WO2009091405A1

WO2009091405A1 - Pressure vessel for reducing unit high pressure during storage and transportation

Info

Publication number: WO2009091405A1
Application number: PCT/US2008/051416
Authority: WO
Inventors: Alexander Lifson; Michael F. Taras
Original assignee: Carrier Corporation
Priority date: 2008-01-18
Filing date: 2008-01-18
Publication date: 2009-07-23

Abstract

Methods that prevent exposure of a vapor compression system to excessive pressure during storage and transportation are described The steps include attaching a high pressure vessel containing refrigerant via at least one flow control device to the vapor compression system. Closing the flow control device to isolate the vapor compression system from the pressure vessel during storage and transportation. Opening at least one connecting flow control device and charging the vapor compression system with refrigerant during installation. Closing the flow control device and removing the high pressure vessel. Alternatively, leaving high pressure vessel attache to act as either a receiver or an accumulator during operation. Such methods permit containment of high refrigerant pressure by the pressure vessel during storage and transportation while allowing lower design pressures for the rest of the vapor compression system components. This reduces cost, weight and complexity of the vapor compression system.

Description

Pressure Vessel for Reducing Unit High Pressure During Storage and Transportation

Technical Field

[0001] This invention relates generally to vapor compression systems and, more particularly, to a method and apparatus for reducing pressure within refrigerant systems that can be exposed to high storage and transportation pressures, which would be typical, for example, for a CO₂ refrigerant systems.

Background of the Invention

[0002] A common approach for packaged and split air conditioning and refrigeration systems is to charge these refrigerant system with the refrigerant at the factory and then store and ship the refrigerant system in the charged condition in order to provide proper operation of the refrigerant system upon installation without any need to add any refrigerant charge. This approach has been satisfactory in systems charged with CFC, HCFC, HFC and similar conventional refrigerants. [0003] With greater concern being given to the environmental issues associated with the conventional refrigerants, it has become desirable to use environmentally benign refrigerants, such as natural refrigerants, as working fluids in vapor compression systems. Carbon dioxide or CO₂ refrigerant is one of such promising refrigerants. However, in order for the CO₂ refrigerant to become technically feasible, it was necessary to develop refrigerant system components, such as compressors, heat exchangers, flow control devices and interconnecting piping, that can withstand high operating pressures, since the working pressures for the CO₂ refrigerant are substantially higher than for the conventional refrigerants mentioned above.

[0004] Furthermore, if the usual practice of charging a vapor compression system is followed for a CO₂ refrigerant systems, additional problems may arise, particularly with respect to the storage and transportation of these refrigerant systems, even if higher operating pressures have been accounted for during the design stage. For example, for the CO₂ supermarket refrigeration systems the pressure on the high side of the system is not expected to exceed 1200 psia, because temperature inside the supermarket normally does not exceed 9O⁰F and the heat rejection heat exchangers are normally located inside the supermarket space. The pressure on the low side of the system is not expected to exceed 1000 psia. However, during storage and transportation, especially when the enclosed transportation containers are exposed to direct sun radiation, the temperature inside the storage or transportation container can reach 16O⁰F causing the pressure inside the transported refrigerant system charged with CO₂ to reach 3000 psia or higher levels. Such high pressure can rupture and/or otherwise damage the unit components that are only designed to withstand pressures the unit would be exposed to during operation. As stated above, the design operating pressure in this case is substantially lower than the storage or transportation pressure. Of particular concern is the low pressure side of the refrigerant system which is normally exposed to a much lower pressure during operation than the high pressure side. However, as the entire system is in thermal equilibrium during storage and transportation, the pressures would be the same on both the high and low system pressure sides. Therefore, pressure on the low system side can become extremely high during storage and transportation as compared to the normal operating pressure of the low side.

[0005] One approach to solving this problem is to over-design the unit, and low pressure side components in particular, such that they can withstand the pressures that the refrigerant system can be exposed to during storage and transportation, typically also including a safety factor of at least of three for a maximum expected pressure. If such an approach is chosen, this, of course, will add substantial cost and weight to the refrigerant system.

[0006] Another alternative is to ship the unit without any refrigerant charge

(or with a minimum amount of refrigerant charge) and charge it after it has been installed. However, this can become inconvenient and impractical, since it requires special charging containers, and can lead to unit overcharging or undercharging.

Disclosure of the Invention

[0007] In accordance with one aspect of the invention, a provision is made to store and transport a vapor compression system in an uncharged condition, but with a charging container fluidly connected to the refrigerant system by way of a flow control device, such as a valve or a rupture disk or its equivalent, such that upon installation of the system, the flow control device may be opened to charge the refrigerant system with the charge amount sufficient for a proper operation of the refrigerant system. After the charging procedure, the high pressure container may be disconnected from the refrigerant system.

[0008] By another aspect of the invention, the container can be designed to withstand substantial pressures that are expected during the storage and transportation stages, and, after the charging process, the container may be used as a receiver or an accumulator within the refrigerant system. [0009] In the drawings as hereinafter described, in addition to depicted preferred embodiments; however, various other modifications and alternate constructions can be made thereto without departing from the spirit and scope of the invention.

Brief Description of the Drawings

[0010] FIG. 1 is a schematic illustration of a vapor compression system with the present invention incorporated therein.

[0011] FIG. 2 is a schematic illustration of an alternative embodiment thereof.

[0012] FIG. 3 is a schematic illustration of another alternative embodiment thereof.

Detailed Description of the Invention

[0013] The invention is shown generally at 10 as applied to a vapor compression refrigerant system 11 which includes, in serial flow relationship, a compressor 12 a heat rejection heat exchanger 13, an expansion device 14 and an evaporator 16. It has to be understood that a basic refrigerant system shown in various embodiments of the invention is exemplary and may include various design options and enhancement features. All these refrigerant system configurations are within the scope and can equally benefit from the invention. [0014] For the refrigerant system to cool, it needs to be charged with the refrigerant. In the past, where such vapor compression systems used relatively low pressure refrigerants, such as CFCs, HCFCs and HFCs, the systems were completely charged with the refrigerant at the manufacturing plant and then shipped for use or storage in this completely charged condition. This process avoided the need to charge the systems in the field and therefore avoided the likelihood of an improper amount of charge being provided to the refrigerant vapor compression system, causing its improper operation, malfunction or damage. [0015] More recently, with the increased awareness of the detrimental environmental effects associated with the conventional refrigerants, more attention is paid to using more benign refrigerants. One of such refrigerants is a CO₂ refrigerant. However, with the use of the CO₂ refrigerant, the vapor compression system would be operating at pressures that are substantially higher, in comparison to the vapor compression systems charged with the conventional refrigerants (i.e. in the range of 5-10 times higher). In order to operate at such high pressures, it has been necessary to design components of the refrigerant vapor compression systems, such as compressors, heat exchangers, flow control devices, interconnecting piping, etc., to withstand these higher pressures, typically including safety factors of three to five in reference to a maximum operating pressure. However, even with the designs satisfying these operational safety requirements, the practice of a complete pre- charging of the vapor compression systems at the factories now becomes a problem. This occurs as the refrigerant system components must be capable of withstanding transportation and storage pressure which can be substantially higher than the pressure within the refrigerant systems during normal operation. High storage and transportation pressures are particularly problematic for the low pressure side of the vapor compression systems where the components would otherwise be designed to operate at relatively low pressures. The present invention is intended to overcome these problems.

[0016] Rather than fully charge the vapor compression system 11 with the refrigerant, at least a portion of the refrigerant is stored in a high pressure vessel 17 which is fluidly connected to the refrigerant system 11 by way of a connecting flow control device 18 such as, for instance, a valve or rupture disk. The charging of the high pressure vessel 17 and the connection to the refrigerant system 11 is accomplished at the factory, with the attachment being made at any one of the three locations A, B or C as shown in Fig. 1. Obviously, any other locations are feasible and are within the scope of the invention.

[0017] The refrigerant system 11 may contain no refrigerant charge at all or only a limited safe amount of the refrigerant charge. The refrigerant system 11 also includes a high pressure vessel 17 that is attached to the refrigerant system. The high pressure vessel 17 has the required refrigerant charge amount and is specifically designed to withstand the required storage and transportation pressures. Since the high pressure vessel 17 is isolated from the refrigerant system 11, and the refrigerant system 11 is empty of refrigerant, or contains a nominal safe refrigerant charge amount, during transportation or storage, the refrigerant system 11 now can be shipped or stored without being exposed to high pressures. In other words, only the relatively small specially designed high pressure vessel 17 may be exposed to high pressures potentially present during storage or transportation, while the rest of the refrigerant system 11 is not exposed to high pressures during storage and transportation. Thus, the refrigerant system 11 would only be exposed to the operating pressures, which are normally much lower than the transportation and storage pressures. This is especially the case for the low pressure side of the refrigerant system.

[0018] When the unit is later delivered and installed, the connecting flow control device 18 is opened (or ruptured, in case of the rupture disk) to thereby release the refrigerant charge contained in the high pressure vessel 17 into the refrigerant system 11. If a valve rather than a rupture disk is used, the valve 18 may then be closed and the high pressure vessel can be removed and reused. [0019] If the high pressure vessel 17 is a reusable container, it is desired to transfer as much refrigerant charge from the high pressure vessel 17 to the refrigerant system 11 as possible. Therefore, if the high pressure vessel 17 is connected to the high pressure side of the refrigerant system 11, it is preferable to open the flow control device 18 and execute the refrigerant charge migration while the refrigerant system 11 is not operating. On the other hand, if the high pressure vessel 17 is connected to the low pressure side of the refrigerant system 11, it is preferable to open the flow control device 18 and execute the initial refrigerant charge migration while the refrigerant system is not operating, and then turn the refrigerant system on. This would allow the pressure on the low pressure side of the refrigerant system 11 and within the high pressure vessel 17 to drop even further, allowing additional refrigerant charge migration from the high pressure vessel 17 into the refrigerant system 11. While operating the refrigerant system 11, the flow control device 18 is closed and the high pressure vessel 17 can be disconnected. In both cases of high and low pressure side connections of the high pressure vessel 17 to the refrigerant system 11, a heater 25 can be applied to the high pressure vessel 17 and turned on during refrigerant migration process, assisting in even more refrigerant charge transition. The heater, for instance, may be of an electric type and located inside the high pressure vessel 17 or on its surface.

[0020] Provisions are also made for leaving the high pressure vessel 17 in its installed position for use in other functions within the refrigerant vapor compression system 11 as will be described with reference to Fig. 2 and Fig. 3. [0021] It should be understood that the entire refrigerant charge may be contained within the high pressure vessel 17, in which case there would be no refrigerant provided to the vapor compression system 11 at the manufacturing plant. However, with the present approach, it is also possible to partially charge the vapor compression system 11, and provide the remaining charge in the high pressure vessel 17 as necessary in order to fully charge the refrigerant system 11. If charged in this way, care must be taken to limit the amount of charge placed in the vapor compression system 11 so that over-pressure conditions do not develop during transportation and storage.

[0022] In Fig. 2, there is shown an alterative arrangement wherein the high pressure vessel 17 is located in such a position and manner so as to allow it to remain within the refrigerant system 11 and to subsequently perform a supplementary function. At the plant, the high pressure vessel 17 is charged with the significant amount of the refrigerant and installed as shown with the two isolating flow control devices such as valves 19 and 21 being in their closed positions. As explained above, the rest of the refrigerant system 11 may or may not contain any refrigerant charge. The refrigerant system 11 is then stored and/or transported in that condition. Upon installation of the refrigerant system 11, the two valves 19 and 21 are opened to release the refrigerant stored in the high pressure vessel 17 into the refrigerant system 11. The high pressure vessel 17 can then remain within the refrigerant system 11 to act as a receiver to store any excess of the CO₂ charge during operation at off-design conditions. Once again, only a high pressure vessel 17 has to be over-designed to withstand potentially extremely high pressures during storage and transportation.

[0023] In Fig. 3, the high pressure vessel 17 is installed in the same manner but in a different location as shown. Again, the charging process of the high pressure vessel 17, and later, the refrigerant system 11, is accomplished in the same manner by use of the flow control devices such as valves 22 and 23. In this location, the high pressure vessel 17 may remain within the refrigerant system 11 as well and act as an accumulator during normal operation.

[0024] This invention can be applied to various types of refrigerant systems, which for example include container and truck-trailer systems, supermarket refrigeration systems, and residential and commercial air conditioning and heat pump systems. It can be applied to a variety of refrigerants including, but not limited to R744, R410A, R22, R407C, and R404A refrigerants. This invention also applies to various types of compressors including, for example, screw compressors, scroll compressors, rotary compressors, and reciprocating compressors. [0025] While the present invention has been particularly shown and described with reference to various embodiments as illustrated in the drawings, it will be understood by one skilled I the art that various changes in detail may be made thereto without departing from the spirit and scope of the invention as defined by the claims.

Claims

We Claim:

1. A method of charging a vapor compression system having in serial flow relationship a compressor, a heat rejection heat exchanger, an expansion device and an evaporator initially having less than a full charge of refrigerant therein, comprising the steps of: connecting the vapor compression system, with at least one connecting refrigerant flow control device in a closed position, to a high pressure vessel containing a refrigerant charge therein; storing and/or transporting the vapor compression system and the connected high pressure vessel to an installation site; and opening the at least one connecting refrigerant flow control device and allowing at least a portion of the stored refrigerant within the high pressure vessel to migrate from the high pressure vessel into the vapor compression system.

2. A method as set forth in claim 1 wherein said high pressure vessel is sized and constructed to accommodate a full refrigerant charge amount for the vapor compression system.

3. A method as set forth in claim 1 wherein said refrigerant is CO₂.

4. A method as set forth in claim 1 wherein said at least one connecting refrigerant flow control device is one of a valve and a rupture membrane.

5. A method as set forth in claim 1 wherein said high pressure vessel has a heater associated therewith wherein said heater is positioned either inside the high pressure vessel or on its surface.

6. A method as set forth in claim 1 wherein said refrigerant migration is executed when the vapor compression system is operating at least for a portion of the refrigerant migration time.

7. A method as set forth in claim 1 wherein said refrigerant migration is executed when the vapor compression system is not operating.

8. A method as set forth in claim 1 wherein said high pressure vessel is connected in one of the following locations: between said heat rejection heat exchanger and said expansion device, between said evaporator and said compressor or between said compressor and said heat rejection heat exchanger.

9. A method as set forth in claim 1 wherein said high pressure vessel is connected between said heat rejection heat exchanger and said expansion device and including the steps of installing said high pressure vessel with a refrigerant flow control device on either side thereof, and further utilizing said high pressure vessel within the vapor compression system as a receiver with both said refrigerant flow control devices being open during normal operation of the vapor compression system.

10. A method as set forth in claim 1 wherein said high pressure vessel is connected between said evaporator and said compressor and including the steps of installing said high pressure vessel with a refrigerant flow control device on either side thereof and further utilizing said high pressure vessel within the vapor compression system as an accumulator with both said refrigerant flow control devices being open during normal operation of the vapor compression system.

11. A method as set forth in claim 1 and including the step of closing the connecting refrigerant flow control device and removing the high pressure vessel from its connection to the vapor compression system.

12. A method of charging a vapor compression system which includes in serial flow relationship a compressor, a heat rejection heat exchanger, an expansion device and an evaporator and which is susceptible to exposure to a higher than operational temperatures and pressures during storage and transportation, comprising the steps of: during the process of manufacturing the vapor compression system, including a high pressure vessel that is fluidly connected to the vapor compression system by way of at least one connecting refrigerant flow control device; charging said high pressure vessel with refrigerant during the manufacturing process and leaving the refrigerant charge in said high pressure vessel during storage and transportation thereof; and upon installation the vapor compression system, opening the at least one connecting refrigerant flow device so as to allow at least a portion of the stored refrigerant within the high pressure vessel to migrate from the high pressure vessel into the vapor compression system.

13. A method as set forth in claim 12 wherein said high pressure vessel is sized and constructed to accommodate a full refrigerant charge amount for the vapor compression system.

14. A method as set forth in claim 12 wherein said refrigerant is CO₂.

15. A method as set forth in claim 12 wherein said at least one connecting refrigerant flow control device is one of a valve and a rupture membrane.

16. A method as set forth in claim 12 wherein said high pressure vessel has a heater associated therewith wherein said heater is positioned either inside the high pressure vessel or on its surface.

17. A method as set forth in claim 12 wherein said refrigerant migration is executed when the vapor compression system is operating at least for a portion of the refrigerant migration time.

18. A method as set forth in claim 12 wherein said refrigerant migration is executed when the vapor compression system is not operating.

19. A method as set forth in claim 12 wherein said high pressure vessel is connected in one of the following locations: between said heat rejection heat exchanger and said expansion device, between said evaporator and said compressor or between said compressor and said heat rejection heat exchanger.

20. A method as set forth in claim 12 wherein said high pressure vessel is connected between said heat rejection heat exchanger and said expansion device and including the steps of installing said high pressure vessel with a refrigerant flow control device on either side thereof, and opening said refrigerant flow control devices, and leaving the high pressure vessel within the vapor compression system to act as a receiver for the vapor compression system.

21. A method as set forth in claim 12 wherein said high pressure vessel is connected between said evaporator and said compressor and including the steps of installing said high pressure vessel with a refrigerant flow control device on either side thereof and opening said refrigerant flow control devices, and leaving the high pressure vessel within the vapor compression system to act as an accumulator for the vapor compression system.

22. A method as set forth in claim 12 and including the step of closing the at least one connecting refrigerant flow control device and removing the high pressure vessel from its connection to the vapor compression system.

23. A vapor compression system comprising: a closed-loop refrigerant circuit for serial flow of refrigerant through a compressor, a heat rejection heat exchanger, an expansion device and an evaporator initially having less than a full charge of refrigerant therein; a high pressure vessel containing a refrigerant charge therein; and at least one refrigerant flow control device interconnecting said closed-loop refrigerant circuit to said high pressure vessel, said at least one refrigerant flow control device being in a closed position for storage and transportation of the vapor compression system but being operable to an open position upon installation of the vapor compression system for the purpose of completing the refrigerant charge while at least a portion of the stored refrigerant within the high pressure vessel migrates from the high pressure vessel into the closed-loop refrigerant circuit of the vapor compression system.

24. A vapor compression system as set forth in claim 23 wherein said high pressure vessel is sized and constructed to accommodate a full refrigerant charge amount for the vapor compression system.

25. A vapor compression system as set forth in claim 23 wherein said refrigerant is CO₂.

26. A vapor compression system as set forth in claim 23 wherein said at least one interconnecting refrigerant control device is one of a valve and a rupture membrane.

27. A vapor compression system as set forth in claim 23 wherein said high pressure vessel has a heater associated therewith, wherein said heater is positioned either inside the high pressure vessel or on its surface.

28. A vapor compression system as set forth in claim 23 wherein said high pressure vessel is connected in one of the following locations: between said heat rejection heat exchanger and said expansion device, between said evaporator and said compressor, or between said compressor and the heat rejection exchanger.

29. A vapor compression system as set forth in claim 23, wherein said high pressure vessel is connected between said heat rejection heat exchanger and said expansion device and further wherein said at least one refrigerant flow control device includes two flow control devices, with one on either side of said high pressure vessel, such that when said high pressure vessel is installed into the closed- loop refrigerant circuit with each of the refrigerant flow control devices being in an open position, the high pressure vessel functions as a receiver in the vapor compression system.

30. A vapor compression system as set forth in claim 23 wherein said high pressure vessel is connected between said evaporator and said compressor and further wherein said at least one refrigerant flow control device comprises two flow control devices, with one on either side of said high pressure vessel, such that when said high pressure vessel is installed in the closed-loop refrigerant circuit with the two refrigerant flow control devices being in the open position, the high pressure vessel serves as an accumulator in the vapor compression system.