HK1118599B - Transcritical carbon dioxide cooler system - Google Patents

Description

Transcritical carbon dioxide cooler system

Cross Reference to Related Applications

The present invention claims the benefit of U.S. patent application No. 60/663,912 entitled "condensate heat transfer for transcritical carbon dioxide refrigeration system" and filed on 3/18/2005. Co-pending application serial No. 05-258 entitled "high side pressure regulation for transcritical vapor compression systems," filed on even date herewith, discloses a prior art and inventive chiller system. The present application discloses possible variations of such a system. The disclosure of this application, which is described in detail, is incorporated herein by reference.

Technical Field

The present invention relates to refrigeration, and more particularly, to a transcritical carbon dioxide chiller system.

Background

CO as a natural and environmentally benign refrigerant₂(R-744) is drawing significant attention. In most air conditioning operating ranges, CO₂The system operates in a transcritical mode. By using CO₂Examples of transcritical vapor compression systems as the working fluid include compressors, gas coolers, expansion devices, evaporators and the like (see fig. 1). Because of CO₂Is 87.8F, the main difference between transcritical operation and conventional operation is that the heat rejection in the gas cooler is in the supercritical region. Thus, the pressure is not only dependent on temperature, but it presents additional control and optimization issues for system operation.

FIG. 1 schematically illustrates a transcritical vapor compression system 20 utilizing CO₂As the working fluid. The system includes a compressor 22, a gas cooler 24, an expansion device 26, and an evaporator 28. The exemplary gas cooler and evaporator may each take the form of a refrigerant-to-air heat exchanger. The air flow through one or both of these heat exchangers may be forced. For example, one or more fans 30 and 32 may drive respective air streams 34 and 36 through the two heat exchangers. Refrigerant flow path40 include extraction ducts that extend from the outlet of the evaporator 28 to an inlet 42 of the compressor 22. A discharge conduit extends from the outlet 44 of the compressor to the inlet of the gas cooler. Additional piping connects the gas cooler outlet to the expansion device inlet and connects the expansion device outlet to the evaporator inlet.

An electronic expansion valve is typically used as the device 26 to control the high side pressure to optimize the CO₂COP of the vapor compression system. Electronic expansion valves typically include a stepper motor attached to a needle valve to change the effective valve opening or change the flow to a large number of possible positions (over 100 passes). Which provides good control of the high side pressure over a wide range of operating conditions. The opening of the valve is electronically controlled by the controller 50 to match the actual high side pressure to the desired set point. The controller 50 is coupled to a sensor 52 to measure the high side pressure.

As the air stream 36 passes over the heat exchanger 28, the cooling of the air stream 36 causes condensation of the water exiting the air stream. The water treatment needs to be performed at the site. One method includes heating water to direct its evaporation using a heat rejection heat exchanger. An example of such a system 60 is shown in fig. 2.

In the illustrated system 60, components similar to those of the system 20 are indicated by similar reference numerals. The controller and sensor components are hidden for illustration. The gas cooler 62 is divided into a first part 64 and a second part 66. Along the refrigerant flow path 66, the first component 64 is upstream of the second component 66. The components 64 and 66 may receive a common air flow 68 along a common air flow path (e.g., driven by a fan 70) or may be on separate air flow paths (e.g., driven by separate fans). The first component may be upstream/downstream of the second component if on a common air flow path.

Water condensed from the air stream 36 is collected by a collection system 80. The exemplary system 80 includes a tray 80, and water is delivered to the tray 80. A portion of the first member 64 is positioned so as to be immersed in the water in the tray. The heating of the water by the first section 64 promotes evaporation of the water.

Disclosure of Invention

However, for beneficial performance, it may be preferable to expose the condensate to further downstream components of the heat rejecting heat exchanger. Bottle cooler (bottle cooler) systems include devices that use atmospheric water condensed from an evaporator to extract the heat from the condenser.

The present invention provides a chiller system comprising: a compressor for driving refrigerant along a 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 for use as a condenser; a second heat exchanger along the flow path upstream of the compressor in the first mode for use as an evaporator to cool items in the system interior volume; and means for extracting heat from a downstream portion within the first heat exchanger using atmospheric water condensed from the second heat exchanger.

The downstream portion of the first heat exchanger may be immersed in the drain pan of the second heat exchanger.

The apparatus may comprise at least one of: a wick that transports condensed water to the downstream portion; a wick that delivers condensed water to the air stream flowing over the downstream portion; at least a first subportion of the downstream portion of the first heat exchanger extending upwardly to receive the flow of condensed water and direct the flow of condensed water to a drain pan; and at least a first subsection of a downstream portion of the first heat exchanger and a second subsection in the drain pan, the first subsection extending upwardly to receive the flow of condensed water and direct the flow of condensed water to the drain pan.

The apparatus may include: a sprayer for spraying the condensed water on the first heat exchanger.

The apparatus may further comprise: a counter-flow heat exchanger between the refrigerant and the condensate water stream.

The system may be a self-contained, externally powered beverage cooler located outdoors.

The refrigerant may include CO 2; and the first heat exchanger and the second heat exchanger may be refrigerant-to-air heat exchangers.

Optionally, the refrigerant may include CO 2; and the first and second heat exchangers are refrigerant-to-air heat exchangers, each having an associated fan, the air flow through the first heat exchanger being an external to external flow and the air flow through the second heat exchanger being a recirculated internal flow.

The system is associated with the article, the article comprising: a plurality of beverage containers in the size range of 0.3-4.0 liters.

The system may be selected from the following group: cash operated vending machines; a showcase having a transparent front door and a closed rear portion; and a top entry cooler bin.

The system is preferably a transcritical system.

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.

Drawings

FIG. 1 is a schematic diagram of a prior art refrigeration system.

Fig. 2 is a schematic diagram of another prior art refrigeration system.

Fig. 3 is a schematic diagram of a refrigeration system of the present invention.

Fig. 4 is a side view of a display case bottle cooler including a refrigerator and air management module.

FIG. 5 is a schematic representation of a chiller and air management module.

Fig. 6 is a partial side schematic view of an alternative module.

Fig. 7 is a partial side schematic view of an alternative module.

Fig. 8 is a partial side schematic view of an alternative module.

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

Detailed Description

Fig. 3 shows a system 100, the system 100 having a compressor 22, an expansion device 26, and a heat absorbing heat exchanger (evaporator) 28. These may be similar to the corresponding components of the systems of fig. 1 and 2. The controller and sensor components are hidden for illustration. The gas cooler 102 is separated into a first part 104 and a second part 106. Along the refrigerant flow path, the first component 104 is upstream of the second component 106. The components 104 and 106 may be along a common air flow path to receive a common air flow 108 (e.g., driven by a fan 110) or may be on separate air flow paths (e.g., driven by separate fans). In the illustrated system, the first component 104 is upstream of the second component 106 and a fan 110 is interposed.

Water condensed from the air stream 36 is collected by a collection system 112. The exemplary system 112 includes a tray 122, and water is delivered to the tray 122. A portion of the second member 106 is positioned to be immersed in the water in the tray 122. The heating of the water by the second member 106 may facilitate the evaporation of the water. In contrast to the system of fig. 2, the components of the gas cooler that distribute heat to the condensate are relatively downstream in the refrigerant flow path (e.g., the temperature in the cooler is reduced by one-half or one-quarter before the expansion device). This will reduce the refrigerant temperature as much as possible by exposing the coldest refrigerant to the condensate. For transcritical CO₂In refrigeration systems, it is critical to minimize the temperature at the outlet of the high side (gas cooler) heat exchanger to maintain maximum efficiency.

This for the reaction of CO₂It is more critical that the outlet temperature of the bottle cooler refrigeration system be minimized. Manufacturing costs are of particular concern. Low cost/relatively low power heat exchangers (including but not limited to wire-tube heat exchangers, coil heat exchangers, finless heat exchangers, etc.) are particularly useful for controlling the manufacturing costs of bottle coolers.

Thus, a particular area of implementation of condensate heat exchange is within bottle coolers, including those that may be placed outdoors or must have outdoor withstand forces (exhibiting large changes in ambient environment). Fig. 4 shows an exemplary cooler 200, the cooler 200 having a movable module 202 that houses a condensate and air handling system. The exemplary module 202 fits within a compartment of a base 204 of the housing. The housing has an interior volume 206 between the left and right side walls, the rear side wall/duct 216, the top wall/duct 218, the front door 220, and the base compartment. A vertically aligned shelf 222 is received to support a beverage container 224.

The exemplary module 202 draws the airflow 108 through a front grille in the base 224 and exhausts the airflow 108 from behind the base. The module can be led out through the front of the base by moving or opening the grid. The exemplary module drives the air flow 36 through the interior 206 and through the rear duct 210 and the top duct 218 on a recirculation flow path.

Fig. 5 shows more details of an exemplary module 202. The heat exchanger 28 is disposed within a chamber 240 defined by an insulated wall 242. The illustrated heat exchanger 28 is disposed mostly in the top rear quarter of the module and directs the air flow 36 generally rearwardly therethrough, turning upwardly after exiting the heat exchanger to exit from the rear portion of the upper end of the module. A drain passage 250 may extend through the bottom of the wall 242 to pass water condensed from the air stream 36 to the drain pan 122. A water accumulation 254 is shown in the tray 122. The disc 122 passes through the air flow 108 downstream of the first part 104 of the heat exchanger along an air duct 256. The second heat exchanger component 106 is positioned to be at least partially immersed in the accumulated water 254. The exposure of the accumulation 254 to the immersed second section 106 and to the heated air in the air flow 108 may promote evaporation.

In the example, the second section 106 extends in a coil, the second section being divided into a first portion generally above the standing water and in the air flow 108 and a second portion generally submerged. The refrigerant flow path may generally pass downstream along the air flow 108, through the first portion, and then into the second portion before reaching the expansion device.

The arrangement of fig. 5 corresponds to a basic redesign of a baseline (baseline) module having a heat rejecting heat exchanger located at the first component 104 and not at the second component. It also conforms to the redesign of the separation system with the hotter components in a later position. However, the illustrated configuration is disadvantageous in that the cooler component is downstream of the hotter component along the air flow path. Thus, it may be desirable to reverse the air flow so that it becomes rear to front. A portion of this rear-to-front airflow may be directed over the cooler door window to avoid fogging of the window.

Alternative implementations may preclude physical separation of the first component 104. One example may be to have only one heat rejecting heat exchanger unit, as represented by the second component 106 in fig. 5. The immersed portion of that exchanger unit can serve as the second section 106, while the exposed portion can serve as the first section 104 (see fig. 6 below). Another simple variation may include positioning the heat exchanger so that water dripping from the drain channel flows over a leading portion of the heat exchanger (i.e., at the upstream end of the warm air stream).

Various implementations may further maximize heat transfer by counter-current exchange of condensed water and refrigerant. This counter flow may be a characteristic method of heat exchange between the condensate and the refrigerant, or may compensate for pan immersion or another mechanism. Fig. 6 shows such a system, wherein the drain 250 has an outlet 260. The length 262 of the refrigerant conduit extends up to the outlet. Length 262 is positioned to direct/wick water droplets from outlet 260 down length 262 to the drain pan. As the refrigerant flows upward through length 324, the refrigerant and water are in counter-current heat exchange. A more upstream (along the refrigerant flow path) length 264 (or portion of the heat rejection heat exchanger) may be immersed in the water 254 in the pan. Still further upstream portion 270 may be in the air stream.

In another example of a complementary situation, a relatively small downstream component of the gas cooler may run through the drain pan 122 or in the drain pan 122. The smaller and more downstream sections can rise into the evaporator drain channels in counter-flow heat exchange (both along their length and/or only two-step counter-flow combining sections in the tray). In the example of fig. 7, the drain 250 is replaced by another convoluted drain 300. The drain 300 has an upwardly directed U-section 302, the section 302 defining a water trap that receives a water plug 304. The drain 300 and the water plug 304 may prevent air leakage between the hot and cold air streams and may be used alone instead of the simple drain 250. The slug is continuously replenished by the flow of condensate into the drain 300 and the condensate is continuously drained down toward the pan 122. A portion 306 of the refrigerant conduit extends from the remainder of the second member 106 and through the drain channel 300. An expansion device (not shown) may be disposed between the downstream end of conduit portion 306 and evaporator 28. Thus, the refrigerant flowing through the pipe portion 306 is in counter-flow heat exchange with the condensate flowing through the drain 300. Although a through drain 300 is shown, the pipe portion 306 may enter the drain outlet 308 and/or exit the drain inlet 310 and more closely follow the path of the drain.

Fig. 8 shows an alternative drain 320 having an outlet 322. The length 324 of the refrigerant tube extends up to the outlet. The length 324 is positioned to direct/wick water droplets from the outlet 322 down the length 324 to the drain pan. As the refrigerant flows upward through length 324, the refrigerant and water are in counter-current heat exchange. The more upstream portion of the heat rejection heat exchanger (along the refrigerant flow path) may be immersed in the water of the pan.

In another implementation, the condensate may be delivered to the air stream (e.g., 108) just prior to its passage over the last portion of the heat rejection heat exchanger (i.e., the gas cooler may be a condenser if conditions are appropriate) to enhance heat transfer and thereby reduce refrigerant temperature. This may be particularly effective in dry climates where evaporative cooling of the air stream is particularly relevant.

The transport of the condensate with air can be carried out in several ways. A wick (wick) may be positioned along the air stream upstream of the heat exchanger relative to the components. A spray device may be similarly positioned to direct the spray of condensate to the air stream. Such sprays may also or alternatively directly contact the associated heat exchanger portion to be cooled by evaporative or conventional cooling methods. Similarly, the wick may contact a heat exchanger to transport water and provide conventional and/or evaporative cooling methods.

Thus, it can be appreciated that for transcritical bottle cooler applications, water that is condensing on the evaporator surface is useful for refrigerant cooling to maintain efficacy. This approach provides, among other things, additional efficiencies, reduced cost, and fouling prevention for heat exchangers such as wire-tube, coil, fin-less heat exchangers, and the like. Which may be comparable in performance to the high efficiency conventional fin-less heat exchangers being used in bottle cooler applications. Protective coatings typically present on low cost heat exchangers (wire-tube, coil, etc.) may provide effective resistance to corrosion from the condensate to which the heat exchanger is exposed.

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 implementing remanufacturing of known systems or reengineering of an existing system configuration, details of the existing configuration may influence details of the implementation. An exemplary baseline system may be a transcritical CO₂The system may alternatively have other operational domains and/or other refrigerants. Accordingly, other embodiments are within the scope of the following claims.

Claims (11)

1. A chiller system comprising:

a compressor (22) for driving refrigerant along a flow path in at least a first mode of system operation;

a first heat exchanger (102) along the flowpath downstream of the compressor in the first mode for use as a condenser;

a second heat exchanger (28) along the flow path upstream of the compressor in the first mode for use as an evaporator to cool items in the system interior volume; and

means for extracting heat from a downstream portion within the first heat exchanger using atmospheric water condensed from the second heat exchanger.

2. The system of claim 1,

the downstream portion (106) of the first heat exchanger (102) is immersed in a drain pan (122) of the second heat exchanger (28).

3. The system of claim 1, wherein the device comprises at least one of:

a wick that transports condensed water to the downstream portion;

a wick that delivers condensed water to an air stream flowing over the downstream portion;

at least a first subsection of a downstream portion of the first heat exchanger extending upwardly to receive a flow of condensed water and direct the flow of condensed water to a drain pan; and

at least a first subportion of the downstream portion of the first heat exchanger and a second subportion in the drain pan, the first subportion extending upwardly to receive the flow of condensed water and direct the flow of condensed water to the drain pan.

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

a sprayer for spraying the condensed water on the first heat exchanger.

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

a counter-flow heat exchanger between the refrigerant and the condensate water stream.

6. The system of claim 1, wherein the system is a self-contained, externally powered beverage chiller disposed outdoors.

7. The system of claim 1,

the refrigerant comprises CO 2; and is

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

8. The system of claim 1, wherein the refrigerant comprises CO 2; and is

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

9. The system of claim 1, in combination with the article, the article comprising: a plurality of beverage containers in the size range of 0.3-4.0 liters.

10. The system of claim 9, wherein the system is selected from the group consisting of:

cash operated vending machines;

a showcase having a transparent front door and a closed rear portion; and

a top entry cooler box.

11. The system of claim 1, wherein the system is a transcritical system.