CO2 cooling and heating apparatus and method having multiple refrigerating cycle circuits

Abstract

A CO2 cooling and heating apparatus and method permit simultaneous production of high-temperature heat source and low-temperature heat source having a temperature difference therebetween. The apparatus/method uses CO2 (carbon dioxide) as a refrigerant, and has a first refrigerating cycle circuit where the refrigerant is compressed to a supercritical zone and then decompressed via an expansion device to a pressure/temperature level of the CO2 triple point or below to thereby attain evaporation. The apparatus can include multistage compressors, intermediate cooler disposed in a first refrigerant flow path between a condenser and the expansion device. A second refrigerating cycle circuit having a second refrigerant flow path, which can branch off from the first refrigerant flow path or provided in an independent closed circuit, can be provided to carry out absorption of evaporation latent heat with the first refrigerant flow path to thereby maintain the pressure/temperature level of the CO2 triple point (Ptr) or above. A third refrigerating cycle circuit having a third refrigerant flow path also can be provided to carry out heat exchange with the second refrigerant flow path.

Description

BACKGROUND

A dual cooling device, comprising two refrigerating cycles of a high-temperature side and a low temperature side cycles, has been used to supply cooling fluid cooled to a very low temperature, in the range of minus tens of degrees C. For example, Japanese Laid-Open Patent Application No. 2004-170007 (hereafter Reference 1) discloses a refrigerator system that uses combined ammonia and CO₂ refrigerating cycles, where its high-temperature side refrigerating cycle uses ammonia as a refrigerant and its low-temperature side refrigerating cycle uses CO₂ as a refrigerant cooled and liquefied by a cascade condenser. A cooling fluid of a very low temperature, lower than the triple point temperature of CO₂ (−56° C.), can be produced by cooling the cooling fluid with the CO₂ refrigerant, which has a lower temperature than the triple point temperature of CO₂, by allowing the CO₂ refrigerant in the low temperature refrigerating cycle to expand to the pressure/temperature level of the CO₂ triple point or below. The CO₂ refrigerant is reduced to a two-phase mixture of solid CO₂ and CO₂ gas by means of an expansion valve provided downstream of the cascade condenser for cooling the CO₂ refrigerant.

Japanese Laid-Open Patent Application No. 2004-308972 (hereafter Reference 2) discloses a CO₂ refrigerator comprising compressors for compressing a CO₂ refrigerant to a saturation or supercritical pressure, an expansion device for decreasing the pressure of condensed CO₂ refrigerant from a condenser to the pressure/temperature level of the CO₂ triple point or below so that the CO₂ refrigerant is reduced to a two-phase mixture of solid CO₂ and CO₂ gas, and a sublimation heat exchanger for allowing the solid CO₂ to sublimate by receiving heat from cooling fluid from cooling loads and send the sublimated CO₂ gas to the compressors. Further, a cascade heat exchanger cools the high-pressure CO₂ gas in the condenser with the refrigerant of a high-temperature side refrigerating cycle such as an ammonia refrigerating cycle.

Although References 1 and 2 disclose supplying cooling fluid to cooling loads, a high-temperature heat source cannot be produced simultaneously. Further, as the CO₂ refrigerant is expanded to the pressure/temperature level of the CO₂ triple point to reduce the CO₂ refrigerant to a two-phase mixture of solid CO₂ and CO₂ gas, and the latent heat of sublimation of the solid CO₂ is used to cool the cooling fluid, the refrigerant flow path can clog or the refrigerant flow path can lose pressure, resulting in unstable operation of the refrigerator.

Accordingly, there remains a need for a CO₂ cooling and heating apparatus (hereafter sometimes referred to simply as the apparatus) having an improved coefficient of performance with stable operation control, and capable of producing a high-temperature heat source and a low temperature cold heat source simultaneously by effectively taking the advantages of CO₂. A CO₂ refrigerant is, not only environmentally friendly since its ozone depleting potential of zero, it is also innoxious, inflammable, and inexpensive. By utilizing the advantage of a heat pump cycle using a CO₂ refrigerant that it is very efficient in producing a hot-water supply. The present invention addresses this need.

SUMMARY OF THE INVENTION

The present invention relates to a cooling and heating apparatus and method having a plurality of refrigerating cycle circuits, with at least one of the circuits using CO₂ (carbon dioxide) as a refrigerant or a primary refrigerant.

According to the present invention, one of the refrigerating cycle circuits operates so that the CO₂ refrigerant is cooled to the pressure/temperature level of the CO₂ triple point or below to reduce CO₂ to a two-phase mixture of solid CO₂ and CO₂ gas, thereby producing a high temperature heat source and a very low temperature cold source simultaneously with stable control of operation and improved coefficient of performance.

One aspect of the present invention is a CO₂ cooling and heating apparatus. The apparatus can include first and second refrigerating cycle circuits. The circuit includes a first refrigerant flow path, a first compressor in the first refrigerant flow path for pressurizing a CO₂ refrigerant to the supercritical region of CO₂, a condenser in the first refrigerant flow path downstream from the first compressor for condensing the pressurized refrigerant, a first intermediate cooler in the first refrigerant flow path downstream of the condenser for further cooling the condensed refrigerant, a first expansion device in the first refrigerant flow path downstream of the first intermediate cooler for further cooling and condensing the refrigerant to a pressure/temperature level of the CO₂ triple point or below to reduce the refrigerant to a mixture of solid CO₂ and CO₂ gas, an evaporator in the first refrigerant flow path downstream of the first expansion device for sublimating the solid CO₂ in the mixture, a second compressor in the first refrigerant flow path downstream of the evaporator for compressing the refrigerant. The refrigerant compressed by the second compressor is introduced into the first compressor.

The second circuit can include a second refrigerant flow path including a first branch path branching off the first refrigerant flow path at a point between the condenser and the first intermediate cooler, a second expansion device in the second refrigerant flow path for further cooling and evaporating part of the refrigerant from the condenser, the first intermediate cooler also in the second refrigerant flow path for further cooling the refrigerant in the first refrigerant flow path and for evaporating the refrigerant in the second refrigerant flow path by heat exchange. The refrigerant passing through the second expansion device is introduced into the first intermediate cooler in the second refrigerant flow path, and the refrigerant passing through the first intermediate cooler is introduced to the first refrigerant flow path between the first compressor and the second compressor so that the second refrigerating cycle circuit operates above the pressure/temperature level of the CO₂ triple point.

The apparatus can further include a second intermediate cooler in the first refrigerant flow path between the first intermediate cooler and the first expansion device, a third compressor in the first refrigerant flow path between the first and second compressors, and a third refrigerating cycle circuit. The third circuit can include a third refrigerant flow path including a second branch path branching off the first refrigerant flow path at a point between the first intermediate cooler and the second intermediate cooler, a third expansion device in the third refrigerant flow path for further cooling and evaporating part of the refrigerant from the first intermediate cooler in the path of the first refrigerant flow path, the second intermediate cooler also in the third refrigerant flow path for further cooling the refrigerant in the first refrigerant flow path and for evaporating the refrigerant in the third refrigerant flow path by heat exchange. The refrigerant passing through the third expansion device is introduced into the first intermediate cooler in the third refrigerant flow path, and the refrigerant passing through the second intermediate cooler is introduced to the first refrigerant flow path between the second compressor and the third compressor so that the third refrigerating cycle circuit operates above the pressure/temperature level of the CO₂ triple point.

The first and second or first, second, and third compressors can be connected in series. The first expansion device can comprise an expansion valve, and the second or third expansion device can comprises a capillary tube or an expansion turbine. The condenser can be a heat exchanger that supplies heated water, and the evaporator can be a heat exchanger that supplies cooling fluid.

According to another embodiment, the apparatus can include first, second, and third refrigerating cycle circuits. The first circuit can include a first compressor for compressing a CO₂ refrigerant to the supercritical region of CO₂, a condenser for condensing the refrigerant compressed by the first compressor, a first expansion device for expanding the refrigerant condensed by the condenser, a first cascade condenser having an evaporating part for vaporizing the refrigerant expanded by the first expansion device. The first compressor compresses the refrigerant vaporized by the first cascade condenser to the supercritical region of CO₂ so that the first refrigerating cycle circuit operates above a pressure/temperature level of the CO₂ triple point.

The second circuit can include a second compressor for compressing a refrigerant of ammonia, HC, or CO₂, the first cascade condenser having a condensing part for condensing the refrigerant compressed by the second compressor, a second expansion device for expanding the refrigerant condensed by the first cascade condenser, and a second cascade condenser having an evaporating part for vaporizing the refrigerant condensed by the second expansion device. The second compressor compresses the refrigerant vaporized by the second cascade condenser so that the second refrigerating cycle circuit operates above the pressure/temperature level of the CO₂ triple point

The third circuit can include a third compressor for compressing a CO₂ refrigerant, the second cascade condenser having a condensing part for condensing the refrigerant compressed by the third compressor, a third expansion device for expanding the refrigerant condensed by the second cascade condenser to the pressure/temperature level of the CO₂ triple point or below to reduce the refrigerant to a mixture of solid CO₂ and CO₂ gas, a sublimation heat exchanger for sublimating the solid CO₂. The third compressor compresses the refrigerant sublimated by the sublimation heat exchanger.

The apparatus can include a fourth refrigerating cycle circuit that uses a refrigerant of CH gas or air or nitrogen gas, and includes the sublimation heat exchanger, which comprises a third cascade condenser that sublimates the solid CO₂ in the third refrigerating cycle circuit.

Each of the first, second, and third cascade condensers can be a direct contact type heat exchanger where heat exchange occurs from a direct contact of a higher-temperature side refrigerant with a lower-temperature side refrigerant.

The apparatus can further include a closed circuit for receiving the refrigerant in liquid phase from the first or third refrigerating cycle circuit, and a refrigerant path provided with a heat exchanger connected to the closed circuit. The closed circuit can have a liquid phase line part and a gas phase line part. The liquid phase line part supplies the refrigerant in liquid phase to the heat exchanger, which vaporizes the refrigerant in liquid phase. The gas phase line part can return the vaporized refrigerant from the heat exchanger. The closed circuit can be provided for each of the first and third refrigerating cycle circuits. A gas-liquid separator can be in the closed circuit between the gas phase line part and the liquid phase line part.

The first, second, and third expansion devices each can be one of an expansion valve, a capillary tube, or an expansion turbine. The condenser can be a heat exchanger that supplies heated water, and the sublimation heat exchanger can supply cooling fluid.

Another aspect of the present invention is a method of cooling and heating fluid. The method includes providing at least first and second refrigerating cycle circuits, operating one of the first and second refrigerating cycle circuits with a CO₂ refrigerant to achieve a pressure/temperature level above the CO₂ triple point so that solid CO₂ is not produced, operating the other of the first and second refrigerating cycle circuits with a CO₂ refrigerant to achieve a pressure/temperature level of the CO₂ triple point or below to reduce CO₂ to a two-phase mixture of solid CO₂ and CO₂ gas, exchanging heat between the refrigerants in the first and second refrigerating cycle circuits to evaporate the refrigerant in the one circuit and evaporate the refrigerant in the other circuit, exchanging heat between the refrigerant in the one circuit and fluid to be heated to obtained heated fluid, and exchanging heat between the refrigerant in the other circuit and fluid to be cooled to obtain cooled fluid. The heated fluid and the cooled fluid are simultaneously obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a first embodiment of a CO₂ cooling and heating apparatus according to the present invention.

FIG. 2 is a pressure-enthalpy diagram of the first embodiment.

FIG. 3 is a block diagram of a second embodiment of the apparatus according to the present invention.

FIG. 4 is a pressure-enthalpy diagram of the second embodiment.

FIG. 5 is a block diagram of a third embodiment of the apparatus according to the present invention.

FIG. 6 is a block diagram of a fourth embodiment of the apparatus according to the present invention.

FIG. 7A is a schematic elevational view of the cascade condenser 54 of the fourth embodiment.

FIG. 7B is a schematic plan view of the cascade condenser 54 of the fourth embodiment.

FIG. 8 is a block diagram of a fifth embodiment of the apparatus according to the present invention.

DETAILED DESCRIPTION

Preferred embodiments of the CO₂ cooling and heating apparatus will now be described with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, relative positions and so forth of the constituent parts in the embodiments shall be interpreted as illustrative only not as limitative of the scope of the present invention.

Referring to FIG. 1, which shows the first embodiment, reference numeral 1 is a refrigerant flow path of a first refrigerating cycle circuit using CO₂ as a refrigerant, and 2 is a refrigerant flow path of a second refrigerating cycle circuit also using CO₂ as a refrigerant. Reference numeral 3 is a high-pressure stage compressor for both the first and second refrigerating cycle circuits, 4 is a low-pressure stage compressor for the first refrigerating cycle circuit, and 5 is a condenser for both the first and second refrigerating cycle circuits. Reference numeral 6 is an intermediate cooler. The refrigerant flow path 2 (hereafter referred to as the second refrigerant flow path) of the second refrigerating cycle circuit branches off from the refrigerant flow path 1 (hereafter referred to as the first refrigerant flow path) of the first refrigerating cycle circuit at a point upstream of the intermediate cooler 6 and is connected via an expansion valve 9 to an evaporating part 6a of the intermediate cooler 6 and to the first refrigerant flow path 1 at a point c upstream of the high-pressure stage compressor 3. The first refrigerant flow path 1 flows through a condensing part 6b of the intermediate cooler 6, through a sublimating part 8a of a sublimation heat exchanger 8 via an expansion valve 7, and to the inlet of the low-pressure stage compressor 4.

Reference numeral 19 is a hot-water supply line. The condenser 5 heats water supplied to the hot-water line 19. Heated water is sent to heating loads not shown in the drawing. Reference numeral 10 is a cooling fluid supply line. Cooling fluid r supplied to the cooling fluid supply line 10 is cooled in the sublimation heat exchanger 8, heating the CO₂ refrigerant to sublimate it and sent to cooling loads not shown in the drawing. Ptr indicates a CO₂ triple point line, below which the CO₂ refrigerant is low, below the triple point temperature thereof.

The operation of the first embodiment will be explained with reference to FIGS. 1 and 2. In FIG. 2, which shows a pressure-enthalpy diagram of the first embodiment, Sl is the saturated liquid line, Sy is the saturated vapor line, Tk is an isothermal line, and K is the critical point (critical temperature of 31.1° C. and critical pressure of 7.38 MPa). Ptr indicates the triple point pressure (0.518 MPa) of the CO₂ refrigerant. The high-pressure stage compressor 3 in the first refrigerating cycle circuit compresses the CO₂ refrigerant to a supercritical state (A→B in FIG. 2). Then, water w cools and condenses the refrigerant in the condenser 5 (B→C in FIG. 2). The refrigerant heats water w, by heat exchange, to about 80° C. Heated water h is supplied to heating loads not shown in the drawing via the hot-water supply line 9.

On the other hand, part of the cooled refrigerant is branched off from the first refrigerant path 1 at a point before the intermediate cooler 6 flows to the second refrigerating path 2 to be reduced in pressure (C→D in FIG. 2) via expansion via the expansion valve 9 and partially vaporized (flash evaporated) by the expansion flows into the evaporating part 6a of the evaporator 6. The other part of the refrigerant not branched off flows into the condensing part 6b of the intermediate cooler 6 for further cooling (C→E in FIG. 2) by the flash evaporated branched refrigerant flowing through the evaporating part 6a and removing heat from the refrigerant flowing in the condensing part 6b. The flash evaporated branched refrigerant is fully evaporated in the evaporating part 6a through receiving heat from the refrigerant flowing in the condensing part 6b and joins the refrigerant of the first refrigerating cycle circuit (D→A and H→A in FIG. 2). The pressure/temperature level above the CO₂ triple point (−56° C., 0.515 MPa) is maintained in the second refrigerant flow path 2.

The refrigerant flowing out from the condensing part 6b is expanded adiabatically (E→F in FIG. 2) through the expansion valve 7 and flows into the sublimating part 8a of the sublimation heat exchanger 8. The refrigerant is reduced in pressure and temperature to a pressure/temperature level below the CO₂ triple point and reduced to a state of mixed solid CO₂ and CO₂ gas. In the sublimation heat exchanger 8, the solid part of the CO₂ refrigerant is sublimated (F→G in FIG. 2) by heat received from the cooling fluid supplied to the sublimation heat exchanger 8 through the cooling fluid supply line 10. On the other hand, cooling fluid r is cooled to very low temperature of −56° C. (the triple point temperature)˜−78° C. (saturated vapor temperature under atmospheric pressure). The refrigerant gas flowing out from the sublimation heat exchanger 8 is sucked into the low-pressure stage compressor 4 for compression (G→H in FIG. 2). Although not shown in FIG. 1, a cooler is provided between the low-pressure stage compressor 4 and the high-pressure stage compressor 3 to cool the CO₂ gas compressed by the compressor 4 to the temperature at A in FIG. 2.

According to the first embodiment, hot water of about 80° C. and cooling fluid of a very low temperature of −56° C. or lower can be produced simultaneously by allowing the apparatus using CO₂ as a refrigerant to operate a refrigerating cycle between the supercritical region of CO₂ and the low pressure/temperature region lower than the CO₂ triple point. As the pressure/temperature of the refrigerant is maintained higher than those of the CO₂ triple point in the second refrigerant flow path 2, solid CO₂ does not develop in the second refrigerant flow path 2, so that increase in flow resistance or clogging does not occur in the second refrigerant flow path 2. Further, as compression of refrigerant is performed in two stages, the coefficient of performance is increased. Moreover, the expansion valve 7, through which the refrigerant is expanded to the pressure/temperature of the CO₂ triple point or lower, is suitable to adopt a capillary tube or expansion turbine as the expansion device, by which increase in flow resistance or clogging in the first refrigerant flow path 1 can be prevented with certainty.

The second embodiment will be explained with reference to FIGS. 3 and 4. In the second embodiment, a third refrigerating cycle circuit is further added to the first embodiment. In FIGS. 3 and 4, devices and parts denoted with reference numerals the same as those of the first embodiment shown in FIG. 1 have the same construction and function as those in the first embodiment, and thus their explanation has been omitted. In the second embodiment, an intermediate-pressure stage compressor 14 is further included between the high-pressure stage compressor 3 and low-pressure stage compressor 4. A second intermediate cooler 12 is provided downstream of the intermediate cooler 6 in the first refrigerant flow path 1, and a refrigerant flow path 11 (hereafter referred to as the third refrigerant flow path) of the third refrigerating cycle circuit branches off from the first refrigerant flow path 1 at a point between the intermediate cooler 6 and second intermediate cooler 12. The refrigerant branched off to the third refrigerant flow path 11 is adiabatically expanded through an expansion valve 13 to be flash evaporated, and the flash evaporated refrigerant enters an evaporating part 12a of the second intercooler 12 for a full evaporation.

In the first refrigerant flow path 1, the refrigerant flowing through a condensing part 12b of the second intermediate cooler 12 is cooled by the branched and flash evaporated refrigerant flowing through the evaporating part 12a. On the other hand, the branched and flash evaporated refrigerant evaporates fully in the evaporating part 12a. The refrigerant vapor enters the first refrigerant flow path 1 at a point c′ between the low-pressure stage compressor 4 and the intermediate-pressure stage compressor 14. A pressure/temperature level above the CO₂ triple point is maintained in the third refrigerant flow path 11.

The operation of the second embodiment will be explained with reference to the P-h diagram of FIG. 4. The high-pressure stage compressor 3 compresses the refrigerant to the supercritical region (I→J in FIG. 4). Then the compressed refrigerant is cooled (J→L in FIG. 4) through water w flowing through the condenser 5. The refrigerant cooled in the condenser 5 is introduced to the intermediate cooler 6 and then to the second intermediate cooler 12. Thus, the refrigerant is cooled in two stages (L→C and C→E in FIG. 4) and condensed. The condensed refrigerant is expanded through the expansion valve 7 to the pressure/temperature level of the CO₂ triple point or lower (E→F in FIG. 4).

On the other hand, the refrigerant branched before entering the intermediate cooler 6 and expanded through the expansion valve 9 flows into the evaporating part 6a of the intermediate cooler 6, where the branched refrigerant flash evaporated through the expansion is fully evaporated and joins the refrigerant from the high-pressure stage compressor 3 at point c (L→M→I in FIG. 4). The refrigerant branched before entering the second intermediate cooler 12 and expanded through the expansion valve 13 flows into the evaporating part 12a of the second intermediate cooler 12, where the branched and flash evaporated refrigerant is fully evaporated and joins the refrigerant from the intermediate-pressure stage compressor 14 at point c′ (C→D→A in FIG. 4). Although not shown in FIG. 3, a cooler is provided between the low-pressure stage compressor 4 and intermediate-pressure stage compressor 14 to cool the CO₂ gas compressed by the compressor 14 to temperature at A in FIG. 4, and a cooler between the intermediate-pressure stage compressor 14 and the high-pressure stage compressor 3 to cool the CO₂ gas compressed by the compressor 4 to the temperature at I in FIG. 4.

According to the second embodiment, hot water h of about 80° C. and cooling fluid of a very low temperature of −56° C. or lower can be produced simultaneously as is with the first embodiment. In addition, as the refrigerant is compressed in three stages, the coefficient of performance is further increased.

In the first and second embodiments, the first and second (and third in the second embodiment) refrigerating cycle circuits share part of the first flow path as these circuits are not isolated from each. In the third, fourth, and fifth embodiments, however, each of the refrigerating cycle circuits are completely isolated from each other. That is, the different circuits do not share the same refrigerants as in the first and second embodiments.

The third embodiment will be explained with reference to FIG. 5. In the third embodiment, a first refrigerating cycle circuit 21 includes a compressor 23, a condenser 24, an expansion valve 25, an evaporating part 26a of a first cascade condenser 26, and a first refrigerant flow path 22, with CO₂ as a refrigerant. A second refrigerating cycle circuit 31 and a third refrigerating cycle circuit 41 are also provided, which are explained below. In the first refrigerant cycle circuit 21, the CO₂ refrigerant is compressed adiabatically by the compressor 23 to the supercritical region of CO₂, then cooled in the condenser 24 by water w, then expanded adiabatically through the expansion valve 25, then introduced to the evaporating part 26a of the first cascade condenser 26. In the first cascade condenser 26, the refrigerant flash evaporated through the expansion valve receives heat from the refrigerant of the second refrigerating cycle circuit 31 flowing in a condensing part 26b of the first cascade condenser 26 to be fully evaporated, and the refrigerant vapor returns to the compressor 23. Water w flowing in a hot-water supply line 27 is heated in the condenser to about 80° C., and heated water h is supplied to heating loads not shown in the drawing.

The second refrigerating cycle circuit 31 can use ammonia or HC or CO₂ as a refrigerant. The second refrigerating cycle circuit includes a compressor 33, a condensing part 26b of the first cascade condenser 26, an expansion valve 34, an evaporating part 35a of a second cascade condenser 35, and a second refrigerant flow path 32. In the second refrigerating cycle circuit 31, the refrigerant compressed by the compressor 33 is introduced to the condensing part 26b of the first cascade condenser 26, where the refrigerant is cooled by the CO₂ refrigerant of the first refrigerating cycle circuit 21 flowing in the evaporating part 26a and condensed. The condensed refrigerant is expanded adiabatically through the expansion valve 34 to be flash evaporated, and flows into the evaporating part 35a of the cascade condenser 35. The flash evaporated refrigerant is fully evaporated in the evaporating part 35a of the cascade condenser 35 through heat received from the refrigerant of the third refrigerating cycle circuit flowing in a condensing part 35b of the cascade condenser 35, and the refrigerant vapor returns to the compressor 33. When a CO₂ refrigerant is used in the second refrigerating cycle circuit 31, the cycle circuit is operated under the pressure/temperature level above the CO₂ triple point.

The third refrigerating cycle circuit 41 uses CO₂ as a refrigerant. The cycle circuit includes a compressor 43, the condensing part 35b of the cascade condenser 35, an expansion valve 44, a sublimation heat exchanger 45, and a third refrigerant flow path 42. In the third refrigerating cycle circuit 41, the CO₂ refrigerant is expanded through the expansion valve 44 to a pressure/temperature level below the CO₂ triple point and reduced to a two-phase mixture of solid CO₂ and CO₂ gas. The solid CO₂ is sublimated in the sublimating part 45a of the sublimation heat exchanger 45 through heat received from cooling fluid r supplied through a cooling load line 46, and cooling fluid r can be cooled to very low temperature of −56° C.˜−78° C.

According to the third embodiment, heated water of about 80° C. for hot-water supply and cooling fluid of a very low temperature of −56° C.˜−78° C. for cooling loads can be produced simultaneously. As the first refrigerating cycle circuit 21 and the second refrigerating cycle circuit 31 are operated in the region of pressure/temperature above the CO₂ triple point, solid CO₂ does not develop and increase in refrigerant flow resistance or clogging does not occur, and stable refrigerating operation is assured. As the second refrigerating cycle circuit 31 is operated using ammonia or HC as a refrigerant, the cycle circuit can be operated with high efficiency.

The fourth embodiment will be explained with reference to FIG. 6, FIG. 7A, and FIG. 7B. In the fourth embodiment further adds to the third embodiment shown in FIG. 5, a fourth refrigerating cycle circuit 51 in which CH gas or air or nitrogen gas can be used as a refrigerant, thereby enabling supply of extremely low temperature cold heat source. In FIG. 6, devices and parts denoted with reference numerals the same as those of the third embodiment shown in FIG. 5 have the same construction and function as those in the third embodiment, and thus explanation has been omitted. The fourth refrigerating cycle circuit 51 uses air or nitrogen as a refrigerant, and the cycle circuit includes a compressor 53, a third cascade condenser 54 instead of the sublimation heat exchanger 45 of the third embodiment of FIG. 5, an expansion turbine 55, a sublimation heat exchanger 57, and a fourth refrigerant flow passage 52. Reference numeral 56 is a drive motor for driving the compressor 53. The drive motor 56 is composed as a recovery motor driven by the expansion turbine 55.

In the fourth refrigerating cycle circuit 51, the refrigerant compressed by the compressor 53 is cooled in the third cascade condenser 54 by the refrigerant of the third refrigerating cycle circuit 41. The cooled refrigerant then expands adiabatically in the expansion turbine 55 to be reduced in temperature to −120° C. and introduced to the sublimation heat exchanger 57, where the refrigerant is sublimated through receiving heat from cooling fluid r supplied through a cooling load line 58, and cooling fluid r is cooled to an extremely low temperature of approximately −100° C.

In FIGS. 7A and 7B, which show the third cascade condenser 54 in elevation and plan view respectively. The third cascade condenser 54 is formed into a cyclone 540 having an inside hollow space. An inlet pipe 541 for introducing the CO₂ refrigerant of the third refrigerating cycle circuit 41 is provided horizontally and tangentially to the cyclone 540 at an upper part thereof. An inlet pipe 543 for introducing the refrigerant (CH gas or air or nitrogen gas) of the fourth refrigerating cycle circuit is provided horizontally and tangentially to the cyclone 540 at a lower part thereof. An outlet pipe 542 of the CO₂ refrigerant is provided horizontally and tangentially to the cyclone 540 at a lower part thereof, and an outlet pipe 544 of the air or nitrogen refrigerant is provided at the top of the cyclone 540. The molecular weight of CO₂ at 44 is heavier than that of air and nitrogen. Accordingly, the CO₂ refrigerant introduced into the cyclone 540 through the inlet pipe 541 flows down spirally along the inside wall of the cyclone 540 in a two-phase mixture state of solid CO₂ and CO₂ gas.

On the other hand, air or nitrogen introduced into the cyclone through the inlet pipe 543 flows upward spirally in the cyclone as it is lighter than the CO₂ refrigerant. The CO₂ refrigerant and air or nitrogen are introduced into the cyclone 540 so that they swirl in counter direction to each other and they flow out through the outlet pipes 544 and 542, respectively. As the third cascade condenser 54 is a direct contact type heat exchanger as explained above, it is superior in heat exchange efficiency. As the CO₂ refrigerant and air or nitrogen differ significantly in specific weight, they separate easily from each other in the cyclone 540 to flow out from the outlet pipe 544 and 542 respectively. According to the fourth embodiment, hot water of about 80° C. and an extremely low temperature cold source of −100° C. or below can be supplied simultaneously, resulting in the apparatus that is high in efficiency, and stable in operation can be provided.

The fifth embodiment will be explained with reference to FIG. 8. In the fifth embodiment, the first refrigerating cycle circuit 21, the second refrigerating cycle circuit 31, and the third refrigerating cycle circuit 41 are composed the same as those of the third embodiment of FIG. 5. Accordingly, the same reference numerals are used, and explanation thereof have been omitted. In FIG. 8, reference numeral 28 and 36 are a gas-liquid separator, respectively. A liquid phase part 28b in the separator 28 is communicated through a branch path 29 to the first refrigerant flow path 22 at a point upstream of the expansion valve 25 via a branch path 29. A liquid phase part 36b in the separator 36 is communicated through a branch path 37 to the third refrigerant flow path 42 at a point upstream of the expansion valve 44.

Reference numerals 61 and 71 are respectively a closed loop for supplying cooling fluid located substantially horizontally in a building 60 such as a hospital, hotel, restaurant, and the like. The closed loop 61 is formed by connecting a gas line 61a thereof to a gas phase part 28a in the gas-liquid separator 28 and connecting a liquid line 61b to the liquid phase part 28b in the separator 28. The closed loop 71 is formed by connecting a liquid line 71a thereof to a gas phase part 36a in the gas-liquid separator 36 and connecting a liquid line 71b to the liquid phase part 36b in the separator 36. Refrigerants flow in the direction of arrows in the closed loop 61 and 71. A heat exchanger 63 is provided in a refrigerant circuit 62 connecting the liquid line 61b to the gas line 61a. The liquid refrigerant flowing in the liquid line 61b is introduced to the heat exchanger 63 where the liquid refrigerant is evaporated through heat received from cooling fluid r which has cooled cooling loads not shown in the drawing and the evaporated refrigerant returns to the gas line 61a of the closed loop 61.

A refrigerant circuit 72, provided with an expansion valve 73 and a heat exchanger 74, is provided between the liquid line 71b and gas line 71a to constitute a refrigerating cycle circuit. The CO₂ refrigerant liquid taken out from the liquid line 71b expands adiabatically through the expansion valve 73 to be flash evaporated and the flash evaporated refrigerant is evaporated in the heat exchanger 74 through heat received from cooling fluid r, which has cooled cooling loads not shown in the drawing, and the evaporated refrigerant returns to the gas line 71a of the closed loop 71. The closed loops 61 and 71 are disclosed in Japanese Laid-Open Patent Application No. 2003-329318, the disclosure of which is incorporated herein by reference.

According to the fifth embodiment, hot water of about 80° C. and an extremely low temperature cold source of near −80° C. can be supplied simultaneously and can meet various demands of heat source and cold source for a buildings, such as hospitals, hotels, restaurants, and the like. Refrigerants supplied to the closed loops 61 and 71 in buildings are CO₂, which is a natural refrigerant, innoxious, and safe in refrigeration operation. As the first and second refrigerating cycles are operated above the pressure/temperature level of the CO₂ triple point and refrigerants flows in the closed loops 61, 71 located in buildings in a pressure/temperature level above the CO₂ triple point, increase in flow resistance or clogging in the refrigerant passages does not occur, and stable and efficient operation can be achieved.

The CO₂ apparatus can have an improved coefficient of performance with stable control of operation, and is capable of supplying high temperature hot water and extremely low temperature cold source simultaneously, thereby meeting various demands for heat source and cold source in a hospital, hotel, restaurant, or the like.

According to one configuration disclosed above, high temperature water of about 80° C., for example, can be supplied, as well as cooling fluid of −56° C.˜−80° C., for example, can be supplied to cooling loads. The apparatus can have a first refrigerating cycle circuit and a second refrigerating cycle circuit. The first refrigerating cycle circuit can include a CO₂ refrigerant flow path, a plurality of compressors connected in series to pressurize CO₂ to the supercritical region of CO₂, a condenser for cooling the pressurized CO₂, an intermediate cooler for further cooling the condensed CO₂, an expansion valve through which the further cooled and condensed CO₂ can be reduced to a pressure/temperature level of the CO₂ triple point or below to be reduced to a mixture of solid CO₂ and CO₂ gas, and an evaporator for sublimating the solid CO₂ in the mixture. The sublimated CO₂ gas can be introduced into the lowest pressure stage compressor among the plurality of the compressors, and the second refrigerating cycle circuit can be formed by providing a branch path branching off the CO₂ refrigerant flow path at a point between the condenser, the intermediate cooler, and an expansion device provided in the branch path so that a part of the cooled CO₂ flowing out of the condenser can be introduced via the expansion device to the intermediate cooler to be further cooled and evaporated therein, and the vaporized CO₂ can be introduced into one of said compressors between the highest pressure stage compressor and the lowest pressure stage compressor. Thus, the second refrigerating cycle circuit can be operated above the pressure/temperature level of the CO₂ triple point.

The second refrigerating cycle circuit can be operated in the pressure/temperature level above the CO₂ triple point, so that solid CO₂ is not produced, to thereby prevent flow resistance or blockage in the expansion device. The apparatus thus can be operated stably. Further, by using a plurality of compressors connected in series, the coefficient of performance of the refrigerating cycle can be increased. By adopting a capillary tube or expansion turbine as an expansion device in a cycle in which the CO₂ refrigerant is reduced to the pressure/temperature level of the CO₂ triple point to be in a state of a mixture of solid CO₂ and CO₂ gas, to prevent flow resistance or clogging in the refrigerant flow path.

According to the another configuration, again both high temperature water and very low temperature cooling fluid can be supplied to cooling loads as is in the first configuration by composing a CO₂ apparatus with combined refrigerating cycles comprising a first refrigerating cycle circuit, a second refrigerating circuit, and a third refrigerating circuit. In the first refrigerating cycle circuit, a CO₂ refrigerant is compressed to the supercritical region of CO₂, the compressed CO₂ is cooled and condensed in a condenser, the condensed CO₂ is expanded via an expansion device and evaporated in an evaporating part of a first cascade condenser, and the vaporized CO₂ refrigerant is again compressed to the supercritical region of CO₂, the cycle circuit being operated above the pressure/temperature level of the CO₂ triple point. In the second refrigerating cycle circuit, which can use ammonia, HC, or CO₂ as a refrigerant, the refrigerant is compressed, the compressed refrigerant is cooled and condensed in a condensing part of the first cascade condenser. The condensed refrigerant can be expanded via an expansion device and evaporated in an evaporating part of a second cascade condenser. The vaporized refrigerant can be again compressed, the cycle circuit being operated above a pressure/temperature level of CO₂ triple point. In the third refrigerating cycle circuit, a CO₂ refrigerant is compressed, the compressed CO₂ can be cooled and condensed in a condensing part of the second cascade condenser, the condensed CO₂ can be expanded via an expansion device to the pressure/temperature level of the CO₂ triple point or below to be reduced to a mixture of solid CO₂ and CO₂ gas, the solid CO₂ can be sublimated in a sublimation heat exchanger, and the sublimated CO₂ gas can be again compressed.

As the first and second refrigerating cycles can be operated in a pressure/temperature level of above the CO₂ triple point, increase in flow resistance or occurrence of clogging in the refrigerant flow path can be prevented. When using ammonia or HC refrigerant in the second refrigerating cycle circuit, the refrigerating efficiency can be further increased. When using CO₂ refrigerant in the second refrigerating cycle circuit, advantage of natural refrigerant CO₂ that it is safe and innoxious can be obtained, and as the same refrigerant can be used in the first and third refrigerating cycles, the apparatus can be reduced in total cost.

By further adding a fourth refrigerating cycle circuit in which CH gas, air or nitrogen gas can be used as a refrigerant, and the sublimation heat exchanger of the third refrigerating cycle circuit can be used as a third cascade condenser, it is possible to supply cooling fluid further decreased in temperature for example to about −120° C. By composing the first to third cascade condensers as direct contact type heat exchangers in which heat exchange is performed by direct contact of higher-temperature side refrigerant with lower-temperature side refrigerant, heat exchange efficiency can be increased.

By further adding a closed loop located substantially horizontally to which the liquid phase refrigerant of the first or third refrigerating cycle circuit can be introduced or closed loops each located substantially horizontally to each of which is introduced the liquid phase refrigerant of each of the first and third refrigerating cycles respectively, and a refrigerant path provided with a heat exchanger can be connected to each closed loop so that liquid phase refrigerant in a liquid phase line part of the closed loop is introduced to the heat exchanger to be evaporated there and the vaporized refrigerant is returned to a gas phase line part of the closed loop, hot water and cooling fluid can be supplied to hospitals, hotels, or restaurants where a variety of heat sources and cold sources are demanded. As CO₂, which is a natural refrigerant, circulates in the refrigerant paths connected to the closed loops, safety in the building can be secured.

Further, by providing a gas-liquid separator between the closed loop and the liquid phase refrigerant flowing part of the refrigerant flow path of the first refrigerating cycle circuit and/or the third refrigerating cycle circuit respectively, CO₂ in the liquid phase can be introduced positively to the closed loop.

The expansion device can be a capillary tube, expansion turbine, or expansion valve, or any known devices that allows expansion of the refrigerant.

While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details can be made therein without departing from the spirit and scope of the present invention. All modifications and equivalents attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention accordingly is to be defined as set forth in the appended claims.

Claims

1. A CO2 cooling and heating apparatus comprising: a first refrigerating cycle circuit comprising: a first refrigerant flow path;a first compressor in the first refrigerant flow path for pressurizing a CO2 refrigerant to the supercritical region of CO2;a condenser in the first refrigerant flow path downstream from the first compressor for condensing the pressurized refrigerant;a first intermediate cooler in the first refrigerant flow path downstream of the condenser for further cooling the condensed refrigerant;a first expansion device in the first refrigerant flow path downstream of the first intermediate cooler for further cooling and condensing the refrigerant to a pressure/temperature level of the CO2 triple point or below to reduce the refrigerant to a mixture of solid CO2 and CO2 gas;an evaporator in the first refrigerant flow path downstream of the first expansion device for sublimating the solid CO2 in the mixture;a second compressor in the first refrigerant flow path downstream of the evaporator for compressing the refrigerant,wherein the refrigerant compressed by the second compressor is introduced into the first compressor; anda second refrigerating cycle circuit comprising: a second refrigerant flow path including a first branch path branching off the first refrigerant flow path at a point between the condenser and the first intermediate cooler;a second expansion device in the second refrigerant flow path for further cooling and evaporating part of the refrigerant from the condenser; andthe first intermediate cooler also in the second refrigerant flow path for further cooling the refrigerant in the first refrigerant flow path and for evaporating the refrigerant in the second refrigerant flow path by heat exchange,wherein the refrigerant passing through the second expansion device is introduced into the first intermediate cooler in the second refrigerant flow path, andwherein the refrigerant passing through the first intermediate cooler is introduced to the first refrigerant flow path between the first compressor and the second compressor so that the second refrigerating cycle circuit operates above the pressure/temperature level of the CO2 triple point.

2. The CO2 cooling and heating apparatus according to claim 1, further comprising: a second intermediate cooler in the first refrigerant flow path between the first intermediate cooler and the first expansion device;a third compressor in the first refrigerant flow path between the first and second compressors; anda third refrigerating cycle circuit comprising:a third refrigerant flow path including a second branch path branching off the first refrigerant flow path at a point between the first intermediate cooler and the second intermediate cooler;a third expansion device in the third refrigerant flow path for further cooling and evaporating part of the refrigerant from the first intermediate cooler in the path of the first refrigerant flow path,the second intermediate cooler also in the third refrigerant flow path for further cooling the refrigerant in the first refrigerant flow path and for evaporating the refrigerant in the third refrigerant flow path by heat exchange,wherein the refrigerant passing through the third expansion device is introduced into the first intermediate cooler in the third refrigerant flow path, andwherein the refrigerant passing through the second intermediate cooler is introduced to the first refrigerant flow path between the second compressor and the third compressor so that the third refrigerating cycle circuit operates above the pressure/temperature level of the CO2 triple point.

3. The CO2 cooling and heating apparatus according to claim 1, wherein the first and second compressors are connected in series.

4. The CO2 cooling and heating apparatus according to claim 2, wherein the first, second, and third compressors are connected in series.

5. The CO2 cooling and heating apparatus according to claim 1, wherein the first expansion device comprises an expansion valve and the second expansion device comprises a capillary tube or an expansion turbine.

6. The CO2 cooling and heating apparatus according to claim 2, wherein the first expansion device comprises an expansion valve and the second and third expansion devices each comprise a capillary tube or an expansion turbine.

7. The CO2 cooling and heating apparatus according to claim 1, wherein the condenser comprises a heat exchanger that supplies heated water, and wherein the evaporator comprises a heat exchanger that supplies cooling fluid.

8. A CO2 cooling and heating apparatus comprising: a first refrigerating cycle circuit comprising: a first compressor for compressing a CO2 refrigerant to the supercritical region of CO2;a condenser for condensing the refrigerant compressed by the first compressor;a first expansion device for expanding the refrigerant condensed by the condenser; anda first cascade condenser having an evaporating part for vaporizing the refrigerant expanded by the first expansion device,wherein the first compressor compresses the refrigerant vaporized by the first cascade condenser to the supercritical region of CO2 so that the first refrigerating cycle circuit operates above a pressure/temperature level of the CO2 triple point;a second refrigerating cycle circuit comprising: a second compressor for compressing a refrigerant of ammonia, HC, or CO2;the first cascade condenser having a condensing part for condensing the refrigerant compressed by the second compressor;a second expansion device for expanding the refrigerant condensed by the first cascade condenser; anda second cascade condenser having an evaporating part for vaporizing the refrigerant condensed by the second expansion device,wherein the second compressor compresses the refrigerant vaporized by the second cascade condenser so that the second refrigerating cycle circuit operates above the pressure/temperature level of the CO2 triple point; anda third refrigerating cycle circuit comprising: a third compressor for compressing a CO2 refrigerant;the second cascade condenser having a condensing part for condensing the refrigerant compressed by the third compressor;a third expansion device for expanding the refrigerant condensed by the second cascade condenser to the pressure/temperature level of the CO2 triple point or below to reduce the refrigerant to a mixture of solid CO2 and CO2 gas; anda sublimation heat exchanger for sublimating the solid CO2,wherein the third compressor compresses the refrigerant sublimated by the sublimation heat exchanger.

9. The CO2 cooling and heating apparatus according to claim 8, further including a fourth refrigerating cycle circuit that uses a refrigerant of CH gas or air or nitrogen gas, and includes the sublimation heat exchanger, which comprises a third cascade condenser that sublimates the solid CO2 in the third refrigerating cycle circuit.

10. The CO2 cooling and heating apparatus according to claim 8, wherein the first and second cascade condensers are direct contact type heat exchangers where heat exchange occurs from a direct contact of a higher-temperature side refrigerant with a lower-temperature side refrigerant.

11. The CO2 cooling and heating apparatus according to claim 9, wherein the first, second, and third cascade condensers are direct contact type heat exchangers where heat exchange occurs from a direct contact of a higher-temperature side refrigerant with a lower-temperature side refrigerant.

12. The CO2 cooling and heating apparatus according to claim 8, further comprising: a closed circuit for receiving the refrigerant in liquid phase from the first or third refrigerating cycle circuit; anda refrigerant path provided with a heat exchanger connected to the closed circuit,wherein the closed circuit has a liquid phase line part and a gas phase line part,wherein the liquid phase line part supplies the refrigerant in liquid phase to the heat exchanger, which vaporizes the refrigerant in liquid phase, andwherein the gas phase line part returns the vaporized refrigerant from the heat exchanger.

13. The CO2 cooling and heating apparatus according to claim 12, wherein the closed circuit is provided for each of the first and third refrigerating cycle circuits.

14. The CO2 cooling and heating apparatus according to claim 12, further including a gas-liquid separator in the closed circuit between the gas phase line part and the liquid phase line part.

15. The CO2 cooling and heating apparatus according to claim 13, further including a gas-liquid separator in each of the closed circuits between the gas phase line part and the liquid phase line part.

16. The CO2 cooling and heating apparatus according to claim 8, wherein the first, second, and third expansion devices each comprises one of an expansion valve, a capillary tube, or an expansion turbine.

17. The CO2 cooling and heating apparatus according to claim 8, wherein the condenser comprises a heat exchanger that supplies heated water, and wherein the sublimation heat exchanger supplies cooling fluid.

18. A method of cooling and heating fluid comprising the steps of: providing at least first and second refrigerating cycle circuits;operating one of the first and second refrigerating cycle circuits with a CO2 refrigerant to achieve a pressure/temperature level above the CO2 triple point so that solid CO2 is not produced;operating the other of the first and second refrigerating cycle circuits with a CO2 refrigerant to achieve a pressure/temperature level of the CO2 triple point or below to reduce CO2 to a two-phase mixture of solid CO2 and CO2 gas;exchanging heat between the refrigerants in the first and second refrigerating cycle circuits to evaporate the refrigerant in the one circuit and evaporate the refrigerant in the other circuit;exchanging heat between the refrigerant in the one circuit and fluid to be heated to obtained heated fluid; andexchanging heat between the refrigerant in the other circuit and fluid to be cooled to obtain cooled fluid,wherein the heated fluid and the cooled fluid are simultaneously obtained.