Patent Publication Number: US-11022356-B2

Title: Refrigeration system and method for automated charging and start-up control

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims the benefit of and priority as a continuation of U.S. patent application Ser. No. 15/587,931, filed May 5, 2017, which claims priority to U.S. Provisional Patent Application No. 62/338,152, filed May 18, 2016. Both are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     The present disclosure relates generally to a refrigeration system. The present disclosure relates more particularly to an automated charging and start-up method for a refrigeration system which does not require input from a technician. 
     Refrigeration systems are often used to provide cooling to temperature controlled display devices (e.g. cases, merchandisers, etc.) in supermarkets and other similar facilities. Vapor compression refrigeration systems are a type of refrigeration system which provide such cooling by circulating a fluid refrigerant (e.g., a liquid and/or vapor) through a thermodynamic vapor compression cycle. In a vapor compression cycle, the refrigerant is typically (1) compressed to a high temperature/pressure state (e.g., by a compressor of the refrigeration system), (2) cooled/condensed to a lower temperature state (e.g., in a gas cooler or condenser which absorbs heat from the refrigerant), (3) expanded to a lower pressure (e.g., through an expansion valve), and (4) evaporated to provide cooling by absorbing heat into the refrigerant. 
     Start-up and installation of a refrigeration system traditionally requires a service technician to go through a step-by-step process to charge the system with refrigerant. These methods can be inefficient and inexperienced technicians may damage the system and result in wasted energy or suboptimal system performance. 
     SUMMARY 
     One implementation of the present disclosure is a system for starting a refrigeration system after installation includes a liquid line regulating valve, a liquid line charging valve, a suction line expansion valve, and a suction line charging valve. The system includes a controller configured to override normal operation of the refrigeration system and transmit a demand signal to the refrigeration system to enable partial system operation. The controller is further configured to operate the liquid line regulating valve and the liquid line charging valve, in response to a demand signal, to charge a receiver tank. The controller is configured to gradually increase the demand signal to a predetermined level of partial system operation, and release the liquid line charging valve to normal operation. The controller is configured to operate the suction line expansion valve and the suction line charging valve, in response to a demand signal, to charge a suction line, gradually increase the demand signal to full system operation, and release the liquid line regulating valve, the suction line expansion valve, and the suction line charging valve to normal operation. 
     In some embodiments, the controller is further configured to cycle one or more compressors of the refrigeration system to control a suction pressure in the refrigeration system. In other embodiments, the controller is further configured to monitor the refrigeration system for a low refrigerant condition. In some embodiments, the low refrigerant condition is a low suction pressure, a low superheat reading, a low refrigerant temperature, a low refrigerant flow rate, or a low refrigerant level. 
     In some embodiments, the controller is further configured to suspend the increase of the demand signal based on a low refrigerant condition. In other embodiments, the controller is further configured to calculate a period of time for which the increase of the demand signal was suspended. 
     In some embodiments, the controller is further configured to decrease the demand signal based on the low refrigerant condition and the period of time. In other embodiments, the controller is further configured to monitor the refrigeration system for a plurality of power source conditions including at least one of a power failure, a partial loss of power, and a phase loss. 
     In some embodiments, the controller is further configured to restart operations based on the plurality of power source conditions. 
     In some embodiments, the controller is further configured to vary the demand signal based on a ramp rate value. In other embodiments, the ramp rate value is set based on at least one of a user input and a plurality of refrigerant conditions. 
     Another implementation of the present disclosure is a method for starting a refrigeration system after installation. The method includes overriding normal operation of the refrigeration system, and transmitting a demand signal to the refrigeration system to enable partial system operation. The method further includes operating a liquid line regulating valve and a liquid line charging valve, in response to a demand signal, to charge a receiver tank, gradually increasing the demand signal to a predetermined level of partial system operation, and releasing the liquid line charging valve to normal operation. The method includes operating a suction line expansion valve and a suction line charging valve, in response to a demand signal, to charge a suction line, gradually increasing the demand signal to full system operation, and releasing the liquid line regulating valve, the suction line expansion valve, and the suction line charging valve to normal operation. 
     In some embodiments, the method includes cycling one or more compressors of the refrigeration system to control a suction pressure in the refrigeration system. In other embodiments, the method includes monitoring the refrigeration system for a low refrigerant condition. In some embodiments, the low refrigerant condition is a low suction pressure, a low superheat reading, a low refrigerant temperature, a low refrigerant flow rate, or a low refrigerant level. 
     In some embodiments, the method includes suspending the increase of the demand signal based on the low refrigerant condition. In other embodiments, the method includes calculating a period of time for which the increase of the demand signal was suspended. 
     In some embodiments, the method includes decreasing the demand signal based on the low refrigerant condition and the period of time. In other embodiments, the method includes monitoring the refrigeration system for a plurality of power source conditions including at least one of a power failure, a partial loss of power, and a phase loss. 
     In some embodiments, the method includes restarting operations based on the plurality of power source conditions. 
     In some embodiments, the method includes varying the demand signal based on a ramp rate value. In other embodiments, the ramp rate value is set based on at least one of a user input and a plurality of refrigerant conditions. 
     Yet another implementation of the present disclosure is a controller including a memory and one or more processors. The processors are configured to override normal operation of the refrigeration system, and transmit a demand signal to the refrigeration system to enable partial system operation. The processors are further configured to operate the liquid line regulating valve and the liquid line charging valve, in response to a demand signal, to charge a receiver tank, gradually increase the demand signal to a predetermined level of partial system operation, and release the liquid line charging valve to normal operation. The processors are configured to operate the suction line expansion valve and the suction line charging valve, in response to a demand signal, to charge a suction line, gradually increase the demand signal to full system operation, and release the liquid line regulating valve, the suction line expansion valve, and the suction line charging valve to normal operation. 
     In some embodiments, the processors are further configured to monitor the refrigeration system for a low refrigerant condition. The processors are configured to calculate a period of time for which the increase of the demand signal is suspended, and suspend the increase of the demand signal based on the plurality of refrigerant conditions for the period of time. In some embodiments, the low refrigerant condition is a low suction pressure, a low superheat reading, a low refrigerant temperature, a low refrigerant flow rate, or a low refrigerant level. 
     In some embodiments, the one or more processors are further configured to decrease the demand signal based on the low refrigerant condition and the period of time. 
     In some embodiments, the processors are further configured to monitor the refrigeration system for a plurality of power source conditions including at least one of a power failure, a partial loss of power, and a phase loss, and restart operations based on the plurality of power source conditions. 
     In some embodiments, the processors are further configured to vary the demand signal based on a ramp rate value. In other embodiments, the ramp rate value is set based on at least one of a user input and a plurality of refrigerant conditions. 
     Those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the devices and/or processes described herein, as defined solely by the claims, will become apparent in the detailed description set forth herein and taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a refrigeration system having a refrigeration circuit, a subcooler assembly, a receiving tank, a condenser assembly, a compressor assembly, and an accumulator assembly, according to an exemplary embodiment. 
         FIG. 2  is a block diagram of a refrigeration system controller for the system of  FIG. 1  and associated components, according to an exemplary embodiment. 
         FIG. 3  is a flowchart of a process for pre-charging the receiver of the refrigeration system of  FIG. 1 , according to an exemplary embodiment. 
         FIG. 4  is a flowchart of a process for charging the suction line of the refrigeration system of  FIG. 1 , according to an exemplary embodiment. 
         FIG. 5  is a flowchart of a process for restarting the system of  FIG. 1  in the event of a power failure, brown out, or phase loss, according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring generally to the FIGURES, a refrigeration system and components thereof are shown, according to various exemplary embodiments. The refrigeration system may be a vapor compression refrigeration system. In some implementations, the refrigeration system may be used to provide cooling for temperature controlled display devices in a supermarket or other similar facility. 
     In some embodiments, the refrigeration system includes a receiving tank (e.g., a flash tank, a refrigerant reservoir, etc.) containing refrigerant, a condenser assembly, a compressor assembly, an accumulator, and a subcooler assembly. The refrigeration system includes a controller for monitoring and controlling the pressure, temperature, and/or flow of the refrigerant throughout the refrigeration system. The controller can operate each of the assemblies (e.g., according to the various control processes described herein) to efficiently regulate the pressure of the refrigerant within the receiving tank. Additionally, the controller can interface with other instrumentation associated with the refrigeration system (e.g., measurement devices, timing devices, pressure sensors, temperature sensors, etc.) and provide appropriate control signals to a variety of operable components of the refrigeration system (e.g., compressors, valves, power supplies, flow diverters, etc.) to regulate the pressure, temperature, and/or flow at other locations within the refrigeration system. Advantageously, the controller may be used to facilitate efficient operation of the refrigeration system, reduce energy consumption, and improve system performance. 
     Before discussing further details of the refrigeration system and/or the components thereof, it should be noted that references to “front,” “back,” “rear,” “upward,” “downward,” “inner,” “outer,” “right,” and “left” in this description are merely used to identify the various elements as they are oriented in the FIGURES. These terms are not meant to limit the element which they describe, as the various elements may be oriented differently in various applications. 
     It should further be noted that for purposes of this disclosure, the term “coupled” means the joining of two members directly or indirectly to one another. Such joining may be stationary in nature or moveable in nature and/or such joining may allow for the flow of fluids, transmission of forces, electrical signals, or other types of signals or communication between the two members. Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another. Such joining may be permanent in nature or alternatively may be removable or releasable in nature. 
     Referring now to  FIG. 1 , a refrigeration system  100  is shown according to an exemplary embodiment. Refrigeration system  100  may be a vapor compression refrigeration system. Refrigeration system  100  is shown to include a system of pipes, conduits, or other fluid channels for transporting the refrigerant between various thermodynamic components of the refrigeration system. The thermodynamic components of refrigeration system  100  are shown to include a subcooler  102 , receiver tank  104 , condenser assembly  106 , compressor assembly  108 , accumulator  110 , and refrigerant tank  130 . Refrigeration system  100  is also shown to include a liquid line charging solenoid valve  112 , a liquid line regulating/electronic expansion valve  114 , subcooler electronic expansion valve  115 , a suction line charging solenoid valve  116 , and a suction line electronic expansion valve  118 . Refrigeration system  100  is further shown to include drop leg/condensing pressure transducer  120 , a suction temperature transducer  122 , and a suction pressure transducer  124 . 
     Accumulator  110  prevents compressor damage from a sudden surge of liquid refrigerant and oil that could enter compressor assembly  108  from the suction line. Accumulator  110  is a temporary reservoir for the refrigerant and oil mixture, and is designed to meter the liquid refrigerant and oil back to compressor assembly  108  at a predefined rate. The flow rate to compressor assembly  108  may be calculated to prevent damage to the valves, pistons, rods, and crankshafts. Accumulator  110  may have a metering ejector device that picks up liquid, vaporizes it, and returns it to compressor assembly  108 . Accumulator  110  prevents liquid slugging and controls oil return. In some embodiments, accumulator  110  may receive vapor refrigerant from the evaporators of refrigeration system  100 . 
     Compressor assembly  108  may compress the refrigerant into a superheated vapor. In some embodiments, the compressor assembly may be a medium temperature assembly. In other embodiments, compressor assembly  108  may be a low temperature assembly, or may be a split suction assembly with both medium temperature and low temperature portions. The output pressure from compressor assembly  108  may vary depending on ambient temperature and other operating conditions. In some embodiments, compressor assembly  108  operates in a transcritical mode. In operation, the refrigerant discharge gas may exit compressor assembly  108  and flow through piping of the system into condenser assembly  106 . 
     Compressors of compressor assembly  108  may be arranged in parallel with other compressors of compressor assembly  108 . Any number of parallel compressors may be present. Compressor assembly  108  may be fluidly connected with condenser assembly  106 . When active, compressors of compressor assembly  108  compress the vapor received from accumulator  110  and discharge the compressed vapor to condenser assembly  106 . 
     Condenser assembly  106  may include one or more heat exchangers or other similar devices for removing heat from the refrigerant. In some embodiments, condenser assembly  106  partially or fully condenses refrigerant vapor into liquid refrigerant (e.g., if system operation is in a subcritical region). The condensation process may result in fully saturated refrigerant liquid or a liquid-vapor mixture (e.g., having a thermodynamic quality between 0 and 1). In other embodiments, condenser assembly  106  may cool the refrigerant vapor (e.g., by removing superheat) without condensing the refrigerant vapor into refrigerant liquid (e.g., if system operation is in a supercritical region). In some embodiments, the cooling/condensation process is an isobaric process. Condenser assembly  106  is shown outputting the cooled and/or condensed refrigerant to receiver tank  104 . 
     Receiver tank  104  collects the refrigerant from condenser assembly  106 . In some embodiments, receiver tank  104  may be a flash tank or other fluid reservoir. Receiver tank  104  includes a liquid portion and a vapor portion and may contain a partially saturated mixture of liquid and vapor refrigerant. In some embodiments, receiver tank  104  separates the liquid refrigerant from the vapor refrigerant. The liquid refrigerant may exit receiver tank  104  toward subcooler  102 . The vapor refrigerant may exit receiver tank  104  through a separate conduit (not shown). 
     Subcooler expansion valve  115 , shown to the left of subcooler  102 , is a flow restricting device that causes a pressure drop of the refrigerant. Subcooler expansion valve  115  may cause the refrigerant to expand to a low temperature, low pressure state. The low temperature, low pressure characteristics induced in the refrigerant at subcooler expansion valve  115  allow the heat in the refrigerant to flow from right to left, as shown in  FIG. 1 . The flow of heat from right to left provides additional cooling for the refrigerant that flows down from subcooler  102  toward liquid line regulating valve  114 . Subcooler  102  allows heat to flow from the refrigerant at a higher pressure (liquid), to the one with lower pressure (gas). Subcooler  102  delivers refrigerant to liquid line regulating valve  114 . 
     Liquid line regulating valve  114  may regulate several properties of refrigeration system  100 , including the pressure and flow rate of refrigerant. In some embodiments, liquid line regulating valve  114  is a stepper valve. Liquid line regulating valve  114  may expand the subcooled refrigerant, which is provided to the evaporators of refrigeration system  100 . In some embodiments, subcooled refrigerant may also pass through a check valve  126  and one or more isolation ball valves  128  as it is provided to accumulator  110 . Refrigerant tank  130  is shown to the right of isolation ball valves  128 . Refrigerant tank  130  may be regulated via isolation ball valves  128 , and may receive excess refrigerant exiting subcooler  102  and supply additional refrigerant to accumulator  110 . 
     Liquid line charging solenoid valve  112  and suction line charging solenoid valve  116  are electronically operated devices. Solenoid valves  112  and  116  control the flow of liquids or gases in a positive, fully-closed or fully-open mode. Solenoid valves are commonly used to replace manual valves or where remote control is desirable. A solenoid valve is operated by opening and closing a channel in the valve body that permits or prevents flow through the valve. The channel is opened or closed using a plunger that is raised or lowered in a tube. Solenoid valves may be operated by energizing the coil of the solenoid. 
     Liquid line regulating/electronic expansion valve  114  and suction line electronic expansion valve  118  may be electronic expansion valves or other similar expansion valves. Expansion valves  114  and  118  may not be adjustable, and may act as bottle necks or restrictors in refrigeration system  100 . In other embodiments, expansion valves  114  and  118  are variably adjustable (e.g., by a controller) between an open and closed position. Expansion valves  114  and  118  may cause the refrigerant to undergo a rapid drop in pressure, thereby expanding the refrigerant to a lower pressure, lower temperature state. The expansion process may be an isenthalpic and/or adiabatic expansion process. In some embodiments, expansion valves  114  and  118  may expand the refrigerant to a lower pressure than charging or regulating valves alone, thereby resulting in a lower temperature refrigerant. 
     Suction line expansion valve  118  may vaporize any liquid refrigerant so that only vapor refrigerant is provided to compressor assembly  108 . The presence of condensed liquid flowing into a compressor could be detrimental to system performance. Suction line expansion valve  118  may ensure that the refrigerant flowing into the compressor (e.g., from the upstream suction side thereof) has a sufficient superheat (e.g., degrees above the temperature at which the refrigerant begins to condense) to ensure that no liquid refrigerant is present. 
     Drop leg pressure transducer  120 , suction temperature transducer  122  and suction pressure transducer  124  may be any kind of transducers. Transducers generally convert one type of energy to another, and are commonly used as sensors when physical quantities such as heat and pressure are converted to electrical signals. Transducers  120 ,  122 , and  124  may be used in combination for superheat protection (i.e., ensuring that only vapor refrigerant is provided to the compressors) and to monitor the condition of the refrigerant in the suction line. Transducers  120 ,  122 , and  124  may be installed in the piping of refrigeration system  100 . 
     Referring now to  FIG. 2 , a block diagram  200  of a refrigeration system controller of the system of  FIG. 1  and associated components is shown, according to an exemplary embodiment. Block diagram  200  is shown to include refrigeration system controller  202 . Refrigeration system controller  202  is shown to include a BMS interface  204 , a communications interface  206 , a start-up controller  208 , and a normal operation controller  210 . Block diagram  200  is also shown to include a BMS circuit controller  236 , a database  238 , and a set of refrigeration system components  240 . 
     Refrigeration system controller  202  includes start-up controller  208  and normal operation controller  210 . Controller  202  may receive electronic data signals from various instrumentation or devices within refrigeration system  100 . For example, controller  202  may receive data input from timing devices, measurement devices (e.g., pressure sensors, temperature sensors, flow sensors, etc.), and user input devices (e.g., a user terminal, a remote or local user interface, etc.). Controller  202  may use the input to determine appropriate control actions for one or more devices of refrigeration system  100 . For example, controller  202  may provide output signals to operable components (e.g., valves, power supplies, flow diverters, compressors, etc.) to control a state or condition (e.g., temperature, pressure, flow rate, power usage, etc.) of system  100 . 
     In some embodiments, controller  202  may be configured to operate regulating valves, expansion valves, compressor assemblies, condenser assemblies, etc. In some embodiments, controller  202  may regulate or control the refrigerant pressure within condenser assembly  106  by operating a high pressure valve. Advantageously, controller  202  may operate high pressure valves in coordination with gas bypass valves and/or other operable components of refrigeration system  100  to facilitate improved control functionality and maintain a proper balance of refrigerant pressures, temperatures, flow rates, or other quantities (e.g., measured or calculated) at various locations throughout system  100 . 
     Controller  202  may receive electronic data signals from one or more measurement devices (e.g., pressure sensors, temperature sensors, flow sensors, etc.) located within refrigeration system components  240 . Controller  202  may use the input signals to determine appropriate control actions for control devices of refrigeration system  100  (e.g., compressors, valves, flow diverters, power supplies, etc.). 
     Controller  202  may receive a setpoint (e.g., a temperature setpoint, a pressure setpoint, a flow rate setpoint, a power usage setpoint, etc.) and operate one or more components of system  100  to achieve the setpoint. The setpoint may be specified by a user (e.g., via a user input device, a graphical user interface, a local interface, a remote interface, etc.) or automatically determined by controller  202  based on a history of data measurements. 
     Controller  202 , which includes start-up controller  208  and operation controller  210 , may be a proportional-integral (PI) controller, a proportional-integral-derivative (PID) controller, a pattern recognition adaptive controller (PRAC), a model recognition adaptive controller (MRAC), a model predictive controller (MPC), or any other type of controller employing any type of control functionality. In some embodiments, controller  202  is a local controller for refrigeration system  100 . In other embodiments, controller  202  is a supervisory controller for a plurality of controlled subsystems (e.g., a refrigeration system, an AC system, a lighting system, a security system, etc.). For example, controller  202  may be a controller for a comprehensive building management system incorporating refrigeration system  100 . Controller  202  may be implemented locally, remotely, or as part of a cloud-hosted suite of building management applications. 
     Refrigeration system controller  202  is shown to include a communications interface  206 . Communications interface  206  can be or include wired or wireless interfaces (e.g., jacks, antennas, transmitters, receivers, transceivers, wire terminals, etc.) for conducting electronic data communications. For example, communications interface  206  may be used to conduct data communications with valves, compressors, condensers, various data acquisition devices within refrigeration system  100  (e.g., temperature sensors, pressure sensors, flow sensors, etc.) and/or other external devices or data sources. Data communications may be conducted via a direct connection (e.g., a wired connection, an ad-hoc wireless connection, etc.) or a network connection (e.g., an Internet connection, a LAN, WAN, or WLAN connection, etc.). For example, communications interface  206  can include an Ethernet card and port for sending and receiving data via an Ethernet-based communications link or network. In another example, communications interface  206  can include a WiFi transceiver or a cellular or mobile phone transceiver for communicating via a wireless communications network. 
     Still referring to  FIG. 2 , start-up controller  208  is shown to have processing circuit  209 , including a processor  211  and memory  213 . Processor  211  can be implemented as a general purpose processor, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGAs), a group of processing components, a microcontroller, or other suitable electronic processing components. Memory  213  (e.g., memory device, memory unit, storage device, etc.) may be one or more devices (e.g., RAM, ROM, solid state memory, hard disk storage, etc.) for storing data and/or computer code for completing or facilitating the various processes, layers and modules described in the present application. 
     Memory  213  may be or include volatile memory or non-volatile memory. Memory  213  may include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described in the present application. According to an exemplary embodiment, memory  213  is communicably connected to processor  211  via processing circuit  209  and includes computer code for executing (e.g., by processing circuit  209  and/or processor  211 ) one or more processes described herein. Memory  213  is shown to include a sensor validator  212 , a connection status detector  214 , a state detector  216 , and a data logger  218 . Memory  213  is further shown to include a setpoint manager  220 , a phase manager  222 , a ramp counter  224 , a refrigerant condition detector  226 , an alarm manager  228 , a signal timer  230 , a power failure detector  232 , and a restart operator  234 . 
     Sensor validator  212  may confirm that all sensors and/or transducers are reading within range (no sensors are shorted or open circuited) and that all sensors are operating properly. Sensor validator  212  may prevent refrigeration system  100  from operating and/or may prevent the start-up process (e.g., process  300 ) from continuing if improper sensor operation is detected. For example, improper operation of drop leg/condensing pressure transducer  120 , suction temperature transducer  122 , and suction pressure transducer  124  of  FIG. 1  may prevent refrigeration system  100  from operating properly. Sensor validator  212  may ensure that these sensors are operating properly to facilitate proper system operation. Sensor validator  212  may communicate with data logger  218  to obtain sensor readings. In some embodiments, sensor validator  212  may compare sensor readings with benchmark readings for the operating conditions to determine whether a sensor is operating normally. For example, benchmark readings may be stored in database  238 , and sensor validator  212  may access database  238  to compare current sensor readings with benchmark readings. Sensor validator  212  may communicate directly with sensors through BMS interface  204  or communications interface  206  to receive sensor readings. In some embodiments, sensor validator  212  may read current sensor readings from memory  213  or database  238 . 
     Connection status detector  214  may determine whether a connection with the building management system (BMS) coupled to refrigeration system  100  is active. In some embodiments, connection status detector  214  confirms the connection is active by evaluating the status of BMS interface  204 . For example, if BMS interface  204  is offline, connection status detector  214  may determine that the BMS connection is not active. Connection status detector  214  may determine whether the BMS connection is active by attempting to transmit a signal to the BMS. In some embodiments, connection status detector  214  may set a value of a variable associated with the connection status in memory  213  or database  238 . Connection status detector  214  may raise a flag with the status of the connection. For example, connection status detector  214  may flag the status of the connection as offline. In some embodiments, the start-up process will not begin until the connection is online. In other embodiments, the start-up process will be delayed. 
     State detector  216  may determine the state of circuit controllers in refrigeration system  100 . State detector  216  may confirm that the BMS has established communications with controllers of refrigeration system components  240 . In some embodiments, state detector  216  communicates with connection status detector  214  to determine whether controllers of refrigeration system components  240  have communicated with the BMS. For example, state detector  216  may determine whether the controllers are in a ready state by communicating with each controller through BMS interface  204  or communications interface  206 . In some embodiments, state detector  216  may set a value of a variable associated with the state of controllers of refrigeration system components  240  in memory  213  or database  238 . State detector  216  may raise a flag with the state of controllers of refrigeration system components  240 . In some embodiments, refrigeration system  100  may not proceed with current operations until state detector  216  has indicated that each controller of refrigeration system components  240  is in a ready state. 
     Data logger  218  may include instructions for receiving (e.g., via communications interface  206 ) pressure information, temperature information, flow rate information, or other measurements (i.e., “measurement information” or “measurement data”) from one or more measurement devices of refrigeration system  100 . In some embodiments, the measurements may be received as an analog data signal. Data logger  218  may include an analog-to-digital converter for translating the analog signal into a digital data value. Data acquisition module may segment a continuous data signal into discrete measurement values by sampling the received data signal periodically (e.g., once per second, once per millisecond, once per minute, etc.). In some embodiments, the measurement data may be received as a measured voltage from one or more measurement devices. Data logger  218  may convert the voltage values into pressure values, temperature values, flow rate values, or other types of digital data values using a conversion formula, a translation table, or other conversion criteria. 
     In some embodiments, data logger  218  may convert received data values into a quantity or format for further processing by start-up controller  208 . For example, data logger  218  may receive data values indicating an operating position of liquid line charging solenoid valve  112 . This position may be used to determine the flow rate of refrigerant through liquid line charging solenoid valve  112 , as such quantities may be proportional or otherwise related. Data logger  218  may include functionality to convert a valve position measurement into a flow rate of the refrigerant through the valve. 
     In some embodiments, data logger  218  outputs current data values for the pressure within receiver tank  104 , the temperature at the outlet of condenser assembly  106 , the valve position or flow rate through any valves, or other data values corresponding to other measurement devices of refrigeration system  100 . In some embodiments, data logger  218  stores the processed and/or converted data values in a local memory  213  of start-up controller  208  or in a remote database  238  such that the data may be retrieved and used by start-up controller  208 . 
     In some embodiments, data logger  218  may attach a time stamp to the received measurement data to organize the data by time. If multiple measurement devices are used to obtain the measurement data, data logger  218  may assign an identifier (e.g., a label, tag, etc.) to each measurement to organize the data by source. For example, the identifier may signify whether the measurement information is received from a temperature sensor located at an outlet of condenser assembly  106 , a temperature or pressure sensor located within receiver tank  104 , etc. Data logger  218  may further label or classify each measurement by type (e.g., temperature, pressure, flow rate, etc.) and assign appropriate units to each measurement (e.g., degrees Celsius (° C.), Kelvin (K), bar, kilo-Pascal (kPa), pounds force per square inch (psi), etc.). Data logger may store user information associated with the user providing commands to refrigeration system  100  through communications interface  206 . Data logger  218  may store information such as name, location, authorization level, etc. In some embodiments, data logger  218  may record a time stamp corresponding to the time at which a command or process is executed. For example, when start-up mode begins, or when a memory module executes. 
     Database  238  may be any kind of remote storage, and may store configuration settings for refrigeration system  100 . Such configuration settings may include control parameters used by controllers  208  and  210  (e.g., proportional gain parameters, integral time parameters, setpoint parameters, etc.), translation parameters for converting received data values into temperature or pressure values, system parameters for a stored system model of refrigeration system  100  (e.g., as may be used for implementations in which controllers  208  and  210  use a model predictive control methodology), or other parameters as may be referenced by various memory modules  212 - 234  in performing the various control processes described herein. 
     Setpoint manager  220  may control setpoints for refrigeration system  100 . Setpoints may be desired operating ranges or points. Setpoints may be controlled by a user of refrigeration system  100 . Setpoint manager  220  may accept input from communications interface  206 . Setpoint manager  220  may communicate with refrigeration system components  240  directly through communications interface  206 . Setpoint manager  220  may communicate with refrigeration system components  240  through BMS circuit controller  236 . Setpoint manager  220  may control setpoints for relevant variables which may not be controlled by refrigeration system components  240 . For example, setpoint manager  220  may control the temperature setpoint for a zone in which refrigeration system  100  is installed. 
     Phase manager  222  may inform refrigeration system  100  and a user of refrigeration system  100  of the phase of operation refrigeration system controller  202  is currently executing. Phase manager  222  may store phase information in memory  213  or a remote database  238 . For example, phase manager  222  may store information that refrigeration system  100  has completed the receiver pre-charging phase and is entering the suction charging phase. In some embodiments, phase manager  222  may store a value corresponding to a phase. In other embodiments, phase manager  222  may change the value of a variable stored in memory  213  or database  238  which is associated with the phase of refrigeration system  100 . For example, phase manager  222  may access database  238  to change the value of a variable REF_SYS_PHS from RPC (receiver pre-charge) to SCP (suction charging phase). 
     Ramp counter  224  may count up or count down and effect a corresponding change in the demand signal sent to refrigeration system controller  202 . For example, ramp counter  224  may count from 0 to 100, where each scalar maps to a percentage of the demand signal. In some embodiments, the demand signal does not represent the percentage of physical circuits that are demanded, but rather represents the percentage of the total system capacity demanded. Ramp counter  224  may count up, which causes the demand signal to increase, or may count down, which causes the demand signal to decrease. Ramp counter  224  allows the demand signal to gradually (e.g., continuously or incrementally) increase or decrease, reducing strain put on refrigeration components  240  which may occur when demand is suddenly increased or decreased. 
     Still referring to  FIG. 2 , memory  213  is shown to include a refrigerant condition detector  226 . Refrigerant condition detector  226  may ensure that the refrigerant flowing into a compressor (e.g., compressor assembly  108 ) contains no condensed liquid refrigerant, as the presence of condensed liquid flowing into a compressor could be detrimental to system performance. Refrigerant condition detector  226  may ensure that the refrigerant flowing into the compressor (e.g., from the upstream suction side thereof) has a sufficient superheat (e.g., degrees above the temperature at which the refrigerant begins to condense) to ensure that no liquid refrigerant is present. 
     In some embodiments, refrigerant condition detector  226  monitors a current temperature “T suction ” and/or pressure “P suction ” of the refrigerant flowing into a compressor. The current temperature T suction  and/or pressure P suction  may be determined by data logger  218  and stored in a local memory  213  of start-up controller  208  or in a remote database  238  accessible by start-up controller  208 . Refrigerant condition detector  226  may compare the current temperature T suction  with a threshold temperature value “T threshold ” stored in database  238 . The threshold temperature value T threshold  may be based on a temperature “T condensation ” at which the refrigerant begins to condense into a liquid-vapor mixture at the current pressure P suction . For example, T threshold  may be a fixed number of degrees T superheat  above T condensation  (e.g., T threshold =T condensation +T superheat ). In an exemplary embodiment, T superheat  may be approximately 10K (Kelvin) or 10° C. In other embodiments, T superheat  may be approximately 5K, approximately 15K, approximately 20K, or within a range between 5K and 20K. Refrigerant condition detector  226  may prevent activation of the compressor associated with the temperature measurement if T suction  is less than T threshold . 
     In some embodiments, refrigerant condition detector  226  monitors a current temperature “T outlet ” of the refrigerant exiting condenser assembly  106 . Refrigerant condition detector  226  may ensure that the refrigerant exiting condenser assembly  106  has the ability to provide sufficient superheat to the refrigerant flowing into compressor assembly  108 . The current temperature T outlet  may be determined by data logger  218  and stored in a local memory  213  of start-up controller  208  or in a remote database  238  accessible by start-up controller  208 . Refrigerant condition detector  226  may compare the current temperature T outlet  with a threshold temperature value “T threshold_outlet ” stored in database  238 . The threshold temperature value T threshold_outlet  may be based on the temperature T condensation  at which the refrigerant begins to condense into a liquid-vapor mixture at the current pressure suction P suction  for compressor assembly  108 . In some embodiments, the threshold temperature value T threshold  may be based on an amount of heat predicted to transfer (e.g., using a heat exchanger efficiency, a temperature differential between T outlet  and T suction , etc.). Refrigerant condition detector  226  may prevent activation of compressor assembly  108  if T outlet  is less than T threshold . 
     Refrigerant condition detector  226  may monitor refrigerant conditions such as refrigerant temperature, refrigerant flow rate, refrigerant pressure, etc. and communicate with alarm manager  228 . In some embodiments, refrigerant condition detector  226  may raise an alarm for conditions such as low superheat, low refrigerant temperature, low flow rate, low pressure, etc. Refrigerant condition detector  226  may set a variable associated with each condition. Refrigerant condition may store the condition in memory  213  or database  238 . Refrigerant condition detector  226  may communicate with alarm manager  228  to raise an alarm. For example, refrigerant condition detector  226  may detect low suction pressure in refrigeration system  100 . Refrigerant condition detector  226  may communicate with alarm manager  228  to set an alarm for low suction pressure. In other embodiments, refrigerant condition detector  226  may not communicate with alarm manager  228  and may flag the condition. For example, refrigerant condition detector  226  may flag a variable associated with suction pressure as being in a low state. Refrigeration system controller  202  may base control decisions on any variables in memory  213  or database  238 , and may evaluate each variable prior to executing commands or processes. 
     Alarm manager  228  may activate, escalate, de-escalate, deactivate, etc. alarms for refrigeration system  100 . Alarm manager  228  may alert a user to undesirable conditions occurring in refrigeration system  100 . For example, alarm manage  228  may set an alarm if one or more of the monitored refrigerant conditions are too low (e.g., below a threshold). In some embodiments, if an alarm is active, refrigeration system  100  may not proceed with ongoing activity. For example, if an alarm is active, the start-up procedure of the present disclosure may be halted until the alarm is cleared. Alarms may be raised, cleared, etc. by a user of refrigeration system  100 . In some embodiments, a user may override an alarm. A user may ignore the alarm, or a user may clear the alarm. In some embodiments, alarm manager  228  and refrigerant condition detector  226  are combined in one module. 
     Signal timer  230  may record temporal data for any signal transmitted or received by refrigeration system controller  202 . In some embodiments, signal timer  230  may record the length of time that the demand signal to refrigeration system  100  has been delayed during the new start-up process discussed in the present disclosure. Signal timer  230  may keep a running clock. For example, signal timer  230  may start counting when the demand signal has been delayed, and may run until the delay has ceased. Signal timer  230  may keep multiple running clocks. In some embodiments, signal timer  230  may track the length of any process. Signal timer  230  may record the start time in memory  213  or remote database  238  and calculate the total time using the stop time. In some embodiments, signal timer  230  communicates with data logger  218  to record timestamps or to access temporal data. For example, signal timer  230  may store a timestamp for the start time of a delay of the demand signal in database  238 . Refrigeration system controller  202  may request the total time that the demand signal has been delayed at present. Signal timer  230  may calculate the total time of delay by accessing database  238  to compare the current time to the stored start timestamp. In some embodiments, signal timer  230  and data logger  218  are combined in one module. 
     Power failure detector  232  may determine that a power failure, or similar event, has occurred. Power failure detector  232  may detect power failures, brown-outs, phase losses, etc. In some embodiments, power failure detector  232  detects conditions requiring a restart of refrigeration system  100  has occurred. For example, power failure detector  232  may detect that a single refrigeration component  240  has experienced a power failure. Power failure detector  232  may determine that a power failure, or similar event, has occurred based on amount of time during which power was lost, an amount of power lost, etc. For example, if refrigeration system  100  has experienced a loss of 3 kW, power failure detector  232  may determine that a power failure has occurred. Power failure detector  232  may be able to detect component errors and initiate a restart of refrigeration system  100 . For example, if power failure detector  232  has determined that a compressor of compressor assembly  108  has lost connection through BMS interface  204  or communications interface  206 , power failure detector  232  may determine that a restart of refrigeration system  100  is necessary. 
     Memory  213  is shown to include restart operator  234 . Restart operator  234  may execute the process of  FIG. 6  in the case that power failure detector  232  has detected a condition requiring a restart. For example, restart operator  234  may restart refrigeration system  100  if a temporary loss of power occurs for 15 minutes. Restart operator  234  may simply contain computer-readable instructions for executing the restart process. In some embodiments, restart operator  234  may be a separate controller. Restart operator  234  may override start-up controller  208  and normal operation controller  210 . Restart operator  234  may block signals from start-up controller  208  and normal operation controller  210 . Restart operator  234  may set its priority higher than start-up controller  208  and normal operation controller  210 . Operation of restart operator  234  is described in detail in the discussion of  FIG. 6 . 
     Normal operation controller  210  may control operation of refrigeration system  100  after the start-up phase or restart phase is complete. Normal operation controller  210  may operate valves  112 - 118 , condensers  106 , and compressor assembly  108  during normal operation. During the start-up process, refrigeration system  100  may override normal operation controller  210 . In some embodiments, start-up controller  208  overrides normal operation controller  210 . In other embodiments, refrigeration system controller  202  may simply send normal operation controller  210  into a standby mode. In some embodiments, refrigeration system controller  202  may block the signal from normal operation controller  210  to each of refrigeration system components  240 . In other embodiments, refrigeration system controller  202  may set a priority for each command and/or message from start-up controller  208  over all controllers, such as normal operation controller  210 . 
     Referring still to  FIG. 2 , refrigeration system components  240  is shown to include exemplary components. Refrigeration system components  240  may include any of the set of components in refrigeration system  100 , as described with reference to  FIG. 1 . For example, refrigeration system components  240  may include compressor  242 , expansion valve  244 , and solenoid valve  246 . Refrigeration system components  240  may also include components not shown in  FIG. 2 , such as condensers, accumulators, suction filters, subcoolers, etc. Refrigeration system components  240  may be communicably coupled to refrigeration system controller  202  through communications interface  206 . Refrigeration system components  240  may receive command data and send information to refrigeration system controller  202  through communications interface  206 . 
     Referring now to  FIG. 3 , a process  300  for pre-charging a receiver tank of a refrigeration system as part of a start-up method is shown, according to an exemplary embodiment. Prior to the beginning of process  300 , several procedures may be completed. For example, full factory end-of-line testing may be completed. End-of-line testing may include debugging, product quality assurance, component testing, assembly testing, system testing, etc. Refrigeration system  100  may have been triple evacuated, and all transducers may have been re-installed. A check may have been performed to ensure that the contractor or technician has used the correct refrigerant for charging system  100 , and that system  100  is connected to the charging ports and ready for start-up. 
     In some embodiments, electronic circuit controllers may be used by refrigeration system  100 . Electronic circuit controllers may have been verified as properly set-up for operation. A check may have been performed to ensure that a building management system (BMS) is communicably coupled to refrigeration system  100  and/or refrigeration system controller  202 . A connected BMS may have commanded all circuits of refrigeration system  100  to enter a standby or off position. 
     Process  300  begins with step  302 , in which system  100  of  FIG. 1  receives power. Power may be received from any source, and may be provided from a facility in which system  100  is installed. In some embodiments, process  300  may be initiated when power is received by refrigeration system controller  202  of  FIG. 2 . 
     Referring still to  FIG. 3 , process  300  may continue upon receiving power after all previous testing and procedures have been completed. Refrigeration system  100  may conduct a self-check, beginning with step  304 , in which refrigeration system controller  202  validates sensor operation of refrigeration system  100 . A component of refrigeration system  100  such as sensor validator  212  may perform step  304 . In some embodiments, refrigeration system  100  may confirm that all sensors and/or transducers are reading within range (no sensors are shorted or open circuited). Some sensors may prevent refrigeration system  100  from operating or process  300  from continuing if their readings are out of range. For example, improper operation of drop leg/condensing pressure transducer  120 , suction temperature transducer  122 , and suction pressure transducer  124  of  FIG. 1  may prevent refrigeration system  100  from operating properly. Accordingly, ensuring that these sensors are functioning properly may ensure proper system operation. 
     Once refrigeration system  100  has confirmed that relevant sensors are functioning properly, process  300  may continue with step  306 , in which refrigeration system  100  confirms BMS interface  204  of  FIG. 2  is active. In some embodiments, refrigeration controller  202  confirms BMS interface  204  is active. In other embodiments, a component of refrigeration controller  202 , such as connection status detector  214 , may perform step  306 . The communications protocol used may be any building management system protocol, such as BACnet, LonWorks, Modbus, ZigBee, etc. The communications protocol may be any wireless communications protocol, such as WiFi, Bluetooth, NFC, etc. In some embodiments, refrigeration system  100  may confirm that interface  204  is active by checking that the connection to BMS circuit controller  236  of  FIG. 2  is active. For example, refrigeration system  100  may confirm that BMS interface  204  is active by checking that the BACnet connection to BMS circuit controller  236  is active. In some embodiments, process  300  may not continue until the connection is online. 
     Process  300  may continue with step  308 , in which refrigeration system  100  confirms that the building management system has established communications with circuit controllers, and that they are in a ready state. In some embodiments, refrigeration system controller  202  confirms that BMS circuit controller  236  has established communications with circuit controllers, and that they are in a ready state. In other embodiments, a component of refrigeration system controller  202 , such as state detector  216 , may perform step  308 . Refrigeration system  100  may not allow process  300  to proceed until circuit controllers are in a ready state or refrigeration system  100  receives an indication of an “OK” status. For example, refrigeration system  100  may not allow process  300  to proceed until circuit controllers transmit a signal indicating they are ready for the receiver pre-charge phase. 
     Process  300  may continue once refrigeration system  100  has completed its self-check procedure and all criteria have been met. The next step of process  300 , step  310 , may include logging a start time and any relevant user data for the receiver pre-charge phase. In some embodiments, step  310  may be performed by a component of refrigeration system controller  202 , such as data logger  218 . The start time may be saved in database  238  of  FIG. 2 . In some embodiments, the start time is saved as a timestamp. The start time may be saved permanently, and may be used in future decision making. 
     Referring still to  FIG. 3 , process  300  may continue with step  312 , in which refrigeration system  100  may override normal operation controller  210 . In some embodiments, refrigeration system controller  202  includes a start-up controller  208  which overrides normal operation controller  210 . Refrigeration system controller  202  may simply send normal operation controller  210  into a standby mode. In some embodiments, refrigeration system controller  202  may block the signal from normal operation controller  210  to each of refrigeration system components  240 . In other embodiments, refrigeration system controller  202  may set a priority for each command and/or message from start-up controller  208  over all controllers, such as normal operation controller  210 . 
     Process  300  may continue with step  314 , in which refrigeration system  100  operates a compressor to maintain a suction setpoint. Setpoints may be managed and set by a user through setpoint manager  220 . In some embodiments, step  314  is performed by refrigeration system controller  202 . Refrigeration system  100  may operate a single compressor to maintain the suction setpoint. The suction setpoint may maintain a certain suction pressure and/or temperature in refrigeration system  100 . In some embodiments, refrigeration system  100  may operate more than one compressor if required to reach the suction setpoint. 
     Process  300  may continue with step  316 , in which refrigeration system  100  may send a demand signal to a building management system for partial system operation. For example, refrigeration system  100  may send a demand signal for 10% of system operation. The demand signal may be sent by refrigeration system controller  202 , through BMS interface  204  to BMS circuit controller  236 . In some embodiments, BMS circuit controller  236  may enable 10% of the circuits in refrigeration system  100  based on total design capacity, not percentage of circuit quantity. For example, if one circuit of eight hundred circuits provides 10% of total system capacity, the one circuit may be enabled. 
     Process  300  may continue with step  318 , in which refrigeration system  100  may close subcooler electronic expansion valve  115  and liquid line regulating valve  114  and open liquid line charging solenoid valve  112 . Closing subcooler electronic expansion valve  115  and liquid line regulating valve  114  and opening liquid line charging solenoid valve  112  may cause refrigerant to accumulate in receiver tank  104 . Subcooler electronic expansion valve  115  and liquid line regulating valve  114  each represent an outlet through which refrigerant may flow. Opening liquid line charging solenoid valve  112  may allow refrigerant to flow into receiver tank  104 , while closing subcooler electronic expansion valve  115  and liquid line regulating valve  114  may prevent refrigerant from flowing out of receiver tank  104 , regardless of whether the refrigerant flows through the right side or left side of subcooler  102 . 
     Process  300  may continue with step  320 , in which refrigeration system  100  may cycle compressors as liquid refrigerant is charged into receiver tank  104 . In some embodiments, multiple compressors have been enabled in step  314 , and compressors may be cycled on and off to modulate suction pressure setpoint and minimize short cycling. Short cycling, in which equipment is started and stopped rapidly, may be detrimental to equipment lifespan and is energy inefficient. Refrigeration system  100  may use a rotational sequence to cycle compressors and reduce short cycling. Refrigeration system  100  may determine whether refrigerant levels have reached some predetermined threshold level in step  322 . If refrigerant levels have reached a predetermined threshold level, process  300  may continue with step  324 . Predetermined threshold levels may be user adjustable. For example, a predetermined threshold level may be 50% of receiver tank  104  capacity. In step  324 , refrigeration system  100  may close liquid line charging solenoid valve  112 . For example, once refrigerant levels reach 50%, refrigeration system  100  may disable the liquid line charging solenoid valve  112  to the flow of refrigerant to receiver tank  104 . If refrigerant levels have not reached the predetermined threshold level, process  300  may continue to cycle compressors in step  320 . 
     Process  300  may terminate with step  326 , in which refrigeration system  100  notifies a user of the completion of the receiver pre-charge phase. In some embodiments, the notification may be transmitted to a user through communications interface  206 . Phase manager  222  of  FIG. 2  may set the phase of refrigeration system  100  to manage the phase in which refrigeration system  100  is currently operating. Once receiver tank  104  has been pre-charged with liquid refrigerant, the next phase may begin. 
     Referring now to  FIG. 4 , a process  400  in which the suction line of refrigeration system  100  is charged with liquid is shown, according to an exemplary embodiment. Process  400  may begin with step  402 , in which refrigerant system  100  may enable the suction line charging valve  116  and release the liquid line regulating solenoid valve (ELPR)  114  to operate normally. Liquid line regulating valve  114  may not be adjustable, and may act as a restrictor, or bottleneck, to the flow of refrigerant. In other embodiments, liquid line regulating valve  114  may be adjustable (e.g., by refrigeration system controller  202 ) between an open position and a closed position. Suction line charging valve  116  may be equipped with an expansion device (e.g., suction line expansion valve  118 ) to increase charging performance and minimize the potential for liquid slugging. 
     Upon opening liquid line regulating valve  114  and suction line charging valve  116 , process  400  may continue with step  404 , in which a controller of refrigeration system  100  (e.g., controller  202 ) operates a single compressor of compressor assembly  108  to maintain the suction setpoint. The suction setpoint may be controlled by setpoint manager  220 . Process  400  may continue with step  406 , in which refrigeration system  100  may detect a low condition of the refrigerant. For example, refrigeration system  100  may detect low suction pressure, low superheat, low refrigerant temperature, low refrigerant flow rate, low refrigerant level, and/or any other condition of the refrigerant that is below a minimum threshold value. Step  406  may be performed by refrigerant condition detector  226  of  FIG. 2 . Refrigeration system  100  may continually check for low conditions of the refrigerant. Multiple low conditions may be detected. For example, refrigeration system  100  can detect low superheat and low suction pressure, and advance process  400  to step  434 . 
     If a low condition of the refrigerant is not detected, process  400  may continue with step  408 , in which refrigeration system  100  may begin a proofing timer. The proofing timer may be an embodiment of signal timer  230 . In some embodiments, signal timer  230  may communicate with database  238  through communications interface  206 . Signal timer  230  may store the start time or a timestamp in database  238 . 
     Process  400  may continue to step  410 , in which refrigeration system  100  determines whether any compressors in compressor assembly  108  are still operating. If no compressors in compressor assembly  108  are operating, process  400  will proceed to step  412  and rotate the lead compressor in compressor assembly  108 . The rotational order of compressor cycling in refrigeration system  100  may prevent or reduce short cycling and improve performance and efficiency of refrigeration system  100 . 
     If at least one compressor in compressor assembly  108  is operating when process  400  reaches step  410 , the process will continue to step  414 , in which refrigeration system  100  resets the demand signal delay timer. The demand signal delay timer may be an embodiment of signal timer  230 . In some embodiments, signal timer  230  may communicate with database  238  through communications interface  206 . Signal timer  230  may store the start time or a timestamp in database  238 . After resetting the demand signal delay timer, process  400  may proceed to step  416 , and clear any alarms relating to monitored refrigerant conditions. In some embodiments, step  416  may involve alarm manager  228  and refrigerant condition detector  226 . 
     As compressor assembly  108  runs, process  400  may continue to step  418 , in which refrigeration system  100  may begin a ramp counter  224  to increase the demand signal for system operation to full operating capacity. For example, ramp counter  224  may increase demand signal from 10% to 100%. The rate at which ramp counter  224  may increase the demand signal may be represented by a variable, “R ramp_up .” In alternative embodiments, R ramp_up  may be expressed as a series of setpoints for the demand signal percentage. R ramp_up  may be set by a user, or it may be set automatically depending on various system conditions. For example, if the demand signal successfully increases at a rate of 5% per 30 minutes for a certain period of time without a detected fault (i.e., a low refrigerant condition), R ramp_up  may automatically increase to 10% per 30 minutes for the rest of the period that the demand signal is increasing. 
     In some embodiments, the time for the demand signal to reach 100% will exceed two hours. Increasing demand for system operation at increments allows refrigeration system  100  to ramp up to reduce strain on system components. As the demand signal increases, process  400  may proceed to step  420 , and refrigeration system  100  may operate additional compressors in compressor assembly  108  in order to match the demand. Refrigeration system  100  may continue to operate additional compressors until the demand signal reaches 100%, in step  422 . 
     If the demand signal and/or ramp counter has reached the desired level of system operation, refrigeration system  100  may begin a “No Alarm Delay” timer in step  424 . The “No Alarm Delay” timer may be used to temporarily delay the system. In some embodiments, this timer may be a component of signal timer  230 . Signal timer  230  may store timestamps or time data in database  238 . The amount of time refrigeration system  100  delays while the timer runs may be predetermined by a user or calculated by refrigeration system  100 . For example, the delay may be 15 seconds, 5 minutes, 30 minutes, etc. In some embodiments, the alarm is for low refrigerant conditions, such as those detected in step  406 . In other embodiments, the alarm is for violations of other conditions of refrigeration system  100 . The timestamp data collected in step  310  of  FIG. 3  may be used to determine whether an alarm has occurred within a predetermined period of time. For example, referring now to  FIG. 2 , refrigeration system controller  202  may access database  238  through communications interface  206  to determine how long it has been since an alarm has occurred. 
     Process  400  continues to step  426 , when the “No Alarm Delay” timer expires and it is confirmed that an alarm has not occurred within the predetermined period of time associated with the timer. At the expiration of the “No Alarm Delay” timer, signal timer  230  may store timestamps or time data in database  238 . Process  400  may proceed to step  428 , in which refrigeration system  100  may close suction line charging valve  116  and release subcooler expansion valve  115  to normal operation. Once suction line charging valve  116  has been closed, the flow of refrigerant to the suction line may stop. Refrigeration system  100  may then release its components to normal operation in step  430 . For example, the compressors of compressor assembly  108  may operate normally to maintain system pressure. In some embodiments, refrigeration system  100  may release components from start-up controller  208 . For example, refrigeration system  100  may alter priority of commands, moving start-up controller  208  behind normal operation controller  210 . In other embodiments, refrigeration system  100  may cease to block commands from normal operation controller  210 , allowing refrigeration system components  240  to receive commands from normal operation controller  210 . Refrigeration system  100  may send start-up controller  208  into a standby mode to cease sending commands to refrigeration system components  240 . 
     Finally, process  400  may conclude with step  432 , in which refrigeration system  100  may transmit a signal to the building management system and/or BMS circuit controller  236  to indicate that start-up mode is complete, and that refrigeration system  100  is ready for normal operation. In some embodiments, refrigeration system controller  202  may transmit a signal to BMS circuit controller  236  through BMS interface  204 . The signal may initiate a change in phase manager  222 , which may indicate that the suction line charging phase is complete. In some embodiments, refrigeration system controller  202  may log times, for example, the amount of time refrigeration system  100  was stopped or the time refrigeration system  100  was in a start-up mode. 
     However, returning to step  406 , if a low condition of the refrigerant is detected, process  400  may proceed with step  434  in order to resolve the condition. In step  434 , a component of refrigeration system  100  (e.g., controller  202 ) may pause increasing the demand signal and/or ramp counter for system operation. For example, refrigeration system  100  may detect low refrigerant level and stop increasing the demand signal for system operation. The demand signal may have reached 60%, and ramp counter  224  may stop at 60% of total system capacity. Stopping ramp counter  224  may stop increasing demand on refrigeration system components  240  and prevent further stress on refrigeration system  100 . 
     Process  400  may continue with step  436 , in which refrigeration system  100  may start a demand signal delay timer. The amount of time the demand signal delay timer runs may be predetermined by a user or calculated by refrigeration system  100 . For example, the delay may be 15 seconds, 5 minutes, 30 minutes, etc. The demand signal delay timer may be an embodiment of signal timer  230 . In some embodiments, signal timer  230  may communicate with database  238  through communications interface  206 . Signal timer  230  may store the start time or a timestamp in database  238 . Once the demand signal delay timer is started, process  400  may proceed to step  438 , when a Level 1 alarm is sent to the BMS. In some embodiments, the alarm may be activated by alarm manager  228 . 
     The demand signal delay timer started in step  436  will run while the low condition of the refrigerant is detected. Proceeding to step  440 , refrigeration system  100  may determine whether the demand signal has been delayed for longer than a predetermined amount of time, and thus the demand signal delay timer has expired. For example, refrigeration system  100  may determine the amount of time that the demand signal has been delayed by checking the time logged by signal timer  230 . Refrigeration system  100  may calculate the amount of time that the demand signal has been delayed by accessing a start timestamp stored in database  238 . For example, the predetermined amount of time may be 30 minutes. Once the demand signal delay timer has expired, process  400  may proceed to step  442 , when a Level 2 alarm is sent to the BMS. A Level 2 alarm may indicate a problem of higher severity than a Level 1 alarm. In some embodiments, the alarm may be activated by alarm manager  228 . 
     If the demand signal delay timer expires (i.e., the total delay time is determined to be longer than the threshold amount of time), process  400  may continue with step  444 . Refrigeration system  100  may reverse ramp counter  224  to decrease the demand signal to refrigeration system  100 . For example, if ramp counter  224  and/or the demand signal is at 65%, refrigeration system  100  may reverse ramp counter  224  to count down toward 0% to decrease the demand signal. Decreasing the demand signal may allow refrigeration system  100  to resolve low conditions of refrigeration system  100 . Decreasing the demand signal can reduce the stress on refrigeration system  100 , and may allow refrigeration system components  240  time to catch up and resolve low conditions of the refrigerant. 
     The rate at which ramp counter  224  may decrease the demand signal may be represented by a variable, “R ramp_down ” In alternative embodiments, R ramp_down  may be expressed as a series of setpoints for the demand signal percentage. R ramp_down  may be set by a user, or it may be set automatically depending on various system conditions. For example, if the demand signal decreases at a rate of 5% per 30 minutes for a period of time and a critically low refrigerant condition is detected during that period, R ramp_down  may automatically increase to 10% per 30 minutes for the rest of the period so that a demand signal of 0% is reached more quickly. In some embodiments, the value of R ramp_up  may equal the value of R ramp_down , or both values may be calculated from the same system conditions. In other embodiments, the value of R ramp_up  may be fully independent from the value of R ramp_down . 
     As the demand signal decreases, process  400  may proceed to step  420 , and refrigeration system  100  may operate fewer compressors in compressor assembly  108  in order to match the demand. Refrigeration system  100  may continue to operate fewer compressors until the demand signal reaches 0%, in step  446 . Once the demand signal reaches 0%, a Level 3 alarm may be sent to the BMS in step  448 . In some embodiments, the alarm may be activated by alarm manager  228 . A Level 3 alarm is the highest severity alarm, and may require a user or technician to manually reset the system. 
     Once the low pressure, low refrigerant level, or low superheat condition has been reset, process  400  may revert to step  406 . From there, process  400  proceeds in the same manner as if no low condition of refrigeration system  100  was ever detected. For example, in step  412 , the lead compressor may be rotated to minimize short cycling, and in steps  418 - 422 , controller  202  may restart the demand increase counter from its prior stopping point and gradually increase the demand signal until it reaches 100%. Process  400  culminates with the expiration of the “No Alarm Delay” timer in step  426 , the closing of the suction line charging valve  116  in step  428 , the release of refrigeration system components  240  in step  430 , and the transmission of the signal to the BMS controller indicating the completion of the start up mode in step  432 . 
     Referring now to  FIG. 5 , a process  500  for restarting refrigeration system  100  is shown, according to an exemplary embodiment. If, at any point in time, refrigeration system  100  experiences a power failure, brown-out, phase loss, etc., refrigeration system  100  may enter a power failure phase or mode, illustrated by process  500 . Process  500  begins with step  502 , in which refrigeration system  100  detects a power failure, brown-out, phase loss, etc. Any loss of connection with power or drop in power may trigger process  500 . In some embodiments, a drop in power of an amount over a predetermined threshold amount may trigger process  500 . Step  502  may be performed by power failure detector  232 . 
     Process  500  may continue with step  504 , in which refrigeration system  100  may determine whether the connection between refrigeration system  100  and a building management system is active. In some embodiments, the connection is BMS interface  204 , and step  504  may be performed by connection status detector  214 . If BMS interface  204  is not active, refrigeration system  100  may increase all delay times in step  506 . For example, delay times may be doubled. In some embodiments, delay times may be increased by a predetermined amount of time. Increasing delay times may allow refrigeration system components  240  to catch up during the restart operation. Process  500  may continue with step  508 . 
     If BMS interface  204  is active, process  500  may continue with step  508 . Refrigeration system  100  may override normal operation controller  210 . In some embodiments, refrigeration system controller  202  includes a start-up controller  208  which overrides normal operation controller  210 . Refrigeration system controller  202  may simply send normal operation controller  210  into a standby mode. In some embodiments, refrigeration system controller  202  may block the signal from normal operation controller  210  to each of refrigeration system components  240 . In other embodiments, refrigeration system controller  202  may set a priority for each command and/or message from start-up controller  208  over all controllers, such as normal operation controller  210 . 
     Process  500  may continue with step  510 , in which refrigeration system  100  enters a power failure mode. Step  510  is followed by step  512 , in which a component of refrigeration system  100  (e.g., refrigeration system controller  202 ) operates a single compressor of compressor assembly  108  to maintain the suction setpoint. The suction setpoint may be controlled by setpoint manager  220 . Process  500  may continue with step  514 , in which refrigeration system  100  may detect a low condition of the refrigerant. For example, refrigeration system  100  may detect low suction pressure, low superheat, low refrigerant temperature, low refrigerant flow rate, low refrigerant level, and/or any other condition of the refrigerant that is below a minimum threshold value. Step  514  may be performed by refrigerant condition detector  226  of  FIG. 2 . Refrigeration system  100  may continually check for low conditions of the refrigerant. Multiple low conditions may be detected. For example, refrigeration system  100  can detect low superheat and low suction pressure, and advance process  500  to step  540 . 
     If a low condition of the refrigerant is not detected, process  500  may continue with step  516 , in which refrigeration system  100  may begin a proofing timer. The proofing timer may be an embodiment of signal timer  230 . In some embodiments, signal timer  230  may communicate with database  238  through communications interface  206 . Signal timer  230  may store the start time or a timestamp in database  238 . 
     Process  500  may continue to step  518 , in which refrigeration system  100  determines whether any compressors in compressor assembly  108  are still operating. If no compressors in compressor assembly  108  are operating, process  500  will proceed to step  520  and rotate the lead compressor in compressor assembly  108 . The rotational order of compressor cycling in refrigeration system  100  may prevent or reduce short cycling and improve performance and efficiency of refrigeration system  100 . 
     If at least one compressor in compressor assembly  108  is operating when process  500  reaches step  518 , the process will continue to step  522 , in which refrigeration system  100  resets the demand signal delay timer. The demand signal delay timer may be an embodiment of signal timer  230 . In some embodiments, signal timer  230  may communicate with database  238  through communications interface  206 . Signal timer  230  may store the start time or a timestamp in database  238 . After resetting the demand signal delay timer, process  500  may proceed to step  524 , and clear any alarms relating to monitored refrigerant conditions. In some embodiments, step  524  may involve alarm manager  228  and refrigerant condition detector  226 . 
     As compressor assembly  108  runs, process  500  may continue to step  526 , in which refrigeration system  100  may begin a ramp counter  224  to increase the demand signal for system operation to full operating capacity. For example, ramp counter  224  may increase demand signal from 10% to 100%. The rate at which ramp counter  224  may increase the demand signal may be represented by a variable, “R ramp_up ” In alternative embodiments, R ramp_up  may be expressed as a series of setpoints for the demand signal percentage. R ramp_up  may be set by a user, or it may set automatically depending on various system conditions. For example, if the demand signal successfully increases at a rate of 5% per 30 minutes for a certain period of time without a detected fault (i.e., a low refrigerant condition), R ramp_up  may automatically increase to 10% per 30 minutes for the rest of the period that the demand signal is increasing. 
     In some embodiments, the time for the demand signal to reach 100% will exceed two hours. Increasing demand for system operation at increments allows refrigeration system  100  to ramp up to reduce strain on system components. As the demand signal increases, process  500  may proceed to step  528 , and refrigeration system  100  may operate additional compressors in compressor assembly  108  in order to match the demand. Refrigeration system  100  may continue to operate additional compressors until the demand signal reaches 100%, in step  530 . 
     If the demand signal and/or ramp counter has reached the desired level of system operation, refrigeration system  100  may begin a “No Alarm Delay” timer in step  532 . The “No Alarm Delay” timer may be used to temporarily delay the system. In some embodiments, this timer may be a component of signal timer  230 . Signal timer  230  may store timestamps or time data in database  238 . The amount of time refrigeration system  100  delays while the timer runs may be predetermined by a user or calculated by refrigeration system  100 . For example, the delay may be 15 seconds, 5 minutes, 30 minutes, etc. In some embodiments, the alarm is for low refrigerant conditions, such as those detected in step  514 . In other embodiments, the alarm is for violations of other conditions of refrigeration system  100 . The timestamp data collected in step  310  of  FIG. 3  may be used to determine whether an alarm has occurred within a predetermined period of time. For example, referring now to  FIG. 2 , refrigeration system controller  202  may access database  238  through communications interface  206  to determine how long it has been since an alarm has occurred. 
     Process  500  continues to step  534 , when the “No Alarm Delay” timer expires and it is confirmed that an alarm has not occurred within the predetermined period of time associated with the timer. At the expiration of the “No Alarm Delay” timer, signal timer  230  may store timestamps or time data in database  238 . Process  500  may proceed to step  536 , in which refrigeration system  100  may then release its components to normal operation. For example, the compressors of compressor assembly  108  may operate normally to maintain system pressure. In some embodiments, refrigeration system  100  may release components from start-up controller  208 . For example, refrigeration system  100  may alter priority of commands, moving start-up controller  208  behind normal operation controller  210 . In other embodiments, refrigeration system  100  may cease to block commands from normal operation controller  210 , allowing refrigeration system components  240  to receive commands from normal operation controller  210 . Refrigeration system  100  may send start-up controller  208  into a standby mode to cease sending commands to refrigeration system components  240 . 
     Finally, process  500  may conclude with step  538 , in which refrigeration system  100  may transmit a signal to the building management system and/or BMS circuit controller  236  to indicate that restart mode is complete, and that refrigeration system  100  is ready for normal operation. In some embodiments, refrigeration system controller  202  may transmit a signal to BMS circuit controller  236  through BMS interface  204 . In some embodiments, refrigeration system controller  202  may log times, for example, the amount of time refrigeration system  100  was stopped or the time refrigeration system  100  was in a restart mode. 
     However, returning to step  514 , if a low condition of the refrigerant is detected, process  500  may proceed with step  540  in order to resolve the condition. In step  540 , refrigeration system  100  may pause increasing the demand signal and/or ramp counter for system operation. For example, a component of refrigeration system  100  (e.g., controller  202 ) may detect low refrigerant level and stop increasing the demand signal for system operation. The demand signal may have reached 60%, and ramp counter  224  may stop at 60% of total system capacity. Stopping ramp counter  224  may stop increasing demand on refrigeration system components  240  and prevent further stress on refrigeration system  100 . 
     Process  500  may continue with step  542 , in which refrigeration system  100  may start a demand signal delay timer. The amount of time the demand signal delay timer runs may be predetermined by a user or calculated by refrigeration system  100 . For example, the delay may be 15 seconds, 5 minutes, 30 minutes, etc. The demand signal delay timer may be an embodiment of signal timer  230 . In some embodiments, signal timer  230  may communicate with database  238  through communications interface  206 . Signal timer  230  may store the start time or a timestamp in database  238 . Once the demand signal delay timer is started, process  500  may proceed to step  544 , when a Level 1 alarm is sent to the BMS. In some embodiments, the alarm may be activated by alarm manager  228 . 
     The demand signal delay timer started in step  542  will run while the low condition of the refrigerant is detected. Proceeding to step  546 , refrigeration system  100  may determine whether the demand signal has been delayed for longer than a predetermined amount of time, and thus the demand signal delay timer has expired. For example, refrigeration system  100  may determine the amount of time that the demand signal has been delayed by checking the time logged by signal timer  230 . Refrigeration system  100  may calculate the amount of time that the demand signal has been delayed by accessing a start timestamp stored in database  238 . For example, the predetermined amount of time may be 30 minutes. Once the demand signal delay timer has expired, process  500  may proceed to step  548 , when a Level 2 alarm is sent to the BMS. A Level 2 alarm may indicate a problem of higher severity than a Level 1 alarm. In some embodiments, the alarm may be activated by alarm manager  228 . 
     If the demand signal delay timer expires (i.e., the total delay time is determined to be longer than the threshold amount of time), process  500  may continue with step  550 . In step  550 , a component of refrigeration system  100  (e.g., controller  202 ) may reverse ramp counter  224  to decrease the demand signal to refrigeration system  100 . For example, if ramp counter  224  and/or the demand signal is at 65%, refrigeration system  100  may reverse ramp counter  224  to count down toward 0% to decrease the demand signal. Decreasing the demand signal may allow refrigeration system  100  to resolve low conditions of refrigeration system  100 . Decreasing the demand signal can reduce the stress on refrigeration system  100 , and may allow refrigeration system components  240  time to catch up and resolve low conditions of the refrigerant. 
     The rate at which ramp counter  224  may decrease the demand signal may be represented by a variable, “R ramp_down ” In alternative embodiments, R ramp_down  may be expressed as a series of setpoints for the demand signal percentage. R ramp_down  may be set by a user, or it may be set automatically depending on various system conditions. For example, if the demand signal decreases at a rate of 5% per 30 minutes for a period of time and a critically low refrigerant condition is detected during that period, R ramp_down  may automatically increase to 10% per 30 minutes for the rest of the period so that a demand signal of 0% is reached more quickly. In some embodiments, the value of R ramp_up  may equal the value of R ramp_down , or both values may be calculated from the same system conditions. In other embodiments, the value of R ramp_up  may be fully independent from the value of R ramp_down . 
     As the demand signal decreases, process  500  may proceed to step  528 , and refrigeration system  100  may operate fewer compressors in compressor assembly  108  in order to match the demand. Refrigeration system  100  may continue to operate fewer compressors until the demand signal reaches 0%, in step  552 . Once the demand signal reaches 0%, a Level 3 alarm may be sent to the BMS in step  554 . In some embodiments, the alarm may be activated by alarm manager  228 . A Level 3 alarm is the highest severity alarm, and may require a user or technician to manually reset the system. 
     Once the low pressure, low refrigerant level, or low superheat condition has been reset, process  500  may revert to step  514 . From there, process  500  proceeds in the same manner as if no low condition of refrigeration system  100  was ever detected. For example, in step  518 , the lead compressor may be rotated to minimize short cycling, and in steps  526 - 530 , controller  202  may restart the demand increase counter from its prior stopping point and gradually increase the demand signal until it reaches 100%. Process  500  culminates with the expiration of the “No Alarm Delay” timer in step  534 , the release of refrigeration system components  240  in step  536 , and the transmission of the signal to the BMS controller indicating the completion of the start up mode in step  538 . 
     The construction and arrangement of the elements of the refrigeration system and pressure control system as shown in the exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.). For example, the position of elements may be reversed or otherwise varied and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present disclosure. 
     The present disclosure contemplates methods, systems and program products on any machine-readable media for accomplishing various operations. The embodiments of the present disclosure may be implemented using existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose, or by a hardwired system. Embodiments within the scope of the present disclosure include program products comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium. Thus, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions. 
     Although the figures show a specific order of method steps, the order of the steps may differ from what is depicted. Also two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations could be accomplished with standard programming techniques with rule based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps. 
     The background section is intended to provide a background or context to the invention recited in the claims. The description in the background section may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in the background section is not prior art to the description and claims and is not admitted to be prior art by inclusion in the background section.