Patent Application
20110138827
The present invention relates to a refrigerant system having an economizer module and a reciprocating compressor. More particularly, the present invention relates to a method and system for operating the refrigerant system in various modes of loading and unloading.
Refrigerant systems are used to condition air in an environment by controlling the temperature and/or the humidity of the air. In a typical air conditioning or refrigeration system, a compressor delivers a compressed refrigerant to an outdoor high pressure heat exchanger, known as a condenser or a gas cooler. If the refrigerant in the outdoor heat exchanger, when cooled, condenses into a liquid this heat exchanger is commonly referred to as a condenser. If the refrigerant exiting the compressor is at a thermodynamic state above critical point, then the refrigerant upon cooling in the heat exchanger may not condense into a liquid but would simply be cooled to a lower temperature. In this case, this heat exchanger is commonly referred to as a gas cooler. From the high pressure heat exchanger, the refrigerant passes through an expansion device, and then to an indoor heat exchanger, known as an evaporator. In the evaporator, the air is blown over the evaporator external surfaces to lower a temperature of the air, and moisture may also be removed from the air to lower its humidity. From the evaporator, the refrigerant is returned back to the compressor.
An economizer cycle may be used in a refrigerant system to increase the capacity and efficiency of the system. When the economizer cycle is actuated, a portion of the refrigerant is tapped from a main refrigerant circuit at a position downstream of the high pressure heat exchanger. The tapped refrigerant is expanded to a lower intermediate pressure and temperature, at which point it passes through an economizer module, which is commonly called an economizer heat exchanger, to further cool high pressure refrigerant in the main refrigerant circuit. The tapped refrigerant is returned back to the compressor, typically at an intermediate pressure. The main refrigerant travels to the evaporator where it has a greater thermodynamic cooling potential (cooling capacity), due to the fact that it has been additionally cooled in the economizer heat exchanger. An economizer cycle can also be achieved through the use of a flash tank, instead of the economizer heat exchanger, as known in the art.
In one design, the refrigerant system may use a reciprocating compressor having two separate sets of cylinder modules, which are configured to receive and compress two separate refrigerant streams. An economizer cylinder module may be used to compress the tapped refrigerant from the economizer module, whereas a main cylinder module may be configured for compressing the main refrigerant from the evaporator. Downstream of the compressor, the two refrigerant streams may be combined before flowing back to the high pressure heat exchanger.
During operation of the refrigerant system, there may be conditions in which it is ineffective to use the economizer cycle, even though the refrigerant system is operating at or near full load. For example, if the ambient air temperature is high and the suction pressure entering the compressor is also high then the economizer cycle engagement may not add any additional cooling and thus the economizer cycle may be disengaged, even if there is a high cooling demand (i.e. full load). At other times, it may be beneficial to operate a refrigerant system in a mode that limits the cooling capacity by limiting a flow of refrigerant through the system, which may be referred to as unloading. The unloading can be achieved by disengaging the economizer circuit or providing by-pass operation. There is a need for improved flexibility to vary a cooling capacity for a refrigerant system having an economizer cycle and a reciprocating compressor with a dedicated economizer cylinder module.
A method and system is described herein for operating a refrigerant system having a reciprocating compressor with a main cylinder module and an economizer cylinder module. In the context of this application a single cylinder module may be substituted by bank of cylinders modules. The refrigerant system provides cooling by circulating a refrigerant through a high pressure heat exchanger, an economizer module, an evaporator, and at least one of the main cylinder modules and at least one of the economizer cylinder modules. The main cylinder module and the economizer cylinder module have separate inlet and outlet streams. The flow of refrigerant into the main cylinder module may be controlled as a function of an operating mode of the refrigerant system, which includes various modes of loading and unloading based, in part, on a cooling demand. The flow of refrigerant into the economizer cylinder module may separately be controlled as a function of the operating mode. In some embodiments, the refrigerant system may include a connector line configured to redirect refrigerant from the economizer cylinder module to the main cylinder module or from the main cylinder module to the economizer cylinder module.
Compressor 12 is a reciprocating compressor and includes main cylinder module 30 and economizer cylinder module 32. It is recognized that one or both of main cylinder module 30 and economizer cylinder module 32 may include more than one cylinder and more than one cylinder module. In an exemplary embodiment, main cylinder module 30 has higher displacement than economizer cylinder module 32. Compressor 12 includes first suction inlet 34, which is connected to main cylinder module 30, and second suction inlet 36, which is connected to economizer cylinder module 32. Similarly, compressor 12 also includes first discharge outlet 38 extending from main cylinder module 30 and second discharge outlet 40 extending from economizer cylinder module 32. System 10 is designed such that main cylinder module 30 and economizer cylinder module 32 each receive a distinct refrigerant stream for compression. As shown in
Two refrigerant streams exit compressor 12 via first outlet 38 and second outlet 40 respectively. Before entering high pressure heat exchanger 14, the refrigerant streams are recombined such that high pressure heat exchanger 14 receives one refrigerant stream. In high pressure heat exchanger 14 operating as a condenser, the vapor refrigerant condenses to form liquid refrigerant. In an alternative embodiment of refrigerant system 10, high pressure heat exchanger 14 may be substituted with a gas cooler, where refrigerant stays in a single phase thermodynamic state.
Once the refrigerant exits high pressure heat exchanger 14, the refrigerant may again be split into two refrigerant streams. A main refrigerant stream flows through main refrigerant line 42a; an economizer refrigerant stream flows through tap line 44a, also referred to as economizer refrigerant line 44a. The refrigerant in tap refrigerant line 44a passes through first expansion device 16 in order to lower its temperature and pressure before passing through economizer module 18. Expansion device 16, as well as second expansion device 20, may include a capillary tube, an orifice, a thermostatic expansion device, or an electronic expansion device.
Inside economizer module 18, the refrigerant flowing through tap line 44a further decreases a temperature of the main refrigerant stream passing through main refrigerant line 42a. Economizer module 18 is used to provide additional cooling capacity to the main refrigerant stream. In an exemplary embodiment, economizer module 18 is a heat exchanger. An alternative embodiment of module 18 is described in further detail below. Also, as known, the economizer refrigerant flow may be tapped downstream (instead of upstream) of economizer module 18. Such system configurations are within the scope and can equally benefit from the invention.
After exiting economizer module 18, the main refrigerant stream passes through second expansion device 20, and then to evaporator 22 through main refrigerant line 42b. The main refrigerant is evaporated inside evaporator 22 by removing heat from air passing over external surfaces of evaporator 22. Main refrigerant line 42c connects evaporator 22 to inlet 34 of main cylinder module 30, and the refrigerant flows through main refrigerant line 42c to undergo compression in a separate compression path in the main cylinder module 30. First valve 24 is located in main refrigerant line 42c and regulates a flow of the main refrigerant between evaporator 22 and compressor 12. The economizer refrigerant stream flows directly from economizer module 18 to compressor 12 through economizer refrigerant line 44b. Second valve 26 is located in economizer line 44b and regulates a flow of the economizer refrigerant between economizer module 18 and compressor 12. More specifically, economizer refrigerant line 44b connects to second inlet 36 of compressor 12.
The present invention includes the use of valves 24 and 26 to control a flow of refrigerant into compressor 12, and more specifically to control a flow of refrigerant through main cylinder module 30 and economizer cylinder module 32. An amount of cooling provided by refrigerant system 10 may be controlled by controlling a circulation of the refrigerant through main cylinder module 30 and economizer cylinder module 32, as described further below. A cooling capacity of refrigerant system 10 may be varied by operating the system in loading or unloading modes. These operational modes are also described in further detail below.
Valve 24 is used to control the flow of refrigerant into main cylinder module 30, which directly impacts an amount of cooling provided by evaporator 22. As more refrigerant is pumped through cylinder module 30, more refrigerant is circulated through evaporator 22, which results in increased amount of cooling of air passing over the evaporator 22. Similarly, valve 26 controls flow of refrigerant through economizer cylinder module 32. As more refrigerant is pumped through cylinder module 32, more refrigerant is circulated through economizer module 18, which provides additional cooling to the refrigerant in main refrigerant line. As described below, valves 24 and 26 are controlled in order to regulate an amount of cooling provided in evaporator 22.
For a refrigerant system similar to system 10, but not including valves 24 and 26, unloading may not be possible, or be very limited, without essentially shutting down system 10, which may be undesirable for several reasons. In refrigerant system 10 of
In the scenario in which both valves 24 and 26 are open (i.e. full loading with economizer), refrigerant system 10 operates the same as a refrigerant system not having valves 24 and 26 for controlling refrigerant flow into the reciprocating compressor 12. In the full loading mode of Table 1, the economizer cycle is being utilized since valve 26 is open. In the economizer mode, economizer module 18 uses refrigerant in the tapped refrigerant line 44a to further cool refrigerant in the main refrigerant line 42a such that the main refrigerant provides additional cooling to the air in evaporator 22. This operating mode is referred to as “Full loading with economizer” since valve 26 in economizer line 44b is open and both cylinder modules 30 and 32 are operating at full capacity.
The economizer cycle is generally used when a ratio of discharge pressure to suction pressure in compressor 12 is high (typically when the system operates at pressure ratio above 3). As such, the pressure at the suction or inlet of compressor 12 is typically low, which is a function of low pressure inside evaporator 22. A low evaporator pressure typically correlates to a low ambient air temperature. In that case, refrigerant system 10 may operate in the economizer mode (i.e. valve 26 open) to further decrease the air temperature.
In the second mode shown in Table 1 and designated as “Mid-level unloading”, the economizer cycle is blocked by closing valve 26, which prevents refrigerant from circulating through economizer module 18. As such, refrigerant in the tapped refrigerant line essentially stops providing cooling to refrigerant in the main refrigerant line in economizer module 18. This mid-level unloading mode may commonly be used at low to moderate pressure ratio applications (typically in pressure ratio range from 1 to 3). When the air requiring cooling is at a high temperature, refrigerant system 10 provides higher cooling capacity when the economizer cycle is not active. A higher ambient air temperature commonly results in a high pressure in the evaporator. As such, a high ambient air temperature usually correlates to a low pressure ratio (discharge to suction). The pressure ratio may commonly be monitored or calculated to determine whether to engage or disengage the economizer cycle.
In the third mode of Table 1, labeled as “Full unloading A”, valve 24 is blocked such that the only refrigerant flowing through compressor 12 is the tapped refrigerant from economizer module 18. Because valve 26 is closed, refrigerant stops circulating through evaporator 22 and ceases to provide cooling to air passing through evaporator 22. This high level of unloading may be used when there is little to no cooling load required, yet it is desirable to continue operating refrigerant system 10, instead of completely shutting it down. By flowing the tapped refrigerant line from economizer module 18 through compressor 12, discharge cooling may be provided to compressor 12.
Finally, the last fourth mode shown in Table 1 and is designated as “Full unloading B” is a mode in which both valves 24 and 26 are closed. As such, the refrigerant stops circulating through refrigerant system 10 and is no longer able to provide cooling to air passing through evaporator 22. Similar to the “Full unloading A” mode above, refrigerant system 10 may operate in this mode when there is minimal, if any, cooling load present. It is recognized that this last mode is an unusual operating condition and additional steps may need to be taken to ensure that compressor 12, as well as other equipment in refrigerant system 10, does not overheat.
Valves 24 and 26 may be ON/OFF valves that have two positions—fully open and fully closed. This type of valve is typically a solenoid valve. Alternatively, either or both of valves 24 and 26 may be a variable opening valve or “stepper motor drive” valve. The stepper motor may position valves 24 and 26 at a fully open position, a fully closed position, and anywhere in between. In preferred embodiments, valves 24 and 26 have a variable opening, since this provides greater flexibility and additional stages of loading and unloading. It is recognized that variations of the four modes shown in Table 1 are possible by adjusting one or both of valves 24 and 26 at an intermediate position between open and closed. If the stepper motor valves are utilized then, for example, for modes three and four, valve 24 may not be fully closed and, in this case, refrigerant system 10 will not have a full unloading operation.
Operation of valves 24 and 26 may be controlled by controller 28, which determines a most effective mode of operation based on particular parameters inside refrigerant system 10. Depending on sensed parameters, controller 28 adjusts valves 24 and 26. In the case of solenoid valves, the adjustments may be either an ON or OFF position. For variable opening valves, controller 28 may adjust the valves from fully open, fully closed or an intermediate position. To determine an operating mode and hence a position of valves 24 and 26, parameters sensed and relayed to controller 28 may include, but are not limited to, a temperature inside evaporator 22, a set point temperature of the air to be conditioned, a pressure at an inlet of compressor 12 (i.e. suction pressure), and a pressure at an outlet of compressor 12 (i.e. discharge pressure).
System 10 includes various sensors that communicate with controller 28. As shown in
Data from sensors 50, 52, 54, 56 and 58 include temperature (T1) and pressures (P1) through (P4), which are inputs to controller 28, as shown in
In the exemplary embodiment shown in
In refrigerant system 10 shown in
Refrigerant system 110 is able to operate in eight different operating modes, based on a position of valves 124, 126 and 172. The operating modes are generally ordered from highest to lowest cooling capacity. For purposes of the description below, a higher level of unloading corresponds to a lower cooling capacity. Four of the eight operating modes shown in Table 2 for refrigerant system 110 are feasible in refrigerant system 10 of
Two “Full loading” operating modes are shown above in Table 2. First, the “Full loading with economizer” mode was described above in reference to refrigerant system 10. Since both valves 124 and 126 are open, and valve 172 is closed, this mode is the same as a system having no valves in lines 142 and 144. The second “Full loading” operating mode, referred to in Table 2 as “Full loading without economizer”, is not feasible for refrigerant system 10 and allows for increased loading (i.e. increased cooling capacity) when the economizer cycle is not being used for low pressure ratio operation.
As described above in reference to
It is recognized that the level of unloading may be adjusted for any given mode based on a position of valves 124, 126 and 172, in those embodiments in which the valves have variable openings.
In operating mode three, designated as low to mid-level unloading, all three valves 124, 126 and 172 are open. As such, at least a portion of flow from economizer refrigerant line 144b flows through connector refrigerant line 170 and is combined with main refrigerant in main refrigerant line 142c. In this mode, a greater portion, if not all of the refrigerant, flows through main cylinder module 130, and economizer cylinder module 132 compresses a minimal amount of refrigerant. Due to a limited capacity of main cylinder module 130, less cooling is provided in evaporator 122 in this mode, as compared to a mode in which all refrigerant from economizer refrigerant line 144b were flowing through economizer cylinder module 130.
For operating mode four, first valve 124 is open, and second valve 126 and third valve 172 are closed. This operating mode was also feasible in refrigerant system 10 and was described above as mid-level unloading in Table 1. The economizer cycle is blocked in operating mode four. Because valve 172 is closed and economizer cylinder module 132 is thus not used, operating mode four provides less cooling as compared to operating mode two (i.e. full loading without economizer), and is therefore designated as an unloading mode. Additional unloading may be accomplished by partially closing first valve 124.
In operating mode five valves 124 and 126 are closed, while third valve 172 in connector refrigerant line 170 is open. Since valve 126 is closed, the economizer cycle is blocked, similar to operating mode four. However, in operating mode five, because valve 124 is also closed, all refrigerant flowing through line 142c from evaporator 122 is directed through connector refrigerant line 170 and into economizer cylinder module 132.
Similar to the mode above, in operating mode six, first valve 124 is closed and third valve 172 is open. However, in contrast to above, the economizer cycle is activated by opening second valve 126. Since valve 124 is closed, the main refrigerant from evaporator 122 is directed through economizer cylinder module 132 in addition to the economizer refrigerant flowing through economizer refrigerant line 144b. In the final two operating modes seven and eight of Table 2, designated as full unloading, third valve 172 in connector refrigerant line 170 is closed. Therefore, these two operating modes are feasible in a refrigerant system without a connector line, like refrigerant system 10 of
Controller 128 regulates a position of valves 124, 126 and 172 in order to operate refrigerant system 110 in an operating mode that aligns with the cooling load demands, while still operating efficiently and avoiding nuisance shutdowns. As described above in reference to controller 28 of refrigerant system 10, controller 128 controls a position of valves 124, 126 and 172 based on sensed parameters in refrigerant system 110. Similar to refrigerant system 10, refrigerant system 110 may include temperature sensors 150 and 160 for measuring, respectively, a temperature (T1) inside evaporator 122 and an ambient air temperature (AT). Refrigerant system 110 also includes pressure sensors 152, 154 and 156 and 158, which are located in similar locations to those shown in
In the exemplary embodiment shown in
Through the use of valves 124, 126, 172 and connector refrigerant line 170, refrigerant system 110 provides superior flexibility during unloading, as well as the feasibility to achieve a greater cooling capacity when the economizer module is not being used. In the exemplary embodiment shown in
In the embodiments shown in
The refrigerant system and operating method described herein may easily be implemented into existing refrigerant systems. The refrigerant systems may include supermarket refrigerant systems, container refrigerant systems, truck/trailer refrigerant systems, rooftop air conditioning and heat pump refrigerant systems, and residential air conditioning refrigerant systems. The valves may be installed in existing refrigerant lines, and in some cases, a connector refrigerant line may also be added between the economizer refrigerant line and the main refrigerant line. The valves and connector refrigerant line described herein may also be incorporated into the design of new refrigerant systems.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2009/052995 | 8/6/2009 | WO | 00 | 2/7/2011 |
| Number | Date | Country | |
|---|---|---|---|
| 61087008 | Aug 2008 | US |
