DUAL-CIRCUIT SERIES COUNTERFLOW CHILLER WITH INTERMEDIATE WATERBOX
A dual refrigeration circuit watercooled chiller has its respective evaporators and condensers interconnected by waterboxes such that the first circuit tubes discharge into the respective waterbox and the flow of water then passes from the respective waterboxes to the respective evaporator/condenser tubes of the second circuit. Instrumentation is attached to the waterboxes to enable the measurement of the leaving temperature differential to provide improved control. Since the first and second circuit tubes are separate and independent, both serviceability and flexibility in design are substantially enhanced.
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This invention relates generally to water cooled chillers and, more specifically, to the interconnection of two vapor compression refrigeration systems in a series-counterflow arrangement.
Water cooled chillers in a series-counterflow arrangement consist of two independent vapor compression refrigeration systems with chilled water and condenser water circuits that are common to both circuits and are arranged in series. This arrangement allows for an increased coefficient of performance (COP) over a single refrigeration circuit design because the separate circuits with series counterflow have a lower average pressure differential between the evaporator and condenser, thus requiring less energy to compress refrigerant from the evaporator to the condenser.
In such a system, water in each of the evaporators and the condensers flows through a plurality of tubes that span both refrigeration circuits, with the refrigeration circuits being separated by a tubesheet which is located at the middle of the tubes, and with each tube being hermetically sealed to the tubesheet, typically by expansion of the tube to the tubesheet.
One problem that arises is that of servicing the tubes such as may be required if a tube fails in operation. Such removal of a tube requires cutting the tube at all locations where it has been expanded and then pulling the tube out. It is not possible to completely remove a tube since there is no access to cut the tube at the center tubesheet location, which is inside the refrigerant boundary. If a tube is cut internally, or if a tube fails in operation, a leak path is created between the circuits that does not allow for operation of either circuit, thus adversely impacting both reliability and serviceability.
Another problem with a dual circuit system is that of control. A critical parameter for control of a water cooled chiller is the use of the leaving temperature differential, which is the difference in the temperature of the water leaving a heat exchanger and the refrigerant temperature within the heat exchanger. Since the water tubes span both refrigerant circuits in a dual system, it is not possible to obtain the leaving water temperatures of the upstream circuit's condenser or evaporator.
In addition to serviceability and control as discussed hereinabove, prior art heat exchanger tubes that span dual circuits pose problems of reliability, shipping and performance. That is, because the common tubes extend across both circuits, it is impossible to optimize the heat transfer tubes in each circuit independently, and shipping of machines that are longer due to the longer tubes can be difficult.
SUMMARY OF THE INVENTIONBriefly, in accordance with one aspect of the invention, each circuit has unique tubesheets that separate the refrigeration circuit from the cooling medium. Between each circuit is an intermediate waterbox that passes water from the upstream circuit to the downstream circuit. The waterbox is removable for service and enables the transporting of the units in pieces with shorter length requirements.
In accordance with another aspect of the invention, since each circuit has its separate and unique tubes, a tube failure in either circuit no longer creates a refrigerant leak path to the adjacent circuit, such that operation of the nonfailed circuit can be maintained, thereby increasing reliability.
By another aspect of the invention, since the intermediate waterbox is accessible from the outside, temperature measurement instrumentation can be installed to obtain the leaving temperature differential of the first circuit, thereby providing better control of the system.
In accordance with another aspect of the invention, the intermediate waterbox causes mixing of the water that leaves the upstream circuit before entering the downstream circuit, thereby increasing heat transfer effectiveness and COP.
By yet another aspect of the invention, use of the waterbox allows for multiple parameters that can be varied in order to optimize the efficiency of each of the circuits. In addition to varying the length of each circuit, the tube material, the tube heat transfer enhancement, and the number of tubes are configurable, and can be unique to each circuit
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 spirit and scope of the invention.
In order to obtain increased COPs, a dual-circuit is connected in series counterflow arrangement as shown in
It will be seen in
Similarly, the evaporator tubes 22 are unitary members that extend across both circuits 13 and 14, with the intermediate tubesheets providing isolation only for the refrigerant in the systems 13 and 14, but allow for the evaporator water to flow continuously from the inlet end of the evaporator 19 to the outlet end of the evaporator 17.
As discussed hereinabove, such dual-circuit systems with heat exchanger tubes that span both circuits present problems with respect to service, reliability, shipping, performance and control.
Referring now to
As shown in
The advantages of the above-described design are numerous. First of all, rather than having long unitary tubes, the tubes, and therefore the refrigeration circuits, are generally only about half as long and can be more easily handled and shipped to a site, with the tubes, and therefore the refrigeration circuits, being independent and separatable from the waterboxes. Second, since the tubes are independent, they can be configurable to optimize performance in each circuit. That is, in addition to the variation in length of the tubes in each circuit, the number of tubes within the second circuit can be different from those in the first circuit as shown in
Other advantages of the present system can be seen by reference to
By using the waterbox 36 as described, the intermediate waterbox 36 is now accessible from the outside and temperature measurement instrumentation 43 can easily be used to obtain the leaving temperature differential of the upstream heat exchangers, thus providing improved control of the system.
Another advantage of the use of waterboxes as described is that of facilitating service and repair. That is, since the waterbox is attached to the tube circuits in a manner that allows removal of the waterbox, as will be described hereinafter, the removal of the waterbox allows service of the tubes at each circuit's tubesheet, thereby substantially improving serviceability. Further, since a tube failure in either circuit does not create a refrigerant leak path to the adjacent circuit, the reliability of the system is substantially enhanced.
Referring now to
Although the waterbox 44 is shown in
Claims
1. A chiller system of the type having first and second refrigeration circuits with each refrigeration circuit having a compressor, a condenser, an expansion device and an evaporator and with the respective evaporators in the first and second circuits having a plurality of tubes to conduct the flow of fluid to be cooled, and with the respective evaporators of the first and second circuits being interconnected in series relationship such that the fluid to be chilled passes serially through the respective evaporators of the first and second, circuits, comprising:
- a waterbox interconnected between the evaporators of the first and second circuits and having a unitary reservoir for conducting the flow of fluid from the tubes in the evaporator of the first circuit and to the tubes of the evaporator of the second circuit.
2. A chiller system as set forth in claim 1 wherein each of said first and second evaporators includes an intermediate tubesheet, and wherein said intermediate waterbox is interconnected between said tubesheets.
3. A chiller system as set forth in claim 2 wherein said intermediate waterbox is cylindrical in form and is connected to said tubesheets at the respective circular ends of the cylinder.
4. A chiller system as set forth in claim 3 wherein said waterbox has a plurality of holes formed longitudinally between its opposite ends and further wherein bolts are passed through the tubesheets and through said holes.
5. A chiller system as set forth in claim 1 and including temperature measurement instrumentation connected to said waterbox to measure the temperature of the water therein.
6. A chiller system as set forth in claim 1 wherein the respective condensers of the first and second circuits are connected in series and are watercooled and include a waterbox interconnected between the condensers.
7. A chiller system as set forth in claim 6 wherein said evaporators of first and second circuit are adapted to conduct the flow of cooling water in counterflow relationship to the flow of cooling water in the condensers of the first and second circuits.
8. A dual-circuit chiller, comprising:
- a first circuit having a compressor, a condenser, an expansion device and an evaporator, with the evaporator having a plurality of tubes for conducting the flow of water to be cooled from an inlet end to an outlet end of the tube;
- a second circuit having a compressor, a condenser, an expansion device and an evaporator with the evaporator having a plurality of tubes for conducting the flow of water to be cooled from an inlet end to an outlet end of the tubes; and
- an evaporator waterbox fluidly interconnected between said first circuit tube outlet ends and the second circuit tube inlet ends, such that water to be cooled flows from said first circuit tube outlet ends, into said evaporator waterbox and then into the second circuit tube inlet ends.
9. A dual-circuit chiller as set forth in claim 8 and including a first intermediate tubesheet surrounding said first circuit tube outlet ends and a second intermediate tubesheet surrounding said second circuit tube inlet ends and further wherein said waterbox is connected to said first and second intermediate tubesheets.
10. A dual-circuit chiller as set forth in claim 9 wherein said waterbox is cylindrical in form.
11. A dual-circuit chiller as set forth in claim 10 wherein said cylinder has holes formed longitudinally between its end surfaces and further wherein bolts pass through said first and second intermediate tubesheets and through said holes to secure the waterbox to said first and second intermediate tubesheets, respectively.
12. A dual-circuit chiller as set forth in claim 8 and including temperature measurement instrumentation attached to said waterbox for measuring the temperature of the water therein.
13. A dual-circuit chiller as set forth in claim 8 wherein said condensers of said first and second circuits are watercooled and are connected in serial flow relationship and further include a condenser waterbox interconnected between the condensers of said first and second circuits.
14. A dual-circuit chiller as set forth in claim 6 wherein the flow of water in said evaporators is in counterflow relationship with the flow of water in said condensers.
Type: Application
Filed: Oct 10, 2006
Publication Date: May 13, 2010
Applicant: Carrier Corproation (Farmington, CT)
Inventors: Scott M. MacBain (Syracuse, NY), Michael A. Stark (Fayetteville, NY), Robert Hong Leung Chiang (Shanghai)
Application Number: 12/444,930
International Classification: F25D 17/02 (20060101); F25B 1/10 (20060101); F25B 39/02 (20060101);