Heat pump with controllable expansion valve

Abstract

A refrigerant circuit system is disclosed. The system may include a refrigerant circuit, a sensor unit and a controller. The refrigerant circuit may include a controllable expansion valve. The sensor unit may include a first sensor and a second sensor configured to determine one or more inputs associated with the refrigerant circuit. The controller may be configured to determine that there may be a demand to energize the refrigerant circuit. Responsive to determining the demand, the controller may determine that the first sensor is faulty. The controller may further control an operation of the controllable expansion valve based on at least one of inputs obtained from the second sensor and historical controllable expansion valve positions, responsive to determining that the first sensor is faulty.

Description

HEAT PUMP WITH CONTROLLABLE EXPANSION VALVECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and benefit of U.S. provisional patent application no. 63 / 657,241 filed June 7, 2024, which is herein incorporated by reference.FIELD

[0002] The present disclosure relates to a heat pump and more specifically to a heat pump with a controllable expansion valve.BACKGROUND

[0003] Heat pump assemblies or refrigerant circuits are used to heat water in water heating systems. Similarly, refrigerant circuits are used in heating, ventilation, and air conditioning (HVAC) systems installed in residential and commercial buildings.

[0004] It is known that operation of such systems is affected when one or more heat pump / system components develop a fault. For example, a conventional heat pump water heating system stops operating when one or more system sensors develop a fault or start to provide incorrect readings. Such instances cause inconvenience to system users, as the users are unable to obtain hot water from the water heating system until the faulty sensors are repaired or replaced.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The detailed description is set forth with reference to the accompanying drawings. The use of the same reference numerals may indicate similar or identical items. Various embodiments may utilize elements and / or components other than those illustrated in the drawings, and some elements and / or components may not be present in various embodiments. Elements and / or components in the figures are not necessarily drawn to scale. Throughout this disclosure, depending on the context, singular and plural terminology7may be used interchangeably.

[0006] FIG. 1 depicts a refrigerant circuit system in accordance with one or more embodiments of the present disclosure.

[0007] FIG. 2 depicts an example pressure-enthalpy diagram associated with a refrigerant circuit in accordance with one or more embodiments of the present disclosure.

[0008] FTG. 3 depicts a block diagram of a controller configured to operate a refrigerant circuit in accordance with one or more embodiments of the present disclosure.

[0009] FIG. 4 depicts a flow diagram of an example method to operate a refrigerant circuit in accordance with one or more embodiments of the present disclosure.DETAILED DESCRIPTION

[0010] The present disclosure is directed towards a heat pump system or a refrigerant circuit system ("‘system”) that may operate efficiently even when one or more system sensors develop a fault. The system may be part of a heating, ventilation, and air conditioning (HVAC) unit, a water heating system (or a water heater) having a water storage tank, or any other similar system that operates using a refrigerant circuit / heat pump.

[0011] The present disclosure is described in the context of a water heating system; however, the system may be part of any vapor compression cycle system, without departing from the scope of the present disclosure. A “vapor compression cycle system” may broadly encompass any system that is configured to heat and / or cool a conditioned space, heat and / or cool a fluid that is provided to a load, and / or perform any other actions associated with a vapor compression cycle. Non-limiting examples of types of a vapor compression cycle systems can include air conditioners (e.g., no reversing valve, only provides cooling mode), heat pumps (e.g., air source or geothermal; has a reversing valve and operates in both heating and cooling modes), heat pump water heaters, integrated heat pump water heaters, split system heat pump water heaters, heat pump water heaters with a circulation pump and a brazed plate heat exchanger, split systems, packaged systems, mini-splits, PTACs, window units, vertical packaged systems, VRF systems, etc. Reference is made herein to a specific use case in which the vapor compression cycle system is an air conditioner that provides cool air to a conditioned space, such as a residential home, however, this is not intended to limit the type of vapor compression cycle system to which the configuration described herein may be applicable).

[0012] The system may include a heat pump assembly or a refrigerant circuit of a vapor compression cycle. The refrigerant circuit may include a plurality of units including, but not limited to. an evaporator (or a first heat exchanger), a compressor, a condenser (or a second heat exchanger), and a controllable expansion valve. During operation of the system, the condenser may be configured to output a high-pressure refrigerant in a liquidstate. The controllable expansion valve may receive the high-pressure refrigerant from the condenser and reduce the pressure and temperature of the received refrigerant, thereby outputting a low-pressure, low-temperature refrigerant. The evaporator may receive the refrigerant from the controllable expansion valve, and output the refrigerant in a vapor state. The compressor may receive the refrigerant from the evaporator and output the refrigerant in high pressure, high temperature vapor state. The condenser may receive the refrigerant from the compressor, thus completing the vapor compression cycle. When the system is part of a water heating system, the water storage tank associated with the water heating system may be configured to obtain heat from the condenser, thereby heating the water stored in the storage tank.

[0013] As will be appreciated, the refrigerant circuit disclosed in the present disclosure may include a reversing valve in which the flow of the refrigerant described above may be reversed. In this manner, the first heat exchanger may be a condenser and / or an evaporator, and the second heat exchanger may be a condenser and / or an evaporator depending on the flow direction of the refrigerant. For simplicity, however, only a single flow direction is shown and described in the present disclosure.

[0014] In some aspects, the controllable expansion valve may be an electronic expansion valve that may have an adjustable orifice size. The flow of refrigerant from the controllable expansion valve may be controlled / optimized by adjusting the orifice size of the expansion valve. In some aspects, the orifice size may be adjusted based on a plurality of parameters associated with the refrigerant circuit I system. For example, the orifice size may be adjusted based on ambient temperature, tank temperature of the water storage tank associated with the water heating system, an evaporator temperature, a suction temperature, a discharge temperature, an amount of current drawn by the system, and / or the like.

[0015] In alternative aspects, the controllable expansion valve may not be an electronic expansion valve, but may instead include a plurality of capillary tubes of different sizes. In this embodiment, the flow of refrigerant from the controllable expansion valve may be adjusted by enabling one or more capillary' tubes to output the refrigerant to the evaporator (while disabling the other capillary tubes from outputting the refrigerant to the evaporator), based on the parameters described above.

[0016] The system may7further include a sensor unit and a controller communicatively coupled with the controllable expansion valve. The controller may be configured tocontrol the operation of the controllable expansion valve based on inputs obtained from the sensor unit. Stated another way, the controller may be configured to adjust the orifice size or select an optimal “valve position’" based on the inputs obtained from the sensor unit.

[0017] In an exemplary aspect, the sensor unit may be a plurality of sensors including, but not limited to, an evaporator thermistor, an evaporator pressure transducer, a suction thermistor, an ambient temperature sensor, a tank temperature sensor, a discharge temperature sensor, a cunent sensor and / or the like. In some aspects, the controller may be configured to enable the system or the refrigerant circuit to continue operation when there is a demand to operate the refrigerant circuit, even when the evaporator thermistor, the evaporator pressure transducer and / or the suction thermistor develop a fault. Stated another way, the controller may enable a system user to continue obtaining hot water from the water heating system, even when the evaporator thermistor, the evaporator pressure transducer and / or the suction thermistor of the refrigerant circuit develop a fault.

[0018] In a first exemplary embodiment, when one or more of the sensors described above develop a fault, the controller may cause the controllable expansion valve to operate at a first fixed position, until the sensor fault is rectified or for a predefined time duration (e.g., for a maximum of 1 or 2 days). Stated another way, the controller may fix or set the position (or a percentage opening of the orifice) of the controllable expansion valve to the first fixed position, when one or more of the sensors described above develop a fault. In this embodiment, the controller may not enable the controllable expansion valve to change its position (i.e.. the percentage orifice opening) from the first fixed position, until the sensor fault is rectified. In some aspects, the controller may determine the first fixed position based on a real-time ambient temperature and / or a real-time tank temperature (as determined via the ambient temperature sensor and the tank temperature sensor). In this case, the controller may first fetch a correlation matrix correlating a plurality of preset expansion valve positions with at least one of a plurality of ambient temperatures and a plurality of tank temperatures. The controller may then correlate the determined real-time ambient temperature and tank temperature with the correlation matrix, to determine the first fixed position. In some aspects, the correlation matrix may be pre-stored by a system manufacturer in a system memory, and may be prepared, for example, by performing a plurality of lab tests on the system / refrigerant circuit. In some instances, the controllermay perform one or more calculations to determine an expansion valve position based on the determined real-time ambient temperature and tank temperature.

[0019] In a second exemplary embodiment, when one or more of the sensors described above develop a fault, the controller may cause the controllable expansion valve to operate at a second fixed position determined based on historical valve positions, until the sensor fault is rectified or for the predefined time duration. In this case, the controller may fetch historical statistics or pattern of valve orifice opening percentages over the past 24 hours (or any other time duration such as 12 hours, 18 hours. 36 hours, and / or the like) from the system memory, and determine the second fixed position based on the historical statistics. In an exemplar}' aspect, the second fixed position may be a mean value, an average value or a highest frequency or probability value of the historical valve positions. Similar to the first fixed position, in this embodiment as well, the controller may not enable the controllable expansion valve to change its position (i.e., the percentage orifice opening) from the second fixed position, until the sensor fault is rectified.

[0020] In a third exemplar ' embodiment, when one or more of the evaporator thermistor or the evaporator pressure transducer develops a fault, the controller may cause the controllable expansion valve to operate at a first dynamic position, until the sensor fault is rectified or for the predefined time duration. In some aspects, the controller may determine the first dynamic position of the controllable expansion valve based on a first superheat temperature, which in turn may be calculated based on a suction temperature (determined via the suction thermistor) and the ambient temperature (determined via the ambient temperature sensor). In an exemplary aspect, the controller may determine the first superheat temperature by calculating a difference between the suction temperature and a sum of the real-time ambient temperature and a predefined offset temperature (which may be in a range of 5 to 25 degree Fahrenheit, for example). In this case, the controller may determine the first dynamic position such that the calculated first superheat temperature reaches to a target superheat temperature. In this embodiment, the position of the valve orifice (i.e., the first dynamic position of the controllable expansion valve) is not fixed, and changes as the suction temperature increases or decreases. Stated another way, in this embodiment, the controller may modify the first dynamic position as the first superheat temperature reaches to (or "chases’’) the target superheat temperature.

[0021] In a fourth exemplary embodiment, when the suction thermistor develops a fault, the controller may cause the controllable expansion valve to operate at a seconddynamic position, until the sensor fault is rectified or for the predefined time duration. In some aspects, the controller may determine the second dynamic position of the controllable expansion valve based on a second superheat temperature, which in turn may be calculated based on the evaporator temperature (as determined by the evaporator thermistor or evaporator pressure transducer) and an estimated suction temperature. In an exemplary aspect, the controller may estimate the suction temperature based on one or more of the tank temperature (as determined by the tank temperature sensor), the discharge temperature (as determined by the discharge temperature sensor), and an isentropic efficiency of the refrigerant circuit. Similar to the first dynamic position described above, in this case as well, the controller may determine the second dynamic position such that the calculated second superheat temperature reaches to the target superheat temperature. In this embodiment also, the position of the valve orifice (i.e., the second dynamic position of the controllable expansion valve) is not fixed, and changes as the estimated suction temperature and / or the evaporator temperature increases or decreases. Stated another way, in this embodiment also, the controller may modify the second dynamic position as the second superheat temperature reaches to (or “chases”) the target superheat temperature.

[0022] When the when the suction thermistor and / or the evaporator thermistors develop a fault, the discharge temperature sensor may also be used to estimate the opening of the expansion valve. For example, the discharge temperature may be determined as the sum of the reading of the bottom thermistor and a fixed temperature delta. The fixed temperature delta may include a range of + / - 10 degree Fahrenheit, for example. This value may differ based on the supplier of the compressor. If the discharge temp is too high (for example, based on a comparison with a threshold valve), the orifice in the expansion valve may be opened more. Likewise, if the discharge temp is too low (for example, based on a comparison with the same or another threshold valve), the orifice in the expansion valve may be reduced in size to build up pressure in the condenser.

[0023] In a fifth exemplary embodiment, when one or more of the evaporator thermistor, the evaporator pressure transducer or the suction thermistor develops a fault, the controller may cause the controllable expansion valve to operate at a third dynamic position, until the sensor fault is rectified or for the predefined time duration. In some aspects, the controller may determine the third dynamic position of the controllable expansion valve based on inputs obtained from the system current sensor. Specifically, thecontroller may determine the third dynamic position such that the system operates within an optimal or “practical” current range (e.g., between 1.2 Ampere to 1.8 Ampere). In some aspects, the controller may “increase” the third dynamic position (i.e., increase the valve orifice size) when the system may be drawing low current (e.g., cunent less than the optimal or practical current range), and may “decrease” the third dynamic position (i.e., decrease the valve orifice size) when the system may be drawing high current (e.g., current more than the optimal or practical current range),. In this embodiment also, the position of the valve orifice (i.e., the third dynamic position of the controllable expansion valve) is not fixed, and changes as the current drawn by the system increases or decreases.

[0024] In some aspects, the controller may use one or more of the five exemplary methods / embodiments described above to control / adjust the position of the controllable expansion valve and enable the system to continue operation (i.e., continue to heat water when the system is a water heating system), even when one or more system sensors described above develop a fault. Since the system continues the operation and does not stop working when the sensors develop a fault, user convenience is considerably enhanced.[0025 [ Although certain examples of the disclosed technology are explained in detail herein, it is to be understood that other examples, embodiments, and implementations of the disclosed technology are contemplated. Accordingly, it is not intended that the disclosed technology is limited in its scope to the details of construction and arrangement of components expressly set forth in the following description or illustrated in the drawings. The disclosed technology can be implemented in a variety of examples and can be practiced or carried out in various ways. In particular, the presently disclosed subject matter is described in the context of being a system and method for operating a refrigerant circuit in a water heating system. The present disclosure, however, is not so limited, and can be applicable in other contexts. The present disclosure, for example and not limitation, can be applied to heating, ventilation, and air conditioning (HVAC) systems as well. Furthermore, the present disclosure can include other fluid heating systems configured to heat a fluid other than water such as process fluid heaters used in industrial applications. Such implementations and applications are contemplated within the scope of the present disclosure. Accordingly, when the present disclosure is described in the context of being a system and method for operating a refrigerant circuit in a water heating system, it will be understood that other implementations can take the place of those referred to.

[0026] Although the term “water’ is used throughout this specification, it is to be understood that other fluids may take the place of the term “water” as used herein. Therefore, although described as a system and method to heat water, it is to be understood that the system and method described herein can apply to fluids other than water. Further, it is also to be understood that the term “water” can replace the term “fluid” as used herein unless the context clearly dictates otherwise.[0027[ Turning now to the drawings, FIG. 1 depicts a refrigerant circuit system 100 (or system 100). While describing FIG. 1, reference will be made to FIG. 2, which depicts an example pressure-enthalpy (PH) diagram 200 associated with a refrigerant circuit in accordance with one or more embodiments of the present disclosure. In some aspects, the system 100 may be part of a heating, ventilation, and air conditioning (HVAC) system / unit. In other aspects, the sy stem 100 may be part of a water heating system having a water storage tank (not shown). The present disclosure is described in the context of a water heating system; however, the description should not be constmed as limiting and applicable only to water heating systems.

[0028] The system 100 may include a refrigerant circuit 102 or a heat pump assembly. The refrigerant circuit 102 / heat pump assembly may collectively form a vapor compression cycle system. Throughout the present disclosure, the terms “refrigerant circuit” and “heat pump” may be interchangeably used.

[0029] The refrigerant circuit 102 may include a plurality of units including, but not limited to. an evaporator 104. a compressor 106, a condenser 108, a controllable expansion valve 110, a fan 1 12, a refrigerant tubing 114, and / or the like. The evaporator 104, the compressor 106, the condenser 108 and the controllable expansion valve 110 may be connected in series via the refrigerant tubing 114 through which, during heat pump operation, a refrigerant may flow in the indicated clockwise direction. Specifically, the refrigerant may sequentially flow from an outlet of the compressor 106, through the condenser 108, through the controllable expansion valve 110, through the evaporator 104, and back to an inlet of the compressor 106. The refrigerant may be, for example, R22 or R410A. Any suitable refrigerant may be used herein.

[0030] During operation of the refrigerant circuit 102 / system 100, the compressor 106 may be configured to output the refrigerant in vapor state towards the condenser 108, via the refrigerant tubing 114. The refrigerant output from the compressor 106 may be at high temperature and high pressure state. The condenser 108 may receive the refrigerantfrom the compressor 106 via the refrigerant tubing 1 14 and may convert the refrigerant into liquid state. In some aspects, the heat dissipated by the condenser 108 while changing the refrigerant phase from vapor to liquid may be used to heat water stored in the water storage tank of the water heating system (e.g., when the heat pump / refrigerant circuit 102 may be part of a water heating system). The condenser 108 may output the refrigerant in liquid state towards the controllable expansion valve 110, via the refrigerant tubing 114. The refrigerant output from the condenser 108 may be at high pressure and medium-to-high temperature state. The controllable expansion valve 110 may receive the refrigerant from the condenser 108 and may output the refrigerant in low pressure, low temperature state towards the evaporator 104 via the refrigerant tubing 114. The refrigerant output from the controllable expansion valve 110 may be in liquid and vapor state. 0032] The evaporator 104 may receive the refrigerant from the controllable expansion valve 110 and may convert the refrigerant into low pressure, vapor state refrigerant. The fan 112 may be configured to draw heat from ambient environment, and may blow hot air towards the refrigerant received from the controllable expansion valve 110 in the evaporator 104, thereby heating and vaporizing the refrigerant. The evaporator 104 mayoutput the refrigerant in high temperature, vapor state towards the compressor 106 via the refrigerant tubing 114. The compressor 106 may receive the refrigerant from the evaporator 104 and may ‘"compress” the refrigerant to output the refrigerant in high pressure, high temperature state, as described above. In some aspects, the compressor 106 may be a pump that provides additional pressure to the refrigerant to enable the refrigerant to flow through the defined path, as indicated in FIG. 1 . In this manner, the refrigerant flows in the refrigerant circuit 102, facilitating heating of water through the condenser 108. 11033] An example pressure-enthalpy (PH) diagram 200 of the refrigerant circuit 102 is depicted in FIG. 2. A curve 202 depicts a liquid region of the refrigerant that flows through the refrigerant circuit 102. A graph line 204 depicts an evaporator PH curve, a graph line 206 depicts a compressor PH curve, a graph line 208 depicts a condenser PH curve and a graph line 210 depicts a controllable expansion valve PH curve. In some aspects, point “A” in the diagram 200 depicts the pressure and enthalpy of the refrigerant when the refrigerant enters the evaporator 104, point “B” depicts the pressure and enthalpy of the refrigerant when the graph line 204 intersects with the curve 202, point “C” depictsthe pressure and enthalpy of the refrigerant when the refrigerant enters the compressor 106, point “D” depicts the pressure and enthalpy of the refrigerant when the refrigerant enters the condenser 108, and point “E” depicts the pressure and enthalpy of the refrigerant when the refrigerant enters the controllable expansion valve 110.1 034] As apparent from the diagram 200, the refrigerant pressure remains substantially constant and the refrigerant temperature increases when the refrigerant flows through the evaporator 104. Similarly, the refrigerant pressure remains substantially constant and the refrigerant temperature decreases when the refrigerant flows through the condenser 108. Further, the refrigerant temperature remains substantially constant and the refrigerant pressure decreases when the refrigerant flows through the controllable expansion valve 110. Furthermore, both the refrigerant pressure and temperature increase when the refrigerant flows through the compressor 106. In some aspects, a difference in temperature / enthalpy between the point “C” and the point ' B ' is referred to as a ‘‘superheat temperature” of the refrigerant circuit 102.[0035J Insome aspects, the compressor 106 may be of any type. For example, the compressor 106 may be a positive displacement compressor, a reciprocating compressor, a rotary screw compressor, a rotary vane compressor, a rolling piston compressor, a scroll compressor, an inverter compressor, a diaphragm compressor, a dynamic compressor, an axial compressor, or any other form of compressor that can be integrated into the heat pump assembly for the particular application.

[0036] Further, in some aspects, the controllable expansion valve 110 may be an electronic expansion valve that may have an adjustable orifice size. The orifice size or diameter may be adjusted in a range of 2 mm to 8 mm. The flow of refrigerant from the controllable expansion valve 110 towards the evaporator 104 may be controlled / optimized by adjusting the orifice size of the controllable expansion valve 110. In some aspects, the orifice size may be adjusted based on a plurality of parameters associated with the refrigerant circuit 102 / system 100. For example, the orifice size may be adjusted based on an ambient temperature, a tank temperature of the water storage tank associated with the w ater heating system, an evaporator temperature, a suction temperature, a discharge temperature, an amount of current drawn by the system 100, and / or the like.

[0037] In alternative aspects, the controllable expansion valve 110 may not be an electronic expansion valve, but may instead include a plurality of capillary' tubes of different sizes. In this embodiment, the flow' of refrigerant from the controllable expansionvalve 1 10 may be adjusted by enabling one or more capillary tubes to output the refrigerant to the evaporator 104 (while disabling the other capillary7tubes from outputting the refrigerant to the evaporator 104), based on the parameters described above.

[0038] The system 100 may further include a sensor unit and a controller 116. The controller 116 may be communicatively coupled with the sensor unit and the controllable expansion valve 110, and may be configured to control the operation (e.g., orifice size) of the controllable expansion valve 110 based on inputs obtained from the sensor unit. The sensor unit may be configured to determine / measure one or more inputs (e g., temperature, current, etc.) associated with the refrigerant circuit 102 and / or the system 100.

[0039] In some aspects, the sensor unit may include an evaporator thermistor 118, a suction thermistor 120, a discharge temperature sensor 122, an evaporator pressure transducer (not shown), and one or more additional sensors 124. The additional sensors 124 may include, for example, an ambient temperature sensor, a tank temperature sensor, a current sensor and / or the like. In some aspects, one or more sensors of the sensor suit may be part of the refrigerant circuit 102, while the remaining sensors may be part of the system 100 (but outside the refrigerant circuit 102).

[0040] The discharge temperature sensor 122 may be configured to measure a discharge temperature, the ambient temperature sensor may be configured to measure a real-time ambient temperature, the tank temperature sensor may be configured to measure a real-time tank temperature of the water storage tank associated with the water heating system, and the current sensor may be configured to measure an amount of current drawn by the refrigerant circuit 102 / system 100 during operation.

[0041] Further, the evaporator thermistor 118 and / or the evaporator pressure transducer may be configured to measure or indicate a saturated evaporator temperature (or "evaporator temperature”). Further, the suction thermistor 120 may be configured to measure the suction temperature, specifically the temperature of the refrigerant entering the compressor 106. In some aspects, during operation of the system 100, a difference between the suction temperature and the evaporator temperature denotes the superheat temperature of the refrigerant circuit 102. Stated another way, when the system 100 may be operating normally (i.e., when the sensors associated with the sensor unit may be operating normally), a difference between the inputs obtained from the suction thermistor120 and the evaporator thermistor 118 (or the evaporator pressure transducer) denotes the superheat temperature of the refrigerant circuit 102. 0042] In some aspects, the controller 116 may control the operation (e.g.. the orifice size) of the controllable expansion valve 110 such that a calculated real-time superheat temperature of the refrigerant circuit 102 (i.e. , a difference between the suction temperature and the evaporator temperature) reaches to or “chases” a target superheat temperature. The controller 116 may be configured to control the operation of the controllable expansion valve 110 even when one or more of the evaporator thermistor 118, the evaporator pressure transducer, and / or the suction thermistor 120 develop a fault, as described below. Stated another way, the controller 116 may continue to control the operation (e.g., the orifice size) of the controllable expansion valve 110 even when the controller 116 is not able to directly receive the readings of the evaporator temperature from the evaporator thermistor 118 (or the evaporator pressure transducer) and / or the suction temperature from the suction thermistor 120. In this manner, the controller 116 enables the refrigerant circuit 102 (and hence the system 100) to continue operation, even when one or more system sensors develop a fault, thereby considerably enhancing user convenience. For example, the system user may continue to receive hot water from the system 100 (when the system 100 may be associated with a water heating system) even when one or more system sensors develop a fault.

[0043] In operation, the controller 116 may first determine if there is a demand to energize the refrigerant circuit 102 (or the heat pump assembly). Stated another way, the controller 116 may first determine if the components of the refrigerant circuit 102 are required to be activated. In some aspects, the controller 1 16 may determine that there may be a demand to energize the refrigerant circuit 102 when the tank temperature (or the temperature of water stored in the water storage tank) may be less than a set-point temperature or a user desired temperature. In other aspects, the controller 116 may determine that there may be a demand to energize the refrigerant circuit 102 when the user draws hot water from the system 100 (e.g., when the system 100 may be part of a water heating system).

[0044] Responsive to determining that there may be a demand to energize the refrigerant circuit 102, the controller 116 may determine if one or more sensors of the sensor unit may be faulty. The controller 116 may activate the refrigerant circuit components normally or enable the refrigerant circuit 102 to operate normally when thecontroller 1 16 determines that all the sensors are working fine and no sensor is faulty. Further, the controller 116 may cause a system alarm (not shown) to activate and not enable the refrigerant circuit 102 to operate when the controller 116 determines that one or more sensors of the sensor unit, different from the suction thermistor 120 and the evaporator thermistor 1 18 (and / or the evaporator pressure transducer), may have developed a fault.

[0045] On the other hand, responsive to determining that one or more of the suction thermistor 120, the evaporator thermistor 118, and the evaporator pressure transducer may have developed a fault, the controller 1 16 may determine an optimal fixed or dynamic controllable expansion valve position (i.e., percentage opening of the valve orifice) at which to set or keep the controllable expansion valve 110, and then enable the refrigerant circuit 102 to operate / activate. In some aspects, the controller 116 may determine the optimal fixed or dynamic controllable expansion valve position (or control operation of the controllable expansion valve 110) based on inputs obtained from one or more sensors of the sensor unit that may not be faulty and / or historical controllable expansion valve positions (or ‘‘historical valve positions”, which may be stored in a system or controller memory, shown as memory 304 in FIG. 3).|0046] The controller 1 16 may implement one or more different methods or embodiments to determine the optimal fixed or dynamic controllable expansion valve position and to ensure that the refrigerant circuit 102 / system 100 continues to operate even when one or more of the suction thermistor 120, the evaporator thermistor 118, and the evaporator pressure transducer develop a fault. Example methods / embodiments implemented by the controller 116 to determine the optimal fixed or dynamic controllable expansion valve position are described below . The following example methods / embodiments should not be constmed as limiting or exclusive.

[0047] In a first exemplary embodiment, when the controller 116 determines that either of the suction thermistor 120, the evaporator thermistor 118, and the evaporator pressure transducer may have developed a fault, the controller 116 may cause the controllable expansion valve 110 to operate at a first fixed position, until the sensor fault is rectified or for a predefined time duration (e.g., for a maximum of 1 or 2 days). Stated another way, the controller 116 may fix or set the position (or a percentage opening of the valve orifice) of the controllable expansion valve 110 to the first fixed position, when one of the sensors described above develop a fault. In this embodiment, the controller 116 maynot enable the controllable expansion valve 1 10 to change its position (i.e., the percentage orifice opening) from the first fixed position, until the sensor fault is rectified. 0048] In some aspects, the controller 116 may determine the first fixed position based on a real-time ambient temperature and / or a real-time tank temperature (as determined via the ambient temperature sensor and the tank temperature sensor of the sensor unit). In this case, the controller 116 may first fetch a correlation matrix (e.g., from the system / controller memory ) correlating a plurality' of preset expansion valve positions with at least one of a plurality of ambient temperatures and a plurality’ of tank temperatures. The controller 116 may then correlate the determined real-time ambient temperature and the tank temperature with the correlation matrix, to determine the first fixed position. In some aspects, the correlation matrix may be pre-stored by a system manufacturer in the system or controller memory, and may be prepared, for example, by performing a plurality of lab tests on the system 100 / refrigerant circuit 102.

[0049] In an exemplary aspect, the first fixed position may be any position between 10-90% of the orifice size, determined based on the correlation matrix and the real-time ambient and / or tank temperatures. Stated another way, the controller 116 may open and set the orifice of the controllable expansion valve 110 to 10-90% of the maximum opening, based on the real-time ambient and / or tank temperatures. As an example, when the ambient temperature may be 40 degree Fahrenheit and the tank temperature may be 85 degree Fahrenheit, the controller 116 may determine an optimal first fixed position of the controllable expansion valve 110 for these ambient and tank temperatures from the correlation matrix, and then set the controllable expansion valve 110 to the determined first fixed position. Responsive to setting the controllable expansion valve 1 10 to the first fixed position, the controller 116 may activate the refrigerant circuit components to energize the refrigerant circuit 102 and enable the system 100 to operate. The controller 116 may reverse to its normal operation mode (i.e., not set / fix the controllable expansion valve 110 to the first fixed position), when the system user gets the faulty sensor repaired or replaced.

[0050] In a second exemplary embodiment, yvhen the controller 116 determines that one or more of the suction thermistor 120, the evaporator thermistor 118, and the evaporator pressure transducer may have developed a fault, the controller 116 may cause the controllable expansion valve 110 to operate at a second fixed position determined based on the historical valve positions, until the sensor fault is rectified or for thepredefined time duration described above. In this case, the controller 1 16 may fetch historical statistics or pattern of valve orifice opening percentages over the past 24 hours (or any other time duration such as 12 hours, 18 hours, 36 hours, and / or the like) from the system / controller memory, and determine the second fixed position based on the historical statistics. In an exemplary aspect, the second fixed position may be a mean value, an average value or a highest frequency or probability value of the historical valve positions. Similar to the first fixed position, in this embodiment as well, the controller 116 may not enable the controllable expansion valve 110 to change its position (i.e., the percentage orifice opening) from the second fixed position, until the sensor fault is rectified.

[0051] In some aspects, the historical valve positions may be recorded and stored in the system / controller memory at a fixed time duration interval (e g., every 5 or 10 seconds). Further, the second fixed position is not limited to being a mean value, an average value or a highest frequency or probability value of the historical valve positions. The controller 116 may use any other statistical model to determine the second fixed position from the historical valve positions.| 052j In a third exemplary embodiment, when the controller 116 determines that one or more of the evaporator thermistor 118 or the evaporator pressure transducer may have developed a fault, the controller 116 may cause the controllable expansion valve 110 to operate at a first dynamic position, until the sensor fault is rectified or for the predefined time duration. In some aspects, the controller 116 may determine the first dynamic position of the controllable expansion valve 110 based on a first superheat temperature, which in turn may be calculated based on a suction temperature (determined via or obtained from the suction thermistor 120) and the ambient temperature (determined via or obtained from the ambient temperature sensor). Stated another way, in this embodiment, when the evaporator thermistor 118 develops a fault, the controller 116 may control the operation of the controllable expansion valve 110 based on inputs obtained from the suction thermistor 120 and the ambient temperature sensor, which may not be fault}'.

[0053] In an exemplary aspect, the controller 116 may determine the first superheat temperature by calculating a difference between the suction temperature and a sum of the real-time ambient temperature and a predefined offset temperature (which may be in a range of 5 to 25 degree Fahrenheit, for example). In this case, the controller 116 may determine the first dynamic position such that the calculated first superheat temperaturereaches to the target superheat temperature (which may be preset for the system 100 / refrigerator circuit 102, based on system usage). In this embodiment, the position of the valve orifice (i. e. , the first dynamic position of the controllable expansion valve 110) is not fixed, and changes as the suction temperature (and / or the ambient temperature) increases or decreases. Stated another way, in this embodiment, the controller 116 may modify the first dynamic position as the first superheat temperature reaches to (or “chases”) the target superheat temperature.[0054 j In a fourth exemplary embodiment, when the controller 116 determines that the suction themiistor 120 may have developed a fault, the controller 116 may cause the controllable expansion valve 110 to operate at a second dynamic position, until the sensor fault is rectified or for the predefined time duration. In some aspects, the controller 116 may determine the second dynamic position of the controllable expansion valve 110 based on a second superheat temperature, which in turn may be calculated based on the evaporator temperature (as determined by and obtained from the evaporator thermistor 118) and an estimated suction temperature. Specifically, the second superheat temperature may be a difference between the estimated suction temperature and the evaporator temperature.H1055] In an exemplary aspect, the controller 116 may estimate the suction temperature based on one or more of the tank temperature (as determined by and obtained from the tank temperature sensor), the discharge temperature (as determined by and obtained from the discharge temperature sensor 122), and / or an isentropic efficiency of the refrigerant circuit 102. In other aspects, the controller 116 may estimate the suction temperature by using a data structure (or a lookup table) that may be pre-stored in the system / controller memory. The data structure may include a mapping of estimated suction temperatures with a plurality of discharge temperatures and / or tank temperatures. The controller 116 may correlate the real-time discharge temperature and tank temperature (as determined via the discharge temperature sensor 122 and the tank temperature sensor) with the data structure to estimate the suction temperature, when the suction thermistor 120 develops a fault.Similar to the first dynamic position described above, in this case as well, the controller 116 may determine the second dynamic position such that the calculated second superheat temperature reaches to the target superheat temperature. In this embodiment also, the position of the valve orifice (i.e., the second dynamic position of the controllableexpansion valve 1 10) is not fixed, and changes as the estimated suction temperature and / or the evaporator temperature increases or decreases. Stated another way, in this embodiment also, the controller 116 may modify the second dynamic position as the second superheat temperature reaches to (or “‘chases”) the target superheat temperature.

[0057] In a fifth exemplary embodiment, when one or more of the evaporator thermistor 118, the evaporator pressure transducer or the suction thermistor 120 develops a fault, the controller 116 may cause the controllable expansion valve 110 to operate at a third dynamic position, until the sensor fault is rectified or for the predefined time duration. In some aspects, the controller 116 may determine the third dynamic position of the controllable expansion valve 110 based on inputs obtained from the current sensor of the sensor unit. Specifically, the controller 116 may determine the third dynamic position such that the system 100 operates within an optimal or “practical” current range (e.g., between 1.2 Ampere to 1.8 Ampere). In some aspects, the controller 116 may “increase” the third dynamic position (i.e., increase the valve orifice size) when the system 100 may be drawing low current (e.g., lower than a first threshold current, which may be 1.2 Ampere), and may “decrease” the third dynamic position (i.e., decrease the valve orifice size) when the system 100 may be drawing high current (e.g., higher than a second threshold current, which may be 1.8 Ampere). In this embodiment also, the position of the valve orifice (i.e., the third dynamic position of the controllable expansion valve 110) is not fixed, and changes as the current drawn by the system 100 increases or decreases.

[0058] A person ordinarily skilled in the art may appreciate from the description above that the controller 116 may use one or more of the five exemplary methods / embodiments described above (or any other methods / embodiments) to control / adjust the position of the controllable expansion valve 110 and enable the system 100 to continue operation (i.e., continue to heat w ater when the system 100 is a water heating system), even when one or more sensors of the sensor unit described above develop a fault. Since the system 100 continues operation and does not stop working w hen the sensors develop a fault, user convenience is considerably enhanced.

[0059] FIG. 3 depicts a block diagram of the controller 116 configured to operate the refrigerant circuit 102 in accordance with one or more embodiments of the present disclosure.

[0060] The controller 1 16 may include a plurality of components including, but not limited to, a processor 302, a memory 304, and a communication interface 306. Thecontroller 1 16 may be a computing device configured to receive data, determine actions based on the received data, and output a control signal instructing one or more refrigerant circuit components (e.g., the controllable expansion valve 110) to perform one or more actions. In some aspects, the controller 116 may be configured to receive the inputs from the sensors included in the sensor unit, as described above.

[0061] In some aspects, the controller 116 may be configured to send and receive wireless or wired signals, and the signals may be analog or digital signals. The wireless signals may include Bluetooth™. BLE. WiFi™, ZigBee™, infrared, microwave radio, or any other type of wireless communication signals as may be suitable for a particular heat pump application. The hard-wired signals can include communication signals between any directly wired connections between the controller 116 and other heat pump components. For example, the controller 116 can have a hard-wired 24 Volts Direct Current (VDC) connection to the sensors described above.

[8062] Alternatively, the controller 116 may communicate with the sensors via a digital connection. The digital connection can include a connection such as an Ethernet or a serial connection and can utilize any suitable communication protocol for the heat pump application, such as Modbus, fieldbus, PROFIBUS, SafetyBus, Ethemet / IP, and / or the like. Furthermore, the controller 116 can utilize a combination of wireless, hard-wired, and analog or digital communication signals to communicate with and control the various heat pump components. A person ordinarily skilled in the art may appreciate that the above configurations are given merely as non-limiting examples and the actual configuration can vary depending on the particular heat pump application.

[0063] Additionally, the controller 1 16 may communicate with a remote device, such as a remote server, which may perform any of the determinations described herein. As a non-limiting example, the remote server may calculate and amount by which the orifice of the expansion valve 110 should be opened and then provide the instructions to cause the expansion valve 1 10 to open by that determined amount.

[0064] The memory 304 may be configured to store a program and / or instructions associated with the functions and methods described herein. The processor 302 may be configured to execute the program and / or instructions stored in the memory 304. The memory 304 can include one or more suitable types of memory (e.g., volatile or nonvolatile memory, random access memory (RAM), read only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory(EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, floppy disks, hard disks, removable cartridges, flash memory, a redundant array of independent disks (RAID), and the like) for storing files including the operating system, application programs (including, for example, a web browser application, a widget or gadget engine, and or other applications, as necessary), executable instructions and data. One, some, or all of the processing techniques or methods described herein can be implemented as a combination of executable instructions and data within the memory 304. In further aspects, the memory 304 may store the correlation matrix, the historical valve positions, and the data structure (or the lookup table) described above.W65| The communication interface 306 may be configured to send or receive communication signals between the various heat pump components (e.g., the controllable expansion valve 110). The communication interface 306 can include hardware, firmware, and / or software that allows the processor 302 to communicate with the other components via wired or wireless networks, whether local or wide area, private or public, as known in the art. The communication interface 306 can also provide access to a cellular network, the Internet, a local area network, or another wide-area network as suitable for the particular heat pump application.Additionally, the controller 116 may have or be in communication with a user interface (not shown) for receiving inputs from the user (e.g., the set point temperature of the water heating system). The user interface may be installed locally on the w ater heating system (of which the heat pump assembly may be a part).[GG67| The operation / function of the controller 116 is already described in conjunction with FIGS. 1 and 2, and hence not described again here for the sake of simplicity and conciseness. 0068] FIG. 4 depicts a flow diagram of an example method 400 to operate the refrigerant circuit 102 in accordance with one or more embodiments of the present disclosure. FIG. 4 may be described with continued reference to prior figures. The following process is exemplary and not confined to the steps described hereafter. Moreover, alternative embodiments may include more or less steps than are shown or described herein and may include these steps in a different order than the order described in the following example embodiments.The method 400 may start at step 402. At step 404, the method 400 may include determining, by the controller 116, whether there is a demand to energize therefrigerant circuit 102 (or the heat pump assembly). When the controller 1 16 determines that there is no demand to energize the refrigerant circuit 102, the controller 116 may continue to check for demand, and the method 400 may move to step 406 when the controller 116 determines a demand to energize the refrigerant circuit 102. 0 70] At the step 406, the method 400 may include determining, by the controller 116, whether one or more sensors of interest may be faulty. In some aspects, the sensors of interest may be, for example, the suction thermistor 120, the evaporator thermistor 118, and the evaporator pressure transducer. Responsive to determining that no sensor of interest is faulty, then at step 408, the controller 116 may activate the refrigerant circuit components normally or enable the refrigerant circuit 102 to operate normally. Alternatively, at the step 408, the controller 116 may cause the system alarm to activate and not enable the refrigerant circuit 102 to operate when the controller 116 determines that one or more sensors of the sensor unit, different from the sensors of interest, may have developed a fault, as described above in conjunction with FIGS. 1 and 2. After the step 408, the method 400 moves to step 410, at which the method 400 stops.

[0071] On the other hand, responsive to determining that one or more sensors of interest may be faulty at the step 406, the method 400 may move to step 412. At the step 412, the method 400 may include determining, by the controller 116, an optimal fixed or dynamic controllable expansion valve position (i.e., percentage opening of the valve orifice) at which to set or keep the controllable expansion valve 110, as described above. At step 414, the method 400 may include setting, by the controller 116, the controllable expansion valve 110 to the optimal fixed or dynamic position and then energizing the refrigerant circuit components for a preset time duration (e.g., 2-5 minutes).

[0072] At step 416, the method 400 may include setting, by the controller 116, a set off timer at the end of the preset time duration. The set off timer may be of, for example, 5 to 10 minutes. In some aspects, the controller 116 may check for demand to energize the refrigerant circuit 102 again at the end of the set-off timer, and the method 400 may repeat.

[0073] At the step 410, the method 400 may end.

[0074] In the above disclosure, reference has been made to the accompanying drawings, which form a part hereof, which illustrate specific implementations in which the present disclosure may be practiced. It is understood that other implementations may be utilized, and structural changes may be made without departing from the scope of thepresent disclosure. References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a feature, structure, or characteristic is described in connection with an embodiment, one skilled in the art will recognize such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0075] It should also be understood that the word “example” as used herein is intended to be non-exclusionaiy and non-limiting in nature. More particularly, the word “example” as used herein indicates one among several examples, and it should be understood that no undue emphasis or preference is being directed to the particular example being described.

[0076] With regard to the processes, systems, methods, heuristics, etc. described herein, it should be understood that, although the steps of such processes, etc. have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating various embodiments and should in no way be construed so as to limit the claims.

[0677] Accordingly, it is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent upon reading the above description. The scope should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the technologies discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the application is capable of modification and variation.

[0678] All terms used in the claims are intended to be given their ordinary meanings as understood by those knowledgeable in the technologies described herein unless an explicit indication to the contrary is made herein. In particular, use of the singular articlessuch as “a,” “the,” “said,” etc., should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary. Conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments could include, while other embodiments may not include, certain features, elements, and / or steps. Thus, such conditional language is not generally intended to imply that features, elements, and / or steps are in any way required for one or more embodiments.

[0079] Example Embodiments|0080] Embodiment E A system comprising: a refrigerant circuit comprising a controllable expansion valve; a sensor unit comprising a first sensor and a second sensor configured to determine one or more inputs associated with the refrigerant circuit; and a controller configured to: determine that the first sensor is fault ’; and control an operation of the controllable expansion valve based on at least one of inputs obtained from the second sensor or historical controllable expansion valve positions, responsive to determining that the first sensor is faulty.

[0081] Embodiment 2. The system of Embodiment 1, wherein the refrigerant circuit further comprises an evaporator, a compressor and a condenser. 082] Embodiment 3. The system of Embodiment 2, wherein the system is part of a heating, ventilation, and air conditioning (EIVAC) system.

[0083] Embodiment 4. The system of any of Embodiments 1-3, wherein the system is part of a water heating system comprising a storage tank.

[0084] Embodiment 5. The system of any of Embodiments 1 -4, wherein the first sensor is at least one of an evaporator thermistor, an evaporator pressure transducer or a suction thermistor, and wherein the second sensor is at least one of an ambient temperature sensor or a tank temperature sensor.

[0085] Embodiment 6. The system of any of Embodiments 1-5, wherein the controller is further configured to: fetch a correlation matrix correlating a plurality of preset expansion valve positions with at least one of a plurality of ambient temperatures or a plurality’ of tank temperatures, responsive to determining that the first sensor is faulty; determine a first fixed position of the controllable expansion valve based on the inputs from the second sensor and the correlation matrix, wherein the inputs from the second sensor comprise at least one of an ambient temperatureor a tank temperature; and cause the controllable expansion valve to operate at the first fixed position for a predefined time duration. 0086] Embodiment 7. The system of any of Embodiments 1-6, wherein the first sensor is at least one of an evaporator thermistor or an evaporator pressure transducer, and wherein the second sensor is a suction thermistor.

[0087] Embodiment 8. The system of any of Embodiments 1-7, wherein the controller is further configured to: obtain an ambient temperature from an ambient temperature sensor; determine a suction temperature based on the inputs obtained from the second sensor; calculate a first superheat temperature based on the suction temperature and the ambient temperature: determine a first dynamic position of the controllable expansion valve based on the first superheat temperature; and cause the controllable expansion valve to operate at the first dynamic position.

[0088] Embodiment 9. The system of any of Embodiments 1-8, wherein the controller calculates the first superheat temperature by calculating a difference between the suction temperature and a sum of the ambient temperature and a predefined offset temperature.

[0089] Embodiment 10. The system of any of Embodiments 1-9, wherein the first sensor is a suction thermistor, and wherein the second sensor is at least one of a tank temperature sensor, a discharge temperature sensor or an evaporator thermistor.

[0090] Embodiment 11 . The system of any of Embodiment 1-10, wherein the controller is further configured to: determine a suction temperature based on the inputs obtained from the tank temperature sensor and the discharge temperature sensor; calculate a second superheat temperature based on the suction temperature and the inputs obtained from the evaporator thermistor, wherein the inputs obtained from the evaporator thermistor comprises an evaporator temperature; determine a second dynamic position of the controllable expansion valve based on the second superheat temperature; and cause the controllable expansion valve to operate at the second dynamic position.

[0091] Embodiment 12. The system of any of Embodiments 1-11, wherein the controller is further configured to determine the suction temperature based on an isentropic efficiency of the compressor.

[0092] Embodiment 13. The system of any of Embodiments 1-12, wherein the first sensor is at least one of an evaporator thermistor, an evaporator pressure transducer or a suction thermistor, and wherein the second sensor is a current sensor.

[0093] Embodiment 14. The system of any of Embodiments 1-13, wherein the controller is further configured to: determine a third dynamic position of the controllable expansion valve based on the inputs obtained from the current sensor; and cause the controllable expansion valve to operate at the third dynamic position. 0094] Embodiment 15. The system of any of Embodiments 1-14, wherein the controller is further configured to: determine a second fixed position of the controllable expansion valve based on the historical controllable expansion valve positions; and cause the controllable expansion valve to operate at the second fixed position for a predefined time duration.[ 095 Embodiment 16. The system of any of Embodiments 1-15, wherein the second fixed position is a mean value, an average value or a highest frequency value of the historical controllable expansion valve positions. 0096] Embodiment 17. The system of any of Embodiments 1-16, wherein the controller is further configured to: determine a demand to energize the refrigerant circuit; and determine that the first sensor is faulty7responsive to determining the demand to energize the refrigerant circuit.[0097 Embodiment 18. The system of any of Embodiments 1-17, wherein the controllable expansion valve is an electronic expansion valve.

[0098] Embodiment 19. A heat pump system comprising: a heat pump assembly comprising a controllable expansion valve; a sensor unit comprising a first sensor and a second sensor configured to determine one or more inputs associated with the heat pump assembly; and a controller configured to: determine a demand to energize the heat pump assembly; determine that the first sensor is faulty, responsive to determining the demand to energize the heat pump assembly; and control an operation of the controllable expansion valve based on at least one of inputs obtained from the second sensor or historical controllable expansion valve positions, responsive to determining that the first sensor is faulty.

[0099] Embodiment 20. A method to operate a refrigerant circuit, the method comprising: determining, by a controller, a demand to energize the refrigerant circuit, wherein the refrigerant circuit is part of a system comprising a sensor unit having a first sensor and a second sensor configured to determine one or more inputs associated with the refrigerant circuit, and wherein the refrigerant circuit comprises a controllable expansion valve; determining, by the controller, that the first sensor is faulty7, responsive to determiningthe demand to energize the refrigerant circuit; and controlling, by the controller, an operation of the controllable expansion valve based on at least one of inputs obtained from the second sensor or historical controllable expansion valve positions, responsive to determining that the first sensor is faulty.

Claims

CLAIMSTHAT WHICH IS CLAIMED IS:

1. A system comprising: a refrigerant circuit comprising a controllable expansion valve; a sensor unit comprising a first sensor and a second sensor configured to determine one or more inputs associated with the refrigerant circuit; and a controller configured to: determine that the first sensor is faulty: and control an operation of the controllable expansion valve based on at least one of inputs obtained from the second sensor or historical controllable expansion valve positions, responsive to determining that the first sensor is faulty.

2. The system of claim 1, wherein the refrigerant circuit further comprises an evaporator, a compressor and a condenser.

3. The system of claim 2, wherein the system is part of a heating, ventilation, and air conditioning (HVAC) system.

4. The system of any of claims 1-3, wherein the system is part of a water heating system comprising a storage tank.

5. The system of any of claims 1-4, wherein the first sensor is at least one of an evaporator thermistor, an evaporator pressure transducer or a suction thermistor, and wherein the second sensor is at least one of an ambient temperature sensor or a tank temperature sensor.

6. The system of any of claims 1-5, wherein the controller is further configured to: fetch a correlation matrix correlating a plurality' of preset expansion valve positions with at least one of a plurality of ambient temperatures or a plurality of tank temperatures, responsive to determining that the first sensor is faulty; determine a first fixed position of the controllable expansion valve based on the inputs from the second sensor and the correlation matrix, wherein the inputs from the second sensor comprise at least one of an ambient temperature or a tank temperature; andcause the controllable expansion valve to operate at the first fixed position for a predefined time duration.

7. The system of any of claims 1-6, wherein the first sensor is at least one of an evaporator thermistor or an evaporator pressure transducer, and wherein the second sensor is a suction thermistor.

8. The system of any of claims 1-7, wherein the controller is further configured to: obtain an ambient temperature from an ambient temperature sensor; determine a suction temperature based on the inputs obtained from the second sensor; calculate a first superheat temperature based on the suction temperature and the ambient temperature; determine a first dynamic position of the controllable expansion valve based on the first superheat temperature; and cause the controllable expansion valve to operate at the first dy namic position.

9. The system of any of claims 1-8, wherein the controller calculates the first superheat temperature by calculating a difference between the suction temperature and a sum of the ambient temperature and a predefined offset temperature.

10. The system of any of claims 1-9, wherein the first sensor is a suction thermistor, and wherein the second sensor is at least one of a tank temperature sensor, a discharge temperature sensor or an evaporator thermistor.

11. The system of any of claims 1-10, wherein the controller is further configured to: determine a suction temperature based on the inputs obtained from the tank temperature sensor and the discharge temperature sensor; calculate a second superheat temperature based on the suction temperature and the inputs obtained from the evaporator thermistor, wherein the inputs obtained from the evaporator thermistor comprises an evaporator temperature; determine a second dynamic position of the controllable expansion valve based on the second superheat temperature; andcause the controllable expansion valve to operate at the second dynamic position.

12. The system of any of claims 1-11, wherein the controller is further configured to determine the suction temperature based on an isentropic efficiency of the compressor.

13. The system of any of claims 1-12, wherein the first sensor is at least one of an evaporator thermistor, an evaporator pressure transducer or a suction thermistor, and wherein the second sensor is a current sensor.

14. The system of any of claims 1-13, wherein the controller is further configured to: determine a third dynamic position of the controllable expansion valve based on the inputs obtained from the current sensor; and cause the controllable expansion valve to operate at the third dynamic position.

15. The system of any of claims 1-14, wherein the controller is further configured to: determine a second fixed position of the controllable expansion valve based on the historical controllable expansion valve positions; and cause the controllable expansion valve to operate at the second fixed position for a predefined time duration.

16. The system of any of claims 1-15, wherein the second fixed position is a mean value, an average value or a highest frequency value of the historical controllable expansion valve positions.

17. The system of any of claims 1-16, wherein the controller is further configured to: determine a demand to energize the refrigerant circuit; and determine that the first sensor is faulty responsive to determining the demand to energize the refrigerant circuit.

18. The system of any of claims 1-17, wherein the controllable expansion valve is an electronic expansion valve.

19. A heat pump system comprising: a heat pump assembly comprising a controllable expansion valve; a sensor unit comprising a first sensor and a second sensor configured to determine one or more inputs associated with the heat pump assembly; and a controller configured to: determine a demand to energize the heat pump assembly; determine that the first sensor is fault}', responsive to determining the demand to energize the heat pump assembly; and control an operation of the controllable expansion valve based on at least one of inputs obtained from the second sensor or historical controllable expansion valve positions, responsive to determining that the first sensor is fault '.

20. A method to operate a refrigerant circuit, the method comprising: determining, by a controller, a demand to energize the refrigerant circuit, wherein the refrigerant circuit is part of a system comprising a sensor unit having a first sensor and a second sensor configured to determine one or more inputs associated with the refrigerant circuit, and wherein the refrigerant circuit comprises a controllable expansion valve; determining, by the controller, that the first sensor is faulty, responsive to determining the demand to energize the refrigerant circuit; and controlling, by the controller, an operation of the controllable expansion valve based on at least one of inputs obtained from the second sensor or historical controllable expansion valve positions, responsive to determining that the first sensor is faulty.

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