FIELD

This disclosure relates to a heat pump system. More specifically, this disclosure relates to a variable refrigerant (VRF) heat pump system in which individual outdoor units are capable of being defrosted separately.

BACKGROUND

A heat pump system is a refrigeration system capable of conditioning a space by either heating or cooling air within the space. A heat pump system generally includes a four-way reversing valve that can be configured to switch between a heating mode and a cooling mode.

SUMMARY

This disclosure relates to a heat pump system. More specifically, this disclosure relates to a variable refrigerant (VRF) heat pump system in which individual outdoor units are capable of being defrosted separately.

A heat pump system including a plurality of outdoor units in fluid communication with one or more indoor units via a heat transfer circuit is described. Each of the plurality of outdoor units is operable in a plurality of operation modes. A first of the plurality of outdoor units includes a compressor, and a first flow control device between the compressor and an outdoor heat exchanger in a first flow direction and between the compressor and a second flow control device in a second flow direction. In a first state, the first flow control device permits flow to the outdoor heat exchanger, and in a second state, the first flow control device permits flow to the second flow control device. A second of the plurality of outdoor units includes a compressor, and a first flow control device between the compressor and an outdoor heat exchanger in a first flow direction and between the compressor and a second flow control device in a second flow direction. In a first state, the first flow control device permits flow to the outdoor heat exchanger, and in a second state, the first flow control device permits flow to the second flow control device. The second flow control devices of the first and second of the plurality of outdoor units are individually controllable to set the first and/or second of the plurality of outdoor units to a defrost mode. A heat pump system including a plurality of outdoor units in fluid communication with one or more indoor units via a heat transfer circuit is described. Each of the plurality of outdoor units is operable in a plurality of operation modes. A first of the plurality of outdoor units includes a compressor, a flow control device between the compressor and an outdoor heat exchanger in a first flow direction and between the compressor and one or more indoor units in a second flow direction, and a pressure control flow path. The pressure control flow path is disposed between the flow control device and the one or more indoor units. When in a first state, the flow control device permits flow to the outdoor heat exchanger, and in a second state, the flow control device permits flow to the one or more indoor units. A second of the plurality of outdoor units includes a compressor, a flow control device between the compressor and an outdoor heat exchanger in a first flow direction and between the compressor and one or more indoor units in a second flow direction, and a pressure control flow path. The pressure control flow path is disposed between the flow control device and the one or more indoor units. When in a first state, the flow control device permits flow to the outdoor heat exchanger, and in a second state, the flow control device permits flow to the one or more indoor units. The pressure control flow paths of the first and second of the plurality of outdoor units are individually controllable to selectively enable and/or disable a pressure control mode of the first and/or second of the plurality of outdoor units.

A method of controlling a heat pump system, the heat pump system including a plurality of outdoor units is described. Each of the plurality of outdoor units includes at least a compressor and an outdoor heat exchanger. The method includes determining whether a frost condition exists and setting a first of the plurality of outdoor units to operate in a defrost mode in response to determining the frost condition exists. The method further includes individually operating a second of the plurality of outdoor units in a same or different operating mode.

A method of controlling a heat pump system, the heat pump system including a plurality of outdoor units is described. Each of the plurality of outdoor units includes at least a compressor and an outdoor heat exchanger. The method includes determining whether a pressure control condition exists and setting a first of the plurality of outdoor units to operate in a pressure control mode in response to determining the pressure control condition exists. The method further includes individually operating a second of the plurality of outdoor units in a same or different operating mode. BRIEF DESCRIPTION OF THE DRAWINGS

References are made to the accompanying drawings that form a part of this disclosure, and which illustrate the embodiments in which the systems and methods described in this Specification may be practiced.

FIG. 1 illustrates a diagram of a variable refrigerant (VRF) heat pump system, according to one embodiment.

FIG. 2A illustrates a diagram of a heat transfer circuit for a heat pump system, according to one embodiment.

FIG. 2B illustrates a diagram of a heat transfer circuit for a heat pump system, according to another embodiment.

FIG 3 illustrates a diagram of a heat transfer circuit for a heat pump system in a heating mode, according to one embodiment.

FIG. 4 illustrates a diagram of a heat transfer circuit for a heat pump system in a defrosting mode, according to one embodiment.

FIG. 5 illustrates a diagram of a heat transfer circuit for a heat pump system in a pressure control mode, according to one embodiment.

FIG. 6 illustrates a method for controlling a heat pump system, according to one embodiment.

FIG. 7 illustrates a method for controlling a heat pump system operating in a heating mode, according to one embodiment.

Like reference numbers represent like parts throughout.

DETAILED DESCRIPTION

This disclosure relates to a heat pump system. More specifically, this disclosure relates to a variable refrigerant (VRF) heat pump system in which individual outdoor units are capable of being defrosted separately.

The embodiments described herein relate to variable refrigerant heat pump systems having a plurality of outdoor units. Each of the plurality of outdoor units can operate in a variety of different operating modes. Examples of operating modes include, but are not limited to, a cooling mode, a heating mode, a pressure control mode, and a defrost mode. In some embodiments, the pressure control mode can be referred to as the frost prevention mode under some circumstances. Each of the plurality of outdoor units of the heat pump system can operate in the same operating mode. In one embodiment, each of the plurality of outdoor units can operate in a different operating mode. For example, one outdoor unit can operate in a heating mode while another unit can operate in a defrost mode. In one embodiment, one or more of the plurality of outdoor units can be inoperative (e.g., shut down for maintenance, broken down, powered off, or the like) and the remaining of the plurality of outdoor units can continue to operate.

A "heat pump system" includes, for example, a refrigeration system capable of conditioning a space by heating or cooling air within the space. The heat pump system can, for example, include a plurality of outdoor units in fluid communication with one or more indoor units via a heat transfer circuit.

A "heat transfer fluid" includes, for example, refrigerant, chilled or heated water, air, a cryogenic liquid such as, but not limited to, liquid nitrogen, liquid carbon dioxide, or the like.

A "heat transfer circuit" includes, for example, a reversible vapor-compression refrigeration circuit including a compressor, at least two heat exchangers, and at least one expansion device. It is to be appreciated that a heat transfer circuit can include additional components such as, but not limited to, one or more flow control devices, a lubricant separator, a heat transfer fluid accumulator, or the like.

An "outdoor unit" includes, for example, a plurality of heat transfer components and a controller. It is to be appreciated that one or more additional components such as, but not limited to, one or more fans, can be included in an outdoor unit.

An "indoor unit" includes, for example, one or more heat transfer components and one or more fans. It is to be appreciated that one or more additional components can be included in an indoor unit, such as, but not limited to, a controller.

FIG. 1 illustrates a schematic diagram of a variable refrigerant (VRF) heat pump system

100, according to one embodiment. The VRF heat pump system 100 includes a plurality of outdoor units 105A and 105B. Two outdoor units 105A and 105B are illustrated in FIG. 1. It is to be appreciated that the VRF heat pump system 100 can include additional outdoor units that are the same as or similar to the outdoor units 105 A and 105B. The outdoor units 105 A and 105B of the VRF heat pump system 100 are generally configured to circulate a heat transfer fluid to one or more indoor units 125 disposed within one or more controlled spaces 130. The one or more indoor units 125 can use the heat transfer fluid to control an environmental condition such as, but not limited to, temperature and/or humidity, or the like, of the one or more controlled spaces 130.

Aspects of the outdoor unit 105 A can be the same as, or similar to, aspects of the outdoor unit 105B. To simplify this Specification, the outdoor unit 105 A will be described. It is to be appreciated that the description is applicable to each of the outdoor units 105 A and 105B. In some embodiments, it is not required that the outdoor units 105 A and 105B be the same. For example, the outdoor units 105 A and 105B can have different capacities, different compressor types, or the like.

The outdoor unit 105 A includes a plurality of heat transfer components 1 10A and a controller 1 15 A. In another embodiment, each of the outdoor units 105 A and 105B need not have a corresponding controller 1 15A and 1 15B, but instead can be controlled by a single controller for all of the outdoor units 105. In another embodiment, the outdoor units 105 A and 105B can have corresponding controllers 1 15 A and 1 15B that are in communication.

The one or more heat transfer components 1 10A can integrate a heat transfer circuit (e.g., heat transfer circuit 200 of FIGS. 2 A - 2B). The heat transfer circuit can include, for example, a compressor (e.g., compressor 205A of FIGS. 2A - 2B), one or more expansion devices (e.g., expansion device 235A of FIGS. 2A - 2B), one or more outdoor heat exchangers (e.g., outdoor heat exchanger 225A of FIGS. 2A - 2B), and one or more flow control devices (e.g., flow control devices 240 A, 250A of FIGS. 2A - 2B) for controlling flow of a heat transfer fluid. The one or more heat transfer components 1 10A can include one or more additional flow control devices (e.g., flow control device 220A of FIGS. 2A - 2B) and one or more subcoolers (e.g., the subcooler 285A of FIGS. 2A - 2B).

The outdoor unit 105 A is controlled by the controller 1 15A to provide the heat transfer fluid to the indoor units 125. The controller 1 15A can control the operation of the outdoor unit 105 A based on, for example, an environmental control requirement of the one or more controlled spaces 130. In one embodiment, the controller 1 15A can control the operation of the outdoor unit 105 A, for example, to prevent frost buildup on the outdoor heat exchanger. The controller 1 15A and the controller 1 15B can be in communication in order to meet an environmental condition requirement to maintain an environmental condition (e.g., temperature and/or humidity, or the like) in the one or more controlled spaces 130. The controller 1 15A and the controller 1 15B can also be configured such that the outdoor unit 105A can be operated in a first operating mode (e.g., a heating mode, a defrost mode, a pressure control mode, or the like) and the outdoor unit 105B can be operated in a second operating mode (e.g., a heating mode, a defrost mode, a pressure control mode, or the like). It is to be appreciated that the first operating mode and the second operating mode can be the same in one embodiment, or different in another embodiment.

The one or more indoor units 125 are disposed in one or more controlled spaces 130. It is to be appreciated that the one or more controlled spaces 130 can represent more than one controlled space in a building including the VRF heat pump system 100 and that one or more of the indoor units 125 can be located within each of the one or more controlled spaces 130. The indoor units 125 include one or more components such as, but not limited to, an indoor heat exchanger, a fan/blower, a thermostat, a controller, one or more sensors, or the like.

In one embodiment, when in a cooling mode, the outdoor unit 105 A can supply a heat transfer fluid to the one or more indoor units 125 in a liquid form, where the heat transfer fluid provided to the one or more indoor units 125 can remove thermal energy from the controlled space.

In one embodiment, when in a heating mode, the outdoor unit 105 A can supply a heat transfer fluid to the one or more indoor units 125 in a gaseous form, where the heat transfer fluid provided to the one or more indoor units 125 can supply thermal energy to the controlled space.

In one embodiment, when in a defrost mode, the outdoor unit 105 A can supply a heat transfer fluid to an outdoor heat exchanger but not to the one or more indoor units 125 in order to remove frost from the outdoor heat exchanger.

In one embodiment, when in a pressure control mode, the outdoor unit 105 A can divert a portion of a high pressure, high temperature heat transfer fluid being provided to the one or more indoor units 125 in order to send the portion of the high pressure, high temperature heat transfer fluid to an outdoor heat exchanger. In some embodiments, this diversion of the high pressure, high temperature heat transfer fluid can reduce or prevent frost from building up on the outdoor heat exchanger.

FIGS. 2 A and 2B illustrate diagrams of a heat transfer circuit 200 for a heat pump system (e.g., VRF heat pump system 100 of FIG. 1), according to some embodiments. Aspects of FIG. 2 A can be the same as or similar to aspects of FIG. 2B. The figures illustrate two outdoor units 105 A and 105B. It is to be appreciated that one or more additional outdoor units can be added to the heat transfer circuit 200 according to the principles described herein.

To simplify this Specification, the outdoor unit 105 A and corresponding components 205 A - 290A will be described. It is to be appreciated that the description is applicable to each of the outdoor units 105 A and 105B.

The outdoor unit 105 A includes a compressor 205 A. The compressor 205 A operates according to principles known in the art to output a heat transfer fluid at a high pressure and a high temperature from a discharge outlet 202A. It is to be appreciated that the compressor 205 A can be any of a variety of compressors suitable for use in a heat pump system. In one

embodiment, the compressor 105 A can be a variable capacity compressor capable of operating at more than one capacity. In one embodiment, a variable capacity compressor can be a variable speed compressor. Examples suitable for the compressor 205 A include, but are not limited to, a screw compressor, a reciprocating compressor, a scroll compressor, a positive displacement compressor, a centrifugal compressor, or the like. It is to be appreciated that in some

embodiments, the outdoor unit 105 A can include a plurality of compressors 205 A. In such embodiments, the compressors 205 A can be of different types, different capacities, or the like.

The heat transfer fluid output from the discharge outlet 202A of the compressor 205 A is directed to inlet 209 A of lubricant separator 21 OA. The lubricant separator 21 OA operates according to principles known in the art. The heat transfer fluid is discharged from outlet 21 1 A of the lubricant separator 21 OA and is directed through a flow control device 215 A. Lubricant can be directed from outlet 212A through a drier/filter 23 OA and a flow reduction device 260 A to be returned to a suction inlet 203 A of the compressor 205 A. The flow control device 215 A can be, for example, a check valve that allows the heat transfer fluid to flow from the lubricant separator 21 OA toward the flow control device 220 A but can prevent flow of the heat transfer fluid from the flow control device 220 A toward the lubricant separator 21 OA. The flow reduction device 260A can, for example, reduce a pressure of the lubricant flowing therethrough.

The flow control device 220A can be a four-way valve, according to one embodiment. In such an embodiment, the flow control device 220A can include four ports for controlling flow of the heat transfer fluid and functions according to principles known in the art. It is to be appreciated that the flow control device 220A can be a flow control device other than a four- way valve that is capable of operating according to similar principles. The flow control device 220 A can be set in a first state or a second state by, for example, energizing or de-energizing a solenoid, respectively. In one embodiment, the first state corresponds to providing high-pressure

high-temperature heat transfer fluid to the outdoor heat exchanger 225 A and the second state corresponds to providing high pressure, high temperature heat transfer fluid to the one or more indoor units 125. The flow control device 220 A can be set to the first state or the second state based on the desired operating mode. The heat transfer fluid directed toward the one or more indoor units 125 passes through a flow control device 250A, a drier/filter 236A, and a flow control device 275A.

The flow control device 250A can be, for example, an electronic two-way valve such as, but not limited to, an electronic two-way ball valve. The flow control device 250A can allow flow therethrough when in a first state or prevent flow therethrough when in a second state. The state of the flow control device 250A can be controlled based on the operating mode of the outdoor unit 105 A. The flow control device 250 A and a flow control device 250B can be set in different states to separately control the outdoor unit 105 A and the outdoor unit 105B.

The flow control device 275A can be, for example, a service valve. The flow control device 275A can be set to generally allow flow therethrough, but capable of being set to prevent flow therethrough such as, for example, to service the outdoor unit 105 A.

A pressure release path 248 A is also present on either side of the flow control device 250A.

In FIG. 2A, the pressure release path 248A includes a flow reduction device 262A. The flow reduction device 262A can reduce a pressure of the heat transfer fluid that passes

therethrough. Aspects of the flow reduction device 262A can be the same as or similar to aspects of the flow reduction device 260A. In one embodiment, heat transfer fluid can flow along the pressure release path 248A in any operating mode. As described in accordance with FIG. 4 below, when in the defrost mode, a portion of high-temperature, high-pressure heat transfer fluid can flow along pressure release path 248A and mix with cooler temperature pressure heat transfer fluid from the defrost flow path 290A.

In FIG. 2B, the pressure release path 248 A includes the flow reduction device 262A, a flow control device 245 A, and a flow control device 217A. The flow control device 245 A can be, for example, a valve having at least a first state (e.g., flow enabled) and a second state (e.g., flow disabled). In some embodiments, the valve can be actuated by a solenoid. The pressure release path 248 A can, for example, be controlled based on an operating mode of the outdoor unit 105 A, a setting of another flow control device (e.g., flow control device 250A), a discharge pressure of the compressor, a suction pressure of the compressor, or the like. Aspects of the flow control device 217A can be the same as or similar to aspects of the flow control device 215 A. The flow control device 217A can allow flow in one direction (e.g., from the flow control device 245A toward the flow reduction device 262A, but not in the opposite direction).

The heat pump circuit 200 includes an outdoor heat exchanger 225A. The outdoor heat exchanger 225A is fluidly connected to one or more indoor heat exchangers (e.g., of the indoor units 125 of FIG. 1). It is to be appreciated that the outdoor heat exchanger 225A and the one or more indoor heat exchangers of the one or more indoor units 125 can be any suitable heat exchanger where the heat transfer fluid passing therethrough can conduct a heat exchange with another heat-exchanging medium. In one embodiment, the outdoor heat exchanger 225A can be configured to function as a condenser (e.g., when operating in a cooling mode). In another embodiment, the outdoor heat exchanger 225 A can be configured to function as an evaporator (e.g., when operating in a heating mode).

Heat transfer fluid returning from the one or more indoor units 125 can pass through a flow control device 240A, a drier/filter 234A, and a subcooler 285 A. The subcooler 285A operates according to principles known in the art and can, for example, increase an efficiency of the heat pump circuit 200. The heat transfer fluid generally can flow from the subcooler 285 A to the expansion device 235 A and the drier/filter 232 A. The flow control device 240 A can be, for example, a service valve. The expansion device 235 A and the drier/filters 232A, 234A, respectively, operate according to principles known in the art in order to reduce a pressure of the heat transfer fluid and filter out contaminants such as, but not limited to, debris, water, or the like. In one embodiment, a portion of the heat transfer fluid can flow along defrost path 290A through an expansion device 280 A and the subcooler 285 A to divert the portion of heat transfer fluid to the accumulator 255A and back to the compressor 205A. The expansion devices 235A and 280A can, for example, be electronically controlled, according to one embodiment.

In some operating modes (e.g., the pressure control mode), heat transfer fluid can be directed along pressure control path 270 A. The pressure control path 270 A can, for example, be used to reduce a pressure of the heat transfer fluid. The pressure control path 270A includes a flow reduction device 264A and flow control devices 247A and 249 A. Aspects of the flow reduction device 264A can be the same as or similar to aspects of the flow reduction devices 260A and 262A. Aspects of the flow control device 247A can be the same as or similar to aspects of the flow control device 245 A (shown in FIG. 2B). Aspects of the flow control device 249A can be the same as or similar to aspects of the flow control device 217A (shown in FIG. 2B), such that flow of heat transfer fluid is permitted toward the outdoor heat exchanger 225 A when the flow control device 247A permits flow therethrough, but can prevent flow of the heat transfer fluid from the opposite direction, regardless of the state of the flow control device 247A.

An accumulator 255A is connected to the flow control device 220A (e.g., a four-way valve) and to the compressor 205 A. The accumulator 255 A functions according to principles known in the art. It is to be appreciated that the drier/filter 23 OA and the accumulator 255 A are not required in some embodiments.

The heat pump circuit 200 can be operated in a plurality of operating modes. FIGS. 3 - 5, respectively, illustrate diagrams of the heat pump circuit 200 for the heat pump system operating in a heating mode, a defrost mode, and a pressure control mode. It is to be appreciated that the list of operating modes is exemplary and that the heat pump circuit 200 can be operated in one or more other operating modes. For example, the heat pump circuit 200 can be operated in a cooling mode.

The cooling mode is now described with reference to FIG. 2A. It is to be appreciated that the cooling mode can function the same or similarly in accordance with FIG. 2B. In the cooling mode, the heat pump circuit 200 can be configured to remove thermal energy from one or more controlled spaces (e.g., the controlled space 130 of FIG. 1). The compressor 205A discharges gaseous heat transfer fluid. The flow control device 220A is in the first state (e.g., energized). The discharged heat transfer fluid is directed toward the outdoor heat exchanger 225 A. In the cooling mode, the outdoor heat exchanger 225 A can operate as a condenser and output a liquid heat transfer fluid which then flows through the subcooler 285A. The liquid heat transfer fluid is provided to the one or more indoor units 125, which can include one or more indoor heat exchangers that can operate as an evaporator. The liquid heat transfer fluid can remove thermal energy from the one or more controlled spaces. The heat transfer fluid is then returned from the one or more indoor units 125 to the flow control device 220 A, where it is directed toward the accumulator 255 A and back to the compressor 205 A. FIGS. 3 - 5 illustrate diagrams of the heat pump circuit 200 for a heat pump system (e.g., the heat pump system 100 of FIG. 1) operating in a heating mode, a defrosting mode, and a pressure control mode, respectively. The various operating modes are controlled by varying a position of the flow control devices to control the flow of the heat transfer fluid within the heat pump circuit 200. A controller (e.g., the controller 115 of FIG. 1) can be configured to control the flow control devices based on, for example, one or more sensor readings. It is to be appreciated that the heat pump system can include one or more additional operating modes such as, but not limited to, a cooling mode.

FIG 3 illustrates a diagram of the heat pump circuit 200 for a heat pump system (e.g., the heat pump system 100 of FIG. 1) in a heating mode, according to one embodiment. In the heating mode, the heat pump circuit 200 can be configured to supply thermal energy to one or more controlled spaces (e.g., the controlled space 130 of FIG. 1). The compressor 205A discharges gaseous heat transfer fluid. The flow control device 220A is in the second state (e.g.,

de-energized). The discharged heat transfer fluid flows toward through the flow control device 250A and to the one or more indoor units 125. The one or more indoor units 125 include one or more indoor heat exchangers that can conduct a heat exchange with the heat transfer fluid for absorbing heat from the heat transfer fluid. The heat transfer fluid then flows from the one or more indoor units 125 and through expansion device 235A, drier/filter 232A, and is directed to the outdoor heat exchanger 225A. The heat exchanger 225A can vaporize the heat transfer fluid by receiving thermal energy from the outdoor air. The heat transfer fluid is directed through the flow control device 220 A and to the accumulator 255 A. The heat transfer fluid then travels from the accumulator 255 A to the compressor 205 A and repeats the process.

FIG. 4 illustrates a diagram of the heat pump circuit 200 for a heat pump system (e.g., the heat pump system 100 of FIG. 1) in a defrost mode, according to one embodiment. In the defrost mode, the outdoor units 105 A and 105B may not be operating in the same mode. In the defrost mode, the heat pump circuit 200 can be configured to continue to supply thermal energy to one or more controlled spaces (e.g., the controlled space 130 of FIG. 1) if a requirement to heat is present while concurrently defrosting the outdoor unit 105 A. The compressor 205 A discharges gaseous heat transfer fluid. The flow control device 220A is in the first state (e.g., energized). The discharged heat transfer fluid flows toward the outdoor heat exchanger 225 A. Because the heat transfer fluid is at a high pressure and a high temperature, the thermal energy can defrost the outdoor heat exchanger 225A. When in the defrost mode, the flow control device 250A is in the second state, preventing flow of high-pressure heat transfer fluid from flowing toward the suction inlet 203 A of the compressor 205A.

A portion of the high-pressure heat transfer fluid flows along pressure control path 248A. Heat transfer fluid from the one or more indoor units 125 can be diverted along defrost path 290A. Higher temperature heat transfer fluid from pressure control path 248A can mix with cooler temperature heat transfer fluid from defrost path 290A, which returns through flow control device 220 A toward the accumulator 255 A and the compressor 205 A, at which point the process can repeat so long as the outdoor unit 105 A is in the defrost mode. An amount of cooler temperature heat transfer fluid flowing through defrost path 290 A can be controlled with the flow control device 280A based on, for example, a discharge pressure, a suction pressure, and/or a discharge temperature of the heat transfer fluid from the compressor 205 A. The suction pressure can, for example, be determined by a pressure sensor, or in another embodiment, can be determined by a temperature of the heat transfer fluid. In some embodiments, the suction pressure can be measured between 220A and 255A. The discharge pressure can, for example, be determined by a pressure sensor, or in another embodiment, can be determined by a temperature of the heat transfer fluid. In some embodiments, the discharge pressure and or discharge temperature can be measured between 202A and 209A.

In one embodiment, the capacity of the compressor 205 A may be reduced when entering the defrost mode. In such an embodiment, the capacity can be reduced by, for example, reducing a speed of the compressor 205 A.

FIG. 5 illustrates a diagram of the heat pump circuit 200 for a heat pump system (e.g., the heat pump system 100 of FIG. 1) in a pressure control mode, according to one embodiment. In the pressure control mode, the outdoor units 105 A and 105B may not be operating in the same mode. In the pressure control mode, the heat pump circuit 200 can be configured to continue to supply thermal energy to one or more controlled spaces (e.g., the controlled space 130 of FIG. 1) if a requirement to heat is present while concurrently preventing frost on the outdoor heat exchanger 225 A of the outdoor unit 105 A.

Aspects of FIG. 5 can be the same as or similar to aspects of FIG. 3. In addition to the operation in FIG. 3, a portion of the heat transfer fluid at a high pressure and high temperature is diverted to the outdoor heat exchanger 225 A through pressure control path 270A. The flow control device 247A is set in the first state and a portion of the gaseous heat transfer fluid is directed through the flow reduction device 264A toward the outdoor heat exchanger 225 A. This diversion of heat transfer fluid can, for example, reduce frost buildup on the outdoor heat exchanger 225 A and increase an amount of time before the outdoor unit 105 A enters the defrost mode (as described in accordance with FIG. 4 above). In one embodiment, a pressure control condition can be a suction pressure of a compressor falling below a suction pressure threshold. In another embodiment, the pressure control condition can be a temperature of a coil in about the middle of the outdoor heat exchanger 225 A falling below a temperature threshold. In some embodiments, the pressure control condition includes both a suction pressure falling below a suction pressure threshold and a temperature of a coil in about the middle of the outdoor heat exchanger 225 A falling below a temperature threshold.

In another embodiment, the pressure control condition can be a discharge pressure of the compressor rising above a discharge pressure threshold.

In another embodiment, the pressure control condition can be a similar condition that indicates frost may be starting to build on the outdoor heat exchanger 225 A.

FIG. 6 illustrates a method 600 for controlling a heat pump system (e.g., the heat pump system 100 of FIG. 1), according to one embodiment. The method 600 generally includes determining whether a frost condition or a pressure control condition occurs and respectively operating an outdoor unit (e.g., the outdoor unit 105A of FIG. 1) in a defrost mode (see FIG. 4 above for a more detailed explanation of the defrost mode) or a pressure control mode (see FIG. 5 above for a more detailed explanation of the pressure control mode). In one embodiment, the method 600 can be performed whenever one or more of the outdoor units are operational. In another embodiment, the method 600 can be performed when one or more of the outdoor units are in a heating mode (e.g., method 700 of FIG. 7).

The method 600 begins at 605 when a controller (e.g., the controller 1 15A or 1 15B) determines whether a frost condition exists. In another embodiment, the method 600 can begin at 615. A frost condition can include a variety of indications that frost may have built up on an outdoor heat exchanger of one of the one or more outdoor units. If there is a frost condition, the corresponding unit (e.g., outdoor unit 105A or 105B of FIG. 1) enters the defrost mode at 610. As described above, the outdoor unit having the frost condition is individually placed into the defrost mode without modifying the operating mode of the one or more other outdoor units by controlling one or more flow control devices (e.g., the flow control devices 220A and 250A). Because the one or more outdoor units are individually controllable, the outdoor unit having the frost condition is placed into the defrost mode and the additional outdoor units can continue operating without entering the defrost mode. In one embodiment, the defrost mode may be run for a specified period of time. In another embodiment, the defrost mode may run and the controller can continue to determine whether there is a frost condition and exit the defrost mode when there is no longer a frost condition.

If there is no frost condition at 605, the controller determines at 615 whether a pressure control condition exists. A pressure control condition can be, for example, based on a suction pressure at a compressor suction inlet, a discharge pressure at a compressor discharge outlet, one or more temperatures (e.g., of the heat transfer fluid discharged from the compressor or provided to the compressor), or the like. If there a pressure control condition, the controller enters the pressure control mode at 620. As described in accordance with FIG. 5 above, the pressure control mode can include enabling flow of a heat transfer fluid along path 270A. Similar to the defrost mode of 610, the pressure control mode can be enabled for the outdoor unit having the pressure control condition and the other outdoor units can continue operating without modification of the operating mode. If there is no pressure control condition, the method 600 can return to 605. The method 600 can repeat while the heat pump system is operating.

In one embodiment, the method 600 can be configured to monitor for frost conditions (e.g., at 605) but not pressure control conditions (e.g., at 615). In another embodiment, the method 600 can be configured to monitor for pressure control conditions (e.g., at 615) but not for frost conditions (e.g., at 605). This can, for example, be based on whether the one or more outdoor units are configured to include a pressure control flow path.

FIG. 7 illustrates a method 700 for controlling a heat pump system (e.g., the heat pump system 100 of FIG. 1) operating in a heating mode (see FIG. 3 above for a more detailed explanation of the heating mode), according to one embodiment. The method 700 generally determines whether a frost condition or a pressure control condition occurs when the heat pump system is operating in the heating mode. In response to a frost condition or a pressure control condition, the method 700 includes modifying the operating mode of the heat pump system to a defrost mode (see FIG. 4 above for a more detailed explanation of the defrost mode) or a pressure control mode (see FIG. 5 above for a more detailed explanation of the pressure control mode) respectively.

The method 700 begins at 705 when a controller determines an operating mode of one or more outdoor units for the heat pump system. At 710, the controller determines whether the operating mode determined at 705 was a heating mode. If the one or more outdoor units are not operating in the heating mode, then the method 700 returns to 705 and continues to monitor for the one or more outdoor units to enter the heating mode. If, at 710, the controller determined the one or more outdoor units are operating in the heating mode, the method 700 continues to 715.

At 715 the controller determines whether a frost condition exists. A frost condition can include a variety of indications that frost may have built up on an outdoor heat exchanger of one of the one or more outdoor units. If there is a frost condition, the corresponding unit will enter the defrost mode at 720. In one embodiment, the defrost mode may be run for a specified period of time. In another embodiment, the defrost mode may run and the controller can continue to determine whether there is a frost condition and exit the defrost mode when there is no longer a frost condition.

If there is no frost condition at 715, the controller determines at 725 whether a pressure control condition exists. A pressure control condition can be, for example, based on a suction pressure, a discharge pressure, one or more temperatures, or the like. If there a pressure control condition, the controller enters the pressure control mode at 730. As described in accordance with FIG. 5 above, the pressure control mode can include enabling flow of a heat transfer fluid along path 270 A. If there is no pressure control condition, the method 700 can return to 705. The method 700 can repeat while the heat pump system is operating.

In one embodiment, the method 700 can be configured to monitor for frost conditions (e.g., at 715) but not pressure control conditions (e.g., at 725). In another embodiment, the method 700 can be configured to monitor for pressure control conditions (e.g., at 725) but not for frost conditions (e.g., at 715). This can, for example, be based on whether the one or more outdoor units are configured to include a pressure control flow path. ASPECTS

It is noted that any of aspects 1 - 6 can be combined with any of aspects 7 - 12, 13 - 17, and any of aspects 18 - 22. Any of aspects 7 - 12 can be combined with any of aspects 13 - 17 and any of aspects 18 - 22. Any of aspects 13 - 17 can be combined with any of aspects 18 - 22.

Aspect 1. A heat pump system, comprising:

a plurality of outdoor units in fluid communication with one or more indoor units via a heat transfer circuit, each of the plurality of outdoor units operable in a plurality of operation modes;

a first of the plurality of outdoor units including:

a compressor, a first flow control device between the compressor and an outdoor heat exchanger in a first flow direction and between the compressor and a second flow control device in a second flow direction, wherein in a first state, the first flow control device permits flow to the outdoor heat exchanger, and in a second state, the first flow control device permits flow to the second flow control device; and

a second of the plurality of outdoor units including:

a compressor, a first flow control device between the compressor and an outdoor heat exchanger in a first flow direction and between the compressor and a second flow control device in a second flow direction, wherein in a first state, the first flow control device permits flow to the outdoor heat exchanger, and in a second state, the first flow control device permits flow to the second flow control device; wherein the second flow control devices of the first and second of the plurality of outdoor units are individually controllable to set the first and/or second of the plurality of outdoor units to a defrost mode.

Aspect 2. The heat pump system according to aspect 1, wherein the plurality of operation modes includes a cooling mode, a heating mode, a defrost mode, and a pressure control mode.

Aspect 3. The heat pump system according to any of aspects 1 - 2, wherein the second flow control device of the first of the plurality of outdoor units prevents a high pressure heat transfer fluid from flowing to a suction side of the compressor of the first of the plurality of outdoor units when in a defrost mode and the first flow control device of the first of the plurality of outdoor units is in the first state. Aspect 4. The heat pump system according to any of aspects 1 - 3, wherein the second flow control device of the second of the plurality of outdoor units prevents a high pressure heat transfer fluid from flowing to a suction side of the compressor of the second of the plurality of outdoor units when in a defrost mode and the first flow control device of the second of the plurality of outdoor units is in the first state.

Aspect 5. The heat pump system according to any of aspects 1 - 4, wherein the first and second of the plurality of outdoor units are operable in different operation modes.

Aspect 6. The heat pump system according to any of aspects 1 - 5, further comprising a defrost flow path, wherein the defrost flow path includes a subcooler and an expansion device disposed between the one or more indoor units and the outdoor heat exchanger.

Aspect 7. A heat pump system, comprising:

a plurality of outdoor units in fluid communication with one or more indoor units via a heat transfer circuit, each of the plurality of outdoor units operable in a plurality of operation modes;

a first of the plurality of outdoor units including:

a compressor, a flow control device between the compressor and an outdoor heat exchanger in a first flow direction and between the compressor and one or more indoor units in a second flow direction, and a pressure control flow path, wherein the pressure control flow path is disposed between the flow control device and the one or more indoor units, and when in a first state, the flow control device permits flow to the outdoor heat exchanger, and in a second state, the flow control device permits flow to the one or more indoor units; and

a second of the plurality of outdoor units including: a compressor, a flow control device between the compressor and an outdoor heat exchanger in a first flow direction and between the compressor and one or more indoor units in a second flow direction, and a pressure control flow path, wherein the pressure control flow path is disposed between the flow control device and the one or more indoor units, and when in a first state, the flow control device permits flow to the outdoor heat exchanger, and in a second state, the flow control device permits flow to the one or more indoor units;

wherein the pressure control flow paths of the first and second of the plurality of outdoor units are individually controllable to selectively enable and/or disable a pressure control mode of the first and/or second of the plurality of outdoor units.

Aspect 8. The heat pump system according to aspect 7, wherein the pressure control flow path is selectively enabled in response to at least one of a suction pressure of the compressor falling below a suction pressure threshold and a temperature of a coil in about a middle of the outdoor heat exchanger falls below a temperature threshold.

Aspect 9. The heat pump system according to any of aspects 7 - 8, wherein the pressure control flow path is selectively enabled in response to a discharge pressure of the compressor being above a discharge pressure threshold.

Aspect 10. The heat pump system according to any of aspects 7 - 8, wherein the pressure control flow path is selectively disabled in response to at least one of the suction pressure of the compressor being above the suction pressure threshold and the temperature of a coil in about the middle of the outdoor heat exchanger being above the temperature threshold.

Aspect 11. The heat pump system according to aspect 9, wherein the pressure control flow path is selectively disabled in response to the discharge pressure of the compressor being below the discharge pressure threshold. Aspect 12. The heat pump system according to any of aspects 7 - 11, wherein the pressure control flow path is selectively enabled by setting a second flow control device to allow flow therethrough. Aspect 13. A method of controlling a heat pump system, wherein the heat pump system includes a plurality of outdoor units, each of the plurality of outdoor units including at least a compressor and an outdoor heat exchanger, the method comprising:

determining whether a frost condition exists;

setting a first of the plurality of outdoor units to operate in a defrost mode in response to determining the frost condition exists; and

individually operating a second of the plurality of outdoor units in a same or different operating mode.

Aspect 14. The method according to aspect 13, further comprising:

performing the determining in response to one or more of the plurality of outdoor units operating in a heating mode.

Aspect 15. The method according to any of aspects 13 - 14, wherein setting the first of the plurality of outdoor units in a defrost mode includes preventing a high-pressure heat transfer fluid from flowing to a suction side of the compressor.

Aspect 16. The method according to any of aspects 13 - 15, wherein setting the first of the plurality of outdoor units to operate in a defrost mode includes reducing a capacity of the compressor.

Aspect 17. The method according to aspect 16, wherein reducing the capacity of the compressor includes reducing a speed of the compressor.

Aspect 18. A method of controlling a heat pump system, wherein the heat pump system includes a plurality of outdoor units, each of the plurality of outdoor units including at least a compressor and an outdoor heat exchanger, the method comprising: determining whether a pressure control condition exists;

setting a first of the plurality of outdoor units to operate in a pressure control mode in response to determining the pressure control condition exists; and

individually operating a second of the plurality of outdoor units in a same or different operating mode.

Aspect 19. The method according to aspect 18, further comprising:

performing the determining in response to one or more of the plurality of outdoor units operating in a heating mode.

Aspect 20. The method according to any of aspects 18 - 19, wherein setting the first of the plurality of outdoor units to operate in a pressure control mode includes enabling a pressure control flow path to permit a portion of heat transfer fluid flowing to one or more indoor units to be diverted through a flow reduction device and to the outdoor heat exchanger.

Aspect 21. The method according to any of aspects 18 - 20, wherein determining whether a pressure control condition exists includes at least one of determining whether a suction pressure is below a suction pressure threshold and whether a temperature of a coil in about a middle of the outdoor heat exchanger is below a temperature threshold.

Aspect 22. The method according to any of aspects 18 - 21, wherein determining whether a pressure control condition exists includes determining whether a discharge pressure is above a discharge pressure threshold. The terminology used in this Specification is intended to describe particular embodiments and is not intended to be limiting. The terms "a," "an," and "the" include the plural forms as well, unless clearly indicated otherwise. The terms "comprises" and/or "comprising," when used in this Specification, specify the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and/or components.

With regard to the preceding description, it is to be understood that changes may be made in detail, especially in matters of the construction materials employed and the shape, size, and/or arrangement of parts without departing from the scope of the present disclosure. The word "embodiment" as used within this Specification may, but does not necessarily, refer to the same embodiment. This Specification and the embodiments described are exemplary only. Other and further embodiments may be devised without departing from the basic scope thereof, with the true scope and spirit indicated by the claims that follow.