Operational envelope control of an HVAC compressor

A heating, ventilation, and air conditioning (HVAC) system includes a compressor having a discharge port and a suction port, a first sensor configured to provide feedback corresponding to a first temperature of the working fluid exiting the compressor proximate the discharge port, a second sensor configured to provide feedback corresponding to a second temperature of the working fluid entering the compressor proximate the suction port, and an automation controller storing data indicative of an operational envelope. The operational envelope defines compressor operation coordinates corresponding to a range of suction temperatures and a range of discharge temperatures inside and outside of a target region of the operational envelope, and the automation controller is configured to control a target range of compressor speeds based on a comparison of the target region to an operation coordinate defined by the feedback from the first sensor and the feedback from the second sensor.

BACKGROUND

The present disclosure relates generally to heating, ventilation, and air conditioning (HVAC) systems, and specifically, to controlling operation of a component in HVAC systems.

Environmental control systems are utilized in residential, commercial, and industrial environments to control environmental properties, such as temperature and humidity, for occupants of the respective environments. The environmental control system may control the environmental properties through control of an air flow delivered to and ventilated from the environment. For example, an HVAC system may transfer heat between the air flow and refrigerant flowing through the system. The HVAC system may use a compressor to pressurize the refrigerant in facilitating the heat transfer. It is now recognized that existing compressors may shut down or otherwise operate at reduced efficiencies at certain superheated or subcooled conditions of the HVAC system.

SUMMARY

In one embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a compressor having a discharge port and a suction port, a first sensor configured to provide feedback corresponding to a first temperature of the working fluid exiting the compressor proximate the discharge port, a second sensor configured to provide feedback corresponding to a second temperature of the working fluid entering the compressor proximate the suction port, and an automation controller storing data indicative of an operational envelope. The operational envelope defines compressor operation coordinates corresponding to a range of suction temperatures and a range of discharge temperatures inside and outside of a target region of the operational envelope, and the automation controller is configured to control a target range of compressor speeds based on a comparison of the target region to an operation coordinate defined by the feedback from the first sensor and the feedback from the second sensor.

In one embodiment, a heating, ventilation, and air conditioning (HVAC) system, includes a compressor having a discharge port and a suction port, where the compressor is configured to compress a working fluid, an automation controller configured to receive feedback from a first sensor corresponding to a first temperature of the working fluid exiting the compressor proximate to the discharge port of the compressor, receive feedback from a second sensor corresponding to a second temperature of the working fluid entering the compressor proximate to the suction port of the compressor, compare an operation coordinate defined by the feedback from the first sensor and the feedback from the second sensor with a target region of an operational envelope, where the operational envelope defines compressor operation coordinates corresponding to a range of suction temperatures and a range of discharge temperatures inside and outside of the target region of the operational envelope, and control a target speed range of the compressor based at least on the comparison of the operation coordinate defined by the feedback from the first sensor and the feedback from the second sensor with the target region of the operational envelope.

In one embodiment, a heating, ventilation, and air conditioning (HVAC) controller includes a tangible, non-transitory, computer-readable medium comprising computer-executable instructions which, when executed, are configured to cause a processor to receive feedback from a first sensor corresponding to a first temperature of a working fluid exiting a compressor proximate to a discharge port of the compressor, receive feedback from a second sensor corresponding to a second temperature of the working fluid entering the compressor proximate to a suction port of the compressor, compare an operation coordinate defined by the feedback from the first sensor and the feedback from the second sensor with a target region of an operational envelope, where the operational envelope defines compressor operation coordinates corresponding to a range of suction temperatures and a range of discharge temperatures inside and outside of the target region of the operational envelope, and control a target speed range of the compressor based at least on the comparison of the operation coordinate defined by the feedback from the first sensor and the feedback from the second sensor with the target region of the operational envelope.

DETAILED DESCRIPTION

The present disclosure is directed to heating, ventilation, and air conditioning (HVAC) systems that use compressors to facilitate heat transfer between an air flow and a refrigerant. For example, the air flow may transfer heat to the refrigerant in an evaporator, which evaporates the refrigerant from a liquid phase into a gas phase. The compressor pressurizes the refrigerant to circulate the refrigerant along a refrigerant loop. The refrigerant may then be cooled in a condenser, such as via fans, and subsequently return to the evaporator to absorb additional heat from the air flow.

During operation of the HVAC system, the compressor may run at various speeds. The speed of the compressor may change based on the operational parameters of the system, such as ambient temperature, desired air flow temperature, a flow rate of the air flow, a suction temperature of refrigerant entering the compressor, a discharge temperature of refrigerant exiting the compressor, or any combination thereof. In some embodiments, the suction temperature may be a saturated suction temperature of the refrigerant, or the temperature at which the refrigerant transforms from a liquid into a gas in the evaporator. In some embodiments, the discharge temperature may be a saturated discharge temperature of the refrigerant, or the temperature at which the refrigerant transforms from a gas into a liquid in the condenser. Operating the compressor when the refrigerant is at certain suction temperatures and discharge temperatures may also affect a longevity and efficiency of the compressor.

Thus, in accordance with certain embodiments of the present disclosure, it is presently recognized that adjusting the compressor speed based on operational parameters of the system, such as suction temperature and discharge temperature, may enable the compressor to operate at a speed or a range of speeds that efficiently pressurizes the refrigerant while increasing a longevity of the compressor. Specifically, an operating speed range of the compressor may be adjusted based on feedback corresponding to the suction temperature and/or the discharge temperature of the refrigerant, to enhance operation of the compressor. Indeed, the operating speed range of the compressor may be adjusted based on any operating parameter that corresponds to suction temperature and/or discharge temperature, such as suction pressure, discharge pressure, a flow rate of refrigerant entering or exiting the compressor, a speed of a motor driving the compressor, and/or other suitable parameters.

The operating parameters may be represented graphically or tabularly as an operational compressor envelope. As used herein, the operational compressor envelope is a series of data encompassing a range of compressor operation coordinates indicative of the operating parameters inside and outside of a target region of the operational compressor envelope. As used herein, the target region represents a range of the operating parameters that limits stress placed on the compressor. For example, threshold operating parameters, operating parameter ratios, and/or allowable differences between operating parameters may be determined that ensure proper lubrication of compressor components and limit overloading of the compressor components. Values of such parameters may be determined at least via experimental testing and utilized to form the target region.

Additionally or alternatively, the target region includes a range of operating parameters that enable the compressor to operate above a threshold efficiency or within a range of compression ratios. As used herein, compressor efficiency may refer to a ratio of an actual power input to a theoretical power input for an isentropic process that achieves the same pressure differential. In some embodiments, the threshold efficiency may be above 40% efficiency, above 60% efficiency, above 80% efficiency, above 90% efficiency, above 95% efficiency, or above another suitable percentage of efficiency. As used herein, a compression ratio is a ratio of discharge pressure to suction pressure. The range of compression ratios may be based on a design compression ratio of the compressor, which is determined from an operating capacity of the compressor.

Further still, the target region may be determined via a low threshold suction temperature, a low threshold discharge temperature, a low threshold compression ratio, a high threshold suction temperature, a high threshold discharge temperature, and/or a high threshold compression ratio. In some cases, the low threshold suction temperature is based on a density and/or mass flow rate of working fluid flowing through the compressor. The low threshold discharge temperature may be based on a condensation temperature of the working fluid flowing through the compressor. Additionally, the low threshold compression ratio may be based on the mass flow rate of the working fluid that leads to a low discharge superheat and/or reduced lubrication. The high threshold suction temperature may be based on forces applied to various compressor components, such as bearings. Further, the high threshold discharge temperature may be based on a voltage supplied to a motor of the compressor and/or a temperature of motor windings. Further still, the high threshold compression ratio may be based on an amount of discharge superheat or an amount of suction superheat.

In some embodiments, the operating parameters include suction temperature and discharge temperature of the refrigerant in the compressor. As such, during operation of the compressor, a current value of the suction temperature and a current value of the discharge temperature generates an operational coordinate point on a graph or a table. The operational coordinate point is compared to the target region of the operational compressor envelope. In some existing systems, when the operational coordinate point is determined to be outside of the target region, the compressor is shut down. However, embodiments of this disclosure adjust the speed range of the compressor when the operational coordinate is determined to be outside of the target region of the operational envelope, in order to attempt to return the operational coordinate point within the target region. Although this disclosure focuses on adjusting compressor speed based on the suction and discharge temperature of the refrigerant, it should be appreciated that other embodiments may include adjusting other components of HVAC systems using other operating parameters to enable the compressor to operate within the operation envelope.

As noted above, HVAC systems may use compressors, such as the compressor42ofFIG. 2or the compressor74ofFIG. 4. The compressor may pressurize refrigerant flowing through the HVAC system to facilitate heat transfer between the refrigerant and an air flow. A speed of the compressor may be adjusted to efficiently pressurize the refrigerant and/or to increase a longevity of the compressor. The operating speed of the compressor may be adjusted based on a suction temperature of the refrigerant entering the compressor and a discharge temperature of the refrigerant exiting the compressor, both of which may affect performance of the HVAC system. Monitoring the suction temperature and the discharge temperature may determine if the compressor and/or the HVAC system are operating within a target efficiency range or at another target performance level. In accordance with present embodiments, adjusting the compressor speed in response to the suction and/or discharge temperatures being outside of a target region of an operational compressor envelope may increase a longevity of the compressor. For example, the compressor may operate within a target range of speeds. If it is detected that the compressor is operating outside of the target region of the operational compressor envelope, the target range of speeds of the compressor may be adjusted until it is determined that the compressor is operating within the target region of the operational compressor envelope. As such, the target range of speeds may be adjusted based on feedback indicative of the suction and/or the discharge temperatures.

FIG. 5is an embodiment of an HVAC system99that includes the compressor74, which may be adjusted using control schemes of the present disclosure. For instance, it should be recognized that the control schemes disclosed herein with reference toFIGS. 5-11may be performed using an automation controller, such as the control board48and/or the control panel82. Specifically, a microprocessor of the automation controller, such as the microprocessor86, may execute instructions stored on memory, such as the non-volatile memory88, to perform the control schemes disclosed herein. The HVAC system99may be a rooftop unit such as the HVAC unit12, a split unit such as the residential heating and cooling system50, or another HVAC system. Similar to the vapor compression system72ofFIG. 4, the HVAC system99is configured to circulate a refrigerant from the compressor74to the condenser76, from the condenser76to the expansion valve or device78, from the expansion valve or device78to the evaporator80, and from the evaporator80back to the compressor74. The operating speed of the compressor74may be adjusted, such as by the control panel82. To determine if the speed of the compressor74should be adjusted, the HVAC system99includes a first sensor100and a second sensor101. The first sensor100is configured to measure a suction temperature of the refrigerant entering the compressor74from the evaporator80and the second sensor101is configured to measure a discharge temperature of the refrigerant exiting the compressor74. As such, the first sensor100may be positioned proximate to a suction port, or inlet, of the compressor74and the second sensor101may be positioned proximate to a discharge port, or outlet, of the compressor74. In other words, the first sensor100and the second sensor101may be positioned with respect to the compressor74to monitor a temperature of the refrigerant entering the compressor and a temperature of the refrigerant exiting the compressor, respectively. The first sensor100and the second sensor101may be communicatively coupled to the control panel82and may be any suitable instrument configured to transmit feedback associated with the temperatures of the refrigerant. As such, the control panel82uses the feedback to determine if adjustments should be made to the speed of the compressor74.

Specifically, the control panel82uses the feedback to generate an operational coordinate point associated with the performance of the HVAC system99based on suction temperatures and discharge temperatures of the refrigerant. In some embodiments, the operational coordinate is compared to an operational compressor envelope that encompasses compressor operation coordinates corresponding to a range of suction temperatures and a range of discharge temperatures inside and outside of a target region of the operational compressor envelope. The target region of the operational compressor envelope may include a set of the compressor operation coordinates that enable the HVAC system99to operate efficiently without imposing undesired stress on components of the HVAC system99, and specifically the compressor74. The operational coordinate point determined by the control panel82is a compressor operation coordinate that represents the current operating status of the compressor74. Based on a comparison of the coordinate point with respect to the target region of the compressor operational envelope, the control panel82determines if the speed of the compressor74should be adjusted. For example, the control panel82may determine whether or not the operational coordinate point is within the target region of the operational compressor envelope or outside of the target region of the operational compressor envelope to adjust the speed of the compressor74.

To illustrate the aforementioned operational envelope,FIG. 6is an embodiment of a control scheme102, or the operational compressor envelope, which visually represents the performance of the HVAC system99and may be used to control the compressor74in the HVAC system99. The control scheme102includes an axis103representing the suction temperature of a refrigerant entering the compressor74and an axis104representing the discharge temperature of the refrigerant exiting the compressor74. As such, an operational coordinate is determined by matching a value of the suction temperature on the axis103with a value of the discharge temperature on the axis104. The location of the operational coordinate may indicate a performance of the compressor74. For example, an inner region106, or target region, of the control scheme102represents the normal operating conditions of the compressor74as determined by the suction and discharge temperatures. As used herein, normal operating conditions refer to operating conditions of the compressor74that enable the HVAC system99to perform efficiently without imposing undesired stress on components of the HVAC system99. A boundary108defining the inner region106is indicative of the target temperature ranges of the refrigerant. Put in other words, operating within the inner region106increases a longevity of the compressor74. When the compressor74is operating within the inner region106, the speed of the compressor74may vary between a target range of operating speeds, including a lower threshold speed and an upper threshold speed. The lower threshold speed and the upper threshold speed may vary among different HVAC systems, and may be based on the application of the compressor74, the application of the HVAC system99, and/or the compressor specifications, for example. At any given time during operation within the inner region106, the speed of the compressor74may be set at a value within the target range of operating speeds. While the compressor74is operating within the inner region106, the lower threshold speed and the upper threshold speed may be maintained such that the target range of operating speeds is constant.

In some embodiments, a deadband region110is included outside of the inner region106. As illustrated in the control scheme102, the deadband region110is defined by the boundary108and by a boundary112. The boundary112is offset from the boundary108by an offset value113. In some embodiments, the offset value113is constant along the boundaries108,112, such that the boundary112forms substantially the same shape compared to the boundary108. As an example, the offset value113may range from 0.1° F. to 5° F., or 0.08° C. to 4° C., which may depend on operating parameters of the compressor74and/or other components of the HVAC system99. The offset value may also be a percentage of a suction or discharge temperature along the boundary112, such as between 0.5% and 20%, between 1% and 15%, or between 2% and 10% of any suction temperature or any discharge temperature along the boundary112. A speed of the compressor74operating within the deadband region110may not be adjusted even though the HVAC system99may operate at a reduced efficiency when compared to the inner region106. That is, an automation controller, such as the control board48and/or the control panel82, may maintain the lower threshold speed and the upper threshold speed of the target range of operating speeds when the system operates outside of the inner region106, and within the deadband region110, of the control scheme102.

The boundary112of the deadband region110represents an operating condition threshold, and is defined by compressor operation coordinates114,116,118,120,122, and124. The coordinates114-124are determined based on corresponding suction and discharge temperatures. The values of the coordinates114-124may vary between different HVAC systems, and may be based on compressor specifications, an application of the compressor74, other components of the HVAC system99, or other suitable operating parameters of the HVAC system99. In some embodiments, values of the coordinates114-124are determined through experimental testing and are values of suction temperatures and discharge temperatures that limit stress placed upon components of the HVAC system99, such as the compressor74. As such, the compressor74may undergo operation at a wide range of suction and discharge temperatures. The performance of the compressor74and/or the HVAC system99may be monitored to determine operating limits of the compressor74and/or maintain an efficiency of the compressor74and/or an efficiency of the HVAC system99above a threshold efficiency. Additionally or alternatively, the coordinates114-124are provided by a manufacturer of the compressor74.

In some embodiments, the control scheme102includes additional deadband regions, such as outer deadband regions126. The outer deadband regions126may be located outside of the deadband region110. For example, a first outer deadband region126may be located at a region where the suction temperature is below the suction temperature of the boundary112and where the discharge temperature is below the discharge temperature of the boundary112. A second outer deadband region126may be located at a region where the suction temperature is above the suction temperature of the boundary112and where discharge temperature is above the discharge temperature of the boundary112. Similar to operations in the inner deadband region110, the controller may not adjust a speed of the compressor74when operating in the outer deadband regions126, such that the outer deadband regions126reduce frequent adjustments of the speed of the compressor74when operating outside of the inner region106. In other words, the deadband region110and the outer deadband regions126maintain a speed of the compressor despite the suction and discharge temperatures being outside of the inner region106. Accordingly, the lower threshold speed and the upper threshold speed of the target range of operating speeds are maintained when the compressor74operates outside of the inner region106and the deadband region110.

Operation outside of the inner region106and the deadband region110may reduce the longevity of the compressor74. For example, operating the compressor74when suction temperatures are greater than the boundary112may result in a higher circulation rate of refrigerant, which may reduce an efficiency of the HVAC system99and/or produce conditions that reduce the longevity of the compressor74. Operating the compressor74when discharge temperatures are less than the boundary112may result in noise and/or also reduce the longevity of the compressor74. As a result, the target speed range of the compressor74may be adjusted to maintain operation of the compressor74within the inner region106.

The speed of the compressor74may be adjusted depending on a position of a generated compressor operation coordinate defined by a monitored suction temperature and a monitored discharge temperature of the refrigerant with respect to the control scheme102. For example, the control scheme102may include a speed up region128, or first control region, and a slow down region130, or second control region, in addition to the deadband region110, or third control region. The speed up region128represents conditions when the suction temperature is above a suction temperature threshold of the boundary112and/or when the discharge temperature is below a discharge temperature threshold of the boundary112. In other words, the speed up region128includes conditions where the suction temperature and the discharge temperature are to the right of, or below, a portion of the boundary112formed by the compressor operation coordinates118,120,122, and124. When operating in the speed up region128, the target operating speed range may be adjusted to cause the compressor74to operate at a higher speed than the compressor74would otherwise operate to achieve a given load demand. As such, the lower threshold speed of the target operating speed range may be increased.

Additionally, the slow down region130represents conditions when the suction temperature is below a suction temperature threshold of the boundary112and/or when the discharge temperature is above a discharge temperature threshold of the boundary112. In other words, the slow down region130includes conditions where the suction temperature and the discharge temperature are to the left of, or above, a portion of the boundary112formed by the compressor operation coordinates114,116,118, and124. When operating in the slow down region130, the target operating speed range may be adjusted to cause the compressor74to operate at a lower speed than the compressor74would otherwise operate to achieve the given load demand. As such, the upper threshold speed of the target operating speed range is reduced. The outer deadband regions126are positioned in between the speed up region128and the slow down region130, proximate to the compressor operation coordinates118and124. As such, frequent adjustment of the speed of the compressor74is reduced when the suction and discharge temperatures are near the compressor operation coordinate118or the compressor operation coordinate124. The adjustment of the target operating speed range may also depend on where the compressor operation coordinate defined by feedback indicative of the suction and discharge temperatures is located in the speed up region128and/or the slow down region130. For example, the adjustment to the upper threshold speed and/or the lower threshold speed of the target operating speed range may be greater if the compressor operation coordinate is further outside of the inner region106and/or the inner deadband region110.

Furthermore, the control scheme102may include a shut down region132, or fourth control region, which represents operating conditions that may significantly reduce longevity of the compressor74. That is, the operating conditions, or compressor operation coordinates, may warrant shut down of the compressor74rather than an adjustment to the speed of the compressor74when operating in the shut down region132. As such, if the operating conditions are determined to be in the shut down region132, the compressor74may immediately begin a shut down process. The shut down region132may be offset from the boundary112by an offset amount133. In some embodiments, the offset amount133is substantially similar, but opposite in direction, to the offset value113and may be between 0.1° F. to 5° F., or 0.08° C. to 4° C. Additionally or alternatively, the offset amount133may be a percentage of a suction or discharge temperature along the boundary112, such as between 0.5% and 20%, between 1% and 15%, or between 2% and 10% of any suction temperature or any discharge temperature along the boundary112, depending on operating parameters of the compressor74and/or other components of the HVAC system99. In other embodiments, the offset amount133differs from the offset value113and may be between temperature values such as 5° F. and 10° F. or 4° C. and 8° C. As such, the shut down region132may create a shut down boundary134offset from the boundary112, such that when the operating conditions fall outside of the shut down boundary134, the compressor74is shut down by the control panel82. In some embodiments, the offset amount133may be constant along the boundaries112,134such that the boundary134forms substantially the same shape compared to the boundary112.

AlthoughFIG. 6illustrates the boundary108, the boundary112, and the shut down boundary134as having a certain six-sided shape, in other embodiments, such boundaries108,112, and134may include a different shape. For example, the compressor operation coordinates114-124may differ in value, based on the type of compressor74, the application of the compressor74, other components of the HVAC system99, another suitable parameter, or any combination thereof. As such, the values of the compressor operation coordinates114-124may determine the ultimate shape of the boundary108, which may thereby change the shape of the boundary112and/or the shut down boundary134that are offset from the boundary108. In other embodiments, the boundary112and/or the shut down boundary134may be offset from the boundary108in manners that change their shapes and/or values with respect to the boundary108.

An embodiment of a process150for adjusting operation of the compressor74is illustrated inFIG. 7. When the compressor74begins operation, the compressor74may operate between an initial range of operating speeds that includes an initial lower threshold speed and an initial upper threshold speed. Throughout operation, as shown in block151, a compressor operation coordinate point is generated by using data associated with feedback indicative of the suction temperature of the refrigerant and the discharge temperature of the refrigerant, such as feedback from the first sensor100and/or the second sensor101. The coordinate point may be compared to a graph, such as the graphical representation of the operational compressor envelope inFIG. 6and/or a lookup table. Generally, the compressor operation coordinate point represents a performance of the HVAC system99, such that the operating conditions of a compressor74of the HVAC system99may be adjusted based on the compressor operation coordinate.

In block152, the location of the generated compressor operation coordinate point is compared to the control scheme102, which may include a graph or lookup table. Specifically, it is determined whether or not the compressor operation coordinate point is within the inner region106, or the target region. If the compressor operation coordinate point is within the inner region106, no change to the initial range of operating speeds of the compressor74is made and the compressor74continues to operate between the initial lower threshold speed and the initial upper threshold speed. Further, in some embodiments, compressor operation coordinate points are continuously generated to monitor the performance of the compressor74. If the compressor operation coordinate point is determined to be outside of the inner region106of the control scheme102, further action may be taken.

Specifically, further analysis to determine where the compressor operation coordinate defined by the operating conditions is positioned with respect to the control scheme102is performed, as shown in block154. For example, the compressor operation coordinate defined by the operating conditions may be determined to be in the deadband region110or in one of the outer deadband regions126, as shown in block156. In this case, no adjustment to the initial range of operating speeds of the compressor74is made. The compressor operation coordinate defined by the operating conditions may also be determined to be in the speed up region128. In response, as shown in block158, a process for adjusting the operation of the compressor74in the speed up region128is performed. Specifically, the speed of the compressor74may be increased to return the operating conditions to a position within the inner region106. Additionally, the compressor operation coordinate defined by the operating conditions may be determined to be in the slow down region130and as a result, as shown in block160, a process for adjusting the operation of the compressor74in the slow down region130is performed to reduce the speed of the compressor74to return the operating conditions to a position within inner region106. Further, the compressor operation coordinate defined by the operating conditions may be determined to be in the shut down region132. In such cases, a method for shutting down the compressor74, as shown in block162, is performed.

FIG. 8illustrates block158ofFIG. 7in greater detail. Specifically,FIG. 8is a block diagram of a process for adjusting the operation of the compressor74when the compressor operation coordinate defined by the operating conditions is in the speed up region128. As described above, when the compressor operation coordinate defined by the operating conditions falls within the inner region106, the compressor74may operate within a target range of operating speeds, bounded by a lower threshold speed and an upper threshold speed. However, when the compressor operation coordinate defined by the operating conditions is in the speed up region128, the target range of operating speeds may be adjusted.

For example, in block200, the lower threshold speed of the target range of operating speeds is increased by an offset value. Specifically, the lower threshold speed may increase by a set rate, such as 1 RPM of the motor94per second, or a percentage rate, such as 1% per second. In some embodiments, the upper threshold speed may remain constant at the initial upper threshold while the lower threshold speed is adjusted. As such, the target range of operating speeds changes and the speed of the compressor74will be controlled to be between a new lower threshold speed and the initial upper threshold speed. As discussed above, the adjustment of the lower threshold speed may depend on where the compressor operation coordinate defined by the operating conditions is located with respect to the control scheme102. For example, if the compressor operation coordinate defined by the operating conditions is in the speed up region128and is proximate to the boundary134, the offset value applied to the lower threshold speed may increase as compared to when the compressor operation coordinate is proximate to the boundary112.

In block202, the controller determines whether the compressor operation coordinate defined by the operating condition is within the inner region106. If it is determined that the coordinate is within the inner region106, the offset value is removed, such that the lower threshold speed decreases towards the initial lower threshold speed, as shown in block204. As such, the target range of operating speeds is adjusted towards the initial range of operating speeds. In some embodiments, the lower threshold speed may be decreased by a set rate or a percentage rate, so long as the compressor operation coordinate defined by the operating condition is within the inner region106.

If the controller determines that the compressor operation coordinate defined by the operating conditions has not returned to within the inner region106, then further analysis of the operating parameters of the HVAC system99may be performed. In some embodiments, a duration, or time value associated with the duration, in which the compressor operation coordinate has been outside of the inner region106may be monitored by the controller, as shown in block206. If the time value has not exceeded a time interval threshold, the lower threshold speed may continue to increase, thereby increasing the speed of the compressor74. However, if the time value has been determined to exceed the time interval threshold, an indicator may be activated and the compressor74may shut down, as shown in block208. In some embodiments, the time interval may be a set value, such as 5 minutes.

As such, the lower threshold speed may continue to increase until the compressor operation coordinate defined by the operating parameter returns to within the inner region106or until the compressor74shuts down. In some embodiments, the time value resets when the compressor operation coordinate defined by the operating parameter returns to within the inner region106. At the same time, the lower threshold speed may be reduced. In some embodiments, the lower threshold speed is reduced at a rate depending on the position of the compressor operation coordinate defined by the operating parameters with respect to the control scheme102. For example, the lower threshold speed may be reduced at a higher rate if the compressor operation coordinate is in a more central location within the inner region106than if the compressor operation coordinate is more proximate to the boundary108. In additional or alternative embodiments, the time value may not reset when the compressor operation coordinate defined by the operating parameters moves from the speed up region128to the deadband region110or to the outer deadband regions126, even though the range of operating speeds is not adjusted.

FIG. 9illustrates block160ofFIG. 7in further detail. Specifically,FIG. 9is a block diagram of process for adjusting the speed of the compressor74when the compressor operation coordinate defined by the operating conditions is within the slow down region130. The process ofFIG. 9includes similar steps as those described above forFIG. 8. In block230, the upper threshold speed of the target range of operating speeds decreases by an offset value, such as at a set rate or at a percentage rate. Similar to block200, the offset value applied to the upper threshold speed may increase if the compressor operation coordinate is determined to be further outside of the boundary112. In some embodiments, the lower threshold speed of the compressor74may remain constant at the initial lower threshold speed. Accordingly, the speed of the compressor74will be set between the lower threshold speed and a new upper threshold speed.

In block232, the controller determines whether the compressor operation coordinate defined by the operating conditions has returned to within the inner region106. If it is determined that the compressor operation coordinate is within the inner region106, the target range of operating speeds is adjusted toward the initial range of operating speeds, as shown in block234. Accordingly, the upper threshold speed increases towards the initial upper threshold speed, such as at a set rate or at a percentage rate, while the lower threshold speed may remain constant. The rate at which the upper threshold speed increases may depend on the position of the compressor operation coordinate defined by the operating conditions within the inner region106. For example, a rate of increasing the upper threshold speed may increase at a higher rate when the position of the compressor operation coordinate defined by the operating conditions is in a central location within inner region106than if the compressor operation coordinate is proximate to the boundary108.

If the compressor operation coordinate defined by the operating conditions is determined to remain outside of the inner region106, further analysis of the operating parameters of the HVAC system99may be performed, similar to the steps described inFIG. 8. That is, in block236, a time value at which the compressor operation coordinate defined by the operating parameters is outside of the inner region106may be determined. If the time value has not exceeded a time interval, such as 5 minutes, the steps in block230and block232may be repeated until the time interval has been exceeded. In that case, an indicator may be activated and the compressor74may shut down, as shown in block208.

Thus, similar toFIG. 8, the target range of operating speeds of the compressor74is adjusted until the compressor operation coordinate defined by the operating conditions is within the inner region106or until the compressor74shuts down. Also, the time value may reset when the compressor operation coordinate defined by the operating conditions is within the inner region106and/or the upper threshold speed may be reduced at that time. However, the time value may not reset when the operation of the compressor74is within the deadband region110or the outer deadband regions126.

FIG. 10illustrates block162ofFIG. 7in detail. Specifically,FIG. 10is a block diagram of method process for adjusting the speed of the compressor74when the compressor operation coordinate defined by the operating conditions is in the shut down region132. In block250, the compressor operation coordinate defined by the operating conditions is determined to be within the shut down region132. As a result, an indicator may be activated and the compressor74may shut down, as shown in block208. In other words, unlike for blocks158and160ofFIG. 7, the compressor74is shut down before the target range of operating speeds is adjusted.

In some embodiments, further actions may be performed after the compressor74has shut down.FIG. 11illustrates a process300for performing such further actions. In block302, the indicator has been activated and the compressor74has shut down. The information related to each shut down of the compressor74may be stored in the non-volatile memory88control board82, for instance. Specifically, the control board82may determine whether a target number of indicators has been activated over a set time interval, as shown in block304. For example, the control board82may determine whether or not there have been more than 3 indicators activated over the past 120 minutes. If the target number of shut downs has not been exceeded, the compressor74may be shut down for a time interval, as shown in block306. After the time interval, the compressor74may automatically resume operating at a speed within the initial range of operating speeds. For example, the compressor74may automatically resume operating after 10 minutes, or another suitable time interval.

If the number of activated indicators has exceeded the previously specified number, the compressor74may remain shut down and generate an indication to notify an operator, as shown in block308. In some embodiments, the compressor74may remain locked out until a user manually resets the compressor74, such as via a user interface. In some embodiments, the indication may be a light, a sound, a text notification, or any combination thereof. The indication enables operators to easily identify that the HVAC system99has frequently been operating outside of the inner region106. As such, an operator may perform maintenance on the compressor74and/or other components of the HVAC system99, to enable the HVAC system99to operate more frequently within the inner region106.

The methods described inFIGS. 7-11may be performed by a control system, such as the control panel82. For example, the microprocessor86may be programmed to perform each of the methods. In some embodiments, the methods may not be available immediately upon startup of the compressor74. That is, the microprocessor86may include a delay before the control system may begin executing the methods ofFIGS. 7-11. As such, the compressor74may reach substantially steady state operation before the methods are performed. By way of example, the control system may not be able to execute the methods until 60 seconds after the compressor74begins operation.

As set forth above, embodiments of the present disclosure may provide one or more technical effects useful in the operation of HVAC systems. For example, a speed of a compressor may be controlled based on feedback associated with operating parameters of the HVAC system. Further, a control system may determine whether such feedback is within an operational envelope that is graphically or tabularly represented using suction temperatures and discharge temperatures of a refrigerant flowing through the compressor. When the feedback is not within a target region of the operational envelope, a target range of speeds of the compressor may be adjusted. For example, a lower threshold speed of the target range of operating speeds is increased to increase the speed of the compressor or an upper threshold speed of the target range of operating speeds is reduced to decrease the speed of the compressor. The control system may continue to monitor the operating parameters of the HVAC system after adjusting the target range of speeds and continuously adjust the target range of speeds if the operating parameters have not returned to within a target region of the operational envelope. Additionally, the control system may shut down the compressor if the operating parameters do not return to within the target region within a certain time and/or if the temperatures are determined to be beyond threshold temperatures of the envelope. The technical effects and technical problems in the specification are examples and are not limiting. It should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems.