Refrigeration – Automatic control – Trapping and discharging refrigerant batches
Patent
1995-06-08
1997-08-12
Wayner, William E.
Refrigeration
Automatic control
Trapping and discharging refrigerant batches
62498, F25B 4100, F25B 100
Patent
active
056553781
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a vapour compression system operating at both subcritical and supercritical high-side pressures.
In conventional vapour compression systems, the high-side pressure is determined by the condensing temperature, via the saturation pressure characteristics of the refrigerant. The high side pressure in such systems is always well below the critical pressure.
In vapour compression systems operating with supercritical high-side pressure, i.e. in a trans-critical cycle, the operating pressure depends on several factors such as momentary refrigerant charge in the high side, component volumes and temperature of heat rejection.
A simple vapour compression system with an expansion device of conventional design, e.g. of the thermostatic type, would also be able to provide trans-critical cycle operation when the heat rejection temperature is above the critical temperature of the refrigerant. Such a system could give a simple and low-cost embodiment for a trans-critical vapour compression cycle using environmentally benign refrigerants such as CO.sub.2. This simple circuit does not include any mechanisms for high-side pressure modulation, and the pressure will therefore be determined by the operating conditions and the system design.
A serious drawback in trans-critical operation of a system that is designed in accordance with common practice from conventional subcritical units is that, most likely, a relatively low refrigerating capacity and a poor efficiency will be obtained, due to far from optimum high side pressures during operation. This will result in a considerable reduction in capacity as supercritical conditions are established in the high side of the circuit. The loss in refrigerating capacity may be compensated for by increased compressor volume, but then at the cost of significantly higher power consumption and higher investments.
Another major disadvantage in trans-critical operation of a conventionally designed system is that leakage of refrigerant will immediately affect the high side pressure, due to the reduction in high-side charge. At supercritical high side conditions, the pressure is determined by the relation between instant refrigerant charge and component volumes, similar to the conditions in a gas-charged pressure vessel.
Still another disadvantage is that excessive pressures can easily build up in a fully charged non-operating system subjected to high ambient temperatures. The latter effect can cause damage, or can be taken into account in the design, but then at the cost of heavy, voluminous and expensive components and tubes.
It is therefore a major object of the present invention to provide a simple, efficient and reliable vapour compression system avoiding these and other shortcomings.
BRIEF DESCRIPTION OF THE DRAWINGS
This and other objects and features of the invention are discussed in more detail below with reference to the accompanying drawings, wherein:
FIG. 1 is a schematic illustration of a conventional vapour compression circuit modified in accordance with one embodiment of the invention.
FIG. 2 is a graphical illustration of the relationship between a gas cooler refrigerant outlet temperature and a high-side pressure of such circuit at supercritical conditions, and
FIG. 3 is a schematic illustration of a preferred embodiment of a transcritical vapour compression cycle device constructed in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1 a conventional vapour compression circuit includes a compressor 1, a heat rejecting heat exchanger 2, an expansion device 3 and an evaporating heat exchanger 4 connected in series.
During trans-critical cycle operation of such circuit, a high-side pressure providing a maximum ratio between refrigerating capacity and compressor shaft power should be provided. A major parameter in the determination of the magnitude of this "optimum" pressure level is the refrigerant temperature at the outlet of the heat rejecting heat exchanger 2, i.e.
REFERENCES:
patent: 1408453 (1922-03-01), Goosmann
patent: 3323318 (1967-06-01), Fisher
patent: 4094169 (1978-06-01), Schmerzler
patent: 4185469 (1980-01-01), Rogers et al.
patent: 4205532 (1980-06-01), Brenan
Sinvent A/S
Wayner William E.
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