Embodiments 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 is based at least partially on the cumulative running time in heating mode. However, triggering a defrost cycle based on the running time in heating mode has some disadvantages. The rate of frost accumulation can vary based on numerous conditions such as air temperature, dew point, operating temperature of the evaporator relative to dew point, rate of airflow across the evaporator heat exchanger, and size of the evaporator heat exchanger, for example.
According to an embodiment, a method for determining when to initiate a defrost mode of a heat pump includes monitoring a heating capacity of an evaporator of the heat pump during operation of the heat pump in a heating mode, determining a threshold associated with the heating capacity, and initiating a defrost mode when the heating capacity of the evaporator is less than or equal to the threshold.
In addition to one or more of the features described herein, or as an alternative, further embodiments monitoring the heating capacity of the evaporator 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 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 at least one of a pressure at an outlet of the evaporator, a pressure at an inlet of a compressor arranged directly downstream from the evaporator relative to a fluid flow through the heat pump in the heating mode, and a pressure between the outlet of the evaporator 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 evaporator, a pressure at an outlet of an expansion device, the expansion device being arranged directly upstream from the evaporator relative to a fluid flow through the heat pump in the heating mode, and a pressure between an outlet of the expansion device and the inlet of the evaporator.
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 outlet of an expansion device, the expansion device being arranged directly upstream from the evaporator relative to a fluid flow through the heat pump in the heating mode.
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 evaporator.
In addition to one or more of the features described herein, or as an alternative, further embodiments determining a threshold associated with the heating capacity further comprises: identifying a reference value associated with the heating capacity and deriving the threshold from the reference value.
In addition to one or more of the features described herein, or as an alternative, further embodiments identifying the reference value further comprises measuring a parameter or operating condition of the heat pump associated with the heating capacity when the evaporator is free of frost.
In addition to one or more of the features described herein, or as an alternative, further embodiments the evaporator is free of frost at a beginning of the heating cycle.
In addition to one or more of the features described herein, or as an alternative, further embodiments identifying the reference value further comprises looking up the reference value in a table.
In addition to one or more of the features described herein, or as an alternative, further embodiments comprising adjusting the reference value to compensate for changes in one or more operating conditions of the heat pump during the heating mode.
In addition to one or more of the features described herein, or as an alternative, further embodiments determining the threshold comprises at least one of: (i) applying a percentage reduction to the reference value, and (ii) applying an offset to the reference value.
In addition to one or more of the features described herein, or as an alternative, further embodiments comprising prohibiting initiation in the defrost mode if a cumulative time of operation of a compressor of the heat pump since operation of the heat pump in the defrost mode is less than a minimum time.
In addition to one or more of the features described herein, or as an alternative, further embodiments comprising prohibiting initiation in the defrost mode for a fixed period of time once a compressor of the heat pump beings operating after being in an idle condition.
In addition to one or more of the features described herein, or as an alternative, further embodiments comprising prohibiting initiation in the defrost mode when a rate of change of the parameter or operating condition indicates transient operating conditions.
In addition to one or more of the features described herein, or as an alternative, further embodiments comprising prohibiting initiation in the defrost mode when a rate of change of the parameter or operating condition exceeds a positive threshold or falls below a negative threshold.
In addition to one or more of the features described herein, or as an alternative, further embodiments comprising prohibiting initiation in the defrost mode when a rate of change of the parameter or operating condition is between a positive threshold and a negative threshold for less than a threshold period of time after the rate of change of the parameter was either above the positive threshold or below the negative threshold.
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 monitor a heating capacity of the system during operation in a heating mode, determine a threshold associated with the heating capacity, and initiate operation in a defrost mode when the heating capacity of the heat exchanger is less than or equal to the threshold.
In addition to one or more of the features described herein, or as an alternative, further embodiments comprising at least one sensor operably coupled to the controller, the sensor being configured to monitor at least one parameter or operating condition of the heat pump associated with the heating capacity.
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.
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 compressor 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 34 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 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. In the second state, shown in
As previously noted, 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 in response to the running time of the heat pump in a heating mode. The process of determining when to transition between the heating mode and the defrost mode can be improved in several ways. In an embodiment, the run time of the heating mode run is configured during equipment installation based on local climate and characteristics of the particular installation (i.e. proximity to sources of moisture, etc.). This configuration may be performed by making adjustments to an equipment control board.
Alternatively, or in addition, the run time of the heating mode can be optimized by monitoring the heating capacity of the second heat exchanger during a heating cycle. A comparison of the heating capacity of the second heat exchanger during operation of the heating cycle and the heating capacity of the second heat exchanger when no frost is present will indicate the reduction in heating capacity due to frost accumulation on the second heat exchanger.
Several parameters of the heat pump can be used to observe a reduction in heating capacity. Heating capacity relates directly to refrigerant mass flow and occurs primarily with refrigerant phase change (i.e. when it condenses into a liquid or evaporates into a vapor). The amount of heat being absorbed or rejected is determined primarily by the mass of refrigerant changing phase. In a closed loop system with a continuous flow of refrigerant, the mass of refrigerant changing phase is indicated by the mass flow rate of refrigerant in the system. Further, under steady state conditions, the mass flow rate is the same at any point in the closed loop system. Therefore, mass flow measured at any point in the loop will provide the same result.
Mass flow can be determined at numerous locations within the refrigerant loop by determining the characteristics of the refrigerant such as temperature, pressure, and phase of the refrigerant at one or several measurement points. For example, mass flow can be determined between the outlet of the second heat exchanger 28 and the suction inlet to the one or more compressors 22. Mass flow into the one or more compressors 22 can be indicated by the volume flow (e.g. cubic centimeters per second) into each compressor 22 and the density of the refrigerant vapor (e.g. grams per cubic centimeter) at the suction inlet to each of the one or more compressors 22. In some systems, the density of the refrigerant vapor at the outlet of the second heat exchanger 28 will indicate the density of the vapor at the inlet to the one or more compressors 22. In another example, mass flow can be determined at the expansion valve 26 using the valve opening size and the temperature and/or pressure of the refrigerant at the inlet and outlet of the expansion valve 26.
Volume flow of a compressor 22 is the product of compressor operating speed (e.g. cycles or revolutions per second) and the volume of vapor that the compressor 22 receives at the inlet and pumps during each cycle. The volume that the compressor 22 pumps is known as the compressor displacement (e.g. cubic centimeters per cycle or revolution). Compressor displacement may be fixed or variable. Compressor speed may be fixed or variable. Volume flow is therefore determined by the sum of the volume flow of each of the one or more compressors 22 in the heat pump 20.
Vapor density of the refrigerant can be determined by measuring the pressure and temperature of the refrigerant at the suction inlet to each of the one or more compressors 22. Vapor superheat may be known or assumed within a certain range due to some control mechanism such as a thermostatic expansion valve 26. When the superheat of the vapor is known, measuring only one of refrigerant temperature or pressure will allow the other parameter to be known (i.e. refrigerant temperature can be determined from refrigerant pressure and superheat, and refrigerant pressure can be determined from refrigerant temperature and superheat). Therefore, measuring only one of either pressure or temperature when superheat is known is sufficient for determining vapor density.
In an embodiment, the heat pump 20 includes a control system 50 configured to monitor one or more operating conditions of the heat pump 20 during the heating mode. With reference to
The at least one sensor S of the control system 50 may include a temperature sensor, such as mounted within the outdoor portion 32 for example, and operable to sense an ambient temperature surrounding the outdoor portion 32. In another embodiment, the at least one sensor S is configured to monitor a temperature of the discharge air output from the second heat exchanger 28. In embodiments where the at least one sensor S includes a temperature sensor, the temperature sensor may be any suitable device, including but not limited to a thermistor, thermocouple, thermostat, infrared sensor, etc. Alternatively, the at least one sensor may be a pressure sensor consisting of any suitable device, including but not limited to a strain gage bridge, for example.
In an embodiment, the at least one sensor S includes a sensor configured to monitor one or more parameters of the refrigeration circuit of the heat pump 20. The at least one sensor may include a pressure sensor arranged at least one of within a suction line connected to the inlet of the compressor 22, at or downstream from an outlet of the expansion device 26, and at or upstream from an inlet of the second heat exchanger 28.
Alternatively, or in addition, the at least one sensor S includes a sensor configured to measure a temperature of the refrigerant, such as at a location near an outlet of the expansion valve 26. The temperature of the refrigerant may be determined by measuring the temperature of the refrigerant itself, or alternatively, by measuring a temperature of a conduit containing the refrigerant, which is configured to be representative of or substantially equal to the temperature of the refrigerant contained therein. In another embodiment, the at least one sensor S includes a mass flow sensor.
A reduction in heating capacity due to frost accumulation may be detected by monitoring the refrigerant mass flow in the heat pump 20 (see
In an embodiment, a reduced heating capacity of the heat pump 20 can be detected by observing a reduction of some other operating parameter indicative of a reduced heat transfer to the second heat exchanger. Accordingly, a reduction in heating capacity due to frost accumulation may be detected by monitoring a reduction in pressure of the refrigerant. In an embodiment, the at least one sensor S includes a pressure sensor configured to monitor one or more of a pressure at an outlet of the second heat exchanger 28, a pressure at an inlet of the compressor 22, or a pressure at any location between the outlet of the second heat exchanger 28 and the inlet of the compressor 22 (see
In an embodiment, a reduction in heating capacity due to frost accumulation is detected by monitoring the temperature of the refrigerant at the outlet of the expansion valve 26 (see
In each of the embodiments described herein, the controller 52 is configured to compare the monitored parameter with a respective threshold to determine when to initiate or trigger operation in the defrost mode. As used herein, the term “monitored parameter” is intended to include parameters or operating conditions that are measured via one or more sensors, or alternatively, parameter or operating conditions that are calculated using the monitored parameters or operating conditions. In an embodiment, the controller 52 is configured to transition the heat pump 20 from the heating mode to the defrost mode automatically in response to the monitored parameter crossing the threshold. In another embodiment, the defrost mode is initiated when the monitored parameter crosses the threshold and remains over the threshold for a minimum period of time. Examples of a minimum period of time include anywhere from about zero minutes to about ten minutes. The minimum period of time may vary based on the parameter, such as pressure or temperature for example.
Alternatively, or in addition, the controller 52 is configured to transition the heat pump 20 from the heating mode to the defrost mode based on a net period of time that the monitored parameter crosses the threshold and remains over the threshold. The net period of time may be calculated by an accumulated time parameter that increases when the monitored parameter exceeds the threshold indicating the need for a defrost, and decreases when the monitored parameter does not exceed the threshold indicating the need for a defrost. The net period of time may be limited from obtaining negative values when the cumulative time where the monitored parameter is less than the threshold exceeds the cumulative amount of time where the monitored parameter exceeds the threshold. The threshold for the net period of time may be anywhere from about zero minutes to about ten minutes.
The controller 52 is configured to determine the threshold for initiating operation of the heat pump 20 in the defrost mode associated with the monitored parameter. In an embodiment, the threshold for the monitored parameter is derived from a reference value of the same parameter associated with operation of the second heat exchanger 28 at the same conditions, but when no frost is present. The reference value of the parameter may be determined by measurement or calculation of that parameter in conditions where the second heat exchanger 28 is free of frost. The second heat exchanger 28 may be considered free or substantially free from frost in the first few minutes of a heating cycle following a defrost cycle. The second heat exchanger 28 may be considered free or substantially free of frost after having operated in a mode where the second heat exchanger 28 was previously operating as a condenser at temperatures known to be above freezing. Alternatively, or in addition, the second heat exchanger 28 may be considered to be free or substantially free from frost after being non-operational for a sufficient period of time while an ambient air temperature was above freezing such that any previously existing frost melted.
In another embodiment, the reference value of the parameter may be determined by observing the parameter within a period of time near the beginning of the heating cycle. The measurement time period may begin anywhere from about zero to about twenty minutes after the beginning of the heating cycle, such as between about two minutes and about five minutes for example. The duration of the measurement time period may be anywhere from about zero to about ten minutes in duration, such as between about one and about three minutes for example. A time duration of zero minutes indicates a measurement that is taken at a single point in time. The reference value of the parameter may be determined by an average value of the parameter within the measurement time period, the maximum value of the parameter within the measurement time period, or some other arithmetic calculation such as the maximum output of a filtered value of the parameter during the measurement time period.
In yet another embodiment, the reference value of the parameter may be determined without taking direct measurements. For a given set of conditions such as ambient temperature, vapor volume flow and air flow across the second heat exchanger 28, the reference value of the parameter will be repeatable within a small margin of error from one cycle to the next. Such reference values may be determined by measuring the characteristics in various combinations of operating conditions and storing values of the reference parameter relating to those operating conditions in a manner that is accessible to the controller 52. An example of a table indicating a reference value based on both the speed of the compressor 22 and the ambient air temperature is illustrated in
The reference value of a parameter may be determined via an algorithm run by the controller 52 that calculates the reference value when provided with the operating conditions, or alternatively, may be in the form of a single or multidimensional lookup table accessible by the controller 52, or some combination of all of these.
In an embodiment, the reference value of the parameter may be adjusted as the operating conditions of the heat pump 20 deviate from the conditions when the reference value of the parameter was obtained. Examples of changes in operating conditions include changes in ambient temperature, and changes in volume flow, such as due to stopping or starting one or more of a plurality of compressors or changing the operating speed of one or more of a plurality of compressors.
The threshold associated with a respective monitored parameter may be derived from the reference value. In an embodiment, the threshold is determined by applying a percentage reduction to the reference value of the parameter. This reduction percentage may be anywhere from 30% to 98% of the capacity for a second heat exchanger 28 operating at the same conditions with no frost accumulation.
In another embodiment, the threshold is derived from the reference value by applying an offset to the reference value of the parameter. When the parameter is one of the mass flow, the outlet pressure at the second heat exchanger 28, and the inlet pressure at the second heat exchanger 28, the offset may be anywhere from about 2% to about 70% of the reference value of the parameter. When the parameter is the inlet temperature of the second heat exchanger 28, the offset may be anywhere between about 2° F. to about 40° F. Further, when the parameter is the discharge temperature of the air at the second heat exchanger 28, the offset may be anywhere between about 2° F. to about 20° F.
Alternatively, the threshold may be determined by applying a percentage reduction to the offset between the ambient air temperature and the reference air discharge temperature determined for a second heat exchanger 28 operating at the same conditions with no frost accumulation thereon. This reduction percentage may be anywhere from about 2% to about 70% of the offset. For example, if the reduction percentage is chosen to be 50%, and the ambient air temperature was 30° F. and the air discharge temperature was 22° F. for a second heat exchanger 28 operating at the same conditions with no frost accumulation, then the offset is determined as (30° F. - 22° F.) x 50% = 4° F. Applied to the ambient air temperature of 30° F., this offset would produce a threshold of 30° F. - 4° F. = 26° F. Alternatively, the threshold offset may be applied to the current ambient temperature. For example, if the ambient air temperature was 30° F. resulting in a threshold offset of 4° F. determined for a second heat exchanger 28 operating at the same conditions with no frost accumulation as previously described, and the ambient air temperature decreases to 28° F. during the heating cycle, the offset of 4° F. applied to the current ambient air temperature would produce a threshold of 28° F. - 4° F. = 24° F.
In yet another embodiment, the threshold value may be determined by applying the desired method (percentage reduction, offset, etc.) to the known characteristics of the second heat exchanger 28 operating with no frost accumulation over the range of expected operating conditions of the second heat exchanger 28. These operating conditions may consist of some or all of ambient temperature, refrigerant vapor volume flow within the second heat exchanger 28 and air flow across the second heat exchanger 28.
Threshold values for all expected combinations of operating conditions can be stored in a manner accessible to the controller 52. The form of such memory may be an algorithm that calculates the reference value and then the respective threshold value when provided with the operating conditions, may be a multidimensional lookup table associated with the reference value, or may be some combination thereof.
In an embodiment, the controller 52 is prohibited from initiating operation of the heat pump 20 in the defrost mode under certain operating conditions. For example, operation in a defrost mode may be prohibited for a fixed period of time after at least one compressor 22 of the heat pump 20 has begun operating after being in an idle condition. In such embodiments, the fixed period of time may be between about zero minutes and about fifteen minutes.
Alternatively, or in addition, the controller 52 may be prohibited from initiating operation of the heat pump 20 in the defrost mode based on the cumulative period of time that at least one compressor 22 has been operating in a heating cycle since the previous defrost cycle. This cumulative time is not reset during an idle period when none of the one or more compressors 22 are operational. The defrost mode may be inhibited until the cumulative time reaches a minimum value anywhere from about zero minutes to about sixty minutes, such as fifteen minutes for example.
In an embodiment, the controller 52 may be prohibited from initiating operation of the heat pump 20 in response to the monitored parameter. The monitored parameter may vary rapidly and over a large range during transient operating conditions such that the monitored parameter crosses the corresponding threshold even though frost accumulation on the second heat exchanger 28 has not reached a quantity sufficient to require a defrost cycle. This condition can be detected by monitoring the rate of change of the monitored parameter and preventing initiation in the defrost mode when the rate of change of the monitored parameter indicates that transient operating conditions may be present (see
In another embodiment, initiation in the defrost mode is prohibited when the rate of change of the monitored parameter rises above a positive threshold or falls below a negative threshold. Further, initiation in the defrost mode may be prohibited when the rate of change of the monitored parameter is between a positive threshold and a negative threshold for a predetermined period of time after the rate of change of the monitored parameter was above the positive threshold or below the negative threshold. In an embodiment, the predetermined period of time is between about zero minutes and about five minutes. In some embodiments, the predetermined period of time is less than about one minute.
The monitored parameter may continue to vary rapidly and over a large range in some conditions when the heat pump 20 is not operating as desired. Such conditions may occur as a result of too much or too little refrigerant charge in the system, a restriction in flow of refrigerant somewhere in the system, or numerous other potential causes. While this manner of operation is not preferred, it may still provide heating at or near the intended capacity. As such, the second heat exchanger 28 may accumulate frost in a manner similar to that of normal operation. In this condition, the decision to inhibit initiation in the defrost mode due to transient conditions may continue indefinitely, which will result in excessive frost accumulation on the second heat exchanger 28 and an inability of the heat pump 20 to provide the desired heating capacity. To address such operating conditions, a maximum time limit that a decision to initiate a defrost cycle is prohibited may be implemented.
With reference now to
The Pressure Trigger parameter shown on the graph does not relate to the values shown on either vertical axis. The Pressure Trigger shows a high value to indicate defrost initiation conditions are met when pressure is below the threshold, and a low value to indicate defrost initiation conditions are not met when pressure is above the threshold. The desired initiation of defrost occurs at minute fifty two on the graph. However, the pressure dropping below the threshold briefly at minutes one and three of the graph may also cause defrost to be initiated frost has accumulated on the second heat exchanger 28.
With continued reference to
In an embodiment, the controller 52 has a limit with respect to the continuous length of time that initiation of operation in a defrost mode can be prohibited. This limit may be a maximum amount of continuous time, such as anywhere from about 30 seconds to about 2 hours. After the decision to inhibit initiation of defrost persists for the maximum amount of time, the controller 52 will be able to transition to operation in the defrost mode. In an embodiment, once the maximum amount of continuous time has passed, prohibition of operation of the heat pump 20 in the defrost mode is blocked for a minimum period of time allowing defrost to occur. The period of time that prohibition of operation in the defrost mode is blocked may be anywhere between about thirty seconds and about thirty minutes for example.
With reference now to
A heat pump or other HVAC system as described herein optimizes the length of time of operation of the heat pump 20 in a heating mode 20 based on the heating capacity of the heat pump 20. As a result, the heat pump 20 operate more efficiently.
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.
This application claims the benefit of U.S. Provisional Application No. 63/288,896 filed Dec. 13, 2021, the disclosure of which is incorporated herein by reference in its entirety.
Number | Date | Country | |
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63288896 | Dec 2021 | US |