Heat Pump Water Heater with Compressor Modulation to Extend Low Ambient Operation

This application claims priority to U.S. 63/571,169, filed on Mar. 28, 2024, entitled “HEAT PUMP WATER HEATER WITH COMPRESSOR MODULATION TO EXTEND LOW AMBIENT OPERATION,” the disclosure of which is hereby incorporated herein by reference in its entirety.

Heat pump water heaters have been developed to provide hot water. Heat pump water heaters may utilize a vapor refrigeration compression cycle in a closed-loop heat exchange circuit to absorb heat from a source (e.g. air) and transfer the heat to water for storage in a hot water tank.

An aspect of the present disclosure is a heat pump water heater system that is configured to increase compressor speed during cold ambient conditions to compensate for reduced mass flow rates that would occur if the compressor were to be operated at the same speed during warm and cold ambient conditions. A heat pump water heater system according to an aspect of the present disclosure may include a compressor having a compressor motor, a compressor inlet, and a compressor outlet. The system includes an evaporator having an evaporator inlet and an evaporator outlet, wherein the evaporator outlet is fluidly connected to the compressor inlet. An evaporator fan causes air to flow through the evaporator when the evaporator fan is actuated. The system further includes a heat exchanger having an inlet that is fluidly connected to the compressor outlet. The heat exchanger also includes an outlet that is fluidly connected to the evaporator inlet, whereby water flowing through the heat exchanger is heated by refrigerant flowing through the heat exchanger. The heated water from the heat exchanger may flow to a hot water tank system. The system further includes a pressure sensor that is configured to detect a pressure of refrigerant upstream of the compressor inlet. The system further includes a controller that is configured to increase a speed of the compressor motor if a pressure detected by the pressure sensor reaches a threshold pressure that is greater than a minimum allowable operating pressure whereby a mass flow rate of the compressor is increased to permit operation of the heat pump water heater system at a lower ambient temperature without reaching the minimum allowable operating pressure. The system may be configured to provide a defrost cycle if the pressure drops below the threshold pressure despite an increase in compressor speed. The defrost cycle may be initiated at an operating pressure between the threshold pressure and the minimum allowable operating pressure.

Another aspect of the present disclosure is a heat pump water heater system including a compressor having a compressor motor that is electrically powered, a compressor inlet, and a compressor outlet. The compressor defines a minimum allowable operating pressure at the compressor inlet. The system includes an evaporator having an evaporator inlet and an evaporator outlet, wherein the evaporator outlet is fluidly connected to the compressor inlet. The system further includes an evaporator fan that is configured to cause air to flow through the evaporator when the evaporator fan is actuated. A heat exchanger has an inlet that is fluidly connected to the compressor outlet, and an outlet that is fluidly connected to the evaporator inlet, whereby water flowing through the heat exchanger is heated by refrigerant flowing through the heat exchanger. The system further includes a pressure sensor that is configured to detect a pressure of refrigerant upstream of the compressor inlet to provide a measured inlet refrigerant pressure. A defrost valve system is configured to cause heated refrigerant from the compressor outlet to flow through the evaporator during a defrost cycle. The system includes a controller that is configured to: 1) increase a speed of the compressor motor if a measured inlet pressure drops to a threshold pressure that is greater than the minimum allowable operating pressure of the compressor whereby a mass flow rate of the compressor is increased to permit operation of the heat pump water heater system at a lower ambient temperature, and: 2) actuate the defrost valve system if a measured inlet pressure reaches a defrost pressure that is below the threshold pressure despite the increased speed of the compressor motor.

Another aspect of the present disclosure is heat pump water heater system including a compressor having a compressor motor that is electrically powered. The compressor defines a minimum allowable operating pressure at the compressor inlet. The system further includes an evaporator, a heat exchanger, and a controller that is configured to: 1) increase electrical power to the compressor motor to maintain a pressure of refrigerant at an inlet of the compressor above the minimum allowable pressure, and: 2) implement a defrost cycle causing heated refrigerant to flow through the evaporator if increasing electrical power to the compressor motor is insufficient to maintain mass flow through the compressor according to predefined criteria.

Another aspect of the present disclosure is a method of controlling a heat pump water heater having a compressor that supplies heated refrigerant to a heat exchanger to heat water, and an evaporator that is exposed to ambient air. The method includes empirically determining a relationship between operating variables including: 1) compressor speeds and 2) evaporator fan speeds that optimize a Coefficient of Performance (COP) based on input parameters, wherein the COP comprises heat output of the heat pump system divided by input power to the heat pump system, and wherein the input parameter comprises: 1) temperature of water at an inlet and/or an outlet of the heat exchanger; 2) ambient air temperature; and 3) temperature and/or pressure of refrigerant at an inlet and/or at an outlet of the compressor. The method further includes controlling compressor speed and/or fan speed utilizing the relationship to maximize COP.

Another aspect of the present disclosure is a method of controlling a heat pump of a water heater, the heat pump having a compressor that supplies heated refrigerant to a heat exchanger to heat water and an evaporator that is exposed to ambient air. A speed of the compressor is increased if measured pressure of refrigerant at an inlet of the compressor is at or below a threshold pressure that is greater than a minimum allowable operating pressure of the compressor, whereby a mass flow rate of the compressor is increased to permit operation of the heat pump water heater system at a low ambient temperature. A defrost valve system of the heat pump is actuated if a measured inlet pressure of refrigerant at an inlet of the compressor is at or below a defrost pressure that is below the threshold pressure, despite the increased speed of the compressor motor.

These and other features, advantages, and objects of the present disclosure will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.

The components in the figure are not necessarily to scale, emphasis instead being placed upon illustrating the principles described herein.

For purposes of description herein the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the disclosure as oriented in the figure. However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. The terms “including,” “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by “comprises a . . . ” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

With reference to, a heat pump water heater systemaccording to an aspect of the present disclosure includes a compressorthat is configured to compress a refrigerant. Compressormay be substantially similar to known compressors, and may include a pump that is driven by an electrically-powered motor. The refrigerant may comprise, for example, COor other suitable medium. Compressorincludes an inletand an outlet, whereby compressorcauses compressed refrigerant to flow through a lineto a gas cooler heat exchangerto heat water flowing through a water circuitto provide hot water to a hot water tank system. The hot water tank systemmay comprise, for example, a hot water system for a building or the like. Control circuitry, such as one or more controllers having a processor and a memory, can control the heat pump water heater system. For example, controlleris configured to control the valves and other components of heat pump water heater system, including a speed of compressor. Heat pump water heater systemmay include a power supplythat is operably connected to controller, compressor, and other components of the system. It is contemplated that the memory of controllercan store instructions that, when executed by controller, cause the control circuitry to perform tasks related to control of the system. Controllermay comprise a Programable Logic Controller (PLC) or other suitable controller that monitors multiple parameters such as inlet and outlet water temperatures of heat exchanger, ambient temperature, refrigerant pressures (e.g. at compressor inlet and outletand), and power consumption (e.g. power supplied to compressorand/or evaporator fans).

In general, the heat pump water heater systemcan be operable in various operating modes, such as a “low-ambient” operating mode and “COP optimization mode.” In this way, the systemcan be dynamically operated to achieve target heat levels in various ambient conditions. The modes can be automatically selected in response to temperature readings, based on a predefined schedule, or manually selected. It will be understood, however, that these operating modes are not necessarily mutually exclusive, and the heat pump water heater systemmay be simultaneously operated in the target COP and low ambient modes.

During operation, refrigerant that has been pressurized by compressorflows through linesto an evaporator. Refrigerant exiting evaporatoris returned to the inletof compressorby lines. During operation, evaporator fansmay be actuated to increase air flow through the evaporatorwhereby the refrigerant flowing through the evaporatorchanges phase from a liquid to a gas. It will be understood that at least some refrigerant flowing through evaporatormay change phase from liquid to gas regardless of whether or not fanshave been actuated. Evaporatormay be located in an ambient space. The ambient spacemay be outside of a building whereby the ambient spaceexperiences low temperatures (e.g. below freezing) if heat pump water heater systemis installed in a climate that experiences cold temperatures. In general, an amount of heat that can be absorbed by the evaporatoris the product of the mass flow rate of the refrigerant multiplied by the change of heat content (enthalpy) that occurs in evaporatoras the refrigerant changes phase from liquid to gas. As the ambient temperature in ambient space(e.g. as measured by an ambient temperature sensor) drops, the evaporatormay be required to operate at lower temperatures in order to keep balance between the energy being released from the air and the energy absorbed into the refrigerant. For pure fluids such as CO, pressure and temperature are dependent as the fluid changes phase from liquid to gas, such that the operating pressure (e.g. pressure of refrigerant at compressor inlet) also drops. For a given speed (e.g. rpm) of the compressor, drops in the mass flow rate of the compressormay also be accompanied by drops in temperature and pressure, decreasing the heat pump's overall capacity to transfer heat and heat water supplied to hot water tank system.

As discussed in more detail below, the speed (mass flow rate) of compressormay be increased at lower ambient temperatures to compensate for reduced mass flow rates that would occur at a constant compressor speed to thereby permit heat pump water heater systemto operate at lower ambient temperatures, or to permit the systemto utilize a smaller compressor.

With continued reference to, heat pump water heater systemmay optionally include a recuperatorwhereby, during normal operation (i.e., not during a defrost cycle), refrigerant flows through recuperatorto transfer heat to refrigerant flowing through linesbefore the refrigerant in linesreturns to the compressor inlet, and the refrigerant exiting recuperatorflows through an expansion valvewhereby a temperature of the refrigerant is reduced before the refrigerant flows through the evaporator.

During a defrost cycle, defrost valvesandmay be actuated by controllerto cause compressed refrigerant from compressorto bypass gas cooler heat exchangerand recuperatorsuch that refrigerant entering evaporatorhas a higher temperature (e.g. above freezing) to thereby temporarily heat the coils of evaporatorto defrost evaporator. The defrost cycle may be substantially similar to known defrost cycles. In general, the defrost cycle may be short enough to minimize energy loss, but long enough to defrost evaporator. As discussed in more detail below, controllermay cause a defrost cycle if a pressure of refrigerant at or upstream of compressor inletdrops below a minimum pressure despite increases in compressor speed.

Heat pump water heater systemmay include a pressure sensorand a temperature sensorthat are configured to measure the pressure and temperature, respectively, of refrigerant flowing through lineupstream of inletof compressor. Controlleris operably connected to the valves and sensors of the system whereby the controllermay control compressorbased on various inputs, including sensor data. The controllermay be configured to control a speed of operation of compressor, whereby a mass flow rate of compressorcan be adjusted. Controllermay optionally comprise a Variable-Frequency Drive (VFD) that controls an rpm of compressor.

With continued reference to, during the operation of heat pump water heater system, controllermay monitor pressure readings from pressure sensor. If the ambient air temperature drops, the operating pressure measurements from sensorwill also tend to decrease. The decrease in pressure measured by pressure sensorgenerally corresponds to a decrease in the mass flow rate. Compressormay have a minimum allowable operating pressure requirement, and controllermay be configured to turn off compressor(e.g. stop the supply of electrical power to the compressor) to prevent operation of compressorat or below the minimum operating pressure. Controllermay also be configured to increase a speed (mass flow rate) of compressorif an operating pressure sensed by pressure sensordrops sufficiently to reach a threshold pressure that is above the minimum allowable operating pressure for compressor. An increase in the operating speed of compressorresults in an increase in the mass flow rate and operating pressure such that the pressure measured by pressure sensordoes not reach the minimum allowable operating pressure.

In general, the threshold pressure may be selected (set) to avoid reaching the minimum allowable pressure without causing unnecessary increases in compressor speed. For example, the threshold pressure may be about 5 psi greater than the minimum allowable pressure, about 10 psi greater than the minimum allowable pressure, about 20 psi greater than the minimum allowable pressure, or other suitable pressure difference as required for a particular heat pump water heater system. In some examples, the threshold pressure may by a target percentage greater than the minimum allowable pressure. For example, the pressure threshold may be about 105%, about 110%, about 115%, or about 120% of the minimum pressure. The pressure difference between the threshold pressure and the minimum allowable operating pressure is preferably great enough to reliably prevent the system from reaching the minimum allowable pressure without causing unnecessary or excessive increases in compressor speed that could result in decreased efficiency. It will be understood that the threshold pressures discussed above are merely examples, and the present disclosure is not limited to any specific pressure threshold. Also, the magnitude of the pressure difference may be set, at least in part, to provide for optimum (e.g. most efficient) operation in a specific geographic area and climate.

Thus, the heat pump water heater systemmay have a cold temperature (low ambient temperature) operating mode that includes increasing the compressor speed to increase the mass flow rate of refrigerant through compressor. Increasing the speed of compressorallows the systemto continue operating at a lower ambient temperature by increasing the mass flow rate to increase heat output and to prevent the operating pressure measured by pressure sensorfrom reaching the minimum allowable pressure. Also, compared to a heat pump system that does not include a cold operating mode, systemmay include a smaller compressor, yet still continue to operate at the same ambient temperature as a heat pump system having a larger compressor that does not include increased compressor speed.

It will be understood that the operating pressure measured by sensoris related to the mass flow rate of the refrigerant through compressor. Thus, the present disclosure is not limited to measuring mass flow rates based on measuring operating pressure. In general, systemmay utilize virtually any suitable mass flow measurement technique to control compressor speed to compensate for reduced mass flow rates that would otherwise occur if the compressor were to be operated at the same speed at both warm and cold ambient conditions. For example, the actual mass flow rate could be measured alone or in combination with one or more additional operating parameters (e.g. ambient temperature), and a suitable minimum mass flow rate could be utilized to trigger increased compressor speed. The energy balance between the air side of the evaporatorand the refrigerant side of the evaporatorcould also be measured, and a suitable energy value could be utilized to trigger increased compressor speed. In general, the operating parameter that is utilized to trigger increased compressor speed may also be used to trigger reductions in compressor speed whereby the compressor speed returns to the “normal” (warm ambient) mode. For example, if pressure measured by sensoris reduced to a first threshold, controllermay increase a speed of compressor, and controllermay reduce a speed of compressorif the pressure measured by sensoris above a second threshold. Thus, controllermay be configured to adjust the speed of compressorto maintain the inlet pressure of compressorwithin a predefined range. However, it will be understood that the measured operating parameter/criteria that is utilized to trigger increased compressor speed does not have to be the same operating parameter/criteria that is used to reduce compressor speed. For example, compressor speed may be increased if the mass flow rate drops to a threshold level (as determined from decreased pressure at inlet), whereas compressor speed may be reduced if the ambient temperature increases to a minimum threshold temperature.

Controllermay be in communication with and/or comprise a Variable-Frequency Drive (VFD) to control the compressor. For example, during normal operating conditions, the VFD may drive a motor of compressorat a frequency of 60 Hz, and during low-ambient temperature conditions (e.g. when the pressure measured by sensorreaches the threshold pressure), the VFD can drive the motor of compressorat a frequency higher than 60 Hz (e.g. 70 Hz). The increases in drive speed of compressormay comprise a single step increase (e.g. 60 Hz to 70 Hz), or it may comprise a series of steps (e.g. from 60 Hz to 65 Hz, 65 Hz to 70 Hz, etc.). In an example, the VFD may increase the frequency 5 Hz (or 10 Hz) each time the pressure measured by sensorreaches a first (lower) threshold, and the frequency may be reduced 5 Hz (or 10 Hz) each time the measured pressure reaches a second (higher) threshold. Alternatively, the increase(s) and/or decrease(s) may comprise a ramp function whereby, for example, the VFD gradually increases the drive frequency from 60 Hz to 70 Hz utilizing a predefined ramp function.

Alternatively, the controllermay be configured to continuously vary the speed of compressorif a threshold pressure is detected by sensorwhereby the operating pressure measured by sensoris maintained at or around (e.g. slightly above) the threshold pressure by varying the speed at compressor.

As discussed above, controllermay be configured to reduce the operating speed of compressorwhen an increased mass flow rate (compressor speed) is no longer required. For example, controllermay be configured to utilize predefined criteria to reduce the compressor speed to return it to the normal or baseline operating speed. The predefined criteria may comprise, for example, a pressure measured by sensorthat is sufficient to prevent the pressure from dropping to the minimum allowable pressure of compressorif the compressor speed is returned to normal. Controllermay be configured to utilize empirical data and/or modeling data to predict or estimate a relationship between a drive speed of compressorand a pressure measured by pressure sensorat a given operating condition (e.g. ambient temperature), and the speed of compressormay be returned to normal if the normal operating speed will not result in the pressure dropping below the minimum allowable (shut off) pressure. Thus, if the heat pump water heater systemis operating in a cold ambient mode wherein a speed of compressoris increased, the controllermay monitor the operating pressure measured by pressure sensorand the ambient temperature to determine if the speed of compressorcan be decreased to a normal operating speed without the pressure dropping below the threshold pressure or, alternatively, without the pressure dropping to or below the minimum allowable pressure.

Still referring to, compressormay also have a maximum allowable drive speed. Thus, if the ambient temperature is sufficiently low, the operating pressure sensed by pressure sensormay drop to the minimum allowable pressure of compressoreven though compressoris being driven at the compressor's maximum allowable speed. If this operating condition occurs, controllermay be configured to turn off (shut down) compressor(e.g. stop supplying electrical power to the compressor). Following shut down of compressor, the controllermay be configured to monitor the ambient temperature and initiate operation of compressorif the ambient temperature is high enough to permit operation of compressoreither at a normal (default or baseline) operating speed or at an increased operating speed (cold ambient mode).

Controllermay be configured to actuate defrost valvesandto cause either refrigerant from compressorto flow through evaporator. In general, controllermay be configured to increase a speed of compressorif an inlet pressure of compressor drops below a threshold value to thereby permit operation to continue at reduced ambient temperatures while maintaining an inlet pressure of compressorabove a minimum allowable inlet pressure of the compressor. However, increases in compressor speed may not be sufficient to maintain the inlet pressure above the minimum allowable inlet pressure for compressor. Accordingly, if an inlet pressure (e.g. a pressure measured by sensor) drops below the threshold pressure after a speed of compressorhas been increased, controllermay actuate a defrost cycle when the inlet pressure reaches the minimum allowable inlet pressure, or when the inlet pressure reaches a defrost inlet pressure that is between the minimum allowable inlet pressure and the threshold inlet pressure. In general, controllermay be configured to continue increasing a speed of compressoruntil a maximum allowable compressor speed is reached, and controllermay then implement a defrost cycle if the inlet pressure reaches the defrost inlet pressure. In general, the defrost inlet pressure may be equal to the minimum allowable inlet pressure. Controllermay also be configured to implement a defrost cycle based on other operating parameters even if a maximum allowable compressor speed has not been reached. For example, under certain operating conditions, it may be more efficient to implement a defrost cycle rather than continue to increase compressor speed.

The controllermay comprise virtually any suitable programmable controller, circuit, or combination thereof. For example, controllermay comprise a Programmable Logic Controller (PLC) that is configured to monitor multiple parameters such as inlet and outlet temperatures of compressor, refrigerant pressures, ambient temperature, and power consumption. The heat pump water heater systemmay utilize return water temperature measured by sensor, and/or water supply temperature measured by temperature sensorto control operation of system. The controllermay be configured to utilize various inputs (e.g. measured temperatures and pressures) to maximize efficiency of systemover a wide range of inlet water temperatures and ambient conditions using a multi variable regression of input parameters measured by the sensors of the heat pump water heater system. Controllermay be configured to maximize efficiency utilizing a Coefficient of Performance (COP) or other suitable efficiency criteria. Equation 1 ofshows a formula for maximum COP (COP), which can correspond to a minimum power (P) that is required to cause the heat pump water heater systemto output heat sufficient to meet a demand (target) heat output. The output of the control system (e.g. algorithm) may vary the speed of compressor, the speed of evaporator fans, or both, to minimize the input power and maximize the heat output for a given set of conditions. In general, the COP is the product of heat output divided by input power, and system(e.g. controller) may be configured to always operate at or near peak COP (COP), or to operate at or near peak COP only when the system is in COP optimization mode. Heat output may be determined or estimated (e.g. by controller) utilizing a difference in temperatures measured by water temperature sensorsand. Heat output may also be based, at least in part, on the mass flow rate and heat capacity of water flowing through heat exchanger. Controllermay be configured to determine input power by measuring and summing power consumed by the system components and/or utilizing power output from power supply. In general, controllermay be configured to maximize efficiency of system, and the controller does not necessarily need to utilize a specific (e.g. unitless) COP to do so.

For example, if the ambient temperature is warmer, which can correspond to higher operating pressures at inletof compressor(if compressorwere to be operated at the same speed), compressorand/or evaporator fan(s)can be operated at lower speeds (frequencies). If the ambient temperature is cooler, the compressorand/or evaporator fan(s)can be controlled to operate at higher speeds (frequencies). For example, a second VFD may be configured to control a frequency of the motor driving evaporator fan(s), and the controllermay communicate instructions or signals to the second VFD to speed up or slow down this/these motors. Thus, the controllerof heat pump water heater systemcan be configured to provide an active and continuous control over the components of the heat pump water heater systemto optimize efficiency (e.g. COP).

Referring now to, a method Mfor operating a heat pump water heater systemincludes measuring the pressure of refrigerant at the inletof the compressorand comparing the measured inlet pressure to a threshold pressure at step M. If the measured pressure is greater than or equal to the threshold pressure, the method Mcontinues to step Mto operate the heat pump water heaterin a standard mode/default mode or a target COP (COP) mode. The target COP (COP) mode is further described below in connection with method M(). If the measured pressure is less than the threshold pressure at step M, the method Mmay compare the ambient temperature TA to a low ambient temperature at step M. If the ambient temperature TA is not low (e.g. not below the low ambient temperature threshold), the method Mmay optionally determine an aberrant condition or an error is present at step M, and the method may include setting an aberrant condition flag and/or generate an aberrant condition signal at step M. For example, if there is a pressure drop at the inletbut not during an ambient temperature TA that is sufficiently low to cause the pressure drop when the components of systemare operating properly, the control circuitry (e.g. controller) can determine that an aberrant condition Mof the heat pump/heat pump water heaterexists. If an aberrant condition is determined to exist at step M, the method may optionally include adjusting (increasing or decreasing) power to compressoror continuing to operate in a standard mode or COPmode (e.g. step M). The system (e.g. controller) may optionally be configured to diagnose the cause of the aberrant condition based on one or more operating parameters and to adjust or stop operation after an aberrant condition is detected based on the results of the diagnoses.

If an aberrant condition is not detected at step, the method may proceed to a low ambient mode(provided the measured pressure is below the threshold pressure at step M). In the low ambient mode, if the ambient temperature TA is below the low temperature threshold, the method Mcan increase the speed of the compressorto permit operation of the heat pump water heater systemat a low ambient temperature at step M. It will be understood that step Mis optional, and compressor speed may be increased (e.g. stepA) even if ambient temperature is not below the low temperature threshold.

At step MB, the measured pressure at inletis compared to a defrost pressure. The defrost pressure can be a second pressure threshold at inletthat is lower than the initial threshold pressure (step M), such that, when the measured pressure at inletis below the defrost pressure, a defrost operating mode is activated at step MD. For example, the defrost valve system can be actuated by controllerto defrost the system. It will be understood that stepsA andB do not necessarily need to occur in a specific sequence, and the measured inlet pressure may be continuously measured and compared to the defrost pressure (and/or other defrost criteria), and a defrost may be actuated (stepD) even if the system is not in low ambient mode(e.g. if an aberrant condition (step M) or other condition requiring defrost is detected). If the measured inlet pressure is not below the defrost pressure, the low ambient mode can continue until a stability of the pressure is determined at step MC. For example, if the measured pressure is maintained above the threshold pressure for a predetermined time, the systemcan be determined as stable, and the method can proceed to step M. In general, stepC may comprise virtually any suitable predefined criteria (e.g. based on various operating parameters) that can be utilized to determine if operation can exit low ambient mode. Also, while the systemis in the low ambient mode (e.g. after an increase in compressor speedA), the measured inlet pressure may be repeatedly measured and compared to the threshold pressure, and the compressor speed may be repeatedly or continuously increased to maintain the measured inlet pressure at or above the threshold pressure, until low ambient mode is exited (e.g. a defrost MD is actuated and/or low ambient mode exit criteria is satisfied at step MC). Method Mcan be performed by virtually any suitable control circuitry and/or programmable controller(s) in combination with the components described above, such as by one or more controllers (e.g. controller) or any control circuitry for the heat pump water heater system.

Referring now to, Equation 1 demonstrates the dependency of COP on the ratio of Heat Output and power (P) input. In general, this ratio may be maximized to thereby maximize COP. Thus, COPmay depend on heat output (e.g. heat required to warm the water supplied to hot water tank system) and minimum power input P. It will be understood that Pin Equation 1 is a power at which the ratio of heat output to power (P) is minimized. If the Heat Output comprises a demand on the system (e.g. a target heat output), the COPwill generally correspond to the smallest input power Pthat is capable of meeting the heat demand (Heat Output). Also, it will be understood that COPof Equation 1 may represent a maximum possible COP that enables the heat pump systemto meet a demand for hot water given the operating conditions (e.g. ambient temperature) present at a given point in time. The heat output may be a function of water temperature/a target change thereof (ATWATER). For example, heat output required to heat the water can be based on the temperature of the incoming water and a temperature setpoint, such that, for large differences in incoming water temperature (e.g. measured by temperature sensor) and outgoing target water temperature, a large heat output can be determined, and vice versa. The Heat Output may also be a function of the volume (mass) flow rate of water entering and exiting heat exchanger. The minimum power Pcan be a function of ambient temperature TA and target power levels for the heat pump, such as a target power of compressorand a target fan power (e.g. target power to evaporator fans). For example, at high ambient temperatures TA, the heat pump may have a lower minimum input power Prequired to reach COPthan at lower ambient temperatures TA, as more heat can be derived from the air under higher ambient temperature conditions. The process (algorithm) of the present disclosure can provide for COPby determining the minimum power P, as a function of ambient temperature TA, that is required to produce the heat output to provide heated water at the setpoint temperature (i.e. meet the heat demand requirements). Also, it will be understood that a ratio of the COP of Equation 1 is not necessarily equal to a ratio of total heat input into the water divided by the total electrical energy consumed by hot water heat pump system. For example, some heat that is input into the water by heat exchangermay escape before the temperature of the water is measured utilizing temperature sensor. Also, the temperature of water flowing into the heat exchangermay be slightly different than the temperature measured by temperature sensor. Nevertheless, a difference in water temperature measured by the temperature sensorsandmay be utilized to determine a heat output and COP that is sufficient to maximize a COP efficiency for purposes of maximizing energy efficiency of heat pump systemduring operation thereof during various operating conditions.

In some examples the controller, or control circuitry for the heat pump water heater system, can provide a look-up table or other data correlation structure to determine the minimum power Pbased on the ambient temperature TA. The minimum power Pcan be correlated to other values, such as the target compressorpower and the target fan power, via similar or different data structures. The target powers can be selected by the controller, from which target speeds, or frequencies, are determined, such that the controllercan control “speed” or power of the compressorand/or the fan(s)via variable control. For example, the control circuitry can communicate signals to a drive (e.g. VFD) of each motor (the compressormotor and the fan motor) that are indicative of a target speed. For example, a pulse-width modulated (PWM) signal or other signal can be communicated to the drive or to the motor control. In general, the power to the compressorand the evaporator fan(s)can be controlled variably, as previously described, to achieve the minimum power Prequired to meet the heat demand to thereby provide COPfor the current operating conditions of the system.

Referring now to, a method Mfor operating a heat pump of a heat pump water heater systemincludes determining an ambient temperature TA at step Mand determining a target heat output for the heat pump at step M. For example, the ambient temperature TA can be measured via the ambient temperature sensor, and the target heat output can be based on a temperature difference ATWATER between inlet water and a setpoint temperature for exiting water. In some examples, the control circuitry (e.g. controller) can determine the target heat output using a look-up table based on ATWATER. At step M, the target COP is determined. For example, the control circuitry can control the heat output to reach a target COP, such as COP. Based on the target COP, the method Mincludes determining the target input power at step M. For example, the controllercan determine target speeds for the compressor (P) and/or the evaporator fan(s) (P) at step MA. As previously described, the target input power can be the minimum input power Pthat is required to supply the heat demand to thereby achieve the COP, and data pairs associated with the target power can be selected by the control circuitry. The method Mincludes controlling the heat pump to achieve the target COP at M. For example, the VFDs can be used to control the motors of the compressorand/or the fan(s).

It is contemplated that the systemsand methods M, Mdescribe herein can provide for low-energy consumption, such that the target COP range can be mapped to a range of ambient temperature TA. Accordingly, the minimum power Pcan be mapped in a similar way, with data pairs (e.g. target compressor power Pand target fan power P) assigned for each minimum power value P. The heat pump water heater systemcan also be dynamically adjustable between the COP optimization algorithm and the “overdrive” algorithm. The controllercan be configured to select between these operating modes based on ambient temperature TA, manual settings, or a pre-programmed schedule. For example, the controllercan execute the low ambient operation in response to reduced compressor inlet pressure and/or ambient temperatures TA at or below a threshold temperature and execute COP optimization or maximization above that threshold. In this way, both methods M, Mcan be executed by the same control circuitry to provide enhanced operation.

It will be understood by one having ordinary skill in the art that construction of the described disclosure and other components is not limited to any specific material. Other exemplary embodiments of the disclosure disclosed herein may be formed from a wide variety of materials, unless described otherwise herein.

It is also important to note that the construction and arrangement of the elements of the disclosure as shown in the exemplary embodiments is illustrative only. Although only a few embodiments of the present innovations have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g. variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements shown as multiple parts may be integrally formed, the operation of the interfaces may be reversed or otherwise varied, the length or width of the structures and/or members or connector or other elements of the system may be varied, the nature or number of adjustment positions provided between the elements may be varied. It should be noted that the elements and/or assemblies of the system may be constructed from any of a wide variety of materials that provide sufficient strength or durability, in any of a wide variety of colors, textures, and combinations. Accordingly, all such modifications are intended to be included within the scope of the present innovations. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the desired and other exemplary embodiments without departing from the spirit of the present innovations.

It will be understood that any described processes or steps within described processes may be combined with other disclosed processes or steps to form structures within the scope of the present disclosure. The exemplary structures and processes disclosed herein are for illustrative purposes and are not to be construed as limiting.

It is to be understood that variations and modifications can be made on the aforementioned structure without departing from the concepts of the present invention, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise.