Sublimation defrost system and sublimation defrost method for refrigeration apparatus

Abstract

A sublimation defrost system for a refrigeration apparatus including: a cooling device in a freezer, and includes a casing containing a heat exchanger pipe; a refrigerating device for cooling and liquefying a CO.sub.2 refrigerant; and a refrigerant circuit connected to the heat exchanger pipe permitting the cooled and liquefied CO.sub.2 refrigerant to circulate. The defrost system includes: a dehumidifier device; a CO.sub.2 circulation path in the heat exchanger pipe, an on-off valve in the heat exchanger; a circulating unit for the CO.sub.2 refrigerant; a first heat exchanger part exchanging heat between a brine as a first heating medium and the circulating CO.sub.2 refrigerant; and a pressure adjusting unit for the circulating CO.sub.2 refrigerant during defrosting so that a condensing temperature of the CO.sub.2 refrigerant becomes equal to or lower than a freezing point of a water vapor in the freezer inner air without a drain receiving unit.

Claims

1. A sublimation defrost system for a refrigeration apparatus including: a cooling device which is disposed in a freezer, and includes a casing and a heat exchanger pipe disposed in the casing; a refrigerating device for cooling and liquefying a CO.sub.2 refrigerant; and a refrigerant circuit which is connected to the heat exchanger pipe and which is configured to permits the CO.sub.2 refrigerant cooled and liquefied in the refrigerating device to circulate to the heat exchanger pipe, the defrost system comprising: a dehumidifier device for dehumidifying freezer inner air in the freezer; a CO.sub.2 circulation path which is formed of a circulation path forming path connected to an inlet path and an outlet path of the heat exchanger pipe, and includes the heat exchanger pipe; an on-off valve disposed in each of the inlet path and the outlet path of the heat exchanger pipe and configured to be closed at a time of defrosting so that the CO.sub.2 circulation path becomes a closed circuit; a circulating unit for CO.sub.2 refrigerant, the circulating unit being disposed in the CO.sub.2 circulation path; a first heat exchanger part configured to cause heat exchange between a brine as a first heating medium and the CO.sub.2 refrigerant circulating in the CO.sub.2 circulation path; and a pressure adjusting unit which adjusts a pressure of the CO.sub.2 refrigerant circulating in the closed circuit at the time of defrosting so that a condensing temperature of the CO.sub.2 refrigerant becomes equal to or lower than a freezing point of a water vapor in the freezer inner air in the freezer; wherein the defrosting is able to be achieved without a drain receiving unit.

2. The sublimation defrost system for the refrigeration apparatus according to claim 1, wherein the circulation path forming path is a defrost circuit branched from the inlet path and the outlet path of the heat exchanger pipe, and the first heat exchanger part is formed in the defrost circuit.

3. The sublimation defrost system for the refrigeration apparatus according to claim 1, wherein the circulation path forming path is a bypass path disposed between the inlet path and the outlet path of the heat exchanger pipe, and the first heat exchanger part is formed in a partial area of the heat exchanger pipe.

4. The sublimation defrost system for the refrigeration apparatus according to claim 1, wherein the CO.sub.2 circulation path is formed with a difference in elevation, and the first heat exchanger part is formed in a lower area of the CO.sub.2 circulation path, and the circulating unit is configured to permits the CO.sub.2 refrigerant to naturally circulate in the closed circuit at the time of defrosting by a thermosiphon effect.

5. The sublimation defrost system for the refrigeration apparatus according to claim 1, further comprising: a second heat exchanger part for heating the brine with a second heating medium; and a brine circuit for permitting the brine heated by the second heating unit to be circulated to the first heating unit, the brine circuit being connected to the first heating unit and the second heating unit.

6. The sublimation defrost system for the refrigeration apparatus according to claim 5, wherein the heat exchanger pipe is provided with a difference in elevation in the cooling device, the brine circuit is formed in the cooling device and in a lower area of the heat exchanger pipe, and the first heat exchanger part is formed between the brine circuit and the lower area of the heat exchanger pipe.

7. The sublimation defrost system for the refrigeration apparatus according to claim 6, wherein each of the heat exchanging pipe and the brine circuit is provided with a difference in elevation in the cooling device and is configured in such a manner that the brine flows from a lower side to an upper side in the brine circuit, and a flowrate adjustment valve is disposed at an intermediate position in the brine circuit in an upper and lower direction, and the first heat exchanger part is formed at a portion of the brine circuit on an upstream side of the flowrate adjustment valve.

8. The sublimation defrost system for the refrigeration apparatus according to claim 5, further comprising a first temperature sensor and a second temperature sensor which are respectively disposed at an inlet and an outlet of the brine circuit to detect a temperature of the brine flowing through the inlet and the outlet.

9. The sublimation defrost system for the refrigeration apparatus according to claim 1, wherein the pressure adjusting unit includes: a pressure sensor for detecting the pressure of the CO.sub.2 refrigerant circulating in the closed circuit; a pressure adjusting valve disposed in the outlet path of the heat exchanger pipe; and a control device for receiving a detected value from the pressure sensor, and controlling an opening aperture of the pressure adjusting valve in such a manner that the condensing temperature of the CO.sub.2 refrigerant circulating in the closed circuit becomes equal to or lower than the freezing point of the water vapor in the freezer inner air in the freezer.

10. The sublimation defrost system for the refrigeration apparatus according to claim 1, wherein the refrigerating device includes: a primary refrigerant circuit in which NH.sub.3 refrigerant circulates and a refrigerating cycle component is disposed; a secondary refrigerant circuit in which the CO.sub.2 refrigerant circulates, the secondary refrigerant circuit led to the cooling device, the secondary refrigerant circuit being connected to the primary refrigerant circuit through a cascade condenser; and a liquid CO.sub.2 receiver for storing the CO.sub.2 refrigerant liquefied in the cascade condenser and a liquid CO.sub.2 pump for sending the CO.sub.2 refrigerant stored in the liquid CO.sub.2 receiver to the cooling device, which are disposed in the secondary refrigerant circuit.

11. The sublimation defrost system for the refrigeration apparatus according to claim 10, further comprising: a second heat exchanger part for heating the brine with a second heating medium; a brine circuit for permitting the brine heated by the second heating unit to be circulated to the first heating unit, the brine circuit being connected to the first heating unit and the second heating unit; and a cooling water circuit led to a condenser provided as a part of the refrigerating cycle component disposed in the primary refrigerant circuit, wherein the second heat exchanger part is a heat exchanger to which the cooling water circuit and the brine circuit are led, the heat exchanger configured to heat the brine circulating in the brine circuit with cooling water heated by the condenser.

12. The sublimation defrost system for the refrigeration apparatus according to claim 10, further comprising: a second heat exchanger part for heating the brine with a second heating medium; a brine circuit for permitting the brine heated by the second heating unit to be circulated to the first heating unit, the brine circuit being connected to the first heating unit and the second heating unit; a cooling water circuit led to a condenser provided as a part of the refrigerating cycle component disposed in the primary refrigerant circuit; and a cooling tower for cooling the cooling water circulating in the cooling water circuit by exchanging heat between the cooling water and spray water, wherein the second heat exchanger part includes a heating tower for receiving the spray water and exchanging heat between the brine circulating in the brine circuit and the spray water, the heating tower being integrally formed with the cooling tower.

13. The sublimation defrost system for the refrigeration apparatus according to claim 1, wherein the refrigerating device is a NH.sub.3/CO.sub.2 cascade refrigerating device including: a primary refrigerant circuit in which NH.sub.3 refrigerant circulates and a refrigerating cycle component is disposed; and a secondary refrigerant circuit in which the CO.sub.2 refrigerant circulates and a refrigerating cycle component is disposed, the secondary refrigerant circuit led to the cooling device, the secondary refrigerant circuit being connected to the primary refrigerant circuit through a cascade condenser.

14. A sublimation defrost method using the sublimation defrost system for the refrigeration apparatus according to claim 1, the method comprising: a first step of dehumidifying the freezer inner air in the freezer with the dehumidifier device so that a partial pressure of the water vapor in the freezer inner air does not become a saturated vapor partial pressure; a second step of closing the on-off valve at the time of defrosting to form the closed circuit; a third step of adjusting the pressure of the CO.sub.2 refrigerant circulating in the closed circuit so that the condensing temperature of the CO.sub.2 refrigerant becomes equal to or lower than the freezing point of the water vapor in the freezer inner air in the freezer; and a fourth step of vaporizing the CO.sub.2 refrigerant by exchanging heat between the brine as a heating medium and the CO.sub.2 refrigerant circulating in the closed circuit; and a fifth step of permitting the CO.sub.2 refrigerant vaporized in the fourth step to circulate in the closed circuit, and removing frost attached on an outer surface of the heat exchanger pipe by sublimation with heat of the CO.sub.2 refrigerant.

15. A sublimation defrost method for the refrigeration apparatus according to claim 14, wherein in the fourth step, the brine and the CO.sub.2 refrigerant circulating in the closed circuit exchange heat in the lower area of the closed circuit provided with a difference in elevation, and in the fifth step, the CO.sub.2 refrigerant is permitted to naturally circulate in the closed circuit by a thermosiphon effect.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a system diagram of a refrigeration apparatus according to one embodiment.

(2) FIG. 2 is a system diagram of a refrigeration apparatus according to one embodiment.

(3) FIG. 3 is a cross-sectional view of a cooling device of the refrigeration apparatus shown in FIG. 2.

(4) FIG. 4 is a cross-sectional view of a cooling device according to one embodiment.

(5) FIG. 5 is a system diagram of a refrigeration apparatus according to one embodiment.

(6) FIG. 6 is a cross-sectional view of a cooling device of the refrigeration apparatus shown in FIG. 5.

(7) FIG. 7 is a system diagram of a refrigeration apparatus according to one embodiment.

(8) FIG. 8 is a system diagram of a refrigeration apparatus according to one embodiment.

(9) FIG. 9 is a system diagram of a refrigeration apparatus according to one embodiment.

(10) FIG. 10 is an arrangement diagram of a refrigeration apparatus according to one embodiment.

DETAILED DESCRIPTION

(11) Embodiments of the present invention shown in the accompanying drawings will now be described in detail. It is intended, however, that dimensions, materials, shapes, relative positions, and the like of components described in the embodiments shall be interpreted as illustrative only and not limitative of the scope of the present invention unless otherwise specified.

(12) For example, expressions indicating a relative or absolute arrangement such as in a certain direction, along a certain direction, parallel to, orthogonal to, center of, concentric to, and coaxially do not only strictly indicate such arrangements but also indicate a state including a tolerance or a relative displacement within an angle and a distance achieving the same function.

(13) For example, expressions such as the same, equal to, and equivalent to indicating a state where the objects are the same, do not only strictly indicate the same state, but also indicate a state including a tolerance or a difference achieving the same function

(14) For example, expressions indicating shapes such as rectangular and cylindrical do not only indicate the shapes such as rectangular and cylindrical in a geometrically strict sense, but also indicate shapes including recesses/protrusions, chamfered portions, and the like, as long as the same effect can be obtained.

(15) Expressions such as comprising, including, includes, provided with, or having a certain component are not exclusive expressions that exclude other components.

(16) FIG. 1 to FIG. 9 show defrost systems for refrigeration apparatuses according to some embodiments of the present invention.

(17) Refrigeration apparatus 10A to 10D in these embodiments include: cooling devices 33a and 33b respectively disposed in freezers 30a and 30b; refrigerating devices 11A and 11B which cool and liquefy CO.sub.2 refrigerant; and a refrigerant circuit (corresponding to secondary refrigerant circuit 14) which permits the CO.sub.2 refrigerant cooled and liquefied in the refrigerating devices to circulate to the cooling devices 33a and 33b. The cooling devices 33a and 33b respectively include: casings 34a and 34b; and heat exchanger pipes 42a and 42b disposed in the casings. The internal temperature of the freezers 30a and 30b is kept as low as 25 C., for example in the refrigeration apparatus 10A to 10D shown in FIG. 1 to FIG. 9 during a refrigerating operation.

(18) In the exemplary configurations of the embodiments, the heat exchanger pipes 42a and 42b are led into the casings 34a and 34b from the outside of the casings 34a and 34b.

(19) Here, areas of heat exchanger pipes 42a and 42b outside partition walls of the casings 34a and 34b and inside the freezers 30a and 30b are referred to as an inlet tube 42c and an outlet tube 42d.

(20) Dehumidifier devices 38a and 38b for dehumidifying freezer inner air are disposed in the freezers 30a and 30b. The dehumidifier devices 38a and 38b are adsorption dehumidifier devices in some embodiments shown in FIG. 1 to FIG. 9. For example, the adsorption dehumidifier device is a desiccant rotor dehumidifier device including a rotary rotor bearing adsorbent on its surface, and continuously and simultaneously performs a step of adsorbing water vapor from the freezer inner air at a partial area of the rotary rotor and a step of separating the adsorbed water vapor with other areas. Outer air a is supplied to the dehumidifier devices 38a and 38b. The dehumidifier devices 38a and 38b adsorb water vapor s and discharged to the outside, and discharges cold dry air d into the freezer.

(21) A CO.sub.2 circulation path is formed of a circulation path forming path connected to the inlet tube 42c and the outlet tube 42d of the heat exchanger pipes 42a and 42b. The circulation path forming path is defrost circuits 50a and 50b connected to the inlet tube and the outlet tube of the heat exchanger pipes 42a and 42b in the embodiments shown in FIG. 1 and FIG. 9, and is bypass tubes 72a and 72b connected to the inlet tube and the outlet tube of the heat exchanger pipes 42a and 42b in the embodiments shown in FIG. 2 to FIG. 6.

(22) An on-off valve for making the CO.sub.2 circulation path become a closed circuit at the time of defrosting is disposed in each of the inlet tube 42c and the outlet tube 42d of the heat exchanger pipes 42a and 42b. In some embodiments shown in FIG. 1 to FIG. 9, the on-off valve is solenoid on-off valves 54a and 54b.

(23) In the example configurations of the embodiments shown in FIG. 1 to FIG. 9, two air openings are formed on the casings 34a and 34b. Fans 35a and 35b are disposed in one of the openings. An airflow flowing in and out of the casings 34a and 34b is formed by an operation of the fans 35a and 35b. The heat exchanger pipes 42a and 42b have a winding shape in a horizontal direction and an upper and lower direction for example.

(24) Pressure adjusting units 45a and 45b for storage spacing pressure of a CO.sub.2 refrigerant circulating in the closed circuit at the time of defrosting are disposed. The pressure of the CO.sub.2 refrigerant in the closed circuit is adjusted by the pressure adjusting units 45a and 45b so that the CO.sub.2 refrigerant has condensing temperature higher than a freezing point (for example, 0 C.) of the water vapor in freezer inner air in the freezers 30a and 30b, at the time of defrosting.

(25) In the example configurations of some embodiments shown in FIG. 1 to FIG. 9, the pressure adjusting units 45a and 45b respectively include: pressure sensors 46a and 46b for detecting the pressure of the CO.sub.2 refrigerant circulating in the closed circuit; pressure regulating valves 48a and 48b disposed in the outlet tube 42d; and control devices 47a and 47b which receive detected values from the pressure sensors 46a and 46b, and control valve apertures of the pressure adjustment valves 48a and 48b so that the pressure of the CO.sub.2 refrigerant is controlled in such a manner that condensing temperature of the CO.sub.2 refrigerant circulating in the closed circuit becomes higher than a freezing point of water vapor in the freezer inner air in the freezers 30a and 30b.

(26) In the example configuration of the embodiment, the pressure regulating valves 48a and 48 are disposed in parallel to the solenoid on-off valves 52a and 52b.

(27) The pressure sensors 46a and 46b are disposed in the outlet tube 42d on the upstream side of the pressure regulating valves 48a and 48b. The control devices 47a and 47b controls the opening aperture of the pressure regulating valves 48a and 48b and thus adjusts the pressure of the CO.sub.2 refrigerant in accordance with the detected values from the pressure sensors. Thus, the condensing temperature of the CO.sub.2 refrigerant circulating in the closed circuit becomes equal to or lower than the freezing point of the water vapor in the freezer inner air in the freezers 30a and 30b.

(28) When the solenoid on-off valves 52a and 52b are closed at the time of defrosting so that the CO.sub.2 circulation path becomes a closed circuit, a circulating unit permits the CO.sub.2 refrigerant to circulate in the closed circuit. The circulating unit is a liquid pump disposed in the CO.sub.2 circulation path for example. Alternatively, the circulating unit may permit the CO.sub.2 refrigerant to naturally circulate by a thermosiphon effect as in some embodiments shown in FIG. 1 to FIG. 10, rather than forcing the refrigerant to circulate.

(29) A brine is used as a heating medium. A first heat exchanger part which heats the CO.sub.2 refrigerant circulating in the CO.sub.2 circulation path with the brine, and thus vaporizes the refrigerant, is disposed. The first heat exchanger part is heat exchanger parts 70a and 70b to which brine branch circuits 61a and 61b, branched from defrost circuits 50a and 50b and a brine circuit 60, are led, in the embodiments shown in FIG. 1 and FIG. 9. The heat exchanger part in the embodiments shown in FIG. 2 to FIG. 6 includes lower areas of the heat exchanger pipes 42a and 42b and brine branch circuits 63a and 61b or 80a and 80b led to the lower areas.

(30) An aqueous solution such as ethylene glycol or propylene glycol can be used as the brine for example.

(31) In the embodiments shown in FIG. 1 and FIG. 9, the circulation path forming path is provided with the defrost circuits 50a and 50b as well as the heat exchanger parts 70a and 70b as the first heat exchanger part.

(32) In the embodiments shown in FIG. 2 to FIG. 6, bypass tubes 72a and 72b are disposed as the circulation path forming path, and the heat exchanger part including the lower areas of the heat exchanger pipes 42a and 42b and the brine branch circuits 61a and 61b led to the lower areas is formed as the heat exchanger part.

(33) In the embodiments shown in FIG. 1 to FIG. 9, the CO.sub.2 circulation path is provided with a difference in elevation in the upper and lower direction, and the first heat exchanger part is formed in the lower area of the CO.sub.2 circulation path

(34) More specifically, in the embodiments shown in FIG. 1 and FIG. 9, the CO.sub.2 circulation path is provided with the difference in elevation because the defrost circuits 50a and 50b are disposed below the cooling devices 33a and 33b. In the embodiments shown in FIG. 2 to FIG. 6, the heat exchanger pipes 42a and 42b forming the CO.sub.2 circulation path are provided with a difference in elevation.

(35) In the CO.sub.2 circulation path with the difference in elevation, the CO.sub.2 refrigerant can be permitted to circulate in the closed circuit formed at the time of defrosting by the thermosiphon effect. More specifically, the CO.sub.2 refrigerant gas vaporized by the first heat exchanger part rises due to the thermosiphon effect. The CO.sub.2 refrigerant gas that has risen exchange heat with the frost that has attached to an outer surface of the heat exchanger part in the heat exchanger pipes 42a and 42b or an upper area of the heat exchanger pipe, and thus removes the frost through sublimation. The CO.sub.2 refrigerant with the potential heat taken away is liquefied. The liquefied CO.sub.2 refrigerant descends in the CO.sub.2 circulation path with gravity. Thus, a loop thermosiphon effect is obtained, and the CO.sub.2 refrigerant is permitted to naturally circulate in the closed circuit.

(36) In some embodiments shown in FIG. 1 to FIG. 6, a second heat exchanger part (corresponding to the heat exchanger part 58) for causing heat exchange between the brine and the heating medium (cooling water) to heat the brine, and a brine circuit 60 (illustrated in dashed line) for causing the brine heated by the second heat exchanger part to circulate to the first heat exchanger part, are disposed. The brine circuit 60 is branched to the brine branch circuits 61a and 61b (illustrated in dashed line) outside the freezers 30a and 30b.

(37) In the embodiments shown in FIG. 1 and FIG. 9, the brine branch circuits 61a and 61b are led to the heat exchanger parts 70a and 70b. In the embodiments shown in FIG. 2 to FIG. 6, the brine branch circuits 61a and 61b are connected to the brine branch circuits 63a and 63b or 80a and 80b (illustrated in dashed line) disposed in the freezers 30a and 30b, through a contact part 62.

(38) At least one embodiment shown in FIG. 2 and FIG. 3, the heat exchanger pipes 42a and 42b are disposed with the difference in elevation in the cooling devices 33a and 33b. The brine branch circuits 63a and 63b are led into the cooling devices 33a and 33b and are disposed in the lower areas of the heat exchanger pipes 42a and 42b. For example, the brine branch circuits 63a and 63b are disposed in the lower areas which are to of an area where the heat exchanger pipes 42a and 42b are disposed.

(39) The first heat exchanger part is formed between the brine branch circuits 63a and 63b and the lower areas of the heat exchanger pipes 42a and 42b.

(40) In the example configuration of the cooling device 33a shown in FIG. 3, the air holes are formed in the upper and side surfaces (not shown) of the casing 34a, and the freezer inner air c flows in through the side surface and flows out through the upper surface.

(41) In the example configuration of the cooling device 33a shown in FIG. 4, the air holes are formed on both side surfaces, and the freezer inner air c flows in and out of the casing 34a through the both side surfaces.

(42) In at least one embodiment shown in FIG. 5 and FIG. 6, the heat exchanger pipes 42a and 42b and the brine branch circuits 80a and 80b are disposed in the cooling devices 33a and 33b, with the difference in elevation. The brine branch circuits 80a and 80b are configured in such a manner that the brine flows from a lower side to an upper side. Flowrate adjustment valves 82a and 82b are disposed at intermediate positions of the brine branch circuits 61a and 61b in the upper and lower direction.

(43) In this configuration, the opening aperture of the flowrate adjustment valves 82a and 82b is narrowed, whereby the first heat exchanger part can be formed in upstream side areas of the flowrate adjustment valves 82a and 82b, that is, the heat exchanger pipes 42a and 42b on the lower side of the flowrate adjustment valves 82a and 82b.

(44) In some embodiments shown in FIG. 1 to FIG. 9, temperature sensors 66 and 68 are respectively disposed at an inlet and an outlet of the brine circuit 60. The temperature of the brine flowing through the inlet and the outlet can be measured by the temperature sensors. It can be determined that the defrosting is almost completed when the difference between the detected valued of the temperature sensor is small. Thus, a threshold (2 to 3 C. for example) may be set for the difference between the detected values, and it may be determined that the defrosting is completed when the difference between the detected values drops to or below the threshold.

(45) In the embodiments shown in FIG. 2 to FIG. 6, a receiver (open brine tank) 64 that temporarily stores the brine and a brine pump 65 for circulating the brine are disposed in a send path of the brine circuit 60.

(46) In the embodiment shown in FIG. 9, an expansion tank 92 for absorbing pressure change and adjusting flowrate of the brine, is disposed instead of the receiver 64.

(47) In some embodiments shown in FIG. 1 to FIG. 6, the refrigeration apparatuses 10A to 10C includes the refrigerating device 11A. The refrigerating device 11A includes a primary refrigerant circuit 12 in which a NH.sub.3 refrigerant circulates and a refrigerating cycle component is disposed, and a secondary refrigerant circuit 14 in which the CO.sub.2 refrigerant circulates. The secondary refrigerant circuit 14 extends to the cooling devices 33a and 33b. The secondary refrigerant circuit 14 is connected to the primary refrigerant circuit 12 through a cascade condenser 24.

(48) The refrigerating cycle component disposed in the primary refrigerant circuit 12 includes a compressor 16, a condenser 18, a NH.sub.3 liquid receiver 20, an expansion valve 22, and the cascade condenser 24.

(49) The secondary refrigerant circuit 14 includes a CO.sub.2 liquid receiver 36 in which a liquid CO.sub.2 refrigerant liquefied by the cascade condenser 24 is temporarily stored, and a CO.sub.2 liquid pump 37 that permits the liquid CO.sub.2 refrigerant stored in the CO.sub.2 liquid receiver 36 to circulate to the heat exchanger pipes 42a and 42b.

(50) A CO.sub.2 circulation path 44 is disposed between the cascade condenser 24 and the CO.sub.2 liquid receiver 36. The CO.sub.2 refrigerant gas introduced into the cascade condenser 24 through the CO.sub.2 circulation path 44 from the CO.sub.2 liquid receiver 36 is cooled and liquefied by the NH.sub.3 refrigerant in the cascade condenser 24, and then returns to the CO.sub.2 liquid receiver 36.

(51) In the refrigerating device 11A, natural refrigerants of NH.sub.3 and CO.sub.2 are used, and thus an attempt to prevent the ozone layer depletion, global warming, and the like is facilitated. Furthermore, the refrigerating device 11A uses NH.sub.3, with high cooling performance and toxicity, as a primary refrigerant and uses CO.sub.2, with no toxicity or smell, as a secondary refrigerant, and thus can be used for room air conditioning and for refrigerating food products and the like.

(52) In at least one example embodiment shown in FIG. 7, the refrigerating device 11B may be disposed instead of the refrigerating device 11A. In the refrigerating device 11B, a lower stage compressor 16b and a higher stage compressor 16a are disposed in the primary refrigerant circuit 12 in which the NH.sub.3 refrigerant circulates. An intermediate cooling device 84 is disposed in the primary refrigerant circuit 12 and between the lower stage compressor 16b and the higher stage compressor 16a. A branch path 12a is branched from the primary refrigerant circuit 12 at an outlet of the condenser 18, and an intermediate expansion valve 86 is disposed in the branch path 12a.

(53) The NH.sub.3 refrigerant flowing in the branch path 12a is expanded and cooled in the intermediate expansion valve 86, and then is introduced into the intermediate cooling device 84. In the intermediate cooling device 84, the NH.sub.3 refrigerant discharged from the lower stage compressor 16b is cooled with the NH.sub.3 refrigerant introduced from the branch path 12a. Providing the intermediate cooling device 84 can improve the COP (coefficient of cooling performance) of the refrigerating device 11B.

(54) The liquid CO.sub.2 refrigerant, cooled and liquefied by exchanging heat with the NH.sub.3 refrigerant in the cascade condenser 24, is stored in the liquid CO.sub.2 receiver 36. Then, the liquid CO.sub.2 pump 37 makes the liquid CO.sub.2 refrigerant circulate in the cooling device 33 disposed in the freezer 30, from the liquid CO.sub.2 receiver 36.

(55) In at least one example embodiment shown in FIG. 8, the refrigerating device 11C may be disposed instead of the refrigerating device 11A. The refrigerating device 11C forms a cascade refrigerating cycle. A higher temperature compressor 88a and an expansion valve 22a are disposed in the primary refrigerant circuit 12 in which the NH.sub.3 refrigerant circulates. A lower temperature compressor 88b and an expansion valve 22b are disposed in the secondary refrigerant circuit 14 connected to the primary refrigerant circuit 12 through the cascade condenser 24.

(56) The refrigerating device 11C is a cascade refrigerating device in which a mechanical compression refrigerating cycle is formed in each of the primary refrigerant circuit 12 and the secondary refrigerant circuit 14, whereby the COP of the refrigerating device can be improved.

(57) In some embodiments shown in FIG. 1 to FIG. 6, the refrigeration apparatuses 10A to 10C include the refrigerating device 11A. In the refrigerating device 11A a cooling water circuit 28 is led to the condenser 18. A cooling water branch circuit 56 including the cooling water pump 57 branches from the cooling water circuit 28. The cooling water branch circuit 56 and the brine circuit 60 (illustrated in a dashed line) are led to the cooling water pump 57 as the second heat exchanger part.

(58) Refrigerant water circulating in the cooling water circuit 28 is heated by the NH.sub.3 refrigerant in the condenser 18. The heated cooling water serves as the heating medium to heat the brine circulating in the brine circuit 60 in the heat exchanger part 58, at the time of defrosting.

(59) When the temperature of the cooling water introduced into the heat exchanger part 58 from the cooling water branch circuit 56 is 20 to 30 C. for example, the brine can be heated up to 15 to 20 C. with this cooling water.

(60) In another embodiment, any heating medium other than the cooling water can be used as the second heating medium. Such a heating medium includes NH.sub.3 refrigerant gas with high temperature and high pressure discharged from the compressor 16, warm discharge water from a factory, a medium that has absorbed heat emitted from a boiler or potential heat of an oil cooler, and the like.

(61) As an example configuration some embodiments, the cooling water circuit 28 is disposed between the condenser 18 and a closed-type cooling tower 26. The cooling water is circulated in the cooling water circuit 28 by the cooling water pump 29. The cooling water that has absorbed exhaust heat from the NH.sub.3 refrigerant in the condenser 18 comes into contact with the outer air in a closed-type cooling tower 26 and is cooled with vaporization latent heat of water.

(62) The closed-type cooling tower 26 includes: a cooling coil 26a connected to the cooling water circuit 28; a fan 26b that blows the outer air a into the cooling coil 26a; and a spray pipe 26c and a pump 26d for spraying the cooling water onto the cooling coil 26a. The cooling water sprayed from the spray pipe 26c partially vaporizes. The cooling water flowing in the cooling coil 26c is cooled with the vaporization latent heat thus produced.

(63) In at least one embodiment shown in FIG. 9, the refrigerating device 11D disposed in the refrigeration apparatus 10D includes a closed-type cooling and heating unit 90 in which the closed-type cooling tower 26 and a closed-type heating tower 91 are integrally formed. The closed-type cooling tower 26 in the present embodiment cools the cooling water circulating in the cooling water circuit 28 through heat exchange with spray water, and has the basic configuration that is the same as that of the closed-type cooling tower 26 shown in FIG. 1 to FIG. 6.

(64) The closed-type heating tower 91 receives spray water used for cooling the cooling water circulating in the cooling water circuit 28 in the closed-type cooling tower 26, and causes heat exchange between the spray water and the brine circulating in the brine circuit 60. The closed-type heating tower 91 includes: a heating coil 91a connected to the brine circuit 60; and a spray pipe 91c and a pump 91d for spraying the cooling water onto the cooling coil 91a. An inside of the closed-type cooling tower 26 communicates with an inside of the closed-type heating tower 91 through a lower portion of a common housing.

(65) The spray water that has absorbed the exhaust heat from the NH.sub.3 refrigerant circulating in the primary refrigerant circuit 12 is sprayed onto the cooling coil 91a from the spray pipe 91c, and serves as a heating medium which heats the brine circulating in the cooling coil 91a and the brine circuit 60.

(66) In some embodiments shown in FIG. 1 to FIG. 9, the secondary refrigerant circuit 14 is branched to CO.sub.2 branch circuits 40a and 40b outside the freezers 30a and 30b. The CO.sub.2 branch circuits 40a and 40b are connected to the inlet tube and the outlet tube of the heat exchanger pipes 42a and 42b outside the freezers 30a and 30b.

(67) The brine circuit 60 extending to a portion near the freezers 30a and 30b from the heat exchanger part 58 is branched to brine branch circuits 61a and 61b (illustrated in dashed line) outside the freezers 30a and 30b.

(68) In the refrigeration apparatus 10A shown in FIG. 1, the brine branch circuits 61a and 61b are led to the heat exchanger parts 70a and 70b disposed in the freezers 30a and 30b.

(69) The sublimation defrosting is performed in the refrigeration apparatus 10A as follows. Specifically, when the freezer inner air in the freezers 30a and 30b has saturated water vapor pressure, the dehumidifier devices 38a and 38b are operated for dehumidification to achieve low water vapor partial pressure. Then, the solenoid on-off valves 52a and 52b are closed so that the CO.sub.2 circulation path, including the heat exchanger pipe 42a and 42b and the defrost circuits 50a and 50b, becomes the closed circuit.

(70) The detected values of the pressure sensors 46a and 46b are input to the control devices 47a and 47b. The control devices 47a and 47b operates the pressure regulating valves 48a and 48b based on the detected values to adjust the pressure of the CO.sub.2 refrigerant circulating in the closed circuit so that the condensing temperature of the CO.sub.2 refrigerant becomes equal to or lower than the freezing point (for example, 0 C.) of the water vapor in the freezer inner air. For example, the CO.sub.2 refrigerant is boosted to 3.0 MPa (condensing temperature 5 C.).

(71) Then, the CO.sub.2 refrigerant is vaporized through the heat exchange between the brine and the CO.sub.2 refrigerant in the heat exchanger parts 70a and 70b. Then, the vaporized CO.sub.2 refrigerant is circulated in the closed circuit, whereby the frost attached to the outer surface of the heat exchanger pipes 42a and 42b is removed through sublimation with the condensing latent heat (249 kJ/kg at 5 C./3.0 MPa) of the CO.sub.2 refrigerant.

(72) The lower limit value of the condensing temperature of the CO.sub.2 refrigerant to be adjusted for the sublimation of the frost is a freezer inner temperature (for example, 25 C.). During the refrigerating operation, the CO.sub.2 refrigerant at a temperature equal to or lower than the freezer inner temperature (for example, 30 C.) is permitted to circulate in the heat exchanger pipes 42a and 42b for cooling in the freezer. Thus, the temperature of the frost is equal to or lower than the freezer inner temperature (for example, 25 C. to 30 C.), accordingly, sublimation of frost through heating can be achieved when the condensing temperature of the CO2 refrigerant is within a range of the freezer inner temperature and the freezing point of the water vapor in the freezer at the time of sublimation defrosting.

(73) In the present embodiment, the defrost circuits 50a and 50b are disposed below the heat exchanger pipes 42a and 42b, and the CO.sub.2 circulation path has the difference in elevation. Thus, the CO.sub.2 refrigerant vaporized in the heat exchanger parts 70a and 70b rises to the heat exchanger pipes 42a and 42b due to the thermosiphon effect. Thus, the frost attached to the outer surfaces of the heat exchanger pipes 42a and 42b is sublimated and thus is liquefied by the potential heat of the CO.sub.2 refrigerant gas that has risen to the heat exchanger pipes 42a and 42b. The liquefied CO.sub.2 refrigerant descends in the defrost circuits 50a and 50b with gravity, and then is vaporized again in the heat exchanger part 70a and 70b.

(74) In the refrigeration apparatus 10B shown in FIG. 2 and FIG. 3 and in the refrigeration apparatus 10C shown in FIG. 5 and FIG. 6, the heat exchanger pipes 42a and 42b as well as the brine branch circuits 63a and 63b or 80a and 80b are disposed in the cooling devices 33a and 33b with the difference in elevation.

(75) Bypass tubes 72a and 72b are connected between the inlet tube and the outlet tube of the heat exchanger pipes 42a and 42b outside the casings 34a and 34b. Solenoid on-off valves 74a and 74b are disposed in the bypass tubes 72a and 72b.

(76) In the inlet tube, the solenoid on-off valves 54a and 54b are disposed on the upstream side of the bypass tubes 52a and 52b. In the outlet tube, the solenoid on-off valves 54a and 54b are disposed on the downstream side of the bypass tubes 52a and 52b.

(77) In the refrigeration apparatus 10B, the brine branch circuits 63a and 63b are led to the lower areas of the heat exchanger pipes 42a and 42b. The heat exchanger part is formed of the lower areas of the heat exchanger pipes 42a and 42b and the brine branch circuits 63a and 63b.

(78) In the refrigeration apparatus 10C, the brine branch circuits 80a and 80b are disposed over substantially the entire area of the area where the heat exchanger pipes 42a and 42b are disposed. The flowrate adjustment valves 82a and 82b are disposed at intermediate portions of the brine branch circuits 80a and 80b in the upper and lower direction. The brine branch circuits 80a and 80b form a flow path in which brine b flows to an upper area from a lower area.

(79) In an example configuration of the cooling devices 33a and 33b, for example, as in the cooling device 33a shown in FIG. 3 or FIG. 6, the heat exchanger pipes 42a and 42b as well as the brine branch circuit 63a and 63b or 80a and 80b have the winding shape and are arranged in the horizontal direction and in the upper and lower direction. The brine branch circuits 80a and 80b form the flow path in which brine b flows to an upper area from a lower area.

(80) The heat exchanger pipe 42a includes headers 43a and 43b in the inlet tube 42c and the outlet tube 42d, outside the cooling device 33a. The brine branch circuits 63a and 80a includes headers 78a and 78b at an inlet and an outlet of the cooling device 33a.

(81) A large number of plate fins 76a are disposed in the upper and lower direction in the cooling device 33a. The heat exchanger pipe 42a and the branch circuit 63a or 80a are inserted in a large number of holes formed on the plate fins 76a and thus are supported by the plate fins 76a. With the plate fins 76a, supporting strength for the pipes is increased, and the heat transmission between the heat exchanger pipe 42a and the brine branch circuit 63a or 80a is facilitated.

(82) During the refrigerating operation, the fan 35a diffuses the freezer inner air c cooled in the cooling device 33a into the freezer 32a. Because no dissolved water is produced at the time of defrosting, a drain pan is not disposed below the casing 34a. The configuration of the cooling device 33a described above is the same as that of the cooling device 33b.

(83) In the refrigerating devices 11B and 11C, the inlet tube 42c and the outlet tube 42d of the heat exchanger pipes 42a and 42b are connected to the CO.sub.2 branch circuits 40a and 40b through the contact part 41, outside the freezers 30a and 30b. The brine branch circuits 63a, 63b, 80a, and 80b are connected to the brine branch circuits 61a and 61b through the contact part 62, outside the freezers 30a and 30b.

(84) In the refrigeration apparatus 10B, the casings 34a and 34b of the freezers 30a and 30b, the heat exchanger pipes 42a and 42b including the inlet tube 42c and the outlet tube 42d, the brine branch circuits 63a and 63b, and the bypass tubes 72a and 72b form the cooling units 31a and 31b that are integrally formed.

(85) In the refrigeration apparatus 10C, the casings 34a and 34b of the freezers 30a and 30b, the heat exchanger pipes 42a and 42b including the inlet tube 42c and the outlet tube 42d, the brine branch circuits 80a and 80b, and the bypass tubes 72a and 72b form the cooling units 32a and 32b that are integrally formed.

(86) The cooling units 31a and 31b or 32a and 32b are detachably connected to the CO.sub.2 branch circuits 40a and 40b and the brine branch circuits 61a and 61b through the contact parts 41 and 62.

(87) In the refrigeration apparatuses 10B and 10C, the solenoid on-off valves 74a and 74b are closed, and the solenoid on-off valves 52a and 52b are opened during the refrigerating operation. The solenoid on-off valves 74a and 74b are opened, and the solenoid on-off valves 52a and 52b are closed at the time of defrosting, whereby the closed circuit including the heat exchanger pipes 42a and 42b and the bypass tubes 72a and 72b is formed.

(88) In the refrigeration apparatus 10B, the CO.sub.2 refrigerant is vaporized by the potential heat of the brine flowing in the brine branch circuits 63a and 63b, in the lower areas of the heat exchanger pipes 42a and 42b, at the time of defrosting. The vaporized CO.sub.2 refrigerant rises to the upper areas of the heat exchanger pipes 42a and 42b, and removes the frost attached to the outer surfaces of the heat exchanger pipes 42a and 42b in the upper areas, through sublimation. The CO.sub.2 refrigerant that has humidified the frost through sublimation is liquefied and descends by gravity, and vaporizes again in the lower area. Thus, the CO.sub.2 refrigerant is naturally circulated in the closed circuit by the thermosiphon effect.

(89) In the refrigeration apparatus 10C, at the time of defrosting, the opening apertures of the flowrate adjustment valves 82a and 82b are narrowed so that the flowrate of the brine b is restricted. Thus, the heat exchanger part in which the CO.sub.2 refrigerant and the brine exchange heat can be formed only in the upstream area (lower area) of the flowrate adjustment valves 82a and 82b.

(90) Thus, the CO.sub.2 refrigerant is naturally circulated by the thermosiphon effect and the frost can be removed through sublimation by the potential heat of the circulating CO.sub.2 refrigerant, between the areas of the heat exchanger pipes 42a and 42b corresponding to the upstream and the downstream areas of the flowrate adjustment valves 82a and 82b.

(91) According to some embodiments shown in FIG. 1 to FIG. 10, the frost attached to the outer surfaces of the heat exchanger pipes 42a and 42b is heated by the heat of the CO.sub.2 refrigerant flowing in the heat exchanger pipe, whereby uniform heating can be achieved in the enter area of the heat exchanger pipe. The condensing temperature of the CO.sub.2 refrigerant is controlled by adjusting the pressure in the closed circuit. Thus, the temperature of the CO.sub.2 refrigerant gas flowing in the closed circuit can be accurately controlled, so that the frost can be heated to a temperature at or above the freezing point accurately, whereby the sublimation defrosting can be achieved.

(92) The fans 35a and 35b are operated at the time of defrosting, so that the air flow flowing in and out of the casings 34a and 34b is formed, whereby the sublimation can be facilitated.

(93) Thus, the frost attached to the heat exchanger pipes 42a and 42b is not melted but is sublimated, and thus a drain pan and a facility for discharging the drainage accumulated in the drain pan are not required, whereby the cost of the refrigeration apparatus can be largely reduced. The frost attached to the heat exchanger pipes 42a and 42b is heated from the inside through a pipe wall of the heat exchanger pipe only. Thus, the heat exchange efficiency can be improved and power saving can be achieved.

(94) The defrosting can be achieved with the CO.sub.2 refrigerant in a low pressure state. Thus, a pipe system device such as the CO.sub.2 circulation path needs not to be pressure resistant, whereby a high cost is not required.

(95) Thus, with the sublimation defrosting achieved, a micro channel heat exchanger pipe, which is considered to be difficult to apply to the cooling device for a freezer due to the large performance degradation caused by frost formation and dew condensation, can be employed. This technique can be applied not only to the freezer, but can also be applied to a defrost method for a batch freezing chamber or a freezer requiring continuous non-defrosting operation for a long period of time.

(96) In the refrigeration apparatus 10A shown in FIG. 1, the defrost circuits 50a and 50b are disposed to form the CO.sub.2 circulation path, whereby the first heat exchanger part formed in the CO.sub.2 circulation path can be more freely disposed.

(97) In the refrigeration apparatus 10B shown in FIG. 2 and FIG. 3, the CO.sub.2 circulation path is formed of the heat exchanger pipes 42a and 42b only, except for the bypass tubes 72a and 72b, and thus there is no need to additionally provide new pipes, whereby a high cost is not required.

(98) In some embodiments shown in FIG. 1 to FIG. 9, the CO.sub.2 refrigerant can be permitted to naturally circulate in the closed circuit by the thermosiphon effect. Thus, a unit for forcibly circulating the CO.sub.2 refrigerant in the closed circuit is not required, and equipment and power (pump power) for the forcing circulation are not required, whereby cost reduction can be achieved.

(99) The brine circuit 60 is provided, and can be disposed in accordance with a disposed position of the heat exchanger part in which the heated brine exchanges heat with the CO.sub.2 refrigerant. Thus, a position where the heat exchanger part is disposed can be more freely determined.

(100) In the embodiments shown in FIG. 2 and FIG. 3, the heat exchanger part involving the brine is formed by the lower areas of the heat exchanger pipes 42a and 42b, and the CO.sub.2 refrigerant is permitted to naturally circulate by the thermosiphon effect. Thus, no additional pipes other than the bypass tubes 72a and 72b are required, and no equipment for forcing circulation is required. All things considered, the cost of the cooling devices 33a and 33b can be reduced.

(101) The brine branch circuits 63a and 63b are not disposed in the upper areas of the heat exchanger pipes 42a and 42b, whereby the power used for the fans 35a and 35b for forming airflow in the cooling devices 33a and 33b can be reduced. The cooling performance of the cooling devices 33a and 33b can be improved by additionally providing the heat exchanger pipes 42a and 42b in a vacant space in the upper area.

(102) In the embodiment shown in FIG. 5 and FIG. 6, the brine branch circuits 80a and 80b are disposed over the entire heat exchanger pipes 42a and 42b in the upper and lower direction, and the brine flowrate is regulated by the flowrate adjustment valves 82a and 82b. Thus, the heat exchanger part can be formed only in the lower areas of the heat exchanger pipes 42a and 42b. Thus, the sublimation defrosting can be achieved with a simple arrangement of adding the flowrate adjustment valves 82a and 82b to the known cooling device.

(103) In some embodiments shown in FIG. 1 to FIG. 9, the timing at which the defrosting is completed can be accurately obtained based on the detected values of the temperature sensors 66 and 68 respectively disposed at the inlet and the outlet of the brine circuit 60. Thus, excessive heating in the freezer or diffusion of the water vapor due to the excessive heating can be prevented, and further power saving can be achieved. Furthermore, a stable temperature in the freezer can be achieved, whereby the quality of food products frozen in the freezer can be improved.

(104) In some embodiments shown in FIG. 1 to FIG. 9, the pressure adjusting units 45a and 45b are disposed as a pressure adjusting unit for the CO.sub.2 refrigerant circulating in the closed circuit. Thus, the pressure can be accurately adjusted easily at a low cost.

(105) In some embodiments shown in FIG. 1 to FIG. 5, the cooling water circuit 28 is led to the heat exchanger part 58, and the cooling water heated in the condenser 18 is used as the heating medium for heating the brine. Thus, no heating source outside the refrigeration apparatus is required. The temperature of the cooling water can be lowered with the brine at the time of defrosting, whereby the condensing temperature of the NH.sub.3 refrigerant during the refrigerating operation can be lowered, and the COP of the refrigerating device can be improved.

(106) The heat exchanger part 58 can be disposed in the closed-type cooling tower 26. Whereby a space where an apparatus used for defrosting is installed can be downsized.

(107) In the embodiments shown in FIG. 9, the heat exchange between the heating medium and the brine takes place in the closed-type heating tower 91 integrally formed with the closed-type cooling tower 26. Thus, a space where the second heat exchanger part is installed can be downsized. By using the spray water in the closed-type cooling tower 26 as the heat source for the brine, the heat can also be acquired from the outer air. When the refrigeration apparatus 10D employs an air cooling system, the cooling water can be cooled and the brine can be heated with the outer air as the heat source, with the heating tower alone.

(108) Furthermore, by using the cooling units 31a, 31b, 32a, and 32b of the configuration described above, the cooling devices 33a and 33b with a defrosting device can be easily attached to the freezers 30a and 30b. When the units are integrally assembled in advance, the attachment to the freezers 30a and 30b is further facilitated.

(109) FIG. 10 shows a still another embodiment. A cargo-handling chamber 100 is disposed adjacent to the freezer 30 of this embodiment. The freezer 30 includes a plurality of the cooling devices 33 having the configuration described above. For example, the cooling device 33 includes the casing 34, the heat exchanger pipe 42, the brine branch circuits 61 and 63, the CO.sub.2 branch circuit 40, and the like having the configuration described above.

(110) The freezer 30 and the cargo-handling chamber 100 each incorporate the dehumidifier device 38 such as the desiccant humidifier. The dehumidifier device 38 takes in the outer air a from the outside of the chamber and discharges the water vapor s from the chamber, whereby the cold dry air d is supplied into the chamber.

(111) The temperature in the cargo-handling chamber 100 is kept at +5 C. for example. An electric heat insulating door 102 is disposed at an entrance for going in and out of the freezer 30 from the cargo-handling chamber 100. Thus, the amount of water vapor entering the freezer 30 when the door is opened/closed is minimized.

(112) For example, when the freezer 30 is cooled to have a temperature of 25 C., and has a volume of 7, 500 m.sup.3 the absolute humidity is 0.4 g/kg at the relative humidity of 100% and the absolute humidity is 0.1 g/kg at the relative humidity of 25%. Thus, the amount of containable water vapor, obtained by multiplying the difference in the absolute humidity by the volume of the freezer 30, is 2.25 kg. Thus, the sublimation defrosting can be well achieved by setting the relative humidity of the freezer inner air to 25%.

INDUSTRIAL APPLICABILITY

(113) According to the present invention the sublimation defrosting can be achieved, whereby the initial and running costs require for the defrosting in the refrigeration apparatus can be reduced, and the power saving can be achieved

REFERENCE SIGNS LIST

(114) 10A, 10B, 10C, 10D refrigeration apparatus 11A, 11B, 11C, 11D refrigerating device 12 primary refrigerant circuit 14 secondary refrigerant circuit 16 compressor 16a higher stage compressor 16b lower stage compressor 18 condenser 20 NH.sub.3 liquid receiver 22, 22a, 22b expansion valve 24 cascade condenser 26 closed-type cooling tower 28 cooling water circuit 29, 57 cooling water pump 30, 30a, 30b freezer 31a, 31b, 32a, 32b cooling unit 33, 33a, 33b cooling device 34, 34a, 34b casing 35a, 35b fan 36 CO.sub.2 liquid receiver 37 CO.sub.2 liquid pump 38, 38a, 38b dehumidifier device 40, 40a, 40b CO.sub.2 branch circuit 41, 62 contact part 42, 42a, 42b heat exchanger pipe 42c inlet tube 42d outlet tube 43a, 43b, 78a, 78b header 44 CO.sub.2 circulation path 45a, 45b pressure adjusting unit 46a, 46b pressure sensor 47a, 47b control device 48a, 48b pressure regulating valve 50a, 50b defrost circuit 52a, 52b, 74a, 74b solenoid on-off valve 56 cooling water branch circuit 58 heat exchanger part (second heat exchanger part) 60 brine circuit 61, 61a, 61b, 63, 63a, 63b, 80a, 80b brine branch circuit 64 receiver 65 brine pump 66 temperature sensor (first temperature sensor) 68 temperature sensor (second temperature sensor) 70 heat exchanger part (first heat exchanger part) 72a, 72b bypass tube 76a plate fin 82a, 82b flowrate adjustment valve 84 intermediate cooling device 86 intermediate expansion valve 88a higher temperature compressor 88b lower temperature compressor 90 closed-type cooling and heating unit 91 closed-type heating tower 92 expansion tank 100 cargo-handling chamber 102 heat insulating door a outer air b brine c freezer inner air d cold dry air