METHOD OF TRIGGERING DEFROST
A method for determining when to initiate a defrost mode of a heat pump includes monitoring a heating capacity of a heat exchanger of the heat pump during operation of the heat pump in a heating mode, initiating the defrost mode when the heating capacity of the heat exchanger is less than or equal to a reduced defrost threshold when a capacity demand of the heat exchanger is less than a maximum capacity demand, and initiating the defrost mode when the heating capacity of the heat exchanger is less than or equal to a maximum defrost threshold when the capacity demand of the heat exchanger is equal to the maximum capacity demand.
This application claims the benefit of U.S. Application No. 63/494,936, filed Apr. 7, 2023, the contents of which are incorporated by reference herein in their entirety.
BACKGROUNDEmbodiments of the present disclosure pertain to the art of heating, ventilation, and air conditioning (HVAC) systems, and more particularly, to a defrost cycle of an HVAC system.
Heat pumps are used in a variety of settings, for example, in heating, ventilation, and air conditioning (HVAC) systems that provide a desired air temperature in a facility. Such heat pumps commonly include a compressor, evaporator, expansion device, and condenser. The heat pumps input work to the refrigerant, e.g., by driving the compressor, thereby enabling the refrigerant to move heat from a colder heat reservoir to a warmer heat sink.
Some heat pumps are provided as “split” systems, having a first heat exchanger arranged inside of the building to be conditioned and a second heat exchanger located outside of the building to be conditioned. When such a heat pump operates in a heating mode, the second heat exchanger operating as an evaporator is disposed outside the building. “Frosting” of the evaporator is a common problem seen in such heat pump split systems. Frosting is caused by moisture accumulation on the evaporator when the evaporator temperature is at or below freezing, for example, at or below 0° C. Accumulation of frost obstructs the flow of air through the evaporator and reduces heat transfer between the evaporator and the air flowing through, both of which reduce operating efficiency.
Frost may be removed by performing periodic defrost cycles. A defrost cycle typically proceeds by reversing the flow of the refrigerant in the heat pump, such that the condenser and evaporator conceptually exchange roles. The result is that the refrigerant warms the evaporator, thereby eliminating, or at least reducing, any accumulated frost.
Existing heat pumps typically perform a defrost cycle in response to a transition decision based on one or more control parameters. This transition decision may be based on the capacity of the evaporator, which typically reduces as frost accumulates thereon. Once the requested capacity of the evaporator is maximized, an auxiliary heater is typically relied upon to compensate for lost heat pump capacity.
BRIEF DESCRIPTIONAccording to an embodiment, a method for determining when to initiate a defrost mode of a heat pump includes monitoring a heating capacity of a heat exchanger of the heat pump during operation of the heat pump in a heating mode, initiating the defrost mode when the heating capacity of the heat exchanger is less than or equal to a reduced defrost threshold when a capacity demand of the heat exchanger is less than a maximum capacity demand, and initiating the defrost mode when the heating capacity of the heat exchanger is less than or equal to a maximum defrost threshold when the capacity demand of the heat exchanger is equal to the maximum capacity demand.
In addition to one or more of the features described herein, or as an alternative, further embodiments monitoring the heating capacity of the heat exchanger further comprises monitoring at least one parameter or operating condition of the heat pump associated with the heating capacity.
In addition to one or more of the features described herein, or as an alternative, further embodiments the at least one parameter or operating condition is a refrigerant mass flow.
In addition to one or more of the features described herein, or as an alternative, further embodiments the at least one parameter or operating condition comprises a temperature of an air discharged from the heat exchanger.
In addition to one or more of the features described herein, or as an alternative, further embodiments the at least one parameter or operating condition comprises at least one of a pressure at an outlet of the heat exchanger, a pressure at an inlet of a compressor arranged directly downstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, and a pressure between the outlet of the heat exchanger and the inlet of the compressor.
In addition to one or more of the features described herein, or as an alternative, further embodiments the at least one parameter or operating condition comprises at least one of a pressure at an inlet of the heat exchanger, a pressure at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, and a pressure between the outlet of the expansion device and the inlet of the heat exchanger.
In addition to one or more of the features described herein, or as an alternative, further embodiments the at least one parameter or operating condition comprises a temperature at an inlet of the heat exchanger, at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, or between the outlet of the expansion device and the inlet of the heat exchanger.
According to an embodiment, a system for conditioning air includes a refrigeration circuit including a compressor, and expansion valve, and a heat exchanger. A controller is configured to transition the refrigeration circuit between operation in a heating mode and a defrost mode. The controller is configured to transition the refrigeration circuit from the heating mode to the defrost mode in response to a heating capacity of the heat exchanger reaching a first defrost threshold when the capacity demand of the heat exchanger is less than the maximum capacity demand. The controller is also configured to transition the refrigeration circuit from the heating mode to the defrost mode in response to the heating capacity of the heat exchanger reaching a second defrost threshold when the capacity demand of the heat exchanger is equal to the maximum capacity demand.
In addition to one or more of the features described herein, or as an alternative, further embodiments including at least one sensor operably coupled to the controller, the at least one sensor being configured to monitor at least one parameter or operating condition of the system associated with the heating capacity.
In addition to one or more of the features described herein, or as an alternative, further embodiments the at least one parameter or operating condition is a refrigerant mass flow.
In addition to one or more of the features described herein, or as an alternative, further embodiments the at least one parameter or operating condition comprises a temperature of an air discharged from the heat exchanger.
In addition to one or more of the features described herein, or as an alternative, further embodiments the at least one parameter or operating condition comprises at least one of a pressure at an outlet of the heat exchanger, a pressure at an inlet of the compressor arranged directly downstream from the heat exchanger relative to a fluid flow through the system in the heating mode, and a pressure between the outlet of the heat exchanger and the inlet of the compressor.
In addition to one or more of the features described herein, or as an alternative, further embodiments the at least one parameter or operating condition comprises at least one of a pressure at an inlet of the heat exchanger, a pressure at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the system in the heating mode, and a pressure between the outlet of the expansion device and the inlet of the heat exchanger.
In addition to one or more of the features described herein, or as an alternative, further embodiments the at least one parameter or operating condition comprises a temperature at an inlet of the heat exchanger, at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, or between the outlet of the expansion device and the inlet of the heat exchanger.
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.
A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.
With reference now to
In operation, the compressor 22 receives a refrigerant vapor from the second heat exchanger 28 and compresses it to a high temperature and pressure. The relatively hot refrigerant vapor is then delivered to the first heat exchanger 24 where it is cooled and condensed to a liquid state via heat exchange relationship with a cooling medium C, such as air or water. Accordingly, when the first heat exchanger 24 receives the refrigerant output from the compressor 22, the first heat exchanger functions as a condenser. The cooled liquid refrigerant flows from the first heat exchanger 24 to the expansion device 26, such as an expansion valve for example, in which the refrigerant is expanded to a lower pressure where the temperature is reduced and the refrigerant may exist in a two-phase liquid/vapor state. From the expansion device 26, the refrigerant is provided to the second heat exchanger 28. Because heat is transferred from a secondary medium, such as air for example, to the refrigerant within the second heat exchanger 28, causing any refrigerant in the liquid phase to vaporize, the second heat exchanger 28 functions as an evaporator. From the second heat exchanger 28, the low-pressure vapor refrigerant returns to the compressor 22 so that the cycle may be repeated.
In embodiments where the air conditioning system 20 is a heat pump, the flow of refrigerant within the vapor compression cycle may be reversed. In such embodiments, the refrigerant may flow clockwise from the compressor 22 to the second heat exchanger 28, the expansion device 26, and the first heat exchanger 24 sequentially. In such instances, the refrigerant within the second heat exchanger 28 is cooled and condensed to a liquid state and the refrigerant within the first heat exchanger is heated to form a low-pressure vapor. Accordingly, when operating in this reverse flow direction, the second heat exchanger 28 functions as the condenser and the first heat exchanger 24 functions as the evaporator of the vapor compression cycle.
With reference now to
As shown, the at least one compressor 22 is located within the outdoor portion 32. The one or more compressors 22 may be any suitable single or multistage compressor, including, but not limited to a screw compressor, reciprocating compressor, centrifugal compressor, scroll compressor, rotary compressor or axial-flow compressor. The compressor(s) 22 may be driven by an electrically powered motor, or another suitable energy source.
The first heat exchanger 24 is also arranged within the first or indoor portion 30 and is directly or indirectly fluidly coupled to the one or more compressors 22. The first heat exchanger 24 may be any suitable type of heat exchanger configured to transfer heat between a refrigerant and air or another medium. For example, the first heat exchanger 24 may include one or more coils of thermally conductive material, such as copper, aluminum, alloys thereof, or combinations thereof. In other embodiments, the first heat exchanger 24 may be a shell- and tube heat exchanger, a printed circuit heat exchanger, a plate-fin heat exchanger, or any combination thereof. In the illustrated, non-limiting embodiment, the air or other medium is moved (drawn or blown) over the first heat exchanger 24 via a first movement mechanism 34, such as a fan for example.
The heat pump 20 includes at least one expansion device 26. Although a single expansion device 26 is illustrated, it should be understood that embodiments having a separate indoor expansion device positioned within the indoor portion and an outdoor expansion device positioned within the outdoor portion are also contemplated herein. The first heat exchanger 24 is fluidly coupled to the expansion device 26.
The second heat exchanger 28 is arranged within the second or outdoor portion 32 of the heat pump 20 and is also fluidly coupled to the expansion device 26. In embodiments including a separate indoor expansion device and outdoor expansion device 26, the first heat exchanger 24 is fluidly coupled to a first (indoor) expansion device and the second heat exchanger 28 is fluidly coupled to a second (outdoor) expansion device. In such embodiments, refrigerant is only configured to flow through one of the expansion devices in each direction of flow through the refrigeration circuit.
Similar to the first heat exchanger 24, the second heat exchanger 28 may be any suitable type of heat exchanger configured to transfer heat between a refrigerant and air or another medium. In the illustrated, non-limiting embodiment, the second heat exchanger 28 is disposed about the outer extent of the outdoor portion 32. However, embodiments where the second heat exchanger 28 is arranged at another location, such as within or proximal to the outdoor portion 32 are also contemplated herein.
The second heat exchanger 28 may have any suitable configuration. For example, the second heat exchanger 28 may include one or more coils of thermally conductive material, such as copper, aluminum, alloys thereof, or combinations thereof. In other embodiments, the second heat exchanger 28 may be a shell- and tube heat exchanger, a printed circuit heat exchanger, a plate-fin heat exchanger, or any combination thereof.
In the illustrated, non-limiting embodiment, the outdoor portion 32 includes a second movement mechanism 36, such as a fan assembly for example, to move air or another medium over the second heat exchanger 28. The second movement mechanism 36 may be arranged adjacent a top 38 of the outdoor portion 32, as shown, or may be positioned near a bottom 40 of the outdoor portion, or at any point between the top 38 and the bottom 40 to push or pull air through the outdoor portion.
The heat pump 20 additionally includes a reversing valve 42 configured to redirect the flow of refrigerant R therein. In the illustrated embodiment, the reversing valve 42 is arranged within the outdoor portion 32 and includes a fluidly separate first flow path and second flow path. In a first state, as shown in
During normal operation of the heat pump 20, the heat pump is operable in a “heating” mode (
During normal operation of the heat pump 20, frost can accumulate on the second heat exchanger 28. When frost accumulates on the second heat exchanger 28, the frost impedes heat transfer from the air to the heat exchanger and therefore provides undesirable insulating properties to the heat exchanger. The undesirable insulating properties result in an increase in the temperature difference between the temperature of the air and the temperature of the heat exchanger. As the extent and thickness of frost increases, the degree of insulating properties of the frost increases. Accordingly, the temperature of the second heat exchanger 28 will continue to decrease indefinitely as frost continues to accumulate.
As frost accumulates on the second heat exchanger 28 and the operating temperature of the second heat exchanger 28 decreases, the operating temperature of the refrigerant within the second heat exchanger 28 decreases as a result. Given a fixed amount of superheat, the density of the refrigerant vapor leaving the second heat exchanger 28 decreases as the temperature of the vapor decreases. Decreasing vapor density for a given volume flow results in decreasing refrigerant mass flow, and the heating capacity of the refrigerant system decreases. Therefore, the extent and thickness of the presence of frost will directly relate to a decrease in mass flow and heating capacity.
To eliminate, or at least mitigate, this frost, the heat pump 20 may transition to a defrost mode, such as by switching the reversing valve 42 to the second state. With the reversing valve 42 in the second state, shown in
With reference to
Existing heat pumps 20 typically transition between a heating mode in which the reversing valve 42 is in the first state and a defrost mode in which the reversing valve 42 is in the second state upon determining that the capacity of the second heat exchanger 28 is reduced. This transition, however, may result in the use of the auxiliary heater 44 before the capacity of the second heat exchanger is reduced to less than or equal to a primary or minimum defrost threshold.
To optimize the run time of the heat pump in a heating mode, the heating capacity of the second heat exchanger 28 can be monitored (directly or indirectly) during a heating cycle. A comparison of the heating capacity of the second heat exchanger 28 during operation of the heating cycle and the heating capacity of the second heat exchanger 28 when no frost is present will indicate the reduction in heating capacity due to frost accumulation on the second heat exchanger 28. The control system 50 may be operable to monitor any of the parameters associated with a reduction in capacity of the heat exchanger as described in U.S. Provisional Patent Application Ser. No. 63/288,896, filed on Dec. 13, 2021, the entire contents of which are incorporated herein by reference. Examples of the parameters that may be monitored include, but are not limited to, a temperature of an air discharged from the second heat exchanger 28, at least one of a pressure at an outlet of the second heat exchanger 28, a pressure at an inlet of a compressor 22 arranged directly downstream from the second heat exchanger 28 relative to a fluid flow through the heat pump 20 in the heating mode, and a pressure between the outlet of the second heat exchanger 28 and the inlet of the compressor 22, at least one of a pressure at an inlet of the second heat exchanger 28, a pressure at an outlet of an expansion device 26 arranged directly upstream from the second heat exchanger 28 relative to a fluid flow through the heat pump 20 in the heating mode, and a pressure between an outlet of the expansion device 26 and the inlet of the second heat exchanger 28, and a temperature at an outlet of an expansion device 26 arranged directly upstream from the second heat exchanger 28 relative to a fluid flow through the heat pump 20 in the heating mode.
The controller 52 is configured to evaluate the available heating capacity of the second heat exchanger 28 from the monitored parameter. With reference to
To further improve the operation of the heat pump and reduce the use of an auxiliary heat source such as auxiliary heater 44, in an embodiment, the control system 50 is configured to implement another or secondary defrost trigger threshold (labeled “Upper Demand Threshold” in
With reference now to
If at block 106, the capacity demand is determined to be equal to the maximum capacity demand, the method will proceed to block 110, where the heating capacity is compared to the maximum demand threshold. If the heating capacity is less than or equal to the maximum demand threshold, the controller 52 will transition the heat pump 20 from a heating mode to a defrost mode, as shown in block 112. However, if the heating capacity of the second heat exchanger 28 is greater than the maximum demand threshold, the method will return to block 102.
A heat pump or air conditioning system 20 as described herein allows for the use of a first, reduced defrost threshold as a defrost trigger when the full capacity of the heat pump is not required to meet the capacity demand on the system. However, by including a second, maximum demand threshold associated with the maximum capacity demand, the heat pump 20 is able to perform more frequent defrost cycles when the capacity demand on the heat pump 20 is high. More frequent defrost cycles reduces the need to use the auxiliary heating methods, thereby improving the overall system efficiency.
The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.
While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.
Claims
1. A method for determining when to initiate a defrost mode of a heat pump, the method comprising:
- monitoring a heating capacity of a heat exchanger of the heat pump during operation of the heat pump in a heating mode;
- initiating the defrost mode when the heating capacity of the heat exchanger is less than or equal to a reduced defrost threshold when a capacity demand of the heat exchanger is less than a maximum capacity demand; and
- initiating the defrost mode when the heating capacity of the heat exchanger is less than or equal to a maximum defrost threshold when the capacity demand of the heat exchanger is equal to the maximum capacity demand.
2. The method of claim 1, wherein monitoring the heating capacity of the heat exchanger further comprises monitoring at least one parameter or operating condition of the heat pump associated with the heating capacity.
3. The method of claim 2, wherein the at least one parameter or operating condition is a refrigerant mass flow.
4. The method of claim 2, wherein the at least one parameter or operating condition comprises a temperature of an air discharged from the heat exchanger.
5. The method of claim 2, wherein the at least one parameter or operating condition comprises at least one of a pressure at an outlet of the heat exchanger, a pressure at an inlet of a compressor arranged directly downstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, and a pressure between the outlet of the heat exchanger and the inlet of the compressor.
6. The method of claim 2, wherein the at least one parameter or operating condition comprises at least one of a pressure at an inlet of the heat exchanger, a pressure at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, and a pressure between the outlet of the expansion device and the inlet of the heat exchanger.
7. The method of claim 2, wherein the at least one parameter or operating condition comprises a temperature at an inlet of the heat exchanger, at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, or between the outlet of the expansion device and the inlet of the heat exchanger.
8. A system for conditioning air comprising:
- a refrigeration circuit including a compressor, and expansion valve, and a heat exchanger;
- a controller configured to transition the refrigeration circuit between operation in a heating mode and a defrost mode;
- wherein the controller is configured to: transition the refrigeration circuit from the heating mode to the defrost mode in response to a heating capacity of the heat exchanger reaching a first defrost threshold when the capacity demand of the heat exchanger is less than the maximum capacity demand; and transition the refrigeration circuit from the heating mode to the defrost mode in response to the heating capacity of the heat exchanger reaching a second defrost threshold when the capacity demand of the heat exchanger is equal to the maximum capacity demand.
9. The system of claim 8, further comprising at least one sensor operably coupled to the controller, the at least one sensor being configured to monitor at least one parameter or operating condition of the system associated with the heating capacity.
10. The system of claim 9, wherein the at least one parameter or operating condition is a refrigerant mass flow.
11. The system of claim 9, wherein the at least one parameter or operating condition comprises a temperature of an air discharged from the heat exchanger.
12. The system of claim 9, wherein the at least one parameter or operating condition comprises at least one of a pressure at an outlet of the heat exchanger, a pressure at an inlet of the compressor arranged directly downstream from the heat exchanger relative to a fluid flow through the system in the heating mode, and a pressure between the outlet of the heat exchanger and the inlet of the compressor.
13. The system of claim 9, wherein the at least one parameter or operating condition comprises at least one of a pressure at an inlet of the heat exchanger, a pressure at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the system in the heating mode, and a pressure between the outlet of the expansion device and the inlet of the heat exchanger.
14. The system of claim 9, wherein the at least one parameter or operating condition comprises a temperature at an inlet of the heat exchanger, at an outlet of an expansion device, the expansion device being arranged directly upstream from the heat exchanger relative to a fluid flow through the heat pump in the heating mode, or between the outlet of the expansion device and the inlet of the heat exchanger
Type: Application
Filed: Apr 3, 2024
Publication Date: Oct 10, 2024
Inventor: Charles Cluff (Zionsville, IN)
Application Number: 18/625,620