SYSTEM AND METHOD FOR LUBRICANT QUALITY CONTROL OF AN HVACR SYSTEM

Description

FIELD

The embodiments described herein pertain generally to systems and methods for lubricant quality control of a heating, ventilation, air conditioning, and refrigeration (HVACR) system. More specifically, the embodiments described herein pertain to controlling lubricant quality by modulating a first flow control device of a suction pipe to control the discharge superheat of a screw compressor, and/or controlling a second flow control device of a bypass pipe to control the discharge superheat of the screw compressor.

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 evaporator first to release heat to, for example, the indoor air, which also condenses the refrigerant vapor to liquid refrigerant. The liquid refrigerant is then typically directed to the condenser through the expander to become a two-phase refrigerant mixture.

SUMMARY

Features in the embodiments disclosed herein may provide a control to modulate a suction valve (e.g., towards a fully-closed position) to reduce the suction pressure of a screw compressor. It is to be understood that lower suction pressure can be useful in e.g., the startup process of the compressor or the system to generate differential pressure for lubricant (e.g., oil and/or oil/refrigerant mixture) and/or refrigerant flow and increase superheat (e.g., discharge superheat and/or suction superheat) without lowering the evaporator refrigerant temperature.

Features in the embodiments disclosed herein may provide control of the suction valve (e.g., towards a fully-closed position) between the evaporator and the compressor that enables a lower pressure at the compressor inlet to be created. It is to be understood that such control is particularly useful for starting up, e.g., a chiller (having a screw compressor) with a low temperature difference between the evaporator process fluid (e.g., air, water, and/or glycol, or the like) and the condenser process fluid, because such scenario typically causes a low differential pressure across the compressor which may result in low lubricant flow to the compressor. It is also to be understood that a lower pressure at the compressor inlet may increase the suction superheat which increases compressor discharge superheat which is necessary for maintaining lubricant quality.

It is further to be understood that in a screw-compressor-based refrigeration heating system (or other refrigeration system where lubricant quality/discharge temperature management is important), maintaining lubricant quality can be critical and may require a minimum amount of discharge superheat. It is to be understood that a heating system can be a system based on a refrigeration cycle where the intended output can be energy in the form of a hot fluid (e.g., water, air, etc.) that can be used as a useful heat source. It is also to be understood that the application can be directed to refrigerant cycle based systems that provide either a hot fluid for heating or a cold fluid for cooling or both. It is further to be understood that the type of the refrigerant, the type of the compressor, and the efficiency of the compressor may result in an undesired discharge condition. For example, there might not be enough discharge superheat to guarantee that the lubricant (which is circulated with the refrigerant) is not diluted (with miscible refrigerant) to a point where the lubrication ability may be diminished. Features in the embodiments disclosed herein may address such an issue. Features in the embodiments disclosed herein may also provide a control to direct a portion of the compressor refrigerant flow from the exit of the compressor back to the entrance of the compressor, bypassing the condenser. Such “bypass” refrigerant flow may increase the compressor inlet enthalpy and increase the discharge superheat of the compressor to maintain adequate lubricant quality. Features in the embodiments disclosed herein may provide a supplement to other means of adding suction superheat and/or when using a suction superheater is not feasible or desirable.

It is to be understood that to maintain reliable operation, a screw-compressor-based refrigeration cycle needs to generate discharge superheat in a sufficient amount to prevent a circulated miscible lubricant from reaching an undesired or a critical level of dilution. This may be typically implemented in a system as a minimum discharge superheat requirement. Such superheat requirement can be particularly challenging with many new low Global Warming Potential (GWP) refrigerants that have a pressure/enthalpy/saturation relationship that often results in very low discharge superheat at the desired discharge conditions. To increase the discharge superheat above the minimum requirement (e.g., based on a desired lubricant quality), many methods may create inherent inefficiencies in the refrigeration cycle. As such, often discharge superheat “enhancement” may involve a tradeoff between optimum values of capacity/efficiency and maintaining adequate lubricant quality for long and reliable compressor operation. Features in the embodiments disclosed herein may provide an optimal solution to such issues.

In an example embodiment, a heating, ventilation, air conditioning, and refrigeration (HVACR) system is provided. The system includes a screw compressor, a condenser, and an evaporator fluidly connected; a suction pipe connecting the evaporator and the screw compressor; an actuator configured to modulate a first flow control device in the suction pipe; and a controller. The controller is configured to determine a discharge superheat of the screw compressor, and to control the actuator to modulate the first flow control device to increase the discharge superheat when the discharge superheat is below a first threshold.

In an example embodiment, a method of operating a heating, ventilation, air conditioning, and refrigeration (HVACR) system is provided. The system includes a screw compressor, a condenser, and an evaporator fluidly connected; a suction pipe connecting the evaporator and the screw compressor; an actuator configured to modulate a first flow control device in the suction pipe; and a controller. The method includes determining a discharge superheat of the screw compressor, and controlling the actuator to modulate the first flow control device to increase the discharge superheat when the discharge superheat is below a first threshold.

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 skills 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 a refrigeration circuit, which may be implemented in an HVACR system, arranged in accordance with at least some embodiments described herein.

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

FIG. 3 is a schematic view of a portion of an HVACR system (including the portion of FIG. 2), arranged in accordance with at least some embodiments described herein.

FIG. 4 is a flow chart illustrating an example processing flow for a discharge superheat control, arranged in accordance with at least some embodiments described herein.

FIG. 5 is a flow chart illustrating another example processing flow for a discharge superheat control, 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”.

It is to be understood that lubricant (e.g., oil and/or oil/refrigerant mixture) characteristics may include, for example, lubricant quality (e.g. the mass fraction of the refrigerant dissolved in the lubricant), lubricant viscosity, lubricant kappa value, and the like. Higher lubricant dilution (and thus lower lubricant quality) may occur when discharge superheat becomes relatively low. For example, higher lubricant dilution can occur when the discharge superheat is below a threshold (e.g., at or about 10° F., etc.). That is, low discharge superheat of a compressor can result in less than sufficient lubricant characteristics such as lubricant quality. Lubricant characteristics such as lubricant quality can be a function of the discharge superheat.

In an example embodiment, lubricant quality (e.g. a mass fraction of lubricant vs. dissolved refrigerant) can be estimated or determined using a discharge superheat measurement of the difference between a saturation temperature and the temperature in the discharge line. It is to be understood that high lubricant characteristics (such as target or better than target lubricant characteristics) can ensure a long lifecycle of the compressor. It is also to be understood that the chemistry of which type of refrigerant is used, and/or which type of lubricant is used can determine the sensitivity of the lubricant characteristics when the discharge superheat changes.

As referenced herein, “superheat” is a term of art that may refer to a difference between the actual temperature of the refrigerant vapor and the saturation temperature (boiling point) of the refrigerant at the same measuring location. In one embodiment, the saturation temperature (boiling point) of the refrigerant can be obtained by measuring a pressure (e.g., discharge pressure or suction pressure) of the refrigerant by using, for example, a pressure sensor, a gauge, or the like and then converting the measured pressure to a temperature (saturation temperature).

As referenced herein, “discharge superheat” is a term of art that may refer to the superheat obtained at the compressor discharge side (e.g., in the lubricant separator, or in the bearing cavity, etc.), which is the measured actual temperature of the refrigerant vapor minus the obtained saturation temperature (boiling point) of the refrigerant at the same measuring location at the compressor discharge side. It is to be understood that lubricant characteristics can be a function of discharge superheat. Perceived low lubricant characteristics (such as less than sufficient lubricant quality) correspond to a low discharge superheat value. It will also be appreciated that at a low (e.g., during a startup process) or partial load (where efficiency is not as important), the compressor might not generate enough superheat to keep the target lubricant characteristics.

As referenced herein, “suction superheat” is a term of art that may refer to the superheat obtained at the compressor suction side (e.g., near the suction inlet of the compressor, in the suction pipe, etc.), which is the measured actual temperature of the refrigerant vapor minus the obtained saturation temperature (boiling point) of the refrigerant at the same measuring location at the compressor suction side. It is to be understood that the suction superheat corresponds to the discharge superheat. That is, the higher the suction superheat is, the higher the discharge superheat might be, and the lower the suction superheat is, the lower the discharge superheat might be.

As referenced herein, “screw compressor” is a term of art that may refer to a compressor where compression chambers are formed and a working fluid such as a refrigerant can be compressed by the rotation of at least one rotor, for example two rotors with the engagement of lobes on each of the rotors. The screw compressor may include one or more bearings receiving lubricant taken in e.g., at a lubricant inlet. The bearings may, for example, support and allow the rotation of components of the compressor such as the rotors of the screw compressor. It is to be understood that due to the structural characteristics and the design requirements of a screw compressor, features of other types of compressors might not be feasible to be combined with features of a screw compressor to achieve the features in the embodiments disclosed herein and the advantages enjoyed by the disclosed features.

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 flow control device (e.g., a valve such as a solenoid valve, a damper, a pump, and the like). It is to be understood that the flow control device can be configured to control a fluid (e.g., working fluid,) flow through e.g., a passage (e.g., a pipe and the like). The flow control device can have a fully-closed position or state at which the fluid can be prevented from flowing through the passage via the flow control device. The flow control device can also have a fully-open position or state at which the fluid can be flowing through the passage via the flow control device without being blocked by the flow control device. The flow control device can further have a partially-open (or partially-closed) position or state at which the fluid can be flowing through the passage via the flow control device with the fluid being partially blocked by the flow control device. It is also to be understood that “modulating” a device 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” a device 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 a refrigeration circuit 100, which may be implemented in an HVACR system, arranged in accordance with at least some embodiments described herein. The refrigerant circuit 100 can include a compressor 120, a condenser 140, an expander 160, and an evaporator 180. The refrigerant circuit 100 may also include a controller 110 configured to control the operations of the compressor 120, the condenser 140, the expander 160, the evaporator 180, and/or other components of the refrigerant circuit 100.

The refrigerant circuit 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 refrigerant circuit 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 refrigerant circuit 100 can be configured to be a heat pump that can operate in a heating/defrost mode. It is appreciated that the refrigerant circuit 100 can be configured to operate in a cooling mode and/or a heating/defrosting mode. In an example embodiment, an HVACR system can include a refrigerant circuit 100 to 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 refrigerant circuit 100 and be utilized to heat or cool the process fluid.

The compressor 120, the condenser 140, the expander 160, and the evaporator 180 can be fluidly connected. An “expander” as described herein may also be referred to as an expansion device. In an embodiment, the expander 160 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 160 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.

The refrigerant circuit 100 is an example and can be configured to include more or less components. For example, in an embodiment, the refrigerant circuit 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 lubricant separator, a receiver tank, a dryer, a suction-liquid heat exchanger, one or more sensors, or the like.

The refrigerant circuit 100 can operate according to generally known principles. The refrigerant circuit 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 refrigerant circuit 100 may be generally representative of a liquid chiller system. The refrigerant circuit 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 refrigerant circuit 100 may be generally representative of an air conditioner and/or heat pump.

In an example embodiment, the refrigerant circuit 100 can operate as a vapor-compression circuit such that the compressor 120 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 120 and flowing through the condenser 140. In accordance with generally known principles, the working fluid flows through the condenser 140 and rejects heat to the process fluid (e.g., water, air, and the like), thereby cooling the working fluid. The cooled working fluid, which is now in a liquid form, flows to the expander 160 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 180. The working fluid flows through the evaporator 180 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 120. The above-described process continues while the heat transfer circuit is operating, for example, in a cooling mode (e.g., while the compressor 120 is enabled).

In an example embodiment, the compressor 120 can compress the working fluid. Lubricant can be supplied to the compressor 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 with the working fluid. Thus, the working fluid discharged from the compressor 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. In other refrigerant circuits, the lubricant can be circulated with the working fluid and can then be supplied through a suction inlet of the compressor 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). In an example embodiment, the compressor 120 is a screw compressor.

FIG. 2 is a schematic view of a portion of an HVACR system 200, arranged in accordance with at least some embodiments described herein.

In an example embodiment, the system 200 includes a compressor 210 and an evaporator 220. The compressor 210 includes a suction port 212 (an inlet of the compressor). The suction port 212 is a port located on the compressor 210 where the working fluid to be compressed enters the compressor 210. In an example embodiment, one or more sensors 214 may be located at or near the suction port 212 to measure parameters including, for example, the temperature and/or the pressure of the working fluid at or near the suction port 212. In an example embodiment, the one or more sensors 214 can include a pressure sensor, a gauge, or the like to measure the pressure of the refrigerant. The one or more sensors 214 can also include a temperature sensor to measure the actual temperature of the refrigerant vapor. The controller (e.g., the controller 110 of FIG. 1) can communicate with the one or more sensors 214 to obtain the sensed data and determine the suction superheat based on the measured pressure of the refrigerant and the measured actual temperature of the refrigerant vapor. In an example embodiment, the compressor 210 is a screw compressor.

In an example embodiment, a suction pipe 240 is a fluid pipe extending from the working fluid outlet 222 of the evaporator 220 to the suction port 212 of the compressor 210. The suction pipe 240 conveys fluid from the working fluid outlet 222 of the evaporator 220 to the suction port 212 of the compressor 210. The fluid entered the compressor 210 at the suction port 212 from the suction pipe 240 includes a working fluid such as a refrigerant used in the refrigeration circuit.

In an example embodiment, the system 200 includes a flow control device 242 and an actuator 244 configured to modulate the flow control device 242. The flow control device 242 can be a valve such as a solenoid valve, a damper, a pump, or the like. The flow control device 242 can be disposed within the suction pipe 240 to adjust the fluid passing through the suction pipe 240 via the flow control device 242. The flow control device 242 can have a fully-closed position or state at which the fluid can be prevented from flowing through the suction pipe 240 via the flow control device 242. The flow control device 242 can also have a fully-open position or state at which the fluid can be flowing through the suction pipe 240 via the flow control device 242 without being blocked by the flow control device 242. The flow control device 242 can further have a partially-open (or partially-closed) position or state at which the fluid can be flowing through the suction pipe 240 via the flow control device 242 with the fluid being partially blocked by the flow control device 242. For example, the flow control device 242 can be at a partially-open (or partially-closed) position or state such as 10% open or closed, 15% open or closed, . . . 95% open or closed, etc.

In an example embodiment, the flow control device 242 can be configured to create or induce a pressure drop (e.g., between the suction inlet of the compressor and the working fluid outlet of the evaporator) of the fluid flowing through the suction pipe 240 via the flow control device 242. The actuator 244 can be a step motor (for modulating the flow control device 242) controlled by, for example, the controller 110 of FIG. 1. It is to be understood that the controller 110 can communicate with and/or control the components (e.g., compressor, evaporator, condenser, expander, actuator, sensor(s), flow control device(s), or the like) of e.g., the refrigerant circuit 100, the system 200, or the like. In an example embodiment, the controller 110 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 110 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 110.

In an example embodiment, the compressor 210 also includes a discharge port 216 (an outlet of the compressor). The discharge port 216 is where the compressed working fluid exits the compressor 210. The fluid exiting the discharge port 216 may include both the working fluid (e.g., the refrigerant) and the lubricant (e.g., the oil from the bearings of compressor 210). The fluid exits the discharge port 216 into a discharge pipe 230. The fluid at the discharge port 216 is at a higher temperature and a higher pressure than the fluid entering the compressor 210 at suction port 212. One or more sensors (218, 219) may be located at the discharge port 216 (or on/along the discharge pipe 230 near the discharge port 216) to measure parameters including pressure and/or temperature of the fluid as it exits the compressor 210. In an example embodiment, the one or more sensors (218, 219) can include a pressure sensor 218, a gauge, or the like to measure the pressure of the refrigerant. The one or more sensors (218, 219) can also include a temperature sensor 219 to measure the actual temperature of the refrigerant vapor. The controller can communicate with the one or more sensors (218, 219) to obtain the sensed data and determine the discharge superheat based on the measured pressure of the refrigerant and the measured actual temperature of the refrigerant vapor.

In an example embodiment, the controller of the system 200 can be configured to control the actuator 244 to actuate and/or modulate the flow control device 242 (e.g., towards the fully-closed position) to increase the discharge superheat (e.g., determined based on the measured pressure of the refrigerant and the measured actual temperature of the refrigerant vapor at the compressor discharge side) of the compressor when the discharge superheat is below a first threshold (e.g., a desired or predetermined or minimum discharge superheat).

In an example embodiment, the controller of the system 200 can be configured to control the actuator 244 to actuate and/or modulate the flow control device 242 (e.g., towards the fully-open position) to decrease the discharge superheat (e.g., determined based on the measured pressure of the refrigerant and the measured actual temperature of the refrigerant vapor at the compressor discharge side) of the compressor when the discharge superheat is at or above a second threshold (e.g., a predetermined or maximum discharge superheat). In an example embodiment, the second threshold (the maximum threshold) can be greater than the first threshold (the minimum threshold). In another example embodiment, the second threshold can be the same as the first threshold.

In an example embodiment, the discharge pipe 230 is a fluid pipe extending from the discharge port 216 of the compressor 210. The discharge pipe 230 conveys fluid from the discharge port 216 of the compressor 210 to the refrigeration circuit in which compressor 210 is incorporated (e.g., to a condenser 310 (e.g., via a lubricant separator 320) of FIG. 3). The fluid discharged at the discharge port 216 and conveyed by the discharge pipe 230 includes a working fluid such as a refrigerant used in the refrigeration circuit and further includes lubricant from the bearings and bearing cavity of the compressor 210.

In an example embodiment, the compressor 210 may include a lubricant inlet (not shown). The lubricant inlet can direct lubricant into a bearing cavity of the compressor 210, which contains one or more bearings. The lubricant inlet may be, for example, a port on a bearing cover or a housing of the compressor 210 extending into a bearing cavity receiving lubricant from the lubricant inlet.

In an example embodiment, the evaporator 220 includes a process fluid inlet pipe 224 and a process fluid outlet pipe 226. A sensor (e.g., a pressure sensor) 228 can be disposed for example at a shell of the evaporator to measure the evaporator shell pressure.

It is to be understood that compared with traditional control of a flow control device (e.g., manually closed for service/maintenance, and open for operation) on a suction pipe, features in the embodiments disclosed herein provide a mechanism to actuate and/or modulate the flow control device. It is also to be understood that at a startup process, the discharge superheat of the compressor is typically low (lower than a minimum required/desired discharge superheat which is e.g., at or around 10° F.). Features in the embodiments disclosed herein may create or induce a pressure drop between the evaporator working fluid outlet and the compressor suction inlet to provide sufficient discharge superheat (e.g., within a desired temperature range). The discharge superheat can be actively modulated throughout the operation of the system, ensuring sufficient differential pressure across the compressor to drive the lubricant supply flow.

It is to be understood that modulating the flow control device 242 (e.g., a suction valve) towards the fully-closed position can create more discharge superheat (compared with the condition when the flow control device 242 is not controlled/modulated), and modulating the flow control device 242 towards the fully-open position can decrease the discharge superheat (compared with the condition when the flow control device 242 is not controlled/modulated). That is, the more the flow control device 242 is closed, the more suction superheat (and the more the corresponding discharge superheat) may be obtained; and the more the flow control device 242 is open, the less suction superheat (and the less the corresponding discharge superheat) may be obtained. A sufficiently high discharge superheat (e.g., at or above the minimum required or desired discharge superheat) is needed for maintaining adequate lubricant quality at the lubricant separator. It is also to be understood that typically, having a pressure drop (at the evaporator working fluid outlet) may impact efficiency; but for reliability, good lubricant quality is needed, and some efficiency may be sacrificed. It is further to be understood that the flow control device 242 can also serve as an isolation device to e.g., isolate charge for freeze protection. An isolation device (e.g., a valve or the like.) can be a device having an open position that allows flow therethrough and a closed position that inhibits flow therethrough. The isolation device can be selectively controlled (e.g., by the controller) based on the operation of the HVACR system, for example, closing the isolation device at stop and/or opening the isolation device for running the system. It should be appreciated that a flow control device described herein may allow for a small amount of leakage in the closed position, e.g., due to wear, manufacturing tolerances or imperfections, and the like, and that the closed position of the flow control device is understood to prohibit flow even though such leakage may occur.

It is to be understood that using a primary HVACR system refrigerant valve (e.g., the expander 160, or the like) to suppress or reduce the suction pressure (to increase the discharge superheat) might drive down the saturation temperature in the evaporator which may cause (undesired) freezing condition. Also, when using the primary HVACR system refrigerant valve to suppress or reduce the suction pressure, the response may be slow, and the control may be sluggish because changing the pressure in the evaporator may take time. Features in the embodiments disclosed herein may provide an easy control of the suction flow control device and/or get faster response. Features in the embodiments disclosed herein may also allow for reducing or dropping the suction pressure (that the compressor gets) without affecting the evaporator refrigerant temperature.

Features in the embodiments disclosed herein may further help to provide pressure drop between the evaporator and the suction pipe, to use that differential pressure to drive the lubricant return flow out of the evaporator back to the compressor, and thus facilitate a thermal syphon lubricant recovery system to recover the lubricant into the suction pipe of the compressor. Features in the embodiments disclosed herein may provide control of differential pressure on startup (with evaporator freeze risk), may provide a mechanism of improving compressor discharge superheat, and can be used to remove lubricant from a thermal syphon lubricant recovery system. Features in the embodiments disclosed herein may further provide a flow control device to control a suction pressure and provide a control algorithm to generate a target or desired suction pressure based on the need to develop differential pressure or compressor discharge superheat.

Features in the embodiments disclosed herein may generate a lower suction pressure to establish differential pressure across the compressor. It is to be understood that to protect the compressor from unintended closure of the flow control device 242, the sensor 214 (e.g., a suction pressure transducer) needs to be located between the flow control device 242 and the compressor 210 (e.g., near the suction port of the compressor on the suction pipe). In addition, the sensor 228 (e.g., an evaporator pressure transducer, an evaporator shell pressure transducer, located on the shell of the evaporator) can be used for freeze protection because the sensor 214 may not reflect the condition of the evaporator if the flow control device 242 is partially closed. It is also to be understood that the flow control device 242 can typically be installed on chillers with screw compressors, and the HVACR system can have the ability to modulate the position of the flow control device 242 to improve reliability during startup and operation.

Features in the embodiments disclosed herein may generate differential pressure for lubricant delivery to compressor, and/or provide compressor discharge superheat control to maintain lubricant quality. Testing data has shown the time or duration needed to generate adequate differential pressure with and without the control of the flow control device 242. The flow control device 242 can be used to create a pressure drop from the evaporator to the compressor suction. It is to be understood that there can be a low or minimum suction pressure limit based on the compressor design. The control logic of the flow control device 242 can help to create a maximum differential pressure while maintaining the suction pressure above the compressor minimum requirement. The control of the flow control device 242 can also help maintain lubricant quality by keeping the compressor discharge superheat at a level high enough to ensure lubricant temperature is high enough to limit the amount of refrigerant dissolved in the lubricant. For example, test data has shown that the discharge superheat can be controlled to a minimum of at or about 10° F. It is to be understood that superheat can be generated by controlling suction pressure. A lower suction pressure can generate (more) suction superheat which can translate to an increased discharge superheat. It is also to be understood that the system 200 can be a partial system within the general system (e.g., the refrigerant circuit 100) of FIG. 1.

FIG. 3 is a schematic view of a portion of an HVACR system 300 (including the portion of FIG. 2), arranged in accordance with at least some embodiments described herein. It is to be understood that FIG. 2 can be a part of FIG. 3, and the components and features described in FIG. 2 apply to FIG. 3. It is also to be understood that the system 300 can be a partial system within the general system (e.g., the refrigerant circuit 100) of FIG. 1.

In addition to the components of FIG. 2, the system 300 can include a lubricant separator 320. The lubricant separator 320 can be located along the discharge pipe 230. The fluid exits the discharge port 216 into the discharge pipe 230. The lubricant separator 320 can be configured to separate lubricant from the flow of fluid discharged from the compressor 210, allowing the refrigerant to continue through the refrigeration circuit, for example, the condenser 310, an expander (e.g., 160 of FIG. 1), and the evaporator 220, while removing a significant portion of the lubricant from the flow discharged by the compressor 210. In an example embodiment, the lubricant separator 320 may include, for example, a filter (not shown) configured to allow passage of refrigerant while trapping lubricant in the discharge flow of the compressor 210. The lubricant separator 320 can be located between the discharge port 216 of the compressor 210 and the condenser 310 of the system 300. The compressor 210, the evaporator 220, and the condenser 310 can be the compressor 120, the evaporator 180, and the condenser 140 of FIG. 1, respectively.

In an example embodiment, the lubricant separator 320 may include, for example, a lubricant storage 324 configured to store lubricant to be provided to the compressor 210. In an example embodiment, the lubricant storage 324 can be a sump, a tank, or the like, connected to the lubricant separator 320. In an example embodiment, the lubricant trapped by lubricant separator 320 collects, for example in a pool included in the lubricant storage 324. In an example embodiment, this pool can be connected to a fluid pipe (see the dotted line connecting the lubricant storage 324 and the compressor 210) via a port or outlet (e.g., the connection point between the lubricant storage 324 and the dotted line) of the lubricant storage 324, and the fluid pipe can be connected to e.g., a lubricant inlet (e.g., the connection point between the compressor 210 and the dotted line) of the compressor 210 so that lubricant from the pool can be directed to the compressor 210 via the lubricant inlet. In an example embodiment, the lubricant storage 324 can be integrated into the lubricant separator 320. In another example embodiment, the lubricant storage 324 can be separated from the lubricant separator 320.

In an example embodiment, the working fluid (e.g., refrigerant) vapor 322 separated from the lubricant separator 320 can be directed to a pipe 330. The pipe 330 connects to a working fluid inlet of the condenser 310 and the condenser 310 can be configured to cool working fluid (refrigerant or the like) vapor to a liquid form, by e.g., exchanging heat with a process fluid (water, air or the like). The condenser 310 includes a process fluid inlet pipe 312 and a process fluid outlet pipe 314.

In an example embodiment, the system 300 includes a flow control device 344. In an example embodiment, the flow control device 344 can be controlled by the controller of the system 300. In another example embodiment, the flow control device 344 can be controlled by the controller via an actuator 342 configured to modulate or control the flow control device 344. The flow control device 344 can be a valve such as a solenoid valve, a damper, a pump, or the like. The flow control device 344 can be disposed within a bypass pipe 340 which can be configured to direct the working fluid (from the discharge pipe 230 via e.g., the lubricant separator 320 to the pipe 330) to the suction port 212 via the suction pipe 240, and thus a portion of the working fluid bypasses the condenser 310. In an example embodiment, the pipes 230, 330 (e.g., the upper portion), and 340 can be referred to as the bypass pipe.

In an example embodiment, the flow control device 344 can have a fully-closed position or state at which the fluid can be prevented from flowing through the bypass pipe 340 via the flow control device 344. The flow control device 344 can also have a fully-open position or state at which the fluid can be flowing through the bypass pipe 340 via the flow control device 344 without being blocked by the flow control device 344. The flow control device 344 can also have a partially-open (or partially-closed) position or state at which the fluid can be flowing through the bypass pipe 340 via the flow control device 344 with the fluid being partially blocked by the flow control device 344. In an example embodiment, the flow control device 344 can be controlled to switch between the fully-closed position and the fully-open position. In another example embodiment, the flow control device 344 can be modulated in a similar/same manner as the flow control device 242 being modulated.

It is to be understood that the working fluid (e.g., the high temperature, high pressure refrigerant in a gaseous form) bypassing the condenser 310 can provide an efficient way to generate discharge superheat. In an example embodiment, when the flow control device 344 is controlled to be open (or modulated towards the fully-open position) and a portion (or more) of the working fluid bypasses the condenser 310, the suction and discharge superheat (and the suction temperature) of the compressor 210 can be increased (compared with the condition when the flow control device 344 is not controlled/modulated to open). When the flow control device 344 is controlled to be closed (or modulated towards the fully-closed position) and less portion (or none) of the working fluid bypasses the condenser 310, the suction and discharge superheat (and the suction temperature) of the compressor 210 can be decreased (compared with the condition when the flow control device 344 is not controlled/modulated to close).

In an example embodiment, when more discharge superheat is needed, the flow control device 242 can be modulated towards the fully-closed position to increase the discharge superheat. It is to be understood that in an example embodiment, a fully-closed position may not be possible as it would eliminate any flow from the evaporator. The flow control device 242 can be modulated (towards the fully-closed position) to increase suction superheat by reducing compressor inlet pressure, but the flow control device 242 may not be allowed to be in the fully-closed position. That is, there may be a minimum open position for the flow control device 242. When the flow control device 242 is modulated to a position (e.g., at or about 30% to at or about 40% closed), further modulating the flow control device 242 towards the fully-closed position may have significant negative effects (e.g., reduction) on the overall system capacity and efficiency. In this situation, if more discharge superheat is needed (and a set of predefined conditions is met, see the description of FIG. 5), the flow control device 344 can be controlled to be open (or modulated towards the fully-open position) to increase the discharge superheat to a first desired level.

In an example embodiment, when less discharge superheat is needed (or desirable in the interest of system efficiency) and a set of predefined conditions is met (see the description of FIG. 5), the flow control device 344 can be controlled to be closed (or modulated towards the fully-closed position) to decrease the discharge superheat. If less discharge superheat is needed, the flow control device 242 can be modulated towards the fully-open position to decrease the discharge superheat, and/or until the flow control device 242 is modulated to the fully-open position, so that the discharge superheat can reach a second desired level. In an example embodiment, the first desired level is the same as the second desired level. In another example embodiment, the first desired level is less than the second desired level.

It is to be understood that when the flow control device 242 is controlled or modulated at a certain position, a first period of time may be needed for the flow control device 242 to be in such certain position to reach the corresponding (e.g., increased or decreased) discharge superheat. When the flow control device 344 is controlled or modulated at a certain position, a second period of time may be needed for the flow control device 242 to be in such certain position to reach the corresponding (e.g., increased or decreased) discharge superheat. That is, a delay for a certain amount of time may be needed for control/modulation purposes.

It is to be understood that compressor bypass flow (a portion of the working bypassing the condenser) can be used for capacity control in the HVACR systems. Features in the embodiments disclosed herein may provide discharge superheat control and in turn lubricant quality management. Compared with other methods of managing or increasing discharge superheat, features in the embodiments disclosed herein may increase capacity.

It is also to be understood that for some type of working fluid (e.g., a hydrofluoroolefin (HFO) refrigerant such as e.g., R-1233zd(E) refrigerant based screw chiller system used for booster type heating, with discharge temperatures ranging from e.g., at or about 160° F. to at or about 300° F.), additional superheat may be specifically required. In such applications, compressing the refrigerant with screw compressors may result in almost zero inherent discharge superheat, and significant suction heating or suction superheat need to be added to maintain lubricant quality. Features in the embodiments disclosed herein may provide a bypass working fluid flow control in conjunction with suction flow control device modulation, which can be used to add suction superheat by adding suction pressure drop at a constant temperature. It is to be understood that modulating the suction flow control device can create significant suction pressure drop, and a portion of bypass flow (e.g., at or about 5%, at or about 10% working fluid flow bypassing the condenser) can impact suction and/or discharge superheat as well. It is to be understood that it is not desirable to allow the bypass flow to approach the amount of flow passing through the primary discharge pipe/line since a bypass flow might cause inefficiency in the refrigeration cycle. As such the bypass pipe/line may be smaller than the discharge pipe/line. The bypass flow, through a combination of the bypass pipe/line size and the bypass flow control device selection, may be sized to allow the amount of bypass flow needed to meet a discharge superheat requirement when used in combination with suction flow control device modulation (for suction pressure drop). In an example embodiment, a combination of pressure drop caused by the suction flow control device modulation and the bypass flow can be selected to optimize efficiency/capacity while still promoting the attainment of target discharge superheat that may be otherwise not attained.

It is to be understood that the bypass pipe 340 can be added to a screw chiller system to route a portion of the main compressor flow from the discharge of the compressor to the suction of the compressor. The bypass pipe 340 can be fitted with a flow control device 344 that is configured to enable flow (e.g., modulating or turning on/off). During the operation of the HVACR system, when needed, the flow control device 344 can be opened (or modulated or regulated towards the fully-open position) to allow discharge gas to flow to the compressor suction, increasing suction enthalpy which in turn increases compressor discharge enthalpy and discharge superheat. The bypass flow is activated only when required to raise discharge superheat above a minimum threshold required for adequate lubricant quality. Adding a bypass flow from the compressor discharge to the compressor suction can increase compressor inlet enthalpy (and suction superheat) and in turn increase discharge superheat above the minimum threshold. Adding the bypass flow may result in a loss of some refrigerant flow through the rest of the HVACR system, but it is preferred over other methods and can be used in conjunction with other means of discharge superheat management as a supplement.

In an example embodiment, the bypass flow can be used in conjunction with the modulating suction flow control device which can add or control discharge superheat by varying or increasing suction pressure drop which can add suction superheat. It is to be understood that when the required suction pressure drop gets above a few pound-force per square inch (PSI) of pressure drop, it may be more efficient to enable a small amount of bypass flow to keep the overall system impact of adding suction pressure drop at a minimum. The bypass flow control in addition to the suction flow control device modulation can include both a modulating portion for control (e.g., the suction flow control device) and the bypass flow supplement which may reduce the amount of suction pressure drop (e.g., by using more closed suction flow control device) needed in key operating regions. The combination of bypass control and suction flow control device modulation can be focused on specific control of discharge temperature for lubricant quality, and can generate the minimum level of required discharge superheat for the HVACR system. When not needed, the bypass flow control device can be shut and have no negative impact. It is to be understood that using the bypass flow control can reduce the need for pressure drop. Bypass flow control can be used when needed, which can be a portion of the operating map (e.g., for full load at most efficient compressor operation), because discharge superheat generally may increase at unloaded condition.

It is to be understood that to maintain reliable operation, a screw compressor-based refrigeration cycle may need to generate discharge superheat in sufficient amount to prevent a circulated miscible lubricant from reaching a critical level of dilution, which can be a minimum discharge superheat requirement. Bypass flow control (e.g., adding bypass flow bypassing the condenser) can increase discharge temperature by increasing suction temperature and/or enthalpy. High temperature refrigerant gas leaving lubricant separator or compressor discharge can be passed to the suction pipe or suction connection of compressor, bypassing the condenser. Increased suction enthalpy can result in increased discharge enthalpy which means a higher discharge temperature. Increasing discharge temperature can result in better or desirable lubricant quality by driving refrigerant out of solution, to e.g., surpass the minimum discharge superheat requirement.

It is to be understood that the bypass flow control is not an unloading mechanism. The bypass flow control is associated with managing discharge temperature, discharge superheat, and lubricant quality, and generally results in capacity increase because it is used as an alternative to less efficient options. When superheat needs dictate a large change to suction superheat needed to create an acceptable level of discharge temperature and/or superheat, it is advantageous to use a small amount (e.g., at or about 5%, at or about 10%, etc.) of bypass flow to affect suction superheat, rather than add a large amount of pressure drop to the suction flow, to achieve an overall capacity and efficiency benefit.

FIG. 4 is a flow chart illustrating an example processing flow 400 for a discharge superheat control, arranged in accordance with at least some embodiments described herein.

It is to be understood that the processing flow 400 disclosed herein can be conducted by one or more controllers including e.g., the controller of the HVACR system of FIGS. 1-3 and/or any other suitable controller, unless otherwise specified.

It is also to be understood that the processing flow 400 can include one or more operations, actions, or functions as illustrated by one or more of blocks 410, 420, 430, 440, and 450. 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. Although illustrated as discrete blocks, obvious modifications may be made, e.g., two or more of the blocks may be re-ordered; further blocks may be added; and various blocks may be divided into additional blocks, combined into fewer blocks, or eliminated, depending on the desired implementation. It is to be understood that before the processing flow 400, operations including initializations or the like may be performed. For example, system parameters may be initialized. It is to be understood that the processes, operations, or actions described in FIGS. 1-3 may be implemented or performed by the controller. Processing flow 400 may begin at block 410.

At block 410 (Determine a discharge superheat), the controller may be configured to determine a discharge superheat of a compressor, e.g., based on sensed data from one or more sensors. In an example embodiment, the discharge superheat can be determined based on the measured actual temperature of the refrigerant vapor minus the obtained saturation temperature (boiling point) of the refrigerant at the same measuring location at the compressor discharge side. The saturation temperature of the refrigerant can be obtained by measuring a pressure (e.g., discharge pressure or suction pressure) of the refrigerant by using, for example, a pressure sensor, a gauge, or the like, and then converting the measured pressure to a temperature (saturation temperature). Processing may proceed from block 410 to block 420.

At block 420 (Modulate a first flow control device to increase the discharge superheat), when the discharge superheat determined at 410 is less than a minimum or a predetermined discharge superheat (e.g., a minimum threshold), the controller may be configured to modulate a first flow control device (e.g., the suction flow control device 242) towards a fully-closed position to increase the discharge superheat. A delay may be needed to reach the discharge superheat corresponding to the modulated position of the first flow control device. When the discharge superheat determined at 410 is at or above the minimum threshold, no action may be taken. Processing may proceed from block 420 to block 430.

At optional block 430 (Control a second flow control device to increase the discharge superheat), when the increased discharge superheat at 420 (e.g., determined by the controller) is less than the minimum threshold and a set of predefined conditions is met (see the description of FIG. 5), the controller may be configured to control (e.g., open or modulate) a second flow control device (e.g., the bypass flow control device 344, towards a fully-open position) to increase the discharge superheat to reach the minimum threshold. A delay may be needed to reach the discharge superheat corresponding to the controlled position of the second flow control device. When the increased discharge superheat at 420 is at or above the minimum threshold, no action may be taken. Processing may proceed from block 430 to block 440.

At optional block 440 (Control the second flow control device to decrease the discharge superheat), when the discharge superheat (e.g., determined by the controller) is at or above a maximum or a predetermined discharge superheat (e.g., a maximum threshold) and a set of predefined conditions is met (see the description of FIG. 5), the controller may be configured to control (e.g., close or modulate) the second flow control device (e.g., the bypass flow control device 344, towards a fully-closed position) to decrease the discharge superheat. A delay may be needed to reach the discharge superheat corresponding to the controlled position of the second flow control device. When the discharge superheat (e.g., determined by the controller) is below the maximum threshold, no action may be taken. Processing may proceed from block 440 to block 450.

At block 450 (Modulate the first flow control device to decrease the discharge superheat), when the decreased discharge superheat at 440 (e.g., determined by the controller) is at or above the maximum threshold, the controller may be configured to modulate the first flow control device (e.g., the suction flow control device 242, towards a fully-open position) to decrease the discharge superheat to be below the maximum threshold. A delay may be needed to reach the discharge superheat corresponding to the modulated position of the first flow control device. When the decreased discharge superheat at 440 (e.g., determined by the controller) is below the maximum threshold, no action may be taken. Processing may proceed from block 450 to block 410.

FIG. 5 is a flow chart illustrating an example processing flow 500 for a discharge superheat control, arranged in accordance with at least some embodiments described herein.

It is to be understood that the processing flow 500 disclosed herein can be conducted by one or more controllers including e.g., the controller of the HVACR system of FIGS. 1-3 and/or any other suitable controller, unless otherwise specified.

It is also to be understood that the processing flow 500 can include one or more operations, actions, or functions as illustrated by one or more of blocks 510, 520, 530, 540, 550, 560, 570, 580, and 590. 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. Although illustrated as discrete blocks, obvious modifications may be made, e.g., two or more of the blocks may be re-ordered; further blocks may be added; and various blocks may be divided into additional blocks, combined into fewer blocks, or eliminated, depending on the desired implementation. It is to be understood that before the processing flow 500, operations including initializations or the like may be performed. For example, system parameters may be initialized. It is to be understood that the processes, operations, or actions described in FIGS. 1-3 may be implemented or performed by the controller. Processing flow 500 may begin at block 510.

At block 510 (Determine Discharge Superheat (DSH)), the controller may be configured to determine a discharge superheat of a compressor, e.g., based on sensed data from one or more sensors. See also the description of block 410 of FIG. 4. Processing may proceed from block 510 to block 520 and/or block 570.

At block 520 (Compare DSH to target), the controller may be configured to compare the discharge superheat determined at 510 (DSH) to a target or a predetermined discharge superheat. If the DSH is above the target discharge superheat (plus a predefined positive tolerance), processing may proceed from block 520 to block 530. If the DSH is below the target discharge superheat (minus a predefined positive tolerance), processing may proceed from block 520 to block 540. If the DSH is at the target discharge superheat (or within a range of the target discharge superheat plus or minus a predefined positive tolerance), processing may proceed from block 520 to block 510.

At block 530 (Modulate when above target), when the DSH is above the target discharge superheat, the controller may be configured to modulate the first flow control device (e.g., the suction flow control device 242, towards a fully-open position) to decrease the discharge superheat to be at or close to the target discharge superheat. A delay may be needed to reach the discharge superheat corresponding to the modulated position of the first flow control device. It is to be understood that the first flow control device can be modulated e.g., up to 100% open. Processing may proceed from block 530 to block 510.

At block 540 (Modulate when below target), when the DSH is below the target discharge superheat, the controller may be configured to modulate the first flow control device (e.g., the suction flow control device 242) towards a fully-closed position to increase the discharge superheat. It is to be understood that the first flow control device may be limited in the amount that it can be modulated towards a fully-closed position to affect an increase in discharge superheat. That is, a fully-closed position may not be possible for the first flow control device as it would eliminate any flow from the evaporator, and there may be a minimum open position for the first flow control device. There can be both a minimum open position (for the first flow control device) and a maximum pressure drop (a pressure drop that can be added between the evaporator and the compressor) which may prevent the first flow control device from fully reaching a desired increased level of DSH that corresponds to the target discharge superheat. It is to be understood that a delay may be needed to reach the discharge superheat corresponding to the modulated position of the first flow control device. Processing may proceed from block 540 to block 550.

At block 550 (Compare position and conditions), the controller may be configured to compare the first flow control device position and system operating conditions such as the pressure entering compressor, the pressure drop across suction valve, or the like. to predefined targets and/or limits. When such a set of conditions is met or satisfied (e.g., the targets/limits are reached), a secondary trigger may be set (that may cause the bypass flow control device to open or modulate towards a full-open position, see the description of block 570 and/or block 580). Processing may proceed from block 550 to block 560 and/or block 570.

At block 560 (Check limits), if the first flow control device position or system operation conditions reach the predefined targets/limits, the controller may be configured to control the first flow control device to close (or modulate to close) no further than the target/limits dictate. Processing may proceed from block 560 to block 510.

At block 570 (Check Trigger), the controller may be configured to check a secondary trigger (see also the description of block 550). The secondary trigger may be determined by, e.g., checking the DSH (e.g., determined at block 510 and/or block 550) and checking the operating parameters such as suction valve position, the pressure drop across suction valve, or the like. Processing may proceed from block 570 to block 580 if the secondary trigger indicates that an opening criterion is met. Processing may proceed from block 570 to block 590 if the secondary trigger indicates that a closing criterion is met. Processing may proceed from block 570 to block 510 if the secondary trigger indicates that no opening criterion nor closing criterion is met.

At block 580 (Open/Modulate when meets open criteria), the controller may be configured to control (e.g., open or modulate) a second flow control device (e.g., the bypass flow control device 344, towards a fully-open position) to increase the discharge superheat to reach the target discharge superheat. A delay may be needed to reach the discharge superheat corresponding to the controlled position of the second flow control device. Processing may proceed from block 580 to block 510.

At block 590 (Close/Modulate when meets close criteria), the controller may be configured to control (e.g., close or modulate) the second flow control device (e.g., the bypass flow control device 344, towards a fully-closed position) to decrease the discharge superheat. A delay may be needed to reach the discharge superheat corresponding to the controlled position of the second flow control device. Processing may proceed from block 590 to block 510.

It is to be understood that when the DSH is higher than the target discharge superheat, the first flow control device (e.g., the suction valve) is generally modulated towards a fully-open position in a manner to attempt to reach the target discharge superheat. When the DSH remains high enough above the target discharge superheat, the second flow control device (e.g., the bypass valve) can be closed or modulated towards a fully-closed position. That is, the first flow control device is modulated to try to reach the target discharge superheat, and a secondary trigger can be set to enable the control of the second flow control device. It is to be understood that the secondary trigger control may be distinct from the closed loop control of the first flow control device which may target a discharge superheat.

It is also to be understood that when a reduced discharge superheat is desirable the modulating of the first flow control device may respond based on a closed loop control and the second flow control device may close or modulate towards a fully-closed position depending on its trigger/control condition (e.g., the secondary trigger). That is, if the DSH is sufficient for the second flow control device to close or be modulated close, it may; but the second flow control device may not close “first” if its trigger condition is not met. This is because the second flow control device may not close or be modulated to close if it may reduce the DSH too much such that the first flow control device may have to be immediately modulated towards a fully-closed position significantly or even cycle the second flow control device back open again.

It is further to be understood that using a combination of the second flow control device open plus modulating the first flow control device can increase the discharge superheat when it is beneficial to the overall cycle efficiency relative to only modulating the first flow control device (which otherwise may add a bigger cycle penalty by adding large amounts of suction pressure drop). That is, the triggers of when to open and/or close the second flow control device need to consider stability, especially when the second flow control device is not modulated but only controlled to be open or close.

It is to be understood that the processes described with reference to the flowcharts of FIGS. 4 and 5 and/or the processes described in other figures may be implemented as computer software programs or in hardware. The computer program product may include a computer program stored in a computer readable non-volatile medium. The computer program includes program codes for performing the method shown in the flowcharts and/or GUIs. The processes and logic flows described in this document can be performed by one or more programmable processors (e.g., controller(s) of an HVACR system) executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., a field programmable gate array, an application specific integrated circuit, or the like.

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors (e.g., controller(s) of an HVACR system), and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random-access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data.

It is to be understood that different features, variations and multiple different embodiments have been shown and described with various details. What has been described in this application at times in terms of specific embodiments is done for illustrative purposes only and without the intent to limit or suggest that what has been conceived is only one particular embodiment or specific embodiments. It is to be understood that this disclosure is not limited to any single specific embodiments or enumerated variations. Many modifications, variations and other embodiments will come to mind of those skilled in the art, and which are intended to be and are in fact covered by both this disclosure. It is indeed intended that the scope of this disclosure should be determined by a proper legal interpretation and construction of the disclosure, including equivalents, as understood by those of skill in the art relying upon the complete disclosure present at the time of filing.

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 screw compressor, a condenser, and an evaporator fluidly connected; a suction pipe connecting the evaporator and the screw compressor; an actuator configured to modulate a first flow control device in the suction pipe; and a controller configured to: determine a discharge superheat of the screw compressor, and control the actuator to modulate the first flow control device to increase the discharge superheat when the discharge superheat is below a first threshold.
  • Aspect 2. The HVACR system of aspect 1, further comprising: a bypass pipe having a second flow control device, wherein the controller is further configured to control the second flow control device to increase the discharge superheat when the discharge superheat is below the first threshold to increase the discharge superheat.
  • Aspect 3. The HVACR system of aspect 2, wherein the bypass pipe is configured to connect an outlet of the compressor and an inlet of the compressor, and to bypass the condenser.
  • Aspect 4. The HVACR system of aspect 2, wherein the second flow control device has a fully-open position, the controller is configured to control the second flow control device towards the fully-open position to increase the discharge superheat.
  • Aspect 5. The HVACR system of aspect 2, wherein the controller is further configured to control the second flow control device to decrease the discharge superheat when the discharge superheat is at or above a second threshold.
  • Aspect 6. The HVACR system of any one of aspects 1-5, wherein the actuator includes a step motor.
  • Aspect 7. The HVACR system of claim any one of aspects 1-6, further comprising at least one sensor, wherein the controller is further configured to determine the discharge superheat based on a measurement from the at least one sensor.
  • Aspect 8. The HVACR system of aspect 7, wherein the at least one sensor includes a pressure sensor and a temperature sensor, and the controller is configured to determine the discharge superheat based on sensed data from the pressure sensor and the temperature sensor.
  • Aspect 9. The HVACR system of any one of aspects 1-8, wherein the first flow control device has a fully-closed position, and the controller is configured to control the actuator to modulate the first flow control device towards the fully-closed position to increase the discharge superheat.
  • Aspect 10. The HVACR system of any one of aspects 1-9, wherein the controller is further configured to control the actuator to modulate the first flow control device to decrease the discharge superheat when the discharge superheat is at or above a second threshold.
  • Aspect 11. A method of operating a heating, ventilation, air conditioning, and refrigeration (HVACR) system, the HVACR system including: a screw compressor, a condenser, and an evaporator fluidly connected; a suction pipe connecting the evaporator and the screw compressor; an actuator configured to modulate a first flow control device in the suction pipe; and a controller, the method comprising: determining a discharge superheat of the screw compressor, and controlling the actuator to modulate the first flow control device to increase the discharge superheat when the discharge superheat is below a first threshold.
  • Aspect 12. The method of aspect 11, wherein the HVACR system further comprises a bypass pipe having a second flow control device, and the method further comprises: controlling the second flow control device to increase the discharge superheat when the discharge superheat is below the first threshold to increase the discharge superheat.
  • Aspect 13. The method of aspect 12, wherein the bypass pipe is configured to connect an outlet of the compressor and an inlet of the compressor, and to bypass the condenser.
  • Aspect 14. The method of aspect 12, wherein the second flow control device has a fully-open position, and the controlling of the second flow control device to increase the discharge superheat includes controlling the second flow control device towards the fully-open position.
  • Aspect 15. The method of aspect 12, further comprising: controlling the second flow control device to decrease the discharge superheat when the discharge superheat is at or above a second threshold.
  • Aspect 16. The method of any one of aspects 11-15, wherein the actuator includes a step motor.
  • Aspect 17. The method of any one of aspects 11-16, wherein the HVACR system further comprises at least one sensor, and the determining of the discharge superheat includes determining the discharge superheat based on a measurement from the at least one sensor.
  • Aspect 18. The method of aspect 17, wherein the at least one sensor includes a pressure sensor and a temperature sensor, and the determining of the discharge superheat includes determining the discharge superheat based on sensed data from the pressure sensor and the temperature sensor.
  • Aspect 19. The method of any one of aspects 11-18, wherein the first flow control device has a fully-closed position, and the controlling of the actuator to modulate the first flow control device to increase the discharge superheat includes controlling the actuator to modulate the first flow control device towards the fully-closed position.
  • Aspect 20. The method of any one of aspects 11-19, further comprising: controlling the actuator to modulate the first flow control device to decrease the discharge superheat when the discharge superheat is at or above a second threshold.

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

With regard to the preceding description, it is to be understood that changes may be made in detail, especially in matters of the construction materials employed and the shape, size, and 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.