Information
-
Patent Grant
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6820434
-
Patent Number
6,820,434
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Date Filed
Monday, July 14, 200320 years ago
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Date Issued
Tuesday, November 23, 200419 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
- Wall Marjama & Bilinski LLP
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CPC
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US Classifications
Field of Search
US
- 062 513
- 062 113
- 062 510
- 062 117
- 062 200
- 062 175
- 062 199
- 062 204
- 062 224
-
International Classifications
-
Abstract
The compressor of a transport refrigeration system is divided into two sections, with each section having a suction inlet. The refrigerant vapor from the evaporator is passed to one of the suction inlets, whereas the refrigerant vapor from a subcooler circuit is passed to the other suction inlet. A valve is operated to selectively insert or remove the subcooler as capacity requirements vary. In one embodiment, a six cylinder reciprocating compressor is used with five cylinders compressing within a first section, and a single cylinder compressing in the other section containing the subcooler circuit.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to vapor compression refrigeration systems and, more particularly, to a method and apparatus for subcooling refrigerant in a transport refrigeration system.
In many refrigeration systems, such as those for preserving food in supermarkets, refrigerators and the like, the load is substantially fixed and the demands of the system are substantially constant throughout the life of the system.
Transport refrigeration systems are different. As the types of food products that are being transported in refrigerated trucks, trailers and containers are always changing, the temperatures at which these products are desirably maintained also change. For example, one day the cargo of a truck may be bananas, with the desired temperature to be maintained at 57° degrees. On the next day, the same trailer may be hauling frozen goods, and the desired temperature to be maintained in the trailer would be 0° F. or below. They also must be able to operate in all ambient conditions as they are portable and need to be able to operate all over the world. Because of this wide range of demands, the design of a refrigeration system for a transport truck/trailer must therefore be very flexible. Thus, they must be designed to meet the maximum capacity requirements, but they are preferably designed to operate efficiently and precisely at much lower capacity requirements during most of their operating life.
Various marketing conditions have tended to exacerbate the problems of meeting the capacity requirements of transport refrigeration systems as discussed hereinabove. For example, because of environmental concerns, it has become necessary to abandon the use of more efficient, but environmentally undesirable, refrigerants, and to replace them with refrigerants that are less efficient. Another development that has occurred because of the need for greater cargo capacity and overall efficiencies, is a tendency to lengthen the refrigerated trailers, and also construct them with thinner side walls.
Current single stage compression systems have limited capacity and cannot meet the market needs as discussed hereinabove. The use of subcooling and refrigeration systems has long been used but the systems have generally been relatively complex, expensive, and difficult to maintain. Examples of such systems include those with suction liquid heat exchangers, subcoolers in condenser coils, and mechanical subcoolers using separate compressors or economizer subcoolers in multi-compressor staged systems.
It is therefore an object of the present invention to provide an improved transport refrigeration system.
Another object of the present invention is the provision in a transport refrigeration system to selectively operate at higher capacity levels in an easy to use and efficient manner.
Yet another object of the present invention is the provision in a transport refrigeration system for operating at a lower capacity level in a reliable and efficient manner.
Still another object of the present invention is the provision for transport refrigeration systems which can be readily and easily boosted in its output capacity.
Yet another object of the present invention is the provision for a transport refrigeration system which is economical to manufacture and effective and efficient in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.
SUMMARY OF THE INVENTION
Briefly, and in accordance with an aspect of the invention, a single compressor of a transport refrigeration system is provided with two sections, with one section being connected to the main system evaporator, and the other section being connected to a subcooling evaporator. An isolation valve and an expansion device are in the subcooler unit so as to allow for control and isolation of the subcooler when not required.
In accordance with another aspect of the invention, a multiple cylinder reciprocal compressor is provided with one or more cylinders being dedicated to use in the subcooler circuit, while the other cylinders are dedicated to the main evaporator circuit.
By yet another aspect of the invention, one or more unloading circuits are provided in the main section of the compression system such that the compressor can be unloaded during periods of low capacity demand.
In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1
is a schematic illustration of a refrigeration system in accordance with a preferred embodiment of the invention.
FIG. 2
is a graphic illustration of the pH diagram of the cycle of that system.
FIG. 3
is a schematic illustration of an alternate embodiment of the invention.
FIG. 4
is a schematic illustration of yet another embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to
FIG. 1
, a vapor compression system for use in a transport refrigeration system, such as a refrigerated truck, trailer or container is shown to include a compressor
11
(shown generally in dashed lines), a condenser
12
, an expansion device
13
and an evaporator
14
, which are connected within a closed circuit to be operated in a conventional manner.
The compressor discharge port
16
is connected to discharge to the condenser
12
by way of the valve
17
, which can be selectively opened or closed for the purpose of isolating the compressor for service, and by the discharge check valve
15
. Downstream of the condenser
12
, a receiver
18
and an associated valve
19
may be included.
Expansion valve
13
is placed just upstream of the evaporator
14
and is responsive to a sensor
21
that senses the temperature of the refrigerant at the downstream end of the evaporator
14
so as to maintain a slightly superheated refrigerant condition. The superheated refrigerant then flows along the line
22
through a valve
23
to a compressor suction inlet
24
. The compressor suction inlet
24
is one of two compressor suction inlets as will be described hereinafter.
In order to obtain greater capacity from the compressor
11
, a subcooler
26
is provided upstream of the evaporator
14
. Upstream of the subcooler
26
, a line
27
divides into lines
28
and
29
, with line
28
passing through the subcooler
26
by way of the heat exchanger element
31
and then by way of line
32
to the expansion device
13
. A line
29
is fluidly interconnected to a valve
33
, a second expansion valve
34
, a heat exchanger element
36
and out to line
37
. A sensor
38
is interconnected to the expansion valve
34
so as to allow the expansion valve
34
to be responsive to the temperature of the refrigerant leaving the subcooler
26
. Line
37
is connected by way of valve
38
to another compressor suction inlet
39
as shown.
In operation, during periods in which the system demand calls for relatively low capacities, the valve
33
is in the closed position and the subcooler
26
is effectively removed from the circuit. The refrigerant flows through lines
27
,
28
, and through the heat exchanger element
31
, to the line
32
and the expansion valve
13
. Downstream of the evaporator
14
, the refrigerant passes into the compressor suction inlet
34
, is compressed in a manner as will be described hereinafter, and is discharged at the compressor discharge port
16
.
During periods of operation wherein greater capacities are required, the valve
33
is opened to allow the flow of refrigerant through line
29
, the valve
33
, the expansion valve
34
, and into the heat exchanger element
36
. Because of the expansion of the refrigerant in the expansion valve
34
, the heat exchange element
34
is cooled, but with the heat exchanger element
36
being in heat exchange relationship with the heat exchanger element
31
, the transfer of heat causes a cooling of the refrigerant flowing through the heat exchanger element
31
, such that the temperature of the refrigerant entering the expansion valve
13
is subcooled. As the subcooled refrigerant passes into the evaporator, it results in a substantially greater performance of the evaporator
14
.
Considering in greater detail the compressor
11
, it will be seen that the compressor
11
is a multiple cylinder reciprocating compressor. Five of the six cylinders are interconnected to provide compression between the suction inlet
24
and the discharge port
16
. These are shown at
41
-
46
. Each of the cylinders has a suction valve
47
, a piston
48
and a discharge valve
49
as shown. A pair of unloaders
51
and
52
are provided to selectively connect the high pressure side back to suction as shown in order to reduce the capacity when it is not needed. Check valves
53
and
54
are also preferably provided on the high pressure side as shown.
Referring now to the sixth cylinder
56
, this cylinder provides compression between the compressor suction inlet
39
and the compressor discharge port
16
. It is identical to the other cylinders in that it has a suction valve
47
, a piston
48
and a discharge valve
49
, but it may well have a different displacement than the other cylinders. During periods in which the subcooler is activated within the system by the opening of the isolation valve
33
, the cylinder
56
will compress the refrigerant being discharged from the subcooler
26
, with the compressed refrigerant being mixed with that compressed by the other five cylinders of the compressor
11
. During periods in which the additional capacity is not required, the isolation valve
33
will be closed and the cylinder
56
will continue to function but will not perform any work. The isolation valve
33
could be integrated with the expansion device
34
by use of an electronic expansion valve as will be more fully discussed hereinafter.
When full capacity is required, all six cylinders will be compressing refrigerant and the evaporator unit will be boosted by use of the subcooled refrigerant. When fall capacity is not required, it may be reduced by turning off the subcooler or partially closing down the subcooler
26
, or by using one or both of the unloaders
51
and
52
, or a combination of these approaches.
Referring now to
FIG. 2
, the pH diagram of the system is shown when using R-404A as the refrigerant. The points
1
-
7
represent the positions on the chart which corresponds with the positions
1
-
7
within the system cycle as shown in FIG.
1
.
At point
1
, upstream of the expansion valve
13
, the refrigerant is at a relatively high pressure and low temperature. At point
2
, just downstream of the expansion valve
13
, the pressure is substantially reduced, and at point
3
, just upstream of the compressor suction inlet
24
, the pressure is relatively low and the temperature is substantially increased. After passing through the compressor, the temperature and pressure are increased to point
4
and after passing through the condenser at position
7
, the pressure remains almost constant but the temperature is substantially reduced. Finally, passing of the refrigerant along line
28
and through the subcooler
26
cools the refrigerant to the point
1
temperature.
Considering now what occurs in the other line
29
of the subcooler
26
, the passing of the refrigerant through the expansion valve
34
reduces the pressure to that at point
5
, and after passing through the subcooler
26
the temperature of that refrigerant is increased to that shown at point
6
.
Referring now to
FIG. 3
, an alternative embodiment is shown wherein the isolation valve
33
and the expansion valve
34
are replaced with an electronic expansion device
57
upstream of the subcooler
26
as shown. The electronic expansion device
57
is controlled by a controller
58
which automatically adjusts the electronic expansion device
57
toward the closed or open conditions in response to various sensed and programmed parameters.
On the downstream side of the subcooler
26
, the sensors
59
and
61
sense pressure and temperature, respectively, of the refrigerant in lines
37
and input those values to the controller
58
. Other inputs, such as saturation point, ambient temperature, suction pressure and discharge pressure, are input into the controller
58
by way of line
62
.
In response to the various input signals and the programmed software embedded therein, the controller sends signals along lines
63
,
64
and
66
to control the electronic expansion device
57
, the unloading function, and the compressor speed, respectively, in order to optimize the system operation in a controlled and efficient manner.
Another embodiment of the present invention is shown in
FIG. 4
wherein, a three way valve
67
is provided in line
37
and ties into line
22
by way of line
68
. The three way valve
67
, which can be controlled by solenoid
69
, would enable the six cylinder
56
to be able to use suction gas from line
37
as described hereinabove, but it also can be used to bring in suction gas from line
22
, along line
68
, to thereby permit the compressor to act as a full six cylinder machine on gas from the evaporator
14
, or as a subcooling cylinder as described hereinabove. One advantage of this arrangement is that the subcooler
26
, and all joints up to the compressor suction valve
38
, would not be under negative pressure when shut off. A possible disadvantage is the need for a three way valve, which is generally not considered to be particularly reliable.
While the present invention has been particularly shown and described with reference to a preferred embodiment as illustrated in the drawings, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the true spirit and scope of the invention as defined by the claims. For example, although the compressor has been described in terms of a six cylinder reciprocating compressor with five cylinders dedicated to one section and one cylinder to the other section, it may just as well be separated at different ratios, such as four and two, or it may have a different number of cylinders, such as one and one in a two cylinder machine, or three and one in a four cylinder machine, for example.
Claims
- 1. A vapor compression system comprising:a single stage compressor having first and second sections connected in parallel with each having a suction inlet and both discharging to a single discharge port; a condenser for receiving high pressure vapor from said discharge port and converting at least a portion thereof to a lower temperature liquid; an expansion device for receiving said liquid and expanding it to a lower pressure vapor; an evaporator for receiving said lower pressure vapor at a low temperature and delivering it to said first section at a higher temperature; and a subcooler for receiving a portion of said liquid refrigerant from said condenser to subcool another portion of said liquid refrigerant passing from said condenser to said expansion valve, said subcooler being fluidly connected to second section of said compressor.
- 2. A compression system as set forth in claim 1 wherein said compressor is a multi-cylinder compressor and each of said two sections is driven by separate cylinder groups.
- 3. A vapor compression system as set forth in claim 2 wherein one section is driven by a plurality of cylinders and another section is driven by a single cylinder.
- 4. A compression system as set forth in claim 3 wherein a circuit containing said subcooler is driven by a single cylinder.
- 5. A compression system as set forth in claim 1 and including unloading circuits in at least one section to fluidly interconnect a high pressure side to a low pressure side of said compressor.
- 6. A compression system as set forth in claim 1 wherein said subcooler has associated therewith an isolation valve which may be closed to effectively remove the subcooler from operation.
- 7. A compression system as set forth in claim 1 and including a subcooler expansion device upstream of said subcooler.
- 8. A compression system as set forth in claim 1 and including a check valve posed between said subcooler and said second suction inlet.
- 9. A method of selectively boosting the capacity of a vapor compression system having a single stage compressor, a condenser, an expansion valve and an evaporator comprising the steps of:providing first and second sections to said compressor said first and second sections connected in parallel with each having a suction inlet and both discharging to a single discharge port; providing a subcooler to receive a first portion of refrigerant from the condenser to cool a second portion of refrigerant from the condenser prior to its flow to the expansion valve; and providing for the flow of said first portion of refrigerant from said subcooler to said second section.
- 10. A method as set forth in claim 9 and including a step of delivering refrigerant from said expansion valve to said first section.
- 11. A method as set forth in claim 10 and including the step of applying multiple cylinders to compress the refrigerant being delivered to said first section.
- 12. A method as set forth in claim 10 and including the step of applying a single cylinder of said compressor to compress the refrigerant being delivered to said second section.
- 13. A vapor compression system for a refrigerated vehicle, comprising:a single stage compressor for receiving a low pressure refrigerant vapor and delivering a high pressure refrigerant vapor, said compressor having first and second sections, connected in parallel with each having a suction inlet and both discharging to a single discharge port; a condenser for receiving refrigerant vapor from said compressor and delivering liquid refrigerant; an expansion valve for receiving at least a portion of said liquid refrigerant and converting it to a low pressure refrigerant vapor; an evaporator for receiving low pressure refrigerant vapor from said expansion valve and delivering higher temperature refrigerant vapor to said first section; and a subcooler for receiving a portion of said liquid refrigerant from said condenser to subcool said portion of said liquid refrigerant passing to said expansion valve, said subcooler being fluidly connected to said compressor second section.
- 14. A system as set forth in claim 13 wherein said subcooler is connected to selectively provide for the flow of refrigerant to said second section.
- 15. A system as set forth in claim 13 wherein said first section has multiple reciprocating cylinders.
- 16. A system as set forth in claim 13 wherein said first section has at least one unloading circuit.
- 17. A system as set forth in claim 13 wherein said second section includes a single reciprocating cylinder.
US Referenced Citations (11)