System and method for low ambient cooling mode transitions

Abstract

A method to operate a Heating, Ventilation, and Air Conditioning (HVAC) system includes receiving a cooling request and comparing ambient temperature with a first threshold temperature. If the ambient temperature is less than the first threshold temperature, the method further includes operating the HVAC system in the low ambient cooling mode. The method further includes communicating a first electronic signal to a fan of a condensing unit to rotate with a preconfigured speed associated with the low ambient cooling mode. The method further includes determining whether the cooling request still exists, the saturated liquid temperature of the working fluid has remained more than a second threshold temperature for more than a predefined duration, and the fan has remained turned on for more than the predefined duration. In response to these conditions being met, the method further includes transitioning from the low ambient cooling mode to a second cooling mode.

Description

SYSTEM AND METHOD FOR LOW AMBIENT COOLING MODE TRANSITIONS TECHNICAL FIELD This disclosure relates generally to Heating, Ventilation, and Air Conditioning (HVAC) 5 systems. More particularly, this disclosure relates to the system and method for low ambient cooling mode transitions. BACKGROUND Heating, ventilation, and air conditioning (HVAC) systems are used to regulate 10 environmental conditions within an enclosed space. Air is cooled via heat transfer with refrigerant flowing through the HVAC system and returned to the enclosed space as conditioned air. SUMMARY OF THE DISCLOSURE 15 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. In some cases, in response to a cooling request / demand to provide cooling to the target space, an HVAC system may be configured to operate in low ambient cooling mode if the ambient temperature 20 is less than a predefined threshold temperature, instead of a normal cooling mode (also referred to herein as a second cooling mode—with the low ambient cooling mode being the first cooling mode). For example, during cold weather (e.g., winter), when the ambient temperature is less than a certain threshold (e.g., 55° Fahrenheit (F) or 12° Celsius (C)), the HVAC system may transition from the second cooling mode to the low ambient cooling mode. The fans of the 25 outdoor condensing unit may operate / rotate at different speeds when the HVAC system is operated in the low ambient cooling mode. In the low ambient cooling mode, the fans of the outdoor condensing unit may operate to regulate the airflow across the outdoor coil to maintain the working fluid’s temperature (and therefore its pressure) flowing inside the outdoor coil within a predefined range required for operating in the low ambient cooling mode. The working2 fluid flows from the compressor to the outdoor coil. Therefore, the working fluid’s temperature (and therefore its pressure) within the compressor is also maintained within a desired range. In some HVAC systems, the criteria for whether to operate the HVAC system in the low ambient cooling mode or the normal cooling mode (i.e., second cooling mode) is based on 5 the ambient temperature that is detected by a temperature sensor circuit. However, in some cases, the placement of the temperature sensor circuit may lead to inaccurate temperature readings due to heat from the coils generated as the fans rotate and / or sunlight, for example. The inaccurate temperature readings may result in unnecessary switching between the low ambient cooling mode and the second cooling mode. For example, when operating in the low 10 ambient cooling mode, the fans of the outdoor condensing unit may have modulated (varying) speed and sometimes turn off. In response, the heat from the outdoor coil may raise the air temperature near the temperature sensor circuit, and therefore, cause the temperature sensor circuit to detect a higher temperature than the actual ambient temperature. Therefore, the HVAC system may incorrectly transition to the second cooling mode. In another example, when the 15 fans of the outdoor heat exchanger are turned on during the second cooling mode, the airflow may cool the temperature sensor circuit and cause the temperature sensor circuit to incorrectly transition to the low ambient cooling mode. These unnecessary transitions between the low ambient cooling and the second cooling modes reduce the reliability of the fans of the outdoor condensing unit as the fans experience more frequent transitions between on and off states 20 and / or between different speeds. These unnecessary transitions between the low ambient cooling and the second cooling modes further reduce the reliability of the compressor that is tasked to operate under the presumption of fluctuating working fluid temperature and pressure, which puts a strain on the compressor and increases the likelihood of its mechanical failures over time. 25 The disclosed system provides a solution to these and other technical problems of conventional HVAC systems. In some embodiments, the disclosed system is configured to use the saturated liquid temperature (SLT) of the working fluid flowing out of the outdoor coil as criteria to determine whether to operate the HVAC system in low ambient cooling mode or second cooling mode. To this end, the disclosed system uses a temperature sensor circuit inside 30 the outdoor coil to monitor and determine the SLT of the working fluid and / or uses a pressure3 sensor circuit downstream of the outdoor coil to determine the pressure of the working fluid and derive the SLT of the working fluid by a converting the pressure value to SLT using a preconfigured formula. By using the SLT of the working fluid as the criteria to determine the appropriate cooling mode, the disclosed system improves the reliability of the fans of the 5 outdoor condensing unit and the compressor. For example, the disclosed system obviates the need to rely on incorrect / inaccurate ambient temperature readings that would be influenced by the heat from the coils or sunlight. Therefore, the fans of the outdoor heat exchanger experience less frequent switching between the low ambient cooling mode and the second cooling mode compared to the 10 conventional HVAC systems that use the ambient temperature readings from a temperature sensor circuit associated with the outdoor coil as the criteria for switching between the low ambient cooling mode and the second cooling mode. In some embodiments, the disclosed HVAC system may comprise a condensing unit which comprises an outdoor coil and a fan. The outdoor coil is configured to transfer heat 15 between the working fluid and the ambient environment. The fan is configured to direct airflow across the outdoor coil to facilitate heat exchange between the working fluid flowing within the outdoor coil and ambient air. The HVAC system further comprises a first temperature sensor circuit associated with the condensing unit and configured to detect a temperature of the ambient air. The HVAC system further comprises a controller that is operably coupled to the 20 fan of the condensing unit and the first temperature sensor circuit. The controller comprises a processor configured to receive a cooling request to provide cooling for a target space. The processor is further configured to obtain first temperature data from the first temperature sensor circuit in response to receiving the cooling request, wherein the first temperature data indicates the temperature of the ambient air. The processor is further configured to compare the 25 temperature of the ambient air with a first threshold temperature. The processor is further configured to operate the HVAC system in a low ambient cooling mode based at least in part upon a determination that the temperature of the ambient air is less than the first threshold temperature, wherein during the low ambient cooling mode, the fan rotates to allow airflow across the outdoor coil to maintain a temperature of the working fluid in a compressor within a 30 predefined temperature range. The processor is further configured to communicate a first4 electronic signal to the fan to rotate with a first preconfigured speed associated with the low ambient cooling mode. 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 5 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 10 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; and FIG. 2 illustrates a flowchart of an example method of operating the HVAC system of FIG. 1. 15 DETAILED DESCRIPTION Embodiments of the present disclosure and its advantages are best understood by referring to FIGS. 1 through 2 of the drawings, like numerals being used for like and corresponding parts of the various drawings. 20 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. In some cases, in response to a cooling request / demand to provide cooling to the target space, an HVAC system may be configured to operate in low ambient cooling mode if the ambient temperature 25 is less than a predefined threshold temperature, instead of a normal cooling mode (also referred to herein as a second cooling mode—with the low ambient cooling mode being the first cooling mode). For example, during cold weather (e.g., winter), when the ambient temperature is less than a certain threshold (e.g., 55° Fahrenheit (F) or 12° Celsius (C)), the HVAC system may transition from the second cooling mode to the low ambient cooling mode. The fans of the 30 outdoor condensing unit may operate / rotate at different speeds when the HVAC system is5 operated in the low ambient cooling mode. In the low ambient cooling mode, the fans of the outdoor condensing unit may operate to regulate the airflow across the outdoor coil to maintain the working fluid’s temperature (and therefore its pressure) flowing inside the outdoor coil within a predefined range required for operating in the low ambient cooling mode. The working 5 fluid flows from the compressor to the outdoor coil. Therefore, the working fluid’s temperature (and therefore its pressure) within the compressor is also maintained within a desired range. In some HVAC systems, the criteria for whether to operate the HVAC system in the low ambient cooling mode or the normal cooling mode (i.e., second cooling mode) is based on the ambient temperature that is detected by a temperature sensor circuit. However, in some 10 cases, the placement of the temperature sensor circuit may lead to inaccurate temperature readings due to, e.g., heat from the coils generated as the fans rotate and / or sunlight. The inaccurate temperature readings may result in unnecessary switching between the low ambient cooling mode and the second cooling mode. For example, when operating in the low ambient cooling mode, the fans of the outdoor condensing unit may have modulated (varying) speed 15 and sometimes turn off. In response, the heat from the outdoor coil may raise the air temperature near the temperature sensor circuit, and therefore, cause the temperature sensor circuit to detect a higher temperature than the actual ambient temperature. Therefore, the HVAC system may incorrectly transition to the second cooling mode. In another example, when the fans of the outdoor heat exchanger are turned on during the second cooling mode, the airflow may cool the 20 temperature sensor circuit and cause the temperature sensor circuit to incorrectly transition to the low ambient cooling mode. These unnecessary transitions between the low ambient cooling and the second cooling modes reduce the reliability of the fans of the outdoor condensing unit as the fans experience more frequent transitions between on and off states and / or between different speeds. These unnecessary transitions between the low ambient cooling and the second 25 cooling modes further reduce the reliability of the compressor that is tasked to operate under the presumption of fluctuating working fluid temperature and pressure, which puts a strain on the compressor and increases the likelihood of its mechanical failures over time. The disclosed system provides a solution to these and other technical problems of conventional HVAC systems. In some embodiments, the disclosed system is configured to use 30 the saturated liquid temperature (SLT) of the working fluid flowing out of the outdoor coil as6 criteria to determine whether to operate the HVAC system in low ambient cooling mode or second cooling mode. To this end, the disclosed system uses a temperature sensor circuit inside the outdoor coil to monitor and determine the SLT of the working fluid and / or uses a pressure sensor circuit downstream of the outdoor coil to determine the pressure of the working fluid 5 and derive the SLT of the working fluid by a converting the pressure value to SLT using a predefined formula. By using the SLT of the working fluid as the criteria to determine the appropriate cooling mode, the disclosed system improves the reliability of the fans of the outdoor condensing unit and the compressor. For example, the disclosed system obviates the need to rely on incorrect / inaccurate ambient temperature readings that would be influenced by 10 the heat from the fans or sunlight. Therefore, the fans of the outdoor heat exchanger experience less frequent switching between the low ambient cooling mode and the second cooling mode compared to the conventional HVAC systems that use the ambient temperature readings from a temperature sensor circuit associated with the outdoor coil as the criteria for switching between the low 15 ambient cooling mode and the second cooling mode. HVAC system 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 20 (e.g., all or a portion of a room, a house, an office building, a warehouse, or the like). 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 system 100 may be located within the building and portion(s) outside the building. The HVAC system 100 may be configured as shown in FIG. 1 or in any 25 other suitable configuration. For example, the HVAC system 100 may include additional components or may omit one or more components shown in FIG. 1. In some embodiments, the HVAC system 100 comprises working fluid conduit subsystems 102, one or more condensing units 104, temperature sensor circuits 114, 116, and 134, pressure sensor circuits 117, a valve 136, a duct system 122, an indoor coil 126, a heating element 128, a blower 130, a thermostat 30 140, and a controller 160.7 The working fluid conduit subsystem 102 facilitates 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 working fluid flows within the working fluid conduit subsystem 102 as illustrated by the arrows in FIG. 1. The working fluid may be any acceptable working fluid including, but 5 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 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 10 achieve the desired cooling or heating request (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 condensing unit 104 comprises a compressor 106, an outdoor coil 108, a fan 110, 15 and a first temperature sensor circuit 114. In some embodiments, the condensing unit 104 is an outdoor unit while other components of the HVAC system 100 may be located indoors. The condensing unit 104 may be an outdoor heat exchanger unit. The compressor 106 is coupled to the working fluid conduit subsystem 102 and is configured to compress (i.e., increase the pressure) the working fluid. The compressor 106 is in signal communication with the controller 20 160 using wired and / or wireless connection. The 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 a status of the compressor 106. The compressor 106 of condensing unit 104 may be a single-speed, variable-speed, or multiple-stage compressor. A variable-speed compressor is generally configured to operate at different speeds to increase the 25 pressure of the working fluid to keep the working fluid moving along the working fluid conduit subsystem 102. In the variable-speed compressor configuration, the speed of compressor 106 can be modified to adjust the cooling capacity of the HVAC system 100. Meanwhile, in the multi-stage compressor configuration, one or more compressors can be turned on or off to adjust the cooling capacity of the HVAC system 100.8 The outdoor coil 108 is configured to facilitate the movement of the working fluid through the working fluid conduit subsystem 102. The outdoor coil 108 is generally configured to transfer heat between the working fluid and the ambient air surrounding the outdoor coil 108. For example, the outdoor coil 108 is configured to remove heat from the working fluid. The 5 outdoor coil 108 may be located downstream of the compressor 106. The outdoor coil 108 may comprise metallic fins and tubing configured to facilitate the heat transfer between the working fluid flowing inside the outdoor coil 108 and the ambient air in the surrounding environment. 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. 10 For example, the fan 110 may be configured to blow outside air through the outdoor coil 108 to help cool the working fluid flowing therethrough. The fan 110 may be in communication with the controller 160 (e.g., via 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. The compressed, cooled working fluid flows from the outdoor coil 108 toward the valve 136. In 15 some embodiments, the fan 110 may include a plurality of fans 110. The first temperature sensor circuit 114 is associated with the condensing unit 104 and may include a temperature sensing element and circuitry. The first temperature sensor circuit 114 may be configured to detect the temperature of the ambient air. The first temperature sensor circuit 114 may be implemented by a hardware circuit. The first temperature sensor circuit 114 20 may include one or more temperature sensor circuits. The first temperature sensor circuit 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. The first temperature sensor circuit 114 may include a plurality of temperature sensor circuits. In some embodiments, the first temperature sensor circuit 114 may be positioned within the 25 condensing unit 104), near the condensing unit 104, or at any suitable location. The first temperature sensor circuit 114 may be attached to a surface using any appropriate means (e.g., threaded connections, clamps, adhesives, or the like). The first temperature sensor circuit 114 is operably coupled to the controller 160 via wired and / or wireless communication. The first temperature sensor circuit 114 may communicate the temperature data 170 that indicates the 30 detected ambient temperature to the controller 160. The first temperature sensor circuit 114 is9 configured to detect the temperature of the ambient air periodically (e.g., every second, every minute, etc.) and / or on demand (e.g., in response to a request from the controller 160). The controller 160 may use the temperature data 170 to determine the operating mode of the HVAC system 100. 5 The second temperature sensor circuit 116 may include a temperature sensing element and circuitry configured to detect the saturated liquid temperature (SLT) of the working fluid flowing out of the outlet of the outdoor coil 108 and through the working fluid conduit subsystem 102 toward the inlet of the valve 136 and indoor coil 126. The second temperature sensor circuit 116 may be implemented by a hardware circuit. The second temperature sensor 10 circuit 116 may include one or more temperature sensor circuits. The second temperature sensor circuit 116 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 second temperature sensor circuit 116 may include a plurality of temperature sensor circuits. In some embodiments, the second temperature sensor circuit 116 may be positioned at or near the 15 outlet of the outdoor coil 108 or along any section of the working fluid conduit subsystem 102 that connects the outlet of the outdoor coil 108 to the valve 136. The second temperature sensor circuit 116 may be attached to a surface using any appropriate means (e.g., threaded connections, clamps, adhesives, or the like). The second temperature sensor circuit 116 is operably coupled to the controller 160 via wired and / or wireless communication. The second 20 temperature sensor circuit 116 may communicate the temperature data 172 to the controller 160, where the temperature data 172 indicates the saturated liquid temperature of the working fluid detected by the second temperature sensor circuit 116. The second temperature sensor circuit 116 is configured to detect the saturated liquid temperature periodically (e.g., every second, every minute, etc.) and / or on demand (e.g., in response to a request from the controller 25 160). The controller 160 may use the temperature data 172 to determine whether to transition the HVAC system 100 between operating modes, such as from the low ambient cooling mode to the second cooling mode, and vice versa. In some embodiments, the system 100 may include a pressure sensor circuit 117 and use pressure data 119 provided by the pressure sensor circuit 117 to derive the SLT of the 30 working fluid. The pressure sensor circuit 117 may include one or more pressure sensing10 elements such as a piezoresistive sensing element, capacitive sensing element, strain gauge, or any other suitable pressure sensor. The pressure sensor circuit 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 119 to the controller 160, where the pressure data 119 includes the 5 determined pressure of the working fluid. The pressure sensor circuit 117 may include one or more hardware pressure sensor circuits 117. The pressure sensor circuit 117 may be positioned along the working fluid conduit subsystem 102 between the outdoor coil 108 and the valve 136, or at any suitable location. The pressure sensor circuit 117 is operably coupled to the controller 160 via wired and / or wireless communication. The controller 160 may receive pressure data 10 119 from the pressure sensor circuit 117 and use a predefined formula, such as SLT = A × P^B + C, where P represents the determined pressure, and A, B, C are derived coefficients based on the specific working fluid characteristics, calibration curves (where the x-axis is the measured pressure data 119 from the pressure sensor circuit 117 and the y-axis is the corresponding SLT of the working fluid), and / or lookup tables to derive the SLT of the working fluid based on the 15 pressure data 119. Thus, the SLT of the working fluid may be determined based on the pressure data 119 and / or the temperature data 172 with respect to the working fluid. In some embodiments, the controller 160 may determine the SLT of the working fluid using the pressure data 119 and / or the temperature data 172 with respect to the working fluid. For example, the temperature sensor circuits 116 may be placed in condensers (e.g., inside the 20 outdoor coil 108 acting as a condenser during the cooling cycle and inside the indoor coil 126 acting as a condenser during the heating cycle). For example, during the cooling cycle, the temperature data from the temperature sensor circuit 116 that is placed inside the outdoor coil 108 may be used to determine the SLT of the working fluid, and during the heating cycle, the temperature data from the temperature sensor circuit 116 that is placed inside the outdoor coil 25 108 may be used to determine the SLT of the working fluid. In the same or another example, the pressure sensor circuits 117 may be placed downstream of condensers (e.g., inside the outdoor coil 108 acting as a condenser during the cooling cycle and inside the indoor coil 126 acting as a condenser during the heating cycle). For example, during the cooling cycle, the pressure data from the pressure sensor circuit 117 that is inside the outdoor coil 108 may be 30 used to derive the SLT of the working fluid, and during the heating cycle, the pressure data11 from the pressure sensor circuit 117 that is inside the indoor coil 126 may be used to derive the SLT of the working fluid. The indoor coil 126 is generally any heat exchanger configured to provide heat transfer between the air flowing through (or across) the indoor coil 126 (i.e., airflow 118 contacting an 5 outer surface of one or more coils of the indoor coil 126) and working fluid 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 fluidically connected to the compressor 106, such that working fluid generally flows from the indoor coil 126 to the condensing unit 104 through compressor 106 when the HVAC system 100 is operating to provide cooling. When the HVAC system 100 is 10 configured to operate as a heat pump, the indoor coil 126 acts as a condenser to heat the flow of air 118 passing therethrough. 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 therethrough. A portion of the HVAC system 100 is configured to move airflow 118 provided by the 15 blower 130 across the indoor coil 126 and out of a duct system 122 as conditioned airflow 120. Return air 124, which may be air returning from the building, fresh air from outside, or some combination, is pulled into a return duct 135. A suction side of the blower 130 pulls the return air 124. The blower 130 discharges airflow 118 into a duct 137 such that airflow 118 crosses the indoor coil 126 and / or heating element 128 to produce conditioned airflow 120. The blower 20 130 is any mechanism for providing airflow 118 through the HVAC system 100. For example, the blower 130 may be a constant speed or variable speed circulation blower or fan. Examples of variable speed blowers include, but are not limited to, belt-drive blowers controlled by inverters, direct-drive blowers with electronic commuted motors (ECM), or any other suitable type of blower. 25 The heating element 128 is generally any device for heating the flow of air 118 and providing heated air 120 to the conditioned space, when the HVAC system 100 operates in a heating mode. For example, the heating element 128 may be a furnace. 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 30 not limited to natural gas, propane, oil, or any other combustible compound. In some12 embodiments, the HVAC system 100 is configured to operate as a heat pump. Generally, when the HVAC system is operating as a heat pump in a heating mode, the flow of refrigerant is reversed, 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 therethrough. If the HVAC system 100 is 5 configured to operate as a heat pump, the HVAC system 100 may include a reversing valve to reverse the flow of working fluid through the HVAC system 100 during operation in the heating mode and an outdoor expansion device for expanding the working fluid 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 10 backup heating to the flow of air 120. The heating element 128 may be in communication with the controller 160 (e.g., via wired and / or wireless communication) to receive control signals for activating the heating element 128 to heat the flow of air 118, when the HVAC system 100 is operated in a 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 15 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 (i.e., such that the flow of air 118 is not heated by heating element 128). The temperature sensor circuit 134 may include a temperature sensing element and circuitry configured to detect the temperature of the indoor conditioned space (e.g., a room). 20 The temperature sensor circuit 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 circuit 134 may include one or more temperature sensor circuits. In some embodiments, the temperature sensor circuit 134 may positioned within the duct 135 or at any suitable location 25 within the indoor section of the HVAC system 100. The temperature sensor circuit 134 may further be configured to measure air humidity and / or any other properties of the conditioned space. The temperature sensor circuit 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 30 HVAC system 100 as needed.13 The valve 136 may 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. The valve 136 is fluidly coupled to the working 5 fluid conduit subsystem 102, and may be positioned at any section of the working fluid conduit subsystem 102 that connects the outlet of the outdoor coil 108 to the inlet of the indoor coil 126. The valve 136 may reduce the pressure and temperature of the working fluid as it moves through the valve 136. The valve 136 may control the flow rate of the working fluid by varying degrees based on the operating mode and system conditions. In some embodiments, the valve 10 136 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 valve 136 based on the operating mode, such as cooling or heating mode. In some embodiments, the 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 working 15 fluid toward the indoor coil 126. The thermostat 140 may generally be an electronic device with which users can 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 20 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 25 controller 160 (originally detected by the temperature sensor circuit 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 30 user, a support entity, and a service provider to perform actions with respect to the HVAC14 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. The controller 160 is communicatively coupled (e.g., via wired and / or wireless connection) to other components in the HVAC system 100 and configured to control their 5 operations. In some embodiments, controller 160 can 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, 10 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, 15 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, 20 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 25 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 the15 controller 160 described in FIGS. 1-2 and one or more operations of the method 200 described in FIG. 2. 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 5 overflow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 166 may be volatile or non-volatile and may comprise a 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 10 store any suitable set of instructions, 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, cooling request 178, temperature data 170, temperature data 172, pressure data 119, threshold temperature 176a, threshold temperature 176b, electronic signals 180a-c, preconfigured speed 182a-b, preconfigured temperature range 15 184, target temperature 186, conditions 188, predefined duration 190, and / or other data, instructions, and operating parameters for components in the system 100. The I / O interface 164 is configured to communicate data and signals with other devices. 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 20 and / or terminals for establishing signal communications between the controller 160 and other devices. 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 between components of system 100 may be wired or wireless. For example, conventional cables and contacts may be used to couple the controller 160 to various components of the HVAC 25 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 such that data is communicated therebetween. In some embodiments, the data bus may include, for example, 30 any combination of hardware, software embedded in a computer-readable medium, or encoded16 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 5 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 10 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 to other components of the HVAC system 100. Operational flow for low ambient cooling mode transitions 15 In some cases, the HVAC system 100 may be operated in the low ambient cooling mode to provide cooling for a target space when the ambient air temperature is less than a first threshold temperature 176a, and be operated in the second cooling mode when the ambient air temperature is more than the first threshold temperature 176a. In other words, the first threshold temperature 176a may be the entry temperature point to operate the HVAC system 100 in the 20 low ambient cooling mode. In some examples, the first threshold temperature 176a may be 55° Fahrenheit (F) or 12° Celsius (C) or any other temperature. In operation, the controller 160 may receive a cooling request 178 to provide cooling for the target space from the thermostat 140 when a user enters a desired temperature to the user interface 142 of the thermostat 140. In response, the controller 160 may obtain the first 25 temperature data 170 from the first temperature sensor circuit 114, where the first temperature data 170 may indicate the ambient air temperature surrounding the condensing unit 104. The controller 160 may compare the obtained ambient air temperature with the first threshold temperature 176a to determine whether the ambient air temperature is less than the first threshold temperature 176a. If the ambient air temperature is determined to be less than 30 the first threshold temperature 176a, the controller 160 may operate the HVAC system 100 in17 the low ambient cooling mode. For example, to operate the HVAC system 100 in the low ambient cooling mode, the controller 160 may cause the processor 162 to execute the software instructions 168. In response to the software instructions 168 being executed, the HVAC system 100 is operated in the low ambient cooling mode. During the low ambient cooling mode, the 5 controller 160 may communicate a first electronic signal 180a to the fan 110 of the condensing unit 104. The first electronic signal 180a may cause the fan 110 to rotate at a first preconfigured speed 182a which is preconfigured according to the low ambient cooling mode. During the low ambient cooling mode, the fan 110 may rotate to allow airflow 112 across the outdoor coil 108 to maintain a temperature of the working fluid in the compressor 10 106 within a predefined temperature range 184, and further to maintain a pressure of the working fluid in the compressor 106 with a predefined pressure range within which the compressor 106 is configured to operate. In some examples, the first preconfigured speed 182a may be a predefined modulated speed associated with the low ambient cooling mode—meaning that the predefined modulated speed varies according to fan speed modulation settings 15 associated with the low ambient cooling mode. This process may allow airflow 112 across the outdoor coil 108 to facilitate heat exchange between the working fluid flowing inside the outdoor coil 108 and the airflow 112. If the ambient air temperature is determined to be more than or equal to the first threshold temperature 176a, the controller 160 may transition the HVAC system 100 to operate 20 in the second cooling mode. In response, the controller 160 may communicate a second electronic signal 180b to the fan 110 to cause the fan 110 to rotate at a second preconfigured speed 182b which is preconfigured according to the second cooling mode. In some examples, the second preconfigured speed 182b may be more than the first preconfigured speed 182a to generate more airflow 112 to reduce the temperature of the working fluid flowing inside the 25 outdoor coil 108. While operating the HVAC system 100 in the low ambient cooling mode, the controller 160 may monitor the system conditions to determine whether it is time to transition from low ambient cooling mode to the second ambient cooling mode, and / or whether the cooling request 178 is met. For example, to determine whether the cooling request 178 is met, the controller 30 160 may compare the temperature within the target space (as detected and provided by the18 temperature sensor circuit 134) with the target temperature 186 associated with the cooling request 178. If it is determined that the temperature within the target space has reached the target temperature 186, the controller 160 may determine that the cooling request 178 is met. In response, the controller 160 may exit the low ambient cooling mode by communicating a 5 third electronic signal 180c to the fan 110 to stop rotating. Otherwise, the controller 160 may continue operating the HVAC system 100 in the low ambient cooling mode. Further, while the HVAC system 100 is in the low ambient cooling mode, the controller 160 may determine whether one or more conditions 188 to transition from the low ambient cooling mode to the second cooling mode is met. In some examples, the conditions 188 may 10 include the determined saturated liquid temperature has been remaining more than the second threshold temperature 176b for more than a predefined duration 190, determining that the fan 110 has been turned on for more than the predefined duration 190, and determining that the cooling request 178 is still not met. In some embodiments, a condition 188 to transition to the second cooling mode may 15 include determining whether the saturated liquid temperature of the working fluid flowing out of the outlet of the outdoor coil 108 remains more than the predefined second threshold temperature 176b, e.g., for at least the predefined duration 190 (e.g., for more than five minutes, ten minutes, etc.). To this end, the controller 160 may obtain second temperature data 172 from the second temperature sensor circuit 116, where the second temperature data 172 indicates the 20 detected saturated liquid temperature of the working fluid. The controller 160 may compare the obtained saturated liquid temperature with the predefined second threshold temperature 176b. For example, the predefined second threshold temperature 176b may be 75 °F, 23 °C, 80° F, 26 °C, or any other suitable temperature. If the obtained saturated liquid temperature remains more than the second threshold temperature 176b, e.g., for at least the predefined duration 190, the 25 controller 160 may determine that the condition 188 is met. The controller 160 may further monitor the operation of the fan 110 over time to determine whether it has been turned on (e.g., rotating with the first preconfigured speed 182a associated with the low ambient cooling mode) for at least the predefined duration 190. In response to determining that the conditions 188 are met, the controller 160 may transition the 30 HVAC system 100 from the low ambient cooling mode to the second cooling mode. For19 example, to this end, the controller 160 may communicate the second electronic signal 180b to the fan 110 to cause the fan 110 to rotate at the second preconfigured speed 182b associated with the second cooling mode. The controller 160 may continue to monitor the system conditions and conditioning demands to determine whether to operate in the heating mode, the 5 low ambient cooling mode, or the second cooling mode. Example method for operating an HVAC system FIG. 2 illustrates a flowchart of an example method 200 of operating the system 100 of FIG. 1. The method 200 may be performed by the controller 160 (see FIG. 1) when one or more 10 processors (e.g., processor 162 of FIG. 1) execute software instructions (e.g., software instructions 168) stored in one or more memories (e.g., memory 166 of FIG. 1). The method 200 may include operations 202-222. Modifications, additions, or omissions may be made to method 200. Method 200 may include more, fewer, or other operations. For example, operations may be performed in parallel or in any suitable order. 15 At operation 202, the controller 160 receives a cooling request 178 to provide cooling for a target space, similar to that described in FIG. 1, and proceeds to operation 204. At operation 204, the controller 160 obtains the first temperature data 170 from the first temperature sensor circuit 114, that indicates the temperature of the ambient air, similar to that described in FIG. 1, and proceeds to operation 206. 20 At operation 206, the controller 160 compares the temperature of the ambient air with the first threshold temperature 176a and proceeds to operation 208. At operation 208, the controller 160 determines whether the temperature of the ambient air is less than the first threshold temperature 176a. If it is determined that the temperature of the ambient air is less than the first threshold temperature 176a (‘Yes’), the method 200 25 proceeds to operation 210. Otherwise (‘No’), the method 200 proceeds to operation 222. At operation 210, the controller 160 communicates the first electronic signal 180a to the fan 110 of the condensing unit 104 to rotate with a first preconfigured (modulated) speed 182a according to the low ambient cooling mode, similar to that described in FIG. 1 and proceeds to operation 212.20 At operation 212, the controller 160 determines whether the cooling request 178 still exists (e.g., the cooling request is still asserted). If it is determined that the cooling request 178 still exists (‘Yes’), the method 200 proceeds to operation 214. Otherwise (‘No’), the method 200 returns to operation 202. 5 At operation 214, the controller 160 obtains the second temperature data 172 from the second temperature sensor circuit 116, that indicates the saturated liquid temperature of the working fluid. In some embodiments, the controller 160 may determine or derive the saturated liquid temperature of the working fluid based on the pressure data 119 and / or second temperature data 172, similar to that described in FIG. 1. 10 At operation 216, the controller 160 monitors the operation of the fan 110, similar to that described in FIG. 1. At operation 218, the controller 160 determines whether the saturated liquid temperature of the working fluid has remained more than the second threshold temperature 176b for more than the predefined duration 190. If it is determined that the saturated liquid temperature of the 15 working fluid has remained more than the second threshold temperature 176b for more than the predefined duration 190 (‘Yes’), the method 200 proceeds to operation 220. Otherwise (‘No’), the method 200 returns to operation 210. At operation 220, the controller 160 determines whether the fan 110 has remained turned on for more than the predefined duration 190. If it is determined that the fan 110 has remained 20 turned on for more than the predefined duration 190 (‘Yes’), the method 200 proceeds to operation 222. Otherwise (‘No’), the method 200 returns to operation 210. At operation 222, the controller 160 initiates the second cooling mode, e.g., by communicating the second electronic signal 180b to the fan 110 to rotate at the second preconfigured speed 182b associated with the second cooling mode, similar to that described in 25 FIG. 1. The controller 160 operates the HVAC system 100 in the second cooling mode as long as the one or more conditions 188 to remain in the second cooling mode are met, similar to that described in FIG. 1. Otherwise, the controller 160 may transition the HVAC system 100 to a different operating mode, such as returning to the low ambient cooling mode or stopping the cooling operation in response to determining that the cooling request 178 has been met.21 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 5 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 as illustrative and not restrictive, and the intention is not to be limited to 10 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 15 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. 20 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

WHAT IS CLAIMED IS:

1. A Heating, Ventilation, and Air Conditioning (HVAC) system comprising: a condensing unit comprising: an outdoor coil configured to transfer heat between working fluid and ambient environment; and a fan configured to direct airflow across the outdoor coil to facilitate heat exchange between the working fluid flowing within the outdoor coil and ambient air; a first temperature sensor circuit associated with the condensing unit, and configured to detect a temperature of the ambient air; and a controller operably coupled to the fan of the condensing unit and the first temperature sensor circuit, the controller comprising a processor configured to: receive a cooling request to provide cooling for a target space; in response to receiving the cooling request, obtain first temperature data from the first temperature sensor circuit, wherein the first temperature data indicates the temperature of the ambient air; compare the temperature of the ambient air with a first threshold temperature; operate the HVAC system in a low ambient cooling mode based at least in part upon a determination that the temperature of the ambient air is less than the first threshold temperature, wherein during the low ambient cooling mode, the fan rotates to allow airflow across the outdoor coil to maintain a temperature of the working fluid in a compressor within a predefined temperature range; and communicate a first electronic signal to the fan to rotate with a first preconfigured speed associated with the low ambient cooling mode.

2. The HVAC system of Claim 1, wherein: the HVAC system further comprises a second temperature sensor circuit positioned within of the condensing unit, and configured to detect a saturated liquid temperature of the working fluid flowing out of an outlet of the outdoor coil to an inlet of an indoor coil through a working fluid conduit subsystem; and23 the processor is further configured to: determine that one or more conditions to transition from the low ambient cooling mode to a second cooling mode are met, wherein determining that the one or more conditions to transition from the low ambient cooling mode to the second cooling mode are met comprises: obtaining second temperature data from the second temperature sensor circuit, wherein the second temperature data indicates the saturated liquid temperature associated with the working fluid; comparing the saturated liquid temperature with a second threshold temperature; determining that the saturated liquid temperature is more than the second threshold temperature; and in response to determining that the one or more conditions to transition from the low ambient cooling mode to the second cooling mode are met, communicate a second electronic signal to the fan to rotate with a second preconfigured speed associated with the second cooling mode.

3. The HVAC system of Claim 2, wherein the one or more conditions comprise the saturated liquid temperature remaining more than the second threshold temperature for more than a predefined duration.

4. The HVAC system of Claim 2, wherein the one or more conditions comprise determining that the fan is turned on for more than a predefined duration.

5. The HVAC system of Claim 2, wherein the one or more conditions comprise determining that the cooling request is still not met.

6. The HVAC system of Claim 1, wherein the processor is further configured to: determine that the cooling request is met by determining that a temperature within the target space has reached a target temperature; and24 in response to determining that the cooling request is met, exit the low ambient cooling mode by communicating a third electronic signal to the fan to stop rotating.

7. The HVAC system of Claim 1, wherein, during the low ambient cooling mode, the first electronic signal further causes the fan to rotate according to a predefined modulated speed associated with the low ambient cooling mode.

8. A method for operating a Heating, Ventilation, and Air Conditioning (HVAC) system comprising: receiving a cooling request to provide cooling for a target space; in response to receiving the cooling request, obtaining first temperature data from a first temperature sensor circuit, wherein the first temperature data indicates a temperature of ambient air; comparing the temperature of the ambient air with a first threshold temperature; operating the HVAC system in a low ambient cooling mode based at least in part upon a determination that the temperature of the ambient air is less than the first threshold temperature, wherein during the low ambient cooling mode, a fan of a condensing unit rotates to allow airflow across an outdoor coil to maintain the temperature of a working fluid in a compressor within a predefined temperature range; and communicating a first electronic signal to the fan to rotate with a first preconfigured speed associated with the low ambient cooling mode.

9. The method of Claim 8, further comprising determining that one or more conditions to transition from the low ambient cooling mode to a second cooling mode are met, determining that the one or more conditions to transition from the low ambient cooling mode to the second cooling mode are met comprises: obtaining second temperature data from a second temperature sensor circuit, wherein the second temperature data indicates a saturated liquid temperature associated with the working fluid; comparing the saturated liquid temperature with a second threshold temperature;25 determining that the saturated liquid temperature is more than the second threshold temperature; and in response to determining that the one or more conditions to transition from the low ambient cooling mode to the second cooling mode are met, communicating a second electronic signal to the fan to rotate with a second preconfigured speed associated with the second cooling mode.

10. The method of Claim 9, wherein the one or more conditions comprise the saturated liquid temperature remaining more than the second threshold temperature for more than a predefined duration.

11. The method of Claim 9, wherein the one or more conditions comprise determining that the fan is turned on for more than a predefined duration.

12. The method of Claim 9, wherein the one or more conditions comprise determining that the cooling request is still not met.

13. The method of Claim 9, wherein, during the low ambient cooling mode, the first electronic signal further causes the fan to rotate according to a predefined modulated speed associated with the low ambient cooling mode.

14. The method of Claim 8, further comprising: determining that the cooling request is met by determining that the temperature within the target space has reached a target temperature; and in response to determining that the cooling request is met, exiting the low ambient cooling mode by communicating a third electronic signal to the fan to stop rotating.

15. A controller of a Heating, Ventilation, and Air Conditioning (HVAC) system comprising a processor configured to: receive a cooling request to provide cooling for a target space;26 in response to receiving the cooling request, obtain first temperature data from a first temperature sensor circuit, wherein the first temperature data indicates a temperature of ambient air; compare the temperature of the ambient air with a first threshold temperature; operate the HVAC system in a low ambient cooling mode based at least in part upon a determination that the temperature of the ambient air is less than the first threshold temperature, wherein during the low ambient cooling mode, a fan of a condensing unit rotates to allow airflow across an outdoor coil to maintain the temperature of a working fluid in a compressor within a predefined temperature range; and communicate a first electronic signal to the fan to rotate with a first preconfigured speed associated with the low ambient cooling mode.

16. The controller of Claim 15, wherein the processor is further configured to determine that one or more conditions to transition from the low ambient cooling mode to a second cooling mode are met, wherein determining that the one or more conditions to transition from the low ambient cooling mode to the second cooling mode are met comprises: obtaining second temperature data from a second temperature sensor circuit, wherein the second temperature data indicates a saturated liquid temperature associated with the working fluid; comparing the saturated liquid temperature with a second threshold temperature; determining that the saturated liquid temperature is more than the second threshold temperature; and in response to determining that the one or more conditions to transition from the low ambient cooling mode to the second cooling mode are met, communicate a second electronic signal to the fan to rotate with a second preconfigured speed associated with the second cooling mode.

17. The controller of Claim 16, wherein the one or more conditions comprise the saturated liquid temperature remaining more than the second threshold temperature for more than a predefined duration.27 18. The controller of Claim 16, wherein the one or more conditions comprise determining that the fan is turned on for more than a predefined duration.

19. The controller of Claim 16, wherein the one or more conditions comprise determining that the cooling request is still not met.

20. The controller of Claim 15, wherein the processor is further configured to: determine that the cooling request is met by determining that the temperature within the target space has reached a target temperature; and in response to determining that the cooling request is met, exit the low ambient cooling mode by communicating a third electronic signal to the fan to stop rotating.