Patent Application
20150300713
This disclosure relates generally to refrigerant vapor compression systems and, more particularly, to improving the energy efficiency and/or low cooling capacity operation of a transcritical refrigerant vapor compression system.
Refrigerant vapor compression systems used in connection with transport refrigeration systems are generally subject to more stringent operating conditions due to the wide range of operating load conditions and the wide range of outdoor ambient conditions over which the refrigerant vapor compression system must operate to maintain product within the cargo space at a desired temperature. The desired temperature at which the cargo needs to be controlled can also vary over a wide range depending on the nature of cargo to be preserved. The refrigerant vapor compression system must not only have sufficient capacity to rapidly pull down the temperature of product loaded into the cargo space at ambient temperature, but also should operate energy efficiently over the entire load range, including at low cooling capacity when maintaining a stable product temperature during transport.
During temperature maintenance, the object is to maintain the temperature within the temperature controlled space, e.g. the cargo box, within a narrow temperature band bounding a control temperature set point. If the refrigerant vapor compression system outputs too much cooling capacity, the temperature within the temperature controlled space will drop below the narrow temperature. Conversely, if the refrigerant vapor compression system outputs too little cooling capacity, the temperature within the temperature controlled space will rise above the narrow temperature band. In conventional practice, it is common to cycle the refrigerant compressor on and off during low capacity operation. However, doing so can result in undesirable repeated overshoot and undershoot of the narrow temperature band bounding the control temperature set point.
Operation of a transcritical refrigerant vapor compression system for supplying temperature conditioned air to a temperature controlled space is controlled when staging up or staging down to avoid undesirable overshoot and undershoot of the narrow temperature band bounding the control temperature set point for the temperature within the temperature controlled space.
In an aspect, a method for operation of a transcritical refrigerant vapor compression system for supplying conditioned air to a temperature controlled space includes operating the refrigerant vapor compression system in a transition mode when staging up or staging down between a higher capacity mode and a lower capacity mode. Operation in a transition mode may include monitoring a first parameter and a second parameter, and staging out of the transition mode in response to a determination that at least one of a first condition related to the first parameter and a second condition related to the second parameter has been established or has been established for a particular period of time. In an embodiment, operation in the transition mode includes: monitoring a temperature control differential, TSETPT−TCRTL, between a control temperature set point, TSETPT, and a sensed control temperature, TCRTL; and establishing a trend in a change of the temperature control differential over an elapsed time, which may include calculating an average derivative of the temperature control differential over the elapsed time.
In an embodiment, the method includes: entering a stage down transition mode for staging down from operation in a high capacity mode to operation in one of a first low capacity mode and a second lower capacity mode; determining whether the average derivative of the temperature control differential has been positive for an elapsed time greater than a preset first period of time; and if the average derivative of the temperature control differential has been positive for an elapsed time greater than the preset first period of time, staging down to the second lower capacity mode and bypassing the first low capacity mode. In this embodiment, the method further includes: if the average derivative of the temperature control differential has not been positive for an elapsed time greater than the preset first period of time, determining whether the temperature control differential is currently less than zero; and if the temperature control differential is currently less than zero, staging down to the first low capacity mode. In this embodiment, the method further includes: if the temperature control differential is not currently less than zero, determining whether the temperature control differential has been greater than zero for a preset second period of time; and if the temperature control differential has been greater than zero for the second preset period of time, staging down to the second lower capacity mode and bypassing the first low capacity mode.
In an embodiment, the method includes: entering a stage up transition mode for staging up from operation in a low capacity mode to operation in one of a first high capacity mode and a second higher capacity mode; determining whether the average derivative of the temperature control differential has been negative for an elapsed time greater than a preset third period of time; and if the average derivative of the temperature control differential has been negative for an elapsed time greater than the preset third period of time, staging up to the second higher capacity mode and bypassing the first high capacity mode. In this embodiment the method further includes: if the average derivative of the temperature control differential has not been negative for an elapsed time greater than the preset third period of time, determining whether the temperature control differential is currently greater than zero; and if the temperature control differential is currently greater than zero, staging up to the first high capacity mode. In this embodiment, the method may further include: if the temperature control differential is not currently greater than zero, determining whether the temperature control differential has been less than zero for a preset fourth period of time; and if the temperature control differential has been less than zero for the fourth preset period of time, staging up to the second higher capacity mode and bypassing the first high capacity mode.
In an aspect, a refrigerant vapor compression system includes: a compression device for compressing a refrigerant vapor from a suction pressure to a discharge pressure, a refrigerant heat rejection heat exchanger and a refrigerant heat absorption heat exchanger arranged in serial refrigerant flow relationship in a transcritical cycle closed-loop primary refrigerant circuit, the refrigerant heat rejection heat exchanger functioning as a refrigerant gas cooler and the refrigerant heat absorption heat exchanger functioning as a refrigerant evaporator; and a controller operatively associated with the refrigerant vapor compression system, the controller configured to control operation of the refrigerant vapor compression system in a transition mode when staging up or staging down between a higher capacity mode and a lower capacity mode, the controller further configured to monitor a temperature control differential, TSETPT−TCRTL, between a control temperature set point, TSETPT, and a sensed control temperature, TCRTL, during operation in the transition mode; and to calculate an average derivative of the temperature control differential over an elapsed time during operation in the transition mode.
In an embodiment, the controller is further configured to: enter a stage down transition mode when staging down from operation in a high capacity mode to operation in one of a first low capacity mode and a second lower capacity mode; determine whether the average derivative of the temperature control differential has been positive for an elapsed time greater than a preset first period of time; and if the average derivative of the temperature control differential has been positive for an elapsed time greater than the preset first period of time, stage down to the second lower capacity mode and bypassing the first low capacity mode. In this embodiment, the controller may be further configured to: if the average derivative of the temperature control differential has not been positive for an elapsed time greater than the preset first period of time, determine whether the temperature control differential is currently less than zero; and if the temperature control differential is currently less than zero, stage down to the first low capacity mode. The controller may be further configured to: if the temperature control differential is not currently less than zero, determine whether the temperature control differential has been greater than zero for a preset second period of time; and if the temperature control differential has been greater than zero for the second preset period of time, stage down to the second lower capacity mode and bypassing the first low capacity mode.
In an embodiment, the controller is further configured to: enter a stage up transition mode for staging up from operation in a low capacity mode to operation in one of a first high capacity mode and a second higher capacity mode; determine whether the average derivative of the temperature control differential has been negative for an elapsed time greater than a preset third period of time; and if the average derivative of the temperature control differential has been negative for an elapsed time greater than the preset third period of time, stage up to the second higher capacity mode and bypassing the first high capacity mode. The controller may be further configured to: if the average derivative of the temperature control differential has not been negative for an elapsed time greater than the preset third period of time, determine whether the temperature control differential is currently greater than zero; and if the temperature control differential is currently greater than zero, stage up to the first high capacity mode. The controller may be further configured to: if the temperature control differential is not currently greater than zero, determine whether the temperature control differential has been less than zero for a preset fourth period of time; and if the temperature control differential has been less than zero for the fourth preset period of time, stage up to the second higher capacity mode and bypassing the first high capacity mode.
In an aspect, a method is provided for controlling low capacity operation of a transcritical refrigerant vapor compression system for supplying conditioned air to a temperature controlled space, the refrigerant vapor compression system having a primary refrigerant flow circuit including a variable speed compressor driven by a variable frequency motor, a refrigerant gas cooler, a high pressure expansion device, a flash tank, an evaporator expansion device, and an evaporator disposed in serial refrigerant flow arrangement in the primary refrigerant flow circuit and a compressor unload circuit including an unload valve selectively positionable to open or close the compressor unload circuit. The method includes: opening the unload valve to allow refrigerant to pass from the compressor through the compressor unload circuit to a suction pressure portion of the primary refrigerant flow circuit; opening the high pressure expansion valve to a full open position; operating the compressor drive motor at a minimum frequency to drive the compressor at a minimum speed; and selectively cycling an air moving device associated with the gas cooler through an on/off duty cycle.
In an aspect, a method is provided for controlling low capacity operation of a transcritical vapor compression system for supplying conditioned air to a temperature controlled space includes controlling operation of at least one of an air moving device associated with the gas cooler or a heating device associated with the evaporator for heating a flow of air drawn from the temperature controlled space. In an embodiment of the method, the air moving device associated with the gas cooler or the heating device associated with the evaporator is controlled in such a way as to preserve the temperature control sensitivity of the variable speed drive driving the variable speed motor driving the compression device.
For a further understanding of the disclosure, reference will be made to the following detailed description which is to be read in connection with the accompanying drawing, wherein:
There is depicted in
Referring now to
The refrigerant vapor compression system 20 includes a multi-stage compression device 30, a refrigerant heat rejection heat exchanger 40, a flash tank 60, and a refrigerant heat absorption heat exchanger 50, also referred to herein as an evaporator, with refrigerant lines 22, 24 and 26 connecting the aforementioned components in serial refrigerant flow order in a primary refrigerant circuit. A high pressure expansion device (HPXV) 45, such as for example an electronic expansion valve, is disposed in the refrigerant line 24 upstream of the flash tank 60 and downstream of refrigerant heat rejection heat exchanger 40. An evaporator expansion device (EVXV) 55, such as for example an electronic expansion valve, operatively associated with the evaporator 50, is disposed in the refrigerant line 24 downstream of the flash tank 60 and upstream of the evaporator 50.
The compression device 30 compresses the refrigerant and circulates the refrigerant through the primary refrigerant circuit as will be discussed in further detail hereinafter. The compression device 30 may comprise a single, multiple-stage refrigerant compressor, for example a reciprocating compressor or a scroll compressor, having a first compression stage 30a and a second stage 30b, wherein the refrigerant discharging from the first compression stage 30a passes to the second compression stage 30b for further compression. Alternatively, the compression device 30 may comprise a pair of individual compressors, one of which constitutes the first compression stage 30a and other of which constitutes the second compression stage 30b, connected in series refrigerant flow relationship in the primary refrigerant circuit via a refrigerant line connecting the discharge outlet port of the compressor constituting the first compression stage 30a in refrigerant flow communication with the suction inlet port of the compressor constituting the second compression stage 30b for further compression. In a two compressor embodiment, the compressors may be scroll compressors, screw compressors, reciprocating compressors, rotary compressors or any other type of compressor or a combination of any such compressors. In both embodiments, in the first compression stage 30a, the refrigerant vapor is compressed from a lower pressure to an intermediate pressure and in the second compression stage 30b, the refrigerant vapor is compressed from an intermediate pressure to higher pressure.
In the embodiment of the refrigerant vapor compression system 20 depicted in
The refrigerant heat rejection heat exchanger 40 may comprise a finned tube heat exchanger 42 through which hot, high pressure refrigerant discharged from the second compression stage 30b (i.e. the final compression charge) passes in heat exchange relationship with a secondary fluid, most commonly ambient air drawn through the heat exchanger 42 by the fan(s) 44. The finned tube heat exchanger 42 may comprise, for example, a fin and round tube heat exchange coil or a fin and flat mini-channel tube heat exchanger. In the depicted embodiment, a variable speed fan motor 46 powered by a variable frequency drive drives the fan(s) 44 associated with the heat rejection heat exchanger 40. The variable speed fan motor 46 may be powered by the same variable frequency drive 34 that powers the compressor motor or by a separate dedicated variable frequency drive 48, as depicted in
When the refrigerant vapor compression system 20 operates in a transcritical cycle, the pressure of the refrigerant discharging from the second compression stage 30b and passing through the refrigerant heat rejection heat exchanger 40, referred to herein as the high side pressure, exceeds the critical point of the refrigerant, and the refrigerant heat rejection heat exchanger 40 functions as a gas cooler. However, it should be understood that if the refrigerant vapor compression system 20 operates solely in the subcritical cycle, the pressure of the refrigerant discharging from the compressor and passing through the refrigerant heat rejection heat exchanger 40 is below the critical point of the refrigerant, and the refrigerant heat rejection heat exchanger 40 functions as a condenser. As the method of operation disclosed herein pertains to operation of the refrigerant vapor compression system 20 in a transcritical cycle, the refrigerant heat rejection heat exchanger will also be referred to herein as gas cooler 40.
The refrigerant heat absorption heat exchanger 50 may also comprise a finned tube coil heat exchanger 52, such as a fin and round tube heat exchanger or a fin and flat, micro-channel or mini-channel tube heat exchanger. Whether the refrigerant vapor compression system is operating in a transcritical cycle or a subcritical cycle, the refrigerant heat absorption heat exchanger 50 functions as a refrigerant evaporator. Before entering the evaporator 50, the refrigerant passing through refrigerant line 24 traverses the evaporator expansion device 55, such as, for example, an electronic expansion valve or a thermostatic expansion valve, and expands to a lower pressure and a lower temperature to enter heat exchanger 52. As the refrigerant traverses the heat exchanger 52, the refrigerant, typically a two-phase (liquid/vapor mix) refrigerant, passes in heat exchange relationship with a heating fluid whereby the liquid refrigerant is evaporated to a vapor and the vapor typically superheated to a desired degree. The low pressure vapor refrigerant leaving the heat exchanger 52 passes through the refrigerant line 26 to the suction inlet of the first compression stage 30a. The heating fluid may be air drawn by an associated fan(s) 54 from a climate controlled environment, such as a perishable/frozen cargo storage zone associated with a transport refrigeration unit, or a food display or storage area of a commercial establishment, or a building comfort zone associated with an air conditioning system, to be cooled, and generally also dehumidified, and thence returned to a climate controlled environment.
The flash tank 60, which is disposed in the refrigerant line 24 between the gas cooler 40 and the evaporator 50, upstream of the evaporator expansion valve 55 and downstream of the high pressure expansion device 45, functions as an economizer and a receiver. The flash tank 60 defines a chamber 62 into which expanded refrigerant having traversed the high pressure expansion device 45 enters and separates into a liquid refrigerant portion and a vapor refrigerant portion. The liquid refrigerant collects in the chamber 62 and is metered therefrom through the downstream leg of the refrigerant line 24 by the evaporator expansion device 55 to flow through the evaporator 50.
The vapor refrigerant collects in the chamber 62 above the liquid refrigerant and may pass therefrom through economizer vapor line 64 for injection of refrigerant vapor into an intermediate stage of the compression process. An economizer flow control device 65, such as, for example, a solenoid valve (ESV) having an open position and a closed position, is interposed in the economizer vapor line 64. When the refrigerant vapor compression system 20 is operating in a economized mode, the economizer flow control device, ESV, 65 is opened thereby allowing refrigerant vapor to pass through the economizer vapor line 64 from the flash tank 60 into an intermediate stage of the compression process. When the refrigerant vapor compression system 20 is operating in a standard, non-economized mode, the economizer flow control device, ESV, 65 is closed thereby preventing refrigerant vapor to pass through the economizer vapor line 64 from the flash tank 60 into an intermediate stage of the compression process.
In an embodiment where the compression device 30 has two compressors connected in serial flow relationship by a refrigerant line, one being a first compression stage 30a and the other being a second compression stage 30b, the vapor injection line 64 communicates with the refrigerant line interconnecting the outlet of the first compression stage 30a to the inlet of the second compression stage 30b. In an embodiment where the compression device 30 comprises a single compressor having a first compression stage 30a feeding a second compression stage 30b, the refrigerant vapor injection line 64 can open directly into an intermediate stage of the compression process through a dedicated port opening into the compression chamber.
The refrigerant vapor compression system 20 also includes a controller 100 operatively associated with the plurality of flow control devices 45, 55, 65 and 75 interdisposed in various refrigerant lines as previously described for selectively controlling the opening, the closing, and, as applicable, the openness. The controller 100 also monitors the ambient air temperature, TAMAIR, supply air temperature, TSBAIR, and return air temperature, TRBAIR. In the embodiment of the refrigerant vapor compression system 20 depicted in
The term “controller” as used herein refers to any method or system for controlling and should be understood to encompass microprocessors, microcontrollers, programmed digital signal processors, integrated circuits, computer hardware, computer software, electrical circuits, application specific integrated circuits, programmable logic devices, programmable gate arrays, programmable array logic, personal computers, chips, and any other combination of discrete analog, digital, or programmable components, or other devices capable of providing processing functions.
The controller 100 is configured to control operation of the refrigerant vapor compression system in various operational modes, including several capacity modes and an unloaded mode. A capacity mode is a system operating mode wherein a refrigeration load is imposed on the system requiring the compressor to run in a loaded condition to meet the cooling demand. In an unloaded mode, the refrigeration load imposed upon the system is so low that sufficient cooling capacity may be generated to meet the cooling demand with the compressor running in an unloaded condition. The controller 100 is also configured to control the variable speed drive 34 to vary the frequency of electric current delivered to the compressor drive motor so as to vary the speed of the compression device 30 to vary the capacity output of the compression device in response to cooling demand.
As noted previously, in transport refrigeration applications, the refrigerant vapor compression system 20 must be capable of operating at high capacity to rapidly pull-down the temperature within the cargo box upon loading and must be capable of operating at extremely low capacity during maintenance of the box temperature within a very narrow band, such as for example as little as +/−0.25° C. (+/−0.45° F.), during transport. Depending upon the particular cargo being shipped, the required box air temperature may range from as low as −34.4° C. (−30° F.) up to 30° C. (86° F.). Thus, the controller 100 will selectively operate the refrigerant vapor compression system in a loaded mode (high refrigeration capacity mode) in response to a high cooling demand, such as during initial pull-down and recovery pull downs, in a standard economized mode or a standard non-economized mode.
Once the box air temperature has been pulled down, that is reduced, to a temperature within a narrow band around a set point box temperature, the controller 100 will also selectively operate the refrigerant vapor compression system 20 in an unload mode (low refrigeration capacity mode) when maintaining the box temperature in the narrow band around a set point box temperature. The narrow temperature band has an upper temperature equal to the control temperature set point, TSETPT, plus an upper bound temperature differential, ΔTUPPER, and a lower bound temperature differential, ΔTLOWER. Typically, the box temperature is controlled indirectly through monitoring and set point control of either one of the temperature, TSBAIR, of the supply box air, i.e. the air leaving the evaporator 50, and the temperature, TRBAIR, of the return box air, i.e. the box air entering the evaporator 50.
In response to the cooling load imposed on the refrigerant vapor compression system 20, the controller 100 is configured to selectively operate the refrigerant vapor compression in one of following operating modes: at least one high capacity economized mode, a moderate capacity non-economized standard mode, and a low/minimum capacity unloaded mode. In the depicted refrigerant vapor compression system 20, wherein the gas cooler fan 44 is driven by a multiple speed or variable speed motor 46, the economized capacity mode includes a maximum capacity economized mode, as well as a high capacity economized mode. In the maximum capacity economized mode, also referred to herein as stage 0, the economizer solenoid valve 65 is open, the unload solenoid valve 75 is closed and the gas cooler fan 44 is operated at a high speed. In the high capacity economized mode, also referred to herein as stage 1, the economizer solenoid valve 65 is open, the unloaded solenoid valve 75 is closed and the gas cooler fan 44 is operated at a low speed. In the moderate capacity non-economized standard mode, also referred to herein as stage 2, the economizer solenoid valve 65 is closed, the unload solenoid valve 75 is closed and the gas cooler fan 44 is operated at a low speed. In the low/minimum capacity unload mode, also referred to herein as stage 3, the economizer solenoid valve 65 is closed, the unload solenoid valve 75 is open and the gas cooler fan 44 is operated in a duty cycle as will be explained in further detail later herein.
The controller 100 also selectively operates the refrigerant vapor compression system 20 in various transition modes when staging down or staging up the refrigerant vapor compression system. For example, when staging down from the economized operation in stage 1, the controller 100 operates the refrigerant vapor compression system for a limited period of time in a first transition down mode referred to as stage 12. When staging down from the non-economized stage 2 to the unloaded operation in stage 3, the controller 100 may also operate the refrigerant vapor compression system 20 for a limited period of time in a second transition down mode referred to as stage 23. Similarly, when staging up from the unloaded mode, stage 3, to the non-economized mode of stage 2, the controller 100 may operate the refrigerant vapor compression system 20 for a limited period of time in a first transition up mode, referred to a stage 32. When staging up from operation in the non-economized mode, stage 2, to operation in the economized mode, stage 1, the controller 100 may operate the refrigerant vapor compression system 20 for a limited period of time in a second transition up mode referred to as stage 21.
The frequency of the current output from the variable speed drive 34 to the compressor motor 32 is varied in stages 0, 1, 2 and 3 for varying the speed of the compression device 30, and maintained at a respective predetermined frequency that may be determined in accordance with a frequency map in each of the respective transition stages 12, 23, 32 and 21 (
The controller 100 controls operation of the refrigerant vapor compression system 20 during transition in such a manner as to reduce, if not eliminate, overshoot and undershoot of the narrow temperature band bounding the box control temperature set point. Referring now to
During operation in the first transition down stage 12, the economizer solenoid valve 65 is open, the unload solenoid valve 75 is closed, the gas cooler fan 44 is operated at a low speed, and the variable speed drive 34 outputs electric current a first predetermined frequency to drive the compression device 30. During operation in the second transition down stage 23, the economizer solenoid valve 65 is closed, the unload solenoid valve 75 is open, the gas cooler fan 44 is operated at a low speed, and the variable speed drive 34 outputs electric current at a second predetermined frequency to drive the compression device 30. During operation in the first transition up stage 32, the economizer solenoid valve 65 is closed, the unload solenoid valve 75 is closed, the gas cooler fan 44 is operated at a low speed, and the variable speed drive 34 outputs electric current at a third predetermined frequency to drive the compression device 30. During operation in the second transition up stage 21, the economizer solenoid valve 65 is open, the unload solenoid valve 75 is closed, the gas cooler fan 44 is operated at low speed, and the variable speed drive 34 outputs electric current at a fourth predetermined frequency to drive the compression device 30. The first, second, third and fourth predetermined frequencies may be determined through use of a frequency map as previously mentioned.
In the transition stages, the controller 100 may be configured to monitor a first parameter and a second parameter and stage out of the transition mode in response to a determination that one or both of a first condition related to the first parameter and a second condition related to the second parameter has been established or established for a particular period of time. It is to be understood that the controller 100 may be configured to use similar logic processes when the refrigerant vapor compression system 20 is operating in any transition down or transition up stage.
For example, in the first transition down stage 12, the controller 100 may selectively transition down from the economized mode, stage 1, at block 210, to the unloaded mode, at block 230, through either of two routes, that is either directly into the unloaded mode, stage 3, at block 230, or first to the non-economized mode, stage 2, at block 220, and thence through the second transition down mode, stage 23, at block 232, to the unloaded mode, stage 3, at block 230. Referring now to the logic process diagram illustrated in
For clarity purposes, the nomenclature used herein will be explained before further discussing the method disclosed herein. The expression “t(condition)” translates: the time that the condition within the parentheses has existed. For example, “t(TEMP1>TEMP2)” would be read as the time that temperature 1 has been greater than temperature 2. “TCTRL” is the control temperature. “TSETPT” is the control temperature set point temperature. “TEMP_TREND” is the average derivative, that is the rate of change, of the temperature differential “TSETPT−TCTRL” over a specified period of time, for example, for purposes of illustration but not limitation, ten seconds.
In an embodiment of the method disclosed herein, when operating in the first transition down mode 12, the controller 100 monitors the rate of change, TEMP_TREND, as the first condition, and the temperature differential TSETPT−TCTRL as the second condition, and repeatedly executes the control loop 300, illustrated in
At block 310, the controller 100 compares an elapsed time at which the TEMP_TREND has been greater than zero to the preset time period, tc1. If the TEMP_TREND has been greater than 0, that is positive, for an elapsed time greater than the preset time period, t1, then the controller 100 stages down the refrigerant vapor compression system 20 to operation in the unloaded mode, stage 3 at block 230. However, if the TEMP_TREND has not been greater than 0, that is not positive, for an elapsed time greater than the preset time period, tc1, then the controller 100 proceeds to block 320.
At block 320, the controller 100 determines whether the temperature differential TSETPT−TCTRL is less than zero, which means that the sensed control temperature, typically either the current sensed TRBAIR or TSBAIR, is greater than the control temperature set point. If the temperature differential TSETPT−TCTRL is less than zero, the controller 100 stages down the refrigerant vapor compression system 20 to operation in the non-economized mode, stage 2 at block 220. However, if the temperature differential TSETPT−TCTRL is not less than zero, the controller 100 continues to execute the control logic 300 until one of the first and second conditions satisfies the control logic or a preset time out limit has been reached. In the event the time out limit has been reached, the controller 100 will transition down the refrigerant vapor compression system to operation in the unloaded mode, stage 3.
In an embodiment, the controller 100 may be configured to stage down from operation in the non-economized stage 2 to operation in the unloaded stage 3 when, during operation in the second transition down stage 23, the following two conditions are met simultaneously: the output frequency of the variable speed drive 34 powering the compression device 30 has been less than or equal to a lower frequency level that is a preset frequency margin above the minimum output frequency of the variable speed drive for an elapsed time greater than a preset period of time, t5; and the TEMP_TREND has been positive for an elapsed time greater than a preset period of time, t6. In this embodiment, if these two conditions are not met simultaneously, operation continues in the second transition down stage 23 until these conditions are simultaneously met.
In an embodiment, the controller 100 may be configured to stage down from the non-economized stage 2 to the unloaded stage 3 when, during operation in the second transition down stage 23, the temperature differential TSETPT−TCTRL has been negative and has had an absolute value greater than a preset temperature differential for an elapsed time greater than a preset period of time, t7. In this embodiment, operation continues in the unloaded low capacity stage 2 until this condition is met. It is to be understood, however, that the transitioning method discussed herein and illustrated in
When the refrigerant vapor compression system 20 is operating in the unloaded mode, stage 3, the controller 100 may be configured to control operation of the gas cooler fan 44 in such a way as to preserve the temperature control sensitivity of the variable speed drive 34 driving the variable speed compressor motor 32. For example, the controller 100 may be configured to pulse the gas cooler fan 44 by on/off cycling. Initially in stage 3, the gas cooler fan 44 will be on and operating at low speed. However, as the variable speed drive 34 cycles down to control temperature, the controller 100 is configured to further reduce the effective speed on the gas cooler fan 44 by selectively powering the gas cooler fan on for a first period of time and then powering the gas cooler fan off for a second period of time and then repeat the cycle. The first and second periods of time constitute a duty cycle. The controller 100 may be configured to adjust the first and second periods of time relative to each other to vary the time the gas cooler fan 44 is on and the fan is off within a duty cycle. In an embodiment, the controller 100 may be configured to selectively operate the gas cooler fan 44 to incrementally further reduce the effective speed of the gas cooler fan 44. For example, in an embodiment, the controller 100 may be configured to operate the gas cooler fan 44 through a series of duty cycles wherein the fan on portion of the duty cycle is decreased incrementally. For example, in an embodiment, the fan on portion of duty cycle decreases in 20% increments: 100% on/0% off; 80% on/20% off; 60% on/40% off; 40% on/60% off; 20% on/80% off; 0% on/100% off. It is be to understood that in other embodiments the fan on portion of the duty cycle may decrease in other increments, such as for example, but not limited to increments of 10%. Each duty cycle may span a preselected time period, such as, for example, 40 seconds. Upon completion of the series of duty cycles, the gas cooler fan 44 will remain powered off.
When the refrigerant vapor compression system 20 is operating in the unloaded mode, stage 3, the controller 100 may also be configured to selectively operate electric heaters 56 (
Referring now to the staging up process illustrated in
When still additional refrigeration capacity is needed to met the cooling demand, the controller 100 is configured of shift operation of the refrigerant vapor compression system 20 from the non-economized mode, stage 2, through the second transition up stage 21 and into operation in one of the economized modes, stage 1 and stage 0. When operating in the second transition up stage 21, the controller 100 again monitors two conditions. In stage 21, the monitored conditions are the rate of change of the temperature differential, TEMP_TREND, and the temperature differential TSETPT−TCTRL. If the rate of change of the temperature differential has been negative for a period of time greater than a present time period t10 (t(TEMP_TREND)<0)>t10), the controller, at block 221, is configured to shift operation of the refrigerant vapor compression system 20 into the maximum capacity economized mode, stage 0, block 200. However, if the rate of change of the temperature differential has not been negative for a period of time greater than a present time period t10 (t(TEMP_TREND)<0)>t10), and the temperature differential TSETPT−TCTRL is positive ((TSETPT−TCTRL)>0), the controller 100, at block 221, is configured to shift operation of the refrigerant vapor compression system 20 into the high capacity economized mode, stage 1, at block 210, rather than into the maximum capacity economized mode, stage 0.
In an embodiment, the controller 100 may be configured to stage up within the economized mode from the high capacity economized mode, stage 1 to the maximum capacity economized mode, stage 0, when, during operation in stage 1, the following two conditions are met simultaneously: the output frequency of the variable speed drive 34 powering the compression device 30 has been greater than a frequency level, FREQ2, for an elapsed time greater than a preset period of time, t8 ((t(TEMP_TREND)<0)>t10)); and the TEMP_TREND has been negative for an elapsed time greater than a preset period of time, t9, (t(TEMP_TREND)<0)>t9)). If these two conditions are simultaneously met, the configured is configured to shift operation of the refrigeration vapor compression system 20 into the maximum capacity economized mode, stage 0. In this embodiment, if these two conditions are not met simultaneously, operation continues in the high capacity economized mode, stage 1, until these conditions are simultaneously met.
In an embodiment, the controller 100 may select the various stage transition frequencies FREQ1, FREQ2 and FREQ3 from a pre-defined frequency map wherein the stage transition frequency is defined as a function of selected operating parameters indicative of cooling demand. For example, the stage transition frequencies may be calculated as a function of the ambient air temperature, TAMBAIR, the supply air temperature, TSBAIR, and the return air temperature, TRBAIR.
The terminology used herein is for the purpose of description, not limitation. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as basis for teaching one skilled in the art to employ the present invention. Those skilled in the art will also recognize the equivalents that may be substituted for elements described with reference to the exemplary embodiments disclosed herein without departing from the scope of the present invention.
While the present invention has been particularly shown and described with reference to the exemplary embodiments as illustrated in the drawing, it will be recognized by those skilled in the art that various modifications may be made without departing from the spirit and scope of the invention. For example, the refrigerant vapor compression system 20 may further include an intercooler heat exchanger (not shown) disposed in the primary refrigerant circuit between the discharge outlet of the first compression stage 30a and the inlet to the second compression stage 30b whereby the partially compressed (intermediate pressure) refrigerant vapor (gas) passing from the discharge outlet of the first compression stage to the inlet to the second compression stage passes in heat exchange relationship with a flow of cooling media, such as, for example, but not limited to the cooling air flow generated by the gas cooler fan.
Therefore, it is intended that the present disclosure not be limited to the particular embodiment(s) disclosed as, but that the disclosure will include all embodiments falling within the scope of the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2013/055904 | 8/21/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61692837 | Aug 2012 | US |
