AUTOCASCADE LIQUID-VAPOR SEPARATOR WITH INTEGRAL BYPASS

Description

FIELD

The embodiments described herein pertain generally to systems and methods for refrigerant control of a heating, ventilation, air conditioning, and refrigeration (HVACR) system. More specifically, the embodiments described herein pertain to modulating or enabling/disabling a separation and/or combination of liquid and/or vapor refrigerant streams.

BACKGROUND

An HVACR system typically includes a compressor, a condenser, an expander, and an evaporator, forming a refrigeration circuit. In a cooling cycle, refrigerant vapor is generally compressed by the compressor, and then condensed to liquid refrigerant in the condenser. The liquid refrigerant can then be directed through the expander to reduce the temperature and become a liquid/vapor refrigerant mixture (two-phase refrigerant mixture). The two-phase refrigerant mixture can be directed into the evaporator to exchange heat with, for example, air or water moving across the evaporator. The two-phase refrigerant mixture can be vaporized to refrigerant vapor in the evaporator. The purpose of the refrigeration cycle can be to either provide cooling through heat exchange in the evaporator and/or provide heat through heat exchange in the condenser.

Some HVACR systems may be able to operate in a reversible heating cycle. These HVACR systems are typically called heat pumps. During this type of heating cycle, the process is generally reversed from the process in the cooling cycle. In the heating cycle, the evaporator in the cooling cycle functions as a condenser, and the condenser functions as an evaporator. After being compressed by the compressor, the compressed refrigerant vapor is typically directed to the cooling-mode evaporator (heating-cycle condenser) first to release heat to, for example, water or the indoor air, which also condenses the refrigerant vapor to liquid refrigerant. The liquid refrigerant is then typically directed to the cooling-mode condenser (heating-cycle evaporator) through the expander to become a two-phase refrigerant mixture.

An HVACR system can include an autocascade refrigerant circuit. The HVACR system can operate in an autocascade refrigerant cycle (or mode) and a non-autocascade refrigerant cycle (or mode). It is to be understood that autocascade refrigerant cycles use a blended refrigerant that separates into liquid and vapor streams, and the composition of this blend can change during operations.

SUMMARY

This disclosure is directed to an HVACR system having an autocascade refrigerant circuit, including but not limited to a reversible heat pump circuit. Features in the embodiments disclosed herein may use modulators and connections between the vapor and liquid outlets of a liquid-vapor separator to modulate (and/or to enable/disable) the separation and/or combination of the liquid and/or vapor streams. Depending on the operating mode, the liquid and/or vapor streams may remain separate, flow through the liquid-vapor separator together, or recombine at a location downstream of the liquid-vapor separator and flow together out to the system.

It is to be understood that an autocascade refrigeration cycle may reduce the compressor pressure ratio required to extract heat from a cold source (where the energy or heat is drawn with the evaporator) and deliver heat to a hot sink (where the condenser is releasing the energy or heat), e.g., when ambient temperature increases. When an autocascade refrigerant circuit is applied as an air-sourced heat pump, this may limit the operating map due to minimum pressure ratio requirements of the compressor. In order to achieve a full operating map, the system may need to disable or reduce the autocascade functionality and/or operate as a standard refrigeration cycle, raising the pressure ratio, for warmer ambient temperature.

Features in the embodiments disclosed herein may combine or mix the liquid and vapor streams from the liquid-vapor separator within the system and provide a method for modulating and/or enabling/disabling the autocascade functionality, to achieve a broader operating map as an air-source heat pump. It is to be understood that features in the embodiments disclosed herein may be applicable to air-air, air-water, water-water, and/or water-air heat pumps.

Features in the embodiments disclosed herein may provide a bypass design for the liquid-vapor separator which may recombine the liquid and/or vapor streams either internally to the liquid-vapor separator or externally in a mixing section. In an example embodiment, the design may include a set of modulators (e.g., valves) integral to or separated from the body of the liquid-vapor separator.

In an example embodiment, a heating, ventilation, air conditioning, and refrigeration (HVACR) system is provided. The system includes a compressor, a condenser, a liquid-vapor separator having a vapor outlet and a liquid outlet, a cascade heat exchanger, an expander, and an evaporator fluidly connected. The system also includes a modulator disposed downstream of the liquid outlet, and a controller. The controller is configured to determine an operation parameter of the system, and to control the modulator to modulate a liquid flow from the liquid outlet based on the determined operation parameter. The expander is disposed downstream of the liquid outlet. The cascade heat exchanger is disposed downstream of the vapor outlet. The modulator is disposed between the liquid outlet and the vapor outlet and upstream of the cascade heat exchanger.

In an example embodiment, a method of operating a heating, ventilation, air conditioning, and refrigeration (HVACR) system is provided. The system includes a compressor, a condenser, a liquid-vapor separator having a vapor outlet and a liquid outlet, a cascade heat exchanger, an expander, and an evaporator fluidly connected; a modulator disposed downstream of the liquid outlet; and a controller. The method includes determining an operation parameter of the system, and controlling the modulator to modulate a liquid flow from the liquid outlet based on the determined operation parameter. The expander is disposed downstream of the liquid outlet. The cascade heat exchanger is disposed downstream of the vapor outlet. The modulator is disposed between the liquid outlet and the vapor outlet and upstream of the cascade heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments of systems, methods, and embodiments of various other aspects of the disclosure. Any person with ordinary skill in the art will appreciate that the illustrated element boundaries (e.g. boxes, groups of boxes, or other shapes) in the figures represent one example of the boundaries. It may be that in some examples one element may be designed as multiple elements or that multiple elements may be designed as one element. In some examples, an element shown as an internal component of one element may be implemented as an external component in another, and vice versa. Non-limiting and non-exhaustive descriptions are described with reference to the following drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating principles. In the detailed description that follows, embodiments are described as illustrations only since various changes and modifications may become apparent to those skilled in the art from the following detailed description.

FIG. 1 illustrates a schematic diagram of an HVACR system including an autocascade refrigerant circuit, arranged in accordance with at least some embodiments described herein.

FIG. 2A is a schematic view of a portion of the HVACR system of FIG. 1, arranged in accordance with at least some embodiments described herein.

FIG. 2B is a schematic view of a portion of the HVACR system of FIG. 1, arranged in accordance with at least some embodiments described herein.

FIG. 3A is a schematic view of a portion of the HVACR system of FIG. 1, arranged in accordance with at least some embodiments described herein.

FIG. 3B is a schematic view of a portion of the HVACR system of FIG. 1, arranged in accordance with at least some embodiments described herein.

FIG. 3C is a schematic view of a portion of the HVACR system of FIG. 1, arranged in accordance with at least some embodiments described herein.

FIG. 3D is a schematic view of a portion of the HVACR system of FIG. 1, arranged in accordance with at least some embodiments described herein.

FIG. 3E is a schematic view of a portion of the HVACR system of FIG. 1, arranged in accordance with at least some embodiments described herein.

FIG. 4A illustrates a relationship between the states of the modulator/expander and the ambient temperature, arranged in accordance with at least some embodiments described herein.

FIG. 4B illustrates a relationship between the pressure ratio and the ambient temperature, arranged in accordance with at least some embodiments described herein.

DETAILED DESCRIPTION

In the following detailed description, particular embodiments of the present disclosure are described herein with reference to the accompanying drawings, which form a part of the description. In this description, as well as in the drawings, like-referenced numbers represent elements that may perform the same, similar, or equivalent functions, unless context dictates otherwise. Furthermore, unless otherwise noted, the description of each successive drawing may reference features from one or more of the previous drawings to provide clearer context and a more substantive explanation of the current example embodiment. Still, the example embodiments described in the detailed description, drawings, and claims are not intended to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings, may be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.

It is to be understood that the disclosed embodiments are merely examples of the disclosure, which may be embodied in various forms. Well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure in virtually any appropriately detailed structure.

Additionally, the present disclosure may be described herein in terms of functional block components and various processing steps. It should be appreciated that such functional blocks may be realized by any number of hardware and/or software components configured to perform the specified functions.

The scope of the disclosure should be determined by the appended claims and their legal equivalents, rather than by the examples given herein. For example, the steps recited in any method claims may be executed in any order and are not limited to the order presented in the claims. Moreover, no element is essential to the practice of the disclosure unless specifically described herein as “critical” or “essential”.

As referenced herein, a “vapor” or “gaseous” stream or phase of a working fluid (e.g., refrigerant) may refer to the working fluid in a predominantly gaseous form, with the understanding that some liquid may persist therein due to, e.g., incomplete separation or subsequent partial condensation, etc. The liquid may be present in the predominantly vapor or gaseous stream as, e.g., entrained droplets.

As referenced herein, a “liquid” stream or phase of the working fluid may refer to the working fluid in a predominantly liquid form, with the understanding that some gas or vapor may persist therein due to, e.g., incomplete separation, subsequent evaporation, incomplete condensation, or the like.

As referenced herein, “directly” upstream or “directly” downstream may refer to that no other components of a fluid circuit, other than fluid lines/connections/pipes for conveying the fluid are provided between such directly related elements. As referenced herein, “upstream” and “downstream” may refer to the direction of flow of the working fluid or a component thereof through the fluid circuit.

As referenced herein, a “scroll compressor” is a term of art that may refer to a compressor that uses two interleaving scrolls to compress a working fluid. In an example embodiment, one of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of fluid between the scrolls. It is to be understood that due to the structural characteristics and the design requirements of a scroll compressor, features of other types of compressors might not be feasible to be combined with features of a scroll compressor to achieve the features in the embodiments disclosed herein and the advantages enjoyed by the disclosed features.

As referenced herein, a “compressor pressure ratio” or “pressure ratio” is a term of art that may refer to a ratio of the fluid pressure exiting a compressor (i.e., the discharge pressure) to the fluid pressure entering the compressor (i.e., the suction pressure). In an example embodiment, the suction pressure can be determined (e.g., by a controller) via a sensed measurement from a pressure sensor disposed at or near the suction port of the compressor. The discharge pressure can be determined (e.g., by the controller) via a sensed measurement from a pressure sensor disposed at or near the discharge port of the compressor. The pressure ratio can be determined (e.g., by the controller) based on the determined discharge pressure and the determined suction pressure. It is to be understood that the value of the pressure ratio is always greater than 1.0.

As referenced herein, the term “modulating” (or “modulate”, “modulation”, and the like) is a term of art that may refer to an action of controlling or adjusting a position or state of a device such as a modulator. The modulator can be a flow control device such as a valve (e.g., a solenoid valve, a ball valve, a three-way valve, a butterfly valve, or the like), a damper, a pump, and the like. It is to be understood that the modulator can be configured to be controlled (e.g., by a controller) to modulate a fluid (e.g., a working fluid) flow through e.g., a passage (e.g., a pipe and the like). The modulator can have a fully-closed position or state at which the fluid can be prevented from flowing through the passage via the modulator. The modulator can also have a fully-open position or state at which the fluid can be flowing through the passage via the modulator without being blocked by the modulator. The modulator can further have a partially-open (or partially-closed) position or state at which the fluid can be flowing through the passage via the modulator with the fluid being partially blocked by the modulator. It is also to be understood that “modulating” includes controlling or adjusting a position or state of the device from a fully-open position or state, to a partially-open or partially-closed position or state, and/or to a fully-closed position or state; or from a fully-closed position or state, to a partially-closed or partially-open position or state, and/or to a fully-open position or state. It is further to be understood that “modulating” is different from simply turning on or off (or simply open or close) the device, where “modulating” the device may include controlling or adjusting the device at a partially-open (or partially-closed) position or state (e.g., 10% open or closed, 15% open or closed, . . . 95% open or closed, etc.).

FIG. 1 illustrates a schematic diagram of an HVACR system 100 including an autocascade refrigerant circuit, arranged in accordance with at least some embodiments described herein. The arrows indicate the direction of the flow of the working fluid (and/or process fluid).

In an example embodiment, the system 100 includes a compressor 102, a condenser 104, a liquid-vapor separator 106, a cascade heat exchanger 108, a sub-cooler 110, a first expander 112, an evaporator 114, a second expander 116, an optional lubricant separator 118, sensor(s) (120, 122, 124, 130), and a controller 126 that is configured to communicate with and/or control the operations of the expanders (112, 116) and/or other components of system 100 (including e.g., sensors 120, 122, 124, 130, or the like). Although illustrated as discrete components, various components may be divided into additional components, combined into fewer components, or eliminated altogether while being contemplated within the scope of the disclosed subject matter. The system 100 is an example and can be configured to include more or less components. For example, in an embodiment, the system 100 can include other components such as, but not limited to, an economizer heat exchanger, one or more flow control devices (e.g., a valve, a pump, and the like), a receiver tank, a dryer, a suction-liquid heat exchanger, modulator(s), connector(s), connections such as pipes, one or more sensors, or the like. It is to be understood that the controller 126 can communicate with and/or control other components (e.g., compressor, evaporator, condenser, heat-exchanger, sub-cooler, expander, modulator, actuator, sensor(s), flow control device(s), or the like) of e.g., the system 100. In an example embodiment, the controller 126 may include (or be connected to) a memory such as RAM and ROM and execute software (including, e.g., algorithms) that can be stored in the RAM (particularly during execution), the ROM (on a generally permanent basis), or another non-transitory computer readable medium such as other memory or disc. If necessary, the controller 126 can be connected to such memory or a disc drive to read such software. A microprocessor or other programmable device with suitable memory and I/O devices could also be used as the controller 126.

The system 100 can generally be applied in a variety of systems used to control an environmental condition (e.g., temperature, humidity, air quality, or the like) in a conditioned space. The conditioned space can be a space within an office building, a commercial building, a factory, a laboratory, a data center, a residential building, or the like. In an example embodiment, the system 100 can be configured to be a cooling system (e.g., an air conditioning system) capable of operating in a cooling mode. In another example embodiment, the system 100 can be configured to be a reversible heat pump that can operate in a heating/defrost mode. It is appreciated that the system 100 can be configured to operate in a cooling mode and/or a heating/defrosting mode. In an example embodiment, the system 100 can heat or cool a process fluid (e.g., air, water and/or glycol, or the like). A working fluid (e.g., one or more refrigerants) can flow through the system 100 and be utilized to heat or cool the process fluid.

The components of the system 100 can be fluidly connected. The expander(s) (112, 116) as described herein may also be referred to as an expansion device. In an embodiment, the expander(s) (112, 116) can be an expansion valve, expansion plate, expansion vessel, orifice, or the like, or other such types of expansion mechanisms. It should be appreciated that the expander(s) (112, 116) may be any suitable type of expander used in the field for expanding a working fluid to cause the working fluid to decrease in pressure and temperature.

In an example embodiment, operation parameter(s) of the system 100 may be determined to serve as a basis for regulating the expander 112 to control a flow of working fluid from a sub-cooler 110 into an evaporator 114. For example, if a measured conductive suction superheat is below a threshold level, as determined by operation of compressor 102, which is indicative of too much working fluid being present in the evaporator due to, e.g., overcharging, the expander 112 may be regulated to restrict the flow of working fluid to the evaporator 114. Operation of compressor 102 may establish a threshold level for conductive suction superheat to ensure e.g., adequate oil quality in the working fluid. In an example embodiment, the controller 126 may be configured to determine optimal suction superheat, based on, e.g., a predetermined mapping, of inlet and/or outlet water temperatures and ambient temperatures.

In an example embodiment, the expander 116 may be controlled to regulate a flow of working fluid at the liquid outlet of the liquid-vapor separator to thereby regulate the liquid working fluid that flows through the compressor 102.

In an example embodiment, a working fluid may separate into liquid and vapor streams or phases downstream of compressor 102. The system 100 may be configured to allow the liquid and vapor phases to exchange heat with one another as features of the autocascade operation. Separated flows of a working fluid may be recombined, with the complete blend exchanging heat with the vapor phase at the cascade heat exchanger 108. In an example embodiment, the system 100 may include additional liquid-vapor separator(s) 106 to thereby further concentrate low boiling point fluids in the working fluid supplied to evaporator 114. However, for descriptive purposes only, the embodiments described and recited herein references a single liquid-vapor separator 106.

In an example embodiment, the compressor 102 is configured to compress working fluid of the system 100 received at suction port 128. Non-limiting examples of compressor 102 may be a scroll compressor, a screw compressor, a centrifugal compressor, or the like. In an application of at or about 650 PSI (pounds of force exerted per square inch, the amount of force that a compressor can deliver, which can be used to measure the amount of pressure placed on a single square inch of space) or above, scroll compressor may be used.

In an example embodiment, the condenser 104 is configured to receive compressed working fluid from compressor 102 and to reject heat from the compressed working fluid to a process fluid, e.g., to an ambient environment, to a hot water supply loop, to a heating coil for heating air, or to another suitable medium.

In an example embodiment, the liquid-vapor separator 106 is configured to receive condensed or partially condensed working fluid, from which heat has been rejected, from condenser 104, to separate the condensed working fluid into distinct liquid and vapor portions of the working fluid. The liquid-vapor separator 106 separates the streams to exploit the pressure-temperature properties of the vapor to thereby raise evaporator pressure.

In an example embodiment, an optional liquid level sensor 130 can be included in or attached to the liquid-vapor separator 106 and can be configured to measure an amount of each resulting liquid contained in the liquid-vapor separator 106.

In an example embodiment, a first stream (e.g., a vapor stream) C1 of the working fluid may pass from the liquid-vapor separator 106 to the cascade heat exchanger 108. The cascade heat exchanger 108 can be configured to facilitate heat exchange between the first stream C1 from the liquid-vapor separator 106 and a second stream (e.g., a liquid stream) C2 flowing from the second expander 116, and/or between the first stream C1 and the working fluid from the sub-cooler 110. Working fluid exiting from the cascade heat exchanger 108 can pass to the suction port 128 of the compressor 102. In an example embodiment, the exchange of heat at the cascade heat exchanger 108 can cool the first stream C1 from the liquid-vapor separator 106.

In an example embodiment, the sub-cooler 110 can be configured to facilitate the exchange of heat between the first stream C1 exiting from the cascade heat exchanger 108 and the working fluid exiting the evaporator 114. The sub-cooler 110 can further cool the first stream C1 prior to passing it to the first expander 112.

In an example embodiment, the first expander 112 can be configured to expand the received first stream C1 of the working fluid from the sub-cooler 110. Non-limiting examples of the expander 112 may include any structure already described above and also, but not limited to, any suitable expansion valve, e.g., electronic expansion valve (EXV); nozzle; orifice; combinations thereof, and the like. That is, the expander 112 may be regulated to restrict the flow of working fluid to the evaporator 114 if e.g., a measured conductive superheat is below a threshold level. The expander 112 may be communicatively connected to controller 126 so that the opening and closing of the expander 112 may be automatically regulated by, e.g., the controller 126.

In an example embodiment, the evaporator 114 can be configured to receive the first stream C1 of the working fluid from the sub-cooler 110, via the first expander 112, and expose the first stream C1 to heat, i.e., the first stream C1 absorbs heat at evaporator 114, to cool the process fluid. At the sub-cooler 110, the first stream C1 of the working fluid passes through to cool the first stream C1 on an opposite side of the sub-cooler 110. The first stream C1 that has passed through the sub-cooler 110, after exiting the evaporator 114, joins a flow of the second stream of the working fluid from the second expander 116 to, in turn, flow through the cascade heat exchanger 108 to the suction port 128 of the compressor 102.

In an example embodiment, the second expander 116 can be configured to receive the second stream C2 of the working fluid from the liquid-vapor separator 106 and to expand the second stream of the working fluid. Non-limiting examples of the second expander 116 may include structures already described above and also, but not limited to any suitable expansion valve, e.g., electronic expansion valve (EXV); nozzle; orifice; combinations thereof; etc. Accordingly, expander 116 may be communicatively connected to controller 126 so that the opening and closing of the expander may be automatically regulated.

In an example embodiment, after exiting the second expander 116, the second stream C2 of the working fluid may join the flow of the first stream C1 that exits the sub-cooler 110 and then flows through the cascade heat exchanger 108 to the suction port 128 of the compressor 102. An optional lubricant separator 118, can be configured to remove at least portions of lubricant from the working fluid passing there-through from the compressor 102, of which the lubricant separator 118 is downstream. The lubricant removed from the working fluid may be any compressor lubricant that has dissolved in or entrained in the working fluid.

In an example embodiment, the sensor(s) (120, 122, 124) may be provided directly upstream of the suction port 128 of the compressor 102 or between an outlet of the cascade heat exchanger 108 and the suction port 128 of the compressor 102. Other sensor(s) may be provided downstream or directly downstream of a discharge port of the compressor 102. The sensor(s) can be e.g., pressure sensor(s), temperature sensor(s), humidity sensor(s), or the like. The controller 126 may communicate with (via a wired or wireless connection) and/or control the sensor(s) to determine operation parameters of the compressor 102, of the system 100, etc.

In an example embodiment, the controller 126 may be programmed, designed, and/or otherwise configured to control one or more components of the system 100, including but not limited to first expander 112 and/or the second expander 116, based on at least the determined operation parameter(s).

In an example embodiment, the system 100 can operate according to generally known principles. The system 100 can be configured to heat and/or cool a liquid process fluid. The liquid process fluid can be a heat transfer fluid or medium (e.g., a liquid such as, but not limited to, water or the like). The system 100 may be generally representative of a liquid chiller system. The system 100 can alternatively be configured to heat and/or cool a gaseous process fluid (e.g., a heat transfer medium or fluid (e.g., a gas such as, but not limited to, air or the like), in which case the system 100 may be generally representative of an air conditioner and/or heat pump.

In an example embodiment, the system 100 can operate as a vapor-compression circuit such that the compressor 102 compresses a working fluid (e.g., a heat transfer fluid such as, but not limited to, refrigerant or the like) from a relatively lower pressure gas to a relatively higher-pressure gas. The relatively higher-pressure gas is at a relatively higher temperature, being discharged from the compressor 102 and flowing through the condenser 104. In accordance with generally known principles, the working fluid flows through the condenser 104 and rejects heat to the process fluid (e.g., water, air, and the like), thereby cooling the working fluid. In a standard refrigerant cycle or mode (i.e., a non-autocascade cycle or mode, see the description of FIG. 2B), the cooled working fluid, which is now in a predominantly liquid form, flows to an expander (e.g., 112) that can reduce the pressure of the working fluid. As a result, a portion of the working fluid is converted to a gaseous form. The working fluid, which is now in a mixed liquid and gaseous form flows to the evaporator 114. The working fluid flows through the evaporator 114 and absorbs heat from the process fluid (e.g., a heat transfer medium such as, but not limited to, water, a solution, air, and the like), heating the working fluid, and converting it to a gaseous form. The gaseous working fluid then returns to the compressor 102. The above-described process continues while the heat transfer circuit is operating, for example, in a cooling mode (e.g., while the compressor 102 is enabled). The process of the autocascade cycle is to be described in FIG. 2A.

In an example embodiment, the compressor 102 can compress the working fluid. Lubricant can be supplied to the compressor 102 to provide lubrication for its moving parts. A lubricant may include one or more types of lubricants. For example, a lubricant can be, but is not limited to, polyolester oils, or the like. The lubricant can be discharged from the compressor 102 with the working fluid. Thus, the working fluid discharged from the compressor 102 may contain lubricant. In some refrigerant circuits, the lubricant can also be separated from the working fluid and the separated lubricant can be circulated back to the compressor 102. In other refrigerant circuits, the lubricant can be circulated with the working fluid and can then be supplied through a suction inlet/port 128 of the compressor 102 as part of the working fluid. In an example embodiment, the working fluid may also include one or more additional components other than lubricant(s) and/or refrigerant(s).

FIGS. 2A and 2B are schematic views of a portion of the HVACR system 100 of FIG. 1, arranged in accordance with at least some embodiments described herein. The arrows in FIGS. 2A and 2B indicate the direction of the flow of the working fluid. It is to be understood that additional components such as modulators (220, 230), connections (e.g., passages such as pipes), connectors (e.g., t-connectors) are shown in FIGS. 2A and 2B.

FIG. 2A shows a portion 200 of the HVACR system 100 (including an autocascade refrigerant circuit) working in an autocascade mode (or cycle). As shown in FIG. 2A, in the autocascade mode, the compressed working fluid (e.g., refrigerant) flows into the inlet 104A of the condenser 104 from the compressor 102 via the optional lubricant separator 118 (see FIG. 1) and is condensed in the condenser 104 in a predominantly liquid form. The condensed working fluid flows out of the condenser 104 from the outlet 104B of the condenser 104, and flows into the liquid-vapor separator 106 via its inlet 106A. The liquid-vapor separator 106 separates the condensed working fluid into a liquid stream (C2 of FIG. 1) and a vapor stream (C1 of FIG. 1). The liquid stream of the working fluid flows out of the liquid-vapor separator 106 via its liquid outlet 106C, and flows through the second expander 116 of FIG. 1 back to the system 100. The vapor stream of the working fluid flows out of the liquid-vapor separator 106 via its vapor outlet 106B, flows through a modulator 220 and a modulator 230, and flows to the cascade heat exchanger 108 of FIG. 1 and back to the system 100. In an example embodiment, the modulator 220 can be a three-way valve, a butterfly valve, a ball vale, a solenoid valve, or the like. The modulator 230 can be a check valve or the like, to allow the working fluid to flow in one direction (toward the cascade heat exchanger 108) while preventing it from flowing backward. In the autocascade mode, the second expander 116 can be controlled (e.g., by the controller 126 of FIG. 1) to regulate the flow rate, the amount of the flow, etc. of the liquid stream out of the liquid outlet 106C. The modulator 220 can be controlled (e.g., by the controller 126 of FIG. 1) to allow the vapor stream out of the vapor outlet 106B passing through to the modulator 230, and to regulate the flow rate, the amount of the flow, etc. of the vapor stream out of the vapor outlet 106B. In an example embodiment, the modulator 220 can be controlled (e.g., by the controller 126 of FIG. 1) to allow or only allow the vapor stream out of the vapor outlet 106B passing through to the modulator 230, and only to regulate the flow rate, the amount of the flow, etc. of the vapor stream out of the vapor outlet 106B. That is, in the autocascade mode, the modulator 220 can be controlled to prevent the liquid stream out of the liquid outlet 106C from passing through the modulator 220.

FIG. 2B shows a portion 201 of the HVACR system 100 (including an autocascade refrigerant circuit) working in a standard mode (or standard cycle) with the autocascade functionality disabled. As shown in FIG. 2B, in the standard mode, the compressed working fluid (e.g., refrigerant) flows into the inlet 104A of the condenser 104 from the compressor 102 via the optional lubricant separator 118 (see FIG. 1) and is condensed in the condenser 104 in a predominantly liquid form. The condensed working fluid flows out of the condenser 104 from the outlet 104B of the condenser 104, and flows into the liquid-vapor separator 106 via its inlet 106A. The liquid-vapor separator 106 separates the condensed working fluid into a liquid stream (C2 of FIG. 1) and a vapor stream (C1 of FIG. 1). The liquid stream of the working fluid flows out of the liquid-vapor separator 106 via its liquid outlet 106C. The second expander 116 of FIG. 1 is controlled to be closed and prevents the liquid stream from passing through the second expander 116. The vapor stream of the working fluid is to be flowing out of the liquid-vapor separator 106 via its vapor outlet 106B but is blocked by the modulator 220. The modulator 220 is controlled to prevent the vapor stream from passing through the modulator 220. The modulator 220 is controlled so that the liquid stream out of the liquid port 106C passes through the modulator 220 and the modulator 230 and flows to the cascade heat exchanger 108 of FIG. 1 and back to the system 100. In an example embodiment, the modulator 220 can be a three-way valve, a butterfly valve, a ball vale, a solenoid valve, or the like. The modulator 230 can be a check valve or the like, to allow the working fluid to flow in one direction (toward the cascade heat exchanger 108) while preventing it from flowing backward. In the standard mode, the second expander 116 can be controlled (e.g., by the controller 126 of FIG. 1) to be closed. The modulator 220 can be controlled (e.g., by the controller 126 of FIG. 1) to allow the liquid stream (or a mixture of the vapor and liquid streams) out of the liquid outlet 106C passing through to the modulator 230, and to regulate the flow rate, the amount of the flow, etc. of the stream(s) out of the liquid outlet 106C. In an example embodiment, the modulator 220 can be controlled (e.g., by the controller 126 of FIG. 1) to allow or only allow the liquid stream (or a mixture of the vapor and liquid streams) out of the liquid outlet 106C passing through to the modulator 230, and only to regulate the flow rate, the amount of the flow, etc. of the stream(s) out of the liquid outlet 106C. That is, in the standard mode, the modulator 220 can be controlled to prevent the vapor stream out of the vapor outlet 106B from passing through the modulator 220.

In FIGS. 2A and 2B, the system 100 works as a reversible heat pump. When the system 100 works in a cooling mode, the cooling expander 210 can be controlled to regulate the working fluid passing through the cooling expander 210 into the system 100. For example, the cooling expander 210 may be regulated to restrict the flow of working fluid to the liquid-vapor separator 106.

In an example embodiment, the system 100 can work in a transition mode transitioning from the autocascade mode (as shown in FIG. 2A) to the standard mode (as shown in FIG. 2B), and/or transitioning from the standard mode to the autocascade mode. When transitioning from the autocascade mode to the standard mode, the second expander 116 can be controlled to be from an open position or state (e.g., a partially-open position such as a maximum allowed position or an optimal open position or a controlled open position depending on the operation parameters) toward a fully-closed position to decrease the amount of liquid stream passing through the second expander 116 back to the system 100. The modulator 220 can be controlled to increase the amount of liquid stream out of the outlet 106C passing through the modulator 220 (and optionally decrease the amount of vapor stream out of the outlet 106B passing through), so that the vapor stream out of the vapor outlet 106B is mixed with the liquid stream out of the liquid outlet 106C and the mixed stream flows to the modulator 230. When the second expander 116 is at the fully-closed position and when the modulator 220 is controlled to prevent the vapor stream out of the outlet 106B from passing through the modulator 220 (and allows or only allows the liquid stream or the mixture of liquid/vapor streams out of the outlet 106C to pass through to the modulator 230), the mode is transitioned into the standard mode.

When transitioning from the standard mode to the autocascade mode, the second expander 116 can be controlled to be from a fully-closed position or state towards an open position (e.g., a partially-open position) to increase the amount of liquid stream passing through the second expander 116 back to the system 100. The modulator 220 can be controlled to increase the amount of vapor stream out of the outlet 106B passing through the modulator 220 (and optionally decrease the amount of liquid stream out of the outlet 106C passing through), so that the vapor stream out of the vapor outlet 106B is mixed with the liquid stream out of the liquid outlet 106C and the mixed stream flows to the modulator 230. When the second expander 116 is at an open position (e.g., at a maximum allowed position or an optimal open position or a controlled open position depending on the operation parameters) and when the modulator 220 is controlled to prevent the liquid stream or the mixed liquid/vapor streams out of the outlet 106C from passing through the modulator 220 (and allows or only allows the vapor stream out of the outlet 106B to pass through to the modulator 230), the mode is transitioned into the autocascade mode.

FIGS. 3A-3E are schematic views of a portion of the HVACR system 100 of FIG. 1, arranged in accordance with at least some embodiments described herein. The arrows in FIGS. 3A-3E indicate the direction of the flow of the working fluid. It is to be understood that additional components such as modulators (315A-315C, 320, 325), connections (e.g., passages such as pipes), connectors (e.g., t-connectors 305, 310) are shown in FIGS. 3A-3E. It is also to be understood that the descriptions regarding the autocascade mode, the standard mode, the transition mode (or transitioning between the autocascade mode and the standard mode) in FIGS. 2A and 2B apply to FIGS. 3A-3E unless explicitly stated otherwise.

As shown in FIGS. 3A-3E, the condensed working fluid flows out of the condenser 104 and flows into the liquid-vapor separator 106 via its inlet 106A. The liquid-vapor separator 106 separates the condensed working fluid into a liquid stream (C2 of FIG. 1) and a vapor stream (C1 of FIG. 1). The liquid stream of the working fluid flows (or is to be flowing) out of the liquid-vapor separator 106 via its liquid outlet 106C. The vapor stream of the working fluid flows (or is to be flowing) out of the liquid-vapor separator 106 via its vapor outlet 106B.

As shown in FIGS. 3A and 3B, a modulator (315A, 315B, 315C) is used to replace the modulator 220 of FIGS. 2A and 2B. In another example embodiment, the modulator 220 of FIGS. 2A and 2B can be used to replace the modulator (315A, 315B, 315C) of FIGS. 3A and 3B. The modulator (315A, 315B, 315C) can be e.g., butterfly valve(s) with one motor or two independent motors driving the linkage 315B to control the valves (315A, 315C) and to act as a three-way valve (e.g., 220 of FIGS. 2A and 2B). The linkage 315B can include bar, chain, belt, gear, or the like. It is to be understood that a three-way valve may have a size up to about 3 inches. For air-cooled products or applications requiring valve size larger than 3 inches, butterfly valves may be used instead of three-way valves. In the embodiments of FIGS. 3A and 3B, a connector 310 (e.g., a t-connector) is disposed downstream of the modulator (315A, 315B, 315C). A first end of the connector 310 is connected to a liquid outlet of the modulator (315A, 315B, 315C) near 315A via a connection (e.g., pipe), a second end of the connector 310 is connected to a vapor outlet of the modulator (315A, 315B, 315C) near 315C via a connection (e.g., pipe), and a third end of the connector 310 is connected to the cascade heat exchanger 108 (e.g., via the modulator 230) via a connection (e.g., pipe). A connector 305 (e.g., a t-connector) is disposed downstream of the liquid outlet 106C of the liquid-vapor separator 106. A first end of the connector 305 is connected to the liquid outlet 106C via a connection (e.g., pipe), a second end of the connector 305 is connected to the second expander 116 via a connection (e.g., pipe), and a third end of the connector 305 is connected to a liquid inlet of the modulator (315A, 315B, 315C) near 315A via a connection (e.g., pipe). The vapor outlet 106B of the liquid-vapor separator 106 is connected to a vapor inlet of the modulator (315A, 315B, 315C) near 315C.

In an example embodiment of FIGS. 3A and 3B, in the autocascade mode, the second expander 116 can be controlled (e.g., by the controller 126 of FIG. 1) to regulate the flow rate, the amount of the flow, etc. of the liquid stream out of the liquid outlet 106C. The modulator (315A, 315B, 315C) can be controlled (e.g., by the controller 126 of FIG. 1) to allow the vapor stream out of the vapor outlet 106B passing through to the connector 310, and to regulate the flow rate, the amount of the flow, etc. of the vapor stream out of the vapor outlet 106B. In an example embodiment, the modulator (315A, 315B, 315C) can be controlled (e.g., by the controller 126 of FIG. 1) to allow or only allow the vapor stream out of the vapor outlet 106B passing through to the connector 310, and only to regulate the flow rate, the amount of the flow, etc. of the vapor stream out of the vapor outlet 106B. That is, in the autocascade mode, the modulator (315A, 315B, 315C) can be controlled to prevent the liquid stream out of the liquid outlet 106C from passing through the modulator (315A, 315B, 315C).

In the standard mode, the second expander 116 can be controlled (e.g., by the controller 126 of FIG. 1) to be closed. The modulator (315A, 315B, 315C) can be controlled (e.g., by the controller 126 of FIG. 1) to allow the liquid stream (or a mixture of the vapor and liquid streams) out of the liquid outlet 106C passing through to the connector 310, and to regulate the flow rate, the amount of the flow, etc. of the stream(s) out of the liquid outlet 106C. In an example embodiment, the modulator (315A, 315B, 315C) can be controlled (e.g., by the controller 126 of FIG. 1) to allow or only allow the liquid stream (or a mixture of the vapor and liquid streams) out of the liquid outlet 106C passing through to the connector 310, and only to regulate the flow rate, the amount of the flow, etc. of the stream(s) out of the liquid outlet 106C. That is, in the standard mode, the modulator (315A, 315B, 315C) can be controlled to prevent the vapor stream out of the vapor outlet 106B from passing through the modulator (315A, 315B, 315C).

When transitioning from the autocascade mode to the standard mode, the second expander 116 can be controlled to be from an open position or state (e.g., a partially-open position such as a maximum allowed position or an optimal open position or a controlled open position depending on the operation parameters) toward a fully-closed position to decrease the amount of liquid stream passing through the second expander 116 back to the system 100. The modulator (315A, 315B, 315C) can be controlled to increase the amount of liquid stream out of outlet 106C passing through the modulator (315A, 315B, 315C) (and optionally decrease the amount of vapor stream out of outlet 106B passing through), so that the vapor stream out of the vapor outlet 106B is mixed with the liquid stream out of the liquid outlet 106C and the mixed stream flows to the connector 310. When the second expander 116 is at the fully-closed position and when the modulator (315A, 315B, 315C) is controlled to prevent the vapor stream out of outlet 106B from passing through the modulator (315A, 315B, 315C) (and allows or only allows the liquid stream or the mixed liquid/vapor streams out of outlet 106C to pass through to the connector), the mode is transitioned into the standard mode.

When transitioning from the standard mode to the autocascade mode, the second expander 116 can be controlled to be from a fully-closed position or state towards an open position (e.g., a partially-open position) to increase the amount of liquid stream passing through the second expander 116 back to the system 100. The modulator (315A, 315B, 315C) can be controlled to increase the amount of vapor stream out of the outlet 106B passing through the modulator (315A, 315B, 315C) (and optionally decrease the amount of liquid stream out of the outlet 106C passing through), so that the vapor stream out of the vapor outlet 106B is mixed with the liquid stream out of the liquid outlet 106C and the mixed stream flows to the connector 310. When the second expander 116 is at an open position (e.g., at a maximum allowed position or an optimal open position or a controlled open position depending on the operation parameters) and when the modulator (315A, 315B, 315C) is controlled to prevent the liquid stream or the mixed liquid/vapor streams out of the outlet 106C from passing through the modulator (315A, 315B, 315C) (and allows or only allows the vapor stream out of the outlet 106B to pass through to the connector 310), the mode is transitioned into the autocascade mode.

As shown in FIGS. 3C and 3D, a modulator 325 and a pump 320 (e.g., a Venturi pump, a Bernoulli vacuum pump, or the like) are used to replace the modulator 220 of FIGS. 2A and 2B. In another example embodiment, the modulator 220 of FIGS. 2A and 2B can be used to replace the modulator 325 and the pump 320 of FIGS. 3C and 3D. The modulator 325 can be a solenoid valve, a ball valve, a butterfly valve, or the like. A first end of the pump 320 is connected to the vapor outlet 106B via a connection (e.g., pipe), a second end of the pump 320 is connected to a first end of the modulator 325 via a connection (e.g., pipe), and a third end of the pump 320 is connected to the cascade heat exchanger 108 (e.g., via the modulator 230) via a connection (e.g., pipe). A connector 305 (e.g., a t-connector) is disposed downstream of the liquid outlet 106C of the liquid-vapor separator 106. A first end of the connector 305 is connected to the liquid outlet 106C via a connection (e.g., pipe), a second end of the connector 305 is connected to the second expander 116 via a connection (e.g., pipe), and a third end of the connector 305 is connected to a second end of the modulator 325 via a connection (e.g., pipe). The pump 320 can be configured to pump the stream up in a direction from the modulator 325 to the second end of the pump 320 and to flow to the cascade heat exchanger 108 via the third end of the pump 320. In an example embodiment, the pump 320 can be configured to use e.g., the Venturi effect to create a partial vacuum and move stream up in a direction from the modulator 325 to the second end of the pump 320 and to flow to the cascade heat exchanger 108 via the third end of the pump 320.

In an example embodiment of FIGS. 3C and 3D, in the autocascade mode, the second expander 116 can be controlled (e.g., by the controller 126 of FIG. 1) to regulate the flow rate, the amount of the flow, etc. of the liquid stream out of the liquid outlet 106C. The modulator 325 can be controlled (e.g., by the controller 126 of FIG. 1) to be closed such that only the vapor stream out of the vapor outlet 106B may pass through the pump 320 to the cascade heat exchanger 108. That is, in the autocascade mode, the modulator 325 can be controlled to prevent the liquid stream out of the liquid outlet 106C from passing through the modulator 325.

In the standard mode, the second expander 116 can be controlled (e.g., by the controller 126 of FIG. 1) to be closed. The modulator 325 can be controlled (e.g., by the controller 126 of FIG. 1) to be open (e.g., fully-open) to allow the liquid stream out of the liquid outlet 106C passing through to the pump 320 and flowing to the cascade heat exchanger 108. In the standard mode, the liquid stream out of the liquid outlet 106C and the vapor stream out of the vapor outlet 106B may be mixed and pass through the pump 320 to flow to the cascade heat exchanger 108.

When transitioning from the autocascade mode to the standard mode, the second expander 116 can be controlled to be from an open position or state (e.g., a partially-open position such as a maximum allowed position or an optimal open position or a controlled open position depending on the operation parameters) toward a fully-closed position to decrease the amount of liquid stream passing through the second expander 116 back to the system 100. The modulator 325 can be controlled to increase the amount of liquid stream passing through the modulator 325 so that the vapor stream out of the vapor outlet 106B is mixed with the liquid stream out of the liquid outlet 106C and the mixed stream flows to the cascade heat exchanger 108 via the pump 320. When the second expander 116 is at the fully-closed position and when the modulator 325 is controlled to be open (e.g., fully-open), the mode is transitioned into the standard mode.

When transitioning from the standard mode to the autocascade mode, the second expander 116 can be controlled to be from a fully-closed position or state towards an open position (e.g., a partially-open position) to increase the amount of liquid stream passing through the second expander 116 back to the system 100. The modulator 325 can be controlled to decrease the amount of liquid stream out of the outlet 106C passing through, so that the vapor stream out of the vapor outlet 106B is mixed with the liquid stream out of the liquid outlet 106C and the mixed stream flows to the cascade heat exchanger 108 via the pump 320. When the second expander 116 is at an open position (e.g., at a maximum allowed position or an optimal open position or a controlled open position depending on the operation parameters) and when the modulator 325 is controlled to prevent the liquid stream or the mixed liquid/vapor streams out of the outlet 106C from passing through the modulator 325, the mode is transitioned into the autocascade mode.

As shown in FIG. 3E illustrating a preferred embodiment, a modulator 325 is used to replace the modulator 220 of FIGS. 2A and 2B. In another example embodiment, the modulator 220 of FIGS. 2A and 2B can be used to replace the modulator 325 of FIG. 3E. The modulator 325 can be a solenoid valve, a ball valve, a butterfly valve, or the like. In the embodiments of FIG. 3E, a connector 310 (e.g., a t-connector) is disposed downstream of the modulator 325. A first end of the connector 310 is connected to a first end of the modulator 325 via a connection (e.g., pipe), a second end of the connector 310 is connected to the vapor outlet 106B via a connection (e.g., pipe), and a third end of the connector 310 is connected to the cascade heat exchanger 108 (e.g., via the modulator 230) via a connection (e.g., pipe). A connector 305 (e.g., a t-connector) is disposed downstream of the liquid outlet 106C of the liquid-vapor separator 106. A first end of the connector 305 is connected to the liquid outlet 106C via a connection (e.g., pipe), a second end of the connector 305 is connected to the second expander 116 via a connection (e.g., pipe), and a third end of the connector 305 is connected to a second end of the modulator 325 via a connection (e.g., pipe). It is to be understood that the connector 305, the modulator 325, and the connector 310 are disposed at position(s) lower than or under the lowest portion of the liquid-vapor separator 106 so that the gravity of the liquid stream out of the liquid outlet 106C may be used to push or drive the flow of the stream(s) through the connector 305, the modulator 325, and the connector 310 towards the cascade heat exchanger 108.

In an example embodiment of FIG. 3E, in the autocascade mode, the second expander 116 can be controlled (e.g., by the controller 126 of FIG. 1) to be open (e.g., a partially-open position such as a maximum allowed position or an optimal open position or a controlled open position depending on the operation parameters) to regulate the flow rate, the amount of the flow, etc. of the liquid stream out of the liquid outlet 106C. The modulator 325 can be controlled (e.g., by the controller 126 of FIG. 1) to be closed to prevent the liquid stream out of the liquid outlet 106C from passing through the modulator 325. That is, only the vapor stream out of the vapor outlet 106B may pass through the connector 310 to flow to the cascade heat exchanger 108.

In the standard mode, the second expander 116 can be controlled (e.g., by the controller 126 of FIG. 1) to be closed. The modulator 325 can be controlled (e.g., by the controller 126 of FIG. 1) to be open (e.g., fully-open) to allow the liquid stream (or a mixture of the vapor and liquid streams) out of the liquid outlet 106C passing through to the connector 310. In the standard mode, the liquid stream out of the liquid outlet 106C and the vapor stream out of the vapor outlet 106B may be mixed and pass through the connector 310 to flow to the cascade heat exchanger 108.

When transitioning from the autocascade mode to the standard mode, the second expander 116 can be controlled to be from an open position or state (e.g., a partially-open position such as a maximum allowed position or an optimal open position or a controlled open position depending on the operation parameters) toward a fully-closed position to decrease the amount of liquid stream passing through the second expander 116 back to the system 100. The modulator 325 can be controlled to increase the amount of liquid stream passing through the modulator 325 so that the vapor stream out of the vapor outlet 106B is mixed with the liquid stream out of the liquid outlet 106C and the mixed stream flows to the cascade heat exchanger 108 via the connector 310. When the second expander 116 is at the fully-closed position and when the modulator 325 is controlled to be open (e.g., fully-open), the mode is transitioned into the standard mode.

When transitioning from the standard mode to the autocascade mode, the second expander 116 can be controlled to be from a fully-closed position or state towards an open position (e.g., a partially-open position) to increase the amount of liquid stream passing through the second expander 116 back to the system 100. The modulator 325 can be controlled to decrease the amount of liquid stream out of the outlet 106C passing through, so that the vapor stream out of the vapor outlet 106B is mixed with the liquid stream out of the liquid outlet 106C and the mixed stream flows to the cascade heat exchanger 108 via the connector 310. When the second expander 116 is at an open position (e.g., at a maximum allowed position or an optimal open position or a controlled open position depending on the operation parameters) and when the modulator 325 is controlled to prevent the liquid stream or the mixed liquid/vapor streams out of the outlet 106C from passing through the modulator 325, the mode is transitioned into the autocascade mode.

In FIGS. 3A and 3C, the liquid-vapor separator 106 is disposed in a vertical position, where the inlet 106A and the vapor outlet 106B are disposed at upper sides opposite to each other, and the liquid outlet 106C is disposed at the bottom. In the vertical position, a height of the liquid-vapor separator 106 is greater than a width/diameter of the liquid-vapor separator 106. In FIGS. 3B, 3D, and 3E, the liquid-vapor separator 106 is disposed in a horizontal position, where the inlet 106A and the vapor outlet 106B are disposed at the top and distanced from each other, and the liquid outlet 106C is disposed at the bottom (e.g., at a location aligned with the vapor outlet 106B vertically). In the horizontal position, a width of the liquid-vapor separator 106 is greater than a height/diameter of the liquid-vapor separator 106. It is to be understood that the liquid-vapor separator 106 in FIG. 3E can also be in a vertical position, similar to FIGS. 3A and 3C.

FIG. 4A illustrates a relationship between the states of the modulator/expander and the ambient temperature, arranged in accordance with at least some embodiments described herein. FIG. 4B illustrates a relationship between the pressure ratio and the ambient temperature, arranged in accordance with at least some embodiments described herein. It is to be understood that a controller (e.g., the controller 126) can be configured to control the operations of the modulator and/or expander.

FIGS. 4A and 4B show an autocascade region 405 in which the system (e.g., system 100 of FIG. 1) runs in an autocascade mode, a standard region 415 in which the system runs in a standard mode, and a transition region 410 in which the system runs in a transition mode (e.g., transitioning between the autocascade mode and the standard mode), separated by the vertical dotted lines.

In FIG. 4A, the vertical coordinate indicates a degree of open/close of the modulator and/or expander, and the horizontal coordinate indicates ambient temperature. Segments (or sections) 422, 424, and 426 indicate a relationship between the degree of open/close of the expander (e.g., the second expander 116) and the ambient temperature. Segments 432, 434, and 436 indicate a relationship between the degree of open/close of the modulator (e.g., modulator 220, 315A/315B/315C, 325) and the ambient temperature. The more the segments move up, the more the modulator/expander opens; and the more the segments move to the right, the higher the ambient temperature is.

Segment 432 indicates that the modulator is at a fully-closed position (e.g., not allowing stream to pass through, or not allowing a first (e.g., liquid) stream to pass through but allowing a second (e.g., vapor) stream to pass through when the modulator is a three-way valve or butterfly valve) in the autocascade mode/region. Segment 436 indicates that the modulator is at a fully-open position (e.g., allowing stream to pass through, or allowing the first (e.g., liquid) stream to pass through but not allowing the second (e.g., vapor) stream to pass through when the modulator is a three-way valve or butterfly valve) in the standard mode/region. Segment 434 indicates that the modulator is at an open position between the fully-open and fully-closed positions (e.g., allowing a portion of stream to pass through, or allowing both the first (e.g., liquid) and the second (e.g., vapor) stream to pass through when the modulator is a three-way valve or butterfly valve) in the transition mode/region. The more the segment 434 move up (or move to the right), the modulator is more toward a fully-open position (allowing more stream to pass through, or allowing more of the first (e.g., liquid) stream and optionally allowing less of the second (e.g., vapor) stream to pass through when the modulator is a three-way valve or butterfly valve).

Segment 422 indicates that the expander is at a maximum allowed open position (or an optimal open position or a controlled open position depending on the operation parameters) in the autocascade mode/region. Segment 426 indicates that the expander is at a fully-closed position (e.g., not allowing stream to pass through) in the standard mode/region. Segment 424 indicates that the expander is at an open position between the open position of segment 422 and the fully-closed position in the transition mode/region. The more the segment 424 moves down (or move to the right), the expander is more toward a fully-closed position (allowing less stream to pass through). The dotted segments above 422 and 424 indicate an upper/positive tolerance of the degree of open/close of the expander, and the dotted segments below 422 and 424 indicate a lower/negative tolerance of the degree of open/close of the expander.

In FIG. 4B, the vertical coordinate indicates the compressor pressure ratio, and the horizontal coordinate indicates ambient temperature. Segments (or sections) 442, 444, and 446 indicate a relationship between the pressure ratio and the ambient temperature. The more the segments move up, the higher the pressure ratio is; and the more the segments move to the right, the higher the ambient temperature is.

Segment 442 indicates that the pressure ratio may be decreasing when the ambient temperature increases in the autocascade mode/region. Segment 444 indicates that the pressure ratio may keep constant or substantially constant when the ambient temperature increases in the transition mode/region, by e.g., controlling and/or modulating the degree of open/close of the expander and/or the modulator, as shown in FIG. 4A. Segment 446 indicates that the pressure ratio may be decreasing when the ambient temperature increases in the standard mode/region.

As shown in FIGS. 4A and 4B, in the autocascade mode/region, when the ambient temperature increases, the pressure ratio drops. When the pressure ratio is at or below a predetermined first threshold (e.g., a point connecting 442 and 444), with a predetermined positive and/or negative tolerance, or at or below the first threshold for a predetermined period of time, or applying a hysteresis algorithm to the first threshold, the system 100 enters in the transition mode/region, where the controller can be configured to control and/or modulate the degree of open/close of the expander and/or the modulator, as shown in FIG. 4A (e.g., increasing the degree of open of the modulator and/or decreasing the degree of open of the expander), to e.g., achieve an optimal efficiency, improve capacity and/or system performance, and/or broaden the operating map.

In the transition mode/region, to keep the pressure ratio from further dropping (e.g. when the ambient temperature increases), the expander is controlled to be more towards a fully-closed position and the modulator is controlled to be more towards a fully-open position. When the expander is controlled to be fully-closed and the modulator is controlled to be fully-open, the system 100 enters to the standard mode/region.

In the standard mode/region, when the ambient temperature decreases, the pressure ratio increases. When the pressure ratio is at or above a predetermined second threshold (e.g., a point connecting 446 and 444), with a predetermined positive and/or negative tolerance, or at or above the second threshold for a predetermined period of time, or applying for example but not limited to a hysteresis algorithm to the second threshold, the system 100 enters in the transition mode/region, where the controller can be configured to control and/or modulate the degree of open/close of the expander and/or the modulator, as shown in FIG. 4A (e.g., increasing the degree of open of the expander and/or decreasing the degree of open of the modulator), to e.g., achieve an optimal efficiency, improve capacity and/or system performance, and/or broaden the operating map.

In the transition mode/region, to keep the pressure ratio from further increasing (e.g. when the ambient temperature decreases), the modulator is controlled to be more towards a fully-closed position and the expander is controlled to be more towards a maximum allowed open position. When the modulator is controlled to be fully-closed and the expander is controlled to be at the maximum allowed open position, the system 100 enters to the autocascade mode/region.

In an example embodiment, the first threshold can be the same as the second threshold. In another example embodiment, the first threshold can be greater than the second threshold. It is to be understood that instead of (or in addition to) using the pressure ratio as an operating parameter to control/modulate the modulator/expander, ambient temperature (and/or the temperature of the process fluid such as water at or near the condenser) can be used as operating parameter(s) to control/modulate the modulator/expander. In an example embodiment, the temperature can be determined e.g., by the controller via corresponding temperature sensor(s).

When the determined temperature is increasing and at or above a first temperature threshold, with a predetermined positive and/or negative tolerance, or at or above the first temperature threshold for a predetermined period of time, or applying for example a hysteresis algorithm to the first temperature threshold, the system can be transitioned from the autocascade mode/region to the transition mode/region. In the transition mode/region, when the temperature increases, the expander can be controlled to be more towards a fully-closed position and the modulator is controlled to be more towards a fully-open position. When the expander is controlled to be fully-closed and the modulator is controlled to be fully-open, the system 100 enters to the standard mode/region.

When the determined temperature is decreasing and at or below a second temperature threshold, with a predetermined positive and/or negative tolerance, or at or below the second temperature threshold for a predetermined period of time, or applying for example a hysteresis algorithm to the second temperature threshold, the system can be transitioned from the standard mode/region to the transition mode/region. In the transition mode/region, when the temperature decreases, the modulator is controlled to be more towards a fully-closed position and the expander is controlled to be more towards a maximum allowed open position. When the modulator is controlled to be fully-closed and the expander is controlled to be at the maximum allowed open position, the system 100 enters to the autocascade mode/region.

It is to be understood that the processes and/or steps described in any of the figures can be conducted, implemented, and/or performed by one or more controllers including e.g., the controller 126 of the HVACR system 100 of FIG. 1 and/or any other suitable controller, unless otherwise specified. It is also to be understood that the processes and/or steps can include one or more operations, actions, or functions. These various operations, functions, or actions may, for example, correspond to software, program code, or program instructions executable by a processor (e.g., a controller) that causes the functions to be performed. Obvious modifications may be made such that two or more of the processes/steps may be re-ordered; further processes/steps may be added; and various processes/steps may be divided into additional processes/steps, combined into fewer processes/steps, or eliminated, depending on the desired implementation. It is to be understood that operations including initializations or the like may be performed. For example, system parameters may be initialized.

Features in the embodiments disclosed herein may operate by recombining the liquid and vapor streams from the liquid-vapor separator, either internally in the liquid-vapor separator or externally in a mixing section. The recombined flow can be delivered to the downstream components of the system, causing the system to function in a standard refrigeration mode/cycle. It is to be understood that the location of the modulator(s) needs to be at a desired location to prevent logging of refrigerant in the liquid-vapor separator. The control can be based on the measured pressure ratio which can modulate or enable/disable the autocascade functionality to remain within the compressor operating limits. The control can be based on a hysteresis algorithm around a fixed pressure ratio, or a more complex pressure ratio map based on the hot sink (water or air) and cold source (water or air) temperatures.

Features in the embodiments disclosed herein may switch between the standard mode/cycle and autocascade mode/cycle based on the operating condition to achieve a broad operating map. It is to be understood that how the flows/streams are recombined may be desirable as is the control method for switching between the modes, including the transition mode(s). In an example embodiment, mounting the liquid-vapor separator in a different orientation to allow gravity draining and passing flow around it might be desired. In another example embodiment, the liquid-vapor separator may be sealed off completely, or using the liquid-vapor separator to store a portion of the charge instead of flowing through.

In an example application, the system may be an air source, low ambient heat pump making hot water. The operating environment may have ambient temperature ranging from e.g., at or around 80° F. to at or about −20° F. It is to be understood that the autocascade mode/cycle may provide good performance at colder ambient temperature, but when the ambient temperature increases, the pressure ratio and temperature difference may be too low for the autocascade mode/cycle to work well, and transition may be needed to disable the autocascade functionality. Similarly, when the autocascade functionality is disabled and the ambient temperature decreases, transition may be needed to enable the autocascade functionality. Features in the embodiments disclosed herein may modulate or enable/disable the autocascade functionality, e.g., based on operation parameters such as pressure ratio or ambient temperature (and/or process fluid temperature such as water temperature).

Aspects

It is appreciated that any one of aspects can be combined with each other.

Aspect 1. A heating, ventilation, air conditioning, and refrigeration (HVACR) system, comprising: a compressor, a condenser, a liquid-vapor separator having a vapor outlet and a liquid outlet, a cascade heat exchanger, an expander, and an evaporator fluidly connected; a modulator disposed downstream of the liquid outlet; and a controller configured to: determine an operation parameter of the system, and control the modulator to modulate a liquid flow from the liquid outlet based on the determined operation parameter, wherein the expander is disposed downstream of the liquid outlet, the cascade heat exchanger is disposed downstream of the vapor outlet, and the modulator is disposed between the liquid outlet and the vapor outlet and upstream of the cascade heat exchanger.

Aspect 2. The HVACR system of aspect 1, wherein the operation parameter is a compressor pressure ratio, the compressor pressure ratio being a ratio of a discharge pressure of the compressor to a suction pressure of the compressor.

Aspect 3. The HVACR system of aspect 1 or aspect 2, wherein the controller is further configured to control the modulator to decrease a portion of the liquid flow passing through the modulator when the operation parameter is above a first threshold.

Aspect 4. The HVACR system of aspect 3, wherein when the operation parameter is above the first threshold, the controller is further configured to control the expander to increase a portion of the liquid flow passing through the expander.

Aspect 5. The HVACR system of aspect 3 or aspect 4, wherein when the operation parameter is above the first threshold, the controller is configured to control the expander and the modulator such that a decreased portion of the liquid flow passing through the modulator is mixed with a vapor flow from the vapor outlet and flows towards the cascade heat exchanger.

Aspect 6. The HVACR system of any one of aspects 1-5, wherein the controller is further configured to control the modulator to increase a portion of the liquid flow passing through the modulator when the operation parameter is below a second threshold.

Aspect 7. The HVACR system of aspect 6, wherein when the operation parameter is below the second threshold, the controller is further configured to control the expander to decrease a portion of the liquid flow passing through the expander.

Aspect 8. The HVACR system of aspect 6 or aspect 7, wherein when the operation parameter is below the second threshold, the controller is configured to control the expander and the modulator such that an increased portion of the liquid flow passing through the modulator is mixed with a vapor flow from the vapor outlet and flows towards the cascade heat exchanger.

Aspect 9. The HVACR system of any one of aspects 1-8, wherein the operation parameter includes ambient temperature.

Aspect 10. The HVACR system of aspect 9, wherein the operation parameter is determined based on the ambient temperature and a temperature of a process fluid of the condenser.

Aspect 11. A method of operating a heating, ventilation, air conditioning, and refrigeration (HVACR) system, the HVACR system including: a compressor, a condenser, a liquid-vapor separator having a vapor outlet and a liquid outlet, a cascade heat exchanger, an expander, and an evaporator fluidly connected; a modulator disposed downstream of the liquid outlet; and a controller, the method comprising: determining an operation parameter of the system, and controlling the modulator to modulate a liquid flow from the liquid outlet based on the determined operation parameter, wherein the expander is disposed downstream of the liquid outlet, the cascade heat exchanger is disposed downstream of the vapor outlet, and the modulator is disposed between the liquid outlet and the vapor outlet and upstream of the cascade heat exchanger.

Aspect 12. The method of aspect 11, wherein the operation parameter is a compressor pressure ratio, the compressor pressure ratio being a ratio of a discharge pressure of the compressor to a suction pressure of the compressor.

Aspect 13. The method of aspect 11 or aspect 12, further comprising: controlling the modulator to decrease a portion of the liquid flow passing through the modulator when the operation parameter is above a first threshold.

Aspect 14. The method of aspect 13, further comprising: when the operation parameter is above the first threshold, controlling the expander to increase a portion of the liquid flow passing through the expander.

Aspect 15. The method of aspect 13 or aspect 14, further comprising: when the operation parameter is above the first threshold, controlling the expander and the modulator such that a decreased portion of the liquid flow passing through the modulator is mixed with a vapor flow from the vapor outlet and flows towards the cascade heat exchanger.

Aspect 16. The method of any one of aspects 11-15, further comprising: controlling the modulator to increase a portion of the liquid flow passing through the modulator when the operation parameter is below a second threshold.

Aspect 17. The method of aspect 16, further comprising: when the operation parameter is below the second threshold, controlling the expander to decrease a portion of the liquid flow passing through the expander.

Aspect 18. The method of aspect 16 or aspect 17, further comprising: when the operation parameter is below the second threshold, controlling the expander and the modulator such that an increased portion of the liquid flow passing through the modulator is mixed with a vapor flow from the vapor outlet and flows towards the cascade heat exchanger.

Aspect 19. The method of any one of aspects 11-18, wherein the operation parameter includes ambient temperature.

Aspect 20. The method of aspect 19, further comprising: determining the operation parameter based on the ambient temperature and a temperature of a process fluid of the condenser.

The terminology used in this specification is intended to describe particular embodiments and is not intended to be limiting. The terms “a,” “an,” and “the” include the plural forms as well, unless clearly indicated otherwise. The terms “comprises” and/or “comprising,” when used in this specification, specify the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and/or components.

With regard to the preceding description, it is to be understood that changes may be made in detail, especially in matters of the construction materials employed and the shape, size, and arrangement of parts without departing from the scope of the present disclosure. This specification and the embodiments described are exemplary only, with the true scope and spirit of the disclosure being indicated by the claims that follow.