoor coil 126, a blower 130, and one or more air ducts 122 for directing air 124 from a target environment through the indoor coil 126 and/or heating element 128 and out as heated air 118. This heated air 118 is used to heat the target environment. The indoor coil 126 is generally any heat exchanger configured to transfer heat between the air flowing through the indoor coil 126 and refrigeration passing through the interior of the indoor coil 126. The indoor coil 126 may include one or more circuits of coils. The indoor coil 126 is fluidly connected to the compressor 106, such that refrigerant generally flows from the outdoor unit 104 through compressor 106 to the indoor coil 126 when the HVAC system 100 is operating as a heating system. The indoor coil 126 transfers heat from the refrigerant to the air 118 when the HVAC system 100 is configured to operate as a heating system. Specifically, the indoor coil 126 acts as a condenser to heat the flow of air 118 passing through it. When the HVAC system 100 is configured to operate in a cooling mode, the indoor coil 126 acts as an evaporator to cool the flow of air 118 passing through it.

A portion of the indoor unit 120 is configured to move airflow 118 provided by the blower 130 across the indoor coil 126 and out of an air duct 122 as conditioned or heated airflow 118. Return air 124, which may be air returning from the target environment, such as but not limited to a building, a house, or other structure that needs heating. A suction side of the blower 130 pulls the return air 124 through a duct 135. The blower 130 discharges airflow into an air duct 122 such that airflow crosses the indoor coil 126 and/or heating element 128 to produce heated or conditioned airflow 118. The blower 130 is any mechanism that provides airflow 118 through the HVAC system 100. For example, the blower 130 may be a constant or variable speed circulation blower or fan. Examples of variable speed blowers, e.g., 100 include, but are not limited to, belt-drive blowers controlled by inverters, direct-drive blowers with electronically commuted motors (ECM), or any other suitable type of blower.

The heating element 128 is generally any device for heating the flow of air 118 and providing heated air 118 to the conditioned space when the HVAC system 100 operates in a heating mode. For example, the heating element 128 may be a furnace or electric heating coil that may provide supplemental heat to the airflow 118 when the heat provided by the indoor coil 126 is insufficient. The heating element 128 may be configured to receive a fuel from a fuel source, where the heating element 128 is configured to ignite the fuel to heat the heating element 128. Exemplary fuels include but are not limited to natural gas, propane, oil, or any other combustible compound.

Generally, when the HVAC system is operating as a heat pump in a heating mode, the flow of refrigerant is such that the outdoor coil 108 acts as an evaporator and the indoor coil 126 acts as a condenser to heat the flow of air 118 passing through it. If the HVAC system 100 is configured to operate as a heat pump, the HVAC system 100 may include a reversing valve 137 to reverse the flow of working fluid through the HVAC system 100 during operation in the heating mode, and the expansion valve 136 acts as an outdoor expansion device for expanding the refrigerant provided to the outdoor coil 108, which acts an evaporator in the heating mode. When the HVAC system 100 is configured to operate as a heat pump, the heating element 128 may provide supplemental and/or backup heating to the flow of air 118. The heating element 128 may communicate via wired and/or wireless communication with the controller 160. The controller receives control signals to activate the heating element 128 to heat the flow of air 118 when the HVAC system 100 is operated in heating mode. Generally, when the HVAC system 100 is operated in a heating mode, the heating element 128 and blower 130 are turned on such that the flow of air 118 is provided across and heated by the heating element 128. When the HVAC system 100 is operated in a cooling mode, the heating element 128 is generally turned off, and the flow of air 118 is not heated by heating element 128.

The temperature sensor 134 may include a temperature sensing element and circuitry configured to detect the temperature of the target environment, such as a room or structure to be heated. The temperature sensor 134 may be implemented by a hardware circuit and may include a temperature sensing element such as a thermocouple, a thermistor, a semiconductor-based temperature circuit board, or any other type of temperature sensor. The temperature sensor 134 may include one or more temperature sensor circuits. In some embodiments, the temperature sensor 134 may be positioned within the duct 135 or at any suitable location within the indoor section of the HVAC system 100. The temperature sensor 134 may further be configured to measure air humidity and/or any other properties of the conditioned space. The temperature sensor 134 and/or any other temperature and pressure sensor circuits may be positioned anywhere within the conditioned space, the HVAC system 100, and/or the surrounding environment to provide sensor data to the controller 160 to operate the HVAC system 100 as needed.

Outdoor Unit

In one or more embodiments, an outdoor unit 104 receives refrigerant from the indoor coil 126 after it passes through the expansion valve 136 and flows through conduit 156. The outdoor unit 104 may comprise an outdoor coil 108, a fan 110, and an OAT sensor 114. In some embodiments, the outdoor unit 104 may also include the reversing valve 137 and the variable compressor 106, along with associated refrigerant conduits 154, 152, and 150. Alternatively, the variable compressor 106 and/or reversing valve 137 may be located in a different location than the outdoor unit 104.

The outdoor coil 108 is generally configured to transfer heat between the refrigerant and the ambient air surrounding the outdoor coil 108. For example, the outdoor coil 108 is configured to absorb heat from the ambient air and add it to the refrigerant when the HVAC system 100 is acting as a heating system. Alternatively, when the HVAC system 100 acts as a cooling system, the outdoor coil 108 transfers heat from the refrigerant to the ambient air. The outdoor coil 108 may comprise metallic fins and tubing configured to facilitate the heat transfer between the refrigerant inside the outdoor coil 108 and the ambient air in the surrounding environment. The outdoor coil 108 may have the same structure and size as the indoor coil 126 or a completely different structure and size than the indoor coil 126. The outdoor coil 108 may take any form and shape, and it is not limited to a coil or the structures just described.

The fan 110 is configured to direct airflow 112 across the outdoor coil 108 to facilitate the heat transfer between the working fluid flowing within the outdoor coil and the ambient air. For example, the fan 110 may be configured to blow outside air through the outdoor coil 108 to help cool or heat the working fluid flowing through it. The fan 110 may communicate with the controller 160 by wired and/or wireless communication to receive control signals for turning the fan 110 on and off and/or adjusting the speed of the fan 110. In some embodiments, the fan 110 may include a plurality of fans 110.

The outdoor unit 104 includes an outdoor air temperature (OAT) sensor 114 in one or more embodiments. The OAT sensor 114 is associated with the outdoor unit 104 and may include a temperature-sensing element and circuitry. The OAT sensor 114 may be configured to detect the temperature of the ambient air. The OAT sensor 114 may include a temperature sensing element such as a thermocouple, a thermistor, a semiconductor-based temperature circuit board, or any other type of temperature sensor that measures a current OAT 171a and provides the temperature to the controller 160.

In one or more embodiments, the OAT sensor 114 may be positioned within the outdoor unit 104, near the outdoor unit 104, on the housing of the outdoor unit 104, or at any suitable location. The OAT sensor 114 may be attached to a surface inside or outside the outdoor unit 104 using any appropriate means, such as but not limited to threaded connections, clamps, or adhesives. The OAT sensor 114 is operably coupled to the controller 160 via wired and/or wireless communication. The OAT sensor 114 may communicate the temperature data 170, which indicates the detected ambient temperature or OAT, to the controller 160. The OAT sensor 114 is configured to detect the OAT periodically, for example, in a non-limiting example, every second, every thirty seconds, every minute, every five minutes, or any other useful predetermined period. Additionally, the OAT sensor 114 is configured to detect the OAT when a heating demand is received. The controller 160 may use the temperature data 170 received from the OAT sensor 114 to determine the operating mode of the HVAC system 100 and when to perform defrost cycles when the HVAC system 100 is operating as a heating system.

In one or more embodiments, an SST sensor 116 is associated with the outdoor coil 108 and determines a saturated suction temperature of the refrigerant received by the outdoor coil 108 from the indoor coil 126. Alternatively, SST may be measured by a suction pressure sensor 117 mounted in conduit 154 or, alternatively, in the suction line conduit 150. The controller 160 may use an SST table 172 to convert the measured pressure to a saturated suction temperature. The SST sensor 116 or suction pressure sensor 117 may be located in any location within the outdoor unit 104 that provides an adequate measurement of SST to the controller 160. The SST measurement may be used in one or more embodiments to determine when to perform a defrost cycle, as will be described in more detail below with regard to the methods of FIGS. 2 and 3.

The SST sensor 116 may include a temperature sensing element and circuitry configured to detect the SST of the refrigerant exiting the outdoor coil 108 that has been received from the expansion valve 136 through conduit 156. The SST sensor 116 may include one or more temperature sensor circuits. The SST sensor 116 may take the form of a temperature sensing element such as a thermocouple, a thermistor, a semiconductor-based temperature circuit board, or any other type of temperature sensor. The SST sensor 116 may include a plurality of temperature sensor circuits. The SST sensor 116 may be attached to a surface using any appropriate means, such as but not limited to threaded connections, clamps, or adhesives. The SST sensor 116 may be operably coupled to the controller 160 via wired and/or wireless communication and provide the controller 160 with SST data. The SST sensor 116 is configured to detect the saturated suction temperature periodically, for example, in a non-limiting example, every second, every thirty seconds, every minute, every five minutes, or any other useful predetermined period. The SST sensor 116 may also detect the temperature on demand in response to a request from the controller 160, such as when a demand is initially received for heating. The controller 160 may use the SST data to determine when to perform defrost cycles on the outdoor coil 108, as will be described in more detail below with regards to the methods of FIGS. 2 and 3.

In some embodiments, the HVAC system 100 may include a pressure sensor 117 and use pressure data provided by the pressure sensor 117 to derive the SST of the refrigerant. The pressure sensor 117 may include one or more pressure sensing elements such as a piezoresistive sensing element, capacitive sensing element, strain gauge, or any other suitable pressure sensor. The pressure sensor 117 may be configured to determine the pressure of the working fluid at or near the outlet of the outdoor coil 108 and provide the pressure data to the controller 160, where the pressure data includes the determined pressure of the refrigerant. The pressure sensor 117 may include one or more hardware pressure sensor circuits. The pressure sensor 117 may be positioned along the working fluid conduit subsystem 102 between the outdoor coil 108 and the reversing valve 137, between reversing valve 137 and compressor 106, or at any other suitable location. The pressure sensor 117 is operably coupled to the controller 160 via wired and/or wireless communication. In one or more embodiments the controller 160 may receive pressure data from the pressure sensor 117 and use a predefined formula, such as but not limited to: SST=A×P{circumflex over ( )}B+C, where P represents the determined pressure, and A, B, C are derived coefficients based on the refrigerant's specific characteristics to determine the current SST 171b.

Variable Speed Compressor and Reversing Valve

A compressor 106 is coupled to the working fluid conduit subsystem 102 and is configured to compress or increase the pressure of the refrigerant. The compressor 106 is in signal communication with the HVAC controller 160 using wired and/or wireless connection. The HVAC controller 160 provides commands and/or signals to control the operation of the compressor 106 and/or receive signals from the compressor 106 corresponding to the status of the compressor 106. The compressor 106 may be located in the outdoor unit 104, as shown in FIG. 1, or another location between the outdoor unit 104 and indoor unit 120. The compressor 106 may be a single-speed, variable-speed, or multiple-stage compressor.

In one or more embodiments, the compressor 106 is a variable-speed compressor. A variable-speed compressor 106 is generally configured to operate at different speeds to modulate the pressure of the refrigerant and keep the refrigerant moving along the working fluid conduit subsystem 102. In the variable-speed compressor configuration, the speed of the compressor 106 may be modified to adjust the cooling and/or heating capacity of the HVAC system 100. Using a variable-speed compressor allows the HVAC system to operate more efficiently since the compressor may be run at the most efficient speed for heating or cooling the target environment.

In one or more embodiments, the variable speed compressor 106 receives low-pressure, low-temperature refrigerant from the reversing valve 137 through a suction line conduit 150. The reversing valve 137 receives the low-pressure, low-temperature refrigerant from either the outdoor coil when configured for heating or the indoor coil when configured for cooling. The variable speed compressor 106 increases the pressure of the low-pressure, low-temperature refrigerant, and by operation of the ideal gas law, the temperature of the refrigerant is also increased. The high-pressure, high-temperature refrigerant then leaves the variable speed compressor 106 via the discharge line conduit 152. It is received by the reversing valve 137 and is directed towards either the outdoor coil 108 when the HVAC system 100 is in a cooling configuration or towards the indoor coil 126 when functioning as a heating system.

In one or more embodiments, the HVAC controller 160 may receive information from a compressor pressure sensor 159, which is disposed in the discharge line conduit 152. In various embodiments, the pressure sensor 158 is, for example, a pressure transducer. A compressor pressure sensor 159 is disposed in the discharge line conduit 152 on the discharge side of the variable speed compressor 106. It is configured to measure a refrigerant temperature in the discharge line conduit 152. According to some embodiments, the compressor pressure sensor 158 and/or compressor temperature sensor 159 provide pressure measurements to the HVAC controller 160, which, in combination with the compressor settings 192, may be used to determine the current load and determine a selected speed 177 to operate the compressor 106 at in order to satisfy the demand for heating and/or cooling.

During operation, the HVAC controller 160 modulates the speed of the variable speed compressor 106 in an effort to optimize the run time of the HVAC system 100. In various embodiments, it is desirable to have the variable speed compressor 106 run as much as possible to improve thermal comfort in the target environment and reduce energy consumption due to cycling losses. In various embodiments, the speed of the variable speed compressor 106 is increased in an effort to lower the refrigerant pressure in the suction line conduit 150 to an ideal value. When the refrigerant pressure is greater than the ideal value, the speed of the variable speed compressor 106 is decreased in an effort to raise the refrigerant pressure in the suction line conduit 150. This ensures that the variable speed compressor 106 and the HVAC system 100 generally operate in the most efficient configuration.

In one or more embodiments, the HVAC system 100 includes a reversing valve 137 that directs the flow of refrigerant from either the outdoor unit or the indoor unit 120 into the compressor 106 through the suction line conduit 150. The reversing valve 137 also receives the compressed refrigerant from the compressor 106 via the discharge line conduit 152. When the HVAC system 100 operates as a heating system and is in heating mode, the indoor coil 126 functions as a condenser, and the outdoor coil 108 functions as an evaporator. When the HVAC system 100 is operating as a cooling system and in cooling mode, the controller 160 switches the reversing valve 137, reversing the flow of the refrigerant so that the indoor coil 126 functions as an evaporator and the outdoor coil functions as a condenser. Further, when the HVAC system 100 is operating as a heating system and a defrost cycle is needed, the controller 160 or processor 162 switches the reversing valve 137, reversing the flow of refrigerant to the outdoor coil 108 so that the outdoor coil 108 acts as a condenser and the outdoor coil 108 is defrosted. In general, it is desirable to operate the outdoor coil 108 in a defrost mode for as short of a period of time as possible, since this results in the cooling of the indoor coil 126, which may potentially reduce the temperature of the target environment.

Thermostat

The thermostat 140 may generally be an electronic device with which users may interact, input data, and view temperature. The thermostat 140 may be positioned within the conditioned space, e.g., a room or building serviced by the HVAC system 100. In some embodiments, the thermostat 140 may be separate from the controller 160 and in signal communication with the controller 160 via wired and/or wireless communication. In some embodiments, the thermostat 140 may be integrated within the controller 160 and in signal communication with the components of the controller 160. The thermostat 140 is configured to allow a user to input a desired temperature or baseline setpoint temperature for the conditioned space. The thermostat 140 may display the current temperature within the conditioned space that it receives from the controller 160, which was originally detected by the temperature sensor 134.

The thermostat 140 may include a user interface 142 and a display 144 for displaying information related to the operation and/or status of the HVAC system 100. For example, the user interface 142 may communicate with the display 144 to show operational, diagnostic, and/or status messages and provide 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. For example, the user interface 142 may communicate with the display 144 to show messages related to the status and/or operation of the HVAC system 100.

HVAC Controller

The HVAC controller 160 is communicatively coupled via wired and/or wireless connection to other components in the HVAC system 100 and configured to control their operations. In some embodiments, HVAC controller 160 may be one or more controllers associated with one or more components of the HVAC system 100. The controller 160 includes a processor 162 in signal communication with a memory 166 and an input/output (I/O) interface 164.

The processor 162 comprises one or more processors. The processor 162 is any electronic circuitry including, but not limited to, state machines, one or more central processing unit (CPU) chips, logic units, cores (e.g., a multi-core processor), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), or digital signal processors (DSPs) that communicatively couples to memory 166 and controls the operation of HVAC system 100. The processor 162 may be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processor 162 is communicatively coupled to and in signal communication with the memory 166. The one or more processors are configured to process data and may be implemented in hardware or software. For example, the processor 162 may be 8-bit, 16-bit, 32-bit, 64-bit, or of any other suitable architecture. The processor 162 may include an arithmetic logic unit (ALU) for performing arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that fetches instructions from memory 166 and executes them by directing the coordinated operations of the ALU, registers, and other components. The processor 162 may include other hardware and software that operates to process information, control the HVAC system 100, and perform any of the functions described herein.

The processor 162 may be configured to execute software instructions to perform operations of the controller 160. For example, the processor 162 may be configured to execute the software instructions 168 to cause the HVAC system 100 to perform one or more of its operations described herein. The processor 162 may execute code/software instructions 168 to perform any of its operations. The processor 162 is not limited to a single processing device and may encompass multiple processing devices. The processor 162 may be configured to perform one or more operations of the controller 160 described in FIG. 1 and one or more operations of the methods 200 and 300 described in FIGS. 2 and 3.

The I/O interface 164 is configured to communicate data and signals with other devices and sensors. For example, the I/O interface 164 may be configured to communicate electrical signals with the other components of the HVAC systems 100. The I/O interface 164 may comprise ports and/or terminals for establishing signal communications between the controller 160 and other devices and sensors such as pressure sensor 158, 117, temperature sensor 114, 116, 134, and components such as the variable speed compressor 106, reversing valve 137, blower 130, heating element 128, thermostat 140 and fan 110. The I/O interface 164 may be configured to enable wired and/or wireless communications. Connections between various components of the HVAC system 100 and the I/O interface 164 may be wired or wireless. For example, conventional cables and contacts may couple the HVAC controller 160 to various components of the HVAC system 100.

In some embodiments, a wireless connection may be employed to provide at least some or all of the connections between components of the HVAC system 100. In some embodiments, a data bus may couple various components of the HVAC system 100 together so that data may be communicated between them. In some embodiments, the data bus 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 may include an accelerated graphics port (AGP) or other graphics bus, a controller area network (CAN) bus, a front-side bus (FSB), a hyper transport (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 PCI-Express (PCI-X) bus, a serial advanced technology attachment (SATA) bus, a video electronics standards association local bus (VLB), or any other suitable bus or a combination of two or more of these. In various embodiments, the data bus may include any number, type, or configuration of data buses, where appropriate. In certain embodiments, one or more data buses, which may each include an address bus and a data bus, may couple the controller 160 through the I/O interface 164 to other components of the HVAC system 100.

The memory 166 may be a non-transitory computer-readable medium. The memory 166 may include one or more disks, tape drives, or solid-state drives and may be used as an overflow data storage device to store programs when such programs are selected for execution and to store instructions 168 and data that are read during program execution. The memory 166 may be volatile or non-volatile. It may comprise read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), dynamic random-access memory (DRAM), and static random-access memory (SRAM). The memory 166 is operable to store any suitable set of instructions 168, logic, rules, and/or code for executing the functions described in this disclosure. For example, the memory 166 may store and retrieve information corresponding to software instructions 168, temperature data 170, SST table 172, Defrost values 174, Defrost speeds 176, cooling settings 178, heating settings 182, compressor settings 192, one or more predetermined amounts of time 190, and/or any other data, instructions, and operating parameters needed for operating the HVAC system 100.

In one or more embodiments, the temperature data 170 may include temperature data received from the OAT sensor 114. This temperature data may include current OAT 171a, defrost OAT, and other temperature data such as that obtained from the temperature sensor 134, the thermostat 140, and other locations. The temperature data 170 may also include data received from the SST sensor 116 or calculated using SST table 172 and pressure data from pressure sensor 117. The SST data may include current SST 171b, clean coil SST, and previous SST values. The OAT and SST data may be used to calculate defrost values 174, such as but not limited to initial defrost value 174a, target defrost value 174b, updated target defrost value 174c, current defrost value 174d, and any other necessary defrost values.

In one or more embodiments, the variable speed compressor is caused to operate at a defrost speed 176 determined and/or stored in the memory 166. The defrost speed 176 may be predetermined and provided by a manufacturer, installer, or other user. Alternatively, the defrost speed 176 may be determined based on detected levels of frost on the outdoor coil 108, previous defrost speeds, or the selected speed 177 that the variable speed compressor 106 is currently being operated at during the heating cycle. The defrost speed 176 may be determined when the processor 162 compares a current defrost value 174d to a target defrost value 174b stored as defrost values 174 in the memory 166.

In one or more embodiments, the memory 166 may include cooling settings 178, heating settings 182, and predetermined amounts of time 190. The heating settings 182 and cooling settings 178 may be used by the processor 162 to control the compressor and reversing valve 137. The predetermined amounts of time may include a first predetermined amount of time and a second predetermined amount of time. The first predetermined amount of time is the amount of time from first receiving a demand and before an initial defrost is performed. The first predetermined amount of time is chosen to allow the variable compressor 106 and outdoor coil 108 to get to a proper operating configuration, but before any significant frost is able to form on the outdoor coil 108 and may be any amount of time, such as but not limited to, one minute, five minutes, ten minutes. A second predetermined amount of time may also be stored in the predetermined amounts of time 190, which is the amount of time after a previous defrost cycle before the controller 160 receives a current SST 171b and current OAT 171a to calculate a current defrost value 174d and compare it with the target defrost value 174b in order to determine if a new defrost cycle is needed. The second predetermined amount of time causes a delay so that controller 160 does not constantly perform the calculations. Alternatively, either the first predetermined amount of time or the second predetermined amount of time may be eliminated, and/or the processor 162 may monitor SST and OAT constantly.

In one or more embodiments, the HVAC system 100 operates as a heating system. Warm refrigerant passes through the indoor coil 126 and heats air 124 from the target environment to produce heated air 118 to heat the target environment. The refrigerant passes through the expansion valve 136 to the outdoor coil 108. The outdoor coil 108 acts as an evaporator and absorbs heat from the ambient air 112. After absorbing heat by the outdoor coil 108, the refrigerant passes through the reversing valve 137 to the variable compressor 106, where the refrigerant is compressed and then flows back to the indoor coil 126.

The processor 162 controls the variable compressor 106 to operate at a selected speed 177 determined from the demand and/or information obtained from the OAT sensor 114 and/or temperature sensor 134. The variable compressor 106 may operate at multiple speeds during a particular heating cycle or at one selected speed 177. During operation as a heating system, frost may build up on the outdoor coil 108, requiring the processor 162 to have the HVAC system 100 perform a defrost cycle.

In one or more embodiments, as will be described in more detail below regarding the methods 200 and 300 of FIGS. 2 and 3, processor 162 determines that a defrost cycle is needed by comparing a current defrost value 174d to a target defrost value 174b stored in memory 166. The current defrost value 174d is the difference between a current OAT 171a and a current SST 171b. The target defrost value 174b is determined using at least an initial defrost value 174a, the defrost speed 176, and the selected speed 177. The initial defrost value 174a, in one or more embodiments, may be obtained by finding the difference between the current OAT 171a and the current SST 171b obtained when a defrost cycle is initially run at a time that is prior to frost forming on the outdoor coil 108. The current defrost and target defrost may be determined by more or less measurements obtained from the SST sensor 116 and OAT sensor 114 as well as data stored in the memory 166. The disclosure is not limited to the current defrost value and the target defrost value being calculated as just described and/or as described below with regards to FIGS. 2 and 3.

If the current defrost value 174d is greater than or equal to the target defrost value 174b, the processor 162 determines that the HVAC system needs to perform a defrost cycle. The processor 162 switches the reversing valve 137 to provide compressed refrigerant from the compressor 106 to the outdoor coil 108 in order to melt the frost or ice on the outdoor coil 108. The processor 162 may also have the compressor 106 operate at a defrost speed 176, which in one or more embodiments may be the same or related to the selected speed 177. Alternatively, in one or more embodiments, the defrost speed 176 may be a higher or lower speed than the selected speed 177 and selected to ensure that defrost happens as quickly and efficiently as possible. Once the defrost cycle runs, a sufficient amount of time to eliminate the ice, either based on a predetermined amount of time stored in the memory 166 or based on measurements from the OAT sensor 114, SST sensor 116, or pressure sensor 117 and/or 158, the processor 162 causes the variable speed compressor 106 to resume operating at the selected speed 177 and the reversing valve 137 is reversed to cause the flow of refrigerant from the outdoor coil 108 to flow towards the compressor 106. This is repeated until the demand is met or the HVAC system 100 is deactivated.

Example Methods for Operating an HVAC System

Turning now to the method 200 shown in FIG. 2. FIG. 2. is a flowchart illustrating a method 200 of operating an HVAC system to perform a heating operation with one or more defrost cycles. The method 200 may be performed by the HVAC system 100 shown and described above with regards to FIG. 1 or may be performed by any HVAC system, e.g., 100 or another heating system. The method of FIG. 2 is not limited to the HVAC system, e.g., 100 described above with regards to FIG. 1. It may take any form that includes a variable speed compressor and provides heating to a target environment.

Method 200 begins by receiving a demand for heating in operation 205. In one or more embodiments, the demand is an electronic signal received from the thermostat 140 and/or based on measurements from the temperature sensor 134 that indicate that the target environment needs heating. The demand may be a simple electronic voltage, or it may be a digital signal that includes information such as the required amount of heat and/or information about the refrigerant and one or more components of the HVAC system 100. Once the demand is received in operation 205 by the processor 162, the processor 162 begins a heating cycle in operation 210.

When performing (e.g., beginning) a heating cycle in operation 210, the processor 162 configures the reversing valve 137 to cause the compressor 106 to receive refrigerant that has received heat from the outside air 112 through the outdoor coil 108. In operation 215, the processor 162 causes the variable compressor 106 to begin operating at a selected speed 177. This selected speed 177 may be determined based on demand, a predetermined value, and/or from other information obtained from the suction pressure sensor 158 and/or the compressor pressure sensor 159.

Once the processor 162 begins the heating cycle in operation 210 and selects the speed of the variable compressor 106 to operate at in operation 215, the processor waits for a first predetermined amount of time in operation 220. The first predetermined amount of time may be stored in memory 166 along with other predetermined amounts of time 190. The predetermined amount of time may be selected to ensure that the HVAC system 100 is operating in a steady state, but not so long that frost may have started to build up on the outside coil 108. This allows for an initial defrost to be performed in operation 225. An example of a method 300 for performing a defrost is described in FIG. 3. However, the defrost performed in operation 225 may take any form and is not limited to the method 300 described in FIG. 3.

Once the initial defrost is completed in operation 225, the processor 162 in operation 230 calculates the initial defrost value using the equation 1 described below:

Initial_defrost_value=current_OAT−current_SST   [Equation 1]

In one or more embodiments, the current OAT 171a and current SST 171b are values obtained from the values stored in the temperature data 170 during operation 225 once the defrost cycle has concluded. This initial defrost value 174a is stored in operation 235 in the defrost values 174 in memory 166.

Once the initial defrost value 174a is stored in operation 235, the processor 162 determines in operation 240 determines if a heating demand is still being received. If the demand is no longer being received in operation 240, processor 162 ends the heating cycle in operation 285, and method 200 ends. If, however, there is still a heating demand in operation 240, method 200 proceeds to operation 245.

In operation 245, the processor 162 waits a second predetermined amount of time. This amount of time may be the same as the first predetermined amount of time or different. This predetermined amount of time may be selected to allow frost to begin to build up on the outdoor coil 108 after a defrost period. The second predetermined amount of time may be any amount of time that is selected to reduce the number of calculations and measurements needed while allowing the processor 162 to determine that a subsequent defrost cycle is required before the HVAC system 100 begins to suffer performance issues due to frost buildup. The second predetermined amount of time may be five minutes, ten minutes, or any other predetermined amount of time. The second predetermined amount of time may be determined by the processor 162 using a table or other system and adjusted depending on the OAT detected by the OAT sensor 114.

Once the second predetermined amount of time passes in operation 245, method 200 proceeds to operation 250, wherein the current SST 171b is obtained from the SST sensor 116 in operation 250, and in operation 255, the current OAT 171a is obtained from the OAT sensor 114. The current SST 171b obtained in operation 250 and the current OAT 171a obtained in operation 255 are then used in operation 260 to calculate the current defrost value using equation 2 below:

Current_defrost_value=current_OAT−current_SST   [Equation 2]

Alternatively, the current defrost value 174d may be calculated using any formula, and the disclosure is not limited to Equation 2.

At the same time or immediately after the processor 162 calculates the current defrost value in operation 260, the processor 162 then calculates a target defrost value 174b or an updated target defrost value 174c in operation 265 using the initial defrost value 174a as calculated, for example, in operation 235, a constant, a system RPM slope, the selected speed and defrost speed. Operation 265 may calculate an initial target defrost value 174b or in subsequent calculation the processor 162 may calculate in operation 265 an updated target defrost value 174c. The target defrost value may be calculated using Equation 3 as described below:

Target_defrost_value=initial_defrost_value+2.3 °F+system_RPM_slope*(selected_speed−defrost_speed)   [Equation 3]

In one or more embodiments the system_RPM_slope is a constant that is associated with the specific HVAC system 100, alternatively in one or more embodiments the system_RPM_slope may be determined using Equation 4 described below:

System_RPM_slope=5.5/(6000−defrost_speed)   [Equation 4]

While operation 265 is described as using both Equation 3 and Equation 4, the disclosure is not limited to either Equation 3 or Equation 4, and the target defrost value 174b and updated target defrost value 174c may be determined using any method or values. For example, a constant other than 2.3 °F may be used, and the various values are simply reflective of one particular HVAC system 100; other HVAC systems 100 may have different values and/or use a different equation to determine the updated target defrost value 174c without departing from the disclosure. In one or more embodiments, the target defrost value 174b is recalculated (using the updated target defrost value 174c) each time the heating system is caused to operate in the defrost cycle. Alternatively, in one or more embodiments, the target defrost value 174b may only be updated periodically or once per demand without departing from the disclosure.

Once the processor 162 calculates the current defrost value in operation 260 and the target defrost value in operation 265, the current defrost value 174d is then compared to the target defrost value 174b or updated target defrost value 174c in operation 270. In operation 270, if the current defrost value is not greater than the target defrost value 174b (or updated target defrost value 174c), the processor 162 causes the HVAC system 100 to continue heating at the selected speed 177 in operation 275, and operations 240-275 repeat until either there is no longer a heating demand in operation 240 or the current defrost value 174d is greater than or equal to the updated target defrost value 174c in operation 270.

If the current defrost value 174d is greater than or equal to the target defrost value 174b or updated target defrost value 174c, then method 200 proceeds to operation 280, where a defrost is performed. This defrost may be performed as described in more detail in FIG. 3 or by any other method that is suitable to the particular HVAC system 100. Once defrost is completed in operation 280, the method 200 returns to operation 240 where the processor 162 repeats operations 240-280 until there is no longer a heating demand in operation 240. When there is no longer a heating demand at operation 240, the heating cycle ends at operation 285, and the method may end.

Modifications, additions, or omissions may be made to method 200, as depicted in FIG. 2. Method 200 may include more, fewer, or other operations. For example, operations may be performed in parallel or in any suitable order. The initial defrost value 174a may be calculated each time a new demand is received, or in one or more embodiments, it may only be calculated periodically, for example, once a day, once a month, or any other interval. While discussed as an HVAC system 100 (or components thereof) performing the operations, any suitable component of HVAC system 100 may perform one or more operations of method 200.

Turning now to the method 300 shown in FIG. 3. FIG. 3 is a flowchart illustrating an exemplary method 300 for performing a defrost in an HVAC system 100. The method 300 may be performed by the HVAC system 100 shown and described above with regards to FIG. 1 or may be performed by any HVAC system, e.g., 100 or other heating system. The method 300 may be performed during operation 235 and/or 280 of the method, e.g., 200 described above with regards to FIG. 2, or it may be performed with one or more other methods, e.g., 200, that determine when to perform a defrost in an HVAC system, e.g., 100 with a variable speed compressor, e.g., 106.

In one or more embodiments, method 300 may be performed when the coil does not have any frost as a sacrificial defrost cycle in order to determine initial defrost values 174a. The method 300 may also be performed as a routine defrost of the outdoor coil 108 when the outdoor coil 108 is determined to have frost, for example, after operation 270 in FIG. 2. The method of FIG. 3 is not limited to the HVAC system, e.g., 100 described above regarding FIG. 1 nor the method of FIG. 2 and may take any form that includes a variable speed compressor, e.g., 106, and provides heating to a target environment.

Method 300 begins by setting the reversing valve 137 to defrost in operation 305. In operation 305, the processor 162 causes the reversing valve 137 to reverse the flow of refrigerant. Instead of the refrigerant flowing from the outdoor coil 108 to the compressor 106 as required during a heating cycle, the reversing valve 137 causes the compressed refrigerant received from the compressor to flow towards the outdoor coil 108, heating the outdoor coil in the same manner as is performed during a cooling cycle.

Once the reversing valve 137 is reversed in operation 305, the processor 162 causes the variable speed compressor 106 to operate at a defrost speed 176 in operation 310. This defrost speed 176 may be the same as the selected speed 177, or it may be a different speed that has been determined to allow for efficient and quick defrosting of the outdoor coil. In one or more embodiments during an initial defrost, the defrosting speed is 3600 RPMs. However, the defrost speed 176 may be any speed provided by a manufacturer, installer, or based on such metrics as OAT, the currently selected speed 177, and SST.

Once the variable speed is caused to operate at a defrost speed 176 in operation 310, the processor causes the HVAC system 100 to perform a defrost 315, which is then completed in operation 320. Since this initial defrost may be performed when no frost is present on the coils, the defrost cycle may be performed for a predetermined amount of time determined to collect accurate data for future calculations rather than based on calculations of the amount of frost present. Alternatively, the defrost time may be determined based on the OAT and/or the capabilities of the compressor fan 110, outdoor coil 108, and/or other components of the HVAC system 100.

Once the defrost is completed in operation 320, the processor 162 sets the reversing valve 137 back to heating in operation 325 and causes the variable speed compressor 106 to operate at the selected speed 177 in operation 330. At the same time or immediately after, the processor 162 receives the current OAT 171a from the OAT sensor 114 in operation 335 and receives the current SST 171b from the SST sensor 116 in operation 340.

Once the processor 162 determines receives the current OAT 171a from the OAT sensor 114 in operation 335 and the current SST 171b from the SST sensor 116 in operation 340, the processor 162 stores the current OAT 171a and the current SST 171b in operation 345 to temperature data 170 of memory 166. Method 300 may then end after storing the current OAT 171a and the current SST 171b in operation 345. Modifications, additions, or omissions may be made to method 300 as depicted in FIG. 3. Method 300 may include more, fewer, or other operations. For example, operations may be performed in parallel or in any suitable order. While discussed as HVAC system 100 (or components thereof) performing the operations, any suitable component of HVAC system 100 may perform one or more operations of method 300.

Although this disclosure has been described in terms of certain embodiments, alterations, and permutations, embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the spirit and scope of this disclosure.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated with another system, or certain features may be omitted or not implemented.

In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

To aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants note that they do not intend any of the appended claims to invoke 35 U.S.C. § 112(f) as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.

Claims

1. A heating system comprising:

a variable speed compressor that is controlled by a processor to operate at a selected speed, wherein the variable speed compressor compresses a refrigerant received from an outdoor coil;

the outdoor coil receives the compressed refrigerant from the variable speed compressor and is located outside of a structure that is to be heated by the heating system;

an outdoor air temperature (OAT) sensor that measures a current OAT associated with a location where the outdoor coil is located;

a saturated suction temperature (SST) sensor that measures a current SST at the outdoor coil; and

the processor is operatively connected to the variable speed compressor, OAT sensor, and SST sensor and is configured to: electronically receive a demand for heating in the structure; determine the selected speed for operating the variable speed compressor based on the demand; cause the variable speed compressor to operate at the selected speed; receive, after a predetermined amount of time from the SST sensor, the current SST; receive, after the predetermined amount of time from the OAT sensor, the current OAT; compare a current defrost value to a target defrost value, wherein: the current defrost value is a difference between the current OAT and the current SST, and the target defrost value is determined using an initial defrost value, a defrost speed, and the selected speed; and cause the heating system to operate in a defrost cycle when the current defrost value is greater than the target defrost value, wherein the variable speed compressor operates at the defrost speed during the defrost cycle.

2. The heating system of claim 1, wherein the defrost speed is a predetermined speed determined prior to electronically receiving the demand.

3. The heating system of claim 1, wherein the defrost speed is determined by the processor when the processor compares the current defrost value to the target defrost value.

4. The heating system of claim 3, wherein the defrost speed is related to the selected speed.

5. The heating system of claim 1, wherein the SST sensor is a pressure sensor mounted in a suction line, and the current SST is determined using a table that provides a correspondence between a measured pressure and an SST value.

6. The heating system of claim 1, wherein the target defrost value is recalculated after each time the heating system is caused to operate in the defrost cycle.

7. The heating system of claim 1, wherein the initial defrost value is determined by finding a difference between the current OAT and the current SST measured when the heating system is initially run, and no frost is present on the outdoor coil.

8. The heating system of claim 1, wherein the heating system is operated in a defrost cycle by switching a reversing valve and operating the variable speed compressor at the defrost speed.

9. The heating system of claim 1, wherein the heating system is a heat pump that forms a heating and cooling system and comprises the variable speed compressor, the outdoor coil, an indoor coil, and a valve.

10. A method for operating a heating system comprising:

receiving a demand for heating a structure;

determining a selected speed for operating a variable speed compressor based on the demand;

causing the variable speed compressor to operate at the selected speed;

receiving, after a predetermined amount of time from a saturated suction temperature (SST) sensor, a current SST;

receiving, after the predetermined amount of time from an outdoor air temperature (OAT) sensor, a current OAT;

comparing a current defrost value to a target defrost value, wherein: the current defrost value is a difference between the current OAT and the current SST, and the target defrost value is determined using an initial defrost value, a defrost speed, and the selected speed; and

causing the heating system to operate in a defrost cycle when the current defrost value is greater than the target defrost value, wherein the variable speed compressor operates at the defrost speed during the defrost cycle.

11. The method of claim 10, wherein the defrost speed is a predetermined speed determined prior to electronically receiving the demand.

12. The method of claim 10, wherein the defrost speed is determined after receiving the current OAT and current SST.

13. The method of claim 10, wherein the target defrost value is recalculated after each time the heating system is caused to operate in the defrost cycle.

14. The method of claim 10, wherein the heating system is operated in a defrost cycle by switching a reversing valve and operating the variable speed compressor at the defrost speed.

15. A controller of a heating system comprising a processor configured to:

receive a demand for heating a structure;

determine a selected speed for operating a variable speed compressor based on the demand;

cause the variable speed compressor to operate at the selected speed;

receive, after a predetermined amount of time from a saturated suction temperature (SST) sensor, a current SST;

receive, after the predetermined amount of time from an outdoor air temperature (OAT) sensor, a current OAT;

compare a current defrost value to a target defrost value, wherein: the current defrost value is a difference between the current OAT and the current SST, and the target defrost value is determined using an initial defrost value, a defrost speed, and the selected speed; and

cause the heating system to operate in a defrost cycle when the current defrost value is greater than the target defrost value, wherein the variable speed compressor operates at the defrost speed during the defrost cycle.

16. The controller of claim 15, wherein the defrost speed is a predetermined speed determined prior to electronically receiving the demand.

17. The controller of claim 15, wherein the defrost speed is determined when the processor compares the current defrost value to the target defrost value.

18. The controller of claim 15, wherein the target defrost value is recalculated after each time the heating system is caused to operate in the defrost cycle.

19. The controller of claim 15, wherein the heating system is operated in a defrost cycle by switching a reversing valve and operating the variable speed compressor at the defrost speed.

20. The controller of claim 15, wherein the initial defrost value is determined by finding a difference between the current OAT and the current SST measured when the heating system is initially run and no frost is present on an outdoor coil.