Patent Description:
A wide range of applications exists for heating, ventilating, and air conditioning (HVAC) systems. For example, residential, commercial, and industrial systems are used to control temperatures and air in residences and buildings using a fluid, such as a refrigerant. The HVAC systems may circulate the refrigerant through a closed loop between an evaporator where the refrigerant absorbs heat and a condenser where the refrigerant releases heat. As an example, the refrigerant may absorb heat from a first fluid and transfer the heat to a second fluid to ultimately cool the first fluid and/or heat the second fluid. The refrigerant evaporates into a vapor when flowing through the evaporator by absorbing the heat from the first fluid. The compressor then compresses the vapor to cause the pressure and/or temperature of the vapor to rise for subsequent cooling by the second fluid in the condenser, thereby transferring heat from the first fluid to the second fluid.

In some cases, the vapor is superheated at the inlet of the compressor to ensure that the refrigerant is in a vapor state before entering the compressor. To control an amount of superheat of the refrigerant entering the compressor, existing systems include a liquid injection device that cools the vapor within the compressor. For example, the liquid injection device injects liquid refrigerant droplets into the compressor, or at an inlet of the compressor, to adjust an amount of superheat of the vapor entering the compressor and/or a temperature of the vapor exiting the compressor. Unfortunately, liquid injection devices include additional components (e.g., tubing, pumps, nozzles, among others) to inject the liquid refrigerant into the compressor. Additionally, injecting liquid refrigerant into the compressor may reduce a performance of the compressor, and thus, reduce a performance of the HVAC system.

<CIT> discloses a refrigerating/Air-conditioning device including a refrigeration cycle and an expansion valve control means which include a target value switching means that adopts the lower one of a target degree of discharge superheat TdSH plus a high pressure saturation temperature and an upper limit value of the discharge temperature Td as a target value. <CIT> discloses a heating, ventilating, and air conditioning (HVAC) system according to the preamble of claim <NUM>, an one or more tangible, non-transitory machine-readable media according to the preamble of claim <NUM> ad a method according to the preamble of claim <NUM> for controlling an expansion device of a vapor compressor system of the HVAC system.

<CIT> discloses a vapor compression type air conditioner using a CO2 refrigerant that is constituted by connecting a compressor, a gas cooler, an expansion valve, and an evaporator in this order through a pipeline, and is divided into high- and low-pressure sides.

In one embodiment, a heating, ventilating, and air conditioning (HVAC) system according to claim <NUM> is provided.

In another embodiment, one or more tangible, non-transitory machine-readable media according to claim <NUM> is provided.

In another embodiment, a method according to claim <NUM> for controlling an expansion device of a vapor compressor system of the HVAC system is provided.

Embodiments of the present invention are directed to a heating, ventilating, and air conditioning (HVAC) system that adjusts a position of an expansion device (e.g., electronic expansion valve (EEV)) to control an amount of superheat of a refrigerant entering a compressor (e.g., suction superheat) and/or a temperature of refrigerant discharged from the compressor (e.g., discharge temperature). In accordance with embodiments of the present invention, the HVAC system includes one or more control devices that are configured to adjust a position of the expansion device to control suction superheat and/or discharge temperature. As discussed above, existing HVAC systems utilize a liquid injection device that injects liquid refrigerant droplets into the compressor. Unfortunately, the liquid injection device utilizes additional components that increase a cost of the HVAC system. Further, liquid injection devices reduce a performance of the compressor as a result of the liquid refrigerant droplets contacting moving components of the compressor.

Accordingly, modulating the expansion device to control suction superheat and/or discharge temperature of the compressor may eliminate a liquid injection device from the HVAC system and improve performance of the compressor. According to the invention, the expansion device is controlled using a first control module (e.g., a suction superheat module) under a first set of operating parameters of the HVAC system, and the expansion device is controlled using a second control module (e.g., a discharge temperature module) under a second set of operating parameters of the HVAC system. For example, the first control module may be utilized during startup conditions (e.g., for a predetermined amount of time upon initiating operation of the compressor) and/or when an amount of superheat of refrigerant (e.g., determined from a pressure and temperature of the refrigerant) entering the compressor exceeds a first threshold. Additionally, the second control module may be utilized when a temperature of refrigerant discharged from the compressor exceeds a second threshold. In certain embodiments, the HVAC system includes a first controller (e.g., a first proportional, integral, derivative (PID) controller) that includes the first control module and a second controller (e.g., a second PID controller) that includes the second control module. In other embodiments, the HVAC system includes a single controller (e.g., a PID controller) that includes both the first control module and the second control module. In any case, the expansion device is adjusted based on an amount of superheat of refrigerant flowing into the compressor (e.g., suction superheat) and a temperature of refrigerant discharged from the compressor (e.g., discharge temperature). As such, a temperature of the refrigerant is controlled without injecting liquid droplets into the compressor, thereby increasing an efficiency of the compressor and/or the HVAC system.

Turning now to the drawings, <FIG> is a perspective view of an embodiment of an environment for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system <NUM> in a building <NUM> for a typical commercial setting. The HVAC&R system <NUM> includes a vapor compression system <NUM> that may supply a chilled liquid, which may be used to cool the building <NUM>. The HVAC&R system <NUM> may also include a boiler <NUM> to supply warm liquid to heat the building <NUM> and an air distribution system which circulates air through the building <NUM>. The air distribution system can also include an air return duct <NUM>, an air supply duct <NUM>, and/or an air handler <NUM>. In some embodiments, the air handler <NUM> may include a heat exchanger that is connected to the boiler <NUM> and the vapor compression system <NUM> by conduits <NUM>. The heat exchanger in the air handler <NUM> may receive either heated liquid from the boiler <NUM> or chilled liquid from the vapor compression system <NUM>, depending on the mode of operation of the HVAC&R system <NUM>. The HVAC&R system <NUM> is shown with a separate air handler on each floor of building <NUM>, but in other embodiments, the HVAC&R system <NUM> may include air handlers <NUM> and/or other components that may be shared between or among floors.

<FIG> is an embodiment of a vapor compression system <NUM> that can be used in the HVAC unit <NUM> described above. The vapor compression system <NUM> may circulate a refrigerant through a refrigerant loop <NUM> starting with a compressor <NUM>. The circuit may also include a condenser <NUM>, an expansion valve(s) or device(s) <NUM>, and an evaporator <NUM>. The vapor compression system <NUM> may further include a control panel <NUM> that has an analog to digital (A/D) converter <NUM>, a microprocessor <NUM>, a non-volatile memory <NUM>, and/or an interface board <NUM>. The control panel <NUM> and its components may function to regulate operation of the vapor compression system <NUM> based on feedback from an operator, from sensors of the vapor compression system <NUM> that detect operating conditions, and so forth.

In some embodiments, the vapor compression system <NUM> may use one or more of a variable speed drive (VSDs) <NUM>, a motor <NUM>, the compressor <NUM>, the condenser <NUM>, the expansion valve or device <NUM>, and/or the evaporator <NUM>. The motor <NUM> may drive the compressor <NUM> and may be powered by the variable speed drive (VSD) <NUM>. The VSD <NUM> receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor <NUM>. In other embodiments, the motor <NUM> may be powered directly from an AC or direct current (DC) power source. The motor <NUM> may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor.

The compressor <NUM> compresses a refrigerant vapor and delivers the vapor to the condenser <NUM> through a discharge passage. In some embodiments, the compressor <NUM> may be a centrifugal compressor. The refrigerant vapor delivered by the compressor <NUM> to the condenser <NUM> may transfer heat to a fluid passing across the condenser <NUM>, such as ambient or environmental air <NUM>. The refrigerant vapor may condense to a refrigerant liquid in the condenser <NUM> as a result of thermal heat transfer with the environmental air <NUM>. The liquid refrigerant from the condenser <NUM> may flow through the expansion device <NUM> to the evaporator <NUM>.

The liquid refrigerant delivered to the evaporator <NUM> may absorb heat from another air stream, such as a supply air stream <NUM> provided to the building <NUM> or the residence <NUM>. For example, the supply air stream <NUM> may include ambient or environmental air, return air from a building, or a combination of the two. The liquid refrigerant in the evaporator <NUM> may undergo a phase change from the liquid refrigerant to a refrigerant vapor. In this manner, the evaporator <NUM> may reduce the temperature of the supply air stream <NUM> via thermal heat transfer with the refrigerant. Thereafter, the vapor refrigerant exits the evaporator <NUM> and returns to the compressor <NUM> by a suction line to complete the cycle.

In some embodiments, the vapor compression system <NUM> may further include a reheat coil in addition to the evaporator <NUM>. For example, the reheat coil may be positioned downstream of the evaporator relative to the supply air stream <NUM> and may reheat the supply air stream <NUM> when the supply air stream <NUM> is overcooled to remove humidity from the supply air stream <NUM> before the supply air stream <NUM> is directed to the building <NUM> or the residence <NUM>.

It should be appreciated that any of the features described herein may be incorporated with the HVAC unit <NUM>, the residential heating and cooling system <NUM>, or other HVAC systems. Additionally, while the features disclosed herein are described in the context of embodiments that directly heat and cool a supply air stream provided to a building or other load, embodiments of the present invention may be applicable to other HVAC systems as well. For example, the features described herein may be applied to mechanical cooling systems, free cooling systems, chiller systems, or other heat pump or refrigeration applications.

As discussed above, in some embodiments, the expansion device <NUM> is an electronic expansion valve (EEV) that may be adjusted to control a temperature of refrigerant entering and/or exiting the compressor <NUM>. Existing systems utilize a liquid injection system to control a temperature of the refrigerant in the compressor <NUM>. Unfortunately, liquid injections systems may reduce an efficiency of the compressor <NUM> and/or the HVAC unit <NUM>. Accordingly, embodiments of the present invention are directed to control of the expansion device <NUM> using a first control module (e.g., a suction superheat module) under a first set of operating parameters of the HVAC system and a second control module (e.g., a discharge temperature module) under a second set of operating parameters of the HVAC system. For example, the first control module may be utilized during startup conditions (e.g., for a predetermined amount of time upon initiating operation of the compressor <NUM>) and/or when a temperature of refrigerant entering the compressor <NUM> exceeds a first threshold. Additionally, the second control module may be utilized when a temperature of refrigerant discharged from the compressor <NUM> exceeds a second threshold.

<FIG> illustrates control circuitry <NUM> that may be used to control operation of the expansion device <NUM> in the vapor compression system <NUM> described in <FIG>. A position of the expansion device <NUM> may be adjusted based on an amount of superheat of refrigerant entering the compressor <NUM> (e.g., a suction port of the compressor <NUM>) and/or a temperature of refrigerant exiting the compressor <NUM> (e.g., a discharge port of the compressor <NUM>). That is, the control circuitry <NUM> may adjust a position of the expansion device <NUM> to obtain a flow of refrigerant that causes an amount of superheat of the refrigerant at the outlet of the evaporator <NUM> and/or the inlet of the compressor <NUM> to reach a target superheat. Additionally, the control circuitry <NUM> may adjust a position of the expansion device <NUM> to reach a flow rate of refrigerant that causes a temperature of the refrigerant discharged from the compressor <NUM> to be reach a target discharge temperature. The control circuitry <NUM> may include a controller <NUM>, such as a microcontroller. The controller <NUM> may include a processor <NUM> operatively coupled to memory <NUM> to execute software, such as software for controlling a position of the expansion device <NUM>. Moreover, the processor <NUM> may include multiple processors, one or more "general-purpose" microprocessors, one or more special-purpose microprocessors, and/or one or more application specific integrated circuits (ASICS), or some combination thereof. For example, the processor <NUM> may include one or more reduced instruction set (RISC) processor, advanced RISC machine (ARM) processor, performance optimization with enhanced RISC (PowerPC) processor, field-programmable gate array (FPGA) integrated circuit, graphics processing unit (GPU), or any other suitable processing device.

The memory <NUM> may include a volatile memory, such as random access memory (RAM), nonvolatile memory, such as read-only memory (ROM), flash memory, or any combination thereof. The memory <NUM> may store a variety of information that may be used for various purposes. For example, the memory <NUM> may store processor- executable instructions (e.g., firmware or software) for the processors <NUM> to execute, such as instructions for controlling the expansion device <NUM>.

The processor <NUM> may execute instructions to receive one or more signals from one or more sensors of the vapor compression system <NUM>. For example, the control circuitry <NUM> (e.g., control system) may include sensors <NUM>, <NUM>, <NUM>, <NUM>, and/or <NUM> positioned on or about various components of the vapor compression system <NUM>. For instance, the control circuitry <NUM> may include a temperature sensor <NUM> and a pressure sensor <NUM> positioned on an outlet of the evaporator <NUM>. The temperature sensor <NUM> may send a signal to the controller <NUM> indicating a temperature of the refrigerant as the refrigerant leaves the evaporator <NUM>. Similarly, the pressure sensor <NUM> may send a signal to the controller <NUM> indicating a pressure of the refrigerant leaving the evaporator <NUM>. The processor <NUM> may receive each of the respective signals from the temperature sensor <NUM> and the pressure sensor <NUM> and determine a superheat of the refrigerant as the refrigerant exits the evaporator <NUM> (and/or enters the compressor <NUM>), which indicates the amount of heat in the refrigerant with respect to a saturation point of the refrigerant. For instance, the processor <NUM> may determine the superheat by utilizing a lookup table stored in the memory <NUM> that defines a relationship of the superheat with respect to the temperature and the pressure of the refrigerant at the outlet of the evaporator <NUM> (and/or at the inlet of the compressor <NUM>). The lookup table may be based on physical properties (e.g., saturation point, quantity, etc.) of the refrigerant.

Additionally, the control circuitry <NUM> may include a temperature sensor <NUM> (e.g., a second temperature sensor) that monitors a temperature of the refrigerant discharged from the compressor <NUM>. As such, the processor <NUM> may determine a discharge temperature of the refrigerant from the compressor <NUM> and compare the discharge temperature to a threshold temperature, a predetermined temperature range, or a combination thereof. Additionally or alternatively, the control circuitry <NUM> may include a temperature sensor <NUM> (e.g., a third temperature sensor) that monitors a temperature of the motor <NUM> that is configured to drive the compressor <NUM>. As such, the processor <NUM> may determine a motor temperature and compare the motor temperature to a threshold motor temperature, a predetermined motor temperature range, or a combination thereof. In some embodiments, an ambient temperature sensor <NUM> may be positioned proximate to the vapor compression system <NUM> to detect temperature of the surrounding air. While the sensors <NUM>, <NUM>, <NUM>, <NUM>, and/or <NUM> are described in detail, any suitable sensors that detect operating conditions of the vapor compression system <NUM> may be used.

The processor <NUM> may receive one or more signals indicating operating conditions (e.g., temperature, pressure, vibrations, etc.) of the vapor compression system <NUM>. The processor <NUM> may then be configured to initiate and/or utilize control modules of the processor <NUM> based on the one or more signals indicative of operating conditions of the vapor compression system <NUM>. For example, the processor <NUM> may compare a predetermined amount of superheat (e.g., target superheat or setpoint superheat) of the refrigerant leaving the evaporator <NUM> (and/or entering the compressor <NUM>) with a measured amount of superheat of the refrigerant leaving the evaporator <NUM> (and/or entering the compressor <NUM>). Additionally, the processor <NUM> may compare a predetermined discharge temperature (e.g., target discharge temperature or setpoint discharge temperature) of the refrigerant exiting the compressor <NUM> with a measured discharge temperature of the refrigerant exiting the compressor <NUM>. The processor <NUM> may then determine a suitable control module to utilize and/or activate based on the comparisons performed by the processor <NUM>.

When the processor <NUM> operates under a first control module (e.g., suction superheat control), the processor <NUM> adjusts the expansion device <NUM> based on a difference between the target superheat and the measured superheat of the refrigerant leaving the evaporator <NUM> and/or entering the compressor <NUM>. For example, if the target superheat is <NUM> degrees Fahrenheit (°F) above the saturation point of the refrigerant and the measured superheat (e.g., based on a temperature and a pressure of the refrigerant exiting the evaporator <NUM> and/or entering the compressor <NUM>) is <NUM> °F above the saturation point, the processor <NUM> may send a signal to an actuator <NUM> (e.g., a motor or a stepper motor) of the expansion device <NUM> to adjust a position of the expansion device <NUM>. As such, the position of the expansion device <NUM> may be adjusted to reduce a flow rate of refrigerant directed to the evaporator <NUM>, thereby increasing an amount of superheat of the refrigerant, to ultimately achieve the target superheat of <NUM> °F.

Additionally, when the processor <NUM> operates under a second control module (e.g., discharge temperature control), the processor <NUM> adjusts the expansion device <NUM> based on a difference between the target discharge temperature and the measured discharge temperature of the refrigerant exiting the compressor <NUM>. For example, when the target discharge temperature is <NUM> °F and the measured discharge temperature is <NUM> °F, the processor <NUM> adjusts a position of the expansion device <NUM> via the actuator <NUM>. As such, the position of the expansion device <NUM> is adjusted to reduce a flow rate of refrigerant through the compressor <NUM> and to increase a temperature of the refrigerant discharged from the compressor <NUM>. Further, in some embodiments, the processor <NUM> may adjust the position of the expansion device <NUM> based on a temperature of the motor <NUM> driving the compressor <NUM> (e.g., measured by the sensor <NUM>) in addition to, or in lieu, of adjusting the position of the expansion device <NUM> based on the discharge temperature of the refrigerant.

The controller <NUM> may include one or more proportional-integral-derivative (PID) controllers, fuzzy logic controllers, or any other suitable controllers <NUM> to perform the control modules that adjust the expansion device <NUM> to achieve the target superheat, the target discharge temperature, and/or a target motor temperature. The controller <NUM> switches between various control modules (e.g., a suction superheat control module, a discharge temperature control module, and/or a motor temperature control module) based on measured operating parameters from the one or more sensors <NUM>, <NUM>, <NUM>, <NUM>, and/or <NUM>.

For example, <FIG> is a block diagram of a flow chart <NUM> that illustrates logic performed by the controller <NUM> to operate and switch between control modules. For example, at block <NUM>, the compressor <NUM> is inactive (e.g., powered off or not operating). As such, the vapor compression system <NUM> may not circulate refrigerant. Thus, the expansion device <NUM> is not adjusted to control a flow rate of refrigerant to the evaporator <NUM> because refrigerant is not circulated through the vapor compression system <NUM> via the compressor <NUM>.

At block <NUM>, a startup sequence of the compressor <NUM> may be initiated, and the controller <NUM> operates under a first control module <NUM> (e.g., suction superheat control). For example, the first control module <NUM> may include the startup sequence, whereby the controller <NUM> sends a signal to the expansion device <NUM> adjusting a position of the expansion device <NUM> to a startup position for a predetermined amount of time (e.g., <NUM> second, <NUM> seconds, <NUM> seconds, <NUM> seconds, <NUM> seconds, or more than <NUM> seconds). For example, when the expansion device <NUM> is in the startup position, the expansion device <NUM> may enable a relatively high flow rate of refrigerant to circulate through the vapor compression system <NUM> so that the vapor compression system <NUM> may quickly reach steady-state operation.

Once the predetermined amount of time for the startup position of the expansion device <NUM> has lapsed, the controller <NUM> may undergo a suction superheat control ramp of the first control module <NUM>, at block <NUM>. For example, once the vapor compression system <NUM> reaches substantially steady state operation, the controller <NUM> adjusts the expansion device <NUM> so that the superheat of refrigerant leaving the evaporator <NUM> and entering the compressor <NUM> (e.g., a suction port of the compressor <NUM>) reaches a target superheat. As such, the controller <NUM> sends a second signal to the expansion device <NUM> to adjust a position of the expansion device <NUM> based on feedback received from the sensors <NUM>, <NUM>, <NUM>, <NUM>, and/or <NUM>. In some embodiments, the controller <NUM> is configured to adjust the expansion device <NUM> to either a threshold position (e.g., a predetermined position that circulates a minimum amount of refrigerant through the vapor compression system <NUM>) or a command position that is based on the target superheat. For example, the command position is determined by the controller <NUM> as a position of the expansion device <NUM> that enables the superheat of refrigerant leaving the evaporator <NUM> and entering the compressor <NUM> to reach the target superheat. The controller <NUM> compares the threshold position to the command position and selects the position that corresponds to a higher flow rate of refrigerant through the vapor compression system <NUM>. In other words, the controller <NUM> may correlate a position of the expansion device <NUM> with a value that is proportional to the flow rate of refrigerant through the vapor compression system <NUM>. As such, the controller <NUM> selects the position (e.g., the threshold position or the command position) that includes the higher value so that refrigerant is not blocked from circulating through the vapor compression system <NUM>.

Additionally, once the measured superheat of the refrigerant reaches the target superheat, the controller <NUM> may operate under suction superheat control of the first control module <NUM>, at block <NUM>. In some embodiments, suction superheat control may be similar to the suction superheat control ramp, as shown in block <NUM>, with smaller adjustments to the position of the expansion device <NUM> (e.g., suction superheat control ramp may make relatively large adjustments to the position of the expansion device <NUM> to reach the target superheat quickly). In other words, suction superheat control at block <NUM> is utilized to maintain the measured superheat of refrigerant leaving the evaporator <NUM> and entering the compressor <NUM> at the target superheat. Thus, relatively minor adjustments to the expansion device <NUM> are made during the suction superheat control at block <NUM>.

During suction superheat control at block <NUM>, the controller <NUM> sends a third signal to the expansion device <NUM> to adjust a position of the expansion device <NUM> based on feedback received from the sensors <NUM>, <NUM>, <NUM>, <NUM>, and/or <NUM>. The controller <NUM> is configured to adjust the expansion device <NUM> to either a threshold position (e.g., a predetermined position that circulates a minimum amount of refrigerant through the vapor compression system <NUM>) or a command position that is based on the target superheat. In some embodiments, the threshold position of the suction superheat control of block <NUM> is the same as the threshold position of the suction superheat control ramp of block <NUM>. However, in other embodiments, the threshold position of the suction superheat control of block <NUM> is different from the threshold position of the suction superheat control ramp of block <NUM>. In any case, the command position is determined by the controller <NUM> as a position of the expansion device <NUM> that enables the superheat of refrigerant leaving the evaporator <NUM> and entering the compressor <NUM> to reach the target superheat. The controller <NUM> compares the threshold position to the command position and selects the position that corresponds to a higher flow rate of refrigerant through the vapor compression system <NUM> (or a higher value corresponding to flow rate of refrigerant through the vapor compression system <NUM>) so that refrigerant is not blocked from circulating through the vapor compression system <NUM>.

As discussed above, the controller <NUM> is configured to switch between the first control module <NUM> and a second control module <NUM> based on operating parameters of the vapor compression system <NUM> monitored by the sensors <NUM>, <NUM>, <NUM>, <NUM>, and/or <NUM>. For example, the controller <NUM> may be configured to switch from the first control module <NUM> (e.g., suction superheat control) to the second control module <NUM> (e.g., discharge temperature control) based at least on the discharge temperature of the refrigerant leaving the compressor <NUM> (e.g., as measured by sensor <NUM>). The controller <NUM> may compare a measured discharge temperature from the sensor <NUM> to one or more discharge temperature thresholds stored in the memory <NUM> of the controller <NUM>. In some embodiments, the controller <NUM> switches from the first control module <NUM> to the second control module <NUM> when the measured discharge temperature exceeds a first discharge temperature threshold for a predetermined amount of time (e.g., <NUM> second, <NUM> seconds, <NUM> seconds, <NUM> seconds, <NUM> seconds, or more than <NUM> seconds). Further, the controller may be configured to immediately switch from the first control module <NUM> to the second control module <NUM> when the measured discharge temperature exceeds a second discharge temperature threshold, where the second discharge temperature threshold is greater than the first discharge temperature threshold by an offset amount. In some embodiments, the offset amount between the first discharge temperature threshold and the second discharge temperature threshold is between <NUM> °F and <NUM> °F, between <NUM> °F and <NUM> °F, or between <NUM> °F and <NUM> °F.

When the controller <NUM> operates under the second control module <NUM>, the controller <NUM> adjusts a position of the expansion device <NUM> based on the measured discharge temperature to achieve the target discharge temperature, as shown in block <NUM>. For example, when the measured discharge temperature falls below the target discharge temperature, the controller <NUM> sends a signal to adjust a position of the expansion device <NUM> to reduce a flow of the refrigerant through the vapor compression system <NUM> (e.g., reducing the flow of refrigerant through the evaporator <NUM> increases a temperature of the refrigerant discharged from the compressor <NUM>). Similarly, when the measured discharge temperature exceeds the target discharge temperature, the controller <NUM> sends a signal to adjust the position of the expansion device <NUM> to increase a flow of the refrigeration through the vapor compression system <NUM> (e.g., increasing the flow of refrigerant through the evaporator <NUM> reduces a temperature of the refrigerant discharged from the compressor <NUM>). As discussed above, in other embodiments, the second control module <NUM> may adjust the position of the expansion device <NUM> based on a temperature of the motor <NUM>, in addition to or in lieu of, the discharge temperature of the refrigerant from the compressor <NUM>.

As discussed above, the signal sent from the controller <NUM> may include a position of the expansion device <NUM> that is selected from a threshold position (e.g., e.g., a predetermined position that circulates a minimum amount of refrigerant through the vapor compression system <NUM>) and a command position that is based on the measured discharge temperature. In some embodiments, the threshold position of the discharge temperature control at block <NUM> is the same or different as the threshold position of the suction superheat ramp control at block <NUM> and/or the suction superheat control at block <NUM>. The command position is determined by the controller <NUM> as a position of the expansion device <NUM> that enables the discharge temperature of refrigerant leaving the compressor <NUM> to reach the target discharge temperature. The controller <NUM> compares the threshold position to the command position and selects the position that corresponds to a higher flow rate of refrigerant through the vapor compression system <NUM>. In other words, the controller <NUM> may correlate a position of the expansion device <NUM> with a value that is proportional to the flow rate of refrigerant through the vapor compression system <NUM>. As such, the controller <NUM> selects the position (e.g., the threshold position or the command position) that includes the higher value so that refrigerant is not blocked from circulating through the vapor compression system <NUM>.

In some embodiments, the second control module <NUM> overrides the first control module <NUM> (e.g., the suction superheat override). For example, in some cases, adjusting the expansion device <NUM> to achieve the target discharge temperature causes the suction superheat to decrease below a predetermined amount. As such, the controller <NUM> overrides the first control module <NUM> despite the superheat of the refrigerant falling below the target superheat.

Additionally, the controller <NUM> receives feedback from the sensors <NUM> and <NUM> indicative of the temperature and pressure of the refrigerant leaving the evaporator <NUM> (and/or entering the compressor <NUM>). As discussed above, the temperature and pressure of the refrigerant leaving the evaporator <NUM> (and/and entering the compressor <NUM>) may be utilized to determine an amount of superheat of the refrigerant. The controller <NUM> may switch from the second control module <NUM> to the first control module <NUM> (e.g., from block <NUM> to block <NUM>) when the measured amount of superheat (e.g., determined from the feedback from the sensors <NUM> and <NUM>) exceeds a first superheat threshold for a predetermined amount of time (e.g., <NUM> second, <NUM> seconds, <NUM> seconds, <NUM> seconds, <NUM> seconds, or more than <NUM> seconds). Additionally, the controller <NUM> may immediately switch from the second control module <NUM> to the first control module <NUM> when the measured amount of superheat exceeds a second superheat threshold, where the second superheat threshold is greater than the first superheat threshold. The controller <NUM> may then operate under the first control module <NUM> and adjust the position of the expansion device <NUM> based on the measured amount of superheat of the refrigerant leaving the evaporator <NUM> (and/or entering the compressor <NUM>).

Claim 1:
A heating, ventilating, and air conditioning, HVAC, system, comprising:
- a vapor compression system (<NUM>) comprising a refrigerant;
- a compressor (<NUM>) of the vapor compression system (<NUM>) configured to circulate the refrigerant through the vapor compression system (<NUM>);
- an expansion device (<NUM>) of the vapor compression system (<NUM>) configured to adjust a flow of the refrigerant through the vapor compression system (<NUM>); and
- a controller (<NUM>) configured to operate according to a first control module (<NUM>) to adjust a position of the expansion device (<NUM>) based on a measured amount of superheat of the refrigerant entering the compressor (<NUM>) to achieve a target amount of superheat, and to operate according to a second control module (<NUM>) to adjust the position of the expansion device (<NUM>) based on a measured discharge temperature of the refrigerant leaving the compressor (<NUM>) to achieve a target discharge temperature,
characterized in that
the controller (<NUM>) is configured to switch from the first control module (<NUM>) to the second control module (<NUM>) when the measured discharge temperature of the refrigerant leaving the compressor (<NUM>) exceeds a first discharge temperature threshold for a first predetermined amount of time or when the measured discharge temperature of the refrigerant leaving the compressor (<NUM>) exceeds a second discharge temperature threshold, wherein the second discharge temperature threshold is greater than the first discharge temperature threshold;
wherein the controller (<NUM>) is configured to switch between the first control module (<NUM>) and the second control module (<NUM>) based on the measured amount of superheat of the refrigerant entering the compressor (<NUM>) and the measured discharge temperature of the refrigerant leaving the compressor (<NUM>); and
wherein the controller (<NUM>) is configured to switch from the second control module (<NUM>) to the first control module (<NUM>) when the measured amount of superheat of the refrigerant entering the compressor (<NUM>) exceeds a first superheat threshold for a second predetermined amount of time or when the measured amount of superheat of the refrigerant entering the compressor (<NUM>) exceeds a second superheat threshold, and wherein the second superheat threshold is greater than the first superheat threshold.