JP2008533428A - High pressure side pressure regulation of transcritical vapor compression system - Google Patents

Abstract

Bottle cooler or small capacity air conditioner, refrigerator or the CO ₂ vapor compression system used in other systems, can be eliminated costly expansion device by selecting an inexpensive pressure regulator.

Description

  Filed March 18, 2005 and claims the benefit of US Patent Application No. 60 / 663,960 entitled "High Pressure Side Pressure Adjustment of Transcritical Vapor Compression System", the disclosure of that patent is Reference to this application.

  The present invention relates to refrigeration. More particularly, the present invention relates to beverage coolers.

As a natural and environmentally friendly refrigerant, CO ₂ (R-744) has received much attention. In most air conditioning operating ranges, the CO ₂ system operates in transcritical mode. FIG. 1 schematically illustrates a transcritical vapor compression system 20 that utilizes CO ₂ as the working fluid. The system has a compressor 22, a gas cooler 24, an expansion device 26, and an evaporator 28. Typical gas coolers and evaporators can each take the form of a refrigerant-air heat exchanger. An air flow across one or both of these heat exchangers can be forced. For example, one or more fans 30, 32 can blow each air stream 34, 36 across two heat exchangers. The refrigerant flow path 40 includes a suction line that extends from the outlet of the evaporator 28 to the inlet 42 of the compressor 22. The discharge line extends from the compressor outlet 44 to the gas cooler inlet. A further line connects the gas cooler outlet to the expander inlet and connects the expander outlet to the evaporator inlet.

The main difference between transcritical operation and conventional operation is that the critical temperature of CO ₂ is 87.8 ° F., so heat removal in the gas cooler is done in the supercritical region. Thus, pressure does not depend solely on temperature, which raises additional control and optimization issues for system operation.

  When the discharge temperature of the gas cooler is constant, the refrigerant outlet enthalpy decreases as the pressure on the high pressure side increases, so the enthalpy difference becomes larger through the gas cooler. The gas cooling capacity depends on the mass flow rate of the refrigerant and the enthalpy difference before and after the gas cooler. In the case of a beverage cooler, the evaporator can basically be the internal temperature of the cooler. It is usually desirable to maintain this temperature in a very narrow range regardless of external conditions. For example, it is desirable to maintain the interior close to 37 ° F. Basically, this temperature determines the steady state compressor suction pressure.

  When the compressor suction pressure is constant, as the high-pressure side pressure increases, the amount of energy used by the compressor increases and the volumetric efficiency of the compressor decreases. As the volumetric efficiency of the compressor decreases, the flow through the system decreases. When balancing these two conflicting actions, the gas cooling capacity usually increases as the high-pressure side pressure increases. However, beyond a certain pressure, the increase in capacity is very small. Since the expansion device normally expands with an equal enthalpy, the evaporation capacity usually increases as the high-pressure side pressure increases.

  The coefficient of performance (COP), which is the energy efficiency of a vapor compression system, is usually expressed as the ratio of system capacity to consumed energy. Normally, as pressure increases, both capacity and energy consumption increase, so the difference between the two determines the total COP. Therefore, there is usually an optimum pressure that provides the highest possible performance.

The electronic expansion valve is typically used as a device 26 that regulates the pressure on the high pressure side to optimize the COP of the CO ₂ vapor compression system. Electronic expansion valves typically have a step motor attached to the needle valve to change the effective valve opening or flow capacity to a number of possible states (usually over 100). Thereby, the high-pressure side pressure can be satisfactorily controlled over a wide range of operating conditions. The valve opening is electronically controlled by the controller 50 to adjust the actual high side pressure to the desired set point. This countermeasure by pressure control requires a fairly expensive valve, a high-performance controller 50, and a sensor 52 for measuring the high-pressure side pressure. This apparatus, CO ₂ increased vapor compression in such expenses considerably systems, CO ₂ vapor compression system is that unattractive compared to HFC (hydrofluorocarbon) system.

  Although it is possible to use a fixed expansion device in a transcritical vapor compression system, this approach has limitations and may compromise performance or functionality. During steady state operation, fixed expansion devices (such as fixed orifices or capillaries) can work well to adjust the high side pressure of the system to a near optimum pressure. When pulling down, if the system is started and the evaporation temperature and pressure can be very high, the flow rate through a constant speed capacity compressor can also be relatively high. Due to this high flow rate, the pressure on the high pressure side may exceed safety limits.

An inexpensive pressure regulator can be selected for the CO ₂ vapor compression system used in bottle coolers or small capacity air conditioners, refrigerators, or other systems to eliminate expensive expansion devices. The possibility of exceeding the pressure is reduced using an inexpensive multistage fixed expansion device based on one or more solenoid valves.

  The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

The present invention relates to the optimization of high side pressure for a CO ₂ vapor compression system. In the case of HVAC & R (heating, ventilation, air conditioning, and refrigeration) products that do not have a wide operating range, the optimum pressure on the high pressure side does not change much for all operating conditions. Thus, a fixed expansion device (eg, an orifice or a capillary) can be used to adjust the high side pressure to a preset constant value for all steady operating conditions of the CO ₂ vapor compression system. This setting, the best overall performance factor CO ₂ vapor compression system a (COP), should be determined so as to obtain the total operating range. Using a fixed expansion device can significantly reduce the cost of the pressure control components of the CO ₂ vapor compression system.

In the pull-down state, the compressor flow is much higher than in the steady state. The high side pressure can maximize the pull-down cooling capacity of the CO ₂ vapor compression system, but the flow through the pressure regulator can exceed the flow through the compressor (so the system pressure becomes too high). Should not be optimized. This high side optimum pressure that maximizes capacity is typically higher than the high side optimum pressure that maximizes overall COP. However, since the compressor flow rate is much higher during pulldown than during steady state, the expansion device can be configured to have a greater flow capacity during pulldown. A simple multi-state inflation device can provide this. This can be accomplished in a number of ways using solenoid valves that allow the pressure control system to assume more than one state.

  The following embodiment shows a modification of the basic system of FIG. Accordingly, the same reference numerals are used to represent the compressor 22, the gas cooler 24, and the evaporator 28. In any situation that is redesigned or remanufactured, these parts can be identical to those of the base system or can be further modified. FIG. 2 shows a system 60 in which the refrigerant flow path 62 is divided into two parallel branch / segments 64, 66 between the outlet of the gas cooler 24 and the inlet of the evaporator 28. The first branch channel 64 has a first fixed expansion device 68. The second branch channel 66 includes a solenoid valve 70 and a second fixed expansion device 72 that exist in series. Although the solenoid valve 70 is shown upstream of the second fixed expansion device 72, this order may be reversed. The illustrated solenoid valve 70 has two settings / states. One setting / state is a fully closed state and no flow can pass through the second branch 66. The second setting / state is the fully open state, which minimizes the pressure loss across the solenoid valve 70 and allows the flow to pass through the second branch 66.

  If the flow rate of the compressor is relatively small during the steady operation state, the solenoid valve 70 remains completely closed. During the pull-down state, the compressor flow rate is relatively high. Solenoid valve 70 is opened to avoid over pressure when pulling down, allowing flow to pass through second fixed expansion device 72. When both expansion devices 68 and 72 are combined, the high pressure side pressure can be adjusted to avoid over pressure while still achieving good system performance.

  In operation, the pull-down condition can be detected using one or more temperature sensors 75 and pressure sensors 74 connected to a controller 76 connected to control the solenoid valve 70. The controller 76 can also be connected to a compressor and / or fan (s) to control the operation of each. For ease of explanation, the sensors and controller, if any, are not shown in the following examples.

  FIG. 3 shows a system 80 in which the refrigerant flow path 82 has two segments / split flow paths 84, 86 that exist in parallel upstream of the first fixed expansion device 88. The first branch channel 84 has a solenoid valve 90. The second branch channel 86 has a second fixed expansion device 92. During steady operation, the solenoid valve 90 is closed to prevent flow along the first branch 84. The second shunt 86 acts as a bypass, and the restricted flow passes through the second fixed expansion device 92 before passing through the first fixed expansion device 88 next time. When in the pull-down state, the solenoid valve 90 opens, allowing an essentially unrestricted flow along the first shunt 84. Further flow flows slightly along the second branch 86 and then the combined flow passes through the first expansion device 88. In an alternative embodiment, the first expansion device 88 may be upstream rather than downstream of the shunt flow. The control method and control components (not shown) of this system and the system described below can be the same as those of the system 60.

  FIG. 4 shows another system 100 in which the flow path 102 has first and second segment / split flow paths 104, 106 between the gas cooler and the evaporator. The fixed expansion device 108 is disposed in the first branch channel 104. The electromagnetic valve 110 is disposed in the second branch channel 106. The electromagnetic valve 110 has both an electromagnetic valve and a fixed expansion device. Specifically, even in the opened state, it can still be relatively limited as compared to the opened state of the electromagnetic valve 90. Therefore, the pressure drop during pull-down through the solenoid valve 110 is large, and the high-pressure side pressure of the system is adjusted to a certain preset optimum value by combining the solenoid valve 110 and the fixed expansion device. In steady operation, the solenoid valve 110 is completely closed and all flow passes through the expansion device 108.

  FIG. 5 shows a system 120 without a diversion channel, in which a solenoid valve 124 and a fixed expansion device 126 are arranged in series along the flow channel 122. The electromagnetic valve 124 is different from the valve 110 in FIG. 4 and combines the electromagnetic valve and the fixed expansion device. Specifically, the valve element (eg, solenoid plunger) of the solenoid valve 124 can have a small orifice, and in its closed state, only a portion is closed. However, in the open state, it is basically completely open and the pressure drop is small. As a result, during steady state operation, the solenoid valve 124 is in its closed state, allowing a relatively small amount of flow to pass and significantly reducing the pressure (alone and in conjunction with the expansion device 126). In steady state, the solenoid valve opens, essentially allowing only the expansion device 126 to define the flow rate. As with other systems, the order of series can be reversed.

  FIG. 6 shows a system 140 that combines the aspects of the systems 80 and 120. Specifically, the flow path 142 has two segment / split flow paths 144 and 146 that exist in parallel upstream of the first fixed expansion device 148. The first branch channel 144 has a solenoid valve 150. The second branch 146 has a fixed expansion device 152. The illustrated electromagnetic valve 150 may have a closed state in which only a part is closed, similar to the electromagnetic valve 124. In the pull-down state, the solenoid valve 150 is open. During steady state, the valve 150 is closed. In steady state, there is relatively little flow along each branch path. When in the pull-down state, a larger flow can pass along the first branch 144 and the remaining flow is along the second branch 146.

  FIG. 7 shows another system 160 in which the flow path 162 has a solenoid valve 164 that functions as a solenoid valve and an orifice. Specifically, since the element of the solenoid valve 144 has an orifice, only a part is closed in the closed state. During steady state, the valve 144 is in its closed state and the orifice allows a relatively small amount of flow to pass. In the pull-down state, the valve is open so that a larger flow passes.

  FIG. 8 shows a system 180 in which the flow path 182 has segment / split flow paths 184 and 186 between the gas cooler and the evaporator. The electromagnetic valves 188 and 190 are disposed in the respective flow paths. These solenoid valve elements can have orifices. By independently controlling the valves, it is possible to have more than two selectable effective flow restriction states. For example, if the orifice dimensions are different, the two valves provide up to four different effective limiting conditions. With both valves open, the limit can be minimized. The limit can be maximized with both valves closed. A pair of intermediate restricted states can be realized by closing one of the valves and opening the other. Adjusting the size of the shunt conduit, adjusting the size of the valve, or opening only one valve to increase the difference between the three states with the least restrictions So, restrictions can be added so that there is basically no free flow. In alternative embodiments, such valves can be featured in series rather than in parallel.

  Various sensors and / or input from the user can be used to control the solenoid valve (s). The sensor 74 can directly measure the pressure on the high pressure side. When this pressure exceeds one or more associated thresholds, controller 76 places the valve (s) in a corresponding relatively free flow state. As an alternative, or in addition to the high side pressure measurement by sensor 74, input may be received from an air temperature sensor. The illustrated sensor 75 can be arranged to be exposed to air in the cooler or air from within the cooler (eg, to the flow 36 upstream of the evaporator 28). The sensor 75 can form part of a control thermostat. Thus, by using only such a sensor, it is possible to save costs through the elimination of pressure sensor 52 or pressure sensor 74.

  For a positive displacement positive displacement compressor, the flow through the system is directly dependent on the density of refrigerant entering the compressor and, to a lesser extent, the pressure ratio of the compressor. The inlet density is directly dependent on the refrigerant saturation temperature and superheat. These in turn depend directly on air temperature, system capacity, and charge. For a simple system, these parameters can be determined at the design stage depending on the temperature of the air passing through the evaporator. A correlation can be derived that matches the evaporator air temperature to the refrigerant inlet density. During operation, the solenoid valve (s) remain open until the output of the evaporator temperature sensor 75 falls below a predetermined value. When the output falls below a predetermined value, one of the single solenoid valve or the plurality of solenoid valves is closed. This can be repeated in the case of a system with multiple solenoid valves, further reducing the effective expansion orifice area when the temperature drops to maintain the high pressure portion of the system at optimum pressure.

  If the high side pressure is measured directly (eg, by sensor 74), a different correlation can be used. The optimum pressure on the high pressure side is known to depend on the evaporator temperature and, optionally, the ambient temperature. One or more solenoid valves can be operated to maintain the pressure within certain limits.

  FIG. 9 shows an exemplary cooler 200 having a removable cassette 202 containing a refrigerant and air treatment system. A typical cassette 202 is attached to a compartment of the base 204 that constitutes the housing. The housing has an interior space 206 between the left and right walls, the rear wall / duct 216, the top wall / duct 218, the front door 220, and the base compartment. Inside is a vertically arranged shelf 222 that holds beverage containers 224.

  A typical cassette 202 draws air stream 34 from the front grid of base 224 and exhausts air stream 34 from the back of the base. The cassette can be pulled out from the front of the base by removing or opening the grid. A typical cassette delivers an air flow 36 through a rear duct 210 and an upper duct 218 to a circulation flow path through the interior 206.

  FIG. 10 shows a typical cassette 202 in more detail. The heat exchanger 28 is disposed in a housing 240 defined by the heat insulating wall 242. The heat exchanger 28 is shown for the most part located in the upper rear quadrant of the cassette and is directed to allow the air stream 36 to pass generally rearwardly, after the air stream has exited the heat exchanger. It turns upward and is discharged from the rear part of the upper end of the cassette. Drain 250 can pass through the bottom of wall 242 and send condensed water from stream 36 to drain pan 252. Accumulated water 254 is seen in pan 252. The pan 252 is along an air duct 256 that passes a stream 34 downstream of the heat exchanger 24. Evaporation can be promoted by touching the water 254 accumulated in the heated air in the stream 34.

  One or more embodiments of the present invention have been described. However, it should be understood that various modifications can be made without departing from the spirit and scope of the invention. For example, when implemented as a remanufacturing of an existing system or a reorganization of an existing system configuration, the details of the existing configuration may affect the implementation details. Accordingly, other embodiments are within the scope of the following claims.

1 is a schematic diagram of a prior art vapor compression system. 1 is a schematic diagram of a first CO ₂ vapor compression system. FIG. FIG. 3 is a schematic diagram of a second CO ₂ vapor compression system. FIG. 3 is a schematic view of a third CO ₂ vapor compression system. FIG. 6 is a schematic view of a fourth CO ₂ vapor compression system. FIG. 6 is a schematic view of a fifth CO ₂ vapor compression system. FIG. 6 is a schematic view of a sixth CO ₂ vapor compression system. FIG. 7 is a schematic view of a seventh CO ₂ vapor compression system. It is a schematic side view of the display case containing a refrigeration and an air management cassette. FIG. 2 is a diagram of a refrigeration and air management cassette.

Claims (11)

A compressor (22) for delivering refrigerant along a flow path (62, 82, 102, 122, 142, 162, 182) in at least a first mode of system operation;
A first heat exchanger (24) along the flow path downstream of the compressor in the first mode;
A second heat exchanger (28) along the flow path upstream of the compressor in the first mode;
Pressure regulating devices (68, 72, 88, 92, downstream of the first heat exchanger (24) and upstream of the second heat exchanger (28) in the flow path in the first mode. 108, 110, 124, 126, 148, 152, 164, 188, 190),
Refrigeration system (60, 80, 100, 120, 140, 160, 180).   The refrigeration system of claim 1, wherein the pressure regulator comprises a fixed orifice expansion device (68, 72, 88, 92, 108, 126, 148, 152) without a valve.   The pressure regulator comprises a valveless fixed orifice expansion device (126, 148) in series with a solenoid valve (124, 150) with a valve element having an orifice. The refrigeration system described.   The pressure regulating device comprises a fixed orifice expansion device (88, 148) without a valve, which exists in series with a combination of a solenoid valve (90, 150) and a bypass conduit (86, 146) in parallel. The refrigeration system according to claim 1.   The refrigeration system according to claim 1, further comprising first and second pressure regulators connected in parallel. The refrigerant is largely composed of CO _2,
The refrigeration system according to claim 1, wherein the first and second heat exchangers are refrigerant-air heat exchangers.   The refrigeration according to claim 1, wherein the first and second heat exchangers and compressors are removable as a unit from the system housing without the need to empty the contents of the system in advance. system. The refrigerant consists essentially of CO _2,
The first and second heat exchangers are refrigerant-air heat exchangers, each having an associated fan, and the first mode air flow across the first heat exchanger is externally applied. The refrigeration system of claim 1, wherein the first mode air flow that flows outward and traverses the second heat exchanger is a recirculating internal air flow.   The refrigeration system according to claim 1, wherein the refrigeration system is a cooler that houses a plurality of beverage containers having a capacity in a range of 0.3 to 4.0 liters. The cooler is
A vending machine that operates with cash,
A display case with a transparent door at the front and a closed rear,
A cooler box to take in and out from the top,
The refrigeration system according to claim 9, wherein the refrigeration system is selected from the group consisting of: A compressor for feeding the CO ₂ based coolant along the flow path at least a first mode of the system operation,
A first heat exchanger along the flow path downstream of the compressor;
A second heat exchanger along the flow path upstream of the compressor;
Means for expanding the refrigerant when there is no electronic expansion device downstream of the first heat exchanger and upstream of the second heat exchanger in the flow path;
Refrigerated system with

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