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Refrigerant composition

Refrigerant composition description/claims

The present invention relates to a refrigerant composition containing dimethyl ether and carbon dioxide used for a heat pump hot water supply.

Carbon dioxide has zero ozone-depleting potential, global warming potential of exactly 1 and extremely small environmental load as well as absence of toxicity, and flammability, safety, low price, and a low critical temperature of 31.1° C. Since in an air conditioning system and a hot-water system, heating can be performed even in a small temperature difference between the refrigerant and the refrigerated fluid due to readily attaining the supercritical point in a high pressure side of the cycling. As a result, in the heating process with large warm-up range as like hot-water supply, carbon dioxide is currently widely used as the refrigerant for a heat pump hot water supply under the naming of “ecocute”, since high coefficient of performance can be obtained; high heating ability in input volume per unit of compressor can be expected; and high thermal conductivity can be obtained.

However, since a working pressure of a carbon dioxide refrigerant is rather high as about 10 MPa compared with other refrigerants and as a result, each and every part of the system device should be assembled by super high pressure specifications, development of an elemental technology of the cycle system with appropriate prices remains a big issue.

An object of the present invention is to provide a safe, non-toxic refrigerant composition for hot water supply/heating as an alternative to carbon dioxide supercritical refrigerant. Such refrigerant composition has a small risk for depleting the ozone layer, has small damaging effect on the global warming, exhibits incombustibility or fire retardancy, and operates at lower pressures while exhibiting excellent performance.

Carbon dioxide has a critical temperature of 31.1° C. and a boiling point of −56.6° C., whereas dimethyl ether has a critical temperature of 126.85° C. and a boiling point of −25° C., indicating a great difference between the two in their physical property. For that reason, carbon dioxide is utilized as a refrigerant in a very high pressure region such as low pressure at about 3 MPa to high pressure at about 10 MPa, whereas dimethyl ether is utilized as a refrigerant in a comparatively low pressure region such as low pressure at about 0.7 MPa to high pressure at about 2 MPa, and is known to exert best performance as the refrigerant under such pressure condition. Consequently, although carbon dioxide and dimethyl ether have been used alone as the refrigerant, an idea of trying to utilize as the refrigerant by mixing carbon dioxide and dimethyl ether having completely different properties has not been made or examined.

Contrary to that, the present inventors have tried to perform an assessment test and a macroscopic test on solubility of carbon dioxide in dimethyl ether and have confirmed that although the amount of mass transfer (dissolved amount) to gas-liquid equilibrium is changed depending on the conditions of temperature and pressure, carbon dioxide was dissolved and diffused well in dimethyl ether. The present inventors have considered the possibilities of obtaining physical properties showing extremely high thermal efficiency by mixing carbon dioxide which has physically high efficiency of heat transfer (0.02 W/mK) and dimethyl ether which has higher specific heat (138 J/molK), continued the development and simulation, and found that the mixture of dimethyl ether and carbon dioxide was a refrigerant for heating/hot water supply which could operate at low pressure while exhibiting excellent coefficient of performance, and completed the present invention.

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