System and method for monitoring a condenser of a refrigeration system

A system for monitoring a remote refrigeration system includes a plurality of sensors that monitor parameters of components of the refrigeration system and a communication network that transfers signals generated by each of the plurality of sensors. A management center receives the signals from the communication network and processes the signals to determine an operating condition of at least one of the components. The management center generates an alarm based on the operating condition.

FIELD OF THE INVENTION

The present invention relates to refrigeration systems and more particularly to predictive maintenance and equipment monitoring of a refrigeration system.

BACKGROUND OF THE INVENTION

Produced food travels from processing plants to retailers, where the food product remains on display case shelves for extended periods of time. In general, the display case shelves are part of a refrigeration system for storing the food product. In the interest of efficiency, retailers attempt to maximize the shelf-life of the stored food product while maintaining awareness of food product quality and safety issues.

The refrigeration system plays a key role in controlling the quality and safety of the food product. Thus, any breakdown in the refrigeration system or variation in performance of the refrigeration system can cause food quality and safety issues. Thus, it is important for the retailer to monitor and maintain the equipment of the refrigeration system to ensure its operation at expected levels.

Refrigeration systems generally require a significant amount of energy to operate. The energy requirements are thus a significant cost to food product retailers, especially when compounding the energy uses across multiple retail locations. As a result, it is in the best interest of food retailers to closely monitor the performance of the refrigeration systems to maximize their efficiency, thereby reducing operational costs.

Monitoring refrigeration system performance, maintenance and energy consumption are tedious and time-consuming operations and are undesirable for retailers to perform independently. Generally speaking, retailers lack the expertise to accurately analyze time and temperature data and relate that data to food product quality and safety, as well as the expertise to monitor the refrigeration system for performance, maintenance and efficiency. Further, a typical food retailer includes a plurality of retail locations spanning a large area. Monitoring each of the retail locations on an individual basis is inefficient and often results in redundancies.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a system for monitoring a remote refrigeration system. The system includes a plurality of sensors that monitor parameters of components of the refrigeration system and a communication network that transfers signals generated by each of the plurality of sensors. A management center receives the signals from the communication network and processes the signals to determine an operating condition of at least one of the components. The management center generates an alarm based on the operating condition.

In one feature, the management center evaluates each of the signals to determine whether each of the signals is within a useful range, to determine whether each of the signals is dynamic and to determine whether each of the signals is valid.

In other features, the system further includes a temperature sensor monitors a temperature of a refrigerant flowing through the refrigeration system and generates a temperature signal. The management center calculates a pressure, a density and an enthalpy of the refrigerant based on the temperature and based on whether the refrigerant is in one of a saturated liquid phase and a saturated vapor phase.

In other features, the system further includes a pressure sensor that monitors a pressure of a refrigerant flowing through the refrigeration system and that generates a pressure signal. The management center calculates a temperature, a density and an enthalpy of the refrigerant based on said pressure and based on whether the refrigerant is in one of a saturated liquid phase and a saturated vapor phase.

In other features, the system further includes a temperature sensor that monitors a temperature of a refrigerant at a suction side of a compressor of the refrigeration system and generates a temperature signal. A pressure sensor monitors a pressure of a refrigerant at the suction side of the compressor and generates a pressure signal. The management center determines an occurrence of a floodback event based on the temperature signal and the pressure signal. The management center determines a superheat temperature of the refrigerant based on the temperature signal and the pressure signal and processes the superheat through a pattern analyzer to determine whether the floodback event has occurred.

In still other features, the system further includes a temperature sensor that monitors a temperature of a refrigerant at a discharge side of a compressor of the refrigeration system and that generates a temperature signal. A pressure sensor monitors a pressure of a refrigerant at the discharge side of the compressor and generates a pressure signal. The management center determines an occurrence of a floodback event based on the temperature signal and the pressure signal. The management center determines a superheat temperature of the refrigerant based on the temperature signal and the pressure signal and processes the superheat through a pattern analyzer to determine whether the floodback event has occurred.

In yet other features, the system further includes a contactor associated with one of the components. The contactor is cycled between an open position and a closed position to selectively operate the component. The management center monitors cycling of the contactor and generates an alarm when one of a cycling rate is exceeded and a maximum number of cycles is exceeded.

In still another feature, the system further includes an ambient condenser temperature sensor that generates an ambient temperature signal, a condenser pressure sensor that generates a pressure signal, a compressor current sensor that generates a compressor current signal and a condenser current sensor that generates a condenser current signal. The management center determines an operating condition of the condenser based on the ambient temperature signal, the pressure signal, the compressor current signal and the condenser current signal.

In yet another feature, the system further includes a discharge pressure sensor that monitors a pressure of a refrigerant at a discharge side of the compressor and that generates a discharge pressure signal. A suction pressure sensor monitors a pressure of a refrigerant at a suction side of the compressor and generates a suction pressure signal. The management center determines loss of refrigerant based on the discharge pressure and the suction pressure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIG. 1an exemplary refrigeration system100includes a plurality of refrigerated food storage cases102. The refrigeration system100includes a plurality of compressors104piped together with a common suction manifold106and a discharge header108all positioned within a compressor rack110. A discharge output112of each compressor104includes a respective temperature sensor114. In input116to the suction manifold106includes both a pressure sensor118and a temperature sensor120. Further, a discharge outlet122of the discharge header108includes an associated pressure sensor124. As described in further detail herein below, the various sensors are implemented for evaluating maintenance requirements.

The compressor rack110compresses refrigerant vapor that is delivered to a condenser126where the refrigerant vapor is liquefied at high pressure. Condenser fans127are associated with the condenser126to enable improved heat transfer from the condenser126. The condenser126includes an associated ambient temperature sensor128and an outlet pressure sensor130. This high-pressure liquid refrigerant is delivered to the plurality of refrigeration cases102by way of piping132. Each refrigeration case102is arranged in separate circuits consisting of a plurality of refrigeration cases102that operate within a certain temperature range.FIG. 1illustrates four (4) circuits labeled circuit A, circuit B, circuit C and circuit D. Each circuit is shown consisting of four (4) refrigeration cases102. However, those skilled in the art will recognize that any number of circuits, as well as any number of refrigeration cases102may be employed within a circuit. As indicated, each circuit will generally operate within a certain temperature range. For example, circuit A may be for frozen food, circuit B may be for dairy, circuit C may be for meat, etc.

Because the temperature requirement is different for each circuit, each circuit includes a pressure regulator134that acts to control the evaporator pressure and, hence, the temperature of the refrigerated space in the refrigeration cases102. The pressure regulators134can be electronically or mechanically controlled. Each refrigeration case102also includes its own evaporator136and its own expansion valve138that may be either a mechanical or an electronic valve for controlling the superheat of the refrigerant. In this regard, refrigerant is delivered by piping to the evaporator136in each refrigeration case102.

The refrigerant passes through the expansion valve138where a pressure drop causes the high pressure liquid refrigerant to achieve a lower pressure combination of liquid and vapor. As hot air from the refrigeration case102moves across the evaporator136, the low pressure liquid turns into gas. This low pressure gas is delivered to the pressure regulator134associated with that particular circuit. At the pressure regulator134, the pressure is dropped as the gas returns to the compressor rack110. At the compressor rack110, the low pressure gas is again compressed to a high pressure gas, which is delivered to the condenser126, which creates a high pressure liquid to supply to the expansion valve138and start the refrigeration cycle again.

A main refrigeration controller140is used and configured or programmed to control the operation of the refrigeration system100. The refrigeration controller140is preferably an Einstein Area Controller offered by CPC, Inc. of Atlanta, Ga., or any other type of programmable controller that may be programmed, as discussed herein. The refrigeration controller140controls the bank of compressors104in the compressor rack110, via an input/output module142. The input/output module142has relay switches to turn the compressors104on an off to provide the desired suction pressure.

A separate case controller (not shown), such as a CC-100 case controller, also offered by CPC, Inc. of Atlanta, Ga. may be used to control the superheat of the refrigerant to each refrigeration case102, via an electronic expansion valve in each refrigeration case102by way of a communication network or bus. Alternatively, a mechanical expansion valve may be used in place of the separate case controller. Should separate case controllers be utilized, the main refrigeration controller140may be used to configure each separate case controller, also via the communication bus. The communication bus may either be a RS-485 communication bus or a LonWorks Echelon bus that enables the main refrigeration controller140and the separate case controllers to receive information from each refrigeration case102.

Each refrigeration case102may have a temperature sensor146associated therewith, as shown for circuit B. The temperature sensor146can be electronically or wirelessly connected to the controller140or the expansion valve for the refrigeration case102. Each refrigeration case102in the circuit B may have a separate temperature sensor146to take average/min/max temperatures or a single temperature sensor146in one refrigeration case102within circuit B may be used to control each refrigeration case102in circuit B because all of the refrigeration cases102in a given circuit operate at substantially the same temperature range. These temperature inputs are preferably provided to the analog input board142, which returns the information to the main refrigeration controller140via the communication bus.

Additionally, further sensors are provided and correspond with each component of the refrigeration system and are in communication with the refrigeration controller140. Energy sensors150are associated with the compressors104and the condenser126of the refrigeration system100. The energy sensors150monitor energy consumption of their respective components and relay that information to the controller140.

Referring now toFIG. 2, the refrigeration controller140and case controllers communicates with a remote network or processing center160. It is anticipated that the remote processing center160can be either in the same location (e.g. food product retailer) as the refrigeration system100or can be a centralized processing center that monitors the refrigeration systems of several remote locations. The refrigeration controller140and case controllers initially communicate with a site-based controller161via a serial connection or Ethernet. The site-based controller161communicates with the processing center160via a TCP/IP connection.

The processing center160collects data from the refrigeration controller140, the case controllers and the various sensors associated with the refrigeration system100. For example, the processing center160collects information such as compressor, flow regulator and expansion valve set points from the refrigeration controller140. Data such as pressure and temperature values at various points along the refrigeration circuit are provided by the various sensors via the refrigeration controller140. More specifically, the software system is a multi-tiered system spanning all three hardware levels. At the local level (i.e., refrigeration controller and case controllers) is the existing controller software and raw I/O data collection and conversion.

A controller database and the ProAct CB algorithms reside on the site-based controller161. The algorithms manipulate the controller data generating notices, service recommendations, and alarms based on pattern recognition and fuzzy logic. Finally, this algorithm output (alarms, notices, etc.) is served to a remote network workstation at the processing center160, where the actual service calls are dispatched and alarms managed. The refined data is archived for future analysis and customer access at a client-dedicated website.

Referring now toFIGS. 3 and 4, for each refrigeration circuit and loop of the refrigeration system100, several calculations are required to calculate superheat, saturation properties and other values used in the hereindescribed algorithms. These measurements include: ambient temperature (Ta), discharge pressure (Pd), condenser pressure (Pc), suction temperature (Ts), suction pressure (Ps), refrigeration level (LREF), compressor discharge temperature (Td), rack current load (Icmp), condenser current load (Icnd) and compressor run status. Other accessible controller parameters will be used as necessary. Foe example, a power sensor can monitor the power consumption of the compressor racks and the condenser. Besides the sensors described above, suction temperature sensors115monitor Tsof the individual compressors104in a rack and a rack current sensor150monitors Icmpof a rack. The pressure sensor124monitors Pdand a current sensor127monitors Icnd. Multiple temperature sensors129monitor a return temperature (Tc) for each circuit.

The present invention provides control and evaluation algorithms in the form of software modules to predict maintenance requirements for the various components in the refrigeration system100. These algorithms include signal conversion and validation, saturated refrigerant properties, watchdog message, recurring notice or alarm message, flood back alert, contactor cycling count, compressor performance, condenser performance, defrost abnormality, case discharge versus product temperature, data pattern recognition, condenser discharge temperature and loss of refrigerant charge. Each is discussed in detail below. The algorithms can be processed locally using the refrigeration controller140or remotely at the remote processing center160.

Referring now toFIG. 5, a signal conversion and validation (SCV) algorithm processes measurement signals from the various sensors. The SCV algorithm determines the value of a particular signal and up to three different qualities including whether the signal is within a useful range, whether the signal changes over time and/or whether the actual input signal from the sensor is valid.

In step500, the input registers read the measurement signal of a particular sensor. In step502, it is determined whether the input signal is within a range that is particular to the type of measurement. If the input signal is within range, the SCV algorithm continues in step504. If the input signal is not within the range an invalid data range flag is set in step506and the SCV algorithm continues in step508. In step504, it is determined whether there is a change (Δ) in the signal within a threshold time (tthresh). If there is no change in the signal it is deemed static. In this case, a static data value flag is set in step510and the SCV algorithm continues in step508. If there is a change in the signal a valid data value flag is set in step512and the SCV algorithm continues in step508.

In step508, the signal is converted to provide finished data. More particularly, the signal is generally provided as a voltage. The voltage corresponds to a particular value (e.g., temperature, pressure, current, etc.). Generally, the signal is converted by multiplying the voltage value by a conversion constant (e.g., ° C/V, kPa/V, A/V, etc.). In step514, the output registers pass the data value and validation flags and control ends.

Referring now toFIG. 6, a block diagram schematically illustrates an SCV block600. A measured variable602is shown as the input signal. The input signal is provided by the instruments or sensors. Configuration parameters604are provided and include Lo and Hi range values, a time Δ, a signal Δ and an input type. The configuration parameters604are specific to each signal and each application. Output parameters606are output by the SCV block600and include the data value, bad signal flag, out of range flag and static value flag. In other words, the output parameters606are the finished data and data quality parameters associated with the measured variable.

Referring now toFIGS. 7 through 10, refrigeration property algorithms will be described in detail. The refrigeration property algorithms provide the saturation pressure (PSAT), density and enthalpy based on temperature. The refrigeration property algorithms further provide saturation temperature (TSAT) based on pressure. Each algorithm incorporates thermal property curves for common refrigerant types including, but not limited to, R22, R401a (MP39), R402a (HP80), R404a (HP62), R409a and R507c.

With particular reference toFIG. 7a refrigerant properties from temperature (RPFT) algorithm is shown. In step700, the temperature and refrigerant type are input. In step702, it is determined whether the refrigerant is saturated liquid based on the temperature. If the refrigerant is in the saturated liquid state, the RPFT algorithm continues in step704. If the refrigerant is not in the saturated liquid state, the RPFT algorithm continues in step706. In step704, the RPFT algorithm selects the saturated liquid curve from the thermal property curves for the particular refrigerant type and continues in step708.

In step706, it is determined whether the refrigerant is in a saturated vapor state. If the refrigerant is in the saturated vapor state, the RPFT algorithm continues in step710. If the refrigerant is not in the saturated vapor state, the RPFT algorithm continues in step712. In step712, the data values are cleared, flags are set and the RPFT algorithm continues in step714. In step710, the RPFT algorithm selects the saturated vapor curve from the thermal property curves for the particular refrigerant type and continues in step708. In step708, data values for the refrigerant are determined. The data values include pressure, density and enthalpy. In step714, the RPFT algorithm outputs the data values and flags.

Referring now toFIG. 8, a block diagram schematically illustrates an RPFT block800. A measured variable802is shown as the temperature. The temperature is provided by the instruments or sensors. Configuration parameters804are provided and include the particular refrigerant type. Output parameters806are output by the RPFT block800and include the pressure, enthalpy, density and data quality flag.

With particular reference toFIG. 9a refrigerant properties from pressure (RPFP) algorithm is shown. In step900, the temperature and refrigerant type are input. In step902, it is determined whether the refrigerant is saturated liquid based on the pressure. If the refrigerant is in the saturated liquid state, the RPFP algorithm continues in step904. If the refrigerant is not in the saturated liquid state, the RPFP algorithm continues in step906. In step904, the RPFP algorithm selects the saturated liquid curve from the thermal property curves for the particular refrigerant type and continues in step908.

In step906, it is determined whether the refrigerant is in a saturated vapor state. If the refrigerant is in the saturated vapor state, the RPFP algorithm continues in step910. If the refrigerant is not in the saturated vapor state, the RPFP algorithm continues in step912. In step912, the data values are cleared, flags are set and the RPFP algorithm continues in step914. In step910, the RPFP algorithm selects the saturated vapor curve from the thermal property curves for the particular refrigerant type and continues in step908. In step908, the temperature of the refrigerant is determined. In step914, the RPFP algorithm outputs the temperature and flags.

Referring now toFIG. 10, a block diagram schematically illustrates an RPFP block1000. A measured variable1002is shown as the pressure. The pressure is provided by the instruments or sensors. Configuration parameters1004are provided and include the particular refrigerant type. Output parameters1006are output by the RPFP block1000and include the temperature and data quality flag.

Referring now toFIG. 11, a block diagram schematically illustrates the watchdog message algorithm, which includes a message generator1100, configuration parameters1102and output parameters1104. In accordance with the watchdog message algorithm, the site-based controller161periodically reports its health (i.e., operating condition) to the remainder of the network. The site-based controller generates a test message that is periodically broadcast. The time and frequency of the message is configured by setting the time of the first message and the number of times per day the test message is to be broadcast. Other components of the network (e.g., the refrigeration controller140, the processing center160and the case controllers) periodically receive the test message. If the test message is not received by one or more of the other network components, a controller communication fault is indicated.

Referring now toFIG. 12, a block diagram schematically illustrates the recurring notice or alarm message algorithm. The recurring notice or alarm message algorithm monitors the state of signals generated by the various algorithms described herein. Some signals remain in the alarm state for a protracted period of time until the corresponding issue is resolved. As a result, an alarm message that is initially generated as the initial alarm occurs may be overlooked later. The recurring notice/alarm message algorithm generates the alarm message at a configured frequency. The alarm message is continuously regenerated until the alarm condition is resolved.

The recurring notice or alarm message algorithm includes a notice/alarm message generator1200, configuration parameters1202, input parameters1204and output parameters1206. The configuration parameters1202include message frequency. The input1204includes a notice/alarm message and the output parameters1206include a regenerated notice/alarm message. The notice/alarm generator1200regenerates the input alarm message at the indicated frequency. Once the notice/alarm condition is resolved, the input1204will indicate as such and regeneration of the notice/alarm message terminates.

Referring now toFIGS. 13 through 15, the flood back alert algorithm is described in detail. Liquid refrigerant flood back occurs when liquid refrigerant reverse migrates through the refrigeration system100from the evaporator through to the compressor102. The flood back alert algorithm monitors the superheat conditions of the refrigeration circuits A, B, C, D and both the compressor suction/discharge. The superheat is filtered through a pattern analyzer and an alarm is generated if the filtered superheat falls outside of a specified range. Superheat signals outside of the specified range indicate a flood back event. In the case where multiple flood back events are indicated, a severe flood back alarm is generated.

The saturated vapor temperature for the compressor suction is calculated from the suction pressure. The superheat is calculated for each refrigeration and compressor by subtracting the return temperature from the saturated vapor temperature. Similarly, assuming a saturated liquid, the superheat for each compressor discharge is calculated by subtracting the compressor discharge temperature from the discharge saturated liquid temperature.

FIG. 13provides a schematic illustration of a superheat monitor block1300that includes an RPFP module1302and a pattern analyzer module1304. Measured variables1306include temperature and pressure and are input to the superheat monitor1300. Configuration parameters1308include refrigerant type and state, data pattern zones and a data sample timer. The refrigerant type and state are input to the RPFP module1302. The data pattern zones and data sample timer are input to the pattern analyzer1304. The RPFP module1302determines the saturated vapor temperature based on the refrigerant type and state and the pressure. The superheat monitor1300determines the superheat, which is filtered through the pattern analyzer1304. Output parameters1310include an alarm message that is generated by the superheat monitor1300based on the filtered superheat signal.

Referring now toFIG. 14, the flood back alert algorithm for the suction side will be described in more detail. In step1400, Psand Tsare measured by the suction temperature and pressure sensors120,118. In step1402it is determined whether any compressors for the current rack are running. If no compressors are running, the next rack is checked in step1404. If a compressor is running, the suction saturation temperature (TSSAT) is determined based on Psin step1406. The superheat is determined based on TSSATand Tsin step1408. The superheat is filtered by the pattern analyzer in step1410. If appropriate, an alarm message is generated in step1412and the algorithm ends. Steps1402through1412are repeated for each rack and steps1408through1412are repeated for each refrigeration circuit.

Referring now toFIG. 15, the flood back alert algorithm is illustrated for the discharge side. In step1500, Pdand Tdare measured by the discharge temperature and pressure sensors. In step1502it is determined whether any compressors for the current rack are running. If no compressors are running, the next rack is checked in step1504. If a compressor is running, the discharge saturation temperature (TDSAT) is determined based on Pdin step1506. The superheat is determined based on TDSATand Tdin step1508. The superheat is filtered by the pattern analyzer in step1510. If appropriate, an alarm message is generated in step1512and the algorithm ends. Steps1502through1512are repeated for each rack and steps1508through1512are repeated for each refrigeration circuit.

Alternative embodiments of the flood back alert algorithm will be described in detail. In a first alternative embodiment, the superheat is compared to a threshold value. If the superheat is greater than or equal to the threshold value then a flood back condition exists. In the event of a flood back condition an alert message is generated.

More particularly, TSATis determined by referencing a look-up table using Psand the refrigerant type. An alarm value (A) and time delay (t) are also provided as presets and may be user selected. An exemplary alarm value is 15° F. The suction superheat (SHSUC) is determined by the difference between Tsand TSAT. An alarm will be signaled if SHSUCis greater than the alarm value for a time period longer than the time delay. This is governed by the following logic:If SHSUC>A and time>t, then alarm.

In another alternative embodiment, the rate of change of Tsis monitored. That is to say, the temperature signal from the temperature sensor118is monitored over a period of time. The rate of change is compared to a threshold rate of change. If the rate of change of Tsis greater than or equal to the threshold rate of change, a flood back condition exists.

The contactor cycling count algorithm monitors the cycling of the various contacts in the refrigeration system100. The counting mechanism can be one of an internal or an external nature. With respect to internal counting, the refrigeration controller140can perform the counting function based on its command signals to operate the various equipment. The refrigeration controller140monitors the number of times the particular contact has been cycled (NCYCLE) for a given load. Alternatively, with respect to external counting, a separate current sensor or auxiliary contact can be used to determine NCYCLE. If NCYCLEper hour for the given load is greater than a threshold number of cycles per hour (NTHRESH), an alarm is initiated. The value of NTHRESHis based on the function of the particular contactor.

Additionally, NCYCLEcan be used to predict when maintenance of the associated equipment or contactor should be scheduled. In one example, NTHRESHis associated with the number of cycles after which maintenance is typically required. Therefore, the alarm indicates maintenance is required on the particular piece of equipment the contact is associated with. Alternatively, NCYCLEcan be tracked over time to estimate a point in time when it will achieve NTHRESH. A predicative alarm is provided indicating a future point in time when maintenance will be required.

The cycle count for multiple contactors can be monitored. A group alarm can be provided to indicate predicted maintenance requirements for a group of equipment. The groups include equipment whose NCYCLEcount will achieve their respective NTHRESH'S within approximately the same time frame. In this manner, the number of maintenance calls is reduced by performing multiple maintenance tasks during a single visit of maintenance personnel.

Referring now toFIGS. 16 and 17, the contactor cycling count algorithm will be described with respect to the compressor motor. A contactor cycle monitoring block1600includes a measured variable input1602and configuration parameter inputs1604. The contactor cycle monitoring block1600processes the measured variable1602and the configuration parameters1604and generates output parameters1606. The measured variable includes NCYCLEfor the particular compressor and the configuration parameters include a cycle rate limit (NCYCRATELIM) and a cycle maximum (NCYCMAX). The output parameters include a rate exceeded alarm and a maximum exceeded alarm. The rate exceeded alarm is generated when the rate at which the contactor is cycled (NCYCRATE) exceeds NCYCRATELIM. Similarly, the maximum exceeded alarm is generated when NCYCLEexceeds NCYCMAX.

FIG. 17illustrates steps of the contactor cycling count algorithm. In step1700the contactor state (i.e., open or closed) is determined. In step1702, it is determined whether a state change has occurred. If a state change has not occurred, the algorithm loops back to step1700. If a state change has occurred, NCYCLEis incremented in step1704. NCYCRATELIMis determined in step1708by dividing NCYCLEby the time over which the closures occurred.

In step1710, the algorithm determines whether NCYCLEexceeds NCYCMAX. If NCYCLEdoes not exceed NCYCLEMAX, the algorithm continues in step1712. If NCYCLEexceeds NCYCMAX, an alarm is generated in step1714and the algorithm continues in step1712. In step1712, the algorithm determines whether NCYCRATEexceeds NCYCRATELIM. If NCYCRATEdoes not exceed NCYCRATELIM, the algorithm loops back to step1700. If NCYCRATEexceeds NCYCRATELIM, an alarm is generated in step1716and the algorithm loops back to step1700.

The compressor performance algorithm compares a theoretical compressor energy requirement (ETHEO) to an actual measurement of the compressor's energy consumption (EACT). ETHEOis determined based on a model of the compressor. EACTis directly measured from the energy sensors150. A difference between ETHEOand EACTis determined and compared to a threshold value (ETHRESH). If the absolute value of the difference is greater than ETHRESHan alarm is initiated indicating a fault in compressor performance.

Referring now toFIGS. 18 and 19, compressor fault detection algorithm will be described in detail. In general, the compressor fault detection algorithm monitors Tdand determines whether the compressor is operating properly based thereon. Tdreflects the latent heat absorbed in the evaporator, evaporator superheat, suction line heat gain, heat of compression, and compressor motor-generated heat. All of this heat is accumulated at the compressor discharge and must be removed. High compressor Td's result in lubricant breakdown, worn rings, and acid formation, all of which shorten the compressor lifespan. This condition can indicate a variety of problems including, but not limited to damaged compressor valves, partial motor winding shorts, excess compressor wear, piston failure and high compression ratios. High compression ratios can be caused by either low Ps, high head pressure, or a combination of the two. The higher the compression ratio, the higher the Tdwill be at the compressor. This is due to heat of compression generated when the gasses are compressed through a greater pressure range.

For each compressor rack with at least one compressor running the discharge saturation temperature (TDSAT) is calculated based on Pd. For each compressor running in the rack SH is calculated by subtracting TDSATfrom Td. The SH data once each minute for 30 minutes using the pattern analyzer. If the accumulated data indicates an abnormal condition an alarm is generated. Alternatively, Tsand Pscan be monitored and compared to compressor performance curves. For this, a block similar to RPFP and RPFT can be created to perform the performance curve calculations for comparison. Specific deviations from the performance curve would generate maintenance notices.

With particular reference toFIG. 18, a compressor performance monitor block1800generates an output parameter1802based on measured variables1804and configuration parameters1806. The output parameter1802includes an alarm and the measured variable includes Tdand Pd. The configuration parameters include refrigerant type and state and data pattern zones and a data sample timer. The compressor performance monitor block1800determines SH and processes SH through the data pattern analyzer and generates the alarm if required.

Referring now toFIG. 19, the compressor fault detection algorithm is illustrated. In step1900, Pdand Tdare measured by the discharge temperature and pressure sensors. In step1902, it is determined whether the current rack is running. If the current rack is not running, the algorithm moves to the next rack in step1904. In step1906and1908, it is determined whether each compressor in the rack is running. In step1910, TDSATis determined for the running compressor based on Pd. The superheat is determined based on TDSATand Tdin step1912. The superheat is filtered by the pattern analyzer in step1914. If appropriate, an alarm message is generated in step1916and the algorithm loops back to step1904. Steps1902through1916are repeated for each rack and steps1906through1916are repeated for each refrigeration circuit.

In an alternative embodiment, the compressor fault detection algorithm compares the actual Tdto a calculated discharge temperature (Tdcalc). Tdis measured by the temperature sensors114associated with the discharge of each compressor102. Measurements are taken at approximately 10 second intervals while the compressors102are running. Tdcalcis calculated as a function of the refrigerant type, Pd, suction pressure (Ps) and suction temperature (Ts), each of which are measured by the associated sensors described above. An alarm value (A) and time delay (t) are also provided as presets and may be user selected. An alarm is signaled if the difference between the actual and calculated discharge temperature is greater than the alarm value for a time period longer than the time delay. This is governed by the following logic:If (Td−Tdcalc)>A and time>t, then alarm

Dirt and debris gradually builds up on the condenser coil and condenser fans can fail, impairing condenser performance. As these events occur, condenser performance degrades, inhibiting heat transfer to the atmosphere. The condenser performance algorithm is provided to determine whether the condenser126is dirty, which would result in a loss of energy efficiency or more serious system problems. Trend data is analyzed over a specified time period (e.g., several days). More specifically, the average difference between the ambient temperature (Ta) and the condensing temperature (TCOND) is determined over the time period. If the average difference is greater than a threshold (TTHRESH) (e.g., 25° F.) a dirty condenser situation is indicated and a maintenance alarm is initiated. Tais directly measured from the temperature sensor128.

Referring specifically toFIGS. 20 and 21, another alternative condenser performance algorithm will be described in detail. As illustrated inFIG. 20, a condenser performance monitor block2000includes an RPFP module2002and a pattern analyzer module2004. The condenser performance monitor block2000receives measured variables2006and configuration parameters2008and generates output parameters2010based thereon. The measured variables include Ta, Pc, Icmpand a condenser load (Icnd). The configuration parameters2008include refrigerant type and state, data pattern zones and a data sampler timer. The output parameters2010include an alarm message.

With particular reference toFIG. 21, Ta, Pc, Icmpand Icndare all measured by their respective sensors in step2100. In step2102, Tcis determined based on Pcusing RPFP, as discussed in detail above. In step2104, condenser capacity (U) is determined according to the following equation:

U=K⁢⁢ICMP(ICND+I0)⁢(Tc-Ta)
where K is a system constant and Iois a calibration value. For example, Iocan be set equal to 10% of the current consumption when all condenser fans are on. In step2106, U is processed through the pattern analyzer and an alarm maybe generated in step2108based on the results. As U varies from ideal, condenser performance may be impaired and an alarm message will be generated.

The defrost abnormality algorithm learns the behavior of defrost activity in the refrigeration circuits A, B, C, D. The learned or average defrost behavior is compared to current or past defrost conditions. More specifically, the defrost time (tDEF), maximum defrost time (tDEFMAX) and defrost termination temperature (TTERM) are monitored. If tDEFachieves tDEFMAXfor a number of consecutive defrost cycles (NDEF) (e.g., 5 cycles) and the particular case or circuit is set to terminate defrost at TTERM, an abnormal defrost situation is indicated. An alarm is initiated accordingly. The defrost abnormality algorithm also monitors TTERMacross cases within a circuit to isolate cases having the highest TTERM.

The case discharge versus product temperature algorithm compares the air discharge temperature (TDISCHARGE) to the case's set point temperature (TSETPOINT) and the product temperature (TPROD) to TDISCHARGE. The case temperature (TCASE) is also monitored. If TDISCHARGEis equal to TSETPOINT, and TPRODis greater than TCASEplus a tolerance temperature (TTOL) a problem with the case is indicated. An alarm is initiated accordingly.

Refrigerant level within the refrigeration system100is a function of refrigeration load, ambient temperatures, defrost status, heat reclaim status and refrigerant charge. A reservoir level indicator (not shown) reads accurately when the system is running and stable and it varies with the cooling load. When the system is turned off, refrigerant pools in the coldest parts of the system and the level indicator may provide a false reading. The refrigerant loss detection algorithm determines whether there is leakage in the refrigeration system100. The liquid refrigerant level in an optional receiver (not shown) is monitored. The receiver would be disposed between the condenser126and the individual circuits A, B, C, D. If the liquid refrigerant level in the receiver drops below a threshold level, a loss of refrigerant is indicated and an alarm is initiated.

Referring now toFIGS. 22 through 24, the data pattern recognition algorithm monitors inputs such as TCASE, TPROD, Psand Pd. The algorithm includes a data table (seeFIG. 22) having multiple bands whose upper and lower limits are defined by configuration parameters. A particular input is measured at a configured frequency (e.g., every minute, hour, day, etc.). as the input value changes, the algorithm determines within which band the value lies and increments a counter for that band. After the input has been monitored for a specified time period (e.g., a day, a week, a month, etc.) alarms are generated based on the band populations. The bands are defined by various boundaries including a high positive (PP) boundary, a positive (P) boundary, a zero (Z) boundary, a minus (M) boundary and a high minus (MM) boundary. The number of bands and the boundaries thereof are determined based on the particular refrigeration system operating parameter to be monitored. For each reading a corresponding band is populated. If the population of a particular band exceeds an alarm limit, a corresponding alarm is generated.

Referring now toFIG. 23, a pattern analyzer block2500receives measured variables2502, configuration parameters2504and generates output parameters2506based thereon. The measured variables2502include an input (e.g., TCASE, TPROD, Psand Pd). The configuration parameters2504include a data sample timer and data pattern zone information. The data sample timer includes a duration, an interval and a frequency. The data pattern zone information defines the bands and which bands are to be enabled. For example, the data pattern zone information provides the boundary values (e.g., PP) band enablement (e.g., PPen), band value (e.g., PPband) and alarm limit (e.g., PPpct).

Referring now toFIG. 24, input registers are set for measurement and start trigger in step2600. In step2602, the algorithm determines whether the start trigger is present. If the start trigger is not present, the algorithm loops back to step2600. If the start trigger is present, the pattern table is defined in step2604based on the data pattern bands. In step2606, the pattern table is cleared. In step2608, the measurement is read and the measurement data is assigned to the pattern table in step2610.

In step2612, the algorithm determines whether the duration has expired. If the duration has not yet expired, the algorithm waits for the defined interval in step2614and loops back to step2608. If the duration has expired, the algorithm populates the output table in step2616. In step2618, the algorithm determines whether the results are normal. In other words, the algorithm determines whether the population of a each band is below the alarm limit for that band. If the results are normal, messages are cleared in step2620and the algorithm ends. If the results are not normal, the algorithm determines whether to generate a notification or an alarm in step2622. In step2624, the alarm or notification message(s) is/are generated and the algorithm ends.