CN107076476B

CN107076476B - Variable refrigerant HVAC system with independent defrost

Info

Publication number: CN107076476B
Application number: CN201480078379.6A
Authority: CN
Inventors: 唐圣; 李艳; 胡永; 柴国红
Original assignee: Trane International Ltd; Trane Air Conditioning Systems China Co Ltd
Current assignee: Trane International Ltd; Trane Air Conditioning Systems China Co Ltd
Priority date: 2014-04-23
Filing date: 2014-04-23
Publication date: 2020-01-14
Anticipated expiration: 2034-04-23
Also published as: CN107076476A; WO2015161461A1

Abstract

A heat pump system (100) and a control method thereof are provided. The heat pump system (100) comprises: a plurality of outdoor units (105A, 105B) operable in a plurality of operating modes, the plurality of outdoor units (105A, 105B) in fluid communication with one or more indoor units (125) through a heat transfer loop (200). The first and second ones of the plurality of outdoor units (105A, 105B) include a compressor (205A, 205B), a first flow control device (220A, 220B), the first flow control device (220A, 220B) being located between the compressor (205A, 205B) and an outdoor heat exchanger (225A, 225B) in a first flow direction and between the compressor (205A, 205B) and a second flow control device (250A, 250B) in a second flow direction. In a first state, the first flow control device (220A, 220B) allows refrigerant flow to the outdoor heat exchanger (225A, 225B). In a second state, the first flow control device (220A, 220B) allows refrigerant flow to the second flow control device (250A, 250B). The second flow control devices (250A, 250B) of the first and second ones of the plurality of outdoor units (105A, 105B) are individually controllable to set the first and/or second ones of the plurality of outdoor units (105A, 105B) to a defrost mode.

Description

Variable refrigerant HVAC system with independent defrost

Technical Field

The present invention relates to a heat pump system. More particularly, the present invention relates to a Variable Refrigerant (VRF) heat pump system in which a single outdoor unit can be separately defrosted.

Background

A heat pump system is a refrigeration system capable of air conditioning a space by heating or cooling air in the space. Heat pump systems typically include a four-way reversing valve that may be configured to switch between heating and cooling modes.

Disclosure of Invention

The present invention relates to heat pump systems. More particularly, the present invention relates to a Variable Refrigerant (VRF) heat pump system in which a single outdoor unit can be separately defrosted.

A heat pump system is described herein that includes a plurality of outdoor units in fluid communication with one or more indoor units via a heat transfer loop. Each of the plurality of outdoor units may operate in a plurality of operating modes. A first one of the plurality of outdoor units includes a compressor and a first flow control device between the compressor and the outdoor heat exchanger in a first flow direction and between the compressor and the second flow control device in a second flow direction. In the first state, the first flow control device allows flow to the outdoor heat exchanger, and in the second state, the first flow control device allows flow to the second flow control device. A second of the plurality of outdoor units includes a compressor, and a first flow control device positioned between the compressor and the outdoor heat exchanger in a first flow direction and between the compressor and the second flow control device in a second flow direction. In the first state, the first flow control device allows flow to the outdoor heat exchanger, and in the second state, the first flow control device allows flow to the second flow control device. The second flow control devices of the first and second ones of the plurality of outdoor units may be individually controlled to set the first and/or second ones of the plurality of outdoor units to the defrost mode.

A heat pump system is described herein that includes a plurality of outdoor units in fluid communication with one or more indoor units via a heat transfer loop. Each of the plurality of outdoor units may operate in a plurality of operating modes. A first one of the plurality of outdoor units includes a compressor, a flow control device between the compressor and the outdoor heat exchanger in a first flow direction, and a pressure control flow path between the compressor and the one or more indoor units in a second flow direction. A pressure control flow path is provided between the flow control device and one or more indoor units. In a first state, the flow control device allows flow to the outdoor heat exchanger, and in a second state, the flow control device allows 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 the outdoor heat exchanger in a first flow direction, and a pressure control flow path between the compressor and the one or more indoor units in a second flow direction. A pressure control flow path is provided between the flow control device and one or more indoor units. In a first state, the flow control device allows flow to the outdoor heat exchanger, and in a second state, the flow control device allows flow to the one or more indoor units. The pressure control flow paths of the first and second ones of the plurality of outdoor units may be individually controlled to selectively enable and/or disable the pressure control mode of the first and/or second ones of the plurality of outdoor units.

A method of controlling a heat pump system including a plurality of outdoor units is described herein. 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 one of the plurality of outdoor units to operate in a defrost mode in response to the determination that the frost condition exists. The method also includes individually operating a second of the plurality of outdoor units in the same or a different mode of operation.

A method of controlling a heat pump system including a plurality of outdoor units is described herein. 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 one of the plurality of outdoor units to operate in a pressure control mode in response to determining that the pressure control condition exists. The method also includes individually operating a second of the plurality of outdoor units in the same or a different mode of operation.

Drawings

Reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration embodiments in which the systems and methods described in the specification may be practiced.

FIG. 1 illustrates a schematic diagram of a Variable Refrigerant (VRF) heat pump system in accordance with one embodiment;

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

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

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

FIG. 4 illustrates a schematic diagram of a heat transfer circuit of the heat pump system in a defrost mode, according to an embodiment;

FIG. 5 illustrates a schematic diagram of a heat transfer circuit of a heat pump system in a pressure control mode, according to an 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 numerals refer to like parts.

Detailed Description

Embodiments described herein relate to a variable refrigerant heat pump system having a plurality of outdoor units. Each of the plurality of outdoor units is capable of operating 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 may be referred to as an anti-frost mode under certain conditions. Each of the plurality of outdoor units of the heat pump system may be operated in the same operation mode. In one embodiment, each of the plurality of outdoor units operates in a different operating mode. For example, one outdoor unit may be operated in a heating mode, while the other unit may be operated in a defrosting mode. In one embodiment, one or more of the plurality of outdoor units may not be operational (e.g., shutdown due to maintenance, damage, power outage, etc.) while the remaining ones of the plurality of outdoor units may continue to operate.

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

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

A "heat transfer circuit" includes, for example, a reversible vapor compression refrigeration circuit comprising a compressor, at least two heat exchangers, and at least one expansion device (expansion device). It is understood that the heat transfer circuit may include other components such as, but not limited to, one or more flow control devices, lube oil separators, heat transfer fluid accumulators, and the like.

The "outdoor unit" includes, for example, a plurality of heat transfer components and a controller. It is understood that one or more other components, such as, but not limited to, one or more fans, are contained within the outdoor unit.

An "indoor unit" includes, for example, one or more heat transfer components and one or more fans. It is understood that one or more other components may be included within 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. Fig. 1 shows two

outdoor units

105A and 105B. It is understood that the VRF heat pump system 100 may include other outdoor units that are the same as or similar to the

outdoor units

105A and 105B. The

outdoor units

105A 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 located within one or more controlled spaces 130. The one or more indoor units 125 may control environmental conditions, such as, but not limited to, temperature and/or humidity of the one or more controlled spaces 130, and the like, using the heat transfer fluid.

Aspects of the outdoor unit 105A may be the same as and similar to aspects of the outdoor unit 105B. To simplify the description, the outdoor unit 105A will be described. It is understood that the description applies to either of the

outdoor units

105A and 105B. In some embodiments, it is not required that the

outdoor units

105A and 105B be identical. For example, the

outdoor units

105A and 105B may have different capacities, different compressor types, and so on.

The outdoor unit 105A includes a plurality of heat transfer members 110A and a controller 115A. In another embodiment, each

outdoor unit

105A and 105B does not require a

respective controller

115A and 115B, but rather all outdoor units 105 may be controlled by a single controller. In another embodiment, the

outdoor units

105A and 105B may have

respective controllers

115A and 115B in communication.

One or more heat transfer members 110A may be combined into a heat transfer loop (e.g., heat transfer loop 200 in fig. 2A-2B). The heat transfer loop may include, for example, a compressor (e.g., compressor 205A in fig. 2A-2B), one or more expansion devices (e.g., expansion device 235A in fig. 2A-2B), one or more outdoor heat exchangers (e.g., outdoor heat exchanger 225A in fig. 2A-2B), and one or more flow control devices (e.g.,

flow control devices

240A, 250A in fig. 2A-2B) for controlling the flow of the heat transfer fluid. The one or more heat transfer components 110A can include one or more other flow control devices (e.g., flow control device 220A in fig. 2A-2B), and one or more subcoolers (e.g., subcooler 285A in fig. 2A-2B).

The controller 115A controls the outdoor unit 105A to provide the heat transfer fluid to the indoor unit 125. The controller 115A may control the operation of the outdoor unit 105A based on, for example, environmental control requirements of one or more controlled spaces 130. In one embodiment, the controller 115A may control the operation of the outdoor unit 105A, for example, to prevent frost from forming on the outdoor heat exchanger. The

controllers

115A and 115B may communicate to meet the requirement of maintaining environmental conditions (e.g., temperature and/or humidity, etc.) within the one or more controlled spaces 130 as required by the environmental conditions. The

controls

115A and 115B may also be configured to allow the outdoor unit 105A to operate in a first mode of operation (e.g., heating mode, defrost mode, pressure control mode, etc.) and the outdoor unit 105B to operate in a second mode of operation (e.g., heating mode, defrost mode, pressure control mode, etc.). It will be appreciated that the first and second modes of operation may be the same in one embodiment, or may be different in another embodiment.

One or more indoor units 125 may be disposed within one or more controlled spaces 130. It is understood that one or more controlled spaces 130 may represent more than one controlled space located within a building that includes VRF heat pump system 100, and one or more indoor units 125 may be located within each of the one or more controlled spaces 130. The indoor unit 125 includes 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, and the like.

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

In one embodiment, when in the heating mode, the outdoor unit 105A may supply the heat transfer fluid in gaseous form to the one or more indoor units 125, wherein the heat transfer fluid supplied to the one or more indoor units 125 may provide thermal energy to the controlled space.

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

In one embodiment, when in the pressure control mode, the outdoor unit 105A may divert a portion of the high-pressure, high-temperature heat transfer fluid provided to the one or more indoor units 125 to deliver the portion of the high-pressure, high-temperature heat transfer fluid to the outdoor heat exchanger. In some embodiments, the transfer of the high pressure, high temperature heat transfer fluid may reduce or prevent frost formation on the outdoor heat exchanger.

Figures 2A and 2B illustrate a schematic diagram of a heat transfer circuit 200 for a heat pump system (e.g., VRF heat pump system 100 shown in figure 1) according to some embodiments. The aspect of fig. 2A may be the same as or similar to the aspect of fig. 2B.

Two

outdoor units

105A and 105B are shown. It is understood that one or more other outdoor units may be added to the heat transfer loop 200 in accordance with the principles described herein.

To simplify the description, the outdoor unit 105A and the respective components 205A-290A will be described. It is understood that the description may be applied to any one of the

outdoor units

105A and 105B.

The outdoor unit 105A includes a compressor 205A. The compressor 205A operates according to principles known in the art to output a high pressure, high temperature heat transfer fluid at the discharge outlet 202A. It is to be understood that the compressor 205A may be any of a variety of compressors suitable for use in heat pump systems. In one embodiment, the compressor 205A may be a variable capacity compressor capable of operating at more than one capacity. In one embodiment, the variable-capacity compressor may be a variable-speed compressor. Suitable examples of compressor 205A include, but are not limited to, screw compressors, reciprocating compressors, scroll compressors, positive displacement compressors, centrifugal compressors, and the like. It is understood that in some embodiments, the outdoor unit 105A may include multiple compressors 205A. In such an embodiment, the compressor 205A may be any type, capacity, etc. of compressor.

The heat transfer fluid discharged from the discharge outlet 202A of the compressor 205A is directed into the inlet 209A of the lube oil separator 210A. The lube oil separator 210A operates according to principles known in the art. The heat transfer fluid exits outlet 211A of lube separator 210A and is channeled through flow control device 215A. From the outlet 212A, the lube oil may be directed through the dryer/filter 230A and the flow reducer 260A and back to the suction inlet 203A of the compressor 205A. Flow control device 215A may be, for example, a check valve that allows heat transfer fluid to flow from lube separator 210A to flow control device 220A, but does not allow heat transfer fluid to flow from flow control device 220A to lube separator 210A. The flow reducer 260A may, for example, reduce the pressure of the lubricating oil flowing therethrough.

According to one embodiment, the flow control device 220A may be a four-way valve. In this embodiment, the flow control device 220A may include four sections for controlling the flow of the heat transfer fluid and operate according to principles known in the art. It is understood that the flow control device 220A may be a flow control device other than a four-way valve capable of operating according to similar principles. The flow control device 220A may set the first state and the second state, respectively, by, for example, turning on or off a solenoid valve. In one embodiment, the first state corresponds to supplying high pressure, high temperature heat transfer fluid to the outdoor heat exchanger 225A and the second state corresponds to supplying high pressure, high temperature heat transfer fluid to one or more indoor units 125. The flow control device 220A may be set to the first state or the second state depending on the desired mode of operation. The heat transfer fluid directed to the one or more indoor units 125 passes through a flow control device 250A, a dryer/filter 236A, and a flow control device 275A.

Flow control device 250A may 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 may be allowed to pass in the first state or prevented from passing in the second state. The state of the flow control device 250A may be controlled according to the operation mode of the outdoor unit 105A. The flow control device 250A and the flow control device 250B may be set to different states to individually control the

outdoor units

105A and 105B.

The flow control device 275A may be, for example, a service valve. The flow control device 275A may be set to normally allow passage, but may also be set to disallow passage, for example, for servicing the outdoor unit 105A.

There may also be a pressure relief path 248A on either side of the flow control device 250A.

In fig. 2A, the pressure relief path 248A includes a flow reducer 262A. The flow reducer 262A may reduce the pressure of the heat transfer fluid passing therethrough. Aspects of the flow reduction device 262A may be the same as or similar to aspects of the flow reduction device 260A. In one embodiment, in any mode of operation, the heat transfer fluid may flow along the pressure relief path 248A. As described with respect to fig. 4 below, when in defrost mode, a portion of the high temperature, high pressure heat transfer fluid may flow along the pressure relief path 248A and mix with the cooled temperature pressure heat transfer fluid from the defrost flow path 290A.

In fig. 2B, pressure relief path 248A includes flow reducing device 262A, flow control device 245A, and flow control device 217A. The flow control device 245A may be, for example, a valve having at least a first state (e.g., allowing flow) and a second state (e.g., not allowing flow). In some embodiments, the valve may be actuated by a solenoid valve. The pressure relief path 248A may be controlled based on, for example, the operating mode of the outdoor unit 105A, the setting of another flow control device (e.g., flow control device 250A), the discharge pressure of the compressor, the suction pressure of the compressor, etc. Aspects of flow control device 217A may be the same or similar to aspects of flow control device 215A. The flow control device 217A may allow flow in one direction (e.g., from the flow control device 245A to the flow reducing device 262A, but not 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., the indoor units 125 in fig. 1). It is to be understood that the outdoor heat exchanger 225A and the one or more indoor heat exchangers of the one or more indoor units 125 may be any suitable heat exchangers wherein a heat transfer fluid passing therethrough may exchange heat with another heat exchange medium. In one embodiment, the outdoor heat exchanger 225A may be configured to function as a condenser (e.g., when operating in a cooling mode). In another embodiment, the outdoor heat exchanger 225A may be configured to function as an evaporator (e.g., when operating in a heating mode).

The heat transfer fluid returning from the one or more indoor units 125 may pass through the flow control device 240A, the dryer/filter 234A, and the subcooler 285A. Subcooler 285A operates according to principles known in the art and may, for example, increase the efficiency of heat pump loop 200. The heat transfer fluid may generally flow from subcooler 285A to expansion device 235A and dryer/filter 232A. The flow control device 240A may be, for example, a service valve. The expansion device 235A and the dryers/filters 232A, 234A, respectively, operate according to principles known in the art to reduce the 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 may flow along the defrost path 290A through the expansion device 280A and the subcooler 285A to divert a portion of the heat transfer fluid to the accumulator 255A and back to the compressor 205A. According to one embodiment,

expansion devices

235A and 280A may be controlled electronically, for example.

In some modes of operation (e.g., pressure control mode), the heat transfer fluid may be directed along pressure control path 270A. The pressure control path 270A may, for example, be used to reduce the pressure of the heat transfer fluid. The pressure control path 270A includes a flow reducing device 264A and flow

control devices

247A and 249A. Aspects of the flow reduction device 264A may be the same as or similar to aspects of the

flow reduction devices

260A and 262A. Flow control device 247A is the same as or similar to flow control device 245A (shown in figure 2B). Aspects of the flow control device 249A may be the same or similar to aspects of the flow control device 217A (shown in fig. 2B) to allow the heat transfer fluid to flow to the outdoor heat exchanger 225A when the flow control device 247A allows passage, but to prevent the heat transfer fluid from flowing in the opposite direction regardless of the state of the flow control device 247A.

The accumulator 255A is connected to a flow control device 220A (e.g., a four-way valve), and to the compressor 205A. Reservoir 255A functions according to principles known in the art. It will be appreciated that in some embodiments, dryer/filter 230A and reservoir 255A are not required.

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

Referring to fig. 2A, the cooling mode is now described. It will be appreciated that the cooling mode functions the same or similar to that shown in figure 2B. In the cooling mode, the heat pump circuit 200 may be configured to remove thermal energy from one or more controlled spaces (e.g., the controlled space 130 of fig. 1). Compressor 205A discharges a gaseous heat transfer fluid. Flow control device 220A is in a first state (e.g., on). The discharged heat transfer fluid is directed to the outdoor heat exchanger 225A. In the cooling mode, the outdoor heat exchanger 225A may operate as a condenser and output a liquid heat transfer fluid that then flows through the subcooler 285A. The liquid heat transfer fluid is supplied to one or more indoor units 125, which may include one or more indoor heat exchangers operable as evaporators. The liquid heat transfer fluid may remove thermal energy from 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 220A, where the heat transfer fluid is directed to the accumulator 255A and returned to the compressor 205A.

Fig. 3-5 illustrate schematic diagrams of a heat pump circuit 200 for a heat pump system (heat pump system 100 of fig. 1) operating in a heating mode, a defrost mode, and a pressure control mode, respectively. The various operating modes are controlled by varying the position of the flow control device to control the flow of the heat transfer fluid within the heat pump circuit 200. A controller (e.g., controller 115A in fig. 1) may be configured to control the flow control device based on, for example, readings from one or more sensors. It is understood that the heat pump system may include one or more other modes of operation, such as, but not limited to, a cooling mode.

Fig. 3 illustrates a schematic diagram of a heat pump circuit in a heating mode for a heat pump system (e.g., heat pump system 100 of fig. 1), according to one embodiment. In the heating mode, the heat pump circuit 200 may be configured to provide thermal energy to one or more controlled spaces (e.g., the controlled space 130 of fig. 1). Compressor 205A discharges a gaseous heat transfer fluid. Flow control device 220A is in a second state (e.g., open). The exhausted heat transfer fluid flows 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 exchange heat 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, through the expansion device 235A, the dryer/filter 232A, and is directed to the outdoor heat exchanger 225A. The heat exchanger 225A may evaporate the heat transfer fluid by receiving thermal energy from the outdoor air. The heat transfer fluid is directed through flow control device 220A into reservoir 255A. The heat transfer fluid then flows from accumulator 255A to compressor 205A and the process repeats.

Fig. 4 illustrates a schematic diagram of a 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 an embodiment. In the defrost mode, the

outdoor units

105A and 105B may not operate in the same mode. In the defrost mode, if there is a demand for heat, the heat pump circuit 200 may still be set to continue to supply thermal energy to one or more controlled spaces (e.g., controlled space 130 of fig. 1) while the outdoor unit 105A is defrosted. Compressor 205A discharges a gaseous heat transfer fluid. Flow control device 220A is in a first state (e.g., on). The discharged heat transfer fluid flows to the outdoor heat exchanger 225A. Because the heat transfer fluid is at a high pressure and temperature, the heat energy can defrost the outdoor heat exchanger 225A. When in the defrost mode, the flow control device 250A is in the second state, preventing the flow of high pressure heat transfer fluid to the suction inlet 203A of the compressor 205A.

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

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

Fig. 5 illustrates a schematic diagram of a heat pump circuit 200 of a heat pump system (heat pump system 100 in fig. 1) in a pressure control mode, according to one embodiment. In the pressure control mode, the

outdoor units

105A and 105B may not operate in the same mode. In the pressure control mode, if there is a heating demand, the heat pump circuit 200 may be configured to continue to supply thermal energy to one or more controlled spaces (e.g., the controlled space 130 in fig. 1) while preventing frost from forming on the outdoor heat exchanger 225A of the outdoor unit 105A.

The aspect of fig. 5 may be the same as or similar to the aspect of fig. 3. In addition to the operation in fig. 3, a portion of the heat transfer fluid at high pressure and temperature is diverted to the outdoor heat exchanger 225A through the pressure control path 270A. The flow control device 247A is disposed in the first state and a portion of the gaseous heat transfer fluid is directed through the flow reduction device 264A into the outdoor heat exchanger 225A. The transfer of the heat transfer fluid may, for example, reduce the formation of frost on the outdoor heat exchanger 225A and increase the amount of time before the outdoor unit 105A enters the defrost mode (as described above with respect to fig. 4). In one embodiment, the pressure control condition may be that the suction pressure of the compressor is below a suction pressure threshold. In another embodiment, the pressure control condition may be that the temperature of the coil in the approximate middle of the outdoor heat exchanger 225A is below a temperature threshold. In some embodiments, the pressure control condition includes the suction pressure being below a suction pressure threshold and the temperature of the coil in the approximate middle of the outdoor heat exchanger 225A being below a temperature threshold.

In another embodiment, the pressure control condition may be that the discharge pressure of the compressor is increased above a discharge pressure threshold.

In another embodiment, the pressure control condition may be a similar condition indicating that frost has started to form on the outdoor heat exchanger 225A.

Fig. 6 illustrates a method 600 for controlling a heat pump system (e.g., the heat pump system of fig. 1), according to one embodiment. The method 600 generally includes determining whether a frost condition or a pressure control condition has occurred and operating an outdoor unit (e.g., the outdoor unit 105A of fig. 1) in a defrost mode (see fig. 4 above for a detailed explanation of the defrost mode) or a pressure control mode (see fig. 5 above for a detailed explanation of the pressure control mode), respectively. In one embodiment, method 600 may be implemented as long as one or more outdoor units are operable. In another embodiment, the method 600 may be implemented when one or more outdoor units are in a heating mode (e.g., the method 700 of fig. 7).

The method 600 begins at 605 when a controller (e.g.,

controller

115A or 115B) determines whether a frost condition exists. In another embodiment, method 600 may begin at 615. The frost condition may include various indications that frost has formed on the outdoor heat exchanger of one of the one or more outdoor units. If a frost condition exists, the corresponding unit (e.g.,

outdoor unit

105A or 105B in FIG. 1) enters a defrost mode at 610. As described above, the outdoor unit having a frost condition is separately put into the defrost mode without changing the operation mode of one or more other outdoor units by controlling one or more flow control devices (e.g.,

flow control devices

220A and 250A). Since one or more outdoor units are individually controllable, the outdoor unit having a frost condition is put into a defrost mode, and the other outdoor units can continue to operate 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 be run and the controller may continue to determine if a frost condition exists and exit the defrost mode when the frost condition no longer exists.

If no frost condition exists at 605, the controller determines whether a pressure control condition exists at 615. The pressure control condition may be, for example, based on a suction pressure at a suction inlet of the compressor, a discharge pressure at a discharge outlet of the compressor, one or more temperatures (e.g., a temperature of a heat transfer fluid discharged from or provided to the compressor), and/or the like. If a pressure control condition exists, the controller enters a pressure control mode at 620. As described above with respect to fig. 5, the pressure control mode may include flowing a heat transfer fluid along path 270A. Similar to the defrost mode of 610, the pressure control mode may be enabled for the outdoor unit having the pressure control condition, while the other outdoor units may continue to operate without changing the operation mode. If the pressure control mode is not present, method 600 may return to 605. The method 600 may be repeated while the heat pump system is operating.

In one embodiment, the method 600 may be configured to monitor frost conditions (e.g., at 605), rather than pressure control conditions (e.g., at 615). In another embodiment, the method 600 may be configured to monitor pressure control conditions (e.g., at 615) instead of frost conditions (e.g., at 605). This may be based, for example, on whether one or more outdoor units are set to include a pressure control flow path.

Fig. 7 illustrates a method for controlling operation of a heat pump system (e.g., the heat pump system 100 of fig. 1) in a heating mode (see fig. 3 above for a 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 a heating mode. In response to a frost condition or a pressure control condition, the method 700 includes changing the operating mode of the heat pump system to a defrost mode (see fig. 4 above for a detailed explanation of the defrost mode) or a pressure control mode (see fig. 5 above for a detailed explanation of the pressure control mode), respectively.

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

At 715, the controller determines whether a frost condition exists. The frost condition may include various indications that frost has formed on the outdoor heat exchanger of one of the one or more outdoor units. If a frost condition exists, the corresponding cell will enter a 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 be run and the controller may continue to determine if a frost condition exists and exit the defrost mode when the frost condition no longer exists.

If no frost condition exists at 715, the controller determines whether a pressure control condition exists at 725. The pressure control condition may be, for example, based on suction pressure, discharge pressure, one or more temperatures, etc. If a pressure control condition exists, the controller enters a pressure control mode at 730. As described above with respect to fig. 5, the pressure control mode may include flowing a heat transfer fluid along path 270A. If pressure control mode is not present, method 700 may return to 705. Method 700 may be repeated while the heat pump system is operating.

In one embodiment, the method 700 may be configured to monitor frost conditions (e.g., at 715) instead of pressure control conditions (e.g., at 725). In another embodiment, the method 700 may be configured to monitor pressure control conditions (e.g., at 725) instead of frost conditions (e.g., at 715). This may be based, for example, on whether one or more outdoor units are set to include a pressure control flow path.

Aspect(s)

It may be noted that any of aspects 1-6 may be combined with any of aspects 7-12,13-17, and 18-22. Any of aspects 7-12 can be combined with any of aspects 13-17, and 18-22. Any of aspects 13-17 may 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 through a heat transfer loop, each of the plurality of outdoor units operable in a plurality of operating modes;

a first one of the plurality of outdoor units comprises:

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 allows flow to the outdoor heat exchanger and in a second state the first flow control device allows flow to the second flow control device; and is

A second one of the plurality of outdoor units comprises:

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 allows flow to the outdoor heat exchanger and in a second state the first flow control device allows flow to the second flow control device;

wherein the second flow control devices of the first and second ones of the plurality of outdoor units are individually controllable to set the first and/or second ones of the plurality of outdoor units to a defrost mode.

Aspect 2

The heat pump system of aspect 1, wherein the plurality of operating 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 one of aspects 1-2, wherein when in the defrost mode and the first flow control device of the first one of the plurality of outdoor units is in the first state, the second flow control device of the first one of the plurality of outdoor units prevents high pressure heat transfer fluid from flowing into the suction side of the compressor of the first one of the plurality of outdoor units.

Aspect 4

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

Aspect 5

The heat pump system of any of aspects 1-4, wherein the first and second ones of the plurality of outdoor units are operable in different operating modes.

Aspect 6

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

Aspect 7

A heat pump system, comprising:

a first one of the plurality of outdoor units comprises:

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

A second one of the plurality of outdoor units comprises:

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

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

Aspect 8

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

Aspect 9

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

Aspect 11

The heat pump system of 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 of 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 one of the plurality of outdoor units to operate in a defrost mode in response to a determination that a frost condition exists; and operating a second one of the plurality of outdoor units individually in the same or a different mode of operation.

Aspect 14

The method according to aspect 13, further comprising:

the determination is made in response to one or more of the plurality of outdoor units operating in a heating mode.

Aspect 15

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

Aspect 16

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

Aspect 17

The method of aspect 16, wherein reducing the capacity of the compressor comprises reducing the speed of the compressor.

Aspect 18

determining whether a pressure control condition exists;

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

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

Aspect 19

The method of aspect 18, further comprising:

the confirmation is made in response to one or more of the plurality of outdoor units operating in a heating mode.

Aspect 20

The method of any of aspects 18-19, wherein setting a first one of the plurality of outdoor units to operate in a pressure control mode comprises activating a pressure control flow path to divert a portion of heat transfer fluid flowing to one or more indoor units to the outdoor heat exchanger through a flow reduction device.

Aspect 21

The method of any of aspects 18-20, wherein determining whether a pressure control condition exists comprises determining at least one of: whether the suction pressure is below a suction pressure threshold and whether the temperature of the coil approximately in the middle of the outdoor heat exchanger is below a temperature threshold.

Aspect 22

The method of any of aspects 18-21, wherein determining whether a pressure control condition exists includes determining whether the discharge pressure is above a discharge pressure threshold.

The terminology used in the description is for the purpose of describing particular embodiments only and is not intended to be limiting. The terms "a", "an" and "the" include plural forms thereof unless expressly specified otherwise. The terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

With respect to the foregoing 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 the parts without departing from the scope of the present invention. The word "embodiment" as used in the specification may, but does not necessarily, refer to the same embodiment. The specification and examples described are exemplary only. Other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A variable refrigerant heat pump system comprising:

a first one of the plurality of outdoor units comprises:

A second one of the plurality of outdoor units comprises:

wherein said second flow control means of said first and second ones of said plurality of outdoor units are individually controllable to set said first and/or second ones of said plurality of outdoor units to a defrost mode.

2. The variable refrigerant heat pump system of claim 1, wherein when in a defrost mode and the first flow control device of the first one of the plurality of outdoor units is in a first state, the second flow control device of the first one of the plurality of outdoor units prevents high pressure heat transfer fluid from flowing into a suction side of the compressor of the first one of the plurality of outdoor units.

3. The variable refrigerant heat pump system of claim 1, wherein when in a defrost mode and the first flow control device of the second one of the plurality of outdoor units is in a first state, the second flow control device of the second one of the plurality of outdoor units prevents high pressure heat transfer fluid from flowing into a suction side of the compressor of the second one of the plurality of outdoor units.

4. The variable refrigerant heat pump system of claim 1, wherein the first and second ones of the plurality of outdoor units are operable in different operating modes.

5. The variable refrigerant heat pump system of claim 1, further comprising a defrost flow path including a subcooler and an expansion device disposed between the one or more indoor units and the outdoor heat exchanger.

6. A variable refrigerant heat pump system comprising:

a first one of the plurality of outdoor units comprises:

a compressor, a flow control device, and a pressure control flow path, the flow control device positioned 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 the pressure control flow path is disposed between the flow control device and the second flow control device, the flow control device allowing flow to the outdoor heat exchanger in a first state, the flow control device allowing flow to the second flow control device in a second state; and is

A second one of the plurality of outdoor units comprises:

a compressor, a flow control device, and a pressure control flow path, the flow control device positioned 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 the pressure control flow path is disposed between the flow control device and the second flow control device, the flow control device allowing flow to the outdoor heat exchanger in a first state, the flow control device allowing flow to the second flow control device in a second state;

wherein the second flow control devices of the first and second ones of the plurality of outdoor units are individually controllable to set the first and/or second ones of the plurality of outdoor units to a defrost mode,

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

7. The variable refrigerant heat pump system of claim 6, wherein the pressure control flow path is selectively enabled in response to at least one of: at least one suction pressure of the compressor falling below a suction pressure threshold, a temperature of a coil approximately in the middle of the outdoor heat exchanger falling below a temperature threshold, and a discharge pressure of the compressor above a discharge pressure threshold.

8. The variable refrigerant heat pump system of claim 7, wherein the pressure control flow path is selectively disabled in response to at least one of: at least one suction pressure of the compressor above the suction pressure threshold, a temperature of a coil approximately in the middle of the outdoor heat exchanger above the temperature threshold, and the discharge pressure of the compressor below the discharge pressure threshold.

9. The variable refrigerant heat pump system of claim 7, wherein the pressure control flow path is selectively enabled by setting a third flow control device to allow flow through the second flow control device.

10. A method of controlling a heat pump system, the heat pump system including 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 one of the plurality of outdoor units to operate in a defrost mode in response to a determination that a frost condition exists, the first one of the plurality of outdoor units including the compressor, and a first flow control device between the compressor and the 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 allows flow to the outdoor heat exchanger and in a second state the first flow control device allows flow to the second flow control device, the second flow control device being controllable to set the first one of the plurality of outdoor units in the defrost mode; and

11. The method of claim 10, wherein setting a first one of the plurality of outdoor units in a defrost mode includes preventing high pressure heat transfer fluid from flowing into a suction side of the compressor.

12. The method of claim 10, wherein setting a first one of the plurality of outdoor units to operate in a defrost mode comprises reducing a capacity of the compressor.

13. The method of claim 12, wherein reducing the capacity of the compressor comprises reducing a speed of the compressor.

14. A method of controlling a heat pump system, the heat pump system including 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 one of the plurality of outdoor units to operate in a pressure control mode in response to a determination that a pressure control condition exists, the first one of the plurality of outdoor units including the compressor, a flow control device positioned between the compressor and the outdoor heat exchanger in a first flow direction and a pressure control flow path between the compressor and a second flow control device in a second flow direction, wherein the pressure control flow path is disposed between the flow control device and the second flow control device, the flow control device allowing flow to the outdoor heat exchanger in a first state, the flow control device allowing flow to the second flow control device in a second state; and

15. The method of claim 14, wherein setting the first one of the plurality of outdoor units to operate in a pressure control mode comprises activating a pressure control flow path to divert a portion of heat transfer fluid to one or more indoor units to the outdoor heat exchanger through a flow reduction device.

16. The method of claim 14, wherein determining whether a pressure control condition exists comprises determining at least one of: whether the suction pressure is below a suction pressure threshold, whether a temperature of a coil approximately in the middle of the outdoor heat exchanger is below a temperature threshold, or whether the discharge pressure is above a discharge pressure threshold.