JP2009522533A - Flash tank refrigerant control - Google Patents

Abstract

  A control algorithm for controlling the economizer circuit of the chiller system (100) is provided. The control algorithm adjusts the position of the feed valve (114) in the economizer circuit in response to the measured system operating parameters to maintain the level of liquid refrigerant in the flash tank (110) of the economizer circuit. . The measured system operating parameters include compressor (102) load, and flash tank refrigerant pressure and temperature.

Description

This patent application claims the benefit of US Provisional Application No. 60 / 755,222, filed Dec. 30, 2005.
The present invention relates generally to controlling an economizer circuit in a chiller system. More specifically, the present invention relates to controlling the level of liquid refrigerant in a flash tank of an economizer circuit.

  In refrigeration and chiller systems, refrigerant gas is compressed by a compressor and then sent to a condenser. The refrigerant vapor sent to the condenser enters a heat exchange relationship with a fluid, such as air or water, and undergoes a phase change to become a refrigerant liquid. Liquid refrigerant from the condenser flows to the evaporator via a corresponding expansion device. The liquid refrigerant in the evaporator enters a heat exchange relationship with another fluid, such as air, water, or other secondary liquid, and undergoes a phase change into refrigerant vapor. Other fluids that pass through the evaporator are cooled or cooled as a result of the heat exchange relationship with the liquid refrigerant and then typically supplied to the enclosed space to cool the enclosed space. Eventually, the vapor refrigerant in the evaporator returns to the compressor to complete the circulation.

  In order to increase the capacity, efficiency and performance of the refrigeration or chiller system, an economizer circuit is incorporated into the system. The economizer circuit comprises an economizer heat exchanger or flash tank, an inlet line leading to the flash tank coupled to the condenser or to the refrigeration circuit downstream of the condenser, an economizer expansion device incorporated in the inlet line, and a compressor An outlet line from the flash tank is typically provided that is coupled to a port within the compression chamber or to the suction inlet of the compressor.

  In the flash tank economizer circuit, liquid refrigerant from the condenser flows to the flash tank via the inlet line and the expansion device. Liquid refrigerant experiences a pressure drop as it passes through the expansion device, at which time at least a portion of the refrigerant expands rapidly, or “flashes,” and is converted from liquid to gas. The liquid refrigerant in the flash tank collects in the lower part of the flash tank, returns to the refrigerant circuit via the first outlet line, and is supplied to the evaporator. The first outlet line incorporates one or more valves to control the amount of liquid refrigerant returned to the refrigerant circuit. The gaseous refrigerant in the flash tank collects at the top of the flash tank and returns to the compressor at a medium pressure via the second outlet line, i.e. to a point in the suction inlet or compressor chamber. The second outlet line can also incorporate one or more valves to control the amount of gaseous refrigerant supplied to the compressor when coupled to the compressor chamber.

  As discussed above, economizer circuits can be used to increase the capacity, efficiency, and performance of refrigeration or chiller systems. For example, an economizer circuit can increase system efficiency by supplying refrigerant gas to the compressor at an intermediate pressure, thereby reducing the amount of work required by the compressor and increasing the efficiency of the compressor. Various parameters of the economizer circuit are controlled to increase the capacity, efficiency, and performance of the refrigeration or chiller system. In order to obtain the desired capacity, efficiency and performance of the refrigeration and chiller system, in particular not only the amount of liquid refrigerant in the flash tank, but also the amount of refrigerant entering and exiting this tank and compressor port locations and the compressor The associated intermediate pressure supplied to is also controlled and selected. Furthermore, the economizer circuit is turned on and off in response to predetermined parameters to further improve the operation of the refrigeration or chiller system.

  In order to control the economizer circuit, when the amount or level of liquid in the flash tank is used, the liquid level of the refrigerant must be measured. The flash tank refrigerant liquid level is usually measured using a sensor or a mechanical device such as a float. The control process then typically adjusts system parameters to maintain the desired refrigerant liquid level in the flash tank. One disadvantage of this technique is that sensors or mechanical devices can fail, thereby preventing the efficient operation of economizer circuits and systems.

  Therefore, what is needed is a system and method that easily and easily controls the level of liquid refrigerant in a flash tank of an economizer circuit to provide improved performance to a refrigeration or chiller system.

  One embodiment of the invention relates to a method for controlling an economizer circuit in a chiller system. The method includes providing an economizer circuit having a flash tank, an inlet line, and a feed valve in a chiller system. The feed valve is arranged in the inlet line. The feed valve is configured to control the flow of refrigerant to the flash tank. The method includes measuring at least one system operating parameter for the chiller system; calculating a valve position for the feed valve in response to the measured at least one system operating parameter; and a liquid in the flash tank Adjusting the feed valve to the calculated valve position to control the refrigerant level.

  Another embodiment of the invention relates to a liquid level control system for an economizer circuit of a chiller system. The system includes a flash tank, an inlet line, and a feed valve. The feed valve is disposed in the inlet line and is configured to control refrigerant flow to the flash tank. The liquid level control system includes a map of a plurality of operating positions of the feed valve. Each of the plurality of operating positions is associated with a predetermined position of the feed valve and the amount of refrigerant in the flash tank. The position of the feed valve and the amount of refrigerant in the flash tank correspond to the flow rate at the predetermined feed valve position. The map is configured to relate a plurality of feed valve operating positions to a plurality of predetermined system operating parameters.

  The system also includes a microprocessor. The microprocessor is configured to control the position of the feed valve to control the level of liquid refrigerant in the flash tank. The microprocessor generates a control signal that positions the adjustable valve arrangement of the economizer circuit based on the map to control the operation of the feed valve.

  Another embodiment of the invention relates to a chiller system. The refrigeration system includes a refrigerant circuit comprising a compressor, a condenser arrangement, an expansion valve, and an evaporator arrangement coupled in a closed refrigerant loop. An economizer circuit is coupled to the refrigerant circuit. The economizer circuit includes a flash tank, an inlet line, and a feed valve. The feed valve is disposed in the inlet line and is configured to control refrigerant flow to the flash tank. A control panel for the chiller system also includes a map of a plurality of operating positions of the feed valve. Each operation position of the plurality of operation positions is related to a predetermined position of the feed valve and an amount of refrigerant in the flash tank corresponding to the flow rate at the predetermined position. The map is configured to relate a plurality of feed valve operating positions to a plurality of predetermined system operating parameters. A microprocessor in the control panel is configured to control the position of the feed valve to control the level of liquid refrigerant in the flash tank. The microprocessor generates a control signal that positions the feed valve based on the map.

  One advantage of the present invention is that a float valve or electronic level sensor is not required for the flash tank, thereby reducing the cost and complexity of the system and increasing the reliability of the system.

  Another advantage of the present invention is that the operation of the economizer circuit can be fine-tuned to obtain the desired level of flash tank by positioning the feed valve in response to system conditions.

Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example only, the principles of the invention.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

  FIG. 1 generally illustrates an application used in the present invention. As shown in FIG. 1, the HVAC, refrigeration or liquid chiller system 100 includes a compressor 102, a condenser arrangement 104, one or more expander devices 105, a liquid chiller or evaporator arrangement 106, and A control panel 108 is provided. The compressor 102 is driven by an electric motor 124 that is powered by a variable speed drive (VSD) 122. In addition, the chiller system 100 has an economizer circuit that includes an economizer heat exchanger or flash tank 110, an inlet line 112, an economizer feed valve 114, a first outlet line 116, and a second outlet line 118.

  The VSD 122 receives AC power having a specific fixed line voltage and fixed line frequency from an AC power source and supplies AC power to the motor 124 at a desired voltage and desired frequency that are both variable to meet specific requirements. . The VSD 122 is preferably capable of supplying the motor 124 with AC power having a voltage and frequency higher than the rated voltage and frequency of the motor 124 and a lower voltage and frequency. The electric motor 124 is preferably an induction motor operable at a variable speed. However, any suitable electric motor that can operate at variable speeds may be used in the present invention.

  The compressor 102 driven by the electric motor 124 compresses the refrigerant vapor and delivers the vapor to the condenser 104 via the discharge line. The compressor 102 is preferably a screw compressor, but may be any suitable type of compressor, such as a centrifugal compressor, a reciprocating compressor, or the like. The refrigerant vapor sent to the condenser 104 by the compressor 102 enters a heat exchange relationship with a fluid, eg, air or water, and becomes a refrigerant liquid through a phase change as a result of the heat exchange relationship with the fluid. The condensed liquid refrigerant from the condenser 104 flows to the evaporator 106 via the expansion device 105.

  The evaporator 106 includes a coupling for the cooling load supply line and return line. A secondary liquid, such as water, ethylene, calcium chloride brine, or sodium chloride brine moves into the evaporator 106 via the return line and exits the evaporator 106 via the supply line. The liquid refrigerant in the evaporator 106 enters a heat exchange relationship with the secondary liquid to reduce the temperature of the secondary liquid. The refrigerant liquid in the evaporator 106 undergoes phase change and becomes refrigerant vapor as a result of the heat exchange relationship with the secondary liquid. The vapor refrigerant in the evaporator 106 exits the evaporator 106 and returns to the compressor 102 by the suction line to complete the circulation. It should be understood that any suitable configuration of the condenser 104 and evaporator 106 can be used with the present system 100 if an appropriate phase change of the refrigerant in the condenser 104 and evaporator 106 is achieved.

  The economizer circuit is incorporated into the main refrigerant circuit between the condenser 104 and the expansion device 105. The economizer circuit has an inlet line 112 that is directly coupled to or in fluid communication with the condenser 104. The inlet line 112 has an economizer feed valve 114 upstream of the flash tank 110. The economizer feed valve 114 operates to adjust the amount of refrigerant that enters the flash tank 110. The refrigerant entering the flash tank 110 is preferably at a pressure lower than the discharge pressure of the compressor 102 and higher than the suction pressure of the compressor 102. In a preferred embodiment, the economizer feed valve 114 can also operate as an expansion valve to reduce the pressure of the liquid refrigerant flowing from the condenser 104 through the economizer feed valve 114. In another embodiment, one or more expansion valves are incorporated into the economizer circuit downstream of the feed valve 114 and before the flash tank 110. Downstream of the economizer feed valve 114, both liquid refrigerant and gaseous refrigerant enter the flash tank 110. Inside the flash tank 110, gaseous refrigerant preferably collects in the upper or upper part of the flash tank 110 and liquid refrigerant preferably accumulates in the lower or lower part of the flash tank 110. The flash tank 110 includes one or more upper level switches 140 and one or more lower level switches 142. The level switches 140, 142 can determine when the liquid level in the flash tank is above or below the corresponding level switch. The level switches 140, 142 can provide a signal to the control panel 108 indicating whether the liquid level in the flash tank is above or below the corresponding level switch. Although any suitable level switch can be used for the level switches 140, 142, a simple, low cost, reliable level switch is recommended.

  The liquid refrigerant in the flash tank 110 flows or moves to the expansion valve 105 via the first outlet line 116. The expansion valve 105 is a thermal expansion valve, an electronic expansion valve, an orifice, or any other suitable metering device or valve. A second outlet line 118 preferably returns the gaseous refrigerant in the flash tank 110 to the economizer port of the compressor 102 that is directly coupled to the compression chamber of the compressor 102. Alternatively, the second outlet line 118 can return the gaseous refrigerant in the flash tank 110 to the suction inlet of the compressor 102. Second outlet line 118 includes one or more economizer port valves to control the flow of gaseous refrigerant from flash tank 110 to compressor 102.

  A conventional HVAC, refrigeration, or liquid chiller system 100 with an economizer circuit includes many other features not shown in FIG. These feature structures have been deliberately omitted to simplify the drawing for ease of illustration. In addition, FIG. 1 illustrates an HVAC, refrigeration, or liquid chiller system 100 with one compressor coupled to a single refrigerant circuit, but the system 100 includes one or more refrigerants. It should be understood that it comprises a multi-compressor coupled to the circuit. In addition, each refrigerant circuit includes its own one or more economizer circuits, as described above.

  The control panel 108 includes an analog / digital (A / D) converter, a microprocessor, a non-volatile storage device, and an interface panel to control the operation of the refrigeration system 100. The control panel 108 can also be used to control the operation of the VSD 122, the electric motor 124, and the compressor 102. The control panel 108 can be used to control the operation of the system 100 and to determine and implement an operational configuration or position for the economizer feed valve 114 to control the level of liquid refrigerant in the flash tank 110. Run multiple control algorithms or software. In one embodiment, these one or more control algorithms may be a computer program or software stored in the non-volatile storage of the control panel 108 and run through a series of control panel 108 microprocessors. Instructions can be included. Although recommended to be implemented in one or more computer programs and executed by a microprocessor, the control algorithms should be implemented and executed by those skilled in the art using digital and / or analog hardware. Should be understood. When using hardware to implement the control algorithm, the corresponding configuration of the control panel 108 can be modified to incorporate the necessary components and to remove any components that are no longer needed. is there.

  The control panel 108 uses a map, table, or database of feed valve operating positions to control the operation of the feed valve 114. The operating position for the feed valve 114 is related to the size of the valve opening and the corresponding amount of refrigerant passing through the valve opening. The map or table used by the control panel 108 relates the feed valve operating position to the system operating parameters. A map or table is created from test data that determines the operating position of the valve in response to specific system operating parameters or conditions. It is preferable that one map is applicable to two or more systems, for example, it will be applicable to a group of products of the same system.

  FIG. 2 illustrates an embodiment of the economizer feed valve control process of the present invention. The feed valve control process is initiated in response to a start command or command from a capacity control process or other control program for the system 100. The economizer feed valve control process may be a single process or program, or it may be incorporated into a larger control process or program, such as a capacity control program for a chiller system.

  The process begins at step 202 by measuring system operating parameters. The measured system operating parameters are preferably the load on the compressor 102 and the pressure and temperature of the refrigerant in the flash tank 110, although additional, fewer, or other system operating parameters may be measured. . The load on the compressor 102 is determined by measuring the system capacity by sensing the temperature of the liquid entering and exiting the evaporator 106, or by sensing the flow of liquid through the evaporator 106, and the speed of the compressor 102. It is measured or determined in several ways, including measurement, sensing the operating frequency of the variable speed drive 122, and sensing the position of the slip valve in the compressor 102. Sensing the pressure and temperature of the refrigerant in flash tank 110 in several ways, including sensing the temperature and pressure of flash tank 110, and sensing the suction and discharge pressure and / or suction and discharge temperature of compressor 102. Sought by.

  In step 204, the measured system operating parameters are compared to map entries to determine the appropriate operating position for the feed valve 114. The map entries correlate measured system operating parameters (compressor 102 load and flash tank 110 refrigerant temperature and pressure) and other information to operating positions for feed valve 114. Other information on the map includes the relationship between the operating position of the feed valve 114 and the corresponding cross-sectional flow area for the feed valve 114, any drive requirements for an electric motor, preferably a stepper motor, for adjusting the operating position of the feed valve 114, And / or can relate to knowledge of compressor performance at measured operating parameters based on compressor measurements or computed mappings in a range of conditions that represent conditions under which the system 100 operates.

  The map is a look-up table having operating positions with respect to the feed valve 114 based on measured system operating parameters. Alternatively, the feed valve position may be calculated based on a multi-variable algorithm or based on a graph curve of one or more variables (these variables can be measured system operating parameters). Good. Some examples of system operating parameters that can be used as variables include temperature and pressure in flash tank 110, suction and discharge pressure and / or suction and discharge temperature in compressor 102, and compressor 102. And the position of the expansion valve 105 or drain valve. The feed valve 114 may be a digital incremental position type or an analog type. Furthermore, the signal for opening or closing the feed valve 114 corresponds to the type of valve used. In one embodiment, the opening and closing of the feed valve 114 is based on the load of the system 100, that is, the valve has a smaller amount of displacement during lighter load conditions and a larger amount of displacement during heavier load conditions. Have The feed valve 114 is preferably controlled to maintain a predetermined level of refrigerant inside the flash tank 110.

  Once the operating position for the feed valve 114 is determined or calculated at step 204, the process proceeds to step 206. At step 206, the position of the feed valve 114 is adjusted to the desired or calculated position. Once the feed valve 114 is positioned, control returns to step 202 and the process is repeated. As discussed in more detail below, the rate of change of the feed valve position is controlled. The system then returns to step 202 and repeats this process. An optional time delay 208 may be incorporated to prevent hunting or instability in the system. In the preferred embodiment, the feed valve 114 is allowed to move from a fully open position to a closed position in a single step, except for a predefined state, to respond to an upper level switch 140 that detects an excess condition. Not. However, under normal conditions, the system controls the rate at which the feed valve position changes to avoid forcing the feed valve 114 to fully open or close in a single step.

  In the preferred embodiment, level switches 140, 142 are used in conjunction with the control process of FIG. 2 to further adjust the level of liquid refrigerant in flash tank 110. If level switches 140, 142 detect that the liquid level in flash tank 110 is above the upper level limit, or if the liquid level in flash tank 110 is below the lower level limit The control panel 108 can alert the operator of the system 100 of the fluid level, or the control system can take other measures apart from the control process of FIG. 2 to correct the situation. It is possible to take Level switches 140, 142 are used to open feed valve 114 in response to a low refrigerant level in flash tank 110 or in response to a high refrigerant level in flash tank 110 until the desired refrigerant level is obtained. An immediate control system signal can be provided to close the valve 114.

  In one embodiment of the present invention, the frequency and duration of deviation or deviation from between the upper and lower level limits can be used to adjust the motion map. To attempt to avoid deviations between the upper and lower level limits, fuzzy logic reasoning or other suitable techniques can be used to update the motion map. Other adjustments or compensations in the operational map or algorithm can be implemented based on specific chiller systems having different operational characteristics.

  In one embodiment, the system implements a lookup table, which is preferably a multidimensional lookup table. Similarly, the map or look-up table is adaptively adjusted based on feedback from the upper and lower limit switches 140,142. It is also possible to use the upper and lower limit switches 140, 142 to compensate for the desired position with respect to the feed valve 114 and adjust the map parameters accordingly. For example, if the refrigerant level in the tank detects only the high level indicator, the map parameter will be compensated downward so that the normal position of the feed valve 114 is less opened, and only the low level is detected. If so, it will be compensated accordingly so that the position of the feed valve 114 is normally in the more open position.

  Although the invention has been described with reference to preferred embodiments, it will be understood that various modifications can be made and equivalents can be substituted for the elements of the invention without departing from the scope of the invention. It will be understood by the contractor. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Accordingly, the invention is not limited to the specific embodiments disclosed as the best mode contemplated for carrying out the invention, but the invention is intended to cover all embodiments that fall within the scope of the appended claims. Is contemplated.

It is a figure which illustrates embodiment of the refrigerating or cooling machine system used for this invention. It is a flowchart which shows embodiment of the economizer feed valve control process of this invention.

Claims (25)

Providing an economizer circuit for a chiller system having a flash tank, an inlet line, and a feed valve disposed in the inlet line and configured to control the flow of refrigerant to the flash tank;
Measuring at least one system operating parameter for the chiller system;
Calculating a valve position relative to the feed valve in response to the measured at least one system operating parameter;
Adjusting the feed valve to the calculated valve position to control the level of liquid refrigerant in the flash tank;
A method for controlling an economizer circuit in a chiller system.   The method of claim 1, wherein the step of measuring the at least one system operating parameter is selected from a compressor load, a refrigerant pressure in the flash tank, or a refrigerant temperature in the flash tank.   The measuring the at least one system operating parameter comprises determining the load on the compressor by determining a system capacity from an inlet fluid temperature and an outlet fluid temperature in an evaporator. The method described in 1.   The method of claim 2, wherein the measuring at least one system operating parameter comprises determining the load on the compressor by sensing a liquid flow through the evaporator.   The method of claim 2, wherein the measuring at least one system operating parameter comprises determining the load on the compressor by measuring a speed of the compressor.   The method of claim 2, wherein the measuring at least one system operating parameter comprises determining the load on the compressor by sensing an operating frequency of a variable speed drive.   The method of claim 2, wherein the measuring at least one system operating parameter comprises determining the load on the compressor by sensing a position of a slip valve in the compressor.   The method of claim 2, wherein the measuring at least one system operating parameter comprises determining the pressure of the refrigerant in the flash tank by sensing pressure in the flash tank.   The method of claim 2, wherein the measuring at least one system operating parameter comprises determining the temperature of the refrigerant in the flash tank by sensing a temperature in the flash tank.   The measuring of at least one system operating parameter comprises determining the pressure of the refrigerant in the flash tank by sensing suction and discharge pressures in the compressor. Method.   The measuring of at least one system operating parameter comprises determining the temperature of the refrigerant in the flash tank by sensing suction and discharge temperatures in the compressor. Method.   The method of claim 1, wherein the calculating a valve position comprises comparing the measured at least one system operating parameter with an entry in a map to determine the position relative to the feed valve.   The method of claim 12, wherein the map correlates the measured at least one system operating parameter and at least one additional criterion with an operating position relative to the feed valve.   The at least one additional criterion includes at least one cross-sectional flow area for the feed valve corresponding to at least one operating position of the feed valve and at least one drive of an electric motor that adjusts the operating position of the feed valve. The method of claim 13, wherein the method is selected from the group consisting of requirements and the performance of the compressor at a plurality of measured operating parameters over a range of system operating conditions.   The method of claim 14, wherein the range of system operating parameters is based on measurements or calculated mappings of the compressor. A liquid level control system for an economizer circuit having a feed valve disposed in an inlet line and configured to control refrigerant flow to a flash tank,
Each operation position of the plurality of operation positions is related to a predetermined position of the feed valve and an amount of refrigerant in the flash tank corresponding to a flow rate of the predetermined position, and the plurality of feed valve operation positions are set to a plurality of operation positions. A map of a plurality of operating positions of the feed valve configured to correlate with predetermined system operating parameters;
A microprocessor configured to control the position of the feed valve to control the level of liquid refrigerant in the flash tank;
A liquid level control system, wherein the microprocessor generates a control signal for positioning an adjustable valve arrangement of a refrigeration system based on the map to control operation of the feed valve.   The system of claim 16, wherein the map is created from test data that determines an operating position for the valve in response to specific system operating parameters or conditions.   The system of claim 16, wherein the map is created from calculated data that determines an operating position for the valve in response to specific system operating parameters or conditions.   The upper and lower level switches further comprising at least one upper level switch that determines a refrigerant level in the flash tank above a predetermined maximum refrigerant level and at least one lower level switch that determines a predetermined minimum refrigerant level. 17. The system of claim 16, wherein the system is configured to generate a signal that indicates to the microprocessor when the level exceeds a respective maximum or minimum refrigerant level.   The system of claim 16, wherein the predetermined system operating parameter is selected from a load of the compressor, a pressure of the refrigerant in the flash tank, or a temperature of the refrigerant in the flash tank.   21. The system of claim 20, wherein the load on the compressor is determined by determining system capacity by sensing the temperature of the incoming liquid and the temperature of the outgoing liquid in the evaporator.   The load on the compressor may sense the flow of liquid through the evaporator, measure the speed of the compressor, sense the operating frequency of the variable speed drive, or in the compressor 21. The system of claim 20, wherein the system is determined by at least one of sensing the position of a slip valve.   21. The pressure of the refrigerant in the flash tank is determined by at least one of sensing the pressure in the flash tank or sensing suction pressure and discharge pressure in the compressor. system.   21. The temperature of the refrigerant in the flash tank is determined by at least one of sensing the temperature in the flash tank or sensing the refrigerant suction and discharge temperatures in the compressor. The system described in. A refrigerant circuit having a compressor, a condenser arrangement, an expansion valve, and an evaporator arrangement, coupled to the closed refrigerant loop;
An economizer circuit coupled to the refrigerant circuit and comprising a flash tank, an inlet line, and a feed valve, and the feed valve is disposed in the inlet line and configured to control the flow of refrigerant to the flash tank. And
A control panel,
The control panel is
The plurality of operation positions of the feed valve are related to a predetermined position of the feed valve and an amount of refrigerant in the flash tank corresponding to a flow rate of the predetermined position, and the plurality of operation positions of the feed valve are A map comprising the plurality of operating positions configured to correlate with predetermined system operating parameters;
A microprocessor configured to control the position of the feed valve to control the level of liquid refrigerant in the flash tank;
The microprocessor generates a control signal for positioning the feed valve based on the map;
Chiller system.

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