CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and benefit of U.S. Provisional Patent Application No. 63/282,881, filed November 24, 2021, which is incorporated herein by reference.

BACKGROUND

When a heat pump pool heater system is operating to increase the temperature of pool water, the evaporator coil temperature can sometimes fall below the ambient air temperature. The temperature difference between the evaporator coil and the ambient air can lead to moisture accumulation on the evaporator coil as moisture in the ambient air condenses on the colder evaporator coil. In certain conditions, the temperature of the evaporator coil will fall below a threshold temperature at which the accumulated moisture can eventually freeze, forming frost and ice. In these conditions, the evaporator coil temperature can fall below zero and moisture in the air can continue to accumulate as frost and ice on the evaporator coil until the coil rises above the freezing temperature of water. As the frost continues to accumulate on the evaporator coil, the heat pump can experience degraded performance and damaged components.

To reduce frost accumulation, some heat pump pool heater systems will operate in a passive defrost cycle in which the compressor is deactivated, such that refrigerant is no longer flowing through the heat pump pool heater system, and the fan near the evaporator is activated to move air across the evaporator coil. This method, however, can be unable to timely defrost the evaporator coil, depending on ambient conditions, for example. Other existing heat pump pool heater systems will operate in a hot gas defrost cycle in which the compressor is activated and a four-way valve (or another type of and/or combination of valves) is energized to direct hot, gaseous refrigerant to the evaporator. This, however, limits the amount of time in which hot, gaseous refrigerant is flowed to the condenser, which can limit the amount of heating that can be provided to the pool water. Further, depending on ambient conditions, this method, too, can be unable to timely defrost the evaporator coil. Alternatively or in addition, some systems can operate in a reverse direction to move heated refrigerant through the frosted coil until the frost is melted. However, redirecting hot refrigerant to the evaporator or running the heat pump in the reverse cycle can excessively remove heat from the pool water, which is counterproductive to the purpose of the heat pump pool heater system and can result in system inefficiency and/or additional energy costs (e.g., to re-heat the pool water to the desired temperature).

Improved systems and methods therefore are needed for maintaining a target water temperature in a pool while reducing frost accumulation on the evaporator coil of a heat pump pool heater system with increased system efficiency and/or decreased energy costs.

SUMMARY

These and other problems are be addressed by the technologies described herein. Examples of the present disclosure relate generally to reducing frost accumulation on a heat pump pool heater system's evaporator coil.

The disclosed technology includes a heat pump pool heater (HPPH) system comprising a heat pump. The heat pump can include a refrigerant circuit fluidly connecting a compressor, a condenser coil, athermal expansion valve, and an evaporator coil via refrigerant conduit such that refrigerant can pass through each of the compressor, condenser coil, thermal expansion valve, and evaporator coil. The HPPH system can include one or more supplemental heat sources configured to output heat. The HPPH system can include a water pump configured to draw water from a pool, pass the water across the condenser coil and the one or more supplemental heat sources, and flow heated water from the condenser coil and/or the one or more supplemental heat sources to the pool. The HPPH system can include a controller configured to selectively transition the heat pump between a water heating mode and a defrost mode. The defrost mode can include ceasing a flow of refrigerant through the condenser coil and engaging the one or more supplemental heat sources to output heat to the water.

The water heating mode can include refrigerant flowing sequentially through the compressor, the condenser coil, the thermal expansion valve, and the evaporator coil. Optionally, the water heating mode can include the one or more supplemental heat sources being deactivated such that heat is provided to the water solely by the heat pump.

The HPPH system can include a water temperature sensor configured to measure a temperature of water associated with the pool. The controller can be configured to receive water temperature data from the water temperature sensor, determine that a current water temperature is less than a target water temperature, and output instructions for at least one of the heat pump or the one or more supplemental heat sources to provide heat to the water.

The HPPH system can include one or more sensors configured to measure one or more corresponding characteristics at or near the evaporator coil. The controller can be configured to receive sensor data from the one or more sensors, determine that a current sensor value fails to satisfy a corresponding target value, and transition the heat pump to the defrost mode.

The one or more sensors can include a coil temperature sensor configured to measure a temperature of the refrigerant in or near the evaporator coil, the current sensor value can be a current coil temperature, and the corresponding target value can be a coil temperature threshold. Determining that the current sensor value fails to satisfy the corresponding target value can include determining that the current coil temperature is less than the coil temperature threshold.

The one or more sensors can include an ambient temperature sensor configured to measure a temperature of ambient air at or near the evaporator coil, the current sensor value can be a current ambient temperature, and the corresponding target value can be an ambient temperature threshold. Determining that the current sensor value fails to satisfy the corresponding target value can include determining that the current ambient temperature is less than the ambient temperature threshold.

The one or more sensors can include an ambient temperature sensor configured to measure a humidity of ambient air at or near the evaporator coil, the current sensor value can be a current ambient humidity, and the corresponding target value can be an ambient humidity threshold. Determining that the current sensor value fails to satisfy the corresponding target value can include determining that the current ambient humidity is less than the ambient humidity threshold.

Transitioning the heat pump to the defrost mode can include outputting instructions for the compressor to cease operation.

Transitioning the heat pump to the defrost mode can include outputting instructions for a reversing valve to reverse a direction of the flow of refrigerant through the heat pump.

Transitioning the heat pump to the defrost mode can include outputting instructions for a valve to open and direct the flow of refrigerant directly from the compressor to the evaporator coil, thereby bypassing the condenser coil. The HPPH system can include a supplemental defrost heat source and a fan configured to pass air across the evaporator coil. Transitioning the heat pump to the defrost mode can include outputting instructions for the supplemental defrost heat source to output heat and for the fan to pass air across the evaporator coil.

The one or more supplemental heat sources can include an electrical resistance heating element. The one or more supplemental heat sources can include combustiontype heating device.

The disclosed technology includes anon-transitory, computer readable medium having instructions stored thereon that, when executed by one or more processors, can cause a controller to receive water temperature data from a water temperature sensor of a heat pump pool heating (HPPH) system, determine that a current water temperature is less than a target water temperature, and output instructions for at least one of a heat pump of the HPPH system or a supplemental heat source of the HPPH system to provide heat to the water. The instructions, when executed by the one or more processors, can cause the controller to receive sensor data from one or more sensors configured to measure one or more corresponding characteristics at or near an evaporator coil of the HPPH system, determine that a current sensor value fails to satisfy a corresponding target value, and transition the HPPH system to a defrost mode. Transitioning the HPPH system to the defrost mode can include outputting instructions for ceasing a flow of refrigerant through a condenser coil of the HPPH system and outputting instructions for the one or more supplemental heat sources to generate heat for heating pool water.

Further features of the disclosed design, and the advantages offered thereby, are explained in greater detail hereinafter with reference to specific examples illustrated in the accompanying drawings, wherein like elements are indicated be like reference designators.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale. The drawings are incorporated into and constitute a portion of this disclosure, illustrating various implementations and aspects of the disclosed technology. Together with the description, the drawings serve to explain the principles of the disclosed technology.

FIG. 1 illustrates a schematic diagram of an example heat pump pool heater system, in accordance with the disclosed technology. FIGS. 2 A and 2B illustrate a schematic diagram of an example heat pump pool heater system, with the FIG. 2A illustrating operation in a normal pool water heating mode and FIG. 2B illustrating operation in a hot gas defrost mode, in accordance with the disclosed technology.

FIG. 3 illustrates a schematic diagram of an example heat pump pool heater system operating in a bypass defrost mode, in accordance with the disclosed technology.

FIG. 4 illustrates a schematic diagram of a controller and various components of a heat pump pool heater system, in accordance with the disclosed technology.

FIGS. 5-8 illustrate flow charts for example methods for reducing frost accumulation on an evaporator coil of a heat pump's water heater, in accordance with the disclosed technology.

DETAILED DESCRIPTION

Throughout this disclosure, systems and methods are described with respect to reducing frost accumulation on the evaporator coil of a heat pump pool heater system. Those skilled in the art, however, will recognize that the disclosed technology can be applicable to multiple scenarios and applications. For example, the disclosed technology can be applied to heat pump systems used in applications that are not limited to pool water heating.

Some implementations of the disclosed technology will be described more fully with reference to the accompanying drawings. This disclosed technology may, however, be embodied in many different forms and should not be construed as limited to the implementations set forth herein. The components described hereinafter as making up various elements of the disclosed technology are intended to be illustrative and not restrictive. Indeed, it is to be understood that other examples are contemplated. Many suitable components that would perform the same or similar functions as components described herein are intended to be embraced within the scope of the disclosed devices and methods. Such other components not described herein may include, but are not limited to, for example, components developed after development of the disclosed technology.

Herein, the use of terms such as "having," "has," "including," or "includes" are open- ended and are intended to have the same meaning as terms such as "comprising" or "comprises" and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as "can" or "may" are intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such.

Unless otherwise specified, all ranges disclosed herein are inclusive of stated end points, as well as all intermediate values. By way of example, a range described as being “from approximately 2 to approximately 4” includes the values 2 and 4 and all intermediate values within the range. Likewise, the expression that a property “can be in a range from approximately 2 to approximately 4” (or “can be in a range from 2 to 4”) means that the property can be approximately 2, can be approximately 4, or can be any value therebetween. Further, the expression that a property “can be between approximately 2 and approximately 4” is also inclusive of the endpoints, meaning that the property can be approximately 2, can be approximately 4, or can be any value therebetween.

The mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Similarly, it is also to be understood that the mention of one or more components in a device or system does not preclude the presence of additional components or intervening components between those components expressly identified.

As used herein, unless otherwise specified, the use of the ordinal adjectives “first,” “second,” “third,” etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.

Although the disclosed technology may be described herein with respect to various systems and methods, it is contemplated that embodiments or implementations of the disclosed technology with identical or substantially similar features may alternatively be implemented as methods or systems. For example, any aspects, elements, features, or the like described herein with respect to a method can be equally attributable to a system. As another example, any aspects, elements, features, or the like described herein with respect to a system can be equally attributable to a method.

Reference will now be made in detail to examples of the disclosed technology that are illustrated in the accompanying drawings and disclosed herein. Wherever convenient, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

As illustrated in FIG. 1, a heat pump pool heater (HP PH) system 100 can be configured to heat water that is circulated to a volume of water, such as a pool. As will be appreciated, the HPPH system 100 can include a refrigerant circuit including a compressor 102, a condenser coil 104, athermal expansion valve (TXV) 106, and an evaporator coil 108. A blower or fan 110 can be configured to direct air across the evaporator coil 108. Thus, the HPPH system 100 can be configured to extract heat from ambient air at the evaporator coil 108 and transfer at least some of the extracted heat to pool water via the condenser coil 104. The HPPH system 100 can include one or more sensors 112 configured to detect and/or measure one or more conditions at or near the evaporator 108, as will be discussed more fully herein. The HPPH system 100 can include one or more supplemental heat sources 114 to provide heat to the pool water outside of any heat provided by the heat pump of the HPPH system.

The condenser coil 104 and/or evaporator coil 108 can be any type of heat exchanger coil used in a heat pump, including, but not limited to, bare tube, plate-type, and finned evaporator coils. The fan 110 can be any type of blower or fan configured to direct air across at least a portion the evaporator coil 108. The fan 110, for example, can be an axial-flow fan, a centrifugal fan, a crossflow fan, or any other type of fan suitable for the application so long as the fan 110 is configured to direct air across the evaporator coil 108. The fan 110 can be coupled with a variable- speed motor or a single-speed motor depending on the application.

To determine the temperature of the evaporator coil 108, the one or more sensor(s) 112 at the evaporator 108 can include a coil temperature sensor, which can be configured to measure the temperature of the refrigerant in the evaporator coil 108 and output the measured temperature to the controller. The coil temperature sensor can be configured to measure the temperature of the evaporator coil 108 continuously or periodically when the HPPH system 100 is shut down, while the HPPH system 100 is operating, or both. The coil temperature sensor can be installed directly on the surface of the evaporator coil 108, inside of the evaporator coil 108, partially inside of the evaporator coil 108, or near the evaporator coil 108. Additionally, the coil temperature sensor can be configured to measure the surface temperature, the core temperature, a temperature of a portion of the evaporator coil 108, or any other method of measuring as would be suitable for the particular application and arrangement. The coil temperature sensor can include any type of sensor capable of measuring the temperature of the evaporator coil 108. For example, the coil temperature sensor can be or include a thermocouple, a resistor temperature detector (RTD), a thermistor, an infrared sensor, a semiconductor, or any other suitable type of sensor for the application.

Alternatively or in addition, the one or more sensor(s) 112 at the evaporator 108 can include an ambient temperature sensor (e.g., a thermocouple, an RTD, a thermistor, an infrared sensor, a semiconductor), which can be configured to detect a temperature of the ambient air to indicate atmospheric conditions near the evaporator coil 108. Alternatively or in addition, the one or more sensor(s) 112 at the evaporator 108 can include a humidity sensor (e.g., capacitive, resistive, thermal). The humidity sensor can be configured to detect ahumidity of the ambient air (e.g., relative humidity).

The HPPH system 100 can include a water pump 120 configured to circulate water between the pool and a heater housing including the condenser coil 104. That is, the water pump 102 can draw water from the pool and flow the water into the heater housing through a water inlet.

103. The water pump 102 can flow the water across the condenser coil 104 and out of the heater housing via a water outlet 105 to return heated water to the pool. The HPPH system 100 can include one or more water temperature sensors 122 configured to measure a temperature of the pool water. As non-limiting examples, the water temperature sensor 122 can be a thermocouple, an RTD, a thermistor, an infrared sensor, a semiconductor, or the like. As illustrated, a water temperature sensor 122 can be located downstream from the condenser coil 104 to measure the temperature of heated water being outputted into the pool. However, the location of the water temperature sensor 122 is not so limited. For example, alternatively or in addition, a water temperature sensor 122 can be located at any location upstream from the water inlet 103 of the heater housing, at any location downstream from the water outlet 105 of the heater housing, at any location within the heater housing, and/or within the pool itself.

The HPPH system 100 can include one or more supplemental heat sources 114. The supplemental heat source(s) 114 can be located in the heater housing that includes the condenser coil 104. For example, the supplemental heat source(s) 114 can be located in the same chamber as the condenser coil 104, as illustrated in FIG. 1. Alternatively or in addition, the supplemental heat source(s) 114 can be located in the heater housing in a chamber that is separate from the chamber including the condenser coil 104. Alternatively or in addition, the supplemental heat source(s) 114 can be located in a housing that is separate and distinct from the heat housing (e.g., in a supplemental heater housing). The supplemental heat source(s) 114 can be or include any type of non-heat-pump heating device. For example, one or more of the supplemental heat source(s) 114 can be an electric heating device (e.g., a resistive heating device). As additional examples, one or more of the supplemental heat source(s) 114 can be a combustion-type heating device (e.g., fueled by natural gas or propane).

The HPPH system 100 can include a controller, as described more fully herein. The controller can be or include a computing device configured to receive data from a user interface and/or one or more sensors, and based on the data, output instructions for operation of the compressor 102, the blower 110, the supplemental heat source(s) 114, and/or the water pump 120.

Referring to FIGS. 2 A and 2B, the HPPH system 100 optionally can be configured to selectively reverse the flow of refrigerant through the refrigerant circuit, such as by a reversing valve, such as four- way valve 216. As shown in FIG. 2 A, the HPPH system 100 can be in a pool- heating mode in which the four- way valve 216 can be in a first configuration for directing refrigerant through the refrigerant circuit such that heat is transferred from ambient air to pool water. As shown in FIG. 2B, the HPPH system 100 can be in a hot gas defrost mode in which the four- way valve 216 can be transitioned (e.g., by the controller) to a second configuration for directing refrigerant through the refrigerant circuit in the opposite direction as compared to the operation depicted by FIG. 2A. Thus, in the hot gas defrost mode, FIG. 2B illustrates heat being drawn from pool water and transferred to the evaporator coil 108 to remove any frost buildup from the evaporator coil 108.

Alternatively or in addition and referring to FIG. 3, the HPPH system 100 can be configured to bypass the condenser coil 104. The HPPH system 100 can include a valve 318 located in a bypass line that can selectively direct refrigerant from a position downstream from the compressor 102 to a location that is between the TXV 106 and the evaporator coil 108. The valve 318 can be a solenoid valve or any other type of valve. For example, the valve 318 can be a normally closed solenoid valve. When the valve 318 is closed, the HPPH system 100 can be configured to operate in a poolheating mode, and when the valve 318 is opened, the HPPH system 100 can be configured to operate in a bypass defrost mode in which hot, gaseous refrigerant is directed from the compressor directly to the evaporator coil 108 to remove any frost buildup from the evaporator coil 108.

Optionally, the HP PH system 100 can include one or more defrost heat source(s) 118. The defrost heat source(s) 118 can be or include any type of non-heat-pump heating device. For example, one or more of the defrost heat source(s) 118 can be an electric heating device (e.g., a resistive heating device). As additional examples, one or more of the defrost heat source(s) 118 can be a combustion-type heating device (e.g., fueled by natural gas or propane). During a defrost mode of operation, the defrost heat source(s) 118 can be configured to output heat, which can be directed to the evaporator coil 108. For example, the heat from the defrost heat source(s) 118 can simply radiate toward the evaporator coil 108, or the fan 110 can be engaged to directed air heated by the defrost heat source(s) 118 over the evaporator coil 108.

Referring to FIG. 4, the controller of the HPPH system 100 can be configured to control operation of various components of the HPPH system 100. The controller 400, as illustrated in FIG. 4, can have memory 402, one or more processors 404, a communication interface 406, and/or a user interface 408. The memory can have instructions stored thereon that, when executed by the processor(s) 404, cause the HPPH system 100 to perform actions, methods, or processes, such as those described herein. More specifically, the controller 400 can be configured to receive data (e.g., via the communication interface 406) from one or more sensors (e.g., sensor(s) 112, water temperature sensor 122), make certain determinations as discussed more fully herein, and output instructions (e.g., via the communication interface 406) for operation of one or more components of the HPPH system 100 (e.g., compressor 102, fan 110, supplemental heat source(s) 114, defrost heat source(s) 118, water pump 120, four-way valve 216, and/or valve 318.

One of skill in the art will understand that the controller 400 can be installed in any location, provided the controller 400 is in communication with at least some of the components of the system. Furthermore, the controller 400 can be configured to send and receive wireless or wired signals and the signals can be analog or digital signals. The wireless signals can include Bluetooth™, BLE, WiFi™, ZigBee™, infrared, microwave radio, or any other type of wireless communication as may be appropriate for the particular application. The hard-wired signal can include any directly wired connection between the controller and the other components. For example, the controller 400 can have a hard-wired 24V AC connection to the compressor 102 and/or the supplemental heat source(s) 114. Alternatively, the components can be powered directly from a power source and receive control instructions from the controller 400 via a digital connection. The digital connection can include a connection such as an Ethernet or a serial connection and can utilize any appropriate communication protocol for the application such as Modbus, fieldbus, PROFIBUS, SafetyBus p, Ethemet/IP, or any other appropriate communication protocol for the application. Furthermore, the controller 400 can utilize a combination of wireless, hard-wired, and analog or digital communication signals to communicate with and control the various components. One of skill in the art will appreciate that the above configurations are given merely as nonlimiting examples and the actual configuration can vary depending on the application.

Regardless, when the temperature of the evaporator coil 108 falls below a certain temperature threshold, (e.g., 50 °F(10 °C)), the HPPH system 100 can be unable to efficiently provide heat to the pool water. Indeed, condensation accumulated on the evaporator coil 108 can freeze, causing a buildup of frost and ice. In these conditions, frost can accumulate to the point where the HPPH system 100 operates with a degraded performance or components become damaged.

FIG. 5 illustrates allow diagram of a method 500 for operating a heat pump pool heater system (e.g., HPPH system 100). As will be appreciated, the method can be performed by a controller (e.g., controller 400), as anon-limiting example. The method 500 can include receiving 502 water temperature data from a water temperature sensor (e.g., water temperature sensor 122) and determining 504 whether the current water temperature is less than a water temperature threshold, which can be a target water temperature for the pool or other water system. The water temperature threshold can be programmed into the controller, or the water temperature threshold can be user inputted and received by the controller via a user interface (e.g., user interface 408). If the current water temperature is less than the water temperature threshold, the method 500 can include determining that the water should be heated.

The method 500 can include receiving 506 sensor data from one or more sensors configured to measure one or more characteristics at or near the evaporator (e.g., sensor(s) 112, such as a refrigerant temperature sensor, an ambient temperature sensor, and/or an ambient humidity sensor). If the sensor data is indicative of a refrigerant temperature and/or an evaporator coil temperature, the method 500 can include determining whether the refrigerant temperature is less than a refrigerant temperature threshold and/or an evaporator coil temperature threshold (e.g., less than 50°F (10 °C), less than 48°F (8.9 °C), less than 46°F (7.8 °C), less than 44°F (6.7 °C)). Alternatively or in addition, if the sensor data is indicative of an ambient air temperature, the method 500 can include determining whether the ambient air temperature is less than an ambient air temperature threshold (e.g., less than 50°F (10 °C), less than 44°F (6.7 °C)). Alternatively or in addition, if the sensor data is indicative of an ambient humidity, the method 500 can include determining whether the ambient humidity is greater than an ambient humidity threshold. The method 500 can include, if (i) the refrigerant temperature is less than the refrigerant temperature threshold and/or an evaporator coil temperature threshold, (ii) the ambient air temperature is less than the ambient air temperature threshold, and/or (iii) the ambient humidity is greater than the ambient humidity threshold, determining 508 that frost is forming, has formed, and/or is likely to soon form on an evaporator coil (e.g., evaporator coil 108). The method can include transitioning 510the heat pump pool heater system to a defrost mode of operation (e.g., from a normal pool water heating mode).

Referring to FIG. 6, transitioning 510 the heat pump pool heater system to a defrost mode of operation can include outputting 602 instructions for the compressor (e.g., compressor 102) to cease operation, such that the heat pump stops transferring heat. This can correspond to a passive defrost mode. Optionally, transitioning 510 to a defrost mode of operation can include outputting 604 instructions for one or more supplemental defrost heat sources (e.g., defrost heat source(s) 118) to output heat at or near the evaporator coil. Optionally, transitioning 510 to a defrost mode of operation can include outputting 606 instructions for a fan or blower (e.g., fan 110) to pass air across the evaporator coil, which can include passing heated air from the defrost heat source(s), if they are used.

Alternatively, referring to FIG. 7, transitioning 510 the heat pump pool heater system to a defrost mode of operation can include outputting 702 instructions for a reversing valve (e.g., four-way valve 216) to reverse the flow of refrigerant through the heat pump pool heater system such that hot, gaseous refrigerant is flowed to the evaporator coil 108. This can correspond to a hot gas defrost mode. Optionally, transitioning 510 to a defrost mode of operation can include outputting 704 instructions for one or more defrost heat sources (e.g., defrost heat source(s) 118) to output heat at or near the evaporator coil. Optionally, transitioning 510 to a defrost mode of operation can include outputting 706 instructions for a fan or blower (e.g., fan 110) to pass air across the evaporator coil, which can include passing heated air from the defrost heat source(s), if they are used.

Alternatively, referring to FIG. 8, transitioning 510 the heat pump pool heater system to a defrost mode of operation can include outputting 802 instructions for a valve (e.g., valve 318) to direct the flow of refrigerant from the compressor to the evaporator coil 108 such that the flow of refrigerant bypasses the condenser coil (e.g., condenser coil 104). This can correspond to a bypass defrost mode. Optionally, transitioning 510 to a defrost mode of operation can include outputting 804 instructions for one or more defrost heat sources (e.g., defrost heat source(s) 118) to output heat at or near the evaporator coil. Optionally, transitioning 510 to a defrost mode of operation can include outputting 806 instructions for a fan or blower (e.g., fan 110) to pass air across the evaporator coil, which can include passing heated air from the defrost heat source(s), if they are used.

Referring back to FIG. 5, the method 500 can include outputting 512 instructions for one or more supplemental heat sources (e.g., supplemental heat source(s) 114) to engage and output heat to the pool water. The method 500 can include outputting 514 instructions for a water pump (e.g., water pump 120) to circulate the pool water, or continue to circulate the pool water, between the pool and the supplemental heat sources.

The method 500 can include receiving 516 subsequent sensor data from the one or more sensors at or near the evaporator (e.g., refrigerant temperature sensor, ambient temperature sensor, ambient humidity sensor). The method 500 can include determining 518 that the subsequent sensor data satisfies the corresponding target values (e.g., the subsequent refrigerant temperature is greater than the refrigerant temperature threshold, the subsequent ambient air temperature is greater than the ambient air temperature threshold, and/or the subsequent ambient humidity is less than the ambient humidity threshold), and the method outputting 520 instructions for the heat pump to return to normal heat pump operation in which heat is transferred from ambient air to the pool water (e.g., undoing the operations discussed in FIGS. 6, 7, or 8).

The method 500 can include receiving 522 subsequent water temperature data from the water temperature sensor and determining 524 that the current water temperature, an indicated by the subsequent water temperature data, is greater than the water temperature threshold. The method 500 can include outputting 526 instructions for the supplemental heat source(s) and/or the heat pump (i.e., the compressor) to cease operation.

As a more specific example, the disclosed technology includes determining that defrost cycle (e.g., defrost mode of operation) is required to remove frost from the evaporator coil (e.g., permit the evaporator coil to thaw) and outputting instructions to (i) cease a flow of power (e.g., 24 VAC) to the compressor and (ii) engage afLow of power (e.g., 24 VAC) to an electric resistance heater that's configured to provide heat to pool water. The flow of power (e.g., 24 VAC) to the evaporator fan can be ceased. The defrost cycle can be configured to have no time limit such that the heat pump can operate in defrost mode and the electrical resistance heater can solely heat the pool water until it is determined that frost has been removed from the evaporator coil.

In this description, numerous specific details have been set forth. It is to be understood, however, that implementations of the disclosed technology may be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail in order not to obscure an understanding of this description. References to "one embodiment," "an embodiment," "one example," "an example," "some examples," "example embodiment," "various examples," "one implementation," "an implementation," "example implementation," "various implementations," "some implementations," etc., indicate that the implementation(s) of the disclosed technology so described may include a particular feature, structure, or characteristic, but not every implementation necessarily includes the particular feature, structure, or characteristic. Further, repeated use of the phrase "in one implementation" does not necessarily refer to the same implementation, although it may.

Further, certain methods and processes are described herein. It is contemplated that the disclosed methods and processes can include, but do not necessarily include, all steps discussed herein. That is, methods and processes in accordance with the disclosed technology can include some of the disclosed while omitting others. Moreover, methods and processes in accordance with the disclosed technology can include other steps not expressly described herein.

Throughout the specification and the claims, the following terms take at least the meanings explicitly associated herein, unless otherwise indicated. The term "or" is intended to mean an inclusive "or." Further, the terms "a," "an," and "the" are intended to mean one or more unless specified otherwise or clear from the context to be directed to a singular form. By "comprising," "containing," or "including" it is meant that at least the named element, or method step is present in article or method, but does not exclude the presence of other elements or method steps, even if the other such elements or method steps have the same function as what is named.

While certain examples of this disclosure have been described in connection with what is presently considered to be the most practical and various examples, it is to be understood that this disclosure is not to be limited to the disclosed examples, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

This written description uses examples to disclose certain examples of the technology and also to enable any person skilled in the art to practice certain examples of this technology, including making and using any apparatuses or systems and performing any incorporated methods. The patentable scope of certain examples of the technology is defined in the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.