Refrigerant system with cascaded circuits and performance enhancement features

Abstract

An improved refrigerant system incorporates at least two circuits arranged in a cascaded relationship. Preferably, the upper circuit utilizes a hydrocarbon refrigerant and preferably the lower circuit utilizes CO2 refrigerant. Preferably, the CO2 circuit mainly operates in a subcritical region. To improve the efficiency and capacity control of the cascaded refrigerant system, at least one of the circuits is equipped with performance enhancement features such as, for example, an economized function provided by a flash tank or economizer heat exchanger. Additional enhancement features can also include a liquid-suction heat exchanger and bypass function.

Description

BACKGROUND OF THE INVENTION[0001]This application relates to refrigerant systems with at least two cascaded circuits, and more particularly, to cascade refrigerant systems with performance enhancement features.[0002]For instance, two distinct refrigerants can be utilized in each of the two circuits, with a hydrocarbon refrigerant utilized only in the upper stage circuit and another refrigerant utilized in the lower stage circuit. The hydrocarbon type of refrigerant can be, for example, propane or isobutene refrigerant. Since the upper stage circuit can be located outside of the enclosed conditioned compartment, it would offer an advantage of locating the flammable refrigerant also outside of the enclosed space, which would mitigate flammability concerns of these refrigerants. By utilizing the two cascaded circuits, the amount of charge in the upper stage circuit would be substantially reduced as compared to a single circuit refrigerant system. Since the amount of charge in the upper...

AI Technical Summary

Benefits of technology

[0010]In this invention, cascaded refrigerant circuits are incorporated into a refrigerant system design. As one particular application, an upper stage circuit includes a hydrocarbon refrigerant, such as for example propane or isobutene, which can be located outdoors. The upper stage circuit is positioned in a cascaded relationship with a lower stage circuit, which would normally utilize the CO2 refrigerant. The upper stage circuit is mainly located in the outdoor environment, while the lower stage circuit is normally located in the indoor environment. However, other locations would also fall within the scope of this invention. As one of the features of this invention, the lower stage inside CO2 circuit operates in a subcritical region while the upper stage outside cascaded circuit would operate in a transcritical region if it was charged with the same CO2 refrigerant. The combination of the two circuits provides performance enhancements for the supercritical region operation of the CO2 circuit. To enhance the operation of the cascaded refrigerant system at least one of the circuits can be equipped with the economized cycle, utilizing either economizer heat exchanger or flash tank arrangements. Additionally, or as a stand alone feature, at least one of the circuits can be equipped with a liquid suction heat exchanger. Further, an unloading feature can be provided for one or both cascaded refrigerant circuits.

Problems solved by technology

However, there are challenges for a refrigerant system designer with regard to utilizing CO2.

Therefore, refrigerant systems utilizing CO2 as a refrigerant do not always operate at the efficiency levels of traditional refrigerant systems.

However, even after splitting a single circuit into two independent cascaded circuits, the refrigerant system designer is still faced with many challenges dealing with further improvements of the system efficiency and capacity control.

However, none of the above-referenced enhancement features has been incorporated into a cascaded refrigerant system.

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