HK1118600B - A transcritical refrigeration system - Google Patents

Description

Transcritical refrigeration system

Cross Reference to Related Applications

This application claims the benefit of U.S. patent application serial No. 60/663,960, filed on 2005, 3/18, entitled high side pressure regulation for transcritical vapor compression systems, the disclosure of which is incorporated by reference as if set forth in detail herein.

Background

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

CO as a natural and environmentally friendly refrigerant₂(R-744) is drawing attention to significance. In most air conditioner operating ranges, CO₂(carbon dioxide) is operated in a transcritical mode. FIG. 1 schematically shows the utilization of CO₂As a working fluid, a transcritical vapor compression system 20. The system includes a compressor 22, a gas cooler 24, an expansion device 26, and an evaporator 28. Exemplary gas coolers may each take the form of a refrigerant-to-air heat exchanger. An air flow may be forced through one or both of these heat exchangers. For example, one or more fans 30 and 32 may each drive an airflow 34 and 36 through both heat exchangers. The refrigerant flow path 40 includes a suction line extending from an outlet of the evaporator 28 to an inlet 42 of the compressor 22. A discharge line extends from the outlet 44 of the compressor to the inlet of the gas cooler. Additional lines connect the outlet of the gas cooler to the inlet of the expansion device and the outlet of the expansion device to the inlet of the evaporator.

Because of CO₂Is 87.8 ° f, the main difference between transcritical and conventional operation is that the heat consumption in the gas cooler is in the supercritical region. Thus, the pressure is not solely dependent on temperature, and this also presents additional control and optimization issues for system operation.

For a given gas cooler discharge temperature, as the high side pressure increases, the outlet enthalpy of the refrigerant decreases, resulting in a higher differential enthalpy through the gas cooler. The capacity of the gas cooler is a function of the difference in the mass flow rate of the refrigerant and the enthalpy across the gas cooler. For a beverage cooler, the evaporator may be essentially at the internal temperature of the cooler. Regardless of the external conditions, it is particularly desirable to maintain this temperature within a narrow range. For example, it may be desirable to maintain the internal temperature very close to 37F. This temperature essentially determines the steady state compressor suction pressure.

For a determined compressor suction pressure, as the high 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 rate through the system decreases. The balance of these two neutralization effects typically increases within the gas cooler volume as the high side pressure increases. However, above a certain pressure, the amount of volume increase becomes very small. Because the expansion device is typically isenthalpic, as the high side pressure increases, the evaporator volume also increases significantly.

The energy efficiency, coefficient of performance (COP), of a vapor compression system is typically expressed as the ratio of system capacity to consumed energy. Since an increase in pressure clearly results in both higher capacity and higher energy consumption, the balance between the two will dominate the overall COP. Thus, there is typically an optimum pressure that produces the highest possible performance.

An electronic expansion valve is typically used as the means 26 to control the high side pressure to CO₂The COP of the vapour compression system is optimised. Electronic expansion valves typically include a stepper motor attached to a needle valve in order to change the opening or flow of the active valve to a number of possible positions (significantly over 100). This provides effective control of the high side pressure over a wide range of operating conditions. The valve opening is electronically controlled by the controller 50 to match the actual high side pressure to the desired set point. This pressure control scheme includes a relatively costly valve, a complex controller 50, and a sensor 52 for sensing the high side pressure. This apparatus feeds CO₂Vapor compression systems add considerable expense to the CO₂Vapor compression systems are less attractive than HFC systems.

The use of a fixed expansion device in a transcritical vapor compression system is possible, but this approach has limitations that may result in loss of performance or functionality. During steady state operation, a fixed expansion device (e.g., a fixed orifice or capillary tube) may work well to regulate the system high side pressure to a near optimum pressure. During pull-down, when the system is put into operation and the evaporating temperature and pressure may be very high, the flow rate through the fixed speed and discharge compressor may become considerably high. This high flow rate may cause the high side pressure to exceed safety limits.

Summary of The Invention

A transcritical refrigeration system comprising: a compressor for driving refrigerant along the flow path in at least a first mode of system operation; a first heat exchanger along the flow path downstream of the compressor in the first mode; a second heat exchanger along the flow path upstream of the compressor in the first mode; and a pressure regulator in the flow passage downstream of the first heat exchanger and upstream of the second heat exchanger in the first mode for regulating pressure at the first heat exchanger in the first mode, the pressure regulator comprising a fixed orifice device. The first and second heat exchangers and the compressor are removable as a unit from the housing of the system without the need to previously empty the contents of the system.

A transcritical refrigeration system comprising: a compressor driven along the flow path to contain a carbon dioxide-containing refrigerant in at least a first mode of 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; and means in the flow path downstream of the first heat exchanger and upstream of the second heat exchanger for expanding the refrigerant in the absence of an electronic expansion device while regulating the pressure on the high pressure side. The mechanism includes a solenoid valve.

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.

Brief Description of Drawings

Fig. 1 is a schematic diagram of a prior art vapor compression system.

FIG. 2 is a first inventive CO₂Schematic of a vapor compression system.

FIG. 3 is a second inventive CO₂Schematic of a vapor compression system.

FIG. 4 is a third inventive CO₂Schematic of a vapor compression system.

FIG. 5 is a fourth inventive CO₂Schematic of a vapor compression system.

FIG. 6 is a fifth inventive CO₂Schematic of a vapor compression system.

FIG. 7 is a sixth inventive CO₂Schematic of a vapor compression system.

FIG. 8 is a seventh inventive CO₂Schematic of a vapor compression system.

Fig. 9 is a side view of a display case including a refrigeration and air management module.

Fig. 10 is a view of a refrigeration and air management module.

Like reference numbers and designations in the various drawings indicate like elements.

Detailed Description

The invention relates to a method for CO₂Vapor compressionThe high side pressure of the system is optimized. For heating, ventilation, air conditioning and refrigeration (HVAC) without a wide operating range&R) product, the optimal high side pressure for all operating conditions does not change much. Therefore, a fixed expansion device (e.g., orifice or capillary tube) can be used to adjust the high side pressure to that for CO₂A preset constant value for all steady state operating conditions of the vapor compression system. This preset value should be determined so that the CO is₂Vapor compression systems can achieve the best overall coefficient of performance (COP) for the entire operating range. Significant CO reduction using a fixed expansion device₂Cost of pressure control components in a vapor compression system.

For the pulldown condition (pulldown condition), the compressor flow rate will be significantly higher than during steady state conditions. The high side pressure can be optimized so that the CO₂The pulldown cooling capacity of the vapor compression system can be increased, however, the flow through the pressure regulator does not exceed the flow of the compressor (so that the system pressure becomes excessive). This optimal high side pressure for increasing capacity is typically higher than the optimal high side pressure for increasing the overall coefficient of performance. However, because the compressor flow rate is higher at the bottom brace than at steady state conditions, the expansion device may be configured to have a greater airflow capacity during the bottom brace. A simple multi-position expansion device may also provide this function. There are a number of ways in which two or more position pressure control systems can be achieved through the use of solenoid valves.

The following example reflects an improvement of the basic system of fig. 1. Therefore, the compressor 22, the gas cooler 24 and the evaporator 28 are denoted by the same reference numerals. These components may also be the same as those in the baseline system, or may be further modified in any rebuild or remanufactured situation. In fig. 2, a system 60 is shown in which a refrigerant flow path 62 is divided into two parallel branches/sections 64 and 66 between the outlet of the gas cooler 24 and the inlet of the evaporator 28. The first branch 64 has a first fixed expansion device 68. The second branch comprises, in series, a solenoid valve 70 and a second fixed expansion device 72. Although the solenoid valve 70 is shown in a position upstream of the second fixed expansion device 72, this sequence may be varied. The exemplary solenoid valve 70 has two settings/conditions, one of which is a fully closed condition in which there is no flow through the second branch 66. The second setting/condition is a fully open condition, allowing flow through the second branch 66 with a minimal pressure loss through the solenoid valve 70.

During steady state operating conditions, the solenoid valve 70 is fully closed when the compressor flow rate is relatively low. During the pull-down condition, the compressor flow rate is relatively high. During pull down, to avoid over-pressurization, the solenoid valve 70 is opened, allowing gas flow through the second fixed expansion device 72. While continuing to provide good system performance, the combination of expansion devices 68 and 72 regulates the high side pressure to avoid over pressurization.

In operation, a pull-down condition may be detected by means of one or more temperature sensors 75 and pressure sensors coupled to a controller 76, the controller 76 being coupled to control the solenoid valve 70. The controller 76 may also be coupled to the compressor and/or fan, respectively, to control their respective operations. For simplicity of illustration, although sensors and controllers may be present, they are not illustrated in the following examples.

Figure 3 illustrates a system 80 in which a refrigerant flow channel 82 has two parallel sections/branches 84 and 86 upstream of a first fixed expansion device 88. The first branch 84 includes a solenoid valve 90. The second branch 86 includes a second fixed expansion device 92. During steady state operating conditions, the solenoid valve is in a closed state to prevent flow through the first branch 84. The second branch 86 acts as a bypass with a restricted flow through a second fixed expansion device 92 before subsequently flowing through the first expansion device 88. During pull-down of the bar, the solenoid valve 90 is open, allowing the necessary unrestricted flow along the first branch 84. A small additional flow may flow through the second branch 86 and the combined flow then flows through the first expansion device 88. In an alternative embodiment, the first expansion device may also be upstream of the bypass rather than downstream. The control methods and components (not shown) of this system, as well as those discussed below, may also be similar to those in system 60.

Fig. 4 illustrates another system 100 in which the flow path has a first segment/leg 104 and a second segment/leg 106 between the gas cooler and the evaporator. A fixed expansion device 108 is located in the first branch 104. A solenoid valve 110 is located in the second branch 106. The solenoid valve 110 combines the features of a solenoid valve and a fixed expansion device. Specifically, the open condition can be relatively restricted as compared with the open condition of the solenoid valve 90. Therefore, the pull-down pressure drop across the solenoid valve is very important and the combination of the solenoid valve 110 and the fixed expansion device controls the high side pressure of the system to a preset constant optimum. For steady state operation, the solenoid valve 110 is fully closed and all flow passes through the expansion device 108.

Fig. 5 illustrates a bypass-less system 120 in which a solenoid valve 124 and a fixed expansion device 126 are positioned in series along a flow path 122. The solenoid valve 124 combines the features of a solenoid valve and a fixed expansion device that is different from the valve 110 of fig. 4. Specifically, the valve element (e.g., solenoid piston) of the solenoid valve 124 may have an orifice such that its closed condition is only a partially closed condition. However, an open condition is a substantially fully open condition with a low pressure drop. Thus, during steady state operating conditions, the solenoid valve 124 is in a closed condition passing relatively little flow and creating a substantial pressure drop (alone and in combination with the expansion device 126). In steady state conditions, the solenoid valve is open, allowing the flow rate to be controlled substantially solely by the expansion device 126. The order of the series may be changed as in other systems.

Fig. 6 illustrates a system 140 that combines features of systems 80 and 100. Specifically, upstream of the first fixed expansion device 148, the flow path 142 has two parallel segments/branches 144 and 146. The first branch 144 includes a solenoid valve 150. The second branch 146 includes a fixed expansion device 152. Similar to the solenoid valve 124, the exemplary solenoid valve 150 may have a closed condition that is only partially closed. During a pull down condition, solenoid valve 150 is open. During steady state conditions, there is relatively little flow along each branch. During a pull-down condition, a substantial amount of flow may flow through the first leg 144, with the remainder flowing through the second leg 146.

FIG. 7 illustrates another system 160 in which a flow passage 162 includes a solenoid valve 164 that combines solenoid valve and orifice functions. Specifically, the components of the solenoid valve 164 include apertures such that the closed condition is only partially closed. During steady state conditions, the solenoid valve 164 is in its closed condition with a relatively small amount of flow through the orifice. During a pull down condition, the valve is open so that a large amount of flow passes through.

Fig. 8 illustrates a system 180 in which a flow channel 182 is included between the gas cooler and the evaporator sections/branches 184 and 186. Solenoid valves 188 and 190 are located on each of the branches. The elements of the solenoid valves may include orifices. Independent control over the valves may provide more than two alternately effective flow restrictions. For example, with different sized orifices, two valves provide four or more different effective restrictions. The smallest restriction may exist when both valves are open. A pair of intermediate stage restrictions can be accomplished with one valve closed and the other open. To provide more subtle differences in the three least restrictive conditions, the bypass conduit or solenoid valve may be sized or may have additional restrictions so that there is substantially no free flow when only one valve is open. Alternative embodiments can exhibit solenoid valves in series as such, rather than in parallel.

Various sensors and/or user inputs may be used to control the solenoid valve. A direct measurement of the high side pressure can be obtained by the sensor 74. When this pressure exceeds one or more associated thresholds, the controller 76 may cause the solenoid valve to assume an auxiliary, relatively free-flow condition. Alternatively or in addition to the high side pressure measurement being sensor 74, an input may also be received from an air temperature sensor. An exemplary sensor 75 may be positioned to be exposed to air at or from the cooler interior (e.g., to the airflow 36 upstream of the evaporator 28). The sensor 75 may form part of a thermostatic control. Thus, by eliminating pressure sensors 52 or 74, the use of such a single sensor alone may enable cost savings.

For compressors with a determined speed and discharge, the flow through the system is a direct function of the pressure ratio of the refrigerant entering the compressor and to a lesser extent the compressor. The inlet density is a direct function of the saturation temperature and the superheat of the refrigerant. These are again direct functions of air temperature, system size and load. For simple systems, these parameters can be determined at the design stage as a function of the temperature of the air flowing through the evaporator. A correlation may be generated that matches the evaporator air temperature to the refrigerant charge density. In operation, the solenoid valve will remain in an open state until the evaporator outlet temperature sensor 75 drops below a predetermined value. When this occurs, the solenoid valve or one of the solenoid valves is closed. For systems with multiple solenoid valves, this step may be repeated to further reduce the effective expansion orifice area as the temperature is pulled down so that at least the optimum pressure is maintained in the high pressure portion of the system.

If the high side pressure is sensed directly (e.g., via sensor 74), a different correlation may be utilized. The optimal high side pressure may be referred to as a function of the evaporator temperature and optionally the ambient temperature. A single solenoid valve or multiple solenoid valves may be operated to maintain the pressure within certain limits.

Fig. 9 illustrates an exemplary chiller 200 having a removable module 202, the removable module 202 containing a refrigerant and an air handling system. The exemplary module 202 is mounted within a compartment of a base 204 of the housing. The housing has an interior cavity 206 between the left and right walls, a rear wall/channel 210, a top wall/channel 218, a front door 220, and a compartment of the base. The interior contains a vertically aligned rack 222 that supports beverage containers 224.

The exemplary module 202 draws in the air stream 34 from a grill in front of the base 204 and discharges the air stream 34 from the rear of the base. The module can be withdrawn from the front of the base by removing or opening the barrier. The exemplary module drives the airflow 36 on the circulating flow path through the interior 206 via the rear channel 210 and the top channel 218.

Fig. 10 illustrates further details of an exemplary module 202. The heat exchanger 28 is located within a recess 240 defined by an insulating wall 242. The heat exchanger 28 is shown primarily in the quadrant of the upper rear of the module and is adapted to deliver the airflow 36 generally rearwardly with an upward turn after exiting the heat exchanger for discharge from the rear portion to the upper end of the module. A drain 250 may extend through the bottom of the wall 242 to transfer water condensed from the airflow 36 to a drain pan 252. The tray 252 is shown with accumulated water 254. The disk 252 follows an air channel 256, the air channel 256 conveying the airflow 34 downstream of the heat exchanger 24. The exposure of the accumulated water 254 to the heated air within the airflow 34 may facilitate evaporation.

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

Claims (14)

1. A transcritical refrigeration system (60; 80; 100; 120; 140; 160; 180) comprising:

a compressor (22) for driving refrigerant along the 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; and

a pressure regulator (68; 72; 88; 92; 108, 110; 124, 126; 148, 152; 164; 188; 190) in the flow passage downstream of the first heat exchanger (24) and upstream of the second heat exchanger (28) in the first mode for regulating pressure at the first heat exchanger in the first mode, the pressure regulator comprising a fixed orifice device,

the first and second heat exchangers and the compressor are removable as a unit from the housing of the system without the need to previously empty the contents of the system.

2. The system of claim 1, wherein the pressure regulator comprises a non-valved fixed orifice expansion device (68; 72; 88; 92; 108; 126; 148; 152).

3. The system of claim 1, wherein the pressure regulator comprises:

a solenoid valve (124; 150) having a first said fixed orifice means within the valve element; and

a second said fixed orifice means being a non-valved fixed orifice expansion means (126; 148) in series with said solenoid valve (124; 150).

4. The system of claim 1, wherein the pressure regulator comprises:

said fixed orifice means being a non-valved fixed orifice expansion means (88; 148);

a parallel combination of a solenoid valve (90; 150) and a bypass conduit (86; 146), the parallel combination being in series with the fixed orifice expansion device.

5. The system of claim 1, wherein the pressure regulator comprises:

a solenoid valve (124; 150) having the fixed orifice arrangement within a valve element of the solenoid valve.

6. The system of claim 1, wherein there is a first said pressure regulator and a second said pressure regulator in parallel.

7. The system of claim 1, wherein:

the refrigerant comprises carbon dioxide; and is

The first heat exchanger and the second heat exchanger are refrigerant-to-air heat exchangers.

8. The system of claim 1, wherein:

the refrigerant consists essentially of carbon dioxide; and is

The first heat exchanger and the second heat exchanger are refrigerant-to-air heat exchangers each having an associated fan, the air flow through the first heat exchanger in the first mode being an outside-to-outside flow, and the air flow through the second heat exchanger in the first mode being a recirculated internal air flow.

9. The system of claim 1, wherein the system further comprises:

a controller coupled to the pressure regulator to operate the pressure regulator with exactly two alternating different effective limits.

10. The system of claim 1, wherein the system further comprises:

a controller coupled to the pressure regulator to operate the pressure regulator with exactly four alternating different effective limits.

11. A transcritical refrigeration system comprising:

driving a compressor of a carbon dioxide containing refrigerant along the flow path in at least a first mode of 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; and

means in the flow path downstream of the first heat exchanger and upstream of the second heat exchanger for expanding the refrigerant in the absence of an electronic expansion device while regulating pressure on the high pressure side, the means comprising a solenoid valve.

12. The system of claim 11, wherein:

the mechanism provides no more than four different effective limits of alternation.

13. The system of claim 11, wherein:

the mechanism provides for different effective limits of alternation of exactly four.

14. The system of claim 11, wherein:

the mechanism is configured to regulate the pressure on the high pressure side by opening the effective limit in response to the measured high pressure side pressure exceeding the target value.