Heat pump system

Abstract

A heat pump system for controlling the interior temperature of a building. The system includes a compressor, a first heat exchanger, an expansion device, and a second heat exchanger fluidly connected together by a flow of refrigerant to define a refrigerant circuit, and a thermal energy storage device thermally connectable to the refrigerant circuit to exchange thermal energy with the refrigerant. The heat pump system is configured to operate in a normal heating mode, a defrost mode, and / or an auxiliary heating mode. The heat pump system includes a switching assembly configured to switch between a normal heating mode, a defrost mode, and / or an auxiliary heating mode, and the switching assembly is configured to direct refrigerant exiting the first heat exchanger to flow through the second heat exchanger when the heat pump system is operated in the defrost mode, and to direct refrigerant exiting the second heat exchanger to flow through the second heat exchanger when the heat pump system is operated in the defrost mode. And the waste heat in the refrigerant is used for defrosting the second heat exchanger.

Description

Technical Field

[0001] This invention relates to heat pump systems and methods for operating heat pump systems. Background Technology

[0002] As is well known, heat pumps can be provided to extract heat energy (i.e., heat) from a heat source (such as ambient air) and then release the extracted heat energy into an enclosed space such as the interior of a building. Any heat source with a temperature above absolute zero contains some heat energy, which can be used to raise the internal temperature of an enclosed space.

[0003] An example of a known heat pump system is an air source heat pump (ASHP), which typically includes an evaporator, a compressor, a condenser, and an expansion unit. The components of an ASHP are fluidly connected via fluid conduits to form a refrigerant circuit. Both the evaporator and condenser include heat exchangers configured to allow heat to be transferred to and / or from the refrigerant flowing through the refrigerant circuit. The evaporator is located externally so that it can transfer heat from the surrounding outside air, while the condenser is typically connected to the building's central heating system.

[0004] The refrigeration circuit begins with the compressor, where the evaporated refrigerant is compressed to form hot vapor. This hot refrigerant vapor is then directed to the condenser, which transfers some heat from the refrigerant, condensing the vapor into a liquid. The liquid refrigerant then flows to the expansion valve, where it expands, reducing its pressure and temperature. The cold refrigerant mixture is then directed through the evaporator, where it transfers heat from the outside air, causing the refrigerant to evaporate. The refrigerant vapor is then directed back to the compressor to restart the refrigeration circuit.

[0005] One known problem with ASHP is that its heat capacity and coefficient of performance (COP) drop sharply when the ambient outside air temperature decreases. This means that ASHP performance degrades to its lowest level when the inflow of heat is most needed to raise the building's internal temperature.

[0006] Another known problem with ASHP is that frost and ice can form on the evaporator coils or fins when the outside temperature drops below approximately 6°C. Icing reduces the evaporator's operating efficiency, potentially causing the ASHP to stop working. Regular defrosting of the evaporator is necessary to prevent icing, especially in cold and humid climates.

[0007] Typical methods for defrosting evaporators involve reversing the flow direction of refrigerant through the loop, directing the refrigerant from the compressor to the evaporator. This so-called "reverse circulation method" is achieved by configuring an ASHP (Automatic Refrigerant Power Supply) to extract heat from the condenser to melt the ice accumulated in the evaporator.

[0008] An alternative approach is to provide a bypass duct or channel for the refrigerant circuit, configured to fluidly connect the compressor's output to the evaporator's input while bypassing the condenser. In this "hot gas bypass method," the compressor is configured to produce thermally vaporized refrigerant, which is then directed to the evaporator to melt any ice that forms thereon.

[0009] Another alternative defrosting method uses a separate electric heater configured to directly heat the outer surface of the evaporator to melt frost and ice that accumulates under cold and humid conditions. This defrosting method uses additional electricity and requires shutting down the ASHP unit during the defrosting process, which results in a heating interruption inside the building.

[0010] During defrosting operations, each of these defrosting methods consumes electricity without providing heat to the building's interior. For example, in the hot gas bypass method, the compressor runs to provide hot refrigerant vapor, but no heat is provided to the building's central heating system because the hot vapor is transferred from the condenser. Alternatively, the reverse circulation method allows cold refrigerant to flow through the condenser on its way to the evaporator. This results in heat being extracted from the condenser, thus lowering the building's interior temperature.

[0011] These defrosting methods all require a backup heat source, such as an electric heater or a gas boiler, to provide heating to the building interior while the evaporator is defrosting. Therefore, each defrosting method significantly reduces the overall coefficient of performance (COP) of the heat pump system.

[0012] This disclosure aims to address one or more of the aforementioned problems with existing heat pump systems. Summary of the Invention

[0013] In its broadest sense, aspects of the present invention provide a heat pump system configured to, when operating in defrost mode, direct residual heat energy from the condenser to the evaporator for defrosting, while simultaneously directing stored heat energy from a heat storage device to the condenser to heat the interior of a building during defrost operation. Aspects of the present invention also provide a method for operating the heat pump system in defrost mode, the method comprising directing residual heat energy from the condenser to the evaporator for defrosting, and directing stored heat energy from a heat storage device to the condenser.

[0014] A first aspect of the invention provides a heat pump system for a building temperature control system, the system comprising: a compressor, a first heat exchanger, an expansion device, and a second heat exchanger, which are fluidly connected together via a refrigerant flow to define a refrigerant circuit, and a thermal energy storage device thermally connected to the refrigerant circuit to exchange heat energy with the refrigerant. The heat pump system is configured to operate in a normal heating mode and a defrost mode. In the normal heating mode, heat energy is transferred from the second heat exchanger to the refrigerant and from the refrigerant via the first heat exchanger to heat the building; in the defrost mode, heat energy is transferred from the thermal energy storage device to the refrigerant and from the refrigerant via the first heat exchanger to heat the building, and from the refrigerant via the second heat exchanger to defrost the second heat exchanger. The heat pump system includes a switching component configured to switch between a normal heating mode and a defrost mode, and the switching component is configured to guide refrigerant leaving the first heat exchanger through the second heat exchanger when the heat pump system is operating in defrost mode, so that the residual heat in the refrigerant defrosts the second heat exchanger.

[0015] The refrigerant circuit can be configured by switching components so that residual heat energy in the refrigerant flowing out of the first heat exchanger is directed to the second heat exchanger to melt the ice that has accumulated on its outer surface.

[0016] Waste heat from the first heat exchanger represents excess heat that was not transferred to the building's central heating system by the first heat exchanger. In known heat pump systems, this "waste heat" is typically wasted. During defrosting, a heat storage device is configured to transfer the stored heat energy into the refrigerant circuit, allowing the first heat exchanger to continue providing heat to the building's central heating system.

[0017] Therefore, the defrosting mode of a heat pump system can combine the defrosting of the second heat exchanger with continuous (i.e., uninterrupted) heating of the building. This feature eliminates the need for a standby heater, thereby significantly improving the coefficient of performance (COP) of the heat pump system and reducing its operating costs.

[0018] The optional features are now listed. These features can be applied individually or in any combination with any aspect.

[0019] It should be understood that, in this document, the term "refrigerant" refers to a heat transfer fluid, such as a fluid capable of transitioning between a gaseous and a liquid phase and usable in a heat transfer process. For example, a refrigerant may include any heat transfer fluid capable of acting as a medium for cooling on one side of a heat transfer process, heating on the other side, and transferring thermal energy from one side of the heat transfer process to the other. Therefore, according to this disclosure, each refrigerant loop described herein may define a heat transfer fluid loop.

[0020] The first and second heat exchangers can be defined as internal and external heat exchangers, respectively. That is, the first heat exchanger can be configured to transfer heat between the heat pump system and the interior space of the building, while the second heat exchanger can be configured to transfer heat between the heat pump system and the external environment. Therefore, the first and second heat exchangers can be defined as the indoor and outdoor heat exchangers (or units) of the heat pump system, respectively. The first heat exchanger can be a condenser. The second heat exchanger can be an evaporator.

[0021] It should be understood that the expansion device can include any expansion device suitably configured to cause refrigerant expansion. For example, the expansion device may include an expansion valve. The expansion device can be configured to operate in either flow direction. Thus, the expansion device may be a capillary tube. Alternatively, the expansion device may include two or more one-way expansion valves arranged in a switchable circuit to cause expansion of the refrigerant flow in either direction, as understood by those skilled in the art. Another expansion device may include two asymmetric expansion devices connected to two one-way valves. Alternatively, the expansion device may include a single asymmetric expansion valve connected to the refrigerant circuit via four control valves, as will be understood by those skilled in the art.

[0022] The switching assembly can be configured to guide refrigerant leaving the first heat exchanger sequentially through the second heat exchanger, the expansion unit, and the compressor when the heat pump system is operating in defrost mode. In this way, the heat pump system can be configured to allow residual heat energy from the first heat exchanger to be carried by the refrigerant for defrosting the evaporator. Therefore, the switching assembly can be located downstream of the first heat exchanger and upstream of the compressor.

[0023] The switching component can be configured to guide refrigerant from the first heat exchanger sequentially through a thermal energy storage device, an expansion device, a second heat exchanger, and a compressor. In this manner, the thermal energy storage device can be configured such that, in normal heating mode, at least some residual heat energy present in the hot refrigerant discharged from the condenser is transferred to the thermal energy storage device. Therefore, in normal heating mode, the thermal energy storage device can be configured to recover residual heat energy from the hot refrigerant leaving the condenser.

[0024] A thermal energy storage device can be connected to the refrigerant circuit between the expansion unit and the compressor to recover and store residual thermal energy carried by the refrigerant.

[0025] The switching component may include a four-way valve that can be configured to directly connect the first heat exchanger to the second heat exchanger when the heat pump system is operating in defrost mode. The four-way valve provides a convenient way to redirect refrigerant flow through the heat pump system.

[0026] Alternatively, it should be understood that the switching assembly may include any appropriately configured "four-way" switching device (e.g., an assembly of four interconnected one-way valves, or an assembly of two interconnected two-way valves).

[0027] The switching component can be configured to bypass the expansion unit (i.e., the first expansion unit) and guide the refrigerant leaving the first heat exchanger sequentially through the second expansion unit, the second heat exchanger, and the compressor when the heat pump system is operating in defrost mode. This allows heat from the thermal energy storage device to be transferred by the refrigerant to defrost the second heat exchanger.

[0028] The switching assembly may include a first bypass assembly, which can be configured to isolate the expansion device (i.e., the first expansion device) from the refrigerant circuit when the heat pump system is operating in defrost mode. This arrangement allows hot refrigerant from the thermal energy storage device to reach the second heat exchanger to melt the ice that has accumulated thereon.

[0029] In one embodiment, the thermal energy storage device may be connected to the refrigerant circuit between the second expansion device and the second heat exchanger.

[0030] The switching assembly may include a second bypass assembly configured to fluidly connect a second expansion device to the refrigerant circuit between the first heat exchanger and the thermal energy storage device when the heat pump system is operating in defrost mode. The second expansion device is thus configured to reduce the pressure of the refrigerant, allowing it to more effectively absorb heat stored in the thermal energy storage device as the refrigerant passes through.

[0031] The heat pump system can operate in a heat-charge mode, in which heat energy can be transferred from the refrigerant to a heat storage device. A switching component can be configured to direct refrigerant leaving the compressor around the second expansion unit and the first heat exchanger when the heat pump system is operating in heat-charge mode. In this mode, when the building's occupants do not require heat, the heat energy from the compressor is directed and stored in the heat storage device.

[0032] The heat pump system can operate in an auxiliary heating mode, in which thermal energy can be transferred from the thermal energy storage device to the refrigerant. A switching component can be configured to bypass the expansion device and the second heat exchanger when the heat pump system is operating in auxiliary heating mode. Therefore, when defrosting of the second heat exchanger (e.g., the evaporator) is not required, the thermal energy stored in the thermal energy storage device can be used to heat the interior of the building.

[0033] Thermal energy storage devices may include phase change materials (PCMs). PCMs can be configured to be in direct thermal contact with the piping of the refrigerant circuit. PCMs can be configured to provide (and store) thermal energy at a substantially constant temperature, which improves control of the heat pump system. PCMs can also be configured to store large amounts of thermal energy in a relatively small volume, which increases the encapsulation efficiency of the heat pump system.

[0034] Thermal energy storage devices can be thermally connected to the piping of a refrigerant circuit via a separate fluid loop that includes a heat transfer fluid (such as water). This separate fluid loop allows the thermal energy storage device to have a large capacity and can be located outside the rest of the heat pump system.

[0035] The heat pump system may also include a refrigerant storage device, which may be fluidly connected to the output of the first heat exchanger. The refrigerant storage device may be configured to accommodate fluctuations in the volume of refrigerant flowing through the refrigerant circuit during operation of the heat pump system.

[0036] The heat pump system may also include a phase separator, which can be fluidly connected to the inlet of the compressor to prevent unwanted fluid from entering the compressor.

[0037] A refrigerant circuit may include a high-pressure stage and a low-pressure stage, which are fluidly connected together by a phase separator. The high-pressure stage may include (i.e., fluidly connected to) a first heat exchanger, and the low-pressure stage may include (i.e., fluidly connected to) a second heat exchanger. Therefore, a heat pump system including a high-pressure stage and a low-pressure stage can define a two-stage heat pump system.

[0038] At least one or each of the high-pressure stage and the low-pressure stage may be fluidly connected to the phase separator. The high-pressure stage may be fluidly connected to the gas-containing section or segment of the phase separator. For example, the high-pressure stage may be configured to receive gaseous refrigerant from the gas-containing section of the phase separator. The low-pressure stage may be fluidly connected to the liquid-containing section of the phase separator. For example, the low-pressure stage may be configured to receive liquid refrigerant from the liquid-containing section of the phase separator. The high-pressure stage may be configured to deliver a mixture of liquid and gaseous refrigerant to the phase separator. Therefore, the high-pressure stage circuit may be configured to deliver a liquid-gas refrigerant mixture to the liquid-containing section of the phase separator.

[0039] A refrigerant circuit can define a refrigerant circuit assembly including a high-pressure stage and a low-pressure stage. The high-pressure stage and the low-pressure stage can be fluidly connected to each other because they can share the same refrigerant circulating around both stages. The refrigerant in the high-pressure stage can be maintained at a higher pressure on average than the equivalent portion of the low-pressure stage. The low-pressure stage can be configured to raise the temperature of the refrigerant from a low temperature (e.g., at the evaporator) to an intermediate temperature (e.g., in the phase separator). The high-pressure stage can be configured to raise the temperature of the refrigerant from an intermediate temperature (e.g., in the phase separator) to a high temperature (e.g., in the condenser).

[0040] A heat pump system can operate in normal heating mode (e.g., by appropriately configuring switching components) to transfer heat from the refrigerant to a thermal energy storage device. For example, this might involve directing a refrigerant flow from a first heat exchanger (e.g., a condenser) to a location in the refrigerant cycle that is thermally connected to the thermal energy storage device to transfer at least some of the heat from the refrigerant to a phase change material, which can then be stored for later use. In this way, the heat pump system can be configured to provide heat to the interior of a building (i.e., via the condenser) while simultaneously charging the thermal energy storage device. This operating mode can define a continuous heating and charging mode.

[0041] A thermal energy storage device can be thermally connected to a phase separator. The thermal energy storage device can be thermally connected to the liquid-containing portion or phase of the phase separator. A phase change material (PCM) can be thermally connected to the phase separator via a separate loop comprising a heat transfer fluid or refrigerant. The PCM can be arranged within the phase separator. The separate refrigerant loop may include switching components and / or pumps configured to control the flow of refrigerant, and thus control the thermal energy between the phase separator and the thermal energy storage device. The PCM can be encapsulated in a housing formed of a thermally conductive material to facilitate heat transfer between the PCM and the refrigerant within the phase separator.

[0042] The compressor may define a compressor assembly including a first compressor fluidly connected to a high-pressure stage. The compressor assembly may also include a second compressor fluidly connected to a low-pressure stage.

[0043] The compressor may include a vapor injection compressor, which is fluidly connected to both a high-pressure stage and a low-pressure stage of the refrigerant circuit. The low-pressure stage may be fluidly connected to the low-pressure inlet of the compressor, while the high-pressure output of the compressor may be fluidly connected to the high-pressure stage. An intermediate inlet may be fluidly connected to a phase separator.

[0044] The expansion device may define an expansion device assembly including a first expansion device fluidly connected to a high-pressure stage. The expansion device assembly may include a second expansion device fluidly connected to a low-pressure stage.

[0045] The switching component can be configured to, when the heat pump system is operating in defrost mode, bypass the first expansion device and guide the refrigerant leaving the first heat exchanger sequentially through the second expansion device, the second heat exchanger, and the phase separator.

[0046] A second aspect of the invention provides a building comprising a heat pump system as described in any of the preceding paragraphs. A second heat exchanger is thermally connected to an external heat source, and a first heat exchanger is thermally connected to the building's central heating system.

[0047] A third aspect of the invention provides a method for operating a heat pump system according to any of the preceding paragraphs. The method is for operating the heat pump system to control the internal temperature of a building. The method includes: when operating the heat pump system in defrost mode, directing refrigerant leaving a first heat exchanger through a second heat exchanger, so that residual heat in the refrigerant defrosts the second heat exchanger.

[0048] According to the present invention, the method may include switching the heat pump system between a normal heating mode and at least one of an auxiliary heating mode and a defrosting mode.

[0049] In embodiments, the method may include: switching the heat pump system between a normal heating mode and a defrost mode when there is no ice on the evaporator. The method may also include: switching the heat pump system between a normal heating mode and an auxiliary heating mode. Furthermore, the method may include: periodically switching between different operating modes to improve the COP of the heat pump system.

[0050] According to each of the switching strategies described above, the heat pump system can be configured to operate as a quasi-two-stage heat pump system by using only a single refrigerant loop (i.e., a single-stage heat pump device). In this way, the heat pump system according to the invention can continuously supply heat to the interior of a building without requiring a complex and expensive two-stage heat pump system.

[0051] In one embodiment, the method may include operating the heat pump system during off-peak electricity consumption periods (i.e., when grid electricity prices are cheaper) according to at least one of a normal heating mode and a charging mode to store thermal energy in a thermal energy storage device for backup. In this way, the COP of the heat pump system can be improved.

[0052] A fourth aspect of the invention provides a method for operating a heat pump system to control the internal temperature of a refrigeration unit. The system includes: a compressor, a condenser, an expansion device, and an evaporator, fluidly connected together via a refrigerant flow to define a refrigerant circuit; and a thermal energy storage device thermally connected to the refrigerant circuit to exchange heat energy with the refrigerant, wherein the refrigerant circuit includes a high-pressure stage and a low-pressure stage, fluidly connected together via a phase separator, wherein the high-pressure stage includes a condenser and the low-pressure stage includes an evaporator. The heat pump system is configured to operate in a charging cooling mode and an auxiliary cooling mode, wherein: In the cooling charge mode, heat energy is transferred from the heat storage device to the refrigerant, and then transferred from the refrigerant through the condenser to heat the ambient air. In auxiliary refrigeration mode, heat energy is transferred from the evaporator to the refrigerant to cool the internal area of ​​the refrigeration unit and from the refrigerant to the heat energy storage device; The method includes isolating the high-pressure stage when the heat pump system is operating in charging-cooling mode, and isolating the low-pressure stage when the heat pump system is operating in auxiliary cooling mode.

[0053] According to a fourth aspect of the invention, the method enables a two-stage heat pump system to operate as a refrigeration system. Specifically, the system can be configured to cool areas requiring cooling, such as refrigeration units or the interior spaces of buildings. It should be understood that for refrigeration (i.e., cooling) applications, the heat pump system can be configured in the opposite arrangement to that for heating applications. For example, the condenser may be exposed to ambient air (e.g., outside the refrigeration zone) and the evaporator may be located where a load is required (e.g., inside the refrigeration zone). In this case, the required load may be a negative heat load (i.e., cold) to reduce the temperature of the refrigeration zone. Therefore, when the heat pump system operates in charge-cooling mode, the switching components can be configured to remove or extract heat energy (i.e., heat) from the thermal energy storage device. This can be considered as "charging" the thermal energy storage device with "cold and hot energy." When the heat pump system operates in auxiliary refrigeration mode, the stored "cold and hot energy" can be used to reduce the temperature of the refrigerant delivered to the evaporator (i.e., by extracting heat energy from the refrigerant and storing it in the thermal energy storage device), thereby cooling the refrigeration zone.

[0054] This method may involve operating the heat pump system in a charging cooling mode during periods of low ambient air temperature (e.g., at night) to store thermal energy in a thermal energy storage device for later use. Then, when the heat pump system operates in auxiliary cooling mode, the thermal energy stored in the thermal energy storage device can be directed to cool the internal space of the cooling unit. In this way, the COP of the heat pump system can be improved.

[0055] A fifth aspect of the invention provides a controller or control system for controlling a heat pump system as described in any of the preceding paragraphs. The controller may be configured to perform the methods described in any of the preceding paragraphs. In particular, the controller may be configured to control a switching device to operate the heat pump system in at least one of a plurality of operating modes.

[0056] Each of the exemplary heat pump systems can be incorporated into an air-source heat pump system, i.e., configured to extract heat energy from ambient air, as understood by those skilled in the art. Alternatively, each of the above-described heat pump systems can be configured for use in a water-source heat pump system and / or a ground-source heat pump system.

[0057] Those skilled in the art will understand that, except in cases of mutual exclusion, the features or parameters described with respect to any of the foregoing aspects can be applied to any other aspect. Furthermore, except in cases of mutual exclusion, any feature or parameter described herein can be combined with any other feature or parameter described herein. Attached Figure Description

[0058] Various aspects and embodiments of this disclosure will now be described by way of example with reference to the accompanying drawings.

[0059] Figure 1 This is a schematic diagram of a single-stage heat pump system according to a first arrangement of the present invention, the heat pump system being configured to operate in normal heating mode.

[0060] Figure 2 yes Figure 1 The pressure-enthalpy curves corresponding to the normal heating mode of the heat pump system are shown.

[0061] Figure 3 yes Figure 1 A schematic diagram of a heat pump configured to operate in defrost mode.

[0062] Figure 4 yes Figure 3 The pressure-enthalpy curves corresponding to the defrosting modes of the heat pump system are shown.

[0063] Figure 5 This is a schematic diagram of a single-stage heat pump system according to a second arrangement of the present invention, which can be configured to operate in a variety of different operating modes.

[0064] Figure 6 yes Figure 5 The diagram shows the pressure-enthalpy curves corresponding to different operating modes of the heat pump system.

[0065] Figure 7 yes Figure 1 , Figure 3 or Figure 5 A schematic diagram of the thermal energy storage components of a heat pump system is shown.

[0066] Figure 8 yes Figure 1 , Figure 3 or Figure 5 The graph shows the coefficient of performance versus time for the operating method of the heat pump system.

[0067] Figure 9 yes Figure 5 The diagram shows an alternative configuration for a single-stage heat pump system.

[0068] Figure 10 This is a schematic diagram of a two-stage heat pump system according to a third arrangement of the present invention, which can be configured to operate in a variety of different operating modes.

[0069] Figure 11 This is a schematic diagram of a two-stage heat pump system according to the fourth arrangement of the present invention, which can be configured to operate in a variety of different operating modes.

[0070] Figures 12 to 16 yes Figure 11 The diagram shows the pressure-enthalpy curves corresponding to different operating modes of the heat pump system.

[0071] Figure 17 yes Figure 11 The diagram shows an alternative configuration for a two-stage heat pump system.

[0072] Figure 18 yes Figure 10 The diagram shows an alternative configuration for a two-stage heat pump system.

[0073] Figure 19 yes Figure 11 The diagram shows an alternative configuration for a two-stage heat pump system.

[0074] Figure 20 yes Figure 10 , Figure 11 and Figures 17 to 19 A schematic diagram of an alternative thermal energy storage component for a heat pump system. Detailed Implementation

[0075] Various aspects and embodiments of the invention will now be discussed with reference to the accompanying drawings. Further aspects and embodiments will be apparent to those skilled in the art.

[0076] Single-stage heat pump system Now refer to Figures 1 to 4 A heat pump system 10 according to a first arrangement is described. The heat pump system 10 forms part of an air source heat pump (ASHP) configured to transfer thermal energy (i.e. heat) from the exterior of a building to the interior of the building (not shown).

[0077] The heat pump system 10 includes a compressor 12, a condenser 14, a thermal energy storage device 16, an expansion device 18, an evaporator 20, and an optional phase separator 22, which are fluidly connected via fluid conduits 24 to define a refrigerant circuit 26. The fluid conduits 24 define a fluid path through which refrigerant is directed between the components of the heat pump system 10, as will be readily understood by those skilled in the art. Therefore, the heat pump system 10 is defined as a single-stage heat pump system because it comprises only a single refrigerant circuit 26.

[0078] The heat pump system 10 is configured to operate in a normal heating mode, in which heat energy is transferred from an external heat source to the refrigerant via the evaporator 20 and from the refrigerant to the interior of the building via the condenser 14.

[0079] The heat pump system 10 also includes a switching component 40, which is configured to operate in normal heating mode (e.g., Figure 1 (as shown) and defrost mode (as shown) Figure 3The system switches between the evaporator 20 and the refrigerant. In normal heating mode, heat energy is transferred from the evaporator 20 to the refrigerant and then directed to the condenser 14 to heat the building. At the same time, the waste heat from the condenser is also directed to heat the heat storage device 16.

[0080] In defrost mode, heat energy is transferred from the heat storage device 16 to the refrigerant and then directed to heat the condenser 14 and evaporator 20. In this way, the heat stored in the heat storage device 16 can be used as a heat source in defrost mode. Therefore, the heat pump system 10 is able to provide continuous heating during defrosting of the evaporator 20, which eliminates the need for a standby heater.

[0081] Now will be of particular reference Figure 1 and Figure 3 The components of the heat pump system 10 are described. The refrigerant is a heat transfer fluid capable of absorbing, retaining, and releasing heat energy, allowing it to be transferred between different components of the refrigerant circuit 26. In an embodiment, the refrigerant comprises 1,1,1,2-tetrafluoroethane (134a), a hydrofluorocarbon and haloalkane material with low ozone depletion potential. It has the chemical formula CF3CH2F and a boiling point of -26.3°C at atmospheric pressure. In alternative embodiments, the refrigerant may be one of a variety of suitably configured heat transfer fluids, as understood by those skilled in the art.

[0082] The gaseous refrigerant is pressurized by compressor 12 and circulated through refrigerant circuit 26. Compressor 12 is an electromechanical device configured to increase the pressure of the refrigerant in refrigerant circuit 26. During operation, compressor 12 typically receives low-pressure refrigerant through its inlet, then pressurizes it and discharges it into refrigerant circuit 26 through its outlet. By increasing the pressure of the refrigerant, compressor 12 also increases the temperature of the refrigerant subsequently circulating around refrigerant circuit 26.

[0083] Each of the evaporator 20 and the condenser 14 includes a heat exchanger configured to be in direct thermal contact with the conduit 24 of the refrigerant circuit 26. Therefore, each of the evaporator 20 and the condenser 14 is configured such that heat energy can be transferred to and from the refrigerant flowing through the refrigerant circuit 26.

[0084] The condenser 14 defines the main radiator of the heat pump system 10. The condenser 14 is thermally connected to the interior of the building. Specifically, the condenser 14 is configured to transfer heat between the refrigerant in the refrigerant circuit 26 and the ambient air within the building. Therefore, the condenser 14 defines an internal heat exchanger 14 for the heat pump system 10. The condenser 14 is thermally connected to the building's central heating system and is configured to transfer heat between the refrigerant in the refrigerant circuit 26 and a separate heat transfer fluid (e.g., water) flowing through the building's central heating system. Such a central heating system can be configured to distribute the heat it receives from the condenser 14 to different areas throughout the building. The circulated heat is then discharged from multiple radiators or underfloor heating components, as readily understood by those skilled in the art.

[0085] The condenser 14 is configured to transfer heat to the building at a heat-generating temperature (e.g., 65°C). In other words, the condenser 14 is configured to receive pressurized vapor refrigerant at a higher temperature (e.g., approximately 91°C).

[0086] In an alternative exemplary arrangement of the heat pump system 10, the building's central heating system includes an internal fan for directing airflow through surfaces of the condenser 14 exposed inside the building (e.g., coils or radiators). In this way, the internal fan can be operated to improve the heat exchange efficiency of the condenser 14.

[0087] Evaporator 20 defines the primary heat source of heat pump system 10. When heat pump system 10 is installed inside a building, evaporator 20 is positioned externally so that it can absorb heat from the surrounding outside air and transfer it to the refrigerant flowing through refrigerant circuit 26. In this way, evaporator 20 defines an external heat exchanger 20 for heat pump system 10. External fan 34 is used to direct airflow across the surfaces of evaporator 20 exposed to the external ambient air (e.g., coils or fins) to improve its heat exchange efficiency. Evaporator 20 is configured to absorb heat from the external environment when the ambient outside air temperature is approximately 0°C.

[0088] The thermal energy storage device 16 includes a thermal energy storage medium configured to retain thermal energy over an extended period of time. According to an exemplary arrangement of the heat pump system 10, the thermal energy storage medium includes a phase change material housed within a housing 30 or periphery, the housing 30 or periphery being thermally insulated to retain the heat stored within the phase change material.

[0089] Phase change materials are substances configured to release and absorb sufficient energy during a phase change to provide useful heating and / or cooling to the refrigerant in the heat pump system 10. In alternative arrangements of the heat pump system 10, the thermal energy storage medium may include a heat transfer fluid, such as water, which may be held in a tank, as will be readily understood by those skilled in the art. Alternatively, the thermal energy storage medium may include multiple heated stones or pebbles configured to transfer heat directly to and from the refrigerant circuit (e.g., via conductive elements) or via a separate heat transfer fluid circuit, as will be readily understood by those skilled in the art.

[0090] The phase change material is configured to undergo a solid / liquid phase change at a temperature between 25°C and 30°C. Accordingly, the phase change material is configured to absorb heat into the refrigerant and release heat from the refrigerant at temperatures between 25°C and 30°C. Thus, the phase change material is configured with substantially constant heat storage and release temperatures, thereby improving the control of heat recovery and release into the refrigerant loop 26.

[0091] It should be understood that the optimal operating temperature range of the thermal energy storage device 16 will depend at least in part on the operating temperatures of the heat source (e.g., the evaporator) and the radiator (e.g., the condenser). In an embodiment, the thermal energy storage device is configured to operate at an intermediate temperature below the operating temperature of the condenser and above the operating temperature of the evaporator (e.g., transferring heat energy into and out of the refrigerant circuit).

[0092] The phase change material is configured to be in direct thermal contact with the piping portion 28 of the refrigerant circuit 26. The piping portion 28 is configured to extend through the inner cavity of the housing 30, such that it is in direct thermal contact with the phase change material, as... Figure 1 As shown. The conduit portion 28 is configured to have a spiral shape to increase its contact area with the phase change material. The conduit portion 28 is at least partially formed of a thermally conductive material and is configured to allow heat energy to be conducted between the refrigerant and the phase change material in the thermal energy storage device 16. Therefore, the thermal energy storage device 16 is configured to transfer (i.e., absorb and release) heat energy into the refrigerant flowing through the conduit portion 28.

[0093] Although in the embodiments described herein, the thermal energy storage device 16 is shown (e.g., in...) Figure 1 The heat pump system 10 has a spiral conduit section 28 passing through the phase change material, but it should be understood that this arrangement is only one possible configuration among many. For example, in an alternative exemplary arrangement, the phase change material may be thermally connected to the refrigerant in the refrigerant circuit via a finned heat exchanger. Without departing from the scope of this disclosure, the heat pump system 10 may include other arrangements of the thermal energy storage device 16.

[0094] The thermal energy storage device 16 is configured to passively transfer thermal energy between the phase change material and the refrigerant in the refrigerant circuit 26. Specifically, the thermal energy storage device 16 is configured such that when the temperature of the refrigerant is lower than the temperature of the phase change material, the thermal energy stored in the phase change material is released into the refrigerant. Alternatively, if the temperature of the refrigerant is higher than the temperature of the phase change material, the latent heat energy in the refrigerant is discharged into and absorbed by the phase change material in the thermal energy storage device 16.

[0095] Special Reference Figure 1 and Figure 3 The thermal energy storage device 16 is located downstream of the condenser 14, allowing it to recover heat from the warm liquid refrigerant discharged from the condenser 14 during normal heating operation. In this way, the thermal energy storage device 16 is configured to operate as a subcooler of the heat pump system 10. During the defrost mode of the heat pump system 10, the recovered heat stored in the phase change material can be released back into the refrigerant during subsequent operation. Therefore, the thermal energy storage device 16 can also be configured to operate as a secondary or auxiliary heat source for the heat pump system 10.

[0096] The expansion device 18 is configured to reduce the pressure of the refrigerant to cause a pressure and temperature drop, and subsequently, the refrigerant evaporates as it passes through the evaporator. Therefore, the expansion device 18 is configured to control the amount of refrigerant released into the evaporator 20. In this way, the expansion valve 18 is designed to regulate the superheat of the vapor leaving the evaporator 20.

[0097] The expansion device 18 includes an orifice through which refrigerant is guided. The orifice is configured to reduce the pressure of the refrigerant flowing through it, and the refrigerant is cooled due to the associated pressure drop. Therefore, the expansion device 18 is configured not to extract heat energy from the refrigerant. In this way, the refrigerant flowing through the expansion device expands due to a substantially isenthalpic process.

[0098] The expansion device 18 includes a capillary tube configured to cause refrigerant expansion as the refrigerant flows through the refrigerant circuit in either flow direction. Alternatively, the expansion device 18 may include two one-way expansion valves arranged in a bypass circuit, as will be readily understood by those skilled in the art.

[0099] Phase separator 22 is a gas-liquid two-phase separator configured to collect condensed liquid refrigerant in the upstream components of refrigerant circuit 26. This condensation may be caused, for example, by cooling or depressurization of the refrigerant. Phase separator 22 is located upstream of compressor 12 and is thus configured to prevent liquid refrigerant from entering compressor 12, which could otherwise cause damage and / or render it inoperable.

[0100] The switching assembly 40 includes a four-way valve 42, which is configured to switch the operation of the heat pump system 10 between a normal heating mode and a defrost mode. This is achieved by adjusting the flow direction of the refrigerant through the refrigerant circuit 26.

[0101] The operating modes of the heat pump system 10 will now be described in more detail. As described above, the normal heating mode is configured to heat the interior of the building while simultaneously charging the heat storage device 16 (i.e., storing heat energy within the phase change material). The defrosting mode is configured to heat the building while also defrosting the evaporator 20.

[0102] When the heat pump system 10 is operating in normal heating mode, the four-way valve 42 is configured to directly connect the condenser 14 to the thermal energy storage device 16, such as Figure 1 As shown. The four-way valve 42 is also configured to connect the evaporator 20 to the compressor 12. In particular, the refrigerant flow leaving the condenser 14 is directed through the four-way valve 42, then to the thermal energy storage device 16, through the expansion device 18, through the evaporator 20, and then through the four-way valve 42 to the compressor 12 via the phase separator 22.

[0103] At the start of the thermodynamic cycle in normal heating mode, compressor 12 draws vapor from separator 22, increasing its pressure and temperature. The superheated refrigerant vapor (e.g., 91°C) is directed to condenser 14, where it transfers heat into the building at a heat-generating temperature (e.g., 65°C). This causes the gaseous refrigerant to condense into a warm liquid at a higher temperature (e.g., 70°C).

[0104] After leaving the condenser 14, the warm liquid refrigerant is directed to the thermal energy storage device 16, where it transfers heat to the phase change material housed therein. This causes the liquid refrigerant to cool to a subcooled temperature (e.g., about 35°C, which is slightly higher than the melting temperature of the phase change material, i.e., 30°C).

[0105] Upon exiting the thermal energy storage unit 16, the subcooled liquid refrigerant then passes through the expansion unit 18 and is guided through the evaporator 20. As the refrigerant passes through the evaporator 20, it absorbs heat energy from the outside air (e.g., 0°C). The refrigerant then exits the evaporator 20 as a cold, low-pressure vapor. Finally, the refrigerant flows to the liquid / vapor separator 22 to begin the next cycle of the refrigerant loop 26. During normal heating mode, each of the internal and external fans 34 is energized to improve the efficiency of heat transfer through the respective condenser 14 and evaporator 20.

[0106] Now refer to, as follows Figure 2The pressure-enthalpy (ph) curves shown describe the thermodynamic characteristics of the normal heating mode. The ph curves described so far are based on an outdoor air temperature of approximately 0°C, a heat production temperature of approximately 65°C (i.e., the operating temperature of the central heating system), and a phase change material with a melting temperature of approximately 30°C.

[0107] At the start of the normal heating mode cycle, hot refrigerant vapor exits from compressor 12 (as shown at point A on the pH curve) and flows to condenser 14 at approximately 70°C. The refrigerant is condensed into a liquid by condenser 14 and then directed to thermal energy storage device 16 (B) at approximately 70°C. Thermal energy storage device 16 recovers heat from the refrigerant and cools it to a subcooled liquid at approximately 35°C (C). After expanding in expansion device 18, the refrigerant exists as a saturated gas-liquid mixture at approximately -10°C (D). The refrigerant then enters evaporator 20, absorbing heat from outdoor air at approximately 0°C. The refrigerant then becomes saturated vapor at approximately -10°C and enters separator 22, subsequently entering compressor 12 (E).

[0108] In known single-refrigerant-loop heat pump systems, "residual" heat energy from the condenser is wasted when the refrigerant is guided through and "throttled" by the expansion device 18. This invention utilizes heat recovered from the refrigerant leaving the condenser 14 to defrost the evaporator 20, thus eliminating the need for an additional electric heater.

[0109] Now, we will refer to the specific details. Figure 3 and Figure 4 Describing the defrost mode of the heat pump system 10. The four-way valve 42 is configured to switch the heat pump system to defrost mode when ice forms on the surface of the evaporator 20. The switching assembly 40 is configured to directly connect the condenser 14 to the evaporator 20 and the thermal energy storage device 16 to the compressor 12. According to this configuration, the refrigerant flow leaving the condenser 14 is directed sequentially through the four-way valve 42, the evaporator 20, the expansion device 18, and the thermal energy storage device 16, and then returns through the four-way valve 42, reaching the compressor 12 via the phase separator 22. In this way, the switching assembly 40 is configured to reverse the flow direction of the refrigerant through the thermal energy storage device 16, the expansion device 18, and the evaporator 20. Therefore, it should be understood that when switching between the normal heating and defrost modes of the heat pump system 10, the inlet and outlet of each relevant component of the refrigerant circuit are reversed.

[0110] As in normal heating mode, when defrosting mode begins, compressor 12 draws vapor from liquid / vapor separator 22 and increases its pressure and temperature. The superheated refrigerant vapor is directed to condenser 14 to transfer heat into the building at a heat-generating temperature (e.g., 65°C). This causes the gaseous refrigerant to condense into a warm liquid at a higher residual temperature (e.g., approximately 70°C).

[0111] After leaving the condenser 14, the warm liquid refrigerant is directed to the evaporator 20, melting the ice on its outer surface. This subcools the warm liquid refrigerant. The subcooled liquid refrigerant is then transferred to the expansion unit 18, which further reduces its temperature and pressure. The refrigerant is then directed to the thermal energy storage unit 16, where it absorbs heat from the phase change material and becomes superheated vapor. This superheated vapor refrigerant is finally directed to the separator 22 before starting the next defrost cycle. In defrost mode, the external fan 34 is de-energized while the evaporator 20 is defrosted.

[0112] In an exemplary arrangement of the heat pump system 10, an internal fan may be provided to guide air through the condenser 14. For example, when the heat pump system 10 is operating in defrost mode, the internal fan may be powered on to improve the efficiency of heat transfer from the condenser 14 to the interior of the building.

[0113] refer to Figure 4 The pH curve shown describes the thermodynamic characteristics of the defrost mode. At the start of the defrost mode cycle, hot refrigerant vapor from compressor 12 (as indicated by point A on the pH curve) condenses in condenser 14 at a temperature of approximately 70°C. The refrigerant exits condenser 14 and enters evaporator 20 (B) at a temperature of approximately 70°C. In this case, evaporator 20 acts as a subcooler in the refrigerant circuit, absorbing heat from the warm liquid refrigerant and cooling it to a subcooled liquid at a temperature slightly higher than that of evaporator 20 (e.g., approximately 40°C), a temperature that varies as ice melts during defrost operation.

[0114] The refrigerant temperature at evaporator 20 increases as the amount of ice decreases until all the ice melts (i.e., until the evaporator is completely defrosted). The subcooled refrigerant is then directed through expansion unit 18. After expanding in expansion unit 18, the refrigerant is in the form of a saturated gas-liquid mixture at a temperature below 30°C (e.g., approximately 25°C) (D). The refrigerant then enters thermal energy storage unit 16, where it is evaporated and superheated to a temperature of approximately 25°C. Finally, the refrigerant is directed through separator 22 toward compressor 12, and the cycle begins again (E).

[0115] It should be understood that in defrost mode, the heat energy recovered by the thermal energy storage device 16 during normal heating mode is used as a heat source to provide heat to the building. Using the thermal energy storage device 16 as an auxiliary heat source improves the COP of the heat pump system 10.

[0116] Specifically, when the heat pump system 10 operates in defrost mode, the temperature rise of the heat pump (i.e., the increase in the temperature of the refrigerant supplied by the compressor 12) is less than the corresponding temperature rise in normal heating mode. This is because the temperature of the phase change material is approximately 30°C, much higher than the outdoor air temperature of approximately 0°C. Therefore, the COP of the heat pump system 10 in defrost mode is significantly higher than that in normal heating mode. This means that once the thermal energy storage device 16 is fully charged, the heat pump system 10 can switch from normal heating mode to defrost mode to achieve a higher COP, even if there is no ice on the evaporator 20.

[0117] To demonstrate the performance difference between normal heating mode and defrost mode, representative simulations of each mode were performed based on data obtained from commercial simulation software.

[0118] For the simulation of normal heating mode, the parameters are determined as follows: • Outdoor air temperature: 0°C • Condenser output temperature: 65°C • Compressor isentropic efficiency: 75% • Melting temperature of phase change materials: 30°C • Approaching temperature difference of 5°C in the condenser (e.g., the minimum temperature difference between the refrigerant in the refrigerant loop and the heat transfer fluid in the building's central heating system). • Approaching temperature difference of 10°C in thermal energy storage devices (e.g., when thermal energy storage devices are used as heat sources).

[0119] The results of the simulation in normal heating mode are summarized as follows: • Refrigerant mass flow rate: 0.027 kg / s • Evaporation pressure: 2 bar • Condensing pressure: 21.28 bar • Compressor power consumption: 1.486 kW (5348 kJ / h) • Thermal power output: 4 kW (=14500 kJ / h) • Heat extracted from outdoor air: 2.514 kW (8182 kJ / h) • COP = 14500 / 5348 = 2.7 • The enthalpy of the refrigerant at state point B, hB = 295.51 kJ / kg • The enthalpy of the refrigerant at state point C, hC = 248.77 kJ / kg • Enthalpy difference: h = hB - hC = 47 kJ / kg • Heat recovered by the thermal energy storage device: m * (hB-hC) = 0.027 * 47 = 1.26 kW.

[0120] For the defrost mode simulation, the parameters are determined as follows: • Thermal energy storage device temperature: 30°C • Condenser output temperature: 65°C • Compressor isentropic efficiency: 75% • Approaching temperature difference of 5°C in the condenser • Approaching temperature difference of 10°C for thermal energy storage devices (e.g., when the thermal energy storage device is used as a heat source).

[0121] The results of the defrost mode simulation are summarized as follows: • Refrigerant mass flow rate: 0.029 kg / s • Evaporation pressure: 6.6 bar • Condensing pressure: 21.28 bar • Compressor power: 0.92 kW (3334 kJ / h) • Condenser heat output: 4 kW (=14400 kJ / h) • Heat extracted from the thermal energy storage device: 3.1 kW (11200 kJ / h) • COP = 14500 / 3334 = 4.35 .

[0122] These simulation results clearly show that the COP in defrost mode (4.35) is significantly higher than that in normal heating mode (2.7). The higher COP in defrost mode means that the heat pump system 10 can preferentially switch from normal heating mode to defrost mode after the thermal energy storage device 16 is fully charged. It is conceivable that, under certain circumstances, configuring the heat pump system 10 to operate periodically and repeatedly in defrost mode could advantageously prevent frost or ice formation on the outer surface of the evaporator 20.

[0123] Therefore, it is necessary to determine how long and how often the heat pump system 10 should operate in normal heating mode and / or defrost mode in order to optimize system performance over time. Based on the simulations above, the thermal energy storage device 16 is able to recover heat from the refrigerant at a power of 1.26 kW in normal heating mode. In defrost mode, the heat recovered from the thermal energy storage device 16 can be transferred back to the refrigerant at a power of 3.1 kW.

[0124] Consider a scenario where heat pump system 10 operates in normal heating mode until the thermal energy storage device 16 is fully charged, and then enters defrost mode to completely release the recovered heat into the refrigerant circuit 26. Assuming energy balance exists in the system, all heat transferred to the thermal energy storage device in normal heating mode can be released in defrost mode, such that:

[0125] Then, rearranging equation (1) yields: Charging time / discharging time = discharging power / charging power (2)

[0126] As can be seen from equation (2), the heat pump system 10 must operate in normal heating mode for 2.46 time units to fully charge the thermal energy storage device. Then the thermal energy storage device 16 will take 1 time unit to fully release the energy.

[0127] It should be understood that the specific time unit spent in each of the normal and defrost modes will depend on the capacity of the thermal energy storage device 16, and the time ratio will also depend on the melting temperature of the phase change material, which determines the amount of heat energy that can be recovered during normal heating mode operation. The time spent in each operating mode will also depend on the temperature at which heat energy can be released from the thermal energy storage device during defrost mode. Therefore, the optimal operating conditions of the heat pump system will be determined by understanding the trade-offs between these two configurations of the thermal energy storage device (i.e., the heat energy input and output refrigerant loops).

[0128] like Figure 8 As shown, periodically switching between normal heating mode and defrost mode is considered to more effectively utilize the heat energy recovered by the thermal energy storage device 16, and thus also utilizes the higher COP of the defrost mode. The time ratio calculated from equation (2) is used to calculate the percentage of time the system can operate in defrost mode to benefit from its higher COP:

[0129] Figure 8 The average COP during the shown operation period is calculated as follows:

[0130] By comparing the result of equation (4) with the alternative using only the normal heating mode (i.e., no defrost mode), the percentage increase in COP can be calculated as follows:

[0131] Therefore, by periodically switching between normal heating mode and defrost mode (such as...) Figure 8 As shown in the figure, the COP of heat pump system 10 can be improved by 15.7% compared with heat pump systems that do not recover waste heat from condensers.

[0132] In summary, the heat pump system 10 exhibits a significantly higher COP when operating in defrost mode. Furthermore, it has been shown that by periodically switching between normal heating mode and defrost mode, a higher system COP can be obtained for a larger proportion of the heat pump system's operating life (even when there is no ice on the evaporator 20).

[0133] During normal heating mode, the subcooling of the refrigerant by the thermal energy storage device 16 reduces irreversible throttling losses caused by the refrigerant flowing through the expansion device 18. In this way, the transfer of heat to the energy storage device 16 increases the COP of the heat pump system 10.

[0134] Furthermore, since no additional electric heating is required to defrost the evaporator, the present invention achieves an efficiency gain of 5-10% higher than known heat pump systems.

[0135] Furthermore, in this case study, by periodically switching to defrost mode to utilize waste heat recovered from the subcooling, the system's COP can be further improved by 15.7% compared to a heat pump that does not recover such waste heat from the condenser. It should be understood that variations in the system's COP will depend on the specific system configuration and operating conditions.

[0136] Now for reference Figures 5 to 8 An alternative heat pump system according to a second arrangement is described.

[0137] For the sake of brevity, Figure 5 The features and functions of [the text] are referenced. Figure 1 and Figure 3 Those features that are described as identical or similar are given similar numerical labels, but with an increase of 100, and are appended with the suffix "a" in appropriate places to distinguish them from the later arrangements, which will not be elaborated here.

[0138] The heat pump system 110a is configured to provide a flexible, multi-mode air source heat pump that utilizes a novel defrosting mechanism and is capable of continuously heating the building in which it is installed.

[0139] Similar to the previously described system, such as Figure 1 and Figure 3 As shown, the heat pump system 110a includes a compressor 112, a condenser 114, a thermal energy storage device 116, a first expansion device EV1 (e.g., a first expansion valve), an evaporator 120, and a phase separator 122, which are sequentially fluidly connected via fluid conduits 124 to define a refrigerant circuit 126. An external fan 134 is used to guide airflow through the coils or fins of the evaporator 120 to improve its operating efficiency.

[0140] The heat pump system 110a also includes a refrigerant storage device 108 disposed between the condenser 114 and the thermal energy storage device 116. The refrigerant storage device 108 comprises a container or tank configured to hold a volume of refrigerant, as readily understood by those skilled in the art. The refrigerant storage device 108 is configured to compensate for any fluctuations in the volume of refrigerant flowing within the fluid loop 124. For example, the heat pump system 110a is configured to maintain a volume of refrigerant in the evaporator 120 during defrost mode (as described below). In this case, the refrigerant storage device 108 is configured to compensate for a reduction in the volume of refrigerant circulating within the loop.

[0141] The thermal energy storage device 116 includes a phase change material housed within a housing 130, which is configured to allow direct thermal contact with a conduit portion 128 of the refrigerant circuit 126. The thermal energy storage device 116 is configured to passively transfer thermal energy between the phase change material and the refrigerant in the refrigerant circuit 126.

[0142] According to an alternative exemplary arrangement, the thermal energy storage device 116a is configured such that the phase change material is thermally connected to the conduit portion 128 of the refrigerant circuit 126 via the heat transfer fluid loop 136, as shown below. Figure 7 As shown. A heat transfer fluid (e.g., water) is guided by a mechanical fluid pump 146 through a secondary circuit 136 and thermally connected to the first refrigerant in the first refrigerant circuit 126 via a heat exchanger 138. It should be understood that a thermal energy storage device 116a can be connected to the refrigerant circuit 126 between points AA-BB, as shown. Figure 1 and Figure 5 As shown.

[0143] The thermal energy storage device 116a is configured such that the transfer of heat to the refrigerant circuit 126 can be actively controlled by the operation of the pump 146, as those skilled in the art will understand.

[0144] The heat transfer fluid loop 136 can be arranged outside the heat pump system. Therefore, it can be configured with a large heat storage capacity (compared to an internally arranged phase change material heat storage unit). The heat transfer fluid loop 136 is configured to operate at atmospheric pressure, which means it can be made of components that are easy to manufacture and control (e.g., low cost).

[0145] The heat pump system 110a has four different operating modes: normal heating mode, defrosting mode, auxiliary heating mode, and charging mode. These four modes correspond to modes 1, 2, 3, and 4 as outlined in Table 1 below.

[0146] Table 1: Four operating modes (valve - open / closed, fan - on / off)

[0147] The heat pump system 110a includes a switching component 140a configured to control the flow of refrigerant around the refrigerant circuit 126 in order to switch between different operating modes of the heat pump system 110a.

[0148] Specifically, the switching assembly includes six control valves V1, V2, V3, V4, V5, and V6, which can be independently configured to achieve the desired operating mode. The switching assembly 140a also includes four bypass assemblies or fluid lines 144a, 144b, 144c, and 144d, which are configured to bypass different components and sections of the refrigerant circuit 126 according to the desired operating mode.

[0149] According to an alternative exemplary arrangement of the heat pump system 110b, six two-way control valves V1-6 are replaced by four three-way valves V10, V12, V14, and V16, as follows: Figure 9 As shown, it defines the system's switching component 140b. It should be understood that, as... Figure 9 The operation of the heat pump system 110b shown is as follows: Figure 5 The basics are the same.

[0150] Table 1 also outlines the different valve configuration combinations (i.e., open / closed) required to configure the heat pump system 110a in the four operating modes. The table also includes the required operating states (i.e., on / off) of the external fan 134, corresponding to each of the four system operating modes.

[0151] When the heat pump system 110a operates in normal heating mode (i.e., mode 1), the refrigerant from the compressor 112 is guided sequentially through the second control valve V2, the thermal energy storage device 116, the first expansion valve EV1, the sixth control valve V6, the evaporator 120, and the phase separator 122, before returning to the compressor 112 to begin a new cycle. In this mode, the heat pump system 110a operates as a typical single-stage heat pump, releasing heat extracted from the outdoor air into the building through the condenser 114. The thermal energy storage device 116 acts as a subcooler to recover heat from the hot liquid refrigerant discharged from the condenser 114. As a byproduct, the liquid refrigerant is subcooled by transferring heat energy from the refrigerant to the phase change material within the thermal energy storage device 116. The recovered heat is stored in the phase change material, allowing it to be used in subsequent activated operating modes of the heat pump system 110a. The thermodynamic cycle corresponding to the normal heating mode is described by points “ABCDEA”, as shown below. Figure 6 The pressure-enthalpy (ph) curve is shown below.

[0152] When the heat pump system 110a operates in defrost mode (i.e., mode 2), the switching assembly 140a is configured to direct heat energy to the evaporator and condenser, as described with respect to the previous embodiment. This is achieved by directing refrigerant through a second expansion device EV2 (e.g., an expansion valve) via a second bypass assembly 144b, wherein the second expansion device EV2 is fluidly connected to the refrigerant circuit 126 between the condenser 114 and the heat storage device 116. The switching assembly 140a is also configured to bypass the first expansion valve EV1 by diverting the refrigerant through a first bypass assembly 144a, wherein the first bypass assembly 144a is configured to isolate the first expansion valve EV1 from the refrigerant circuit 126.

[0153] Specifically, the refrigerant leaving compressor 112 is guided through the first control valve V1 and the second expansion valve EV2, where it expands, thereby reducing its pressure and temperature. Therefore, expansion valve EV2 is configured to lower the refrigerant temperature below the operating temperature of thermal energy storage device 116, ensuring that thermal energy is transferred from storage device 116 to the refrigerant. It is also configured to balance the refrigerant pressure within the refrigerant circuit.

[0154] After the second expansion valve EV2, the refrigerant is then guided through the thermal energy storage device 116, becoming superheated refrigerant vapor. Thus, the thermal energy storage device 116 functions as both an evaporator and a superheater. Upon leaving the thermal energy storage device 116, the refrigerant is split into two streams. The first stream is guided sequentially through the fourth control valve V4, the third bypass assembly 144c, the phase separator 122, and finally the compressor 112.

[0155] The second stream is directed through the fifth control valve V5, the second bypass assembly 144b, and then into the evaporator 120. According to the defrost mode configuration of the heat pump system 110a, the heat storage device 116 is thermally connected to the refrigerant circuit 126 between the second expansion valve EV2 and the evaporator 120. Thus, the refrigerant vapor flowing through the heat storage device 116 releases its latent heat to melt the ice on the outer surface of the evaporator 120. The liquid refrigerant formed during this condensation process is temporarily retained in the evaporator 120 until the system switches to normal heating mode.

[0156] The first refrigerant stream leaving the thermal energy storage unit 116 is directed to the condenser 114 to provide heat to the building, while the second refrigerant stream is used to defrost the evaporator 120. Therefore, the system provides continuous heat to the building interior during the evaporator defrosting process.

[0157] refer to Figure 6 The continuous heating cycle of the first refrigerant stream is represented by the sequence "GBHFG", and the second refrigerant stream is represented by the sequence "GBHFI". In particular, the sequence "FI" represents the heat released when the superheated refrigerant vapor stream enters the evaporator 120 via the first bypass assembly 144a.

[0158] When operating in defrost mode, the switching component 140a uses the heat recovered from the refrigerant in the condenser (which is usually wasted during throttling) as the heat source for defrosting the evaporator 120, thereby eliminating the need for additional heat input for evaporator defrosting.

[0159] The heat pump system can operate in an auxiliary heating mode, in which heat energy is transferred from the heat storage device 116 to the refrigerant without any input from the evaporator 120. For this purpose, the switching component 140a is configured to bypass the expansion valve EV1 and the evaporator 120.

[0160] Specifically, the refrigerant from compressor 112 is guided sequentially through condenser 114, first control valve V1, first expansion valve EV1, thermal energy storage device 116, fourth control valve V4, third bypass assembly 144c, and phase separator 122, finally returning to compressor 112 to begin a new cycle. In this mode, thermal energy storage device 116 operates as the system's evaporator, and the heat stored in thermal energy storage device 116 is used as an auxiliary heat source. The corresponding thermodynamic cycle is denoted by "FGBHF", as shown below. Figure 6 As shown.

[0161] Similar to the defrosting mode in the first embodiment (e.g.) Figures 1 to 4As shown), the auxiliary heating mode of this embodiment is configured to exhibit a higher COP than the normal heating mode. For example, in the exemplary arrangement of the heat pump system 110a, the COP values ​​for the normal heating mode and the auxiliary heating mode are 2.8 and 4.35, respectively. This is because, in the auxiliary heating mode, the thermal energy storage device 116 replaces the evaporator 120 as the main heat source of the system. Compared to outdoor air (~0°C), the phase change material transfers heat to the refrigerant at a significantly higher temperature (~30°C), resulting in a higher COP level (for the reasons described in the first embodiment).

[0162] An exemplary operating scheme for the heat pump system 110a involves periodically switching between two heating modes, such as... Figure 8 As shown. The timing and duration of each switch were determined so that 28.9% of the time was spent in auxiliary heating mode, resulting in a 15.7% improvement in COP compared to using only normal heating mode. Another advantage of the heat pump system 110a is that the switching component 140a allows the refrigerant circuit 126 to easily switch between normal heating mode (e.g., to charge the thermal energy storage device 116) and auxiliary heating mode (e.g., to utilize the stored thermal energy), thereby increasing the system's flexibility.

[0163] The heat pump system 110a can also operate in a heat charge mode (i.e., mode 4), in which heat energy is transferred from the refrigerant to the heat storage device 116. In this mode, the switching component 140a is configured to guide the refrigerant leaving the compressor 112 around the second expansion valve EV2 and the condenser 114.

[0164] When operating in heat charging mode, the refrigerant from the compressor is guided to flow sequentially through the third control valve V3, the fourth bypass assembly 144d, the thermal energy storage device 116, the first expansion valve EV1, the evaporator 120, and the phase separator 122, and then returns to the compressor 112 to start a new cycle.

[0165] In this heat-charging mode, condenser 114 can be shut off and thermal energy storage device 116 can be used as a secondary condenser. This operating mode is particularly advantageous when the building has no heat demand but the outdoor temperature is high, allowing heat to be efficiently extracted from the external environment and stored in thermal energy storage device 116 for later use. This may occur, for example, when no one is in the building during the day. The corresponding thermal cycle is denoted by "EJKLE", such as... Figure 6 As shown.

[0166] In known single-stage heat pump systems, heat is stored at the condenser's operating temperature (i.e., heat is absorbed from the refrigerant as it flows between the compressor and the condenser). The heat-charging mode according to the invention allows heat to be absorbed by the thermal energy storage device 116 at an intermediate temperature (i.e., heat is transferred from the refrigerant as it flows out of the condenser). By configuring and operating the heat pump system in this manner, the heat-charging mode reduces the thermal energy storage capacity by 1 / COP while maintaining the condenser's operating temperature. Therefore, the heat pump system 110a can be configured with a relatively small thermal energy storage capacity, which reduces system complexity and cost. According to the above exemplary case study, the COP of the heat-charging mode is 4.35. Therefore, the thermal energy storage capacity can be reduced by 1 / 4.35 = 23%.

[0167] According to an alternative exemplary arrangement, the thermal energy storage device 116a is configured such that the phase change material is thermally connected to the conduit 128 of the refrigerant circuit 126 via the heat transfer fluid circuit 136, as shown in the example. Figure 7 As shown. A heat transfer fluid (e.g., water) is guided by a fluid pump 146 through a second circuit 136. The heat transfer fluid in the second refrigerant circuit 136 is thermally connected to the refrigerant in the first refrigerant circuit 126 via a heat exchanger 138.

[0168] The thermal energy storage device 116a is configured such that the transfer of heat to the refrigerant circuit 126 can be actively controlled by the operation of the pump 146, as those skilled in the art will understand. This is similar to, for example... Figure 5 The arrangement shown presents a contrast, in which the thermal energy storage device 116 is configured to passively transfer energy into and out of the refrigerant circuit 126.

[0169] Advantageously, the thermal energy storage device 116a can be located outside the heat pump system 110a, thus allowing for a larger heat capacity (i.e., a larger volume of phase change material). The larger capacity thermal energy storage device 116a can be used to store heat during off-peak times when electricity and / or warm air are more readily available but heat demand in the building is low.

[0170] Two-stage heat pump system The previously described heat pump systems 10, 110a, and 110b are all single-stage heat pump systems because they each consist of only a single refrigerant circuit 26, 126. Reference will now be made to... Figures 10 to 17 Describes a plurality of two-stage heat pump systems 210a, 210b, 210c according to another aspect of this disclosure.

[0171] For the sake of brevity, Figures 10 to 17 The features and functions of [the text] are referenced. Figures 1 to 9 Those characteristics that are described as identical or similar are given a similar numerical label, but with an additional 100, which will not be elaborated further here.

[0172] refer to Figure 10 The heat pump system 210a includes a first compressor 212a, a condenser 214, and a first expansion device EV21 (e.g., a first expansion valve), which are sequentially fluidly connected via fluid conduit 224 to define a first refrigerant circuit 226a. The heat pump system 210a also includes a second compressor 212b, a second expansion device EV22, and an evaporator 220, which are sequentially fluidly connected via fluid conduit 224 to define a second refrigerant circuit 226b.

[0173] A two-phase gas-liquid separator 222 (e.g., a flash tank) is fluidly connected between a first refrigerant circuit 226a and a second refrigerant circuit 226b. The first refrigerant circuit 226a is connected to the gas-containing portion (e.g., the upper part) of the phase separator 222, while the second refrigerant circuit 226b is connected to the liquid-containing portion (e.g., the lower part). The phase separator 222 is positioned upstream of the first compressor 212b, downstream of the first expander EV21, downstream of the second compressor 212b, and upstream of the second expander EV22, as shown below. Figure 10 As shown. During operation of the heat pump system 210a, the piping downstream of the expansion unit EV21 contains a liquid-gas mixture of refrigerant. Therefore, the output of the high-pressure stage can be fluidly connected to either the liquid-containing or gas-containing section of the phase separator 222. The input of the high-pressure stage is fluidly connected to the gas-containing section, such as... Figure 10 As shown.

[0174] During operation of the heat pump system 210a, the refrigerant in the first loop 226a circulates at a higher pressure and temperature than the refrigerant in the second loop 226b. Therefore, the first refrigerant loop 226a and the second refrigerant loop 226b represent the high-pressure / temperature stage and the low-pressure / temperature stage of the heat pump system 210a, respectively. The phase separator 222 is fluidly connected between the refrigerant loops 226a and 226b, representing an intermediate pressure / temperature state within the heat pump system 210a.

[0175] Each of the high-pressure and low-pressure stages is configured to transfer heat from one location to another within its respective refrigerant circuits 226a and 226b. For example, when the heat pump system 210a is operating in heating mode, the high-pressure stage transfers heat from the phase separator 222 to the condenser 214, while the low-pressure stage transfers heat from the evaporator 220 to the phase separator 222. Therefore, the first refrigerant circuit 226a and the second refrigerant circuit 226b are effectively two single-stage heat pump systems connected together via the phase separator 222.

[0176] The two-stage heat pump system 210a is suitable for situations where there is a large temperature difference (i.e., temperature rise) between the outdoor and indoor environments, such as between 50°C and 70°C. Depending on the exemplary operating conditions of the heat pump system 210a, the ambient air temperature can be in the range of -10°C to 10°C (i.e., at the evaporator 220). The building's central heating system may require heat to be generated at temperatures between 50°C and 60°C (i.e., at the condenser 214). In this case, the phase separator 222 is arranged within the heat pump system 210a at an intermediate temperature between 20°C and 30°C. Therefore, each low-pressure stage and high-pressure stage provides a temperature rise of approximately 25°C to 35°C.

[0177] The two-stage heat pump system 216a is also configured to operate at a higher COP than an equivalent single-stage heat pump system operating at the same temperature rise. For example, the two-stage heat pump system 210a has two compressors, thus reducing the pressure difference (i.e., pressure ratio) across each compressor compared to a single compressor in a single-stage heat pump system. The phase separator 222 is configured to remove "flash" gas at an intermediate pressure, preventing the gas from being throttled to the evaporation pressure and instead recompressing it, thereby saving compression power. The phase separator 222 also provides intercooling for the gas discharged from the low-pressure stage compressor 212b, further reducing the compression power required by the high-pressure stage compressor 212a.

[0178] At least some of the problems associated with operating a known single-stage heat pump system also apply to a known two-stage heat pump system. For example, a known two-stage heat pump system is configured to defrost its outdoor heat exchanger by extracting heat from the indoor heat exchanger (i.e., the reverse cycle method) or by extracting hot vapor generated by the compressor (i.e., the hot gas bypass method).

[0179] Each of these defrosting processes can take several minutes to completely defrost the outdoor heat exchanger. During defrosting, the indoor heat exchanger is effectively shut down, so the heat pump does not continuously provide heating. Therefore, a backup electric heater is often needed to provide heat during the outdoor heat exchanger defrosting process, which can reduce the annual average COP of the heat pump system by 5-10%.

[0180] like Figure 10 As shown, the two-stage heat pump system 210a according to this disclosure includes a thermal energy storage device 216a thermally connected to a phase separator 222. By thermally connecting the thermal energy storage device 216a to the phase separator 222, the heat pump system 210a can operate more efficiently, thereby solving the problems of known two-stage heat pump systems.

[0181] The thermal energy storage device 216 includes a phase change material housed within a housing 230. The phase change material is thermally connected to a phase separator 222 via a heat transfer fluid loop 236. A heat transfer fluid (e.g., water) is guided through the heat transfer fluid loop 236 by a mechanical fluid pump 246 and thermally connected to a liquid refrigerant housed in the liquid-containing section of the phase separator 222 via a heat exchanger 238.

[0182] The thermal energy storage device 216 is arranged outside the heat pump system 216a. Therefore, it can be configured to have a large thermal storage capacity (compared to internally arranged phase change material thermal storage units). Furthermore, arranging the thermal energy storage device 216 outside other components of the heat pump system provides the possibility of recovering waste heat from other external sources. For example, warm wastewater from a bathtub or shower can be guided through a pipe 500 thermally connected to the thermal energy storage device, such as... Figure 10 As shown.

[0183] A switching assembly 240a may be provided to control the refrigerant flow within the heat pump system 210a, thereby determining the system's operating mode. The switching assembly 240a includes a set of valves V21, V22, V23, and V24, which are configured to switch the operation of the heat pump system 210a between different operating modes, as will be explained in more detail below.

[0184] Figure 11 An alternative two-stage heat pump system 210b according to this disclosure is shown. The heat pump system 210b includes... Figure 10 The heat pump system 210a shown has essentially the same components. However, the switching assembly 240b is configured differently to allow the heat pump system 210b to operate in continuous heating and defrosting modes, which will be explained in more detail below.

[0185] Specifically, the switching assembly 240b includes a first bypass assembly 244a that fluidly connects the first refrigerant circuit 226a (located immediately downstream of the condenser 214) to the second refrigerant circuit 226b (located immediately upstream of the second expansion valve EV22), such as... Figure 11 As shown. Therefore, the first bypass assembly 244a is configured to bypass valves V21, V23, the first expansion valve EV21, and the phase separator 222.

[0186] Switching assembly 240b also includes a second bypass assembly 244b, which fluidly connects a second refrigerant circuit 226b located immediately downstream of evaporator 220 to a first refrigerant circuit 226a located immediately upstream of first expansion valve EV21, such as... Figure 11As shown. Therefore, the second bypass assembly 244b is configured to bypass the second compressor 212b and the switching valve V24. Switching valves V25 and V26 are used to control the refrigerant flow through the first bypass assembly 244a and the second bypass assembly 244b, respectively.

[0187] Now refer to Figures 12 to 16 The pressure-enthalpy (ph) curves shown describe the operation of heat pump systems 210a and 210b. Heat pump system 210a has four operating modes: normal heating mode, charge mode, auxiliary heating mode, and enhanced heating mode. These four operating modes correspond to modes 1, 4, 3, and 5, as outlined in Table 2 below. Heat pump system 210b has the same four modes as heat pump system 210a (i.e., modes 1, 4, 3, and 5), and it also has an additional defrost mode, which corresponds to mode 2 in Table 2 below.

[0188] Table 2: Operating Modes (Valves—Open / Closed; Compressors and Pumps—On / Off)

[0189] Table 2 outlines the different configurations of valves V21-V26 (i.e., open / closed), pump 246 (i.e., open / closed), and compressors 212a and 212b (i.e., open / closed) required to operate heat pump systems 210a and 210b in different modes.

[0190] When heat pump systems 210a and 210b are operated in normal heating mode (i.e., mode 1), compressors 212a and 212b are turned on, switching valves V21-V24 are opened, and pump 246 is turned off. Additionally, for heat pump system 212b, valves V25 and V26 are closed. Accordingly, the high-pressure stage refrigerant is guided by the first compressor 212a through the condenser 214, the first valve V21, the first expansion valve EV21, the phase separator 222, and the second valve V22, before returning to compressor 212 to begin a new cycle. Simultaneously, the low-pressure stage refrigerant is guided by the second compressor 212b through the phase separator 222, the third valve V23, the second expansion valve EV22, the evaporator 220, and the fourth valve V24, before returning to the second compressor 212b to begin a new cycle. In this mode, heat pump system 110a operates as a typical two-stage heat pump, releasing heat extracted from the outdoor air into the building through condenser 214. The thermodynamic cycles corresponding to the high-pressure stage and the low-pressure stage under normal heating mode are as follows: Figure 12 As shown.

[0191] During the heat-charging mode (i.e., mode 4), valves V21, V22, V25, and V26 are closed, and the first compressor 212a is shut down. Therefore, the high-pressure stage is deactivated. Simultaneously, valves V23 and V24 remain open, and the second compressor 212b is activated. Furthermore, pump 246 is activated to guide heat between the phase separator 222 and the thermal energy storage devices 216a and 216b. Thus, the phase separator 222, combined with TES 216a and 216b, forms a condenser, effectively serving as the low-pressure stage of the heat pump systems 210a and 210b. This can be achieved by controlling the pressure within the phase separator 222. Consequently, heat from the outside air is transferred through the low-pressure stage to the intermediate temperature range and subsequently used to charge the thermal energy storage devices 216a and 216b. The thermodynamic cycle corresponding to the heat-charging mode is described by the point “HIJGH”, as follows: Figure 13 As shown.

[0192] This operating mode is particularly suitable for situations where heat may not be needed, such as when the building's occupants are not present during the day but the outdoor temperature is warm (i.e., high COP conditions). The heat energy collected in the thermal energy storage devices 216a and 216b is stored for later use, such as when the building's occupants return at night when the outdoor temperature is low and the heat demand is high. Once the phase change material in the thermal energy storage devices 216a and 216b is fully charged, the low-pressure stage can also be shut down by switching the second compressor 212b and pump 246.

[0193] During the auxiliary heating mode (i.e., mode 3), valves V21 and V22 are open, and valves V23, V24, V25, and V26 are closed. The first compressor 212a and pump 246 are both on, while the second compressor 212b is off. Therefore, the low-pressure stage is deactivated. By reducing the pressure in the phase separator 222, it is effectively used as the evaporator of the high-pressure stage of the heat pump systems 210a and 210b. Heat is extracted from the thermal energy storage devices 216a and 216b and transferred to the refrigerant in the phase separator 222, and then circulated from the high-pressure stage to the condenser 214. The thermodynamic cycle corresponding to the auxiliary heating mode is described by the dot “KABLK”, as shown below. Figure 14 As shown.

[0194] Heat pump systems 210a and 210b are effectively transformed into single-stage heat pump systems that use thermal energy storage devices 216a and 261b as heat sources to provide heat. It should be understood that thermal energy storage devices 216a and 216b are preferably fully charged when operating in auxiliary heating mode. Auxiliary heating mode is particularly suitable for operation on cold nights following long, warm days, when the building's occupants have left and the system is already in charged mode.

[0195] During the enhanced heating mode (i.e., mode 5), valves V21-V24 are open, while valves V25 and V26 (in system 216b) are closed. Compressors 212a and 212b are both open, as is pump 246. In this operating mode, the pressure in phase separator 222 decreases, causing its temperature to drop slightly below the melting temperatures of thermal energy storage devices 216a and 216b. Therefore, the heat energy from thermal energy storage devices 216a and 216b is diverted to the refrigerant in phase separator 222. Thus, phase separator 222 acts as both a high-pressure stage phase separator and an evaporator, and the system effectively transforms into a dual-evaporator and dual-compressor heat pump system. The thermodynamic cycle corresponding to the enhanced heating mode is as follows: Figure 15 As shown.

[0196] When operating in enhanced heating mode, heat from thermal energy storage devices 216a and 216b and heat from the outdoor air (i.e., heat absorbed by the evaporator 220) are simultaneously used as heat sources to increase the heat capacity of heat pump systems 210a and 210b. Therefore, this mode is particularly suitable for situations where heating demand peaks at night but outdoor temperatures are low.

[0197] During the defrost mode (i.e., mode 2) applicable only to heat pump system 216b, valves V21, V22, V25, and V26 are open while valves V23 and V24 are closed. The first compressor 212a and pump 246 are on, while the second compressor 212b is off. Therefore, the low-pressure stage is deactivated. The warm liquid refrigerant leaving condenser 214 is directed through evaporator 220, releasing its excess heat to melt any ice that has formed on it. The refrigerant is then throttled by the second bypass assembly 244b into phase separator 222. Thus, heat pump system 210b uses the excess heat carried by the warm liquid refrigerant leaving condenser 214 to defrost evaporator 220. The unused heat from condenser 214 is a waste heat source and therefore does not require internal heating of the building. The thermodynamic cycle corresponding to the defrost mode is described by the point “KANLK”, as follows: Figure 16 As shown.

[0198] During defrost mode, phase separator 222 transforms into an evaporator for the high-pressure stage. Heat stored in thermal energy storage device 216b is extracted and used to heat the refrigerant in phase separator 222 to the temperature required for efficient operation of the high-pressure stage of heat pump 210a. Thus, heat pump system 216b is converted into a single-stage system using thermal energy storage device 216b as a heat source. In this way, evaporator 220 can defrost without interrupting continuous heating of condenser 214. Furthermore, unlike conventional defrost modes in two-stage heat pump systems, defrosting evaporator 220 does not require additional power. Defrost mode is particularly suitable for situations where the outdoor ambient temperature is low and evaporator 220 begins to frost.

[0199] Figure 17 An alternative two-stage heat pump system 210c according to this disclosure is shown. Heat pump system 210c includes substantially the same components as heat pump systems 210a and 210b, such as... Figure 10 and Figure 11 As shown. However, its switching component 240c is configured to provide an alternative method for defrosting the evaporator 220.

[0200] Switching assembly 240c includes a first bypass assembly 244c, which is fluidly connected to the second refrigerant circuit 226b at a first location immediately downstream of phase separator 222 and a second location immediately upstream of evaporator 220, as shown below. Figure 17 As shown in the diagram. Therefore, the first bypass assembly 244c is configured to bypass the third valve V23 and the second expansion valve EV22. The second bypass assembly 244d is fluidly connected between the second refrigerant circuit 226b at a first location immediately downstream of the evaporator 220 and the liquid-containing portion of the phase separator 222. Therefore, the second bypass assembly 244d is configured to bypass the second compressor 212b and the fourth switching valve V24. Switching valves V27 and V28 are used to control the refrigerant flow through the first bypass assembly 244c and the second bypass assembly 244d, respectively. The heat transfer fluid circuit 236 is equipped with a first pump 246a to control the refrigerant flow between the phase separator 222 and the thermal energy storage device 216b, and the second bypass assembly 244d is equipped with a second pump 246b located downstream of valve V28.

[0201] During operating modes 1, 4, 3, and 5, heat pump system 216c operates in a manner similar to the previously described two-stage heat pump systems 216a and 261b. During these operating modes, valves V27 and V28 are closed and pump 246b is off. When operating in defrost mode, valves V23 and V24 are closed, while valves V27 and V28 are open and the second pump 246b is activated. Therefore, warm refrigerant from phase separator 222 is pumped through bypass components 244c and 244d and directed through evaporator 220 to melt the ice on it. It should be understood that this configuration of heat pump 216c requires an additional fluid pump 246b, which increases the complexity and cost of the system. Defrosting time may also be longer than that of heat pump system 216b, such as... Figure 11 As shown, this is because the liquid refrigerant in phase separator 222 is colder (e.g., 25°C) than the hot liquid refrigerant leaving condenser 214 (e.g., >65°C).

[0202] Compared to single-stage heat pump systems and known two-stage heat pump systems, two-stage heat pump systems 210a, 210b, and 210c offer improved operational flexibility. For example, they provide the flexibility to utilize off-peak electricity and / or warm outdoor air during the day to power thermal energy storage units 216a and 216b when heat is not needed but outdoor temperatures are warm (e.g., during the day). The two-stage heat pump systems of this disclosure also maximize heat production during peak heat demand by using thermal energy storage units and outdoor air as heat sources. Furthermore, the heat pump system can store heat at intermediate temperatures (i.e., at phase separator 222), which requires a smaller storage size than storing heat at production temperatures (i.e., at condenser 214). For example, an intermediate-pressure thermal energy storage unit (according to this disclosure) can be 20-40% smaller than an equivalent high-pressure thermal energy storage unit while maintaining the same performance. This size reduction is related to the COP (e.g., 1 / COP) of the high-pressure stage. For example, if the COP of the high-pressure stage is 3, the size reduction of the intermediate thermal energy storage unit could be 33%.

[0203] Furthermore, heat pump systems 216b and 216c can continuously supply heat to condenser 214 while defrosting evaporator 220. This system does not require reversing the refrigerant cycle to defrost evaporator 220. Additionally, this system does not consume additional power at low-pressure stage compressor 212b during defrosting.

[0204] Furthermore, defrosting does not require a backup heater because the high-pressure stage continuously provides heat during defrosting operation. Switching units 240a, 240b, and 240c rely on low-cost valves and bypass components that are easy to install and control.

[0205] The previously described heat pump systems 210a, 210b, and 210c each include two independent compressors 212a and 212b (i.e., one compressor for the high-pressure stage and one for the low-pressure stage). Reference will now be made to... Figure 18 and Figure 19 A pair of alternative two-stage heat pump systems 310a and 310b are described, each system including a vapor injection compressor 312 according to another aspect of this disclosure.

[0206] For the sake of brevity, Figure 18 and Figure 19 The features and functions of [the text] are referenced. Figures 10 to 17 Those characteristics that are described as identical or similar are given a similar numerical label, but with an additional 100, which will not be elaborated further here.

[0207] refer to Figure 18 The heat pump system 310a includes a vapor injection compressor 312, which is fluidly connected to the system’s condenser 314, evaporator 320 and phase separator 322 via a separate fluid conduit 324.

[0208] The vapor injection compressor 312 has a low-pressure input terminal for receiving refrigerant from the evaporator 320, a high-pressure output terminal for outputting high-pressure refrigerant to the condenser 314, and a medium-pressure input terminal for receiving the gas-containing portion of refrigerant from the phase separator 322. During operation, the pressure of the vaporized refrigerant received from the phase separator 322 is higher than that of the refrigerant leaving the evaporator 320, but lower than that leaving the compressor 312. The refrigerant from the phase separator 322 is "injected" into the compressor 312, thereby being compressed to its normal output pressure (i.e., the high pressure output to the condenser 314), while only a portion of the refrigerant passes through the compressor 312.

[0209] The heat pump system 310a also includes a first expansion device EV31, which is fluidly connected between the condenser 314 and the phase separator 322. A second expansion device EV32 is sequentially disposed between the phase separator 322 and the evaporator 320, as shown below. Figure 18 As shown. At least one of the first expansion device EV31 and the second expansion device EV32 is configured to control the downstream pressure of the refrigerant in the circuit 326, as those skilled in the art will understand. For example, at least one expansion device is an adjustable expansion valve.

[0210] The thermal energy storage device 316 is fluidly connected to the phase separator 322 via a separate refrigerant loop 336 in the same manner as described above with respect to heat pump systems 210a, 210b, and 210c. Heat pump system 310a is also provided with a switching assembly 340a, which includes valves V31 and V32. The switching assembly 340a is configured to switch the operation of heat pump system 310a between different operating modes, which will be explained in more detail below.

[0211] The arrangement of the phase separator 322 and compressor 312 means that heat pump 310a does not include two separate refrigerant circuits, as in the previously described two-stage heat pump systems 210a, 210b, and 210c. However, the low-pressure stage of heat pump 310a is defined by a refrigerant flow from phase separator 322 sequentially to the second expansion device EV32, through evaporator 320, and to the low-pressure input of compressor 312. Similarly, the high-pressure stage of heat pump system 310a is defined by a refrigerant flow sequentially from compressor 312, through condenser 314, through first expansion device EV31, and to phase separator 322. The intermediate pressure stage of the heat pump system is defined, for example, by a refrigerant flow from phase separator 322 to the intermediate pressure input of compressor 312.

[0212] Figure 19 An alternative two-stage heat pump system 310b is shown, which also includes a vapor injection compressor according to this disclosure. The heat pump system 310b includes... Figure 18The heat pump system 310a shown has essentially the same components. However, the switching component 340b is configured differently to allow the heat pump system 310b to operate in continuous heating and defrosting modes, which will be explained in more detail below.

[0213] Specifically, the switching assembly 340b includes an additional valve V33 sequentially disposed between the condenser 314 and the first expansion valve EV31. The assembly also includes a first bypass assembly 244a, which fluidly connects the refrigerant circuit 326 downstream of the condenser 314 to a location upstream of the second expansion valve EV32, as shown in Figure 19. Therefore, the first bypass assembly 344a is configured to bypass valves V31, V33, the first expansion valve EV31, and the phase separator 322. The switching assembly 240b also includes a second bypass assembly 344b, which fluidly connects the refrigerant circuit 326 upstream of the first expansion valve EV31, as shown in Figure 19. Figure 19 As shown. Therefore, the second bypass assembly 344b bypasses the compressor 312 and the switching valves V32, V33 and the condenser 314. The switching valves V34 and V35 are used to control the flow of refrigerant through the first bypass assembly 344a and the second bypass assembly 344b, respectively.

[0214] The operation of heat pump systems 310a and 310b will now be described with reference to Table 3 below. Heat pump system 310a has four different operating modes: normal heating mode, heat charge mode, enhanced heating mode, and auxiliary heating mode. These four operating modes correspond to modes 1, 4, 5, and 3 as outlined in Table 3, respectively. Heat pump system 310b has an additional defrosting mode corresponding to mode 2, as outlined in Table 3.

[0215] Table 3: Operating Modes (Valves—Open / Closed; Compressors and Pumps—On / Off)

[0216] Table 3 outlines the different configurations of valves V31-V36 (i.e., open / closed) and pump 346 (i.e., on / off) required for operating heat pump systems 310a and 310b in different modes. Compressor 312 is activated in each operating mode. The table also indicates the relative temperature of the refrigerant in phase separator 322 with respect to the phase change material temperature in thermal energy storage device 316.

[0217] It should be understood that each numbered operating mode described in Table 3 (i.e., 1, 4, 5, 3 and 2) corresponds to the operating modes of heat pump systems 210a and 210b outlined in Table 2 above.

[0218] Therefore, during normal heating mode (i.e., mode 1), pump 346 is shut off, causing the thermal energy storage device 316 to separate from the phase separator 322. Furthermore, valves V31, V32, and V33 are opened to enable heat pump systems 310a and 310b to operate as conventional two-stage heat pumps.

[0219] During the charging mode (i.e., mode 4), valves V31, V32, and V33 are open, and valves V34 and V35 are closed. Pump 346 is activated to connect the thermal energy storage system 316 to the phase separator 322. During the charging mode, the high-pressure stage operates to supply heat to the condenser 314 (as in normal heating mode). However, unlike normal heating mode, during the charging mode, pump 346 is activated, thereby connecting the thermal energy storage system 316 to the phase separator 322. Simultaneously, the expansion device EV31 is regulated to control the pressure within the phase separator 322, ensuring that the refrigerant temperature is slightly higher than the melting temperature of the phase change material within the thermal energy storage system 316. This allows heat from the refrigerant to be extracted and stored in the thermal energy storage system 316.

[0220] The difference between heat pump systems 310a and 310b and heat pump systems 210a, 210b and 210c is that during the charging mode (mode 4), the heat pump continues to supply heat to the condenser 314 (i.e., the "charging mode" of heat pump systems 310a and 310b is actually a "continuous heating and charging mode"), while heat pump systems 210a, 210b and 210c can operate to charge the thermal energy storage device without also supplying heat to the condenser 214 (i.e., the "charging mode" of heat pump systems 210a, 210b and 210c is actually a "pure charging mode").

[0221] During the enhanced heating mode (i.e., mode 5), valves V31, V32, and V33 are open, while valves V34-V35 are closed. Pump 346 is activated, causing the thermal energy storage device 316 and evaporator 320 to simultaneously function as heat sources, thereby increasing the heating capacity of heat pump systems 316a and 316b. During this operating mode, the refrigerant pressure in phase separator 322 is regulated so that the refrigerant temperature is below the melting point of the phase change material in thermal energy storage device 316. This results in heat from thermal energy storage device 316 being absorbed by the refrigerant in phase separator 322.

[0222] During the auxiliary heating mode (i.e., mode 3), valves V31, V32, V34, and V35 are closed, and valve V33 is open. Pump 346 is activated to transfer heat from the thermal energy storage device 316 to the refrigerant in the phase separator 322. The low-pressure stage is deactivated, so the phase separator 315, together with the thermal energy storage device 316, serves as the evaporator for the high-pressure stage. As in mode 5, the pressure in the phase separator 322 is controlled so that the refrigerant temperature is below the melting temperature of the phase change material in the thermal energy storage device 316.

[0223] During the defrosting and continuous heating modes (i.e., mode 2) applicable to the heat pump system 310b, valves V31, V32, and V33 are closed, while valves V34 and V35 are open. The warm liquid refrigerant leaving the condenser 312 is directed through the evaporator 320 to release heat and melt any ice that has formed on it. The cooled refrigerant is then throttled in the expansion valve EV31 before entering the phase separator 322. In this mode, the phase separator 322, together with the thermal energy storage device 316, transforms into a high-pressure stage evaporator, allowing the heat stored in the thermal energy storage device 316 to be extracted and raised to the heat production temperature.

[0224] It should be understood that each of operating modes 1, 4, 5, 3, and 2 is preferably suited to substantially the same conditions as described above with respect to the dual-compressor two-stage heat pump systems 210a, 210b, and 210c. Furthermore, the vapor injection compressor heat pump systems 310a and 310b have the additional advantage of being easier to integrate into a building's central heating system because they require fewer components (e.g., fewer compressors and fewer fluid piping sections and valves, etc.).

[0225] Heat pump systems 210a, 210b, 210c, 310a, 310b, such as Figure 10 , Figure 11 and Figures 17 to 19 As shown, this can also be applied to refrigeration applications (e.g., in refrigerators, freezers, or air conditioning systems). It should be understood that for refrigeration applications, a two-stage heat pump system is configured in reverse, with the condenser exposed to ambient air (i.e., the radiator), while the evaporator is located where the load is required (e.g., inside a refrigerator). In this case, the required load is a negative heat load (i.e., a cooling load), thereby reducing the temperature of the refrigerated area.

[0226] Two-stage heat pump systems 210a, 210b, 210c, 310a, and 310b are particularly beneficial when the radiator temperature (i.e., the outdoor ambient air temperature) is too high and / or the required temperature drop is too large. The operation of two two-stage heat pump systems, 210a and 310a, for refrigeration applications is described below.

[0227] Based on the exemplary operating conditions of the refrigeration heat pump system, the ambient air temperature (i.e., at the condenser) is between 30°C and 40°C, and the cooling load temperature is around -20°C. The thermal energy storage device is thermally connected to the phase separator, which operates at an intermediate temperature of 5°C to 10°C. Therefore, the total temperature drop is approximately 55°C, with the low-pressure stage and high-pressure stage each providing a temperature drop of approximately 25°C to 30°C.

[0228] like Figure 10As shown, the heat pump system 210a can operate in four different cooling modes, referred to as normal cooling mode, auxiliary cooling mode, charging mode, and cooling enhancement mode. These four modes correspond to modes 6, 7, 8, and 9, as outlined in Table 4 below.

[0229] Table 4: Operating Modes (Valves - Open / Closed; Compressors and Pumps - On / Off)

[0230] During normal cooling mode (i.e., mode 6), pump 246 is off, and each of valves V21-V24 is open. The heat pump system 210a operates as a conventional two-stage cooling system by absorbing heat from the evaporator 220 and transferring it to the condenser 214. In this way, the heat pump system 210a uses outside air (i.e., at the evaporator 220) as a radiator.

[0231] The auxiliary cooling mode is particularly useful when high outdoor air temperatures reduce the normal operating efficiency of the refrigeration system. When operating in auxiliary cooling mode (i.e., mode 7), pump 246 is turned on, valves V21 and V22 are closed, and the first compressor 212a is turned off. Therefore, the high-pressure stage is deactivated, and the low-pressure stage is configured to direct heat to the thermal energy storage device 216a. This is equivalent to extracting cooling heat energy (i.e., "cooling" of energy) from the thermal energy storage device 216a and directing it to the refrigerant in the phase separator 222. In this way, the heat pump uses the thermal energy storage device 216a as a radiator to dissipate heat from the evaporator 220.

[0232] During the charge-cooling mode (i.e., mode 8), pump 246 starts and valves V21 and V22 open, while valves V23 and V24 close. This arrangement effectively transforms the heat pump into a single-stage system, using ambient air (i.e., at condenser 214) as a radiator. At intermediate temperatures between 5°C and 10°C, the heat pump operates to extract heat from the thermal energy storage device 216a into the refrigerant in the phase separator 222. The charge-cooling mode is particularly advantageous when cooling demand is low, especially when the outdoor ambient temperature is also low.

[0233] The enhanced cooling operation mode is particularly advantageous when cooling demand is high. When operating in enhanced cooling mode (i.e., mode 9), each of valves V21-V24 is open, and compressors 212a and 212b and pump 246 are all activated. Both the high-pressure and low-pressure stages are activated to direct heat energy into the heat storage device 216a and the ambient air (i.e., at the condenser 214). By using the heat storage device 216a as an additional radiator, the cooling performance of the heat pump is improved.

[0234] like Figure 18As shown, the vapor injection compressor two-stage heat pump system 310a can also operate as a refrigeration system. Specifically, the heat pump system 310a can operate in four different refrigeration modes, referred to as normal refrigeration mode, refrigeration enhancement mode, refrigeration and energy charging combination mode, and charging mode. These four modes correspond to modes 10, 11, 12, and 13 shown in Table 5 below, respectively. The compressor 312 is activated during each operating mode.

[0235] Table 5: Operating Modes (Valve - Open / Closed; Pump - On / Off)

[0236] When operating in normal cooling mode (i.e., mode 10), valves V31 and 32 are open and pump 346 is closed. Therefore, heat pump system 310a operates as a conventional two-stage cooling heat pump system, i.e., by extracting heat from evaporator 320 and directing it to condenser 314, wherein the thermal energy storage device 316 is deactivated.

[0237] During the enhanced cooling mode (i.e., mode 11), pump 346 is turned on and valves V31 and V32 are opened. The pressure in phase separator 322 is regulated so that the temperature of the refrigerant is higher than the melting temperature of the phase change material in thermal energy storage device 316a. Therefore, the heat pump operates as a two-stage refrigeration system, using thermal energy storage device 316a as a recooler for the refrigerant and using ambient air at condenser 214 as a radiator.

[0238] When operating in a combined cooling and charging mode (i.e., mode 12), valves V31 and V32 open, and pump 346 starts. The pressure of the refrigerant in phase separator 322 is regulated so that the refrigerant temperature is below the melting point of the phase change material in thermal energy storage device 316. This causes heat from thermal energy storage device 316 to be absorbed by the refrigerant in phase separator 322, effectively storing cooling heat energy in thermal energy storage device 316. This operating mode is particularly suitable when the ambient temperature is relatively low because it allows the heat pump to operate as a two-stage system, with ambient air acting as a radiator while simultaneously extracting heat from thermal energy storage device 316.

[0239] When cooling is not required, it is advantageous to use the charge cooling mode (i.e., mode 13). During operation, valves V31 and V32 are closed, thus converting the heat pump into a single-stage system. Similarly, the pressure of the refrigerant in phase separator 322 is regulated so that the refrigerant temperature is below the melting point of the phase change material. Therefore, heat is extracted from the thermal energy storage device 316 at a temperature of approximately 5°C to 10°C for later use (e.g., during mode 11) and directed to the condenser 314, which serves as a radiator.

[0240] When heating and cooling demands are mismatched, heat pump systems 210a, 210b, 210c, 310a, and 310b, such as... Figure 10 and Figure 18 As shown, this can also be applied to combined heating and cooling operations. In this case, thermal energy can be stored at an intermediate temperature in a thermal energy storage device, allowing the system to match production and demand as needed.

[0241] In any alternative exemplary arrangement of a two-stage heat pump system, the thermal energy storage device may be arranged within the phase separator 422, such as... Figure 20 As shown. The thermal energy storage device 416 includes multiple individual thermal energy storage elements (e.g., spherical or spherical). Each storage element includes a volume of phase change material encapsulated within a housing 430. Unlike the thermal energy storage devices 216, 316 described above, the internal thermal energy storage device 416 does not include a pump or heat transfer fluid loop. Instead, each housing 430 of the multiple storage elements is configured to allow thermal energy to passively flow (e.g., via thermal conduction) between the phase change material contained therein and the refrigerant contained within the phase separator 422. For example, the housing 430 may be formed of a metallic material. By providing multiple smaller storage elements, this increases the surface area of ​​the phase change material in contact with the refrigerant in the phase separator 422.

[0242] It should be understood that the "internal" thermal energy storage device 416 may have a larger thermal energy storage device than the "externally" installed thermal energy storage device (e.g., Figure 10 The device 216 shown has a smaller capacity. However, the internal thermal energy storage device 416 is easier to accommodate within a heat pump system because it can be encapsulated within the space occupied by the phase separator 422. Furthermore, the passive internal thermal energy storage device 416 has no moving parts, which makes operation and maintenance easier and cheaper.

[0243] Case 1—Two-stage heating system To illustrate the performance differences between normal heating mode and a combination of charging and auxiliary heating modes, we conducted a representative simulation of the heat pump system based on data obtained from commercial simulation software.

[0244] The operating conditions are determined as follows: • Outdoor air temperature varies between 0°C and 10°C throughout the day. • Condenser output temperature: 65°C • Compressor isentropic efficiency: 70% • Melting temperature of phase change materials: 30°C • Evaporator approach temperature 10°C • Approach temperature of the condenser: 3°C • Approach temperature of thermal energy storage device 3°C • Refrigerant: R134a.

[0245] A two-stage heat pump system is used as the baseline for the following analysis. The system operates in normal heating mode (i.e., mode 1) and undergoes the following steps: High-temperature refrigerant vapor at 80.3°C enters the condenser, releasing heat to the water in the central heating system, then condenses and cools to 70°C. The water from the central heating system returns at 40°C and is heated to 65°C in the condenser. The hot liquid refrigerant at 70°C and 21.28 bar is throttled to 33°C and 8.39 bar by the first expansion device and then enters the phase separator. The vapor is removed by the high-pressure stage compressor, while the liquid refrigerant is further throttled to -20°C and 1.33 bar by the second expansion device. The mixture then enters the evaporator, absorbing heat from the ambient air at 0°C and cooling it to -10°C. The mixture then completely evaporates into low-pressure saturated vapor at -20°C. The low-pressure stage compressor extracts the low-pressure vapor and compresses it to the intermediate pressure of the phase separator. After compression, the superheated vapor bubbles through the liquid refrigerant in the phase separator and is cooled into saturated vapor. Together with the steam generated through the first throttling process, it is extracted and compressed by the high-pressure stage compressor and directed to the condenser pressure to begin a new cycle.

[0246] The parameters and results of the simulation in normal heating mode (i.e., mode 1) are summarized as follows: • Outdoor air temperature: 0°C • Evaporation pressure: 1.33 bar • Condensing pressure: 21.28 bar • Low-pressure stage compressor power consumption: 0.905 kW • Low-pressure stage compressor mass flow rate: 0.017 kg / s • High-pressure stage compressor power consumption: 0.781 kW • High-pressure stage compressor mass flow rate: 0.029 kg / s • Condenser thermal power output at 65°C: 4kW (= 14400 kJ / h) • Heat extracted from outdoor air at 0°C: 2.314 kW (= 8330.4 kJ / h) • The COP of the system in normal heating mode is 4 / (0.905 + 0.781) = 2.37 .

[0247] The simulation results for the heat charging mode (i.e., mode 4) are summarized as follows: When daytime heat demand is low and outdoor air temperature is high (e.g., 10°C), the charging mode is used. During this mode, the high-pressure stage is shut down, and the low-pressure stage is isolated to charge the thermal energy storage unit. The evaporator extracts 2.51 kW of heat from the ambient air and cools it from 10°C to 0°C. The phase separator temperature is maintained at 33°C, and the phase change material temperature in the thermal energy storage unit is 30°C. The phase separator and thermal energy storage unit effectively function as the condenser for the low-pressure stage. Heat is stored in the thermal energy storage unit at a power of 3.25 kW. The low-pressure stage compressor consumes 0.73 kW, therefore the heat pump COP is [not specified]. L for 4.45 .

[0248] The simulation results for the auxiliary heating mode (i.e., mode 3) are summarized as follows: In auxiliary heating mode, the high-pressure stage operates in isolation, thereby removing heat from the thermal energy storage unit via a phase separator and boosting it for heating. The thermal energy storage unit stores 30°C of heat, with a temperature approaching 3°C; therefore, the phase separator temperature is maintained at 27°C. The phase separator and thermal energy storage unit effectively act as the evaporator for the high-pressure stage, generating heat at the condenser with a power output of 4kW. The high-pressure stage compressor consumes 0.92kW, and the thermal energy storage unit releases 3.08kW at 30°C. Therefore, the calculated COP of the heat pump for the isolated high-pressure stage is... H for 4.35 .

[0249] By operating the heat pump system 216a in a combined charge and auxiliary heating mode, the system can more efficiently deliver heat under conditions where the ambient temperature varies throughout the day. These two operating modes are possible because each of the high-pressure and low-pressure stages of the heat pump system can operate independently and isolated from each other. To illustrate this effect, the overall COP of the heat pump system can be calculated based on the COP values ​​corresponding to the charge and auxiliary heating modes, as determined above.

[0250]

[0251] The calculated overall COP is 2.48 This is 5% higher than the baseline case that extracts heat directly from the 0°C air and generates 65°C of heat at night.

[0252] Case Study 2—Two-Stage Refrigeration System To illustrate the performance differences between normal cooling mode and a combination of charging and auxiliary cooling modes, we conducted a representative simulation of the heat pump system based on data obtained from commercial simulation software.

[0253] The operating conditions are determined as follows: • Outdoor air temperature varies between 20°C and 35°C throughout the day. • Evaporator input temperature: -25°C • Compressor isentropic efficiency: 70% • Melting temperature of phase change materials: 5°C • Evaporator approach temperature 10°C • Approach temperature of the condenser: 10°C • Approach temperature of thermal energy storage device 3°C • Refrigerant: R134a.

[0254] The two-stage heat pump system 210a is used as the benchmark for the following analysis. The system operates in normal cooling mode (i.e., mode 6) and undergoes the following steps: High-temperature refrigerant vapor at 67.2°C enters the condenser, releasing heat to the ambient air at 35°C. The hot liquid refrigerant at 55°C and 14.96 bar is then throttled to 8°C and 3.87 bar by the first expansion device before entering the phase separator. The vapor is removed by the high-pressure stage compressor, while the liquid refrigerant is further throttled to -25°C and 1.06 bar by the second expansion device. The mixture then enters the evaporator to absorb heat from the cooling load. The mixture eventually evaporates completely at -25°C into low-pressure saturated vapor. The low-pressure stage compressor extracts the low-pressure vapor and compresses it to an intermediate pressure, which is also the pressure of the phase separator. After compression, the superheated vapor bubbles through the liquid refrigerant in the phase separator, cooling into saturated vapor. Together with the vapor generated by the first throttling process, it is then extracted and compressed to the condenser pressure by the high-pressure stage compressor.

[0255] The parameters and results of the simulation in normal cooling mode (i.e., mode 6) are summarized as follows: • Outdoor air temperature: 35°C • Evaporation pressure: 1.06 bar • Condensing pressure: 14.96 bar • Low-pressure stage compressor power consumption: 0.821 kW • Low-pressure stage compressor mass flow rate: 0.023 g / s • High-pressure stage compressor power consumption: 1.479 kW • Mass flow rate of high-pressure stage compressor: 0.039 g / s • Heat output of the condenser at 55°C: 6.34 kW (= 22840 kJ / h) • Cooling capacity extracted from the evaporator's cooling load at -25°C: 4.04 kW (= 14560 kJ / h) • The COP of the system in normal heating mode is 4.04 / (0.821 + 1.479) =1.76 .

[0256] According to an exemplary operating method of the refrigeration system, the isolated high-pressure stage can be used to first extract heat from the thermal energy storage device when the ambient temperature is low at night, thus resulting in a higher COP. Then, the depleted phase change material absorbs heat energy when the outdoor ambient temperature is high the next day, further improving the system's COP. To evaluate the potential energy-saving effect of this flexible operating strategy, a simulation case is considered, in which the heat pump operates in a charging cooling mode (i.e., mode 8) at night and then in an auxiliary cooling mode (i.e., mode 7) the next day.

[0257] The simulation results for the charge-cooling mode (i.e., mode 8) are summarized as follows: During charge-cooling mode, cooling demand is low, and outdoor air temperature is also low (e.g., 20°C), therefore the high-pressure stage is isolated to extract heat from the thermal energy storage device. The temperature of the thermal energy storage device is 5°C, with a charge-discharge temperature difference of 3°C. Correspondingly, the phase separator temperature is maintained at 2°C. The phase separator and thermal energy storage device serve as the evaporator for the high-pressure stage. The heat pump system provides a cooling capacity of 4.627 kW, stored in the thermal energy storage device, while the high-pressure stage compressor consumes 1.128 kW. The calculated cooling COP for the isolated high-pressure stage is... H for 4.1 .

[0258] The simulation results for the auxiliary cooling mode (i.e., Mode 7) are summarized as follows: During auxiliary cooling mode, the low side of the system is isolated, and heat is discharged to the thermal energy storage device via the phase separator. The thermal energy storage device replaces the ambient air, which is warmer during the day, as a radiator. For this simulation, it is assumed that the cooling heat stored in the thermal energy storage device is 5°C, the heat transfer approach temperature is 3°C, and the phase separator is maintained at 8°C. The phase separator and thermal energy storage device are used as the condenser of the low-pressure stage, providing cooling at a power of 4kW. The low-pressure stage compressor power consumption is 0.87 kW. Therefore, the calculated low-pressure stage cooling COP is... L for 4.6 .

[0259] Based on the calculated COP of the two isolated stages of the cooling system, the energy flow follows this decoupled and staggered operating strategy. The overall COP of this operation can then be calculated.

[0260] The calculated overall COP is 1.94 This is 10.5% higher than the baseline case that extracts heat directly at -25°C during the day and releases it into the air at 35°C.

[0261] As referenced in this article Figures 1 to 20The several exemplary heat pump systems described share one or more features having similar structure and / or function. Furthermore, it should be understood that each exemplary heat pump system is not limited to the specific arrangement described and illustrated therein. For example, each of the exemplary heat pump systems may incorporate additional features or may be incorporated into other systems (e.g., building heating systems) without departing from the scope of this disclosure. Moreover, it should be understood that any feature of an exemplary heat pump system may be combined with any feature of another exemplary heat pump system without departing from the scope of this disclosure.

Claims

1. A heat pump system for controlling the interior temperature of a building, the system comprising: A compressor, a first heat exchanger, an expansion device, and a second heat exchanger are fluidly connected together via a refrigerant flow to define a refrigerant circuit, and a thermal energy storage device is thermally connected to the refrigerant circuit to exchange heat with the refrigerant flow. The heat pump system is configured to operate in normal heating mode, defrost mode, and / or auxiliary heating mode, wherein: In normal heating mode, heat energy is transferred from the second heat exchanger to the refrigerant stream, and then from the refrigerant stream through the first heat exchanger to heat the building. In defrost mode, heat energy is transferred from the heat storage device to the refrigerant stream, and then transferred from the refrigerant stream through the first heat exchanger to heat the building, and then transferred from the refrigerant stream through the second heat exchanger to defrost the second heat exchanger. In auxiliary heating mode, thermal energy is transferred from the thermal energy storage device to the refrigerant stream, and then transferred from the refrigerant stream through the first heat exchanger to heat the building. The heat pump system includes a switching component configured to switch between a normal heating mode, a defrost mode, and / or an auxiliary heating mode. The switching component is configured to, when the heat pump system is operating in defrost mode, direct refrigerant leaving the first heat exchanger through the second heat exchanger, allowing residual heat in the refrigerant to defrost the second heat exchanger. The switching component is also configured to, when the heat pump system is operating in auxiliary heating mode, bypass the expansion device and the second heat exchanger.

2. The heat pump system of claim 1, wherein the switching component is configured to, when the heat pump system is operated in defrost mode, guide refrigerant leaving the first heat exchanger sequentially through the second heat exchanger, the expansion device, and the compressor.

3. The heat pump system according to claim 1 or claim 2, wherein the thermal energy storage device is connected to the refrigerant circuit between the expansion device and the compressor.

4. The heat pump system of claim 2 or claim 3, wherein the switching component includes a four-way valve configured to directly connect the first heat exchanger to the second heat exchanger when the heat pump system is operating in defrost mode.

5. The heat pump system of claim 1, wherein the switching component is configured to, when the heat pump system is operated in defrost mode, bypass the expansion device and guide the refrigerant leaving the first heat exchanger sequentially through the second expansion device, the thermal energy storage device, the second heat exchanger, and the compressor.

6. The heat pump system of claim 5, wherein the switching component includes a first bypass component configured to isolate the expansion device from the refrigerant circuit when the heat pump system is operating in defrost mode.

7. The heat pump system according to claim 5 or claim 6, wherein the thermal energy storage device is connected to the refrigerant circuit between the second expansion device and the second heat exchanger.

8. The heat pump system of claim 7, wherein the switching component includes a second bypass component configured to fluidly connect the second expansion device to the refrigerant circuit between the first heat exchanger and the thermal energy storage device when the heat pump system is operated in defrost mode.

9. The heat pump system according to any one of claims 5 to 8, wherein the heat pump system can operate in a heat-charging mode, in which heat energy is transferred from the refrigerant to the heat energy storage device, wherein the switching component is configured to guide refrigerant leaving the compressor to bypass the second expansion device and the first heat exchanger when the heat pump system is operating in the heat-charging mode.

10. The heat pump system according to any one of the preceding claims, wherein the thermal energy storage device comprises a phase change material.

11. The heat pump system of claim 10, wherein the phase change material is configured to be in direct thermal contact with the piping of the refrigerant circuit.

12. The heat pump system of claim 10, wherein the phase change material is thermally connected to the pipe of the refrigerant circuit via a circuit including a heat transfer fluid.

13. The heat pump system according to any one of the preceding claims, wherein the refrigerant circuit comprises a high-pressure stage and a low-pressure stage, the high-pressure stage and the low-pressure stage being fluidly connected together by a phase separator, wherein the high-pressure stage comprises the first heat exchanger and the low-pressure stage comprises the second heat exchanger.

14. The heat pump system of claim 13, wherein the thermal energy storage device is thermally connected to the phase separator.

15. The heat pump system of claim 13 or claim 14, wherein the compressor defines a compressor assembly comprising a first compressor fluidly connected to the high-pressure stage and a second compressor fluidly connected to the low-pressure stage.

16. The heat pump system of claim 13 or claim 14, wherein the compressor comprises a vapor injection compressor fluidly connected to a high-pressure stage and a low-pressure stage of the refrigerant circuit.

17. The heat pump system according to any one of claims 13 to 16, wherein the expansion device defines an expansion device assembly comprising a first expansion device fluidly connected to the high-pressure stage and a second expansion device fluidly connected to the low-pressure stage.

18. The heat pump system of claim 17, wherein the switching component is configured to, when the heat pump system is operated in defrost mode, bypass the first expansion device and guide the refrigerant leaving the first heat exchanger sequentially through the second expansion device, the second heat exchanger, and the phase separator.

19. A building comprising a heat pump system according to any one of claims 1 to 18, wherein the second heat exchanger is thermally connected to a second heat source, and wherein the first heat exchanger is thermally connected to a central heating system of the building.

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