Cold Climate Heat Pump with Vapor Injection System

This application claims priority to and benefit of U.S. provisional patent application No. 63/647,806 filed May 15, 2024, which is herein incorporated by reference.

This disclosure relates generally to cold climate heat pump systems. In particular, embodiments of the disclosure are related to rooftop cold climate heat pump systems with vapor injection.

Conventional rooftop heat pump systems can be used in rooftop environments for various air conditioning purposes. Such systems may include vapor injection to aid in compressor operation. However, an amount of vapor injection is typically not controlled when the system has more than one compressor, resulting in inaccurate or uncontrolled amounts of vapor injection provided to the compressor, which results in suboptimal operation of such rooftop systems.

This disclosure relates generally to cold climate heat pump systems that employ multiple compressors. In particular, embodiments of the present disclosure relate to tandem compressor rooftop cold climate heat pump systems that have vapor injection.

illustrates a block diagram of a heat pump systemwith vapor injection according to an embodiment of the present disclosure. Heat pump systemincludes a first compressorand a second compressor. In some embodiments, more than two compressors may be present. Merely for ease of description, the figures illustrate two compressors. In some embodiments, the first compressorand the second compressormay be tandemly operated scroll compressors. Heat pump systemmay use a fluid (e.g., refrigerants like water, R134A, R454B, R32, Hydrocarbons, Hydrocarbon blends, R717, CO2 R744, R-22, R410A, R600 series, hydrofluoroolefins (HFOs) and HFO blends, and the like) for its operation. The first compressorand the second compressormay have a common input port(e.g., input port manifold) and a common output port(e.g., outlet port manifold). The common input portserves as an input port through which the fluid enters both the first compressorand the second compressor. The common output portservers as the output port through which the fluid exits both the first compressorand the second compressor. The first compressorhas a first vapor injection portand the second compressorhas a second vapor injection port.

It is be noted that throughout the disclosure, ports described as being in “fluid communication” with each other have one or more refrigerant lines or other appropriate means of fluid communication that facilitate flow of a fluid between these ports. The systemincludes a reversing valvethat is in fluid communication with the common input portand the common output port. Reversing valvemay be any commonly known reversing valve in the art. The reversing valvechanges the direction of refrigerant flow in the systemdepending on the mode of operation of the system. By reversing the flow of refrigerant, the heat pump cycle is changed from cooling to heating or vice versa. The reversing valvemay have four ports. A first portof the reversing valveis in fluid communication with the common input portof the first compressorand the second compressor. A second portof the reversing valveis in fluid communication with a first portof a first heat exchanger. The first portof the first heat exchangeris in fluid communication with the second portof reversing valve. A third portof reversing valveis in fluid communication with a first portof a charge compensator. The charge compensatorincreases system efficiency by storing extra refrigerant in the heating mode. The charge compensatorreturns refrigerant back into circulation in the cooling mode. The fourth portof the reversing valveis in fluid communication with the common output portof the first compressorand the second compressor. As is known in the art, reversing valves can be operated in multiple modes in which flow of fluid can be controlled and directed based on the operational requirements of heat pump system(e.g., heating mode and cooling mode).

A second portof the charge compensatoris in fluid communication with a first portof a second heat exchanger. In some embodiments, the second heat exchangercan be an outdoor heat exchanger that is located external to the premises being served by heat pump systemor otherwise is in thermal communication (e.g., via one or more air ducts) with the outdoor ambient environment. The second heat exchangercan act as a condenser or an evaporator depending on the mode of operation of heat pump system. A third portof the charge compensatoris in fluid communication with a second portof the first heat exchangerat a pointbetween a second expansion valveand the second port. Charge compensatorcan be any device of its type known in the art. In various implementations, the charge compensatormay be omitted.

A second portof the second heat exchangeris in fluid communication with a first expansion valve. The first expansion valvemay be realized using known devices in the art. The first expansion valveremoves pressure from the fluid and allows expansion or change of state of the fluid. In some embodiments, a first check valvemay be positioned in parallel to the first expansion valveto provide a bypass path for the fluid in heat pump system. The check valveprevents fluid flowing from a filter drierto the second heat exchangerand helps to direct the fluid from the filter drierto the first expansion valveduring the heating operation mode. In other embodiments, the first check valvemay be integrated into the first expansion valve.

The expansion valveis in fluid communication with a first portof the filter drier. The filter drieris a filtration device that is designed to remove contaminants, including moisture, from the fluid. Filter driermay be realized using any known device in the art. A second portof the filter drieris in fluid communication with a first portof a third heat exchanger.

In one embodiment, the third heat exchanger(or any other heat exchanger described herein) may be a brazed plate heat exchanger. As a brazed plate heat exchanger, the third heat exchangermay be configured for exchanging heat between water and refrigerant for heating water as a part of a water heating system. In another embodiment, the third heat exchangermay be realized by using a flash tank, a shell and tube heat exchanger, tube-in-tube heat exchanger, or any other suitable heat exchanger. One skilled in the art will realize that other types of heat exchangers that serve a similar purpose may also be used. The specific type of heat exchanger used is not germane to the disclosure. For ease of explanation of the various embodiment of the present disclosure, a brazed plate heat exchanger is used herein.

The third heat exchangerhas four ports. The first portof the third heat exchangeris in fluid communication with the second portof the filter drierand in fluid communication with a second solenoid valve. A fourth portof the third heat exchangeris in fluid communication with a first solenoid valveand in fluid communication with the second expansion valve. A second portof the third heat exchangeris in fluid communication with a third expansion valve. A third portof the third heat exchangeris in fluid communication with a first control valveand a second control valve. The first solenoid valveis in fluid communication with the fourth portof the third heat exchanger. The first solenoid valveis also in fluid communication with the third expansion valve. The second solenoid valveis in fluid communication with the first portof the third heat exchanger. The second solenoid valveand the first solenoid valveare in fluid communication with the same port of the third expansion valve. In other words, the third expansion valveis fluid communication with both the first solenoid valveand the second solenoid valve, as is clearly shown in.

In one embodiment, the third heat exchanger, the first solenoid valveand the second solenoid valveand third expansion valvetogether define an economizer. The economizerallows efficient exchange of thermal energy between two fluids passing through the third heat exchanger. In some implementations, the economizermay be replaced with a flash tank or other structure for providing a supply of vapor to one or more vapor injection ports of one or more compressors. The two fluids may either flow in the same direction within the third heat exchangeras shown inor the two fluids may flow in opposite directions (counter flow) within the third heat exchangeras shown in. The first solenoid valve, the second solenoid valve, and the third expansion valveform a vapor injection circuit. In the embodiment shown in, the first solenoid valveand the second solenoid valveare shown as solenoid valves, though any other suitable shut-off valve may be used, such as needle valves, ball valves, gate valves, or the like.

The second expansion valveis in fluid communication with the fourth portof the third heat exchanger. The second expansion valveis also in fluid communication with the second portof the first heat exchanger. In some embodiments, the first heat exchangermay be located indoor in the premises being served by heat pump systemor otherwise is in thermal communication (e.g., via one or more air ducts) with the indoor ambient environment.

In some embodiments, a second check valvemay be disposed in parallel to the second expansion valve. In other embodiments, the second check valvemay be integrated into the second expansion valve.

Each of the first control valveand the second control valveare in fluid communication with the third portof the third heat exchangerfor receiving vapor from the economizer, a flash tank, or other such structure. The first control valveis in fluid communication with the first vapor injection portof the first compressorand the second control valveis fluid communication with the second vapor injection portof the second compressor. The first control valveand the second control valvemay be specialized valves that allow for precise control of an amount of vapor that is to be injected in each of the first compressorand the second compressor. In some embodiments, a special control loop may be implemented in order to control the amount of vapor injected into the first compressorand the second compressor. Details of the structure and operation of such a control system are provided below with references to.

illustrates operation of heat pump system in a first mode of operation (e.g., heating mode). Specifically,illustrates a heating mode of operation. In this mode, hot and compressed vapor of a fluid (e.g., refrigerants like R454B, R32, water, R134A, Hydrocarbons, R717, CO2 R744, R-22, R410A, R600 series, and the like) is output by the first compressorand the second compressor. Reversing valveis placed in one of its states in which it receives the fluid output from the compressors and directs the fluid to the first portof the first heat exchanger(e.g., a condenser in the first mode of operation) via the second port. In the first heat exchanger, the fluid transfer its heat to another fluid, such as, air, that may be circulated by a blower unit (not shown) that is coupled to the first heat exchangerfor circulating heated air within a premises. The fluid then travels via the second check valvetowards the third heat exchanger. Before the fluid reaches the third heat exchanger, the fluid is split into two portions. A first portion of the fluid travels via the first solenoid valve, which is open in this mode. The second solenoid valveis closed in this mode, so the first portion of the fluid cannot travel via the second solenoid valve. The second portion of the fluid enters the third heat exchanger, via the fourth portand along the primary refrigerant flow path.

The first portion of the fluid that travels via the first solenoid valveand passes through the third expansion valve. Here the first portion of the fluid expands and cools down to generate a two-phase fluid of liquid and vapor refrigerant. The first portion of the fluid then exits the third expansion valveand enters the third heat exchangervia the second portand along the vapor injection path. Within the third heat exchanger, the first portion of the fluid is heated by the second portion of the fluid into vapor and that vapor is then output from the third heat exchangervia the third port. The vapor is then directed towards the first vapor injection portof the first compressorand/or the second vapor injection portof the second compressorvia the first control valveor the second control valve, respectively. As is common knowledge in the art, vapor injection is used to cool down the compressor so that the compressor can function efficiently in cold ambient temperatures without overheating, such as below 30° F.

As can be seen in, the primary refrigerant flow pathand the vapor injection flow pathare in counter-flow directions. In other words, the primary refrigerant flow pathand the vapor injection flow path are in opposite directions to each other within the third heat exchanger.

The second portion of the fluid travels via the third heat exchangeralong the primary refrigerant flow pathand exits the third heat exchangervia the first port. The second portion of the fluid is then directed to the second portof the filter drier. The second portion of the fluid exits the filter driervia the first portand passes via the first expansion valveto the second portof the second heat exchanger. The first check valveis configured such that it prevents flow of the second portion of the fluid through it.

At the second heat exchanger, the second portion of the fluid is heated or boiled, such as, by blowing warm outdoor air over the second heat exchangerusing a fan (not shown). The second portion of the fluid leaves the second heat exchangervia the first portas a slightly super-heated vapor. Superheating occurs when the temperature of the vapor rises above the boiling point of the corresponding liquid. Thus, in this instance, the vapor of the fluid is heated above its boiling point. This vapor passes through the charge compensatorand enters the reversing valvevia the third port. The reversing valve directs the slightly super-heated vapor, via the first port, to the common input portof the first compressorand the second compressor.

The slightly super-heated vapor that is used for vapor injection is directed from the third heat exchangervia the third porttoward the first control valveand the second control valve. Depending on the operational data of the first compressorand the second compressor, the first control valve, the second control valve, or both are operated to allow a precise amount of vapor to be injected into each of the first compressoror the second compressor. The operational data may include one or more of discharge temperature, injection pressure, or the compressor speed. The first control valveand the second control valvemay be specialized control valves that allow precise control of amount of vapor that is injected into each of the first compressorand the second compressor. In some embodiments, the first control valveand the second control valvemay be vapor mass flow controllers. The first control valveand the second control valvemay be operated in the range of between 0-100%, wherein 0% may indicate that the valve is fully closed and 100% may indicate that the valve is fully open. In some embodiments, the first control valveand the second control valvemay be controllable in 1% increments to allow precise control of vapor flow through the valves. In other embodiments an even finer or coarser control of the valves may be possible. The choice of a particular type of control valve may depend on the nature and operation of heat pump system.

In some implementations, the heat pump systemmay be for a water heating system. In such implementations, the reversing valve may be omitted, the system may operate in the heating mode, and the first heat exchanger acts as a condenser and is a refrigerant-to-water heat exchanger. The refrigerant-to-water heat exchanger may be a wrapped condenser heat exchanger (e.g., condenser tubing wrapped around a water storage tank), a brazed plate heat exchanger with a water circuit and a refrigerant circuit, a shell and tube heat exchanger, or any other suitable refrigerant-to-water heat exchanger. Please expand on this as needed. This is also applicable to any other heat pump system described herein.

illustrates structure and operation of heat pump systemin a second mode of operation according to an embodiment of the present disclosure. In particular,illustrates operation of heat pump systemin a cooling mode. In this mode, the premises being served by heat pump system is to be cooled and the outside ambient air temperature is warmer than inside the premises.

In this mode, the first compressor, or the second compressor, or both output compressed and vaporized fluid (e.g., refrigerants like R454B, R32, water, R134A, Hydrocarbons, R717, CO2 R744, R-22, R410A, R600 series, and the like) to the reversing valve. Reversing valvereceives this fluid via the fourth port. Reversing valveis placed in a state in which it directs the vaporized fluid to charge compensatorvia its third port. Charge compensatorreceives the fluid at the first portand outputs the fluid from the second port. From there the fluid flows through to the second heat exchanger. The second heat exchangerreceives the fluid via the first portand outputs the fluid via the second port. In some embodiments, the second heat exchangercan be located externally to the premises being served or otherwise is in thermal communication (e.g., via one or more air ducts) with the outdoor ambient environment. After exiting the second heat exchanger, the fluid passes through the first check valve. In some embodiments, the first check valvecan be integrated with the first expansion valve. The fluid exits the first check valveand enters the filter driervia the first port. The fluid exits the filter driervia the second portand flows towards the third heat exchanger. Prior to entering the third heat exchanger, the fluid is split into two portions. A first portion of the fluid enters the third heat exchangervia the first portand the second portion of the fluid is directed towards the third expansion valvevia the second solenoid valve. In this mode, the second solenoid valveis open while the first solenoid valveis closed. This prevents the second portion of the fluid from flowing via the first solenoid valvetowards the third heat exchanger.

The second portion of the fluid leaves the third expansion valveand enters the third heat exchangervia the second port. The second portion of the fluid then leaves the third heat exchangervia the third portin the form of a slightly super-heated vapor. This vapor is then used for vapor injection into the first compressor, or the second compressor, or both the compressors.

The first portion of the fluid passes through the third heat exchangerand exits the third heat exchangervia the fourth port. The first portion of the fluid the flows towards the second expansion valve. Since the first solenoid valveis closed, it prevents the first portion of the fluid from flowing towards the third expansion valve.

As can be seen in, the first portion of the fluid travels along the primary refrigerant flow pathand the second portion of the fluid travels along the vapor injection path. Within the third heat exchanger, the first and the second portions of the fluid travel in the same direction (e.g., flow pathsandare in the same direction) as is shown by the arrows associated with the third heat exchanger.

The first portion the fluid passes through the second expansion valveand enters the first heat exchangervia the second port. In some embodiments, the first heat exchangermay be located inside the premises being cooled or otherwise is in thermal communication (e.g., via one or more air ducts) with the indoor ambient environment. In the first heat exchanger, the first portion of the fluid absorbs heat from the warm air from inside the premises and cools that air and in the process becomes slightly super-heated. The air may be blown over the first heat exchangerusing a blower unit (not shown) coupled to the first heat exchanger.

The slightly super-heated vaporized fluid exits from the first heat exchangervia the first portand is directed towards the reversing valve. The second portion of the fluid (e.g., the slightly super-heated vaporized fluid) enters reversing valvevia the second portand exits the reversing valve via the first port. The second portion of the fluid is then directed to the common input portof the first compressorand the second compressor. The first compressorand the second compressorthen pressurize the vaporized fluid and the cycle repeats again until the cooling mode is active.

The slightly super-heated vapor generated using the second portion of the fluid exits the third heat exchangervia the third portand is directed towards the first control valveand the second control valve. The rest of the operation of the system for vapor injection is similar to what is described above with reference to.

illustrates a heat pump systemaccording to another embodiment of the present disclosure. The difference between heat pump systemand heat pump systemofis the addition of an accumulatorand removal of the first solenoid valveand the second solenoid valve. Accumulatoris disposed between reversing valveand the common input port. Accumulatortraps any fluid in a liquid form and oil and prevents any liquid or oil from entering the first compressorand the second compressorvia the common input port.illustrates a heating mode of operation of heat pump system. The functioning of heat pump systemin the heating mode is similar to what is described above with reference to, the difference being that after the portion of the fluid exits the first portof the reversing valve, it enters the accumulatorvia port. The fluid then exits the accumulatorvia portand is then directed to the common input portof the first compressorand the second compressor. Accumulatortraps any oil or fluid in a liquid form and prevents any liquid from entering the first compressorand the second compressor.

Similar to, in the embodiment illustrated in, the primary refrigerant flow pathand the vapor injection flow pathare in counter-flow directions. In other words, the primary refrigerant flow pathand the vapor injection flow path are in opposite directions to each other within the third heat exchanger.

illustrates a heat pump systemaccording to another embodiment of the present disclosure. The difference between heat pump systemand heat pump systemofis the addition of an accumulatorand removal of the first solenoid valveand the second solenoid valve. Accumulatoris disposed between reversing valveand common input port. Accumulatortraps any fluid in a liquid form and oil and prevents any liquid or oil from entering the first compressorand the second compressorvia the common input port.illustrates a cooling mode of operation of heat pump system. The functioning of heat pump systemin the cooling mode is similar to what is described above with reference to, the difference being that after the portion of the exits the first portof the reversing valve, the portion of the fluid enters the accumulatorvia port. The portion of the fluid then exits accumulatorvia portionand is then directed towards the common input portof the first compressorand the second compressor. Accumulatortraps any oil or fluid in a liquid form and prevents any liquid from entering the first compressorand the second compressor.

Similar to the embodiment illustrated in, in the embodiment of, the primary refrigerant flow pathand the vapor injection flow pathare in the same direction. In other words, the primary refrigerant flow pathand the vapor injection flow path are in a same direction within the third heat exchanger.

illustrates a functional block diagram for a vapor injection control systemaccording to an embodiment of the present disclosure. Vapor injection control systemincludes a controller. Controllercan be realized using various techniques or devices. In an embodiment, the controllermay be a central processing unit (CPU) specially programmed to carry out the below disclosed functions. In other embodiments, controllermay be an application specific integrated circuit (ASIC), or a microcontroller, or the like.

Controlleris communicatively coupled to compressorsand. Compressormay be akin to the first compressorand the compressormay be akin to the second compressorillustrated in. Controlleris also communicatively coupled to control valvesand. Control valveis in fluid communication with the compressorand the control valveis in fluid communication with the compressor. Although two compressors are shown in, one skilled in the art will realize that the embodiments described in this specification are equally applicable to systems with more than two compressors and correspondingly more than two control valves.

A vapor injection sourceis in fluid communication with both the control valvesand. Vapor injection sourcemay be any suitable source that can provide the requisite amount of vapor at a desired temperature. In an embodiment, vapor injection sourcecan be the economizerdescribed in, a flash tank, or other suitable structure for supplying vapor for vapor injection.

During operation of heat pump system, controllercontinually monitors the operational data of the compressorsandand ambient environment data. Based on the operational data, or the ambient environment data, or both, the controllermay control valvesandto open or close to the desired level to allow the right amount of vapor to be injected into compressorand, respectively. The control valvesandallow precise control of the amount of vapor that is allowed to go to the compressors. For example, control valvesandmay be realized using the appropriate mass flow controllers for the fluid being used. Operational data of compressorsandmay include, but is not limited to, capacity of the compressors, compressor speed (e.g., measured in revolutions per minute (RPM)), suction temperature, suction pressure, discharge pressure, discharge temperature, compressor operating envelope, and the like. Ambient environment data may include but is not limited to outside air temperature, inside air temperature, elevation, barometric pressure, and the like.

is a tablethat illustrates the various operational modes associated with, for example, the vapor injection systemofaccording to an embodiment of the present disclosure. It is to be noted that the details of operational parameters shown in tableare for illustrative purposes only and one skilled in the art will realize that more, or less, or different operational parameters than the ones shown in tablecan be used to control the control valvesandof. The following description of the operation of vapor injection systemwill be explained using bothand. In order to explain the operation of control valvesanda scale of 0%-100% is used to illustrate how open or close each of valve is. This also illustrates the precise nature of control of these valves.

In table, there are multiple modes of operationshown. For sake of brevity and for illustration purposes only, five modes of operation are shown. However, one skilled in the art will realize that there can be less or more number of operation modes possible based on the number of operational parameters used. Columnillustrates some of the operational parameters of compressor. Columnillustrates some of the operational parameters of compressor. Columnillustrates the status of control valvethat is coupled to compressor. Columnillustrates the status of control valvethat is coupled to compressor.

Operation 1 is the first mode of operation of the system. In this mode, controlleris configured to determine or determines whether any of the two compressorsoris OFF, such as, not working or idle. As shown in table, compressor 1 () is ON, such as, operating or running currently, and compressor 2 () is OFF, such as, not operating or running currently. In this instance, controllersends a first signal to control valveto open. ‘Open’ in this instance may be fully open (e.g., 100%) or open partially (e.g., anywhere between 0% and 100% open). Controllersends a second signal to control valveto close fully (e.g., 0%). In some instances, valvemay not close fully, but the amount of vapor passing through valvemay be negligible or about 0. In an embodiment, the amount of vapor may be measured in vapor volume. In an embodiment, the vapor volume may be designated in liters. Since compressoris not operational, it does not need vapor injection and hence no vapor is provided to compressor. It is to be noted that “ON” and “OFF” in this is instance refers to the current operational status of the individual compressor. A compressor may be powered and generally functional while being “OFF” or not operating currently.

Operation 2 illustrates a second mode of operation where both compressorsandare operational currently (e.g., running/operating). In this mode, controlleris configured to determine or determines based on operational data received from the compressors or other sources, that both compressorsandare of the same capacity or substantially same capacity (e.g., 5 Tons each) and that currently they are running at a same speed. All other things being equal, controllerdetermines that both compressors are to be supplied with an equal amount of vapor. Controllerthen sends individual signals to both control valvesandsuch that they each allow substantially equal amount of vapor, from the available total vapor volume, to be directed to the respective compressor coupled to valvesand. For example, if the total amount of available vapor is 10 liters, then that may be substantially equally split between the two compressorsandby opening both control valvesandby approximately 50%.

Operation 3 illustrates a third mode of operation where both compressorsandare operational currently (e.g., running/operating). In this mode, controlleris configured to determine or receives the operational data of the compressors and determines that compressor 1 is bigger in capacity compared to compressor 2. Since compressor 1 is bigger in capacity, it may need more vapor volume compared to compressor 2. Based on this information, and optionally additional operational parameters of the two compressors, controllerdetermines that the amount of vapor to be provided to compressor 1 is greater than the amount of vapor to be provided to compressor 2. In some embodiments, controllermay determine the exact amount of vapor to be supplied to each of the compressors. In other embodiments, the ratio of the relative capacities of the two compressors may be used to determine the amount of vapor to be supplied to each compressor. Controllerthen sends the appropriate signals to the two valvesandto open such that the determined amount of vapor is provided to each of the respective compressors. For example, consider that compressorhas a capacity of 6 ton and compressorhas a capacity of 4 ton. In this instance, the ratio associated with compressorwill be 0.6 (6/(6+4)) and the ratio associated with compressorwill be 0.4 (4/(6+4)). Based on these ratios, control valvemay be opened to 60% and control valvemay be opened to 40%. This will allow the appropriate amount of vapor to be supplied to each of the compressorand compressor.

Operation 4 illustrates a fourth mode of operation where both compressorsandare ‘ON’. Controllerdetermines based on the operational data that both compressors are of the same capacity or substantially of the same capacity, but they are running at diff speeds. In this instance, controllermay operate control valvesandsuch that the compressor running at a higher speed is provided with a greater amount of vapor than the compressor that is running at a lower speed. This is because the compressor running at a higher speed is likely to have higher temperature and as a result needs more cooling vapor than the compressor that is running slower. In some instances, the relative ratios of the speeds of the compressorsandmay be used to determine the amount of vapor injection to be provided to each of the compressorand compressor. For example, consider that compressoris running at 2000 RPM and compressoris running at 4000 RPM. In this instance, the speed ratio associated with compressorwill be 0.33 (2000/(2000+4000)) and the speed ratio associated with compressoris 0.66 (4000/(2000+4000)). Based on these ratios, the control valvemay be opened to 33% and control valvemay be opened to 66%. This will allow the appropriate amount of vapor to be supplied to each of the compressorand compressor.

Operation 5 illustrates a fifth mode of operation where both compressorsandare operational currently (e.g., running or operating). In this mode, controllerreceives the operational data of the compressorsandand determines that both compressorsandare of different capacity (e.g., compressor 1 is bigger than compressor 2 or vice versa) and that both compressors are running at a different speeds (e.g., compressor 1 may be running faster than compressor 2 or vice versa). In this instance, controlleragain determines the amount of vapor to be provided to each of the compressors based on their individual capacity and current operating speed and accordingly instructs each of control valvesandto open proportionally to allow the determined amount of vapor to be provided to each of the compressors. In one embodiment, the compressor having the higher capacity may get more vapor injection regardless of the speed at which the compressors are operating. In another embodiment, the compressor running at the higher speed may get more vapor injection regardless of the capacity of the two compressors. One skilled in the art will realize that the amount of vapor injected into each of the compressors can be determined using other combinations of capacity and speed. In one embodiment, an effective capacity of each compressor may be determined and the control valves may be operated based on the relative ratios of the effective capacity of each of the compressors. For example, consider that compressorhas a capacity of 5 tons and is running at 80% of its maximum speed and compressorhas a capacity of 10 tons and is running at 50% of its maximum speed. In this instance the effective capacity of compressoris 4 ton (5T*0.8) and the effective capacity of compressoris 5 ton (10*0.5). The relative ratio of the effective capacity of compressorwill be 0.45 (4/(4+5)) and the relative ratio of the effective capacity of compressorwill be 0.55 (5/(4+5)). Based on these ratios, control valvemay be opened to 45% and control valvemay be opened to 55% to provide the appropriate amount of vapor injection to each of the compressorsandrespectively.

As used above, the term “substantially” is meant to convey that the capacity and the speeds of the two compressors are within 5%-10% of each other.

Although an air-based heat pump system is described above, it is for illustration purposes only. The vapor injection system described in this specification can be used in other application as well. For example, the above described techniques can also be used in split system, water cool system, a heat pump water heater (HPWH) system or in refrigeration systems. As such, any of the heat exchangers described herein may be a brazed plate heat exchanger configured for exchanging heat between water and refrigerant for heating the water.

It should be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. References to a composition containing “a” constituent is intended to include other constituents in addition to the one named.

Also, in describing the disclosed technology, terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

Ranges may be expressed herein as from “about” or “approximately” or “substantially” one particular value and/or to “about” or “approximately” or substantially” another particular value. When such a range is expressed, the disclosed technology can include from the one particular value and/or to the other particular value. Further, ranges described as being between a first value and a second value are inclusive of the first and second values. Likewise, ranges described as being from a first value and to a second value are inclusive of the first and second values.