Systems and Methods to Defrost an Evaporator

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and the benefit of U.S. provisional application No. 63/672,457, filed Jul. 17, 2024, which is hereby incorporated by reference herein in its entirety.

FIELD

The present disclosure relates to systems and methods to defrost an evaporator of a refrigerant circuit and more specifically to systems and methods to defrost an evaporator based on a coefficient of performance (COP) of the refrigerant circuit and/or an opening percentage of an expansion valve.

BACKGROUND

Refrigerant circuits are used in many application areas such as heat pump water heating systems, Heating, Ventilation, and Air Conditioning (HVAC) systems, commercial refrigerant systems such as cooled warehouses or supermarket coolers, etc. A refrigerant circuit typically includes a compressor, an evaporator, an expansion device (e.g., an expansion valve or a capillary), and a condenser. It is known that in some instances ice accumulates or forms on the evaporator (e.g., on evaporator coils) when the refrigerant circuit operates in a moist environment with an ambient temperature of less than a threshold (e.g., less than five degrees Celsius or 41 degrees Fahrenheit). Ice works as an insulation layer between the air and the evaporator, and as such, reduces the heat flow from the air to the refrigerant included in the evaporator. This deteriorates the system's coefficient of performance (COP) and, in extreme cases, can prevent correct system operation. In such situations, defrosting may be used to melt/remove the ice from the evaporator.

BRIEF DESCRIPTION OF THE DRAWINGS

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 terminology may be used interchangeably.

FIG. 1 depicts a block diagram of an example refrigerant system in accordance with one or more embodiments of the present disclosure.

FIG. 2 depicts an example graph of a coefficient of performance (COP) of a refrigerant circuit with time in accordance with one or more embodiments of the present disclosure.

FIG. 3 depicts a block diagram of a controller in accordance with one or more embodiments of the present disclosure.

FIG. 4 depicts a flow diagram of an example first method to defrost an evaporator in accordance with one or more embodiments of the present disclosure.

FIG. 5 depicts a flow diagram of an example second method to defrost an evaporator in accordance with one or more embodiments of the present disclosure.

FIG. 6 depicts a flow diagram of an example third method to defrost an evaporator in accordance with one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure is directed towards a refrigerant system (or a refrigeration system) that may include a refrigerant circuit, a sensor unit and a controller. In some instances, the refrigerant circuit may be a vapor compression cycle system that may be part of a water heating system configured to heat water. In other instances, the refrigerant circuit may be part of a heating, ventilation, and air conditioning (HVAC) unit, commercial refrigerant systems such as cooled warehouses or supermarket coolers, or the like. In some aspects, the refrigerant system may be a water heating system, an HVAC unit, a supermarket cooler, a cooled warehouse, and/or the like.

In certain embodiments, the refrigerant circuit may include a first heat exchanger and a second heat exchanger. The second heat exchanger may be configured to output a high-pressure refrigerant in a liquid state. In some aspects, the second heat exchanger may be a condenser. The refrigerant circuit may further include an expansion device (e.g., an expansion valve or a capillary) that may receive the refrigerant from the second heat exchanger. Hereinafter, in the present disclosure, the expansion device is referred to as expansion valve; however, such terminology should not be construed as limiting. The expansion valve may reduce the pressure and temperature of the received refrigerant and output a low-pressure, low-temperature refrigerant. The first heat exchanger may receive the refrigerant from the expansion valve and may output the refrigerant in a vapor state. In some aspects, the first heat exchanger may be an evaporator. In some aspects, the evaporator may include a fan that may draw heat from ambient environment/air and may blow hot air towards the refrigerant received from the expansion valve, thereby heating and vaporizing the refrigerant. The refrigerant circuit may further include a compressor that may receive the refrigerant from the first heat exchanger and output the refrigerant in high pressure, high temperature vapor state. The second heat exchanger may receive the refrigerant from the compressor, thus completing the vapor compression cycle.

As will be appreciated, the refrigerant circuit may additionally include a reversing valve, which may reverse the flow of refrigerant described above based on a mode of operation of the refrigerant system/circuit. For the sake of simplicity, a single flow direction of the refrigerant is described above.

It is known that ice forms on the first heat exchanger/evaporator when the refrigerant system operates in a moist environment and the evaporator temperature is equivalent to or less than a threshold value, which may be, for example, zero degree Celsius (32 degrees Fahrenheit) or when the ambient temperature is less than or equivalent to 6-7 degrees Celsius. Ice works as an insulation layer between the ambient air and the evaporator, and hence reduces the heat flow from ambient air to the refrigerant included in the evaporator when ice is formed on the evaporator. This may reduce the capability of the evaporator to effectively draw heat from the ambient air, thus reducing the capability of the evaporator to effectively heat and vaporize the refrigerant. This in turn may reduce the refrigerant system's efficiency or coefficient of performance (COP). A COP is typically defined as a ratio of the thermal power output by the refrigerant circuit and an electric energy input into the refrigerant system or electric energy required to operate the refrigerant system.

When ice is formed on the evaporator, the evaporator may be “defrosted” to remove or melt the ice. The evaporator may be de-frosted by many known methods, for example, by reversing the refrigeration cycle or reversing the flow of refrigerant in the refrigerant circuit via the reversing valve, using a hot gas bypass defrost or bypassing a refrigeration cycle, and/or the like. It is known that the refrigerant system ceases to operate or operates in a less optimal manner (e.g., instead of transferring heat into the home, the refrigerant system transfers heat from the home to outside or transfers less heat into the home, when the refrigerant system is an HVAC unit) when the evaporator is defrosted or executes a “defrost cycle”. The stopping or less optimal operation of the refrigerant system operation affects the refrigerant system's efficiency/COP. Therefore, it is important to defrost the evaporator at an optimal time or a right time, which is not too early or too late. If the evaporator is defrosted early, energy may be wasted on unnecessary defrosting (which may affect the refrigerant system's COP). On the other hand, if defrosting is performed late, the refrigerant system operates relatively long with a low COP as the evaporator is not able to effectively heat and vaporize the refrigerant. Consequently, irrespective of whether the evaporator is defrosted earlier or later than the optimal or “right” time, the refrigerant system's COP may get negatively affected. Therefore, it is important to initiate the defrost cycle of the evaporator at the right time.

The controller may be configured to determine an optimal defrosting time for the evaporator based on inputs/parameters measured by and obtained from the sensor unit. In some aspects, the parameters measured by the sensor unit may include an amount of electric energy input into the refrigerant system or required to operate the refrigerant system, an amount of thermal energy output from the refrigerant system, an ambient temperature, an evaporator temperature, a condenser temperature, an ambient pressure value, an ambient humidity level, and/or the like.

In some aspects, the controller may implement one or more different approaches/methods to determine the optimal time to defrost the evaporator. In a first exemplary approach, the controller may determine a real-time COP of the refrigerant system based on the real-time amount of electric energy input into the refrigerant system or required to operate the refrigerant system and the real-time amount of thermal energy output from the refrigerant system. The controller may further monitor the electric energy input and the thermal energy output to/from the refrigerant system since a predefined start time (which may be, e.g., an initiation time of a previous defrost cycle) and calculate (and continuously update) an average COP of the refrigerant system based on the monitoring.

The controller may further compare the real-time COP and the average COP when the refrigerant system may be operating in a normal/heat mode (i.e., not already executing a defrost cycle). The controller may determine the optimal defrosting time for the evaporator as the time when the real-time COP becomes equivalent to the average COP. Stated another way, the controller may initiate a new defrost cycle of the evaporator when the real-time COP becomes equivalent to the average COP. As described above, in an exemplary aspect, the controller calculates the average COP since the initiation time of a previous defrost cycle.

In a second exemplary approach, the controller may determine the real-time COP when the ambient temperature may be equivalent to or less than a predefined threshold temperature (e.g., six or seven degree Celsius) or when the evaporator temperature may be equivalent to or less than 0 degree Celsius, and when the refrigerant system may be operating in the normal/heat mode. In the second exemplary approach, the controller may determine the real-time COP based on a mapping of a plurality of COPs with a plurality of environmental conditions (which may be pre-stored in a system memory). In this case, the controller may correlate the real-time ambient environmental conditions measured by the sensor unit with the mapping stored in the system memory and may determine the real-time COP based on the correlation.

Further, in this case, the controller may compare the real-time COP with a threshold or expected COP value of the refrigerant system at the real-time ambient environmental conditions and may initiate the new defrost cycle when the real-time COP becomes less than the threshold COP value.

In a third exemplary approach, the controller may determine a real-time opening percentage of the expansion valve with an expected opening percentage of the expansion valve at the real-time ambient environmental conditions and may initiate the new defrost cycle when the real-time opening percentage becomes less than the expected opening percentage. In this case, the expansion valve may be an adjustable valve that may adjust its orifice diameter based on parameters such as amount of heat transfer (from ambient air) at the evaporator, desired water temperature from the refrigerant system/water heating system, the real-time COP of the refrigerant circuit, and/or the like. It is known that the expansion valve starts to close or decrease its orifice diameter when the heat transfer from ambient air at the evaporator decreases, e.g., when ice starts to form at the evaporator. The controller may use this phenomenon to determine the time when ice starts to form at the evaporator, and hence determine the optimal time to defrost the evaporator.

The controller may be further configured to determine an optimal time duration for the defrost cycle based on parameters such as ambient temperature/pressure/humidity level, an amount of ice present on the evaporator, and/or the like and may cause the refrigerant system to execute the defrost cycle for the optimal time duration.

The present disclosure describes a refrigerant system that executes a defrost cycle for an evaporator at an optimal time, thereby ensuring that the system's COP is not considerably reduced/affected. The refrigerant system optimizes the defrost cycle initiation time, the time duration and the termination of the defrost cycle to maximize the heating output as well as the overall performance of the refrigerant system.

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 heating water with a heat pump/refrigerant circuit or providing cool or hot air via an HVAC unit. The present disclosure, however, is not so limited, and can be applicable in other contexts. 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 heating water with a heat pump/refrigerant circuit or providing cool or hot air via an HVAC unit, it will be understood that other implementations can take the place of those referred to.

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 methods 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.

Turning now to the drawings, FIG. 1 depicts a block diagram of an example refrigerant system 100 (or a refrigeration system) in accordance with one or more embodiments of the present disclosure. While describing FIG. 1, references will be made to FIG. 2. In some aspects, the refrigerant system 100 may be part of a water heating system. In other aspects, the refrigerant system 100 may be part of a Heating, Ventilation, and Air Conditioning (HVAC) unit, commercial refrigerant systems such as cooled warehouses or supermarket coolers, or the like. The description below is described in the context of the refrigerant system 100 being part of a water heating system; however, the application area of the refrigerant system 100 should not be construed as limited only to a water heating system.

The refrigerant system 100 may include a plurality of components including, but not limited to, a refrigerant circuit 102, a controller 104, a sensor unit 106, and/or the like, which may be communicatively coupled with each other.

The refrigerant circuit 102 may be a heat pump assembly that may form a vapor compression cycle system. The refrigerant circuit 102 may include a first heat exchanger 108, a compressor 110, a second heat exchanger 112 and an expansion device 114 (hereinafter referred to as expansion valve 114) connected in series by refrigerant tubing 116 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 110, through the second heat exchanger 112, through the expansion valve 114, through the first heat exchanger 108, and back to an inlet of the compressor 110.

In some aspects, the refrigerant circuit 102 may additionally include a reversing valve (not shown) through which the flow of refrigerant shown in FIG. 1 and described above may be reversed. Depending on the mode of operation in which the refrigerant system 100 may be operating, the flow of refrigerant may be reversed. Consequently, the flow of refrigerant depicted in FIG. 1 should not be construed as limiting.

The refrigerant may be selected from a variety of materials. The refrigerant may be any material capable of supplying favorable thermodynamic properties to a cooling system. The refrigerant, for example, may be selected based on a desired boiling point, a high heat of vaporization, a moderate liquid density, a high critical temperature, and/or other aspects. Accordingly, the refrigerant may be any chlorofluorocarbon, chlorofluoroolefin, hydrochlorofluorocarbon, hydrochlorofluoroolefin, hydrofluorocarbon, hydrofluoroolefin, hydrochlorocarbon, hydrochloroolefin, hydrocarbon, hydroolefin, perfluorocarbon, perfluoroolefin, perchlorocarbon, perchloroolefin, halon, or haloalkane. For example, the refrigerant may be any refrigerant designated as such by, and compliant with, the standards, rules, and regulations set forth by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) (e.g., ASHRAE Standard 34-2019). For example, the refrigerant may be R-410A or R-134a. In some embodiments, the refrigerant may be or may include a hydrofluoroolefin, such as HFO-1234yf or blends thereof, including R-454B.

In the exemplary embodiment depicted in FIG. 1, the first heat exchanger 108 may be an evaporator (having evaporator coils, not shown) and the second heat exchanger 112 may be a condenser. Hereinafter, the first heat exchanger 108 is referred to as evaporator 108, and the second heat exchanger 112 is referred to as condenser 112.

The compressor 110 may be configured to output the refrigerant in vapor state towards the condenser 112, via the refrigerant tubing 116. The refrigerant output from the compressor 110 may be at high temperature and high pressure state. The condenser 112 may receive the refrigerant from the compressor 110 via the refrigerant tubing 116 and may convert the refrigerant into liquid state. In some aspects, the heat dissipated by the condenser 112 while changing the refrigerant phase from vapor to liquid may be used to heat water (e.g., when the refrigerant system 100 may be part of a water heating system).

The condenser 112 may output the refrigerant in liquid state towards the expansion valve 114, via the refrigerant tubing 116. The refrigerant output from the condenser 112 may be at high pressure and medium-to-high temperature state. The expansion valve 114 may receive the refrigerant from the condenser 112 and may output the refrigerant in low pressure, low temperature state towards the evaporator 108 via the refrigerant tubing 116. The refrigerant output from the expansion valve 114 may be in a mixture of liquid and vapor states.

The evaporator 108 may receive the refrigerant from the expansion valve 114 and may convert the refrigerant into low pressure, vapor state refrigerant. The evaporator 108 may include a fan (not shown) that may draw air from ambient environment and blow it towards the evaporator 108. The evaporator 108 may draw heat/warmth from the air that is received from the fan, and may transfer the warmth towards the refrigerant received from the expansion valve 114, thereby vaporizing the refrigerant. The evaporator 108 may output the refrigerant in vapor state towards the compressor 110 via the refrigerant tubing 116. The compressor 110 may receive the refrigerant from the evaporator 108 and may “compress” the refrigerant to output the refrigerant in high pressure, high temperature state, as described above. In some aspects, the compressor 110 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 112 when the refrigerant system 100 is part of a water heating system.

The compressor 110 may be of any type. For example, the compressor 110 may be a positive displacement compressor, a reciprocating compressor, a rotary screw compressor, a rotary vane compressor, a rolling piston compressor, a scroll 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. The example compressors described here may be controlled by an inverter, or may operate at a fixed speed.

As described above, the evaporator 108 may include a fan that that may draw air from ambient environment and blow it towards the evaporator 108. The evaporator 108 may draw heat/warmth from the air that is received from the fan, and may transfer the warmth towards the refrigerant received from the expansion valve 114, thereby vaporizing the refrigerant. It is known that when the refrigerant system 100 operates in a moist environment (i.e., having presence of water vapors in air) with ambient temperatures equivalent to or less than 6 or 7 degree Celsius temperature (e.g., 43 degrees Fahrenheit) or evaporator temperature less than or equivalent to 0 degree Celsius, ice is formed on the evaporator 108 or evaporator coils. Ice works as an insulation layer between the ambient air and the evaporator 108, and as such, reduces the heat flow from ambient air to the refrigerant included in the evaporator 108. This may reduce the capability of the evaporator 108 to effectively draw heat/warmth from the ambient air, thus reducing the capability of the evaporator 108 to effectively heat and vaporize the refrigerant. This in turn may reduce the refrigerant system's efficiency or coefficient of performance (COP). A COP is typically calculated or defined as a ratio of the thermal power output by the refrigerant circuit 102 or the thermal power/energy delivered to the condenser 112 and an electric energy input into or required to operate the refrigerant system 100 or the refrigerant circuit 102. For example, the COP may be 300% if 100 units of electric energy is input into the refrigerant system 100 and 300 units of thermal energy is delivered to the condenser 112 or output from the refrigerant system 100.

When ice is formed on the evaporator 108, the evaporator 108 may be “defrosted” to remove or melt the ice. The evaporator 108 may be de-frosted by many known methods, for example, by reversing the refrigeration cycle or reversing the flow of refrigerant in the refrigerant circuit 102 via a reversing valve (e.g., having hot refrigerant to pass through the evaporator coils to defrost). Another method is to do a hot gas bypass defrosting or bypass a refrigeration cycle. The methods to defrost the evaporator 108 described herein should not be construed as limiting, and any known methods of defrosting may be implemented on the evaporator 108 to remove or melt the ice formed on the evaporator 108.

In some aspects, the refrigerant circuit 102/refrigerant system 100 ceases operation or operates in a less optimal manner (e.g., instead of transferring heat into the home, the refrigerant system transfers heat from the home to outside or transfers less heat into the home, when the refrigerant system is an HVAC unit) when the evaporator 108 is defrosted or when the refrigerant circuit 102 executes a “defrost cycle”. This leads to loss of cooling or heating power of the refrigerant system 100. Further, defrosting generally uses energy (e.g., to activate the reversing valve), which effectively lowers the refrigerant system's efficiency/COP. Consequently, it is important to defrost the evaporator 108 at an optimal time or a right time, which is not too early or too late. If the evaporator 108 is defrosted early, energy may be wasted on unnecessary defrosting (which may affect the refrigerant system's COP). Further, in this case, the refrigerant system 100 may cease operation earlier than needed, which may be undesirable. On the other hand, if defrosting is performed late, the refrigerant system 100 operates relatively long with a low COP as the evaporator 108 is not able to effectively heat and vaporize the refrigerant. Consequently, irrespective of whether the evaporator 108 is defrosted earlier or later than the optimal or “right” time, the refrigerant system's COP may get negatively affected. Therefore, it is important to initiate the defrost cycle of the evaporator 108 at the right time.

In some aspects, the controller 104 may be configured to determine the optimal or right time to defrost the evaporator 108 and initiate the evaporator's defrost cycle at the determined optimal time, based on inputs obtained from the sensor unit 106. The sensor unit 106 may include a plurality of sensors including, but not limited to, temperature sensors, humidity sensors, energy measurement sensors, and/or the like. Some sensors of the sensor unit 106 may be included in the refrigerant circuit 102, and remaining sensors may be disposed outside of the refrigerant circuit 102. The sensor unit 106 may be configured to measure one or more parameters associated with refrigerant system 100, the refrigerant circuit 102, and the ambient environment where the refrigerant system 100 may be installed/operating. Examples of such parameters measured by the sensor unit 106 include, but are not limited to, an amount of electric energy input into the refrigerant system 100 or required to operate the refrigerant system 100, an amount of thermal energy delivered to the condenser 112, an ambient temperature, an ambient pressure, an evaporator temperature, a condenser temperature, an ambient humidity level, and/or the like.

The controller 104 may be configured to implement one or more different methods to determine the optimal or right time to defrost the evaporator 108 based on the parameters measured by the sensor unit 106. Examples of such methods are described below, which should not be construed as limiting.

In a first exemplary embodiment for determining an optimal defrosting time for the evaporator 108, the controller 104 may first determine that the refrigerant system 100 is operating in a heat mode or a normal mode (i.e., in a non-defrost mode). Stated another way, the controller 104 may first determine that the evaporator 108 is not already getting defrosted or is not in the middle of a defrosting cycle. Responsive to determining that the refrigerant system 100 is operating in the heat/normal mode, the controller 104 may determine/calculate a real-time COP associated with the refrigerant circuit 102 or the refrigerant system 100 based on the parameters measured by the sensor unit 106. In the first exemplary embodiment, the controller 104 may determine the real-time COP by calculating a ratio of the real-time thermal power output by the refrigerant circuit 102 or the thermal power/energy delivered to the condenser 112 and a real-time electric energy input into or required to operate the refrigerant system 100 or the refrigerant circuit 102.

In addition to determining the real-time COP, the controller 104 may be configured to monitor the thermal power/energy delivered to the condenser 112 and the electric energy input into the refrigerant system 100 or the refrigerant circuit 102 since a predefined start time. The predefined start time may be an initiation time of a previous defrost cycle of the refrigerant circuit 102/evaporator 108, or any other time in the past. For example, the controller 104 may monitor the thermal power/energy delivered to the condenser 112 and the electric energy input into the refrigerant system 100 or the refrigerant circuit 102 since the past 30 minutes or 60 minutes (e.g., a time duration during which the ambient environment conditions are expected to remain substantially the same).

Responsive to monitoring the energy values described above, the controller 104 may calculate (and continuously update) an average COP associated with the refrigerant system 100/refrigerant circuit 102 since the predefined start time, based on the monitoring. The controller 104 may further continuously compare the real-time COP with the average COP when the refrigerant system 100 may be operating in the heat/normal mode. The controller 104 may determine the optimal time to defrost the evaporator 108 as the time when the real-time COP becomes equivalent to the average COP. An example graph depicting a real-time COP curve 202 and an average COP curve 204 with time is shown in FIG. 2. In the graph depicted in FIG. 2, the Y-axis depicts the COP associated with the refrigerant system 100/refrigerant circuit 102, and the X-axis depicts time.

The graph depicted in FIG. 2 is an example of a COP during and after a reverse cycle defrost, where heat is drawn from the home in order to melt the ice. This leads to negative COP, as shown in FIG. 2. In an alternative aspect (not shown), when the refrigerant system 100 performs hot gas bypass defrosting, the COP becomes low during the defrosting operation; however, it does not become negative.

In an exemplary aspect, referring to the graph depicted in FIG. 2, the evaporator's previous defrost cycle may have been initiated at time T=0 and may have lasted till time T=T1. As described above, since the refrigerant system 100 ceases to operate during the defrost cycle and the refrigerant system 100 consumes energy during this time duration, the real-time COP associated with the refrigerant system 100/refrigerant circuit 102 may reduce substantially when the evaporator 108 is defrosting, as apparent from the real-time COP curve 202 between the time T=0 and time T=T1. During this time duration, the average COP of the refrigerant system 100 may also reduce, as apparent from the average COP curve 204 between the time T=0 and time T=T1.

Between the time duration of time T=0 and time T=T1, the ice formed on the evaporator 108 may have melted. When the previous defrost cycle stops (or would have stopped, i.e., at the time T=T1) and the refrigerant system 100 resumes operation in the normal/heat mode, the real-time COP curve 202 starts to quickly increase and gradually reaches to its maximum value at time T=T2. Between the time duration of time T=T1 and time T=T2, the average COP also gradually increases, as apparent from the average COP curve 204 between the time T=T to time T=T2.

At time T=T2, the real-time COP may start to gradually decrease. Further, after time T=T2, the average COP may continue to increase slightly or may start to become stable/flat. At time T=T3, the real-time COP may become equivalent to the average COP, or the real-time COP curve 202 may intersect with the average COP curve 204. In some aspects, the time T=T3, at which the real-time COP becomes equivalent to the average COP, may be the optimal time to initiate a new defrost cycle of the evaporator 108/refrigerant circuit 102. The rationale of this method/approach for determining the optimal time to defrost the evaporator 108 is provided below.

During a defrost cycle (i.e., between the times T=0 and T=T1), energy is supplied to the refrigerant system 100 while there is little or even negative heat production in the condenser 112. Therefore, during and shortly after the defrost cycle, the average COP since defrost initiation is very low or negative. After termination of the defrost cycle (i.e., at time T=T1), when system's normal operation starts, the real-time COP starts to quickly increase. After some time, new ice starts to grow on the evaporator 108 and the real-time COP decreases. When the real-time COP becomes equivalent to the average COP (i.e., at time T=T3) in the system's normal operational mode, the average COP since previous defrost initiation is at its maximum value. Initiating a new defrost cycle before this moment (i.e., before time T=T3) may give a lower average COP, because relatively much energy will be lost to defrost cycles as compared to useful heat production. Therefore, initiating the new defrost cycle before time T=T3 is not desirable. On the other hand, initiating the new defrost cycle after time T=T3 may decrease the long-time average COP of the refrigerant system 100, as the real-time COP will be lower than average due to the effects of ice and this will reduce the long-time average COP. Therefore, time T=T3 may be the optimal time to initiate the new defrost cycle of the evaporator 108/refrigerant circuit 102.

Responsive to determining that the real-time COP is equivalent to the average COP (i.e., at time T=T3), the controller 104 may initiate the new defrost cycle of the refrigerant circuit 102 (e.g., by transmitting a command signal to the reversing valve to reverse the flow of refrigerant or by using any other known defrosting method). As described above, the controller 104 initiates the new defrost cycle to remove/melt the ice formed on the evaporator 108 after time T=T1 (i.e., after the termination of the previous defrost cycle). The controller 104 may follow the same process as described above for initiating subsequent defrost cycles.

Although the description above describes an aspect where the controller 104 determines the optimal defrosting time for the evaporator 108 by comparing the real-time COP with the average COP, the present disclosure is not limited to such an aspect. In additional or alternative aspects, the controller 104 may compare the real-time thermal output of the refrigerant system 100 with the average thermal output since the last defrost initiation, and initiate a new defrost at the moment when the average thermal output is equivalent to the real-time thermal output.

When the controller 104 compares COPs, the average COP is maximized; however, when the controller 104 compares real-time and average thermal output, the average thermal output is maximized.

In a second exemplary embodiment for determining an optimal defrosting time for the evaporator 108, the controller 104 may determine the real-time COP associated with the refrigerant circuit 102/refrigerant system 100 as is determined in the first exemplary embodiment; however, the method of determining the real-time COP is different in the second exemplary embodiment, as described below.

In some aspects, in addition to the components described above, the refrigerant system 100 may further include a memory (shown as memory 310 in FIG. 3), which may or may not be part of the controller 104. The memory may be configured to store a first mapping of a plurality of COP values associated with the refrigerant circuit 102 with a plurality of parameters. The examples of the parameters may be, but are not limited to, ambient temperature values, evaporator temperature values, condenser temperature values, ambient humidity level values, ambient pressure values, and/or the like. The first mapping may be provided and stored in the memory by the refrigerant circuit manufacturer.

The memory may be further configured to store a second mapping of a plurality of expected COP values in no-frost conditions (i.e., when no ice is formed on the evaporator 108) with a plurality of ambient temperature values. The second mapping may also be provided and stored in the memory by the refrigerant circuit manufacturer.

In some aspects, to determine the optimal defrosting time for the evaporator 108, the controller 104 may first determine that the refrigerant system 100/refrigerant circuit 102 is operating in a normal/heat mode (i.e., not already undergoing a defrost cycle). The controller 104 may additionally determine that the ambient temperature is equivalent to or less than a threshold temperature (e.g., close to 0 degree Celsius). The controller 104 may determine the ambient temperature based on parameters/inputs measured by and obtained from the sensor unit 106.

Responsive to determining that the ambient temperature is equivalent to or less than the threshold temperature and the refrigerant circuit 102 is operating in the normal/heat mode, the controller 104 may fetch the first mapping and the second mapping from the memory. The controller 104 may further correlate the first mapping with the real-time system and/or environmental parameters measured by the sensor unit 106 and determine the real-time COP of the refrigerant circuit 102 based on the correlation. For example, the controller 104 may correlate the real-time ambient temperature, the real-time evaporator temperature, the real-time condenser temperature, the real-time ambient humidity level, and/or the like measured by the sensor unit 106 with the first mapping to determine the real-time COP of the refrigerant circuit 102. The controller 104 may further correlate the real-time ambient temperature with the second mapping to determine an “expected” COP (or a “threshold COP value”) of the refrigerant circuit 102 in no-frost conditions at the real-time ambient temperature.

Responsive to determining the real-time COP and the threshold COP value, the controller 104 may compare the real-time COP with the threshold COP value. The controller 104 may determine the optimal defrosting time for the evaporator 107 as the time when the real-time COP becomes equivalent to or is less than the threshold COP value. Stated another way, the controller 104 may initiate the new defrost cycle when the real-time COP is equivalent to or less than the threshold COP value.

In alternative aspects, similar to the first exemplary embodiment described above, in the second exemplary embodiment also, the real-time COP may be determined/calculated based on actual measurements of the heating capacity/output of the refrigerant system 100 and the power consumption of the refrigerant system 100 (as opposed to using the first mapping stored in the memory). In this case, the controller 104 may determine the heating capacity either on the refrigerant side or the water side (or the air side, in the case of an air-to-air system) of the water heating system, e.g., by means of flow rate and inlet/outlet condition measurements. The controller 104 may determine the power consumption by means of current and voltage measurements. As described above, the real-time COP may be the ratio of the heating capacity and the power consumption. In this case also, the controller 104 may compare the real-time COP with the threshold COP value and initiate the new defrost cycle when the real-time COP is less than or equivalent to the threshold COP value.

In some aspects, in addition to determining the optimal defrosting time as described above, the controller 104 may be configured to determine an optimal time duration (e.g., an optimal length of time) for which the defrost cycle may be executed for the evaporator 108. The controller 104 may determine the optimal time duration based on one or more of the real-time ambient temperature, the real-time ambient pressure value, the real-time time humidity level, an amount of ice on the evaporator 108, a difference between the real-time COP and the threshold COP value, and/or the like. In one exemplary aspect, the memory may store a third mapping between one or more parameters described above and optimal time durations for defrosting the evaporator 108, and the controller 104 may determine the optimal time duration by correlating the real-time parameters measured by the sensor unit 106 and the third mapping. In a second exemplary aspect, the controller 104 may determine the optimal time duration such that the real-time COP becomes equivalent to or more than the threshold COP value.

Responsive to determining the optimal time duration as described above, the controller 104 may cause the refrigerant circuit 102 to operate in the defrost cycle for the optimal time duration.

In a third exemplary embodiment for determining the optimal defrosting time for the evaporator 108, the controller 104 may determine the optimal defrosting time based on an opening percentage of the expansion valve 114. In some aspects, the expansion valve 114 may be an adjustable valve that may adjust its orifice diameter (which may vary from 3 to 6 mm) based on parameters such as amount of heat transfer (from ambient air) at the evaporator 108, desired water temperature from the refrigerant system 100/water heating system, the real-time COP of the refrigerant circuit 102, and/or the like. In an exemplary aspect, the expansion valve 114 may start to close or decrease its orifice diameter when the heat transfer from ambient air at the evaporator 108 decreases, e.g., when ice starts to form at the evaporator 108, to maintain the same superheat value.

The controller 104 may implement the third exemplary embodiment in addition to or alternative to the first exemplary embodiment or the second exemplary embodiment described above. In the third exemplary embodiment, the controller 104 may first determine a real-time opening percentage of the expansion valve 114 when the refrigerant system 100 is operating in the heat/normal mode (i.e., not already executing a defrost cycle). The controller 104 may determine the real-time opening percentage based on inputs obtained from the sensor unit 106 or inputs obtained directly from the expansion valve 114.

Responsive to determining the real-time opening percentage, the controller 104 may compare the real-time opening percentage with a threshold opening percentage and initiate the new defrost cycle when the real-time opening percentage may be less than the threshold opening percentage. In some aspects, the threshold opening percentage may be based on ambient temperature, ambient pressure value and/or ambient humidity level. In this case, the memory may store a fourth mapping between a plurality of expected opening percentages of the expansion valve 114 with a plurality of different ambient temperatures/pressure values/humidity levels (in no-frost conditions), and the controller 104 may correlate the real-time ambient temperature/pressure value/humidity level (as measured by the sensor unit 106) with the fourth mapping to determine the threshold opening percentage at the real-time ambient temperature/pressure value/humidity level.

In some aspects, the monitoring of the opening percentage of the expansion valve 114, as described above, is extremely beneficial when the refrigerant circuit 102/controller 104 has the ability to vary the speed of the compressor 110. In this context, the controller 104 may first decrease the compressor speed with the goal to keep the real-time COP above the threshold COP value. When the real-time COP drops below the threshold COP value (because the compressor speed cannot be decreased further), the same defrost process, as described above, may start. This particular algorithm has the advantage to further minimize the number of times the refrigerant circuit 102 needs to go into a full defrost mode.

In some aspects, the controller 104 may initiate the defrost cycle of the evaporator 108 when either of the conditions described above in the first, second or third exemplary embodiments are satisfied.

FIG. 3 depicts a block diagram of the controller 104 in accordance with one or more embodiments of the present disclosure. The controller 104 may include a plurality of components including, but not limited to, a processor 305, a memory 310, and a communication interface 315. The controller 104 may be a computing device configured to receive data, determine actions based on the received data (e.g., the inputs obtained from the sensor unit 106) and output a control signal instructing one or more refrigerant circuit 102 components (e.g., the reversing valve) to perform one or more actions (e.g., defrost the evaporator 108).

In some aspects, the controller 104 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 refrigerant system application. The hard-wired signals can include communication signals between any directly wired connections between the controller 104 and other refrigerant system components. For example, the controller 104 can have a hard-wired 24 Volts Direct Current (VDC) connection to the sensors included in the sensor unit 106 described above.

Alternatively, the controller 104 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 refrigerant system application, such as Modbus, fieldbus, PROFIBUS, SafetyBus, Ethernet/IP, and/or the like. Furthermore, the controller 104 can utilize a combination of wireless, hard-wired, and analog or digital communication signals to communicate with and control the various refrigerant system 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 refrigerant system application.

The memory 310 may be configured to store a program and/or instructions associated with the functions and methods described herein. The processor 305 may be configured to execute the program and/or instructions stored in the memory 310. The memory 310 can include one or more suitable types of memory (e.g., volatile or non-volatile 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 310.

The communication interface 315 may be configured to send or receive communication signals between the various refrigerant system components. The communication interface 315 can include hardware, firmware, and/or software that allows the processor 305 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 315 can also provide access to a cellular network, the Internet, a local area network, or another wide-area network as suitable for the particular refrigerant system application.

Additionally, the controller 104 may have or be in communication with a user interface (not shown) for receiving inputs from a refrigerant system user. The user interface may be installed locally on the refrigerant system 100.

The function of the controller 104 is already described above in conjunction with FIGS. 1 and 2, and hence is not described again here for the sake of simplicity and conciseness.

FIG. 4 depicts a flow diagram of an example first method 400 to defrost the evaporator 108 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 104, the real-time COP based on one or more methods described above in the context of the first and second exemplary embodiments for determining the optimal defrosting time. In some aspects, the controller 104 may determine the real-time COP when the refrigerant system 100 may be operating in the normal/heat mode (i.e., not implementing a defrost cycle). In further aspects, the controller 104 may determine the real-time COP when the ambient temperature may be less than or equivalent to a threshold temperature (e.g., 6-7 degree Celsius) or when the evaporator temperature may be equivalent to or less than 0 degree Celsius.

At step 406, the method 400 may include determining, by the controller 104, the average COP, as described above in the context of the first exemplary embodiment for determining the optimal defrosting time. At step 408, the method 400 may include determining, by the controller 104, that the real-time COP is equivalent to the average COP when the refrigerant system 100 is operating in the normal/heat mode. At step 410, the method 400 may include initiating, by the controller 104, a new defrost cycle of the evaporator 108 responsive to determining that the real-time COP is equivalent to the average COP.

The method 400 may stop at step 412.

FIG. 5 depicts a flow diagram of an example second method 500 to defrost the evaporator 108 in accordance with one or more embodiments of the present disclosure. FIG. 5 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 500 may start at step 502. Step 504 may be the same as the step 404 described above in conjunction with the method 400. At step 506, the method 500 may include determining, by the controller 104, the threshold COP value as described above in the context of the second exemplary embodiment for determining the optimal defrosting time.

At step 508, the method 500 may include determining, by the controller 104, that the real-time COP is less than the threshold COP value. At step 510, the method 500 may include initiating, by the controller 104, a new defrost cycle of the evaporator 108 responsive to determining that the real-time COP is less than the threshold COP value.

The method 500 may stop at step 512.

FIG. 6 depicts a flow diagram of an example third method 600 to defrost the evaporator 108 in accordance with one or more embodiments of the present disclosure. FIG. 6 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 600 may start at step 602. At step 604, the method 600 may include determining, by the controller 104, the real-time opening percentage of the expansion valve 114, as described above in the context of the third exemplary embodiment for determining the optimal defrosting time. At step 606, the method 600 may include determining, by the controller 104, the threshold opening percentage for the ambient temperature/pressure/humidity level at which the refrigerant system 100 may be operating. At step 608, the method 600 may include determining, by the controller 104, that the real-time opening percentage is less than the threshold opening percentage. At step 610, the method 600 may include initiating, by the controller 104, a new defrost cycle of the evaporator 108 responsive to determining that the real-time opening percentage is less than the threshold opening percentage.

The method 600 may stop at step 612.

In some aspects, the steps described above in conjunction with FIGS. 4, 5 and 6 may be performed independent of each other, or some or all of the steps may be performed in conjunction with each other. For example, some or all of the steps described for FIG. 6 may be performed in conjunction with the steps described for FIG. 4 or 5.

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 the present 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.

It should also be understood that the word “example” as used herein is intended to be non-exclusionary 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.

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.

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.

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 articles such 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.